JP4167100B2 - Image processing apparatus, image forming apparatus, image processing method, computer program, and recording medium - Google Patents

Description

ここで、Ｒ，Ｇ，Ｂは、Ｒ，Ｇ，Ｂの補数を示す。マトリクス係数ａｉｊは入力系と出力系（色材）の分光特性によって決まる。ここでは、１次マスキング方程式を例に挙げたが、Ｂ２，ＢＧのような２次項、あるいはさらに高次の項を用いることにより、より精度良く色補正することができる。また、色相によって演算式を変えたり、ノイゲバウアー方程式を用いるようにしても良い。何れの方法にしても、Ｙ，Ｍ，ＣはＢ，Ｇ，Ｒ（またはＢ，Ｇ，Ｒでもよい）の値から求めることができる。
【００５４】
一方、ＵＣＲ処理は次式を用いて演算することにより行うことができる。
Ｙ’ ＝ Ｙ− α・ ｍｉｎ（Ｙ，Ｍ，Ｃ）
Ｍ’ ＝ Ｍ− α・ ｍｉｎ（Ｙ，Ｍ，Ｃ）
Ｃ’ ＝ Ｃ− α・ ｍｉｎ（Ｙ，Ｍ，Ｃ）
Ｂｋ ＝ α・ ｍｉｎ（Ｙ，Ｍ，Ｃ）・・・（２）
上式において、αはＵＣＲの量を決める係数で、α＝１の時１００％ＵＣＲ処理となる。αは一定値でも良い。例えば、高濃度部では、αは１に近く、ハイライト部（低画像濃度部）では、０に近くすることにより、ハイライト部での画像を滑らかにすることができる。
【００５５】
前記の色補正係数は、ＲＧＢＹＭＣの６色相をそれぞれ更に２分割した１２色相に、更に黒および白の１４色相毎に異なる。色相判定回路４２４は、読み取った画像データがどの色相に判別するかを判定する。判定した結果に基づいて、各色相毎の色補正係数が選択される。
【００５６】
変倍回路４０７では縦横変倍が行われ、画像加工（クリエイト）回路４０８ではリピート処理などが行われる。プリンタγ補正回路４０９で、文字、写真などの画質モードに応じて、画像信号の補正が行われる。また、地肌飛ばしなども同時に行うこともできる。プリンタγ補正回路４０９は、前述したエリア処理回路４０２が発生した領域信号に対応して切り替え可能な複数本（例えば１０本）の階調変換テーブルを有する。この階調変換テーブルは、文字、銀塩写真（印画紙）、印刷原稿、インクジェット、蛍光ペン、地図、熱転写原稿など、それぞれの原稿に最適な階調変換テーブルを複数の画像処理パラメータの中から選択することができる。
【００５７】
階調処理回路４１０はＳＩＭＤ型のプロセッサによって構成される。図１４はＳＩＭＤ型プロセッサの概略構成を示す説明図である。ＳＩＭＤ（Single Instruction Stream Multiple Data stream）は複数のデータに対し、単一の命令を並列に実行させるもので、複数のＰＥ（プロセッサ・エレメント）より構成される。このＳＩＭＤ型プロセッサは図１７におけるプロセッサ・アレー部１４０４内に配設される。それぞれのＰＥはデータを格納するレジスタ（Ｒｅｇ）２００１、他のＰＥのレジスタをアクセスするためのマルチプレクサー（ＭＵＸ）２００２、バレルシフター（Shift Expand）２００３、論理演算器（ＡＬＵ）２００４、論理結果を格納するアキュムレーター（Ａ）２００５、アキュムレーターの内容を一時的に退避させるテンポラリー・レジスタ（Ｆ）２００６から構成される。
【００５８】
各レジスタ２００１はアドレスバスおよびデータバス（リード線およびワード線）に接続されており、処理を規定する命令コード、処理の対象となるデータを格納する。レジスタ２００１の内容は論理演算器２００４に入力され、演算処理結果はアキュムレータ２００５に格納される。結果をＰＥ外部に取り出すために、テンポラリ・レジスタ２００６に一旦退避させる。テンポラリ・レジスタ２００６の内容を取り出すことにより、対象データに対する処理結果が得られる。命令コードは各ＰＥに同一内容で与え、処理の対象データをＰＥごとに異なる状態で与え、隣接ＰＥのレジスタ２００１の内容をマルチプレクサ２００２において参照することによって演算結果は並列処理され、各アキュムレータ２００５に出力される。例えば、画像データ１ラインの内容を各画素ごとにＰＥに配置し、同一の命令コードで演算処理させれば、１画素ずつ逐次処理するよりも短時間で１ライン分の処理結果が得られる。特に、空間フィルタ処理はＰＥごとの命令コードは演算式そのもので、ＰＥ全てに共通に処理を実施することができる。
【００５９】
次に、画像処理装置のＳＩＭＤ型画像データ処理部と逐次画像データ処理部とについて説明する。図１５は、ＳＩＭＤ型画像データ処理部１５００と、逐次画像データ演算処理部１５０７との構成を示す図である。本実施形態では、まず、ＳＩＭＤ型画像データ処理部１５００について説明し、続いて逐次型画像データ処理部１５０７について説明する。
【００６０】
画像データ並列処理部１５００と画像データ逐次処理部１５０７とは、一方向に配列された複数の画素で構成される複数の画素ラインとして画像を処理するものである。図１６は、画素ラインを説明するための図であり、画素ラインａ〜ｄの４本の画素ラインを示している。また、図中に斜線を付して示した画素は、今回処理される注目画素である。本実施形態では、注目画素の誤差拡散処理に当たり、注目画素に対して周囲の画素の影響を、同一の画素ラインに含まれる画素、異なる画素ラインに含まれる画素の両方について考慮している。そして、注目画素とは異なる画素ラインに含まれる画素との間の誤差拡散処理をＳＩＭＤ型画像データ処理部１５００で行い、注目画素と同一の画素ラインに含まれる画素（図中に▲１▼、▲２▼、▲３▼を付して示した画素）との間の誤差拡散処理を逐次型画像データ処理部１５０７で行う。
【００６１】
ＳＩＭＤ型画像データ処理部１５００は、ＳＩＭＤ型プロセッサ１５０６と、ＳＩＭＤ型画像データ処理部１５００に画像データおよび制御信号を入力する５つのデータ入出力用バス１５０１ａ〜１５０１ｅと、データ入出力用バス１５０１ａ〜１５０１ｅをスイッチングしてＳＩＭＤ型プロセッサ１５０６に入力される画像データおよび制御信号を切り替えるとともに、接続されたバスのバス幅を切り替えるバススイッチ１５０２ａ，１５０２ｂ，１５０２ｃと、入力された画像データの処理に使用されるデータを記憶する２０個のＲＡＭ１５０３と、各々対応するＲＡＭ１５０３を制御するメモリコントローラ１５０５ａ、メモリコントローラ１５０５ｂ、メモリコントローラ１５０５ａまたはメモリコントローラ１５０５ｂの制御にしたがってＲＡＭ１５０３をスイッチングする４つのメモリスイッチ１５０４ａ，１５０４ｂ，１５０４ｃ，１５０４ｄとを有している。なお、以上の構成では、バススイッチ１５０２ａ〜１５０２ｃによって制御されるメモリコントローラをメモリコントローラ１５０５ｂとし、バススイッチ１５０２ａ〜１５０２ｃの制御を受けないメモリコントローラをメモリコントローラ１５０５ａとして区別した。
【００６２】
前述のＳＩＭＤ型プロセッサ１５０６は、レジスタ０（Ｒ０）〜レジスタ２３（Ｒ２３）を備えている。Ｒ０〜Ｒ２３の各々は、ＳＩＭＤ型プロセッサ１５０６にあるＰＥとメモリコントローラ１５０５ａ，１５０５ｂとのデータインターフェースとして機能する。バススイッチ１５０２ａは、Ｒ０〜Ｒ３に接続されたメモリコントローラ１５０５ｂを切り替えてＳＩＭＤ型プロセッサに制御信号を入力する。また、バススイッチ１５０２ｂは、Ｒ４，Ｒ５に接続されたメモリコントローラ１５０５を切り替えてＳＩＭＤ型プロセッサに制御信号を入力する。また、バススイッチ１５０２ｃは、Ｒ６〜Ｒ９に接続されたメモリコントローラ１５０５を切り替えてＳＩＭＤ型プロセッサに制御信号を入力する。そして、バススイッチ１５０２ｃは、Ｒ６〜Ｒ９に接続されたメモリコントローラ１５０５ｂを切り替えてＳＩＭＤ型プロセッサに制御信号を入力する。
【００６３】
メモリスイッチ１５０４ａは、Ｒ０〜Ｒ５に接続されたメモリコントローラ１５０５ｂを使用してＳＩＭＤ型プロセッサ１５０６内部のＰＥとＲＡＭ１５０３との間で画像データを授受している。また、メモリスイッチ１５０４ｂは、Ｒ６，Ｒ７に接続されたメモリコントローラ１５０５ｂを使用してＳＩＭＤ型プロセッサ１５０６内部のＰＥとＲＡＭ１５０３との間で画像データを授受している。また、メモリスイッチ１５０４ｃは、Ｒ８〜Ｒ１３に接続されたメモリコントローラ１５０５ａまたはメモリコントローラ１５０５ｂを使用してＳＩＭＤ型プロセッサ１５０６内部のＰＥとＲＡＭ１５０３との間で画像データを授受している。そして、メモリスイッチ１５０４ｄは、Ｒ１４〜Ｒ１９に接続されたメモリコントローラ１５０５ａを使用してＳＩＭＤ型プロセッサ１５０６内部のＰＥとＲＡＭ１５０３との間で画像データを授受している。
【００６４】
図示しない画像データ制御部は、画像データとともに画像データを処理するための制御信号をデータ入出力用バス１５０１ａ〜１５０１ｅを介してバススイッチ１５０２ａ〜１５０２ｃに入力させる。バススイッチ１５０２ａ〜１５０２ｃは、制御信号信号に基づいて接続されているバスのバス幅を切り替える。また、間接的に、あるいは直接接続されたメモリコントローラ１５０５ｂを制御し、画像データの処理に必要なデータをＲＡＭ１５０３から取り出すようにメモリスイッチ１５０４ａ〜１５０４ｃをスイッチングさせる。
【００６５】
ＳＩＭＤ型画像データ処理部１５００は、誤差拡散処理を行う場合、画像データ制御部を介して読取ユニットおよび図示しないセンサ・ボード・ユニットによって作成された画像データを入力する。そして、注目画素が含まれる画素ライン（現画素ライン）よりも前に処理された画素ライン（前画素ライン）に含まれる画素の画素データと所定の閾値との差である誤差データと注目画素の画素データとを加算する。
【００６６】
ＳＩＭＤ型画像データ処理部１５００では、ＳＩＭＤ型プロセッサ１５０６を用い、誤差データとの加算を複数の注目画素について並列的に実行する。このため、ＳＩＭＤ型プロセッサ１５０６に接続されているＲＡＭ１５０３のいずれかには、ＳＩＭＤ型プロセッサ１５０６で一括して処理される画素の数に対応する複数の誤差データが保存されている。本実施形態では、ＳＩＭＤ型プロセッサ１５０６において１画素ライン分の加算処理を一括して行うものとし、ＲＡＭ１５０３に１画素ライン分の誤差データを保存するものとした。ＳＩＭＤ型プロセッサ１５０６で一括して処理された１画素ライン分の画像データと誤差データとの加算値は、Ｒ２０，Ｒ２１，Ｒ２３，Ｒ２２の少なくとも２つから逐次型画像データ処理部１５０７に１つずつ出力される。また、以上の処理に使用される誤差データは、後述する逐次型画像データ処理部１５０７によって算出され、ＳＩＭＤ型プロセッサ１５０６に入力されるものである。
【００６７】
一方、逐次型画像データ処理部１５０７ａ，１５０７ｂは、コンピュータプログラムの制御によらず稼動するハードウェアである。なお、図１５では、逐次型画像データ処理部１５０７をＳＩＭＤ型プロセッサ１５０６に２個接続するものとしているが、本実施形態に係る画像処理装置ではこのうちの１５０７ｂを逐次行う誤差拡散処理専用に使用するものとし、もう１つの逐次型画像データ処理部１５０７は、γ変換などのテーブル変換用として用いるように機能特化している。
【００６８】
画像処理プロセッサのハードウェア構成について説明する。
図１７は、本画像処理プロセッサ１２０４の内部構成を示すブロック図である。同図において、画像処理プロセッサ１２０４は、外部とのデータ入出力に関し、複数個の入出力ポート１４０１を備え、それぞれデータの入力および出力を任意に設定することができる。また、入出力ポート１４０１と接続するように内部にバス・スイッチ／ローカル・メモリ群１４０２を備え、使用するメモリ領域、データバスの経路をメモリ制御部１４０３において制御する。入力されたデータおよび出力のためのデータは、バス・スイッチ／ローカル・メモリ群１４０２をバッファ・メモリとして割り当て、それぞれに格納し、外部とのＩ／Ｆを制御される。バス・スイッチ／ローカル・メモリ群１４０２に格納された画像データに対してプロセッサ・アレー部１４０４において各種処理を行い、出力結果（処理された画像データ）を再度バス・スイッチ／ローカル・メモリ群１４０２に格納する。プロセッサ・アレー部１４０４における処理手順、処理のためのパラメータ等は、プログラムＲＡＭ１４０５およびデータＲＡＭ１４０６との間でやりとりが行われる。
【００６９】
プログラムＲＡＭ１４０５、データＲＡＭ１４０６の内容は、シリアルＩ／Ｆ１４０８を通じて、図示しないプロセス・コントローラからホスト・バッファ１４０７にダウンロードされる。また、前記プロセス・コントローラがデータＲＡＭ１４０６の内容を読み出して、処理の経過を監視する。処理の内容を変更したり、システムで要求される処理形態が変更になる場合は、プロセッサ・アレー１４０４が参照するプログラムＲＡＭ１４０５およびデータＲＡＭ１４０６の内容を更新して対応する。なお、特殊処理１（１４０９）ではテーブル変換やγ変換などの変換処理が主に行われ、特殊処理２（１４１０）では誤差拡散処理が行われる。以上述べた構成のうち、プロセッサ・アレー１４０４が、本実施形態にかかるＳＩＭＤ型画像データ処理部と逐次型画像データ処理部とに相当する。
【００７０】
図１８は逐次型画像データ処理部１５０７ｂの構成を示すブロック図である。図示した逐次型画像データ処理部１５０７ｂは、誤差データ算出部１８０１と、誤差データ算出部１８０１が算出した誤差データから一つを選択するマルチプレクサ１８０７と、マルチプレクサ１８０７によって選択された誤差データを加工してＳＩＭＤ型画像データ処理部１５００から入力したデータに加算する誤差データ加算部１８０８とを備えている。また、逐次型画像データ処理部１５０７ｂは、誤差データの選択に必要な信号をマルチプレクサ１８０７に入力するデコーダ１８０６と、逐次型画像データ処理部１５００に対し、あらかじめ設定されている誤差拡散のモード（２値誤差拡散、３値誤差拡散、４値誤差拡散）のうちのいずれによって誤差拡散を実行するか、あるいは誤差拡散処理に使用される演算係数を設定できる誤差拡散処理ハードウェアレジスタ群１８０５を備えている。さらに、逐次型画像データ処理部１５０７ｂは、ブルーノイズ信号発生部１８０９を備え、誤差拡散処理にブルーノイズを使用するか否かをも誤差拡散処理ハードウェアレジスタ群１８０５の設定によって選択可能に構成されている。
【００７１】
誤差データ算出部１８０１は、現画素ラインに含まれる画素の画素データと所定の閾値との差である誤差データを算出する構成である。誤差データ算出手段１８０１は、３つの量子化基準値保存部１８０３ａ，１８０３ｂ，１８０３ｃと、３つのコンパレータ１８０４ａ，１８０４ｂ，１８０４ｃと、３つのマルチプレクサ１８０２ａ，１８０２ｂ，１８０２ｃのそれぞれに接続された閾値テーブル群１８１０ａ，１８１０ｂ，１８１０ｃを備えている。閾値テーブル群１８１０ａ，１８１０ｂ，１８１０ｃは、例えばそれぞれ６つの閾値テーブルＴＨｘＡ〜ＴＨｘＦ（ｘ＝０，１，２）から構成される。これは、誤差拡散処理ハードウェアレジスタ群１８０５の設定によって選択可能であり、本実施形態における階調処理では、ＭａｇｅｎｔａおよびＣｙａｎの画像データの階調処理に用いる画像処理プロセッサと、ＹｅｌｌｏｗおよびＢｌａｃｋの画像データを階調処理する画像プロセッサの２つの画像プロセッサを使用する。
【００７２】
以下、ＭａｇｅｎｔａおよびＣｙａｎの画像データ処理用の画像プロセッサを例にとって説明する。
【００７３】
Ｍａｇｅｎｔａ用にＴＨｘＡ，ＴＨｘＢ，ＴＨｘＣ（ｘ＝０，１，２）を、Ｃｙａｎ用にＴＨｘＤ，ＴＨｘＥ，ＴＨｘＦ（ｘ＝０，１，２）を使用する。Ｍａｇｅｎｔａ用として用いるＴＨｘＡ〜ＴＨｘＣ（ｘ＝０，１，２）は、文字、写真、中間などの画像の特徴量による抽出結果に応じて、閾値テーブルがそれぞれ選択されるようにしておくことが可能である。文字部分では主走査もしくは副走査の位置によらない固定閾値を設定した単純な誤差拡散、写真部分では線数が低いディザ閾値を設定した誤差拡散拡散、中間部分では写真部より高線数の閾値を設定した誤差拡散を行うことができ、より好ましい画像を形成することができる。ＴＨ０Ａ，ＴＨ１Ａ，ＴＨ２Ａは、同じ特徴量に判定された画素に対する閾値である。Ｃｙａｎ用についても同様である。また、ＹｅｌｌｏｗおよびＢｌａｃｋの画像データを処理するプロセッサについては、上の説明のＭａｇｅｎｔａをＹｅｌｌｏｗに、ＣｙａｎをＢｌａｃｋに読み替えたものと同様である。
【００７４】
ただし、ディザ処理用のスクリーン角は色毎に異なっており、ディザ処理パラメータの一例を図１９に示す。
【００７５】
本実施形態では、量子化基準値保存部１８０３ａ、コンパレータ１８０４ａ、閾値テーブル群１８１０ａに接続されたマルチプレクサ１８０２ａが１組となって動作する。また、量子化基準値保存部１８０３ｂ、コンパレータ１８０４ｂ、閾値テーブル群１８１０ｂに接続されたマルチプレクサ１８０２ｂが１組となって動作し、量子化基準値保存部１８０３ｃ、コンパレータ１８０４ｃ、閾値テーブル群１８１０ｃに接続されたマルチプレクサ１８０２ｃが１組となって動作する。
【００７６】
逐次型画像データ処理部１５０７には、画像データと誤差データとの加算値（加算値データ）がＳＩＭＤ型プロセッサ１５０６から入力される。この画像データは、今回処理される注目画素の画像データであり、誤差データは、注目画素以前に処理された画素の誤差データである。入力された加算値データは、以前に処理された画素の誤差データに基づいて誤差データ加算部１８０８が算出した値を加算され、演算誤差低減のために１６、または３２で除算される。さらに、除算された加算値データは、誤差データ算出部１８０１の３つのコンパレータ１８０４ａ〜１８０４ｃのすべてに入力される。なお、誤差データ加算部１８０８が以前に処理された画素の誤差データに基づいて算出した値については、後述する。
【００７７】
コンパレータ１８０４ａ〜１８０４ｃには、それぞれ接続された閾値テーブル群に接続されているマルチプレクサ１８０２ａ〜１８０２ｃから閾値が入力される。そして、入力された加算値データから閾値を差し引き、画像データが作成される。また、加算値データからそれぞれの量子化基準値保存部１８０３ａ〜１８０３ｃに保存されている量子化基準値を差し引いた値を誤差データとしてマルチプレクサ１８０７に出力する。この結果、マルチプレクサ１８０７には、合計３つの誤差データが同時に入力することになる。
【００７８】
なお、誤差拡散処理にブルーノイズを使用する場合には、ブルーノイズ信号発生部１８０９がブルーノイズデータを比較的高周期でオン、オフしてブルーノイズを発生する。閾値はコンパレータ１８０４ａ〜１８０４ｃに入力する以前にブルーノイズから差し引かれる。ブルーノイズを用いた処理により、閾値に適当なばらつきを持たせて画像に独特のテクスチャーが発生することを防ぐことができる。
【００７９】
閾値テーブル１８０２ａ〜１８０２ｃには、それぞれ異なる値の閾値が保存されている。本実施形態では、閾値テーブル１８０２ａ〜１８０２ｃのうち、閾値テーブル１８０２ａが最も大きい閾値を保存し、次いで閾値テーブル１８０２ｂ、閾値テーブル１８０２ｃの順序で保存される閾値が小さくなるものとした。また、量子化標準値保存部１８０４ａ〜１８０４ｃは、接続された閾値テーブル１８０２ａ〜１８０２ｃに応じて保存する量子化基準値が設定されている。たとえば、画像データが０〜２５５の２５６値で表される場合、量子化基準値保存部１８０３ａには２５５が、また、量子化基準値保存部１８０３ｂには１７０が、量子化基準値保存部１８０３ｃには８５が保存される。
【００８０】
コンパレータ１８０４ａ〜１８０４ｃは、作成した画像データを論理回路１８０６に出力する。論理回路１８０６は、このうちから注目画素の画像データを選択してマルチプレクサ１８０７に入力する。マルチプレクサ１８０７は、入力された画像データに応じて３つの誤差データのうちのいずれかを注目画素の誤差データとして選択する。選択された誤差データは、ＳＩＭＤ型プロセッサ１５０６のＰＥを介してＲＡＭ１５０３のいずれかに入力される。さらに、論理回路（デコーダ）１８０６が出力した画像データは、マルチプレクサ１８０７に入力される以前に分岐され、ＳＩＭＤ型プロセッサ１５０６のＰＥのいずれかに入力される。本実施形態では、画像データを上位ビット、下位ビットの２ビットで表されるデータとした。このため、この処理では、コンパレータ１８０４ａは使用されていない。なお、本実施形態では、以降、注目画素の画像データを画素データと称する。
【００８１】
選択された誤差データは、誤差データ加算部１８０８に入力される。誤差データ加算部１８０８は、図１６で▲１▼、▲２▼、▲３▼を付して示した画素、つまり注目画素に対して３つ前に処理された画素の誤差データ（図１８では誤差データ３と記す）、２つ前に処理された画素の誤差データ（図１８では誤差データ２と記す）、１つ前に処理された画素の誤差データ（図１８では誤差データ１と記す）を保存している。
【００８２】
誤差データ加算部１８０８は、誤差データ３に演算係数である０または１を乗じる。また、誤差データ２に演算係数である１または２を乗じ、誤差データ１に演算係数である２または４を乗じる。そして、３つの乗算値を足し合わせ、この値（重み付け誤差データ）をＳＩＭＤ型プロセッサ１５０６から次ぎに入力した加算値データと足し合わせる。この結果、注目画素に近い位置にある画素ほど注目画素の誤差拡散処理に大きい影響を及ぼすことになり、画素の誤差を適切に拡散し、元画像のイメージに近い画像を形成することができる。
【００８３】
以上述べた逐次型画像データ処理部１５０７における画像データの作成は、一般的にＩＩＲ型フィルタシステムと呼ばれる構成を用いて行われている。図２０はそのシステム構成を示す図である。ＩＩＲ型フィルタシステムで用いられる演算式は、
ＯＤｎ＝（１−Ｋ）×ＯＤｎ−１＋Ｋ・ＩＤｎ ・・・（３）
ＯＤｎ：演算後の画素濃度
ＯＤｎ−１：一つ前の画素データを用いての演算結果
ＩＤｎ：現画素データ
Ｋ：重み係数
と表す。
【００８４】
式（３）および図２０から明らかなように、演算後の濃度ＯＤｎは、１つ前の画素データを用いての演算結果ＯＤｎ−１と現画素データＩＤｎの値から求められる。一般的にＩＩＲ型フィルタシステムは、現画素より以前に処理された画素を用いた演算結果を使用して現画素についての演算を行う、いわゆる逐次変換を行うための専用の回路である。本実施形態に係る画像処理装置の逐次型画像データ処理部５０７は、後述の図２１に示した処理によらず、図２０に示したような逐次変換の全般に使用することができる。
【００８５】
図２２は、誤差拡散処理ハードウェアレジスタ群１８０５に設定するレジスタを説明するための図である。本実施形態に係る画像処理装置は、図示したレジスタの設定によって
・２値誤差拡散で誤差拡散処理を行うモード（２値誤差拡散モード）
・３値誤差拡散で誤差拡散処理を行うモード（３値誤差拡散モード）
・４値誤差拡散で誤差拡散処理を行うモード（４値誤差拡散モード）
のいずれで誤差拡散処理を行うか選択することができる。また、誤差データ加算部１８０８で使用される演算係数を設定することができる。さらに、誤差拡散処理にブルーノイズを使用するか否かを選択することもできる。
【００８６】
図２２に示した誤差拡散処理ハードウェアレジスタ群１８０５は、量子化基準値保存部１８０３ａの量子化基準値０を設定するレジスタ３００１、量子化基準値保存部１８０３ｂの量子化基準値１を設定するレジスタ３００２、量子化基準値保存部１８０３ｃの量子化基準値２を設定するレジスタ３００３を備えている。また、誤差拡散処理ハードウェアレジスタ群１８０５は、閾値テーブル１８０２ｃに設定される閾値０を設定するレジスタ３００４、閾値テーブル１８０２ｂに設定される閾値１０〜１７を設定するレジスタ３００５、閾値テーブル８０２ａに設定される閾値２０〜２７を設定するレジスタ３００６、ブルーノイズ値を設定するレジスタ３００７、誤差拡散処理ハードウェアコントロールレジスタ３００８を有している。各レジスタには、それぞれ８ビットが割り当てられていて、レジスタ全体は、６４ビットのデータ量を持っている。
【００８７】
２値誤差拡散モードは、レジスタ３００１〜３００３のすべてに同一の値を設定する。そして、レジスタ３００４、レジスタ３００５にＦＦＨを設定することによって実現できる。また、３値誤差拡散モードは、レジスタ３００１、レジスタ３００２に同一の値を設定し、レジスタ３００４にＦＦＨを設定する。さらに、２値誤差拡散モード、３値誤差拡散モードでは、レジスタ３００５、レジスタ３００６に同一の値を設定するか、異なる値を設定するかによって固定閾値誤差拡散処理と変動閾値誤差拡散処理とを切り替えることができる。
【００８８】
誤差拡散処理にブルーノイズを用いる場合は、レジスタ３００７にブルーノイズを使用することを示す値を設定する。そして、レジスタ３００５にブルーノイズデータのオンオフを示すスイッチングデータを設定する。スイッチングデータが１の場合にはブルーノイズ値を各閾値に加算し、スイッチングデータが０の場合には閾値をそのまま使用する。さらに、誤差データ加算部１８０８で使用される演算係数は、誤差拡散処理ハードウェアコントロールレジスタの設定値を変更することによって選択できる。
【００８９】
