JP2005014344A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus capable of performing gradation-density control optimal for each image mode when the gradation-density characteristics of C, M and Y are matched to the gradation-density characteristics of K in which a color desired by a user can be reproduced at all times regardless of environmental variation. <P>SOLUTION: The image forming apparatus comprises an image forming means P for forming patches 64 and 65 on a transfer material 11, a means 42 for detecting the chromaticity of the patches 64 and 65, a control means for forming correction tables T140, T141 and T142 based on the chromaticity 42, and a means 132 for correcting the image forming conditions by converting image data according to the correction tables T140, T141 and T142 wherein the control means forms the correction tables T140, T141 and T142 for each image processing mode. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

本実施例の画像形成手段Ｐは、画像処理モード毎に階調性の異なるパッチを形成する。
【０１１６】
ここで、写真モードはハイライトの階調性を重視するため、表１の写真モードの欄に示すように、１０ｈ〜７０ｈのハイライトを中心にした単色パッチに、最大値としてＦＦｈの単色パッチを加えた単色パッチパターンを形成する。
【０１１７】
中間転写体２７上に形成された単色パッチパターンは濃度センサ４１によって濃度を検知され、検知された濃度から補間により階調−濃度曲線が生成される。濃度検知結果が図９の黒丸で示したようになった場合には、例えば線形補間のような補間により階調−濃度曲線１００を生成する。
【０１１８】
そして、設定されたデフォルトのターゲットテーブルの階調−濃度曲線３００を基準に、階調−濃度曲線１００の逆特性の階調−濃度曲線２００を算出し、これに対応する濃度補正テーブルを求めて、入力画像データに対する濃度補正テーブルＴ１４０として更新する（図６のＳ１１４）。
【０１１９】
入力画像データを、この濃度補正テーブルＴ１４０で変換することにより、入力階調度と出力濃度の関係が、階調−濃度曲線３００のようになる。
【０１２０】
次に、混色単色制御を行う。
【０１２１】
まず、混色単色制御の混色についての調節を行う。
【０１２２】
Ｓ１１５では、Ｓ１１４で生成された階調−濃度曲線２００を定める濃度補正テーブルＴ１４０を用いて、ＣＭＹ混色パッチ及びブラック（Ｋ）のパッチからなる混色パッチパターンを転写材１１上に形成し、カラーセンサ４２で検知する。
【０１２３】
各パッチの内容を表２に示す。
【０１２４】
表２は、本発明の転写材上に形成する混色パッチパターンの内容を示す表である。
【０１２５】
【表２】

表２に示すように、混色パッチパターンは、Ｃ，Ｍ，ＹのプロセスグレーのパッチＮｏ．１〜Ｎｏ．６及びＫのパッチＮｏ．７からなっている。
【０１２６】
Ｃ_００〜Ｃ_０５、Ｍ_００〜Ｍ_０５、Ｙ_００〜Ｙ_０５の値は、ある所定の基準値Ｃ_０，Ｍ_０，Ｙ_０から特定の色のみを所定の変化量±α変化させた値とする。本実施例ではαの値はＣ，Ｍ，Ｙで同一にしたが、色毎に異なる値としてもよい。
【０１２７】
そして、パッチＮｏ．７はＫの単色パッチで、あらかじめ定められた値Ｋ_０で形成される。
【０１２８】
なお、所定の基準値Ｃ_０，Ｍ_０，Ｙ_０は、Ｋの濃度特性が階調−濃度曲線３００の状態に調整され、Ｃ，Ｍ，Ｙが典型的な階調−濃度曲線の状態であれば、Ｃ_０，Ｍ_０，Ｙ_０の値を混色するとＫ_０とほぼ同じ色となるような値である。
【０１２９】