次に、前述のＳＩＭＤ型プロセッサ１５０６、逐次型画像データ処理部１５０７ｂで行われる処理について、フローチャートおよび処理手順を示した図を用いて説明する。図２３はＳＩＭＤ型プロセッサ１５０６で行われる誤差拡散処理の処理手順を示すフローチャート、図２４は逐次型画像データ処理部１５０７ｂで行われる誤差拡散処理の処理手順を説明するための図、図２５はラインシフトを説明するための図である。
【００９０】
図２３のフローチャートにおいて、ＳＩＭＤ型プロセッサ１５０６は、まず、現画像データが１ライン目かどうかを判断し（Ｓ２１０１）、１ライン目である場合には、前２ライン分の誤差加算値を初期化する（Ｓ２１０１）。次いで、今回の誤差拡散演算する画像データが１ＳＩＭＤ目であるかどうかを判断し（Ｓ２１０３）、１ＳＩＭ目（現ラインの先頭部分の画像データ）である場合には、誤差加算値を初期化する（Ｓ２１０５）。１ＳＩＭＤ目でない場合には、前のＳＩＭＤで誤差拡散演算後の誤差データが、現在演算している画像データと同じ色かどうかを判断し（Ｓ２１０４，Ｓ２１０６）、異なる色の場合には、前ＳＩＭＤの演算結果を前ラインの違う色として保存し（Ｓ２１０７、図２５の処理Ａ２）、ブルーノイズテーブルの参照位置も保存し（Ｓ２１０９）、同じ色の前回誤差拡散演算時のブルーノイズ参照位置を呼び出す（Ｓ２１１０）。
【００９１】
Ｓ２１０６で同じ色である場合には、同じ色の前ラインの１ＳＩＭＤの演算結果として保存する（Ｓ２１０８、図２５の処理Ａ１）。同じ色かどうかの判断は、例えば、これから誤差拡散演算しようとしている色が、Ｍａｇｅｎｔａ版の画像データである場合に、違う色の画像データとは、Ｃｙａｎ版の画像データについては違う色として判断し、Ｍａｇｅｎｔａ版の画像データである場合には、同じ色として判断する。
【００９２】
そして、２ライン前の誤差加算値データを前ＳＩＭＤの１ライン前のデータとして保存し（Ｓ２１１１、図２５の処理Ｂ）、現ＳＩＭＤの２ライン前分のデータをメモリから呼び出す（Ｓ２１１２、図２５の処理Ｄ，Ｅ）。次いで、現ＳＩＭＤのデータを現ラインから呼び出した（図２５の処理Ｃ）後、誤差加算値を演算する（Ｓ２１１３）。その後、逐次型画像データ処理部１５０７ｂにより誤差拡散処理の演算を行う（Ｓ２１１４）。
【００９３】
一方、逐次型画像データ処理部１５０７は、図２４に示すように、ステップＳ２１０２においてＳＩＭＤ型プロセッサ１５０６が出力した加算値データを入力する（ステップＳ２２０１）。そして、入力した加算値データに誤差データ加算部１８０８で生成された重み付け誤差データを加算する（ステップＳ２２０２）。重み付け誤差データが加算された加算値データは、１６または３２で除算され（ステップＳ２２０３）、誤差データ算出部１８０１に入力される。誤差データ算出部１８０１は、入力したデータに基づいて誤差データおよび画素データを生成し（ステップＳ２２０４）、誤差データをマルチプレクサ１８０７に入力する。また、画素データを、論理回路１８０６およびＳＩＭＤ型プロセッサ１５０６に入力する。
【００９４】
マルチプレクサ１８０７は、論理回路１８０６から入力した画像データに応じて誤差データを一つ選択する（ステップＳ２２０５）。そして、選択した誤差データをＳＩＭＤ型プロセッサ１５０６および誤差データ加算部１８０８に出力する（ステップＳ２２０６）。誤差データを入力した誤差データ加算部１８０８は、誤差データに基づいて重み付け誤差データを算出する（ステップＳ２２０７）。逐次型画像データ処理部１５０７は、入力してくる加算値データに対して逐次的に以上の処理を繰り返し実行する。
【００９５】
図２１は画像処理部の構成を示すブロック図で、同図を参照して画像処理方式について説明する。
画像処理部は、多階調の画像データ１１００を受け取り、その量子化データ１１０１を出力するもので、量子化処理部１１２０、画像特徴抽出部１１３０、量子化閾値発生部１１４０、量子化処理部１１２０と画像特徴抽出部１１３０とのタイミング調整のための信号遅延部１１５０から構成される。この信号遅延部１１５０は必要に応じて設けられるものであり、例えば所要ライン数のラインメモリからなる。入力される画像データ１１００は、例えばスキャナによって６００ｄｐｉで読み取られた８ビット／１画素のデータである。一般に、このような画像データ１１００は、中間調を滑らかに表現するために平滑化フィルタを通してから入力される。通常、１５０Ｌｐｉ程度の画像周期から平滑化されるため、グラビア印刷などで用いられる１７５Ｌｐｉ以上の高線数網点画像の周期性成分は画像データ１１００には残っていない。
【００９６】
量子化処理部１１２０は、量子化閾値発生部１１４０で生成された量子化閾値を用いて多階調の画像データを誤差拡散法により量子化するものであり、本実施形態においては図示のように、量子化器（比較器）１１２１、誤差計算部１１２２、誤差記憶部１１２３、誤差拡散マトリクス部１１２４、誤差加算部１１２５からなる。画像データ１１００は、信号遅延部１１５０によってタイミングを調整されて誤差加算部１１２５に入力される。誤差加算部１１２５によって拡散誤差を加算された画像データは量子化器１１２１に入力される。量子化器１１２１は、入力された画像データを量子化閾値発生部１１４０より与えられる量子化閾値を用いて量子化し、量子化結果を量子化データ１１０１として出力する。
【００９７】
本実施形態においては、２ビットの誤差拡散処理を例にとって説明する。
量子化閾値発生部１１４０で量子化閾値１〜３（ｔｈ１〜ｔｈ２）を生成する。量子化閾値の関係は、
量子化閾値１（ｔｈ１）≦量子化閾値２（ｔｈ２）≦量子化閾値３（ｔｈ３）
とする。量子化器１１２１は入力された画像データを閾値ｔｈ１〜ｔｈ３と比較し、それぞれ、ｔｈ３より大きい場合に“３”、ｔｈ２より大きい場合に“２”、ｔｈ１より大きい場合に“１”、ｔｈ１より小さい場合に“０”の値をとる２ビットの量子化データ１１０１を出力するものとして説明する。
【００９８】
誤差計算部１１２２は量子化器１１２１の量子化誤差を算出するものである。ここでは８ビットの画像データを扱っているため、この誤差計算においては、例えば、量子化データ１１０１の”３”を２５５（１０進）、“２”を１９２（１０進）、“１”を１２８（１０進）、”０”を０（１０進）として扱う。算出された量子化誤差は誤差記憶部１１２３に一時的に記憶される。この誤差記憶部１１２３は、注目画素の周辺の処理済み画素に関する量子化誤差を保存するためのものである。本実施形態では、次に述べるように量子化誤差を２ライン先の周辺画素まで拡散させるため、例えば３ラインのラインメモリが誤差記憶部１１２３として用いられる。
【００９９】
誤差拡散マトリクス部１１２４は、誤差記憶部１１２３に記憶されている量子化誤差データから次の注目画素に加算する拡散誤差を計算するものである。本実施形態では、誤差拡散マトリクス部１１２４は、図２６に示すような副走査方向が３画素、主走査方向が５画素のサイズの誤差拡散マトリクスを用いて拡散誤差データを算出する。図２６において、＊印は次の注目画素の位置に相当し、ａ，ｂ，．．．，ｋ，ｌは周辺の１２個の処理済み画素の位置に対応した係数（総和は３２）である。誤差拡散マトリクス部１１２４では、それら１２個の処理済み画素に対する量子化誤差と対応した係数ａ〜ｌとの積和を３２で除した値を、次の注目画素に対する拡散誤差として誤差加算部１１２５に与える。
【０１００】
画像特徴抽出部１１３０は、エッジ検出部１１３１と領域拡張処理部１１３２とからなる。エッジ検出部１１３１は、画像データ１１００のエッジ検出を行うもので、本実施形態ではレベル０（エッジ度最大）からレベル８（非エッジ）までのエッジレベルを表す４ビットのエッジデータを出力する。より具体的には、例えば図２７に示す４種類の５×５の微分フィルタを用いて、主走査方向、副走査方向、主走査方向から±４５°傾いた方向の４方向についてエッジ量を検出し、その中で絶対値が最大のエッジ量を選び、そのエッジ量の絶対値をレベル０からレベル３までの４レベルのエッジレベルに量子化して出力する。
【０１０１】
領域拡張処理部１１３２は、エッジ検出部１１３１により検出されたエッジに対し７画素幅の領域拡張処理を行うもので、エッジ検出部１１３１より出力されたエッジデータを参照し、注目画素の周囲の７×７画素の領域（主走査方向の前後３画素、副走査方向の前後３画素の範囲）の中で最小のエッジレベル（最大のエッジ度合）を注目画素のエッジレベルとして、それを４ビットのエッジデータとして出力する。このエッジデータは量子化閾値発生部１１４０に与えられる。
【０１０２】
量子化閾値発生部１１４０は、領域拡張処理部１１３２より出力されたエッジデータで表されるエッジレベルに応じた振動幅で、画像空間上で周期的に振動する量子化閾値を生成し、それを量子化処理部１１２０の量子化器１１２１に与えるもので、ディザ閾値発生部１１４１と、このディザ閾値発生部１１４１の出力値にエッジデータで示されるエッジレベルに対応した係数（０〜３）を掛ける乗算部１１４２、及び乗算部１１４２の出力値に固定値（この実施形態で１２８としている）を加算する加算部１１４３から構成される。
【０１０３】
本実施形態では、ディザ閾値発生部１１４１は、図２８及び図２９に示すような１から６までの閾値を小さいものから順に（１が最小、６が最大）ラインを成長させるように配置した４×４のディザ閾値マトリクスを用い、画像空間上で周期的に１から６まで振動するディザ閾値を出力する。ここで、同じ値の画素は同じ閾値を使用している。ディザ閾値周期は、これは６００ｄｐｉの画像形成の場合には１６８Ｌｐｉに相当する。このようなディザ閾値発生部１１４１は、前記ディザ閾値マトリクスを格納したＲＯＭと、画像データの主、副走査のタイミング信号をカウントして、このＲＯＭの読み出しアドレスを発生するカウンタなどによって容易に実現できる。ここで、図２８及び図２９で１と設定された画素は主走査方向に並べることにより、主走査方向に２画素並んだドットを最初に形成することを表す。このように、安定したドット形成がなされることを意図して、エネルギーが少ない書き込みレベルである１値を２画素並べる。この場合のスクリーン角とラインの成長方向を図３０に示した。ラインの成長方向は、図中の“ラインが成長する方向１“に示した。
【０１０４】
乗算部１１４２は、画像特徴抽出部１１３０からのエッジデータで示されるエッジレベルがレベル０（非エッジ）の時に係数３を、レベル１の時に係数２を、レベル２の時に係数１を、レベル３（最大エッジ度合）の時に係数０を、ディザ閾値発生部１１４１の出力値に乗じる。
【０１０５】
以上のように構成された画像処理装置の量子化データ１１０１を例えば電子写真方式のプリンタなどに与えれば、文字、画像の変化点や比較的低線数の網点画像部などは解像性が良く、写真、画像の変化の少ない部分、高線数の網点画像などは滑らかで安定性が良く、それら領域が違和感なく整合した高品位な画像を形成可能である。これについて以下説明する。
【０１０６】
画像中の文字や線画のエッジ部のような変化が急峻でエッジレベルがレベル３（エッジ度合最高）となる部分では、量子化閾値発生部１１４０で生成される量子化閾値は固定され、量子化処理部１１２０で固定閾値を用いた純粋な誤差拡散法による量子化処理が行われるため、解像性の良い画像を形成できる。
【０１０７】
本実施形態においては、図１５に示す逐次処理演算部を有するＳＩＭＤプロセッサを２つ使用し、ＹＭＣＫの画像データに対して、Ｙ（Ｙｅｌｌｏｗ）の画像データとＫ（Ｂｌａｃｋ）の画像データで１つ逐次処理演算部を有するＳＩＭＤプロセッサを使用し、Ｃ画像信号Ｍの画像データの２組の画像データをもう１つの１つ逐次処理演算部を有するＳＩＭＤプロセッサを用いて階調処理を行う。そのため、ＳＩＭＤプロセッサに入力される階調処理前の２つの画像データ（ＹＫもしくはＣＭ）と、ＳＩＭＤプロセッサから２つの画像データ（ＹＫもしくはＣＭ）を出力する２入力２出力の画像データを処理する。誤差拡散処理を行う場合には、入力した２つの画像データに対して、ＳＩＭＤ処理可能な画像データ数毎に、１つ逐次処理演算部を有するＳＩＭＤプロセッサを切り替えて処理を行う。
【０１０８】
図３１は画像プロセッサの状態遷移図である。同図に示すように、画像プロセッサは、コマンド→メイン１（Ｍａｇｅｎｔａ／Ｙｅｌｌｏｗ画像データの処理）→メイン２（Ｃｙａｎ／Ｂｌａｃｋの画像データの処理）→コマンド→メイン１…と処理状態がループしている。
【０１０９】
図３２のフローチャートに基づいて、２入力２出力時の画像処理プロセッサの動作を説明する。
メイン処理１では、ＭａｇｅｎｔａもしくはＹｅｌｌｏｗの画像データの処理を行い、メイン処理２では、Ｃｙａｎもしくは、Ｂｌａｃｋの画像データの処理を行う。ＳＩＭＤプロセッサ１５０６に対して、Ｍａｇｅｎｔａ（Ｙｅｌｌｏｗ）の入力をデータ入出力用バス１５０１ａを用いて入力し、データ入出力用バス１５０１ｃを用いて出力する。同様に、Ｃｙａｎ（Ｂｌａｃｋ）の画像データの入力を、データ入出力用バス１５０１ｂを用いて入力し、データ入出力用バス１５０１ｄを用いて出力する。データ入出力用バス１５０１ｃはデバッグ用の出力などに用いる。
【０１１０】
メイン処理１にて、ＳＩＭＤプロセッサ１５０６へのデータ入力がある場合には（Ｓ２３０１）、画像データをメモリ１５０３への取り込み処理を開始する（Ｓ２３０２）。１ライン取り込みが終了した場合には（Ｓ２３０３）、ＳＩＭＤ処理プロセッサ１５０６が処理できる画像データの単位で階調処理（ここでは誤差拡散処理）を開始する（Ｓ２３０４）。１ライン処理が終了したら（Ｓ２３０５）、１ライン出力を開始する（Ｓ２３０６）。Ｓ２３０２、Ｓ２３０６などの画像データのメモリ取り込み・出力開始処理は、各メモリコントローラ１５０５ａ〜１５０５ｂへの処理開始コマンドをレジスタに設定し、ＳＩＭＤプロセッサは次の制御へ移行（状態遷移）する。階調処理（誤差拡散処理）の開始（Ｓ２３０４）は、逐次処理演算部１５０７ｂへの開始処理コマンドを誤差拡散処理ハードウェアコントロールレジスタ２００８開始コマンドに相当する所定の設定値を書き込むことにより行う。
【０１１１】
メイン処理２も同様にＳＩＭＤプロセッサ１５０６へのデータ入力がある場合には（Ｓ２４０１）、画像データをメモリ１５０３への取り込み処理を開始する（Ｓ２４０２）。１ライン取り込みが終了した場合には（Ｓ２４０３）、ＳＩＭＤ処理プロセッサ１５０６が処理できる画像データの単位で階調処理（ここでは誤差拡散処理）を開始する（Ｓ２４０４）。１ライン処理が終了したら（Ｓ２４０５）、１ライン出力を開始する（Ｓ２４０６）。Ｓ２４０２、Ｓ２４０６などの画像データのメモリ取り込み・出力開始処理は、各メモリコントローラ１５０５ａ〜１５０５ｂへの処理開始コマンドをレジスタに設定し、ＳＩＭＤプロセッサは次の制御へ移行（状態遷移）する。階調処理（誤差拡散処理）の開始（Ｓ２４０４）は、逐次処理演算部１５０７ｂへの開始処理コマンドを誤差拡散処理ハードウェアコントロールレジスタ２００８開始コマンドに相当する所定の設定値を書き込むことにより行う。
【０１１２】
コマンド処理では、ＳＩＭＤプロセッサ１５０６に対する制御ＣＰＵからのコマンドの受付処理を行う（Ｓ２５０１，Ｓ２５０２）。
【０１１３】
画像濃度（階調性）の自動階調補正（ＡＣＣ：Auto Color Calibration）の呼び出し手順を説明する。
【０１１４】
図３３は操作部１４２全体を示す正面図である。操作部で自動階調補正メニュー（ＡＣＣメニュー）呼び出すと、図３４の操作画面が表示される。コピー使用時、あるいはプリンタ使用時用の自動階調補正の［実行］を選択すると、図３４に示した操作画面が表示される。コピー使用時を選択した場合には、コピー使用時に使用する階調補正テーブルが、プリンタ使用時を選択するとプリンタ使用時の階調補正テーブルが参照データに基づいて変更される。変更後のＹＭＣＫ階調補正テーブルで画像形成を行った結果が、望ましくない場合には、処理前のＹＭＣＫ階調補正テーブルを選択することができるように、［元の値に戻す］キーが図３４の画面中に表示されている。
【０１１５】
図３５は画像濃度（階調性）の自動階調補正（ＡＣＣ）の制御手順を示すフローチャートである。画像濃度の自動階調補正では、ステップＳ３１０１で図３６の画面中の印刷スタートキーを押し下げると、ステップＳ３１０２で図３７に示すような、ＹＭＣＫ各色、及び文字、写真の各画質モードに対応した複数の濃度階調パターンを転写材上に形成する。濃度階調パターンは、あらかじめＩＰＵのＲＯＭ中に記憶・設定がなされている。パターンの書き込み値は、例えば１６進数表示で１１ｈ，２２ｈ，…，ＥＥｈ，ＦＦｈ、と００ｈ（転写紙の地肌部）で、図に示したような配置で形成する。濃度階調パターンは、ＹＭＣＫそれぞれに文字部用および写真部用のプリンタγテーブルを算出するための濃度階調パターンを形成する。文字部用の濃度階調パッチでは、一例として誤差拡散などの階調処理を行い、写真部用の濃度階調パッチでは、前述したＤＡＴＥ処理が行われたパターンを出力する。図では、地肌部を除いて１５階調分のパッチを表示しているが、それぞれのパッチは００ｈ−ＦＦｈの８ビット信号の任意の値を選択することができる。
【０１１６】
図３７に示した自動階調補正用のパターンを出力した転写紙には、上述した濃度階調パターンに加えて、感光体の感度ムラ、転写などの作像部の感度ムラなどに起因する濃度むらの補正のために、基準パターンを左からＬｅｆｔ、Ｌｅｆｔ−Ｍｉｄｄｌｅ（ＬＭ）、Ｃｅｎｔｅｒ、Ｒｉｇｈｔ−Ｍｉｄｄｌｅ（ＲＭ）、Ｒｉｇｈｔの計５カ所に例えば３３ｈ、４４ｈ、５５ｈの３パッチを形成している。その隣にも同様なパッチを形成しているが、これは隣接するパターンによるフレアの影響を主走査方向の場所Ｌｅｆｔ、ＭＬ、Ｃｅｎｔｅｒ、ＭＲ、Ｒｉｇｈｔによらずほぼ同等とするためである。ただし、Ｃｅｎｔｅｒ、Ｒｉｇｈｔ−Ｍｉｄｄｌｅ（ＲＭ）のパッチの右隣には黒パッチを配置し、左隣にはＹｅｌｌｏｗパッチを配置しているのに対し、それ以外のＬｅｆｔ、Ｌｅｆｔ−Ｍｉｄｄｌｅ（ＬＭ）、ＲｉｇｈｔにはＹｅｌｌｏｗパッチを配置していない。これは、Ｙｅｌｌｏｗの明度が高いことによりフレアの影響の絶対値が小さいと見積もられることと、Ｂｌａｃｋの読み取りの際に、スキャナのＲＧＢ信号のうち、Ｇｒｅｅｎ（もしくはＲｅｄ）信号を用いるためである。Ｙｅｌｌｏｗが主に影響するのはＢｌｕｅ成分であることから、Ｇｒｅｅｅｎ（もしくはＲｅｄ）信号を用いることにより、隣接するＹｅｌｌｏｗパッチの影響を低減することができる。
【０１１７】
ステップＳ３１０３で転写材にパターンが出力された後、転写材を原稿台１１８上に載置するように、操作画面上には図３８に示す画面が表示される。画面の指示に従い、パターンが形成された転写紙を原稿台に載置して、図３８の画面で“読み取りスタート”を選択するか、または“キャンセルを選択する。”キャンセル“を選択した場合にはここで処理を終える（ステップＳ３１０４）。一方、“読み取りスタート”を選択すると、スキャナが走行し、ＹＭＣＫ濃度パターンのＲＧＢデータを読み取る（ステップＳ３１０５）。このとき、パターン部のデータと転写材の地肌部のデータを読み取る。次いで、パターン部のデータが正常に読み取られたかを判断し（ステップＳ３１０６）。正常に読み取られない場合には、再び図３８の画面が表示される。２回正常に読み取られない場合には処理を終了する（ステップＳ３１０７）。
【０１１８】
ステップＳ３１０６でデータが正常に読み取られていれば、ステップＳ３１０８でＡＣＣの機差補正値による補正を行い、ステップＳ３１０９でムラの検出および補正を行うか否かを判断し、補正を行うのであれば、ステップＳ３１１０でムラの検出および補正を行い、行わないのであればそのままステップＳ３１１１の処理にスキップする。
【０１１９】
ステップＳ３１１１では、図３４の画面で“地肌の補正”に“実行”が選択されているか否かを判断し、“実行”が選択されている場合には、ステップＳ３１１２で読み取りデータに対する地肌データによる補正を行う。次いで、ステップＳ３１１３で、図３４の画面で“高画像濃度部の補正”に“実行”が選択されているか否かを判断し、“実行”が選択されている場合には、ステップＳ３１１４で参照データの高画像濃度部のデータに補正処理を行う。
【０１２０】
そして、ステップＳ３１１５で、以上処理を行われたデータを用いて、ＹＭＣＫ階調補正テーブルを作成し、各色のＹＭＣＫ階調補正テーブルが全て作成されると（ステップＳ３１１６）、これらの処理を写真、文字の各画質モード毎について実行する（ステップＳ３１１７）。
【０１２１】
処理中には、操作画面には図３９の画面が表示される。処理終了後のＹＭＣＫ階調補正テーブルで画像形成を行った結果が、望ましくない場合には、処理前のＹＭＣＫ階調補正テーブルを選択することができるように、［元に値に戻す］キーが図３４の画面中に表示されている。なお、図４０は図３３の液晶表示画面（タッチパネル）の詳細を示す正面図である。
【０１２２】
以下、それぞれの処理の詳細を説明する。
【０１２３】
図３７は、ムラを補正するために使用する基準パッチを示す図である。この基準パッチでは、Ｌｅｆｔ０〜１５（以後Ｌ０〜Ｌ１５と略す）、Ｌｅｆｔ−Ｍｉｄｄｌｅ０〜１５（以後ＭＬ０〜ＭＬ１５と略す）、Ｃｅｎｔｅｒ０−１５同Ｃ０〜Ｃ１５）、Ｒｉｇｈｔ−Ｍｉｄｄｌｅ０−１５（同ＭＲ０〜ＭＲ１５）、Ｒｉｇｈｔ ０−１５（同Ｒ０〜Ｒ１５）のパッチが使用される。これらのパターンは、写真用の階調処理がなされている。その理由は、写真モードの階調処理のＹＭＣを重ね合わせた場合のグレーバランスの主走査方向の位置のバラつきを低減することを発明の第１の目的としているからである。
【０１２４】
図４１はムラの補正値の算出方法を説明するための４元チャートである。同図において、第１象現（図４１の［Ｉ］）の横軸は階調パッチの書き込み値、縦軸はスキャナの読み取り値でグラフは、階調パッチの読み取り値を表す。第２象現（図４１の［ＩＩ］）の横軸はプリンタγ変換テーブルへの入力値で、グラフは自動階調補正（ＡＣＣ）の調整目標（ターゲット）、もしくはＡＣＣ実行後のプリンタγの調整結果を表す。第３象現（図４１の［ＩＩＩ］）の縦軸は、階調処理への入力値で、グラフはムラを補正するための補正量を表す。このグラフは求める値を図示したものである。第４象現（図４１の［ＩＶ］）は階調処理の特性である。
【０１２５】
第１象現のａ）〜ｃ）は、それぞれ
ａ）補正の基準値
ｂ）基準より濃度が濃い場合
ｃ）基準より濃度が薄い場合
を例示したものである。たとえば、図３７に示した階調パターンのＣ０〜Ｃ１５を基準とし、それ以外のＬ０〜Ｌ１５、ＭＬ０〜ＭＬ１５、ＭＲ０〜ＭＲ１５、Ｒ０〜Ｒ１５の読み取り結果のうち、濃度が薄い場合にはｂ）、濃度が濃い場合にはｃ）として図示した。
【０１２６】
ＡＣＣのターゲットは、主走査方向のムラにかかわらず一定であるので、ムラがある場合には、第２象現のグラフ出力した結果ｄ）〜ｆ）に示したように主走査方向の位置により出力結果がばらつく。ここで、ｄ）はａ）に対するプリンタγテーブルである。このような場合には、ＹＭＣ三色を重ね合わせた場合などでムラが生じる。それを防ぐために、主走査方向の位置に応じて作像部の感度ムラを補正し、場所によらない画像濃度の調整結果（図４１の［ＩＩ］）が得られるように、プリンタγテーブル（図４１の［ＩＶ］）への補正量（同第ＩＩＩ象現）を主走査方向の位置によって変更する。第ＩＩＩ象現に得られたグラフの傾きを求め、これを補正量の傾きとする。
【０１２７】
上記のようにして得た主走査位置による補正量の概念図を図４２に示す。
【０１２８】
ＡＣＣパターンに形成されたＬｅｆｔ， Ｌｅｆｔ−Ｍｉｄｄｌｅ （ＬＭ）、Ｃｅｎｔｅｒ、Ｒｉｇｈｔ−Ｍｉｄｄｌｅ （ＲＭ）、Ｒｉｇｈｔの各階調パターンの読み取り値から算出した補正量の傾きをＣｅｎｔｅｒの値を基準にしたグラフを図４２ａ）に示した。図４２ｂ）は、ムラの検知パターンのある場所から、検知パターンがない場所へと傾きを補間した結果である。図４２ｂ）は、ＳＩＭＤプロセッサが一度に処理可能な画素数毎に主走査方向の画像幅を区切っている。階調処理前の画像信号を、上記のようにして得られた傾きを用いて補正する。これにより、簡単な計算で効率的に主走査方向のムラを補正することができる。
【０１２９】
図４３はＳＩＭＤプロセッサにおけるムラ補正処理の処理手順を示すフローチャートである。この図４３に示す処理では、まず、ステップＳ３２０１で、画像データをＳＩＭＤプロセッサに入力し、ステップＳ３２０２で、画像データから画像のエッジ度を算出する（特徴量抽出）。次いで、ステップＳ３２０３で主走査方向のムラを補正し、ステップＳ３２０４で前述した階調処理を行う。そして、ステップＳ３２０５で画像信号をＳＩＭＤプロセッサから出力する。
【０１３０】
図４４及び図４５は補正用の階調パターンの数を減らした場合の出力例を示す図である。これらは、ムラの補正量を検知するためのＬｅｆｔ，Ｌｅｆｔ−Ｍｉｄｄｌｅ（ＬＭ）、Ｃｅｎｔｅｒ，Ｒｉｇｈｔ−Ｍｉｄｄｌｅ（ＲＭ）、Ｒｉｇｈｔのムラ検知パターンの数を減らし、階調パターン出力の際のトナーの消費量を減らした階調パターンの例である。
【０１３１】
図４４の階調パターンは、は検知するパターンに隣接してパターンを配置したパターンで、スキャナのフレアの影響がある場合に有効である。すなわち、検知するパターン（一例としてＬｅｆｔ）に隣接したパターン（Ｌｅｆｔ−ｓｕｂ…図中でＬ−ｓｕｂと記載）がない地肌の場合には、検知するパターンの隣にパターンが存在しない場合に比べて地肌の影響を受けて、明るく（画像濃度が薄く）読まれる可能性がある。それを防ぐためにムラを検知するためのパターン〜Ｌｅｆｔ，ＲＭ、Ｒｉｇｈｔ〜に隣接して同程度の書き込み値のパターン〜Ｌｅｆｔ−ｓｕｂ（Ｌ−ｓｕｂ），ＲＭ−ｓｕｂ，Ｒｉｇｈｔ−ｓｕｂ（Ｒ−ｓｕｂ）〜を配置した。ＬＭパターン、Ｃｅｎｔｅｒパターンについては、隣接して階調補正用のＢｌａｃｋパターンがあるために他のパターンとフレアに対する影響は同程度と判断し、形成する必要はないと判断した。
【０１３２】
図４５は、スキャナのフレアの影響が無視できる場合で、この場合は、トナーの消費量を低減するためにムラ検知するパターンＬｅｆｔ，ＲＭ、Ｒｉｇｈｔ〜に隣接するパターン〜Ｌｅｆｔ−ｓｕｂ（Ｌ−ｓｕｂ），ＲＭ−ｓｕｂ，Ｒｉｇｈｔ−ｓｕｂ（Ｒ−ｓｕｂ）〜を省略した。ムラを検知するためのパターンＬｅｆｔ，Ｌｅｆｔ−Ｍｉｄｄｌｅ（ＬＭ）、Ｃｅｎｔｅｒ，Ｒｉｇｈｔ−Ｍｉｄｄｌｅ（ＲＭ）、Ｒｉｇｈｔ３〜５段目のうちの少なくとも１点を用いて、図４６の４元チャートに示すように、第３（［ＩＩＩ］）象現の補正量の傾きを求める。
【０１３３】
地肌の補正について説明する。
【０１３４】
地肌補正の目的は２つある。１つは、ＡＣＣ時に使用される転写材の白色度を補正することである。これは、同一の機械に、同じ時に画像を形成しても、使用する転写材の白色度によって、スキャナで読み取られる値が異なるためである。地肌を補正しない場合のデメリットとしては、例えば、白色度が低い、再生紙などをこのＡＣＣに用いた場合、再生紙は一般にイエロー成分が多いために、イエローの階調補正テーブルを作成した場合に、イエロー成分が少なくなるように補正する。この状態で、次に、白色度が高いアート紙などでコピーをした場合に、イエロー成分が少ない画像となって望ましい色再現が得られない場合がある。
【０１３５】
他の１つは、ＡＣＣ時に用いた転写紙の厚さ（紙厚）が薄い場合には、転写材を押さえ付ける圧板などの色が透けてスキャナに読み取られてしまうことである。例えば、圧板の代わりにＡＤＦ（Auto Document Feeder）と呼ばれる原稿自動送り装置を装着している場合には、原稿の搬送用にベルトを用いているが、これが使用しているゴム系の材質により、白色度が低く、若干の灰色味がある。そのため、読み取られた画像信号も、見かけ上、全体に高くなった画像信号として読み取られるために、ＹＭＣＫ階調補正テーブルを作成する際に、その分薄くなるように作成する。この状態で、今度は紙厚が厚く、透過性が悪い転写紙を用いた場合には、全体の濃度が薄い画像として再現されるため、必ずしも望ましい画像が得られない。これらの不具合を防ぐために、紙の地肌部の読み取り画像信号からパターン部の読み取り画像信号の補正を行っている。
【０１３６】
しかし、上記の補正を行わない場合にもメリットがあり、常に再生紙のように、イエロー成分が多い転写紙を用いる場合には、補正をしない方が、イエロー成分が入った色に対しては色再現が良くなる場合ができる。また、常に、紙厚が、薄い転写紙のみしか用いない場合には、薄い紙に合わせた状態に階調補正テーブルが作成されるというメリットがある。
【０１３７】
上記のように、使用者の状況と好みとに応じて、地肌部の補正をＯＮ／ＯＦＦを行うことができる。
【０１３８】
転写紙上に形成した階調パターン（図３７）の書き込み値を ＬＤ［ｉ］（ｉ＝０，１，…，９）、形成されたパターンのスキャナでの読み取り値をベクトル型式で
ｖ［ｔ］［ｉ］≡（ｒ［ｔ］［ｉ］，ｇ［ｔ］［ｉ］，ｂ［ｔ］［ｉ］）
（ｔ＝Ｙ，Ｍ，Ｃ， ｏｒ Ｋ， ｉ＝０，１，…，９）
とする。（ｒ，ｇ，ｂ）の代わりに、明度、彩度、色相角（Ｌ＊，ｃ＊，ｈ＊），あるいは、明度、赤み、青み（Ｌ＊，ａ＊，ｂ＊） などで表しても良い。あらかじめＲＯＭ４１６またはＲＡＭ４１７中に記憶してある基準となる白の読み取り値を（ｒ［Ｗ］，ｇ［Ｗ］，ｂ［Ｗ］）とする。
【０１３９】
ＡＣＣ実行時におけるγ変換処理部４１０で行われる階調変換テーブル（ＬＵＴ）の生成方法について説明する。
【０１４０】
パターンの読み取り値
ｖ［ｔ］［ｉ］≡（ｒ［ｔ］［ｉ］，ｇ［ｔ］［ｉ］，ｂ［ｔ］［ｉ］）
において、ＹＭＣトナーの各補色の画像信号はそれぞれ
ｂ［ｔ］［ｉ］，ｇ［ｔ］［ｉ］，ｒ［ｔ］［ｉ］
であるので、それぞれの補色の画像信号のみを用いる。ここでは、後の記載を簡単にするために、
ａ［ｔ］［ｉ］（ｉ＝０，１，２，…，９；ｔ＝Ｃ，Ｍ，Ｙ，ｏｒＫ）
を用いて表す。階調変換テーブルを作成すると処理が簡単である。なお、ブラックトナーについては、ＲＧＢのいずれの画像信号を用いても十分な精度が得られるが、ここでは、Ｇ（グリーン）成分を用いる。
【０１４１】
参照データは、スキャナの読み取り値
ｖ０［ｔ］［ｉ］≡（ｒ０［ｔ］［ｉ］，ｇ０［ｔ］［ｉ］，ｂ０［ｔ］［ｉ］）
及び対応するレーザの書き込み値
ＬＤ［ｉ］（ｉ＝１，２，…，ｍ）
の組によって与えられる。 同様に、ＹＭＣの補色画像信号のみを用いて、後の記載を簡単にするために、
Ａ［ｔ］［ｎ［ｉ］］（０ ≦ ｎ［ｉ］ ≦ ２５５； ｉ＝１，２，…，ｍ； ｔ ＝ Ｙ，Ｍ，Ｃ， ｏｒ Ｋ）
と表す。ｍ は参照データの数である。
【０１４２】
機差補正値の一例を図４７に示す。図４７の値は、Ｂｌａｃｋ（Ｇ），Ｃｙａｎ（Ｒ），Ｍａｇｅｎｔａ（Ｇ），Ｙｅｌｌｏｗ （Ｂ）のそれぞれのトナーに対応する補正値で、（）内は、自動階調補正の時に使用するスキャナのＲｅｄ（Ｒ），Ｇｒｅｅｎ（Ｇ），Ｂｌｕｅ（Ｂ）の信号を示す。それぞれの色のトナーに対し、ｋ（０）、ｋ（１０２３）は、参照データ値 ０及び参照データ値１０２３（１０ビット信号）に対する補正値を表す。
【０１４３】
補正後の参照データの値を
Ａ１［ｔ］［ｎ［ｉ］］
として、図４７の値を用いて参照データ
Ａ［ｔ］［ｎ［ｉ］］
を
Ａ１［ｔ］［ｎ［ｉ］］＝Ａ［ｔ］［ｎ［ｉ］］＋（ｋ（１０２３）−ｋ（０））×ｎ［ｉ］／１０２３＋ｋ（０） ・・・（４）
のように補正する。
【０１４４】
上記の関数を図で表わすと例えば図４８のようになる。図４７の補正値は、製造時に設定され、機械内に保持されている。また、図４９に示す操作部の液晶画面（タッチパネル）からタッチ入力により設定することが可能である。
【０１４５】
なお、以下では、式４のＡ１［ｔ］［ｎ［ｉ］］を、新たにＡ［ｔ］［ｎ［ｉ］］として使用する。
【０１４６】
ＹＭＣＫ階調変換テーブルは、前述したａ［ＬＤ］とＲＯＭ４１６中に記憶されている参照データＡ［ｎ］とを比較することによって得られる。ここで、ｎは、ＹＭＣＫ階調変換テーブルへの入力値で、参照データＡ［ｎ］は、入力値ｎをＹＭＣＫ階調変換した後のレーザ書き込み値ＬＤ［ｉ］で出力したＹＭＣトナー・パターンをスキャナで読み取った読み取り画像信号の目標値である。ここで、参照データは、プリンタの出力可能な画像濃度に応じて補正を行う参照値Ａ［ｎ］と補正を行わない参照値Ａ［ｎ］との２種類の値とからなる。補正を行うかどうかの判断は、予めＲＯＭまたはＲＡＭ中に記憶されている後述する判断用のデータにより判断される。この補正についての後述する。
【０１４７】
前述したａ［ＬＤ］から、Ａ［ｎ］に対応するＬＤを求めることにより、ＹＭＣＫ階調変換テーブルへの入力値ｎに対応するレーザ出力値ＬＤ［ｎ］を求める。これを、入力値
ｉ＝０，１，…，２５５（８ｂｉｔ信号の場合）
に対して求めることにより、階調変換テーブルを求めることができる。その際、ＹＭＣＫ階調変換テーブルに対する入力値
ｎ＝００ｈ，０１ｈ …，ＦＦｈ（１６進数）
に対するすべての値に対して、上記の処理を行う代わりに、
ｎｉ＝０，１１ｈ，２２ｈ， …，ＦＦｈ
のようなとびとびの値について上記の処理を行い、それ以外の点については、スプライン関数などで補間を行うか、あるいは、予めＲＯＭ４１６中に記憶されているＹＭＣＫγ補正テーブルの内、上記の処理で求めた
（０，ＬＤ［０］），（１１ｈ，ＬＤ［１１ｈ］），（２２ｈ，ＬＤ［２２ｈ］），…，（ＦＦｈ，ＬＤ［ＦＦｈ］）
の組を通る、最も近いテーブルを選択する。
【０１４８】
上記の処理を図５０の４元チャートに基づいて説明する。図の第１象現（ａ）の横軸は、ＹＭＣＫ階調変換テーブルへの入力値ｎ、縦軸は、スキャナの読み取り値（処理後）で、前述した参照データＡ［ｉ］を表す。スキャナの読み取り値（処理後）は、階調パターンをスキャナで読み取った値に対し、ＲＧＢγ変換（ここでは変換を行っていない）、階調パターン内の数ヶ所の読み取りデータの平均処理及び加算処理後の値であり、演算精度向上のために、ここでは、１２ビットデータ信号として処理する。
【０１４９】
図５０の第２象現（ｂ）の横軸は、縦軸と同じく、スキャナの読み取り値（処理後）を表す。第３象現（ｃ）の縦軸は、レーザ光（ＬＤ）の書き込み値を表す。このデータａ［ＬＤ］は、プリンタ部の特性を表す。また、実際に形成するパターンのＬＤの書き込み値は、００ｈ（地肌），１１ｈ，２２ｈ，…，ＥＥｈ，ＦＦｈの１６点であり、飛び飛びの値を示すが、ここでは、検知点の間を補間し、連続的なグラフとして扱う。第４象現のグラフ（ｄ）は、ＹＭＣＫ階調変換テーブルＬＤ［ｉ］で、このテーブルを求めることが目的である。グラフ（ｆ）の縦軸・横軸は、グラフ（ｄ）の縦軸・横軸と同じである。検知用の階調パターンを形成する場合には、グラフ（ｆ）に示したＹＭＣＫ階調変換テーブル（ｇ）を用いる。グラフ（ｅ）の横軸は、第３象現（ｃ）と同じであり、階調パターン作成時のＬＤの書き込み値と階調パターンのスキャナの読み取り値（処理後）との関係を表すための、便宜上の線形変換を表す。ある入力値ｎに対して参照データＡ［ｎ］が求められ、Ａ［ｎ］を得るためのＬＤ出力ＬＤ［ｎ］を階調パターンの読み取り値ａ［ＬＤ］を用いて、図中の矢印（ｌ）に沿って求める。
【０１５０】
インターフェースＩ／Ｆ・セレクタ４１１は、スキャナ４０１で読み込んだ画像データを外部の画像処理装置などで処理するために出力したり、外部のホストコンピューターやあるいは画像処理装置からの画像データをプリンタ４１３で出力するための切り替え機能を有する。
【０１５１】
以上の画像処理回路はＣＰＵ４１５により制御される。ＣＰＵ４１５は、ＲＯＭ４１４とＲＡＭ４１６とＢＵＳ４１８で接続されている。また、ＣＰＵ４１５はシリアルＩ／Ｆを通じて、システムコントローラ４１７と接続されており、図示しない操作部などからのコマンドが、システムコントローラ４１７を通じて送信される。送信された画質モード、濃度情報及び領域情報等に基づいて上述したそれぞれの画像処理回路に各種パラメータが設定される。パターン発生回路４２１は画像処理部で使用する階調パターンを発生させる。
【０１５２】
レーザ変調回路のブロック図を図５１に示す。書き込み周波数は、１８．６［ＭＨｚ］であり、１画素の走査時間は、５３．８［ｎｓｅｃ］である。８ビットの画像データはルックアップテーブル（ＬＵＴ）４５１でγ変換を行うことができる。パルス幅変調回路（ＰＷＭ）４５２で８ビットの画像信号の上位３ビットの信号に基づいて８値のパルス幅に変換され、パワー変調回路（ＰＭ）４５３で下位５ビットで３２値のパワー変調が行われ、レーザダイオード（ＬＤ）４５４が変調された信号に基づいて発光する。フォトディテクタ（ＰＤ）４５５で発光強度をモニターし、１ドット毎に補正を行う。
【０１５３】
レーザ光の強度の最大値は、画像信号とは独立に、８ビット（２５６段階）に可変できる。１画素の大きさに対し、主走査方向のビーム径（これは、静止時のビームの強度が最大値に対し、１／ｅ２に減衰するときの幅として定義される）は、６００ ＤＰＩでは、１画素４２．３［μｍ］では、ビーム径は主走査方向５０［μｍ］、副走査方向６０［μｍ］が使用される。
【０１５４】
図５２は画像読み取り系のブロック図、図５３は原稿読み取り装置（スキャナ）の概略構成図である。以下、これらの図に基づいて画像読み取り系について説明する。
【０１５５】
原稿は、露光ランプ５５０１により照射され、原稿面から反射した反射光は、ＣＣＤ（Charge Coupled Device）５４０１のＲＧＢフィルタにより色分解されて読み取られ、増幅回路５４０２により所定レベルに増幅される。ＣＣＤドライバ５４０９は、ＣＣＤを駆動するためのパルス信号を供給する。ＣＣＤドライバ５４０９を駆動するために必要なパルス源は、パルスジェネレータ５４１０で生成され、パルスジェネレータ５４１０は、水晶発振子などからなるクロックジェネレータ５４１１を基準信号とする。パルスジェネレータ５４１０は、サンプルホールド（Ｓ／Ｈ）回路５４０３がＣＣＤ５４０１からの信号をサンプルホールドするための必要なタイミングを供給する。Ｓ／Ｈ回路５４０３によりサンプルホールドされたアナログカラー画像信号は、Ａ／Ｄ変換回路５４０４で８ビット信号（一例である）にデジタル化される。黒補正回路５４０５は、ＣＣＤ５４０１のチップ間、画素間の黒レベル（光量が少ない場合の電気信号）のばらつきを低減し、画像の黒部にスジやムラを生じることを防ぐ。シェーディング補正回路５４０６は、白レベル（光量が多い場合の電気信号）を補正する。白レベルは、スキャナ４２０を均一な白色版の位置に移動して照射した時の白色データに基づき、照射系、光学系やＣＣＤ５４０１の感度ばらつきを補正する。図５４に白補正・黒補正の画像信号の概念図を示した。
【０１５６】
シェーディング補正回路５４０５からの信号は、画像処理部５４０７により処理され、プリンタ４１３で出力される。上記回路は、ＣＰＵ５４１４により制御され、ＲＯＭ５４１３及びＲＡＭ５４１５に制御に必要なデータを記憶する。ＣＰＵ５４１４は、画像形成装置全体の制御を行うシステムコントローラ４１９とシリアルＩ／Ｆにより通信を行っている。ＣＰＵ５４１４は、図示しないスキャナ駆動装置を制御し、スキャナ１２１の駆動制御を行う。
【０１５７】
増幅回路５４０２の増幅量は、ある特定の原稿濃度に対して、Ａ／Ｄ変換回路５４０４の出力値が所望の値になるように決定する。一例として、通常のコピー時に原稿濃度が、０．０５（反射率で０．８９１）のものを８ビット信号値で２４０値として得られるようにする。一方、シェーディング補正時には、増幅率を下げてシェーディング補正の感度を上げる。その理由は、通常のコピー時の増幅率では、反射光が多い場合には、８ビット信号で２５５値を超える大きさの画像信号となると、２５５値に飽和してしまい、シェーディング補正に誤差が生じるためである。
【０１５８】
図５５は、増幅回路５４０２で増幅された画像の読み取り信号がＳ／Ｈ回路５４０３でサンプルホールドされる状態を示す模式図である。横軸は、増幅後のアナログ画像信号がＳ／Ｈ回路５４０３を通過する時間で、縦軸は、増幅後のアナログ信号の大きさを表す。所定のサンプルホールド時間５５０１でアナログ信号がサンプルホールドされて、Ａ／Ｄ変換回路５４０４に信号が送られる。図は前述した白レベルを読み取った画像信号で、増幅後の画像信号は、コピー時は、一例として、Ａ／Ｄ変換後の値として２４０値、白補正時は、１８０値とした増幅後の画像信号の例である。
【０１５９】
なお、図５３のスキャナ４２０はシートスルー方式とフラットベッド方式の２つの方式に対応し、しかもこの例の場合、図１とは異なり両面読み取り可能な構成になっている。
【０１６０】
なお、プログラムはＲＯＭ１３１、記憶装置１８１、プログラムＲＡＭ１４０５等にダウンロードされ、ＣＰＵ１３０により実行される。その際、必要なプログラムが記録された例えばＣＤ−ＲＯＭなどの情報記録媒体からダウンロードし、あるいはネットワークを介してサーバからダウンロードされて使用される。
【０１６１】
【発明の効果】
以上のように本発明によれば、階調処理前の画像信号を、４元チャートの第３象限の特性の傾きとして表し、前記傾きから読み取り位置に応じたムラを補正するので、簡単な計算で効率的に主走査方向のムラを補正することができる。
【図面の簡単な説明】
【図１】本発明の実施形態に係るカラー複写機の概略構成を示す図である。
【図２】図１のカラー複写機の制御系の概略を示すブロック図である。
【図３】図１のカラー複写機の制御構成を示す図である。
【図４】図２のカラー複写機の画像処理部の構成を示すブロック図である。
【図５】適応エッジ強調回路の例を示すブロック図である。
【図６】平滑化フィルタの係数の例を示す図である。
【図７】ラプラシアンフィルタの係数の例を示す図である。
【図８】副走査方向エッジ検出フィルタの係数の例を示す図である。
【図９】主走査方向エッジ検出フィルタの係数の例を示す図である。
【図１０】斜め方向検出フィルタの係数の例を示す図である。
【図１１】斜め方向検出フィルタの係数の他の例を示す図である。
【図１２】第２の平滑化フィルタの係数の例を示す図である。
【図１３】テーブル変換回路で変換されるフィルタ係数とエッジ度との関係を示す図である。
【図１４】ＳＩＭＤ型プロセッサの概略構成を示す説明図である。
【図１５】ＳＩＭＤ型画像データ処理部及び逐次画像データ演算処理部の構成を示す図である。
【図１６】画素ラインを説明するための図である。
【図１７】画像処理プロセッサ１２０４の内部構成を示すブロック図である。
【図１８】逐次型画像データ処理部の構成を示すブロック図である。
【図１９】シアン、マゼンタ、イエロー、ブラック各色に対応するディザ処理パラメータを示す図である。
【図２０】ＩＩＲ型フィルタシステムのシステム構成を示す図である。
【図２１】画像処理部の構成を示すブロック図である。
【図２２】誤差拡散処理ハードウェアレジスタ群に設定するレジスタの説明図である。
【図２３】ＳＩＭＤ型プロセッサで行われる誤差拡散処理の処理手順を示すフローチャートである。
【図２４】逐次型画像データ処理部で行われる誤差拡散処理の処理手順を示す説明図である。
【図２５】図２３の処理で実行されるラインシフトを示す説明図である。
【図２６】誤差拡散マトリクス部のマトリクスの状態を示す図である。
【図２７】エッジ検出部で使用される微分フィルタの例を示す図である。
【図２８】ディザ閾値発生部のディザ閾値マトリクスの例を示す図である。
【図２９】ディザ閾値発生部のディザ閾値マトリクスの他の例を示す図である。
【図３０】スクリーン角とラインの成長方向を示す説明図である。
【図３１】画像プロセッサの状態遷移図である。
【図３２】２入力２出力時の画像処理プロセッサの動作手順を示すフローチャートである。
【図３３】操作部の全体を示す正面図である。
【図３４】操作部のタッチパネルの自動階調補正画面の一例を示す正面図である。
【図３５】自動階調補正（ＡＣＣ）の処理手順を示すフローチャートである。
【図３６】操作部のタッチパネルの自動階調補正画面のテストパターン印刷画面を示す正面図である。
【図３７】自動階調補正（ＡＣＣ）の階調パターンの出力例（その１）を示す図である。
【図３８】操作部のタッチパネルの自動階調補正画面のテストパターン読み取り画面を示す正面図である。
【図３９】操作部のタッチパネルの自動階調補正画面の読み取り処理画面を示す正面図である。
【図４０】操作部のタッチパネルのコピー画面の一例を示す正面図である。
【図４１】濃度ムラの算出方法を示す４元チャート（その１）である。
【図４２】像担持体の主走査位置と補正量との関係を示す概念図である。
【図４３】ＳＩＭＤプロセッサにおける濃度ムラの補正処理手順を示すフローチャートである。
【図４４】自動階調補正（ＡＣＣ）の階調パターンの出力例（その２）を示す図である。
【図４５】自動階調補正（ＡＣＣ）の階調パターンの出力例（その３）を示す図である。
【図４６】濃度ムラの算出方法を示す４元チャート（その２）である。
【図４７】機差の補正値の例を示す図である。
【図４８】自動階調補正（ＡＣＣ）の機差補正値の補正方法を示す説明図である。
【図４９】自動階調補正（ＡＣＣ）の機差補正値を入力するための液晶画面の正面図である。
【図５０】自動階調補正（ＡＣＣ）の演算方法を示す４元チャートである。
【図５１】レーザ変調回路を示すブロック図である。
【図５２】画像読み取り系を示すブロック図である。
【図５３】原稿読み取り装置（スキャナ）の概略構成を示す図である。
【図５４】白補正・黒補正の画像信号の概念図である。
【図５５】図５３の増幅回路で増幅された画像の読み取り信号がＳ／Ｈ回路でサンプルホールドされる状態を示す模式図である。
【符号の説明】
４１０ 階調処理
４１３ プリンタ
４１５ ＣＰＵ
４２０ スキャナ
４２１ パターン生成回路
１２０４ 画像処理プロセッサ
１４０３ メモリ制御部
１４０４ プロセッサアレー
１５００ ＳＩＭＤ型画像データ処理部
１５０１ａ〜１５０１ｅ データ入出力用バス
１５０２ａ〜１５０２ｃ バススイッチ
１５０３ ＲＡＭ
１５０４ａ〜１５０４ｄ メモリスイッチ
１５０５ａ，１５０５ｂ メモリコントローラ
１５０６ ＳＩＭＤ型プロセッサ
１５０７ａ，１５０７ｂ 逐次型画像データ処理部
１８０１ 誤差データ算出部
１８０５ 誤差拡散処理ハードウエアレジスタ群[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an image processing apparatus that corrects CCD reading values of automatic gradation correction (ACC), a digital copying machine equipped with the image processing apparatus, an image forming apparatus such as a printer, a FAX, an image processing method, and a computer. The present invention relates to a computer program that is downloaded and executes the image processing method, and a recording medium on which the computer program is recorded so as to be readable by a computer.
[0002]
[Prior art]
Currently, there is a so-called MFP (Multi Function Peripheral) image forming composite apparatus configured as a composite apparatus of image forming apparatuses such as a copier, a facsimile, a printer, and a scanner. In such an MFP, an image processing unit of SIMD (Single Instruction Multiple Date Stream) type and an auxiliary calculation processing unit are provided, and both are used according to the type of image processing. The image is processed in a programmable manner. Since the SIMD type arithmetic processing unit inputs a plurality of data used for processing at a time and processes a plurality of input data in parallel, a large amount of data can be processed at a time. There is an advantage that arithmetic processing can be performed.
[0003]
[Problems to be solved by the invention]
Incidentally, there is one gradation process of image processing. There are two types of gradation processing: one for ensuring gradation characteristics based on input image data, and the other for correcting unevenness during image formation. Actually, the unevenness appears on the output image when the image is formed based on the input image data. Therefore, image density variation is reduced by correcting unevenness corresponding to the image forming position of the image carrier with a correction amount corresponding to the image forming position in the image data. However, since the sensitivity of the photoconductor and the development characteristics of the developer vary depending on the number of sheets used and the environment, if the unevenness that varies depending on the image forming position is corrected with a fixed correction amount, the correction amount may be insufficient or excessive. There was a case.