転写材１１上には、図１０に示すように、パッチＮｏ．１〜パッチＮｏ．７の混色パッチパターンが形成され、混色パッチパターンは定着装置３０通過後、カラーセンサ４２で検知され、ＲＧＢ値が出力される。
【０１３０】
次に、図６のＳ１１６で、センサのＲＧＢ出力値から、Ｋ_０のパッチの色と一致するＣ_０′，Ｍ_０′，Ｙ_０′の値（階調度）を算出する。
【０１３１】
以下、Ｃ_０′，Ｍ_０′，Ｙ_０′の値（階調度）の算出方法について述べる。
【０１３２】
混色パッチパターンの各パッチのＲＧＢ出力値を、パッチＮｏ．１＝（ｒ_００、ｇ_００、ｂ_００），パッチＮｏ．２＝（ｒ_０１、ｇ_０１、ｂ_０１），…，パッチＮｏ．６＝（ｒ_０５、ｇ_０５、ｂ_０５）とし、パッチＮｏ．７のＫのパッチのＲＧＢ出力値を（ｒ_ｋ０、ｇ_ｋ０、ｂ_ｋ０）とする。
【０１３３】
まず、ＲＧＢ出力のＲ出力について説明する。
【０１３４】
表３は、転写材１１上に形成する混色パッチパターンの内容と、目的変量Ｒとを示す表である。
【０１３５】
【表３】

ここで、表３に示すように、Ｃ，Ｍ，Ｙの階調度を説明変量、Ｒを目的変量として、以下の重回帰式の係数ｒ_ｃ０、ｒ_ｃ１、ｒ_ｃ２、ｒ_ｃ３を求める。
【０１３６】
Ｒ＝ｒ_ｃ１×Ｃ＋ｒ_ｃ２×Ｍ＋ｒ_ｃ３×Ｙ＋ｒ_ｃ０
係数ｒ_ｃ０、ｒ_ｃ１、ｒ_ｃ２、ｒ_ｃ３は以下のようにして求める。
【０１３７】
【数１】

ただし、
【０１３８】
【数２】

とすると、
【０１３９】
【数３】

でｒ_ｃ１、ｒ_ｃ２、ｒ_ｃ３が求まる。
【０１４０】
さらに、
【０１４１】
【数４】

でｒ_ｃ０が求まる。
【０１４２】
次に、ＲＧＢ出力のＧ出力、Ｂ出力についても、Ｒ出力と同様に、下記の重回帰式の係数を求めることができる。
Ｇ＝ｇ_ｃ１×Ｃ＋ｇ_ｃ２×Ｍ＋ｇ_ｃ３×Ｙ＋ｇ_ｃ０
Ｂ＝ｂ_ｃ１×Ｃ＋ｂ_ｃ２×Ｍ＋ｂ_ｃ３×Ｙ＋ｂ_ｃ０
ここで、Ｋの出力値（ｒ_ｋ０、ｇ_ｋ０、ｂ_ｋ０）に対するＣ，Ｍ，Ｙの値を（Ｃ_０′，Ｍ_０′，Ｙ_０′）として上記の式に代入し、これを行列で書くと、
【０１４３】
【数５】

となり、
【０１４４】
【数６】

によって（Ｃ_０′，Ｍ_０′，Ｙ_０′）が求まる。
【０１４５】
この（Ｃ_０′，Ｍ_０′，Ｙ_０′）が、プロセスグレーの色度と、Ｎｏ．７のＫのパッチの色度とを一致させるシアン、マゼンダ、イエローの量（階調度）となる。
【０１４６】
すなわち、この（Ｃ_０′，Ｍ_０′，Ｙ_０′）によって作成したプロセスグレーの色は、Ｋ_０の色と一致する。
【０１４７】
このようにして、あらかじめ定められた値Ｋ_０の色度と一致するＣ_０′，Ｍ_０′，Ｙ_０′の値を算出できる。
【０１４８】
次に、同様の手法により、Ｎｏ．１（Ｃ_１０，Ｍ_１０，Ｙ_１０）〜Ｎｏ．６（Ｃ_１５，Ｍ_１５，Ｙ_１５）と、Ｎｏ．７（Ｋ_１）とからなる混色パッチパターンを形成して、Ｋ_１と一致するＣ_１′，Ｍ_１′，Ｙ_１′を求めることができる。
【０１４９】
さらに、Ｋ_２と一致するＣ_２′，Ｍ_２′，Ｙ_２′、Ｋ_３と一致するＣ_３′，Ｍ_３′，Ｙ_３′、・・・、Ｋ_Ｎと一致するＣ_Ｎ′，Ｍ_Ｎ′，Ｙ_Ｎ′を求めることができる。
【０１５０】
すなわち、Ｋ_Ｎ（Ｎ＝０，１，２，…，ｎ）の階調度に対する所定の基準値（Ｃ_Ｎ，Ｍ_Ｎ，Ｙ_Ｎ）（Ｎ＝０，１，２，…，ｎ）から、Ｃ_Ｎ０〜Ｃ_Ｎ５、Ｍ_Ｎ０〜Ｍ_Ｎ５、Ｙ_Ｎ０〜Ｙ_Ｎ５の値のパッチＮｏ．１〜Ｎｏ．６と、Ｋ_Ｎの値のＮｏ．７とを形成し、Ｋ_Ｎの階調度と一致する（Ｃ_Ｎ′，Ｍ_Ｎ′，Ｙ_Ｎ′）を求めることができる。
【０１５１】
本実施例ではｎ＝７とした。
【０１５２】
Ｋ_０〜Ｋ_７の値を表４に示す。
【０１５３】
表４は、本発明の転写材上に形成するＫ_０〜Ｋ_７のパッチの内容をまとめた表である。
【０１５４】
【表４】

本実施例の画像形成手段Ｐは、画像処理モード毎に階調性の異なるパッチを形成する。
【０１５５】
濃度センサ４１で読み取るパターンと同様、写真モードでは、表４の写真モードの欄に示すようにハイライトを中心に形成する。
【０１５６】
これによって、モード毎に適切な階調性を重視することも担保できる。
【０１５７】
次に、このようにして求めた（Ｃ_Ｎ′，Ｍ_Ｎ′，Ｙ_Ｎ′）と、所定の基準値（Ｃ_Ｎ，Ｍ_Ｎ，Ｙ_Ｎ）との関係を調べる。
【０１５８】
シアンの関係が図１１の黒丸のようになったとする。
【０１５９】
このとき、黒丸の間の値を例えば線形補間して曲線１５０を作り、それに対応する色補正テーブルを求める。
【０１６０】
元のターゲットテーブルに対応する図９の階調−濃度曲線３００に対して、色補正テーブルに対応する図１１の曲線１５０を掛け合わせ、図１２に示すように、階調−濃度曲線４００を生成し、この階調−濃度曲線４００から新しいシアンのターゲットテーブルを求める。具体的には入力階調度を色補正テーブルでテーブル変換した後にターゲットテーブルにしたがって変換して階調−濃度曲線４００を生成し、新しいターゲットテーブルを求める。