[0004]
In addition, as the cause of unevenness on the image carrier, there are sensitivity unevenness in the main scanning direction and sub-scanning direction of the photoconductor, inclination of the transfer roller in the longitudinal direction of the pressure, inclination of the gap in the longitudinal direction of the developing roller, Even when the image carrier is exposed with uniform exposure energy, the density unevenness (density gradient) may occur in the image on the transfer paper depending on the position.
[0005]
Further, when reproducing the gray achromatic color by superimposing the 3 (4) colors of YMC (K), the gray balance may be shifted depending on the location on the transfer paper, and a uniform gray may not be obtained.
[0006]
The present invention has been made in view of such a state of the art, and an object of the present invention is to be able to determine a correction amount according to gradation characteristics when the image forming apparatus is used.
[0007]
Another object is to simplify the adjustment procedure when performing the correction so that unevenness can be corrected efficiently at low cost.
[0008]
[Means for Solving the Problems]
  In order to achieve the object, the first means is:RollAn image reading unit that reads a plurality of reference density patterns having substantially the same gradation density and density output on a copy sheet, and outputs a plurality of signals having different spectral sensitivities, and the gradation pattern read by the image reading unit and A correction unit that corrects the read signal of the reference density pattern and the image data according to an image forming position on an image carrier, and a correction amount storage unit that stores a correction amount of the image data according to the image forming position. The correction meansButThe correction amount of the image data corresponding to the image forming position is changed based on the gradation pattern formed on the transfer paper and the read values of a plurality of reference patterns.An image processing apparatus for correcting density unevenness depending on the image forming position of the image carrier.,The correction means has a gradation patch read value with the horizontal axis representing the gradation patch write value, the vertical axis representing the scanner read value, and the second quadrant characteristic represented by the horizontal axis. As an input value to the gradation correction table, the gradation correction adjustment target or the adjustment result after gradation correction is used, and the characteristics shown in the third quadrant are used to correct unevenness using the vertical axis as the input value after correction to the correction means. The four-way chart in which the characteristic shown in the fourth quadrant indicates the gradation characteristic of the correction means, and the reference pattern gradation characteristic for detecting the reference irregularity is shown. Based on the read value, a target value for gradation correction is obtained by the characteristic of the second quadrant, and the obtained result is expressed as the inclination of the characteristic of the third quadrant, and unevenness corresponding to the reading position is corrected from the inclination. DoIt is characterized by that.
[0009]
  The second means isRollAn image reading unit that reads a plurality of reference patterns having substantially the same gradation and density using a plurality of coloring materials output on a copy paper, and outputs a plurality of signals having different spectral sensitivities, and is read by the image reading unit Further, parameter setting means for setting image processing parameters based on the read signal of the gradation pattern and reference data stored in advance, and correction means for correcting the image data according to the image forming position on the image carrier. Correction amount storage means for storing a correction amount of image data corresponding to the image forming position, and the correction meansButThe correction amount of the image data corresponding to the image forming position and the gradation parameter are changed based on the read data of the gradation pattern and the reference pattern formed on the transfer paper.An image processing apparatus that corrects density unevenness depending on the image forming position of the image carrier, wherein the correction means has a characteristic indicated by the first quadrant in which the horizontal axis indicates the writing value of the gradation patch, and the vertical axis indicates The reading value of the gradation patch as the reading value of the scanner, the adjustment target after gradation correction or the adjustment result after gradation correction, with the characteristics shown in the second quadrant as the input value to the gradation correction table. A quaternary chart in which the characteristics shown in the three quadrants indicate the correction amount for correcting unevenness using the vertical axis as the input value to the correction means, and the characteristics shown in the fourth quadrant show the gradation characteristics of the correction means. Is used to obtain a target value for gradation correction based on the reading value of the gradation characteristic of the reference pattern for detecting the reference unevenness with the characteristic of the second quadrant, and the obtained result is Expressed as the slope of the characteristics of the third quadrant, Correcting the unevenness corresponding to the reading position from the airIt is characterized by that.
[0010]
The third means further comprises image parallel processing means for processing the image data in parallel in the first or second means, and the image parallel processing means corrects the image data every predetermined number of data or less. It is characterized by doing.
[0011]
  The fourth means is the first or second means, whereinDensity unevenness depending on the image forming position of the image carrier is density unevenness in the main scanning direction.It is characterized by that.
[0012]
  The fifth means is any one of the first to third means.Pattern output means for outputting a plurality of reference density patterns having substantially the same gradation pattern and density onto the transfer paper;It is characterized by that.
[0013]
  The sixth means is the first to fifthThe image forming apparatus includes the image processing apparatus according to any one of the meansIt is characterized by that.
[0014]
  The seventh means isA first step of reading a plurality of reference density patterns having substantially the same density and gradation pattern output on the transfer paper, and outputting a plurality of signals having different spectral sensitivities, and the gradation read in the first step A second step of correcting the read signal of the pattern and the reference density pattern, and the image data according to the image forming position on the image carrier, and a third step of storing a correction amount of the image data corresponding to the image forming position. And a fourth step of changing the correction amount of the image data according to the stored image forming position, based on the gradation pattern formed on the transfer paper and the read values of a plurality of reference patterns, An image processing method for correcting density unevenness depending on an image forming position of an image carrier, wherein in the fourth step, the characteristics shown in the first quadrant are a written value of a gradation patch on a horizontal axis and a vertical axis on a vertical axis. Sca The read value of the tone patch is used as the read value of the tone, the adjustment target after the tone correction or the adjustment result after the tone correction is obtained with the characteristic indicated in the second quadrant as the input value to the tone correction table. A quaternary chart in which the characteristic shown in the quadrant indicates the correction amount for correcting unevenness using the vertical axis as the input value to the correction means, and the characteristic shown in the fourth quadrant shows the gradation characteristic of the correction means. A target value for gradation correction is obtained from the characteristic of the second quadrant based on the read value of the gradation characteristic of the reference pattern used to detect the unevenness used as a reference, and the obtained result is obtained as the first result. Expressed as the slope of the characteristics of the three quadrants, and corrects unevenness according to the reading position from the slopeIt is characterized by that.
[0015]
  The eighth means isRollA first step of reading a plurality of gradation patterns and a plurality of reference patterns having substantially the same density using a plurality of coloring materials output on a copy paper, and outputting a plurality of signals having different spectral sensitivities; and The read gradation patternReadingSampling signal,And set image processing parameters based on pre-stored reference dataA second step of:Image data is corrected by the image forming position on the image carrierA third step ofStores the correction amount of image data according to the image forming positionA fourth step ofA fifth step of changing a correction amount and a gradation parameter of the image data in accordance with the image forming position based on reading data of the gradation pattern and the reference pattern formed on the transfer paper, An image processing method for correcting density unevenness depending on an image forming position, wherein in the fifth step, the characteristics shown in the first quadrant are the written values of the gradation patches on the horizontal axis and the read values of the scanner on the vertical axis. The gradation patch reading value is shown in the second quadrant, and the horizontal axis is the input value to the gradation correction table, and the gradation correction adjustment target or the adjustment result after gradation correction is shown in the third quadrant. Using a quaternary chart in which the vertical axis is the input value to the correction means, the correction amount for correcting unevenness, and the characteristic shown in the fourth quadrant is the gradation characteristic in the correction means, respectively. Standard A target value for gradation correction is obtained with the characteristic of the second quadrant based on the read value of the gradation characteristic of the reference pattern for detecting the color, and the obtained result is obtained as a slope of the characteristic of the third quadrant. Expressed as, and correct the unevenness according to the reading position from the tiltIt is characterized by that.
[0016]
  The ninth means isRollOutput on paperFloorA first pattern which reads a plurality of reference patterns having substantially the same tone pattern and density and outputs a plurality of signals having different spectral sensitivitiesprocedureAnd the gradation pattern read in the first procedureAnd the reference density patternReading signal,In addition, the image data is corrected by the image forming position on the image carrier.Second toprocedureWhen,Stores the correction amount of image data according to the image forming positionThe third toprocedureAnd saidThe correction amount of the image data corresponding to the stored image forming position is changed based on the gradation pattern formed on the transfer paper and the read values of a plurality of reference patterns.The fourth toprocedureWhenIs a computer program for correcting density unevenness that is loaded on a computer and depends on an image forming position. In the fourth procedure, the characteristics shown in the first quadrant are written in gradation patches with the horizontal axis Value, the vertical axis is the reading value of the gradation patch, and the characteristic shown in the second quadrant is the horizontal axis is the input value to the gradation correction table. The adjustment result shows that the characteristic shown in the third quadrant is the correction amount for correcting unevenness with the vertical axis as the input value to the correction means, the characteristic shown in the fourth quadrant is the gradation characteristic of the correction means, Using the quaternary charts shown respectively, the target value for gradation correction is obtained with the characteristic of the second quadrant based on the read value of the gradation characteristic of the reference pattern for detecting the reference irregularity, Sought result The expressed as the slope of the third quadrant of the characteristic, to correct the non-uniformity in accordance with the reading position from the slopeIt is characterized by that.
[0017]
  The tenth means isRollOutput on the copy paperUsing multiple colorantsA first procedure for reading a plurality of reference patterns having substantially the same gradation pattern and density, and outputting a plurality of signals having different spectral sensitivities, and the gradation pattern read by the first procedureSet image processing parameters based on read signal and pre-stored reference dataA second procedure toImage data is corrected by the image forming position on the image carrierAnd a third procedureStores the correction amount of image data according to the image forming positionA fourth procedure toA fifth procedure for changing a correction amount and a gradation parameter of image data according to the image forming position based on reading data of a gradation pattern and a reference pattern formed on the transfer paper;IncludingThe computer program for correcting density unevenness depending on the image forming position loaded in the computer, wherein the characteristic shown in the first quadrant indicates the writing value of the gradation patch in the horizontal axis in the fifth procedure. The gradation patch reading value with the vertical axis as the reading value of the scanner, the characteristics shown in the second quadrant as the input value to the gradation correction table with the characteristics shown in the second quadrant as the gradation correction adjustment target or adjustment after gradation correction The result shows that the characteristic shown in the third quadrant is the correction amount for correcting unevenness with the vertical axis as the input value to the correction means, and the characteristic shown in the fourth quadrant is the gradation characteristic in the correction means. Using the quaternary chart shown, a target value for gradation correction is obtained from the characteristic of the second quadrant based on the read value of the gradation characteristic of the reference pattern for detecting the reference unevenness, and the obtained value is obtained. The Represents results as the slope of the third quadrant of the characteristic, to correct the non-uniformity in accordance with the reading position from the slopeIt is characterized by that.
[0018]
  The eleventh means isIn the ninth or tenth means, the third procedure includes a procedure for determining whether to perform background correction and / or reference data correction, and when performing the correction, the YMCK floor after the correction is performed. Create an adjustment tableIt is characterized by that.
[0019]
  The twelfth meansThe secondIn 11 means,After correcting each color of YMCK with reference to the YMCK gradation correction table, each image quality mode is corrected.It is characterized by that.
[0020]
  The thirteenth means isA computer program according to any of the ninth to twelfth means is recorded on a recording medium so as to be readable by a computer.It is characterized by that.
[0022]
  1st, 1st7And the second9According to the means, a plurality of reference patterns and gradation patterns are formed at different positions on the transfer paper, and the formed patterns are read by the reading means. Based on the read data of the reference pattern and the gradation pattern, the correction amount of the image data corresponding to the formation position on the image carrier is calculated. Thereby, according to the read data of the gradation pattern, by changing the correction amount of unevenness according to the image forming position, the change in the gradation characteristics of the image forming portion of the image forming apparatus and the environmental change are corrected, It is possible to accurately correct the density unevenness corresponding to the image forming position.
  At this time, the number of patches for detecting unevenness is reduced to several, and the correction amount for the reference gradation characteristic is expressed as a slope with respect to the input value to the gradation processing table. In this case, when correction is not performed, a through table is obtained. That is, when the input value is set to the output value, 0 → 0, 1 → 1,... 255 → 255. By correcting the input data using this inclination, it is possible to efficiently correct the unevenness in the main scanning direction with a simple calculation.
[0023]
  2nd, 2nd8And the second10According to the above means, the pattern for correcting the automatic gradation and the pattern for correcting the unevenness in image formation are formed on one transfer sheet, and each pattern is read when the transfer sheet on which the pattern is formed is read. , And gradation correction and density unevenness correction are performed based on the read image data. Thereby, the trouble of adjustment can be simplified.
  At this time, the number of patches for detecting unevenness is reduced to several, and the correction amount for the reference gradation characteristic is expressed as a slope with respect to the input value to the gradation processing table. In this case, when correction is not performed, a through table is obtained. That is, when the input value is set to the output value, 0 → 0, 1 → 1,... 255 → 255. By correcting the input data using this inclination, it is possible to efficiently correct the unevenness in the main scanning direction with a simple calculation.
[0024]
According to the third means, since the parallel processing means is used, it is realized by a low cost image processing apparatus.
[0026]
  First4According to the above means, by correcting the density unevenness in the main scanning direction, it can be extended in the sub-scanning direction, and correction can be made over the entire circumference of the image carrier.
[0027]
  First5With this means, the image processing means itself can output a plurality of reference density patterns having substantially the same gradation pattern and density from the image carrier to be corrected onto the transfer paper. The density correction can be performed only with
[0028]
  First6Means of the first to the first5Since the image forming apparatus includes the image processing apparatus according to the above means, the image forming apparatus itself can correct density unevenness depending on the position of the image carrier.
[0029]
According to the eleventh and twelfth means, correction is performed in consideration of background correction and reference data correction, and correction is performed for each color and each image quality mode, so that correction with higher accuracy is possible.
[0030]
  First13According to the means, it is possible to easily perform processing according to a program simply by downloading to a computer.
[0031]
In the following embodiments, the image reading unit is the scanner 420, the correction unit is the gradation processing circuit 410, the correction amount storage unit is the RAM 1503, the parameter setting unit is the CPU 415, and the image parallel processing unit is the SIMD type image. The data processing unit 1500 and the pattern output unit correspond to the printer 413, respectively.
[0032]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described below with reference to the drawings.
[0033]
FIG. 1 is a diagram showing a schematic configuration of a color copying machine according to an embodiment of the present invention. In FIG. 1, an image forming system A is formed at a substantially central portion of the copying machine body 101, an optical writing system B is formed above the image forming system A, a reading system C is formed above the optical writing system B, A sheet feeding system D and a control system E are arranged from the side of the image forming system A to the upper part. Further, an automatic document feeder (ADF) is provided on the upper part of the copying machine main body 101.
[0034]
The image forming system A is for an intermediate transfer belt 109 as an image carrier, and for black, cyan, magenta, and yellow provided along the upper surface of the intermediate transfer belt 109. The four photoconductive drums 102a, 102b, 102c, and 102d, and various image forming elements provided on the outer circumferences of the photoconductive drums 102a to 102d. The image forming element irradiates a semiconductor laser beam onto the surface of the uniformly charged photosensitive drums 102a to 102d provided along the outer periphery of each of the photosensitive drums 102a to 102d to form an electrostatic latent image. Developing devices 105, 106, 107, and 108 for supplying each color toner to the laser optical system 104 to be formed and the electrostatic latent images on the photosensitive drums 102a to 102d for development, and obtaining a toner image for each color. Bias rollers (transfer rollers) 110a, 110b, 110c, 110d for applying a transfer voltage to the intermediate transfer belt 109 in order to sequentially transfer the toner images of the respective colors formed on 102a to 102d to the intermediate transfer belt 109, transfer Cleaning device for removing toner remaining on the surface of the subsequent photosensitive drums 102a to 102d (each photosensitive drum 1 2), and a charge eliminating unit that removes charges remaining on the surfaces of the photosensitive drums 102a to 102d after transfer, and in this order, along the outer peripheral surface of the photosensitive drums 102a to 102d. Are arranged sequentially. The intermediate transfer belt 109 has a transfer bias roller 113 for applying a voltage for transferring the transferred toner image to the transfer material, and a belt cleaning device 114 for cleaning the toner image remaining on the transfer material after transfer. Is arranged.
[0035]
Further, on the downstream side of the intermediate transfer belt 109 in the paper conveyance direction, a conveyance belt 115 that conveys a transfer material (paper) on which a color image has been transferred, and a fixing device 116 that fixes the image transferred on the transfer material are arranged. Further, a paper discharge tray 117 is provided on the downstream side. The fixing device 116 fixes the toner image transferred on the surface of the transfer material by heating and pressurizing, and functions as a fixing system together with the conveying belt 115.
[0036]
The reading optical system C includes a contact glass 118 serving as a document placement table disposed on the upper portion of the copying machine main body 101, an exposure lamp 120 for irradiating the document on the contact glass 118 with scanning light, first to third mirrors 119a, 119b, 119c and the reflected light from the document are guided to the imaging lens 121 by the first to third mirrors 119a to 119c, and are incident on the image sensor array 122 of a CCD (Charge Coupled Device) which is a photoelectric conversion element. The image signal converted into an electrical signal by the CCD image sensor array 122 is controlled by a semiconductor laser in the laser optical system 104 of the optical writing system B through an image processing device (not shown). The exposure lamp 120, the reflection mirror 120a, and the first mirror 119a are mounted on the first traveling system, and the second and third mirrors 119b and 119c are mounted on the second traveling system, respectively, and move at a speed ratio of 2: 1. It is driven so that the optical path length of the reading light incident on the image sensor array 122 from the document surface does not change depending on the reading position.
[0037]
Next, the control system E built in the copying machine main body 101 will be described with reference to FIGS.
[0038]
FIG. 2 is a block diagram showing a schematic configuration of the control system E. As shown in FIG. 2, the control system E includes a main control unit (CPU) 130, and a predetermined ROM 131 and RAM 132 are attached to the main control unit 130, and the main control unit 130 includes the main control unit 130 illustrated in FIG. As shown, various sensor control units 160, a power source / bias control unit 161, a communication control unit 162, a drive control unit 163, an operation unit 142, a scanner / IPU control unit, and the like are connected via an interface I / O 133. Control or communicate with the copier inside and outside.
[0039]
The environmental sensor 138, optical sensors 136a, 136b, and 136c, the photoreceptor surface potential sensor 139, and the toner density sensor 137 are connected to the various sensor control units 160, and the power supply / bias control unit 161 includes the power supply circuit 135, the developing device. 105, 106, 107, and 108 are connected, and the drive control unit 163 is connected to a laser optical system control unit 134, a toner supply circuit 140, and an intermediate transfer belt drive unit 141. The laser optical system control unit 134 adjusts the laser output of the laser optical system 104, and the power supply circuit 135 gives a predetermined charging discharge voltage to the charging charger 113, and the power supply / bias control unit 161 Is configured to give a developing bias of a predetermined voltage to the developing devices 105, 106, 107, and 108 and to apply a predetermined transfer voltage to the bias rollers 110 a to 110 d and the transfer bias roller 113.
[0040]
The communication control unit 162 is connected to the Internet or an intranet (registered trademark) 512 via a communication line 518 and also controls the storage device 181 via the storage device control unit 182.
[0041]
The optical sensors 136a to 136c are respectively opposed to the photoconductor 102 and are opposed to the optical sensor 136a for detecting the toner adhesion amount on the photoconductor 102 and the transfer belt 109, and the toner adhesion amount on the transfer belt 109 is measured. An optical sensor 136b for detecting and an optical sensor 136c for detecting the toner adhesion amount on the conveyor belt 115 while facing the conveyor belt 115 are shown. In practice, any one of the optical sensors 136a to 136c (hereinafter generally indicated by reference numeral 136) may be detected.
[0042]
The optical sensor 136 includes a light-emitting element such as a light-emitting diode and a light-receiving element such as a photosensor that are arranged in proximity to the post-transfer area of the photoconductor drum 102, and a detection pattern latent image formed on the photoconductor drum 102. The toner adhesion amount on the toner image and the toner adhesion amount on the background are detected for each color, and the so-called residual potential after the charge removal from the photoreceptor is detected. The detection output signal from the photoelectric sensor 136 is applied to a photoelectric sensor control unit (not shown). The photoelectric sensor control unit obtains a ratio between the toner adhesion amount in the detection pattern toner image and the toner adhesion amount in the background portion, compares the ratio value with a reference value, detects a change in image density, and detects the toner density sensor 137. The control value is corrected.
[0043]
Further, the toner concentration sensor 137 detects the toner concentration based on a change in magnetic permeability of the developer present in the developing devices 105 to 108. The toner density sensor 137 compares the detected toner density value with a reference value, and when the toner density falls below a certain value and becomes a toner shortage state, a toner replenishment signal having a magnitude corresponding to the shortage is supplied to the toner. A function of applying to the supply circuit 140 is provided. The potential sensor 139 detects the surface potential of the photoconductor 102 that is an image carrier, and the intermediate transfer belt driving unit 141 controls the driving of the intermediate transfer belt.
[0044]
A developer containing black toner and a carrier is accommodated in the black developing device 105, and this is agitated by the rotation of the agent agitating member, and the amount of the developer pumped on the sleeve by the developer regulating member on the developing sleeve. Adjust. The supplied developer is magnetically carried on the developing sleeve and rotates as a magnetic brush in the rotation direction of the developing sleeve.
[0045]
FIG. 4 is a block diagram showing the configuration of the image processing unit. 4, 420 is a scanner, 401 is a shading correction circuit, 423 is an area processing circuit, 402 is a scanner γ conversion circuit, 403 is an image memory, 404 is an image separation circuit, 405 is an MTF filter, and 406 is a color conversion UCR processing circuit. , 407 is a zoom circuit, 408 is an image processing (create) circuit, 409 is an image processing printer γ conversion circuit, 410 is a gradation processing circuit, 411 is an interface (I / F) selector, and 412 is for an image forming unit. A printer γ correction circuit, 413 is a printer, 414 is a ROM, 415 is a CPU, 416 is a RAM, 417 is a system controller, 418 is an external computer, 419 is a printer controller, and 421 is a pattern generation circuit.
[0046]
An original to be copied is color-separated into R, G, and B by a color scanner 420 and read as a 10-bit signal as an example. The read image signal is corrected for unevenness in the main scanning direction by the shading correction circuit 401 and output as a 10-bit signal. In the area process 423, an area signal for distinguishing which area in the document the image data currently being processed belongs to is generated. The parameters used in the subsequent image processing unit are switched according to the region signal generated by this circuit. These areas include color correction coefficients, spatial filters, and tone conversions that are optimal for each original, such as text, silver halide photographs (photographic paper), printed originals, inkjets, highlighters, maps, and thermal transfer originals. Image processing parameters such as a table can be set according to the image area.
[0047]
In the scanner γ conversion circuit 402, a read signal from the scanner is converted from reflectance data to lightness data. The image memory 403 stores the image signal after the scanner γ conversion. In the image separation circuit 404, the character portion and the photograph portion are determined, and the chromatic / achromatic color is determined.
[0048]
In the MTF filter 405, in addition to processing for changing the frequency characteristics of the image signal, such as edge enhancement and smoothing according to the user's preference, such as a sharp image or a soft image, the edge according to the edge degree of the image signal Perform enhancement processing (adaptive edge enhancement processing). For example, so-called adaptive edge enhancement, in which edge enhancement is performed on a character edge and edge enhancement is not performed on a halftone image, is performed on each of the R, G, and B signals.
[0049]
FIG. 5 shows an example of an adaptive edge enhancement circuit. The adaptive edge coordination circuit includes a first smoothing filter 1101, a Laplacian filter 1102, an edge amount detection filter 1103, a second smoothing filter 1104, and a table conversion unit 1105. The image signal converted from the reflectance linearity to the lightness linearity by the scanner γ conversion circuit 402 is smoothed by the first smoothing filter circuit 1101. For example, the coefficients shown in FIG. 6 are used as the smoothing filter.
[0050]
From the image signal smoothed by the first smoothing filter 1101, the differential component of the image data is extracted by the 3 × 3 Laplacian filter 1102 at the next stage. Specifically, the Laplacian filter 1102 has a coefficient as shown in FIG. Of the 10-bit image signal that is not subjected to γ conversion by the scanner γ conversion circuit 402, the edge amount detection filter 1103 detects the edge of the upper 8 bits (one example). Specific examples of the edge amount detection filter are shown in FIGS. 8 is an example of the sub-scanning direction edge detection filter, FIG. 9 is an example of the main scanning direction edge detection filter, FIG. 10 is an example of the oblique direction detection filter 1, and FIG. Among the edge amounts obtained by the edge detection filters as shown in FIGS. 8 to 11, the maximum value is used as the edge degree in the subsequent stage. The edge degree is smoothed by the second smoothing filter 1104 at the subsequent stage as necessary. This reduces the influence of the sensitivity difference between the even and odd pixels of the scanner. As the second smoothing filter, for example, coefficients as shown in FIG. 12 are used.
[0051]
The image signal smoothed by the second smoothing filter 1104 is subjected to table conversion of the obtained edge degree by the table conversion circuit 1105. The values of this table can specify the darkness of lines and dots (including contrast and density) and the smoothness of halftone dots. An example of the table is shown in FIG. The edge degree is the largest with black lines or dots on a white background, and the edge degree becomes smaller as the pixel boundaries become smoother, such as finely printed halftone dots, silver halide photographs, and thermal transfer originals. The product (image signal D) of the edge degree (image signal C) converted by the table conversion circuit 1105 and the output value (image signal B) of the Laplacian filter 1102 is the image signal (image signal A) after the smoothing process. ) And transmitted to the subsequent image processing circuit as an image signal E.
[0052]
The color conversion UCR processing circuit 406 corrects the difference between the color separation characteristics of the input system and the spectral characteristics of the output system color material, and calculates the amount of the color material YMC necessary for faithful color reproduction; It consists of a UCR processing unit for replacing the part where the three colors of YMC overlap with Bk (black). The color correction process can be realized by performing a matrix operation as shown in the following equation.
[0053]
[Expression 1]

Here, R, G, and B indicate the complements of R, G, and B. The matrix coefficient aij is determined by the spectral characteristics of the input system and the output system (color material). Here, the primary masking equation is taken as an example, but color correction can be performed with higher accuracy by using a quadratic term such as B2 and BG, or a higher-order term. The arithmetic expression may be changed depending on the hue, or the Neugebauer equation may be used. In any method, Y, M, and C can be obtained from the values of B, G, and R (or B, G, and R may be used).
[0054]
On the other hand, UCR processing can be performed by calculating using the following equation.
Y ′ = Y−α · min (Y, M, C)
M ′ = M−α · min (Y, M, C)
C ′ = C−α · min (Y, M, C)
Bk = α · min (Y, M, C) (2)
In the above equation, α is a coefficient that determines the amount of UCR, and when α = 1, 100% UCR processing is performed. α may be a constant value. For example, when α is close to 1 in the high density portion and close to 0 in the highlight portion (low image density portion), the image in the highlight portion can be smoothed.
[0055]
The color correction coefficient is changed to 12 hues obtained by further dividing the 6 hues of RGBYMC into 2 parts and further to every 14 hues of black and white. The hue determination circuit 424 determines which hue the read image data determines. Based on the determined result, a color correction coefficient for each hue is selected.
[0056]
The scaling circuit 407 performs vertical / horizontal scaling, and the image processing (create) circuit 408 performs repeat processing and the like. The printer γ correction circuit 409 corrects the image signal in accordance with the image quality mode such as characters and photographs. Moreover, it is also possible to perform a background skip. The printer γ correction circuit 409 has a plurality of (for example, 10) gradation conversion tables that can be switched in accordance with the area signal generated by the area processing circuit 402 described above. This gradation conversion table is an optimum gradation conversion table for each original such as characters, silver halide photographs (printing paper), printed originals, ink jets, fluorescent pens, maps, thermal transfer originals, etc. You can choose.
[0057]
The gradation processing circuit 410 is configured by a SIMD type processor. FIG. 14 is an explanatory diagram showing a schematic configuration of a SIMD type processor. SIMD (Single Instruction Stream Multiple Data Stream) is to execute a single instruction in parallel for a plurality of data, and is composed of a plurality of PEs (processor elements). This SIMD type processor is disposed in the processor array unit 1404 in FIG. Each PE has a register (Reg) 2001 for storing data, a multiplexer (MUX) 2002 for accessing the registers of other PEs, a barrel shifter (Shift Expand) 2003, a logical operation unit (ALU) 2004, and a logical result. An accumulator (A) 2005 to be stored and a temporary register (F) 2006 for temporarily saving the contents of the accumulator.
[0058]
Each register 2001 is connected to an address bus and a data bus (read line and word line), and stores an instruction code defining processing and data to be processed. The contents of the register 2001 are input to the logical operation unit 2004, and the operation processing result is stored in the accumulator 2005. In order to retrieve the result outside the PE, the result is temporarily saved in the temporary register 2006. By extracting the contents of the temporary register 2006, the processing result for the target data is obtained. The instruction code is given to each PE with the same contents, the processing target data is given in a different state for each PE, and the operation result is processed in parallel by referring to the contents of the register 2001 of the adjacent PE in the multiplexer 2002. Is output. For example, if the content of one line of image data is arranged in the PE for each pixel and is processed by the same instruction code, the processing result for one line can be obtained in a shorter time than the sequential processing of each pixel. In particular, in the spatial filter processing, the instruction code for each PE is an arithmetic expression itself, and the processing can be performed in common for all the PEs.
[0059]
Next, the SIMD type image data processing unit and the sequential image data processing unit of the image processing apparatus will be described. FIG. 15 is a diagram showing the configuration of the SIMD type image data processing unit 1500 and the sequential image data calculation processing unit 1507. In the present embodiment, first, the SIMD type image data processing unit 1500 will be described, and then the sequential type image data processing unit 1507 will be described.
[0060]
The image data parallel processing unit 1500 and the image data sequential processing unit 1507 process an image as a plurality of pixel lines composed of a plurality of pixels arranged in one direction. FIG. 16 is a diagram for explaining pixel lines, and shows four pixel lines of pixel lines a to d. In addition, pixels indicated by hatching in the figure are target pixels to be processed this time. In the present embodiment, in the error diffusion process of the target pixel, the influence of surrounding pixels on the target pixel is considered for both pixels included in the same pixel line and pixels included in different pixel lines. Then, error diffusion processing between pixels included in a pixel line different from the target pixel is performed by the SIMD type image data processing unit 1500, and pixels included in the same pixel line as the target pixel ((1), The sequential image data processing unit 1507 performs error diffusion processing with respect to (2) and (3).