【０１６１】
同様にマゼンダ，イエローについても新しいターゲットテーブルを求める。
【０１６２】
そして、図６のＳ１１７に示すように、新しいターゲットテーブルを更新する（メモリｍ２に写真モード用ターゲットテーブルＴ１５０として保存する）。
【０１６３】
次に、混色単色制御の単色制御を行う。
【０１６４】
次に、Ｓ１１８で、Ｓ１１７で更新されたシアン、マゼンダ、イエローのターゲットテーブルを用いて改めて単色制御を行うことで、濃度補正テーブルを再度更新し、写真モード用濃度補正テーブルＴ１４０としてメモリｍ２に格納する。
【０１６５】
以上で、写真モード用の階調−濃度制御が終了する（図６のＳ１１０）。
【０１６６】
続いてグラフィックモード用の階調−濃度制御が行われる。
【０１６７】
グラフィックモード用の階調−濃度制御は、写真モード用の階調−濃度制御と同じ手順で行われるため、詳細は省略する。
【０１６８】
ただし、グラフィックモード用の階調−濃度制御時には、色変換処理部１３１へグラフィックモード用色変換テーブルＴ１３７、ハーフトーン処理部１３３へグラフィックモード用ハーフトーンテーブルＴ１４５をロードする。
【０１６９】
また、グラフィックモードは、ハイライトからシャドウへの全体の階調性を重視するため、濃度センサ４１で読み取るために形成する単色パッチは、Ｃ，Ｍ，Ｙ，Ｋの階調度として表１のグラフィックモードの欄に示すように、ハイライトからシャドウまでを均等に選ぶ。
【０１７０】
さらに、カラーセンサ４２で読み取るために形成する混色パッチパターンも、（Ｃ_Ｎ，Ｍ_Ｎ，Ｙ_Ｎ）、Ｋ_Ｎの値として、表４のグラフィックモードの欄に示すように、ハイライトからシャドウまでを均等に選ぶ。
【０１７１】
また、グラフィックモード用の階調−濃度制御によって生成されたターゲットテーブルは、グラフィックモード用ターゲットテーブルＴ１５１としてメモリｍ２に保存し、濃度補正テーブルは、グラフィックモード用濃度補正テーブルＴ１４１としてメモリｍ２に格納する（図６のＳ１２０）。
【０１７２】
グラフィックモード用の階調−濃度制御が終わると、最後に文書モード用の階調−濃度制御が行われる。
【０１７３】
文書モード用の階調−濃度制御も、写真モード用の階調−濃度制御と同じ手順で行われるため、詳細は省略する。
【０１７４】
ただし、文書モード用の階調−濃度制御時には、色変換処理部１３１へ文書モード用色変換テーブルＴ１３８、ハーフトーン処理部１３３へ文書モード用ハーフトーンテーブルＴ１４６をロードする。
【０１７５】
また、文書モードは、シャドウの階調性を重視するため、濃度センサ４１で読み取るために形成する単色パッチは、Ｃ，Ｍ，Ｙ，Ｋの階調度として表１の文書モードの欄に示すように、シャドウを中心に選ぶ。
【０１７６】
さらに、カラーセンサ４２で読み取るために形成する混色パッチパターンも、（Ｃ_Ｎ，Ｍ_Ｎ，Ｙ_Ｎ）、Ｋ_Ｎの値として、表４の文書モードの欄に示すように、シャドウを中心に選ぶ。
【０１７７】
また、文書モード用の階調−濃度制御によって生成されたターゲットテーブルは、文書モード用ターゲットテーブルＴ１５２としてメモリｍ２に保存し、濃度補正テーブルは、文書モード用濃度補正テーブルＴ１４２としてメモリｍ２に格納する（図６のＳ１３０）。
【０１７８】
以上の階調−濃度制御が行われた後に、通常プリント状態に入る（図６のＳ１４０）ことで、カートリッジ交換モードが終了する。
【０１７９】
次に、通常プリント時の階調−濃度制御について図１３を用いて説明する。
【０１８０】
本実施例において、通常プリント時の階調−濃度制御では、画像形成手段Ｐは、ユーザが指定した画像処理モードに対してパッチを形成し、ＣＰＵ（不図示）等の制御手段は、ユーザが指定した画像処理モードに対して濃度補正テーブルを更新する。
【０１８１】
ユーザはあらかじめプリンタドライバやプリンタのパネルの設定などにより、どの画像モードに対して階調−濃度制御を行うかを指定しておく。このとき、複数の画像モードを指定しておくこともできる。
【０１８２】
通常プリント状態Ｓ１４０では、通常プリントを行う。そして、カートリッジ交換、印字枚数をチェックすべく、Ｓ２１２へ進む。
【０１８３】
Ｓ２１２では、いずれかの色のカートリッジが交換されたかどうかを判断する。交換された場合は、環境が大きく変わるため、図６〜図１２を用いて説明したカートリッジ交換モードＳ１０１を行った後、通常プリント状態Ｓ１４０へ戻る。Ｓ２１２で、カートリッジが交換されていない場合は、Ｓ２１３へ進む。
【０１８４】
Ｓ２１３では、所定枚数印字したか否かを判断する。印字している場合は、Ｓ２１４へ進み、印字していない場合は、通常プリント状態Ｓ１４０へ戻る。
【０１８５】
Ｓ２１４〜Ｓ２１７では、ユーザが指定した画像モードに対して単色制御を行う。
【０１８６】