[0061]
The SIMD type image data processing unit 1500 includes a SIMD type processor 1506, five data input / output buses 1501a to 1501e for inputting image data and control signals to the SIMD type image data processing unit 1500, and data input / output buses 1501a to 1501a. 1501e is switched to switch image data and control signals input to the SIMD type processor 1506, and the bus switches 1502a, 1502b, and 1502c to switch the bus width of the connected bus and are used to process the input image data. 20 RAMs 1503 for storing the data to be stored, and the memory controller 1505a, the memory controller 1505b, the memory controller 1505a, or the memory controller 1505b for controlling the corresponding RAM 1503. Four memory switches 1504a for switching RAM1503 Therefore has 1504b, 1504c, and 1504d. In the above configuration, the memory controller controlled by the bus switches 1502a to 1502c is distinguished as the memory controller 1505b, and the memory controller not controlled by the bus switches 1502a to 1502c is distinguished as the memory controller 1505a.
[0062]
The aforementioned SIMD type processor 1506 includes a register 0 (R0) to a register 23 (R23). Each of R0 to R23 functions as a data interface between the PE in the SIMD type processor 1506 and the memory controllers 1505a and 1505b. The bus switch 1502a switches the memory controller 1505b connected to R0 to R3 and inputs a control signal to the SIMD type processor. The bus switch 1502b switches the memory controller 1505 connected to R4 and R5 and inputs a control signal to the SIMD type processor. The bus switch 1502c switches the memory controller 1505 connected to R6 to R9 and inputs a control signal to the SIMD type processor. The bus switch 1502c switches the memory controller 1505b connected to R6 to R9 and inputs a control signal to the SIMD type processor.
[0063]
The memory switch 1504a transfers image data between the PE in the SIMD type processor 1506 and the RAM 1503 using the memory controller 1505b connected to R0 to R5. The memory switch 1504b exchanges image data between the PE in the SIMD type processor 1506 and the RAM 1503 using the memory controller 1505b connected to R6 and R7. The memory switch 1504c exchanges image data between the PE in the SIMD processor 1506 and the RAM 1503 using the memory controller 1505a or the memory controller 1505b connected to R8 to R13. The memory switch 1504d transfers image data between the PE in the SIMD type processor 1506 and the RAM 1503 using the memory controller 1505a connected to R14 to R19.
[0064]
An image data control unit (not shown) inputs control signals for processing image data together with the image data to the bus switches 1502a to 1502c via the data input / output buses 1501a to 1501e. The bus switches 1502a to 1502c switch the bus width of the connected bus based on the control signal signal. In addition, the memory switches 1504a to 1504c are switched so that the memory controller 1505b connected indirectly or directly is controlled to take out data necessary for processing image data from the RAM 1503.
[0065]
When performing error diffusion processing, the SIMD type image data processing unit 1500 inputs image data generated by a reading unit and a sensor board unit (not shown) via the image data control unit. Then, error data that is a difference between pixel data included in a pixel line (previous pixel line) processed before the pixel line (current pixel line) including the target pixel (previous pixel line) and a predetermined threshold value and the target pixel Add pixel data.
[0066]
The SIMD type image data processing unit 1500 uses the SIMD type processor 1506 to execute addition with error data for a plurality of target pixels in parallel. For this reason, a plurality of error data corresponding to the number of pixels processed in batch by the SIMD processor 1506 is stored in any of the RAMs 1503 connected to the SIMD processor 1506. In this embodiment, the addition processing for one pixel line is collectively performed in the SIMD type processor 1506, and error data for one pixel line is stored in the RAM 1503. The addition value of the image data and error data for one pixel line collectively processed by the SIMD type processor 1506 is one by one in the sequential image data processing unit 1507 from at least two of R20, R21, R23, and R22. Is output. The error data used in the above processing is calculated by a sequential image data processing unit 1507, which will be described later, and is input to the SIMD type processor 1506.
[0067]
On the other hand, the sequential image data processing units 1507a and 1507b are hardware that operates regardless of the control of the computer program. In FIG. 15, two sequential image data processing units 1507 are connected to the SIMD processor 1506, but the image processing apparatus according to the present embodiment is used exclusively for error diffusion processing in which 1507b is sequentially performed. The other sequential image data processing unit 1507 is specialized in function so as to be used for table conversion such as γ conversion.
[0068]
A hardware configuration of the image processor will be described.
FIG. 17 is a block diagram showing the internal configuration of the image processor 1204. In the figure, an image processor 1204 includes a plurality of input / output ports 1401 for data input / output with the outside, and can arbitrarily set data input and output. In addition, a bus switch / local memory group 1402 is provided inside so as to be connected to the input / output port 1401, and the memory control unit 1403 controls the memory area to be used and the path of the data bus. The input data and the data for output are assigned to the bus switch / local memory group 1402 as a buffer memory, stored in each, and the external I / F is controlled. Various processing is performed in the processor array unit 1404 on the image data stored in the bus switch / local memory group 1402, and the output result (processed image data) is again sent to the bus switch / local memory group 1402. Store. The processing procedure in the processor array unit 1404, parameters for processing, and the like are exchanged between the program RAM 1405 and the data RAM 1406.
[0069]
The contents of the program RAM 1405 and the data RAM 1406 are downloaded from the process controller (not shown) to the host buffer 1407 through the serial I / F 1408. The process controller reads the contents of the data RAM 1406 and monitors the progress of processing. When the processing contents are changed or the processing mode required by the system is changed, the contents of the program RAM 1405 and the data RAM 1406 referred to by the processor array 1404 are updated. In special processing 1 (1409), conversion processing such as table conversion and γ conversion is mainly performed, and in special processing 2 (1410), error diffusion processing is performed. Among the configurations described above, the processor array 1404 corresponds to the SIMD type image data processing unit and the sequential type image data processing unit according to the present embodiment.
[0070]
FIG. 18 is a block diagram showing the configuration of the sequential image data processing unit 1507b. The sequential image data processing unit 1507b shown in the figure processes an error data calculation unit 1801, a multiplexer 1807 for selecting one from the error data calculated by the error data calculation unit 1801, and the error data selected by the multiplexer 1807. And an error data adding unit 1808 for adding to the data input from the SIMD type image data processing unit 1500. Further, the sequential image data processing unit 1507b inputs a signal required for selecting error data to the multiplexer 1807 and an error diffusion mode (2) set in advance for the sequential image data processing unit 1500. An error diffusion processing hardware register group 1805 that can set an operation coefficient used for error diffusion processing, or whether error diffusion is executed by any one of value error diffusion, three-value error diffusion, and four-value error diffusion). Yes. Further, the sequential image data processing unit 1507b includes a blue noise signal generation unit 1809, and is configured to be able to select whether or not to use blue noise for error diffusion processing by setting the error diffusion processing hardware register group 1805. ing.
[0071]
The error data calculation unit 1801 is configured to calculate error data that is a difference between pixel data of a pixel included in the current pixel line and a predetermined threshold value. The error data calculation means 1801 includes a threshold table group 1810a connected to each of the three quantization reference value storage units 1803a, 1803b, and 1803c, the three comparators 1804a, 1804b, and 1804c, and the three multiplexers 1802a, 1802b, and 1802c. , 1810b, 1810c. The threshold value table groups 1810a, 1810b, and 1810c are each composed of, for example, six threshold value tables THxA to THxF (x = 0, 1, 2). This can be selected by setting the error diffusion processing hardware register group 1805. In the gradation processing in this embodiment, an image processing processor used for gradation processing of Magenta and Cyan image data, and Yellow and Black images are used. Two image processors are used, an image processor that performs gradation processing on the data.
[0072]
Hereinafter, an example of the image processor for image data processing of Magenta and Cyan will be described.
[0073]
THxA, THxB, THxC (x = 0, 1, 2) is used for Magenta, and THxD, THxE, THxF (x = 0, 1, 2) is used for Cyan. For THxA to THxC (x = 0, 1, 2) used for Magenta, a threshold value table can be selected according to the extraction result based on the feature amount of an image such as a character, a photograph, or an intermediate image. It is. Simple error diffusion with a fixed threshold that does not depend on the main scanning or sub-scanning position in the character part, error diffusion diffusion with a dither threshold with a low number of lines in the photograph part, and a threshold with a higher number of lines than the photograph part in the intermediate part Can be performed, and a more preferable image can be formed. TH0A, TH1A, and TH2A are thresholds for pixels determined to have the same feature amount. The same applies to Cyan. The processor that processes the image data of Yellow and Black is the same as that described above by replacing Magenta with Yellow and Cyan with Black.
[0074]
However, the screen angle for dither processing differs for each color, and an example of the dither processing parameters is shown in FIG.
[0075]
In the present embodiment, the quantization reference value storage unit 1803a, the comparator 1804a, and the multiplexer 1802a connected to the threshold table group 1810a operate as a set. Further, the multiplexer 1802b connected to the quantization reference value storage unit 1803b, the comparator 1804b, and the threshold table group 1810b operates as a set, and is connected to the quantization reference value storage unit 1803c, the comparator 1804c, and the threshold table group 1810c. Multiplexers 1802c operate as a set.
[0076]
An addition value (addition value data) between the image data and the error data is input from the SIMD type processor 1506 to the sequential image data processing unit 1507. This image data is the image data of the target pixel processed this time, and the error data is the error data of the pixel processed before the target pixel. The input added value data is added with a value calculated by the error data adding unit 1808 based on previously processed pixel error data, and is divided by 16 or 32 to reduce the calculation error. Further, the divided addition value data is input to all the three comparators 1804a to 1804c of the error data calculation unit 1801. Note that the value calculated by the error data adding unit 1808 based on the error data of the pixel previously processed will be described later.
[0077]
Threshold values are input to the comparators 1804a to 1804c from the multiplexers 1802a to 1802c connected to the connected threshold value table group. Then, the threshold value is subtracted from the input addition value data to create image data. Further, a value obtained by subtracting the quantization reference value stored in each of the quantization reference value storage units 1803a to 1803c from the added value data is output to the multiplexer 1807 as error data. As a result, a total of three error data are simultaneously input to the multiplexer 1807.
[0078]
When blue noise is used for error diffusion processing, the blue noise signal generator 1809 turns on and off the blue noise data at a relatively high cycle to generate blue noise. The threshold is subtracted from the blue noise before entering the comparators 1804a-1804c. By the process using blue noise, it is possible to prevent the occurrence of a unique texture in the image by giving an appropriate variation in the threshold value.
[0079]
Different threshold values are stored in the threshold value tables 1802a to 1802c. In this embodiment, the threshold value table 1802a stores the largest threshold value among the threshold value tables 1802a to 1802c, and then the threshold value stored in the order of the threshold value table 1802b and the threshold value table 1802c decreases. In addition, quantization reference values to be stored in the quantization standard value storage units 1804a to 1804c are set according to the connected threshold value tables 1802a to 1802c. For example, when the image data is represented by 256 values from 0 to 255, 255 is stored in the quantization reference value storage unit 1803a, 170 is stored in the quantization reference value storage unit 1803b, and quantization reference value storage unit 1803c. Is stored with 85.
[0080]
The comparators 1804a to 1804c output the created image data to the logic circuit 1806. The logic circuit 1806 selects the image data of the target pixel from these and inputs it to the multiplexer 1807. The multiplexer 1807 selects one of the three error data as the error data of the target pixel in accordance with the input image data. The selected error data is input to one of the RAMs 1503 via the PE of the SIMD type processor 1506. Further, the image data output from the logic circuit (decoder) 1806 is branched before being input to the multiplexer 1807 and input to one of the PEs of the SIMD type processor 1506. In this embodiment, the image data is data represented by 2 bits of an upper bit and a lower bit. For this reason, the comparator 1804a is not used in this process. In the present embodiment, the image data of the target pixel is hereinafter referred to as pixel data.
[0081]
The selected error data is input to the error data adding unit 1808. The error data adding unit 1808 has error data (in FIG. 18) of pixels indicated by (1), (2), and (3) in FIG. 16, that is, pixels processed three times before the target pixel. Error data of the pixel processed two times before (denoted as error data 2 in FIG. 18) Error data of the pixel processed one time ago (denoted as error data 1 in FIG. 18) Is saved.
[0082]
The error data adding unit 1808 multiplies the error data 3 by 0 or 1 that is a calculation coefficient. Further, the error data 2 is multiplied by a calculation coefficient 1 or 2, and the error data 1 is multiplied by a calculation coefficient 2 or 4. Then, the three multiplication values are added together, and this value (weighting error data) is added to the addition value data inputted next from the SIMD type processor 1506. As a result, a pixel closer to the target pixel has a larger influence on the error diffusion process of the target pixel, and the error of the pixel can be appropriately diffused to form an image closer to the original image.
[0083]
Creation of image data in the sequential image data processing unit 1507 described above is generally performed using a configuration called an IIR filter system. FIG. 20 is a diagram showing the system configuration. The arithmetic expression used in the IIR filter system is
ODn = (1−K) × ODn−1 + K · IDn (3)
ODn: Pixel density after calculation
ODn-1: calculation result using the previous pixel data
IDn: Current pixel data
K: Weight coefficient
It expresses.
[0084]
As is apparent from the equation (3) and FIG. 20, the density ODn after the calculation is obtained from the calculation result ODn−1 using the previous pixel data and the value of the current pixel data IDn. In general, the IIR filter system is a dedicated circuit for performing so-called sequential conversion, which performs an operation on the current pixel using an operation result using a pixel processed before the current pixel. The sequential image data processing unit 507 of the image processing apparatus according to the present embodiment can be used for the entire sequential conversion as shown in FIG. 20 regardless of the processing shown in FIG.
[0085]
FIG. 22 is a diagram for explaining registers set in the error diffusion processing hardware register group 1805. The image processing apparatus according to this embodiment is configured by setting the illustrated register.
-Mode for performing error diffusion processing with binary error diffusion (binary error diffusion mode)
-Mode for performing error diffusion processing with ternary error diffusion (ternary error diffusion mode)
-Mode for performing error diffusion processing with 4-level error diffusion (4-level error diffusion mode)
It is possible to select which of the error diffusion processing is performed. In addition, a calculation coefficient used in the error data adding unit 1808 can be set. Furthermore, it is possible to select whether or not to use blue noise for error diffusion processing.
[0086]
The error diffusion processing hardware register group 1805 shown in FIG. 22 sets the register 3001 for setting the quantization reference value 0 of the quantization reference value storage unit 1803a and the quantization reference value 1 of the quantization reference value storage unit 1803b. A register 3002 and a register 3003 for setting the quantization reference value 2 of the quantization reference value storage unit 1803c are provided. The error diffusion processing hardware register group 1805 is set in the register 3004 for setting the threshold value 0 set in the threshold value table 1802c, the register 3005 for setting the threshold values 10-17 set in the threshold value table 1802b, and the threshold value table 802a. A register 3006 for setting threshold values 20 to 27, a register 3007 for setting a blue noise value, and an error diffusion processing hardware control register 3008. Each register is assigned 8 bits, and the entire register has a data amount of 64 bits.
[0087]
In the binary error diffusion mode, the same value is set in all of the registers 3001 to 3003. This can be realized by setting FFH in the registers 3004 and 3005. In the ternary error diffusion mode, the same value is set in the registers 3001 and 3002, and FFH is set in the register 3004. Further, in the binary error diffusion mode and the ternary error diffusion mode, the fixed threshold error diffusion processing and the variation threshold error diffusion processing are switched depending on whether the same value is set in the register 3005 and the register 3006 or different values. be able to.
[0088]
When blue noise is used for error diffusion processing, a value indicating that blue noise is used is set in the register 3007. Then, switching data indicating on / off of blue noise data is set in the register 3005. When the switching data is 1, the blue noise value is added to each threshold value. When the switching data is 0, the threshold value is used as it is. Further, the calculation coefficient used in the error data adding unit 1808 can be selected by changing the set value of the error diffusion processing hardware control register.
[0089]
Next, processing performed by the above-described SIMD type processor 1506 and sequential image data processing unit 1507b will be described with reference to a flowchart and a diagram showing a processing procedure. FIG. 23 is a flowchart showing the processing procedure of error diffusion processing performed by the SIMD type processor 1506, FIG. 24 is a diagram for explaining the processing procedure of error diffusion processing performed by the sequential image data processing unit 1507b, and FIG. It is a figure for demonstrating a shift.
[0090]
In the flowchart of FIG. 23, the SIMD type processor 1506 first determines whether or not the current image data is the first line (S2101), and if it is the first line, initializes the error addition value for the previous two lines. (S2101). Next, it is determined whether or not the current image data to be subjected to error diffusion calculation is the first SIMD (S2103). If it is the first SIM (the image data at the beginning of the current line), the error addition value is initialized ( S2105). If it is not the first SIMD, it is determined whether the error data after the error diffusion calculation in the previous SIMD is the same color as the currently calculated image data (S2104, S2106). (S2107, processing A2 in FIG. 25), the reference position of the blue noise table is also stored (S2109), and the blue noise reference position in the previous error diffusion calculation of the same color is called. (S2110).
[0091]
If they are the same color in S2106, they are stored as the 1 SIMD calculation result of the previous line of the same color (S2108, process A1 in FIG. 25). For example, when the color to be subjected to error diffusion calculation is the Magenta version of image data, the color of the different color is different from the image data of the Cyan version. In the case of the Magenta version image data, they are determined as the same color.
[0092]
Then, the error added value data of two lines before is stored as data of one line before the previous SIMD (S2111, process B in FIG. 25), and the data of two lines before the current SIMD is retrieved from the memory (S2112, FIG. 25). Process D, E). Next, after calling the current SIMD data from the current line (process C in FIG. 25), an error addition value is calculated (S2113). Thereafter, the sequential image data processing unit 1507b performs error diffusion processing (S2114).
[0093]
On the other hand, as shown in FIG. 24, the sequential image data processing unit 1507 inputs the addition value data output from the SIMD type processor 1506 in step S2102 (step S2201). Then, the weighted error data generated by the error data adding unit 1808 is added to the input added value data (step S2202). The added value data added with the weighting error data is divided by 16 or 32 (step S2203) and input to the error data calculation unit 1801. The error data calculation unit 1801 generates error data and pixel data based on the input data (step S2204), and inputs the error data to the multiplexer 1807. Further, the pixel data is input to the logic circuit 1806 and the SIMD type processor 1506.
[0094]
The multiplexer 1807 selects one error data according to the image data input from the logic circuit 1806 (step S2205). Then, the selected error data is output to the SIMD type processor 1506 and the error data adder 1808 (step S2206). The error data adding unit 1808 that has input the error data calculates weighted error data based on the error data (step S2207). The sequential image data processing unit 1507 repeatedly executes the above processing sequentially for the input addition value data.
[0095]
FIG. 21 is a block diagram showing the configuration of the image processing unit. The image processing method will be described with reference to FIG.
The image processing unit receives multi-gradation image data 1100 and outputs the quantized data 1101. The quantization processing unit 1120, the image feature extraction unit 1130, the quantization threshold generation unit 1140, and the quantization processing unit 1120 And a signal delay unit 1150 for adjusting the timing of the image feature extraction unit 1130. The signal delay unit 1150 is provided as necessary, and includes, for example, a line memory having a required number of lines. The input image data 1100 is, for example, 8-bit / 1-pixel data read by a scanner at 600 dpi. In general, such image data 1100 is input after passing through a smoothing filter in order to smoothly express a halftone. Usually, since smoothing is performed from an image cycle of about 150 Lpi, the periodic component of a high-line number halftone dot image of 175 Lpi or more used in gravure printing or the like does not remain in the image data 1100.
[0096]
The quantization processing unit 1120 quantizes the multi-tone image data by the error diffusion method using the quantization threshold generated by the quantization threshold generation unit 1140. In the present embodiment, as illustrated in the figure. , A quantizer (comparator) 1121, an error calculation unit 1122, an error storage unit 1123, an error diffusion matrix unit 1124, and an error addition unit 1125. The image data 1100 is adjusted in timing by the signal delay unit 1150 and input to the error addition unit 1125. The image data to which the diffusion error is added by the error adder 1125 is input to the quantizer 1121. The quantizer 1121 quantizes the input image data using the quantization threshold given from the quantization threshold generator 1140 and outputs the quantization result as quantized data 1101.
[0097]
In the present embodiment, a 2-bit error diffusion process will be described as an example.
The quantization threshold value generator 1140 generates quantization threshold values 1 to 3 (th1 to th2). The quantization threshold relationship is
Quantization threshold 1 (th1) ≦ quantization threshold 2 (th2) ≦ quantization threshold 3 (th3)
And The quantizer 1121 compares the input image data with the thresholds th1 to th3. When the value is larger than th3, the quantizer 1121 is “3”, when larger than th2, “2”, when larger than th1, “1” and from th1. A description will be made assuming that 2-bit quantized data 1101 having a value of “0” is output when the value is small.
[0098]
The error calculation unit 1122 calculates the quantization error of the quantizer 1121. Since 8-bit image data is handled here, in this error calculation, for example, “3” in quantized data 1101 is 255 (decimal), “2” is 192 (decimal), and “1” is set. 128 (decimal) and “0” are treated as 0 (decimal). The calculated quantization error is temporarily stored in the error storage unit 1123. The error storage unit 1123 is for storing a quantization error related to a processed pixel around the target pixel. In this embodiment, as will be described below, for example, a 3-line line memory is used as the error storage unit 1123 in order to diffuse the quantization error to peripheral pixels ahead of 2 lines.
[0099]
The error diffusion matrix unit 1124 calculates a diffusion error to be added to the next target pixel from the quantization error data stored in the error storage unit 1123. In this embodiment, the error diffusion matrix unit 1124 calculates diffusion error data using an error diffusion matrix having a size of 3 pixels in the sub-scanning direction and 5 pixels in the main scanning direction as shown in FIG. In FIG. 26, the mark * corresponds to the position of the next pixel of interest, and a, b,. . . , K, l are coefficients corresponding to the positions of the 12 processed pixels in the vicinity (the sum is 32). In the error diffusion matrix unit 1124, a value obtained by dividing the product sum of the quantization error for the 12 processed pixels and the corresponding coefficients a to l by 32 is sent to the error addition unit 1125 as a diffusion error for the next pixel of interest. give.
[0100]
The image feature extraction unit 1130 includes an edge detection unit 1131 and a region expansion processing unit 1132. The edge detection unit 1131 performs edge detection of the image data 1100, and outputs 4-bit edge data representing edge levels from level 0 (maximum edge degree) to level 8 (non-edge) in this embodiment. More specifically, for example, using four types of 5 × 5 differential filters shown in FIG. 27, the edge amount is detected in the four directions of the main scanning direction, the sub-scanning direction, and the direction inclined by ± 45 ° from the main scanning direction. Then, an edge amount having the maximum absolute value is selected, and the absolute value of the edge amount is quantized into four level edge levels from level 0 to level 3 and output.
[0101]
The region expansion processing unit 1132 performs region expansion processing with a width of 7 pixels on the edge detected by the edge detection unit 1131. The region expansion processing unit 1132 refers to the edge data output from the edge detection unit 1131 and generates 7 pixels around the target pixel. The minimum edge level (maximum edge degree) in the 7 pixel area (range of 3 pixels before and after in the main scanning direction and 3 pixels before and after in the sub-scanning direction) Output as edge data. This edge data is given to the quantization threshold value generator 1140.
[0102]
The quantization threshold generation unit 1140 generates a quantization threshold that periodically oscillates in the image space with a vibration width corresponding to the edge level represented by the edge data output from the region expansion processing unit 1132. This is given to the quantizer 1121 of the quantization processing unit 1120. The dither threshold value generation unit 1141 and the output value of the dither threshold value generation unit 1141 are multiplied by a coefficient (0 to 3) corresponding to the edge level indicated by the edge data. A multiplier 1142 and an adder 1143 that adds a fixed value (128 in this embodiment) to the output value of the multiplier 1142.
[0103]
In the present embodiment, the dither threshold value generation unit 1141 is arranged so as to grow the lines in order of increasing threshold values from 1 to 6 as shown in FIGS. 28 and 29 (1 is the minimum and 6 is the maximum). Using a × 4 dither threshold matrix, a dither threshold that periodically vibrates from 1 to 6 in the image space is output. Here, the same threshold value is used for pixels having the same value. The dither threshold period corresponds to 168 Lpi in the case of 600 dpi image formation. Such a dither threshold value generation unit 1141 can be easily realized by a ROM that stores the dither threshold value matrix, a counter that counts main and sub-scan timing signals of image data, and generates a read address of the ROM. . Here, the pixels set to 1 in FIG. 28 and FIG. 29 indicate that dots arranged in the main scanning direction are first formed by arranging them in the main scanning direction. In this way, for the purpose of stable dot formation, two pixels of 1 value, which is a writing level with less energy, are arranged. The screen angle and line growth direction in this case are shown in FIG. The growth direction of the line is indicated by “direction 1 in which the line grows” in the drawing.
[0104]
The multiplying unit 1142 gives a coefficient 3 when the edge level indicated by the edge data from the image feature extracting unit 1130 is level 0 (non-edge), a coefficient 2 when it is level 1, a coefficient 1 when it is level 2, and a level 3 At the time of (maximum edge degree), the coefficient 0 is multiplied by the output value of the dither threshold value generator 1141.
[0105]
If the quantized data 1101 of the image processing apparatus configured as described above is given to, for example, an electrophotographic printer or the like, the resolution of characters, image change points, a relatively low number of halftone dot image portions, and the like can be obtained. In addition, a photograph, a portion with little change in the image, a halftone dot image with a high number of lines, etc. are smooth and stable, and it is possible to form a high-quality image in which these regions are aligned without a sense of incongruity. This will be described below.
[0106]
The quantization threshold generated by the quantization threshold generation unit 1140 is fixed at a portion where the change is steep and the edge level is level 3 (edge degree is the highest) in the image, such as the edge of a character or line drawing. Since the processing unit 1120 performs a quantization process by a pure error diffusion method using a fixed threshold value, an image with high resolution can be formed.
[0107]
In the present embodiment, two SIMD processors having the sequential processing operation unit shown in FIG. 15 are used, and Y (Yellow) image data and K (Black) image data are one for YMCK image data. A SIMD processor having a sequential processing operation unit is used, and gradation processing is performed on two sets of image data of the C image signal M using another SIMD processor having another sequential processing operation unit. Therefore, two image data (YK or CM) before gradation processing input to the SIMD processor and two-input two-output image data that outputs two image data (YK or CM) from the SIMD processor are processed. When error diffusion processing is performed, processing is performed on two input image data by switching a SIMD processor having one sequential processing operation unit for each number of image data that can be subjected to SIMD processing.
[0108]
FIG. 31 is a state transition diagram of the image processor. As shown in the figure, the image processor loops the processing state from command → main 1 (processing of Magenta / Yellow image data) → main 2 (processing of Cyan / Black image data) → command → main 1… Yes.
[0109]
The operation of the image processor at the time of two inputs and two outputs will be described based on the flowchart of FIG.
In the main process 1, Magenta or Yellow image data is processed. In the main process 2, Cyan or Black image data is processed. Input of Magenta (Yellow) is input to the SIMD processor 1506 using the data input / output bus 1501a and output using the data input / output bus 1501c. Similarly, Cyan (Black) image data is input using the data input / output bus 1501b and output using the data input / output bus 1501d. The data input / output bus 1501c is used for debugging output.
[0110]
When there is data input to the SIMD processor 1506 in the main process 1 (S2301), a process of taking image data into the memory 1503 is started (S2302). When one line has been captured (S2303), gradation processing (here, error diffusion processing) is started in units of image data that can be processed by the SIMD processor 1506 (S2304). When the one-line processing is completed (S2305), one-line output is started (S2306). In the image data memory capture / output start processing such as S2302 and S2306, processing start commands to the respective memory controllers 1505a to 1505b are set in the registers, and the SIMD processor shifts to the next control (state transition). The gradation processing (error diffusion processing) is started (S2304) by writing a predetermined setting value corresponding to the error diffusion processing hardware control register 2008 start command as a start processing command to the sequential processing calculation unit 1507b.
[0111]
Similarly, when there is data input to the SIMD processor 1506 in the main process 2 (S2401), the process of taking image data into the memory 1503 is started (S2402). When one line has been captured (S2403), gradation processing (here, error diffusion processing) is started in units of image data that can be processed by the SIMD processor 1506 (S2404). When the one-line processing is completed (S2405), one-line output is started (S2406). In the image data memory capture / output start processing such as S2402 and S2406, processing start commands to the respective memory controllers 1505a to 1505b are set in the registers, and the SIMD processor shifts to the next control (state transition). The gradation processing (error diffusion processing) is started (S2404) by writing a predetermined setting value corresponding to the error diffusion processing hardware control register 2008 start command to the sequential processing operation unit 1507b.
[0112]
In the command processing, command reception processing from the control CPU to the SIMD processor 1506 is performed (S2501, S2502).
[0113]
A procedure for calling automatic gradation correction (ACC: Auto Color Calibration) of image density (gradation) will be described.
[0114]
FIG. 33 is a front view showing the entire operation unit 142. When the automatic gradation correction menu (ACC menu) is called on the operation unit, the operation screen shown in FIG. 34 is displayed. When [Execute] of automatic gradation correction for copy use or printer use is selected, the operation screen shown in FIG. 34 is displayed. When the copy use is selected, the gradation correction table used when using the copy is changed. When the printer is used, the gradation correction table when the printer is used is changed based on the reference data. If the result of image formation with the changed YMCK tone correction table is not desirable, the [Restore to original value] key is displayed so that the YMCK tone correction table before processing can be selected. 34 is displayed on the screen.
[0115]
FIG. 35 is a flowchart showing a control procedure of automatic gradation correction (ACC) of image density (gradation). In the automatic gradation correction of the image density, when the print start key in the screen of FIG. 36 is depressed in step S3101, a plurality of YMCK color, character and photo image quality modes as shown in FIG. 37 are displayed in step S3102. The density gradation pattern is formed on the transfer material. The density gradation pattern is stored and set in the IPU ROM in advance. The pattern writing values are, for example, 11h, 22h,..., EEh, FFh, and 00h (background portion of the transfer paper) in hexadecimal notation, and are formed in the arrangement shown in the figure. The density gradation pattern forms a density gradation pattern for calculating the printer γ table for the character portion and the photographic portion for each of YMCK. For example, the density gradation patch for the character portion performs gradation processing such as error diffusion, and the density gradation patch for the photographic portion outputs a pattern on which the above-described DATE processing has been performed. In the figure, patches for 15 gradations are displayed except for the background portion, but each patch can select an arbitrary value of an 8-bit signal of 00h-FFh.
[0116]
In addition to the above-described density gradation pattern, the transfer paper output with the automatic gradation correction pattern shown in FIG. 37 has a density caused by the sensitivity unevenness of the photoconductor and the sensitivity unevenness of the image forming unit such as transfer. In order to correct the unevenness, three patches of 33h, 44h, and 55h, for example, 33h, 44h, and 55h are formed from the left, the left, the left-middle (LM), the center, the right-middle (RM), and the right for the reference pattern. . A similar patch is formed next to the same because the influence of flare caused by the adjacent pattern is made almost the same regardless of the positions Left, ML, Center, MR, and Right in the main scanning direction. However, while the black patch is arranged on the right side of the patch of the Center and Right-Middle (RM) and the Yellow patch is arranged on the left side, the other Left, Left-Middle (LM), The Yellow patch is not arranged in Right. This is because the absolute value of the influence of flare is estimated to be small due to the high brightness of Yellow and the Green (or Red) signal among the RGB signals of the scanner is used when reading Black. Since the yellow component mainly affects the blue component, the influence of the adjacent yellow patch can be reduced by using the green (or red) signal.
[0117]
After the pattern is output on the transfer material in step S3103, a screen shown in FIG. 38 is displayed on the operation screen so that the transfer material is placed on the document table 118. When the transfer paper on which the pattern is formed is placed on the platen according to the instructions on the screen, and “read start” is selected on the screen of FIG. 38 or “cancel” is selected. The processing ends here (step S3104) On the other hand, if “reading start” is selected, the scanner runs and reads the RGB data of the YMCK density pattern (step S3105). Next, the data of the background portion is read, and it is determined whether the data of the pattern portion has been read normally (step S3106) If the data is not read correctly, the screen of Fig. 38 is displayed again. If it cannot be read, the process ends (step S3107).
[0118]
If the data is normally read in step S3106, correction is performed using the ACC machine difference correction value in step S3108, and whether or not unevenness is detected and corrected is determined in step S3109. In step S3110, unevenness is detected and corrected. If not, the process skips to step S3111.
[0119]
In step S 3111, it is determined whether or not “execution” is selected for “background correction” on the screen of FIG. 34. If “execution” is selected, in step S 3112, based on the background data for the read data. Make corrections. Next, in step S3113, it is determined whether or not “execution” is selected for “correction of high image density portion” on the screen of FIG. 34. If “execution” is selected, reference is made in step S3114. Correction processing is performed on the data in the high image density portion of the data.
[0120]
Then, in step S3115, a YMCK tone correction table is created using the data processed as described above, and when all the YMCK tone correction tables for each color are created (step S3116), these processes are performed on a photo, This is executed for each character quality mode (step S3117).
[0121]
During the process, the screen of FIG. 39 is displayed on the operation screen. If the result of image formation using the YMCK tone correction table after the end of processing is not desirable, the [Restore value] key is used so that the YMCK tone correction table before processing can be selected. It is displayed in the screen of FIG. 40 is a front view showing details of the liquid crystal display screen (touch panel) of FIG.
[0122]
Details of each process will be described below.
[0123]
FIG. 37 is a diagram illustrating a reference patch used for correcting unevenness. In this reference patch, Left 0-15 (hereinafter abbreviated as L0-L15), Left-Middle 0-15 (hereinafter abbreviated as ML0-ML15), Center0-15, C0-C15), Right-Middle0-15 (MR0-MR15). ), Right 0-15 (same R0 to R15) patches are used. These patterns are subjected to photographic gradation processing. The reason is that the first object of the invention is to reduce the variation in the position of the gray balance in the main scanning direction when the YMC of the gradation processing in the photographic mode is overlapped.
[0124]
FIG. 41 is a quaternary chart for explaining a method of calculating the unevenness correction value. In the figure, the horizontal axis of the first quadrant ([I] in FIG. 41) represents the gradation patch writing value, the vertical axis represents the scanner reading value, and the graph represents the gradation patch reading value. The horizontal axis of the second quadrant ([II] in FIG. 41) is the input value to the printer γ conversion table, and the graph is the adjustment target (target) of automatic gradation correction (ACC) or the printer γ after execution of ACC. Represents the adjustment result. The vertical axis of the third quadrant ([III] in FIG. 41) is an input value to the gradation processing, and the graph represents a correction amount for correcting unevenness. This graph shows the values to be obtained. The fourth quadrant ([IV] in FIG. 41) is a characteristic of gradation processing.
[0125]
The first quadrants a) to c) are respectively
a) Reference value for correction
b) When the density is higher than the standard
c) When the density is lower than the standard
Is illustrated. For example, with reference to C0 to C15 of the gradation pattern shown in FIG. 37, if the density is low among the other reading results of L0 to L15, ML0 to ML15, MR0 to MR15, R0 to R15, b) When the density is high, it is shown as c).
[0126]
Since the ACC target is constant regardless of unevenness in the main scanning direction, if there is unevenness, the result of graph output of the second quadrant depends on the position in the main scanning direction as shown in the results d) to f). The output results vary. Here, d) is a printer γ table for a). In such a case, unevenness occurs when the three YMC colors are superimposed. In order to prevent this, the sensitivity variation of the image forming unit is corrected according to the position in the main scanning direction, and the printer γ table ( 41 [IV]) in FIG. 41 is changed according to the position in the main scanning direction. The slope of the graph obtained in the third quadrant is obtained, and this is used as the slope of the correction amount.
[0127]
FIG. 42 shows a conceptual diagram of the correction amount based on the main scanning position obtained as described above.
[0128]
A graph based on the value of the center of the correction amount slope calculated from the read values of the respective gradation patterns of Left, Left-Middle (LM), Center, Right-Middle (RM), and Right formed in the ACC pattern. 42a). FIG. 42 b) shows the result of interpolation of the inclination from a place where there is a non-uniformity detection pattern to a place where there is no detection pattern. FIG. 42B) divides the image width in the main scanning direction for each number of pixels that the SIMD processor can process at a time. The image signal before gradation processing is corrected using the inclination obtained as described above. Thereby, the unevenness in the main scanning direction can be efficiently corrected with a simple calculation.
[0129]
FIG. 43 is a flowchart showing the procedure of unevenness correction processing in the SIMD processor. In the process shown in FIG. 43, first, in step S3201, image data is input to the SIMD processor, and in step S3202, the edge degree of the image is calculated from the image data (feature amount extraction). Next, unevenness in the main scanning direction is corrected in step S3203, and the gradation processing described above is performed in step S3204. In step S3205, the image signal is output from the SIMD processor.
[0130]
44 and 45 are diagrams showing output examples when the number of gradation patterns for correction is reduced. These reduce the number of unevenness detection patterns of Left, Left-Middle (LM), Center, Right-Middle (RM), and Right for detecting the amount of unevenness correction, and consumption of toner at the time of gradation pattern output It is an example of a gradation pattern with a reduced amount.
[0131]
The gradation pattern in FIG. 44 is a pattern in which a pattern is arranged adjacent to the pattern to be detected, and is effective when there is an influence of scanner flare. That is, in the case of a background having no pattern (Left-sub..., L-sub in the figure) adjacent to the pattern to be detected (Left as an example), compared to a case in which no pattern exists next to the pattern to be detected. Under the influence of the background, it may be read brightly (light image density is low). In order to prevent this, a pattern for detecting non-uniformity-a pattern of the same write value adjacent to the pattern for Left, RM, and Right-Left-sub (L-sub), RM-sub, Right-sub (R-sub) ) Arranged. Regarding the LM pattern and the Center pattern, since there is a black pattern for gradation correction adjacent to each other, it is determined that the influence on flare is the same as that of other patterns and it is not necessary to form the pattern.
[0132]
FIG. 45 shows a case where the influence of the flare of the scanner is negligible. In this case, the pattern adjacent to the patterns Left, RM, and Right for detecting unevenness in order to reduce the amount of toner consumption, Left-sub (L-sub ), RM-sub, Right-sub (R-sub) ˜ are omitted. As shown in the quaternary chart of FIG. 46, using at least one of the patterns Left, Left-Middle (LM), Center, Right-Middle (RM), and the third to fifth stages for detecting unevenness. The slope of the correction amount of the third ([III]) quadrant is obtained.
[0133]
The background correction will be described.
[0134]
There are two purposes for background correction. One is to correct the whiteness of the transfer material used during ACC. This is because even if an image is formed on the same machine at the same time, the value read by the scanner differs depending on the whiteness of the transfer material used. Disadvantages when the background is not corrected include, for example, when recycled paper or the like with low whiteness is used for this ACC, since recycled paper generally has a lot of yellow components, a yellow tone correction table is created. The correction is made so that the yellow component is reduced. In this state, when copying is next performed on art paper or the like having high whiteness, an image with a small amount of yellow components may be obtained and a desired color reproduction may not be obtained.
[0135]
The other is that when the thickness of the transfer paper (paper thickness) used at the time of ACC is thin, the color of the pressure plate for pressing the transfer material is seen through and read by the scanner. For example, when an automatic document feeder called ADF (Auto Document Feeder) is installed instead of the pressure plate, a belt is used for conveying the original, but depending on the rubber material used, The whiteness is low and there is a slight gray taste. For this reason, the read image signal is also read as an image signal that is apparently high, so that when the YMCK tone correction table is created, the image signal is created so as to be thinner. In this state, when a transfer sheet having a thick paper thickness and poor transparency is used, an image having a low overall density is reproduced, so that a desirable image is not necessarily obtained. In order to prevent these problems, the read image signal of the pattern portion is corrected from the read image signal of the background portion of the paper.
[0136]
However, there is an advantage even when the above correction is not performed, and when using a transfer paper with a large amount of yellow components, such as recycled paper, it is better not to correct for colors containing yellow components. Color reproduction can be improved. In addition, when only the transfer paper having a thin paper thickness is always used, there is an advantage that the gradation correction table is created in a state matched to the thin paper.
[0137]
As described above, the correction of the background portion can be turned ON / OFF according to the user's situation and preference.
[0138]
LD [i] (i = 0, 1,..., 9) is the written value of the gradation pattern (FIG. 37) formed on the transfer paper, and the read value of the formed pattern by the scanner is a vector type.
v [t] [i] ≡ (r [t] [i], g [t] [i], b [t] [i])
(T = Y, M, C, or K, i = 0, 1,..., 9)
And Instead of (r, g, b), it is expressed by brightness, saturation, hue angle (L *, c *, h *) or brightness, redness, blueness (L *, a *, b *) Also good. A reference white reading value stored in advance in the ROM 416 or the RAM 417 is defined as (r [W], g [W], b [W]).
[0139]
A method of generating a gradation conversion table (LUT) performed by the γ conversion processing unit 410 during ACC execution will be described.
[0140]
Pattern reading
v [t] [i] ≡ (r [t] [i], g [t] [i], b [t] [i])
The image signals of the complementary colors of YMC toner are respectively
b [t] [i], g [t] [i], r [t] [i]
Therefore, only the complementary color image signals are used. Here, to simplify the following description,
a [t] [i] (i = 0, 1, 2,..., 9; t = C, M, Y, orK)
It expresses using. Processing is simple if a gradation conversion table is created. For black toner, sufficient accuracy can be obtained by using any of RGB image signals, but here, a G (green) component is used.
[0141]
Reference data is the scanner reading
v0 [t] [i] ≡ (r0 [t] [i], g0 [t] [i], b0 [t] [i])
And the corresponding laser writing value
LD [i] (i = 1, 2,..., M)
Given by the pair. Similarly, in order to simplify the following description using only the YMC complementary color image signal,
A [t] [n [i]] (0 ≦ n [i] ≦ 255; i = 1, 2,..., M; t = Y, M, C, or K)
It expresses. m is the number of reference data.
[0142]
An example of the machine difference correction value is shown in FIG. The values in FIG. 47 are correction values corresponding to the respective toners of Black (G), Cyan (R), Magenta (G), and Yellow (B), and the values in parentheses are used for automatic gradation correction. Red (R), Green (G), and Blue (B) signals. For each color toner, k (0) and k (1023) represent correction values for the reference data value 0 and the reference data value 1023 (10-bit signal).
[0143]
The reference data value after correction
A1 [t] [n [i]]
Reference data using the values in FIG.
A [t] [n [i]]
The
A1 [t] [n [i]] = A [t] [n [i]] + (k (1023) −k (0)) × n [i] / 1023 + k (0) (4)
Correct as follows.
[0144]
The above function is represented by a diagram as shown in FIG. The correction values in FIG. 47 are set at the time of manufacture and are held in the machine. Moreover, it is possible to set by touch input from the liquid crystal screen (touch panel) of the operation unit shown in FIG.
[0145]
In the following, A1 [t] [n [i]] in Equation 4 is newly used as A [t] [n [i]].
[0146]
The YMCK gradation conversion table is obtained by comparing a [LD] described above with reference data A [n] stored in the ROM 416. Here, n is an input value to the YMCK gradation conversion table, and the reference data A [n] is a YMC toner pattern output with the laser writing value LD [i] after the input value n is YMCK gradation converted. Is a target value of the read image signal read by the scanner. Here, the reference data includes two types of values: a reference value A [n] that is corrected according to the image density that can be output by the printer, and a reference value A [n] that is not corrected. The determination as to whether or not to perform the correction is made based on determination data, which will be described later, stored in advance in the ROM or RAM. This correction will be described later.
[0147]
The laser output value LD [n] corresponding to the input value n to the YMCK gradation conversion table is obtained by obtaining the LD corresponding to A [n] from the a [LD] described above. This is the input value
i = 0, 1,..., 255 (in the case of 8-bit signal)
To obtain a gradation conversion table. At that time, the input value for the YMCK gradation conversion table
n = 00h, 01h ..., FFh (hexadecimal number)
Instead of doing the above for all values for,
ni = 0, 11h, 22h, ..., FFh
The above-described processing is performed for the jump value like the above, and the other points are interpolated by a spline function or the like, or obtained by the above-mentioned processing in the YMCKγ correction table stored in the ROM 416 in advance. The
(0, LD [0]), (11h, LD [11h]), (22h, LD [22h]), ..., (FFh, LD [FFh])
Select the closest table that passes through the pair.