単色制御ではまず、画像モード指定信号Ｘによりユーザの指定した画像モードを指定し、指定された画像モードに対応した色変換テーブル、ディザテーブルをそれぞれ色変換処理部１３１、ハーフトーン処理部１３３にロードする（Ｓ２１４）。
【０１８７】
次に、階調−濃度特性のターゲットテーブルとして、前回の混色単色制御時に生成されたターゲットテーブルを設定し、濃度補正テーブル１３２には、カートリッジ交換モード時と同様に、スルーのテーブルを設定する（Ｓ２１５）。
【０１８８】
Ｓ２１６では、図６のＳ１１３と同様に、中間転写体２７上に単色パッチパターンを形成し、濃度センサ４１によって読み取る。このときの単色パッチパターンは、表１の写真モードの欄，グラフィックモードの欄，文書モードの欄の中からユーザ指定の画像モードに対応したものを選ぶ。
【０１８９】
Ｓ２１７では、検知された濃度から補間により階調−濃度曲線を生成する。
【０１９０】
そして、Ｓ２１５で設定したターゲットテーブルの階調−濃度曲線を基準に、Ｓ２１７で生成した階調−濃度曲線の逆特性の階調−濃度曲線を算出し、これに対応する濃度補正テーブルを求めて、入力画像データに対する濃度補正テーブルＴ１４０として更新する。
【０１９１】
次に、Ｓ２１８で、ユーザが指定したすべての画像モードに対して単色制御を行ったかどうかを判断する。行っていない場合は、他の画像モードに対して単色制御を行うべくＳ２１４へ戻る。行っている場合はＳ２１９へ進む。
【０１９２】
Ｓ２１９では、前回混色単色制御を実施してから現在まで、単色制御を規定回数Ａ回行ったかどうかを判断する。規定回数Ａ回行っていない場合には、再び通常プリント状態Ｓ１４０に戻る。規定回数Ａ回行った場合には、Ｓ２２０へ進み混色単色制御を実施する。
【０１９３】
なお、このＳ２１９により、図５に示した制御が可能となる。
【０１９４】
図１３のＳ２２０〜Ｓ２２５では、ユーザが指定した画像モードに対して混色単色制御を行う。
【０１９５】
まず、混色単色制御の混色についての調節を行う。
【０１９６】
Ｓ２２０では、ユーザが指定した画像モードに対応した色変換テーブル、ディザテーブルをそれぞれ色変換処理部１３１、ハーフトーン処理部１３３にロードする。
【０１９７】
Ｓ２２１では、ユーザが指定した画像モードに対応した濃度補正テーブルを濃度補正処理部１３２にロードする。
【０１９８】
Ｓ２２２では、ＣＭＹ混色パッチ及びブラック（Ｋ）のパッチからなる混色パッチパターンを転写材１１上に形成し、カラーセンサ４２で検知し、ＲＧＢ値を出力する。この時のパッチパターンは表４の写真モードの欄，グラフィックモードの欄，文書モードの欄の中からユーザ指定の画像モードに対応したものを選ぶ。
【０１９９】
その後、Ｓ２２３〜Ｓ２２４で、図６のＳ１１６〜Ｓ１１７と同様の処理を行う。ただし、Ｓ２２４で新しいターゲットテーブル作成時には、前回の混色単色制御で生成されたターゲットテーブルに対して、新しい色補正テーブルを掛け合わせて階調−濃度曲線を生成し、この階調−濃度曲線から新しいターゲットテーブルを求める。
【０２００】
そして、新しいターゲットテーブルを更新する（メモリｍ２に保存する）。
【０２０１】
次に、混色単色制御の単色制御を行う。
【０２０２】
Ｓ２２５で、Ｓ２２４で更新されたシアン、マゼンダ、イエローのターゲットテーブルを用いて改めて単色制御を行うことで、濃度補正テーブルを再度更新し、ユーザが指定した画像モード用濃度補正テーブルとしてメモリｍ２に格納する。
【０２０３】
次に、Ｓ２２６では、ユーザ指定のすべての画像モードに対して混色単色制御を行ったかを判断する。すべての画像モードで混色単色制御を行った場合は、通常プリント状態Ｓ１４０へ戻る。すべての画像モードで混色単色制御を行っていない場合は、他の画像モードに対して混色単色制御を行うべく、Ｓ２２０へ戻る。
【０２０４】
なお、本実施例では、精度を重視して上記のようにターゲットテーブルを更新する構成をとったが、ターゲットテーブルは更新せずに濃度補正テーブルを更新し、その後図１１の色補正テーブル１５０を掛け合わせる構成をとってもよい。
【０２０５】
また、本実施例では最適なＣ，Ｍ，Ｙの値を算出するのに３次元の線形補間を用いたが、補間の方法としては２次関数近似や３次関数近似、あるいはスプライン補間のような非線形な方法を用いてもよい。
【０２０６】
さらに、本実施例ではカラーセンサ４２はＲＧＢ出力としたが、Ｌ＊ａ＊ｂ＊やＬ＊ｃ＊ｈ＊、ＸＹＺ等の色度を出力するものでもよい。
【０２０７】
さらに、本実施例ではＣＭＹの混色パッチを、Ｃ，Ｍ，Ｙが典型的な階調−濃度曲線の状態であれば、ブラック（Ｋ）のパッチとほぼ同じ色となるようなパッチとしたが、カラーセンサ４２でＣＭＹの混色パッチのＬ＊ａ＊ｂ＊値等を測定し、例えばａ＝０，ｂ＝０の無彩色軸をターゲットにしてＣ，Ｍ，Ｙの混色が無彩色となる最適な階調度を算出し、単色制御にフィードバックしてもよい。
【０２０８】
【発明の効果】
以上説明したように、本発明の構成によれば、カラーセンサの出力値を用いて、Ｃ，Ｍ，Ｙの階調−濃度特性と、Ｋの階調−濃度特性とを合わせる際に、各画像モードに最適な階調−濃度制御を行うことができ、環境変動が起きても常にユーザの所望する色を再現可能な画像形成装置を提供できる。
【図面の簡単な説明】
【図１】本発明のカラー画像形成装置を示す構成図である。
【図２】本発明の濃度センサの構成の一例を示す図である。
【図３】（ａ）は、本発明のカラーセンサの構成の一例を示す図、（ｂ）は、電荷蓄積型センサの受光部を示す図である。
【図４】画像形成装置の画像処理部における処理の一例を示す図である。
【図５】本発明の単色制御と混色単色制御とを組み合わせた階調−濃度特性制御を示すフローチャートである。
【図６】本発明のカートリッジ交換モードの制御を示すフローチャートである。
【図７】本発明のデフォルトのターゲットテーブルの階調−濃度曲線を示す図である。
【図８】本発明の中間転写体上に形成するパッチパターンを示す図である。
【図９】本発明の単色制御を示す図である。
【図１０】本発明の転写材上に形成する混色パッチパターンを示す図である。
【図１１】本発明の混色単色制御の混色についての調節を示す図である。
【図１２】本発明のターゲットテーブルの階調−濃度特性を示す図である。
【図１３】本発明の通常プリント時の階調−濃度特性の制御の詳細を示すフローチャートである。
【符号の説明】
１１ 転写材
２１ａ、２１ｂ 給紙部
２２Ｙ〜２２Ｋ 感光ドラム
２３Ｙ〜２３Ｋ 注入帯電手段
２４Ｙ〜２４Ｋ スキャナ部
２５Ｙ〜２５Ｋ トナーカートリッジ部
２６Ｙ〜２６Ｋ 現像手段
２７ 中間転写体
２８ａ、２８ｂ 転写ローラ
２９ クリーニング手段
３０ 定着装置
３１ 定着ローラ
３２ 加圧ローラ
３３、３４ ヒータ
４１ 濃度センサ
４２ カラーセンサ
５１ 赤外発光素子
５２ａ、５２ｂ 受光素子
５３ 白色発光素子
５４ａ ＲＧＢオンチップフィルタ付き電荷蓄積型センサ
５４ｂ 受光部
Ｐ 画像形成手段
Ｑ 画像処理部[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an image forming apparatus that forms a color image based on an image signal.
[0002]
[Prior art]
In recent years, color image forming apparatuses employing an electrophotographic system such as a color printer or a color copying machine, an ink jet system, and the like have been required to improve the output image quality. In particular, the gradation of the density and its stability have a great influence on the judgment of the quality of an image given by a human.
[0003]
However, in the image forming apparatus, the density of the obtained image fluctuates if there are fluctuations in each part of the apparatus due to environmental changes or prolonged use. In particular, in the case of an electrophotographic color image forming apparatus, there is a possibility that the color balance may be lost even by a slight change in density, so it is necessary to always maintain a constant gradation-density characteristic.
[0004]