[0148]
The above process will be described with reference to the quaternary chart of FIG. In the figure, the horizontal axis of the first quadrant (a) is the input value n to the YMCK gradation conversion table, and the vertical axis is the scanner read value (after processing), representing the reference data A [i] described above. The scanner reading value (after processing) is the RGB γ conversion (no conversion is performed here) to the value read by the scanner, and the average processing and addition processing of the read data in several places in the gradation pattern This is a later value, and is processed here as a 12-bit data signal in order to improve calculation accuracy.
[0149]
The horizontal axis of the second quadrant (b) in FIG. 50 represents the reading value (after processing) of the scanner, like the vertical axis. The vertical axis of the third quadrant (c) represents the writing value of the laser beam (LD). This data a [LD] represents the characteristics of the printer unit. In addition, the LD writing values of the pattern to be actually formed are 16 points of 00h (background), 11h, 22h,... EEh, FFh, which indicate skipping values. And treated as a continuous graph. The graph (d) of the fourth quadrant is a YMCK gradation conversion table LD [i], and the purpose is to obtain this table. The vertical axis and horizontal axis of the graph (f) are the same as the vertical axis and horizontal axis of the graph (d). When forming a gradation pattern for detection, the YMCK gradation conversion table (g) shown in the graph (f) is used. The horizontal axis of the graph (e) is the same as that of the third quadrant (c), and represents the relationship between the LD writing value at the time of gradation pattern creation and the reading value (after processing) of the gradation pattern scanner. Represents a linear transformation for convenience. Reference data A [n] is obtained for a certain input value n, and an LD output LD [n] for obtaining A [n] is used as an arrow in the figure using a gradation pattern read value a [LD]. Obtain along (l).
[0150]
The interface I / F selector 411 outputs the image data read by the scanner 401 for processing by an external image processing apparatus or the like, and outputs image data from an external host computer or image processing apparatus by the printer 413. Has a switching function.
[0151]
The above image processing circuit is controlled by the CPU 415. The CPU 415 is connected to the ROM 414, the RAM 416, and the BUS 418. The CPU 415 is connected to the system controller 417 through a serial I / F, and commands from an operation unit (not shown) are transmitted through the system controller 417. Various parameters are set in each of the image processing circuits described above based on the transmitted image quality mode, density information, region information, and the like. The pattern generation circuit 421 generates a gradation pattern used in the image processing unit.
[0152]
A block diagram of the laser modulation circuit is shown in FIG. The writing frequency is 18.6 [MHz], and the scanning time for one pixel is 53.8 [nsec]. The 8-bit image data can be subjected to γ conversion by a look-up table (LUT) 451. The pulse width modulation circuit (PWM) 452 converts the 8-bit image signal into an 8-value pulse width based on the 8-bit image signal, and the power modulation circuit (PM) 453 performs 32-value power modulation with the low-order 5 bits. The laser diode (LD) 454 emits light based on the modulated signal. The light emission intensity is monitored by a photo detector (PD) 455, and correction is performed for each dot.
[0153]
The maximum value of the intensity of the laser beam can be varied to 8 bits (256 levels) independently of the image signal. With respect to the size of one pixel, the beam diameter in the main scanning direction (this is defined as the width when the beam intensity at rest attenuates to 1 / e2 with respect to the maximum value) is 600 DPI, In one pixel 42.3 [μm], the beam diameter is 50 [μm] in the main scanning direction and 60 [μm] in the sub-scanning direction.
[0154]
FIG. 52 is a block diagram of an image reading system, and FIG. 53 is a schematic configuration diagram of a document reading device (scanner). The image reading system will be described below based on these drawings.
[0155]
The original is irradiated by an exposure lamp 5501, and the reflected light reflected from the original surface is color-separated and read by an RGB filter of a CCD (Charge Coupled Device) 5401 and amplified to a predetermined level by an amplifier circuit 5402. The CCD driver 5409 supplies a pulse signal for driving the CCD. A pulse source necessary for driving the CCD driver 5409 is generated by a pulse generator 5410. The pulse generator 5410 uses a clock generator 5411 made of a crystal oscillator or the like as a reference signal. The pulse generator 5410 supplies necessary timing for the sample hold (S / H) circuit 5403 to sample and hold the signal from the CCD 5401. The analog color image signal sampled and held by the S / H circuit 5403 is digitized into an 8-bit signal (an example) by the A / D conversion circuit 5404. The black correction circuit 5405 reduces variations in the black level (electric signal when the amount of light is small) between the chips of the CCD 5401 and between pixels, and prevents streaks and unevenness in the black portion of the image. The shading correction circuit 5406 corrects the white level (electric signal when the amount of light is large). The white level corrects variations in sensitivity of the irradiation system, the optical system, and the CCD 5401 based on white data when the scanner 420 is moved to a uniform white plate position and irradiated. FIG. 54 shows a conceptual diagram of image signals for white correction and black correction.
[0156]
A signal from the shading correction circuit 5405 is processed by the image processing unit 5407 and output from the printer 413. The above circuit is controlled by the CPU 5414 and stores data necessary for control in the ROM 5413 and the RAM 5415. The CPU 5414 communicates with a system controller 419 that controls the entire image forming apparatus through a serial I / F. The CPU 5414 controls a scanner driving device (not shown) and controls the driving of the scanner 121.
[0157]
The amplification amount of the amplification circuit 5402 is determined so that the output value of the A / D conversion circuit 5404 becomes a desired value for a specific document density. As an example, a document having a document density of 0.05 (reflectance of 0.891) during normal copying can be obtained as an 8-bit signal value of 240 values. On the other hand, at the time of shading correction, the gain is lowered to increase the sensitivity of shading correction. The reason for this is that with an amplification factor during normal copying, if there is a large amount of reflected light, an 8-bit signal that exceeds 255 values will saturate to 255 values, resulting in errors in shading correction. This is because it occurs.
[0158]
FIG. 55 is a schematic diagram showing a state in which an image read signal amplified by the amplifier circuit 5402 is sampled and held by the S / H circuit 5403. The horizontal axis represents the time for the amplified analog image signal to pass through the S / H circuit 5403, and the vertical axis represents the magnitude of the amplified analog signal. An analog signal is sampled and held at a predetermined sample and hold time 5501, and a signal is sent to the A / D conversion circuit 5404. The figure shows an image signal obtained by reading the white level described above. The amplified image signal is, for example, 240 values as a value after A / D conversion at the time of copying and 180 values at the time of white correction. It is an example of an image signal.
[0159]
The scanner 420 shown in FIG. 53 is compatible with two methods, a sheet-through method and a flat bed method, and in this example, unlike the case shown in FIG.
[0160]
The program is downloaded to the ROM 131, the storage device 181, the program RAM 1405, etc., and is executed by the CPU. At that time, it is downloaded from an information recording medium such as a CD-ROM in which a necessary program is recorded, or downloaded from a server via a network and used.
[0161]
【The invention's effect】
  As described above, according to the present invention,The image signal before gradation processing is expressed as the inclination of the characteristic of the third quadrant of the quaternary chart, and the unevenness corresponding to the reading position is corrected from the inclination, so that the main scanning direction can be efficiently performed with simple calculation.Unevenness can be corrected.
[Brief description of the drawings]
FIG. 1 is a diagram showing a schematic configuration of a color copying machine according to an embodiment of the present invention.
FIG. 2 is a block diagram showing an outline of a control system of the color copier of FIG.
FIG. 3 is a diagram showing a control configuration of the color copying machine of FIG. 1;
4 is a block diagram showing a configuration of an image processing unit of the color copying machine of FIG. 2. FIG.
FIG. 5 is a block diagram illustrating an example of an adaptive edge enhancement circuit.
FIG. 6 is a diagram illustrating an example of coefficients of a smoothing filter.
FIG. 7 is a diagram illustrating an example of coefficients of a Laplacian filter.
FIG. 8 is a diagram illustrating an example of coefficients of a sub-scanning direction edge detection filter.
FIG. 9 is a diagram illustrating an example of coefficients of a main scanning direction edge detection filter;
FIG. 10 is a diagram illustrating an example of a coefficient of an oblique direction detection filter.
FIG. 11 is a diagram illustrating another example of the coefficient of the oblique direction detection filter.
FIG. 12 is a diagram illustrating an example of coefficients of a second smoothing filter.
FIG. 13 is a diagram illustrating a relationship between a filter coefficient converted by a table conversion circuit and an edge degree.
FIG. 14 is an explanatory diagram showing a schematic configuration of a SIMD type processor.
FIG. 15 is a diagram illustrating a configuration of a SIMD type image data processing unit and a sequential image data calculation processing unit.
FIG. 16 is a diagram for explaining pixel lines;
17 is a block diagram showing an internal configuration of an image processor 1204. FIG.
FIG. 18 is a block diagram illustrating a configuration of a sequential image data processing unit.
FIG. 19 is a diagram illustrating dither processing parameters corresponding to cyan, magenta, yellow, and black colors.
FIG. 20 is a diagram showing a system configuration of an IIR filter system.
FIG. 21 is a block diagram illustrating a configuration of an image processing unit.
FIG. 22 is an explanatory diagram of registers set in the error diffusion processing hardware register group;
FIG. 23 is a flowchart showing a processing procedure of error diffusion processing performed by a SIMD type processor.
FIG. 24 is an explanatory diagram showing a processing procedure of error diffusion processing performed in a sequential image data processing unit.
25 is an explanatory diagram showing line shift executed in the process of FIG. 23. FIG.
FIG. 26 is a diagram illustrating a matrix state of an error diffusion matrix unit.
FIG. 27 is a diagram illustrating an example of a differential filter used in an edge detection unit.
FIG. 28 is a diagram illustrating an example of a dither threshold value matrix of a dither threshold value generation unit.
FIG. 29 is a diagram illustrating another example of the dither threshold value matrix of the dither threshold value generation unit.
FIG. 30 is an explanatory diagram showing a screen angle and a growth direction of a line.
FIG. 31 is a state transition diagram of the image processor.
FIG. 32 is a flowchart showing an operation procedure of the image processor at the time of two inputs and two outputs.
FIG. 33 is a front view showing the entire operation unit.
FIG. 34 is a front view showing an example of an automatic gradation correction screen on the touch panel of the operation unit.
FIG. 35 is a flowchart showing a processing procedure of automatic gradation correction (ACC).
FIG. 36 is a front view showing a test pattern printing screen of an automatic gradation correction screen of the touch panel of the operation unit.
FIG. 37 is a diagram illustrating an output example (No. 1) of a gradation pattern for automatic gradation correction (ACC).
FIG. 38 is a front view showing a test pattern reading screen of an automatic gradation correction screen of the touch panel of the operation unit.
FIG. 39 is a front view showing a reading processing screen of an automatic gradation correction screen on the touch panel of the operation unit.
FIG. 40 is a front view illustrating an example of a copy screen on the touch panel of the operation unit.
FIG. 41 is a four-way chart (part 1) illustrating a method for calculating density unevenness.
FIG. 42 is a conceptual diagram showing the relationship between the main scanning position of the image carrier and the correction amount.
FIG. 43 is a flowchart illustrating a procedure for correcting density unevenness in the SIMD processor.
FIG. 44 is a diagram illustrating an output example (part 2) of the gradation pattern of automatic gradation correction (ACC).
FIG. 45 is a diagram illustrating an output example (No. 3) of a gradation pattern for automatic gradation correction (ACC);
FIG. 46 is a quaternary chart (part 2) illustrating a method of calculating density unevenness.
FIG. 47 is a diagram illustrating an example of a machine difference correction value;
FIG. 48 is an explanatory diagram showing a correction method of automatic difference correction (ACC) machine difference correction values.
FIG. 49 is a front view of a liquid crystal screen for inputting an automatic gradation correction (ACC) machine difference correction value.
FIG. 50 is a quaternary chart showing a calculation method of automatic gradation correction (ACC).
FIG. 51 is a block diagram showing a laser modulation circuit.
FIG. 52 is a block diagram illustrating an image reading system.
FIG. 53 is a diagram showing a schematic configuration of a document reading device (scanner).
FIG. 54 is a conceptual diagram of image signals for white correction and black correction.
FIG. 55 is a schematic diagram showing a state in which an image read signal amplified by the amplifier circuit of FIG. 53 is sampled and held by the S / H circuit.
[Explanation of symbols]
410 gradation processing
413 Printer
415 CPU
420 scanner
421 pattern generation circuit
1204 image processor
1403 Memory control unit
1404 processor array
1500 SIMD type image data processing unit
1501a to 1501e Data input / output bus
1502a to 1502c bus switch
1503 RAM
1504a to 1504d memory switch
1505a, 1505b Memory controller
1506 SIMD type processor
1507a, 1507b Sequential image data processing unit
1801 Error data calculation unit
1805 Error diffusion processing hardware register group

Claims (13)

An image reading means for transcription gradation pattern and density output on paper are read substantially equal plurality of reference density pattern, and outputs a plurality of signals having different spectral sensitivities,
Correction means for correcting the read signal of the gradation pattern and the reference density pattern read by the image reading means, and the image data according to the image forming position on the image carrier;
Correction amount storage means for storing a correction amount of image data corresponding to the image forming position;
With
Said correcting means, on the basis of the readings of the gradation pattern and a plurality of reference patterns formed on the transfer sheet, and changes the correction amount of the image data corresponding to the imaging position, the imaging position of the image bearing member An image processing apparatus that corrects density unevenness that depends on
The correction means includes
The characteristics shown in the first quadrant are gradation patch reading values with the horizontal axis as the gradation patch writing value and the vertical axis as the scanner reading value.
The characteristic shown in the second quadrant is the adjustment target after gradation correction or the adjustment target after gradation correction, with the horizontal axis as the input value to the gradation correction table.
The characteristic shown in the third quadrant is a correction amount for correcting unevenness with the vertical axis as an input value after correction to the correction means.
The characteristic shown in the fourth quadrant is the gradation characteristic of the correction means.
Use the quaternary charts shown respectively,
A target value for gradation correction is obtained from the characteristic of the second quadrant based on the read value of the gradation characteristic of the reference pattern for detecting a reference unevenness, and the obtained result is obtained in the third quadrant. An image processing apparatus, wherein the image processing apparatus is expressed as an inclination of a characteristic, and unevenness corresponding to a reading position is corrected from the inclination . An image reading means for the gradation pattern and concentration using a plurality of colorants outputted transcription on paper read substantially equal plurality of reference patterns, and outputs a plurality of signals having different spectral sensitivities,
Parameter setting means for setting image processing parameters based on a read signal of the gradation pattern read by the image reading means and reference data stored in advance;
Correction means for correcting the image data according to the image forming position on the image carrier;
Correction amount storage means for storing a correction amount of image data corresponding to the image forming position;
With
It said correcting means, on the basis of the read data of the gradation pattern and the reference pattern formed on a transfer sheet, a correction amount of the image data corresponding to the image forming position, and change the tone parameters, the image bearing member An image processing apparatus for correcting density unevenness depending on the image forming position of
The correction means includes
The characteristics shown in the first quadrant are gradation patch reading values with the horizontal axis as the gradation patch writing value and the vertical axis as the scanner reading value.
The characteristic shown in the second quadrant is the adjustment target after gradation correction or the adjustment target after gradation correction, with the horizontal axis as the input value to the gradation correction table.
The characteristic shown in the third quadrant is a correction amount for correcting unevenness using the vertical axis as an input value to the correction means,
The characteristic shown in the fourth quadrant is the gradation characteristic of the correction means.
Use the quaternary charts shown respectively,
A target value for gradation correction is obtained from the characteristic of the second quadrant based on the read value of the gradation characteristic of the reference pattern for detecting a reference unevenness, and the obtained result is obtained in the third quadrant. An image processing apparatus, wherein the image processing apparatus is expressed as an inclination of a characteristic, and unevenness corresponding to a reading position is corrected from the inclination . Further comprising image parallel processing means for processing the image data in parallel;
The image processing apparatus according to claim 1, wherein the image parallel processing unit corrects the image data every predetermined data number or less. 3. The image processing apparatus according to claim 1, wherein the density unevenness depending on an image forming position of the image carrier is a density unevenness in a main scanning direction . The image processing apparatus according to any one of claims 1 to 3, characterized in that it comprises a pattern output means for the gradation pattern and density outputs substantially equal plurality of reference density pattern on the transfer sheet. An image forming apparatus comprising the image processing apparatus according to claim 1 . A first step of reading a plurality of reference density patterns having substantially the same gradation pattern and density output on the transfer paper, and outputting a plurality of signals having different spectral sensitivities;
A second step of correcting the read signal of the gradation pattern and the reference density pattern read in the first step, and the image data according to the image forming position on the image carrier;
A third step of storing a correction amount of the image data according to the image forming position;
A fourth step of changing the correction amount of the image data in accordance with the stored image forming position based on the gradation pattern formed on the transfer paper and the read values of a plurality of reference patterns;
An image processing method for correcting density unevenness depending on the image forming position of the image carrier,
In the fourth step,
The characteristics shown in the first quadrant are gradation patch reading values with the horizontal axis as the gradation patch writing value and the vertical axis as the scanner reading value.
The characteristic shown in the second quadrant is the adjustment target after gradation correction or the adjustment target after gradation correction, with the horizontal axis as the input value to the gradation correction table.
The characteristic shown in the third quadrant is a correction amount for correcting unevenness using the vertical axis as an input value to the correction means,
The characteristic shown in the fourth quadrant is the gradation characteristic of the correction means.
Use the quaternary charts shown respectively,
A target value for gradation correction is obtained from the characteristic of the second quadrant based on the read value of the gradation characteristic of the reference pattern for detecting a reference unevenness, and the obtained result is obtained in the third quadrant. An image processing method, wherein the image processing method is expressed as an inclination of a characteristic, and unevenness corresponding to a reading position is corrected from the inclination . A first step of transcription gradation pattern and concentration using a plurality of coloring materials, which are output to the paper read a plurality of reference patterns substantially equal, and outputs a plurality of signals having different spectral sensitivities,
A second step of setting the image processing parameter based on the read-signal of the gradation pattern read by the first step, and reference data stored in advance,
A third step of correcting the image data according to the image forming position on the image carrier;
A fourth step of storing a correction amount of image data corresponding to the image forming position ;
A fifth step of changing a correction amount and a gradation parameter of image data corresponding to the image forming position based on reading data of a gradation pattern and a reference pattern formed on the transfer paper;
An image processing method for correcting density unevenness depending on the image forming position of the image carrier,
In the fifth step,
The characteristics shown in the first quadrant are gradation patch reading values with the horizontal axis as the gradation patch writing value and the vertical axis as the scanner reading value.
The characteristic shown in the second quadrant is the adjustment target after gradation correction or the adjustment target after gradation correction, with the horizontal axis as the input value to the gradation correction table.
The characteristic shown in the third quadrant is a correction amount for correcting unevenness using the vertical axis as an input value to the correction means,
The characteristic shown in the fourth quadrant is the gradation characteristic in the correction means.
Use the quaternary charts shown respectively,
A target value for gradation correction is obtained from the characteristic of the second quadrant based on the read value of the gradation characteristic of the reference pattern for detecting the reference irregularity, and the obtained result is obtained in the third quadrant. It expressed as the slope of the characteristic, an image processing method characterized by correcting the unevenness corresponding to the reading position from the slope. A first step in transcription reading a plurality of reference patterns substantially equal gradation pattern and density outputted on paper, and outputs a plurality of signals having different spectral sensitivities,
A second procedure for correcting the read signal of the gradation pattern and the reference density pattern read in the first procedure and the image data according to the image forming position on the image carrier;
A third procedure for storing a correction amount of image data according to the image forming position ;
A fourth procedure for changing the correction amount of the image data corresponding to the stored image forming position based on the gradation pattern formed on the transfer paper and the read values of a plurality of reference patterns ;
A computer program for correcting density unevenness that is loaded on a computer and depends on an image forming position,
In the fourth procedure,
The characteristics shown in the first quadrant are gradation patch reading values with the horizontal axis as the gradation patch writing value and the vertical axis as the scanner reading value.
The characteristic shown in the second quadrant is the adjustment target after gradation correction or the adjustment target after gradation correction, with the horizontal axis as the input value to the gradation correction table.
The characteristic shown in the third quadrant is a correction amount for correcting unevenness using the vertical axis as an input value to the correction means,
The characteristic shown in the fourth quadrant is the gradation characteristic of the correction means.
Use the quaternary charts shown respectively,
A target value for gradation correction is obtained from the characteristic of the second quadrant based on the read value of the gradation characteristic of the reference pattern for detecting a reference unevenness, and the obtained result is obtained in the third quadrant. A computer program which is expressed as an inclination of characteristics and corrects unevenness according to a reading position from the inclination . A first step in transcription gradation pattern and concentration using a plurality of coloring materials, which are output to the paper read a plurality of reference patterns substantially equal, and outputs a plurality of signals having different spectral sensitivities,
A second procedure for setting image processing parameters based on the read signal of the gradation pattern read in the first procedure and reference data stored in advance ;
A third procedure for correcting the image data according to the image forming position on the image carrier;
A fourth procedure for storing a correction amount of image data according to the image forming position ;
A fifth procedure for changing a correction amount and a gradation parameter of image data according to the image forming position based on reading data of a gradation pattern and a reference pattern formed on the transfer paper;
Only including, loaded in a computer, a computer program for correcting density irregularity depending on the image forming position,
In the fifth procedure,
The characteristics shown in the first quadrant are gradation patch reading values with the horizontal axis as the gradation patch writing value and the vertical axis as the scanner reading value.
The characteristic shown in the second quadrant is the adjustment target after gradation correction or the adjustment target after gradation correction, with the horizontal axis as the input value to the gradation correction table.
The characteristic shown in the third quadrant is a correction amount for correcting unevenness using the vertical axis as an input value to the correction means,
The characteristic shown in the fourth quadrant is the gradation characteristic in the correction means.
Use the quaternary charts shown respectively,
A target value for gradation correction is obtained from the characteristic of the second quadrant based on the read value of the gradation characteristic of the reference pattern for detecting the reference unevenness, and the obtained result is obtained in the third quadrant. A computer program which is expressed as an inclination of characteristics and corrects unevenness according to a reading position from the inclination . The third procedure includes a procedure for determining whether to perform background correction and / or reference data correction, and when performing the correction, a YMCK gradation correction table is created after the correction. The computer program according to claim 9 or 10 . 12. The computer program according to claim 11 , wherein each image quality mode is corrected after correcting each color of YMCK with reference to the YMCK gradation correction table . 13. A recording medium in which the computer program according to claim 9 is recorded so as to be readable by a computer .

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