Therefore, the absolute humidity measured by the temperature / humidity sensor is provided for each color toner with gradation correction means such as several kinds of exposure amounts and development biases according to the absolute humidity, development bias, and lookup table (LUT). Based on the above, the process condition at that time and the optimum value for gradation correction are selected. In addition, a toner patch for density detection is created on the intermediate transfer body or drum with toner of each color so that a constant gradation-density characteristic can be obtained even if fluctuations occur in each part of the apparatus, and the unfixed toner patch The density of the toner is detected by a density detection sensor for unfixed toner, and the density control is performed by feeding back process conditions such as exposure amount and development bias based on the detection result, thereby obtaining a stable image. .
[0005]
The density control using the non-fixed toner density detection sensor detects a patch by forming a patch on an intermediate transfer member, a drum or the like, and the color of the image by subsequent transfer to a transfer material and fixing. There is no control over changes in balance. The color balance also changes depending on the transfer efficiency in transferring the toner image to the transfer material, and heating and pressurization by fixing. This change cannot be handled by density control using the density detection sensor for unfixed toner.
[0006]
Accordingly, a density or chromaticity sensor (hereinafter referred to as a color sensor) that detects the density of a single-color toner image on a transfer material or the chromaticity of a full-color image after transfer and fixing is installed, and a color toner patch for controlling density or chromaticity ( (Hereinafter referred to as a patch) is formed on the transfer material, and the detected density or chromaticity is fed back to the exposure conditions, process conditions, process conditions such as a look-up table (LUT), and the final output image formed on the transfer material. An image forming apparatus that controls density or chromaticity is also considered (see, for example, Patent Document 1, Patent Document 2, and Patent Document 3).
[0007]
In this case, the color sensor uses, for example, a light source that emits red (R), green (G), and blue (B) as a light emitting element to identify CMYK or detect density or chromaticity. The element is composed of a light source that emits white (W) and three types of filters having different spectral transmittances such as red (R), green (G), and blue (B) formed on the light receiving element. . CMYK can be identified and density can be detected from three different outputs obtained by this, for example, RGB output. Further, the chromaticity can be detected by performing a mathematical process on the RGB output by linear conversion or the like, or converting the RGB output by a lookup table (LUT).
[0008]
Also in an ink jet printer, the color balance changes due to a change in ink discharge amount with time, an environmental difference, and an individual difference of ink cartridges, and the tone-density characteristic cannot be kept constant.
[0009]
Therefore, it is considered to install a color sensor near the output unit of the printer, detect the density or chromaticity of the patch on the transfer material, and perform density or chromaticity control.
[0010]
There are various methods for controlling density or chromaticity.
[0011]
For example, there is a method of performing gamma characteristic control from the measured density and correcting the color matching table or color separation table from the measured chromaticity.
[0012]
On the other hand, an ordinary color image forming apparatus is equipped with a plurality of image processing modes (photo mode, graphic mode, document mode, etc.). In general, the content of color conversion processing is changed according to the image processing mode, or the content of halftone processing is changed.
[0013]
[Patent Document 1]
JP 2003-084532 A
[0014]
[Patent Document 2]
JP 2003-107830 A
[0015]
[Patent Document 3]
JP 2003-107835 A
[0016]
[Problems to be solved by the invention]
However, when the image processing mode is changed, the control of density or chromaticity is affected.
[0017]
That is, when the halftone process is changed by changing the image processing mode, for example, the density characteristics of a single color change, and further, the characteristics of mixed color transfer and fixing change. For this reason, even if a patch output in a certain image processing mode is measured by a color sensor and density or chromaticity control is performed, there is a problem that the color shifts when the image processing mode changes.
[0018]
In addition, the characteristics of the target of the color conversion process are different for each mode. For example, in the case of the photo mode, emphasis is placed on highlights, and in the case of the graphic mode, emphasis is placed on gradation from highlight to shadow. For this reason, even if a patch optimized for a certain image processing mode is output, measured by a color sensor, and density or chromaticity control is performed, if the image processing mode changes, control that matches the image processing cannot always be performed. There is a problem.
[0019]
The present invention has been made in view of the above-described problems, and the target process is to use C, M, Y gradation-density characteristics and K using the output value of the color sensor. Provides an image forming apparatus that can perform optimum tone-density control for each image mode when matching the tone-density characteristics of the image, and can always reproduce the color desired by the user even if the environment fluctuates. There is to do.
[0020]
[Means for Solving the Problems]
The present invention has achieved the above object by the following technical configuration.
[0021]
(1) Image forming means for forming a patch on a transfer material, chromaticity detection means for detecting the chromaticity of the patch, control means for creating a correction table based on the chromaticity, and an image by this correction table An image forming apparatus having correction means for correcting image forming conditions by converting data, wherein the control means creates the correction table for each image processing mode.
[0022]
(2) The image forming apparatus according to (1), wherein the image forming unit forms a patch for each image processing mode, and the control unit creates the correction table for each image processing mode. .
[0023]
(3) The image forming apparatus according to (1) or (2), wherein the image forming unit forms patch patterns having different gradations for each image processing mode.
[0024]
(4) The image forming apparatus according to (1) or (2), wherein the image forming unit sequentially forms patches for all image processing modes.
[0025]
(5) The image forming apparatus according to (1) or (2), wherein the image forming unit forms a patch for an image processing mode designated by a user.
[0026]
(6) The image forming unit forms a mixed color patch and a black patch, and the control unit creates a process gray having a chromaticity close to that of the black patch from the chromaticity of the mixed color patch and the black patch. The image forming apparatus according to (1) or (2), wherein the cyan, magenta, and yellow amounts are calculated, and the correction table is created so that the process gray matches black.
[0027]
(7) The image forming apparatus according to (6), wherein the color mixture patch is formed by changing the amounts of cyan, magenta, and yellow by a predetermined change amount from a predetermined reference value.
[0028]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described below using examples.
[0029]
(Example)
FIG. 1 is a configuration diagram showing a tandem color image forming apparatus that employs an intermediate transfer member 27 as an example of an electrophotographic color image forming apparatus.
The image forming apparatus includes an image forming unit P, a density detecting unit 41, a chromaticity detecting unit 42 shown in FIG. 1, an image processing unit Q shown in FIG.
[0030]
11 is a transfer material, 21a and 21b are sheet feeding sections, 22Y, 22M, 22C and 22K are photosensitive drums as photosensitive members, 23Y, 23M, 23C and 23K are injection charging means, 23YS, 23MS, 23CS and 23KS are sleeves, 24Y, 24M, 24C, and 24K are scanner units, 25Y, 25M, 25C, and 25K are toner cartridge units, 26Y, 26M, 26C, and 26K are developing units, 26YS, 26MS, 26CS, and 26KS are sleeves, 27 is an intermediate transfer member, 28a is a transfer roller that is in contact with the intermediate transfer member 27, 28b is a transfer roller that is separated from the intermediate transfer member 27, 29 is a cleaning means, 30 is a fixing device, 31 is a fixing roller, and 32 is a pressurizing member. Rollers, 33 and 34 are heaters, 41 is a density sensor as density detection means, and 42 is a color sensor as chromaticity detection means. Sensor, P is an image forming means.
[0031]
Paper feeding units 21a, 21b, photosensitive drums 22Y, 22M, 22C, 22K for each station arranged in parallel for development colors, injection charging units 23Y, 23M, 23C, 23K as primary charging units, toner cartridge units 25Y, 25M, 25C, 25K, developing means 26Y, 26M, 26C, and 26K, intermediate transfer member 27, transfer rollers 28a and 28b, fixing device 30 and the like constitute image forming means P.
[0032]
The operation of the image forming unit P will be described with reference to FIG.
[0033]
The image forming unit P forms an electrostatic latent image with exposure light that is turned on based on the exposure time converted by the image processing unit Q, which will be described later, and develops the electrostatic latent image to form a single color toner image. The single color toner images are superimposed to form a multicolor toner image, the multicolor toner image is transferred to the transfer material 11, and the multicolor toner image on the transfer material 11 is fixed.
[0034]
The photosensitive drums 22Y, 22M, 22C, and 22K are configured by applying an organic optical transmission layer on the outer periphery of an aluminum cylinder, and are rotated by a driving force of a driving motor (not shown). The driving motor is a photosensitive drum 22Y. , 22M, 22C, and 22K are rotated counterclockwise in accordance with the image forming operation.
[0035]
As primary charging means, four injection charging means 23Y for charging the photosensitive drums 22Y, 22M, 22C, and 22K of yellow (Y), magenta (M), cyan (C), and black (K) for each station, 23M, 23C, 23K, and each injection charging means is provided with sleeves 23YS, 23MS, 23CS, 23KS.
[0036]
Exposure light to the photosensitive drums 22Y, 22M, 22C, and 22K is sent from the scanner units 24Y, 24M, 24C, and 24K, and electrostatic exposure is performed by selectively exposing the surfaces of the photosensitive drums 22Y, 22M, 22C, and 22K. A latent image is formed.
[0037]
As developing means, in order to visualize the electrostatic latent image, four developing means 26Y, 26M for developing yellow (Y), magenta (M), cyan (C), and black (K) for each station. Each developing means is provided with sleeves 26YS, 26MS, 26CS, and 26KS. Each developing means is detachably attached.
[0038]
The intermediate transfer member 27 is in contact with the photosensitive drums 22Y, 22M, 22C, and 22K, and rotates clockwise when forming a color image. The intermediate transfer member 27 rotates in accordance with the rotation of the photosensitive drums 22Y, 22M, 22C, and 22K. The toner image is transferred. Thereafter, a transfer roller, which will be described later, comes into contact with the intermediate transfer member 27 to sandwich and convey the transfer material 11, and the multicolor toner image on the intermediate transfer member 27 is transferred to the transfer material 11.
[0039]
The transfer roller contacts the transfer material 11 while the multicolor toner image is being transferred onto the transfer material 11 (see the transfer roller 28a), and is separated after the printing process (see the transfer roller 28b).
[0040]
The fixing device 30 melts and fixes the transferred multi-color toner image while conveying the transfer material 11, and as shown in FIG. 1, a fixing roller 31 for heating the transfer material 11, a transfer material, and the like. And a pressure roller 32 for bringing the pressure roller 11 into pressure contact with the fixing roller 31. The fixing roller 31 and the pressure roller 32 are formed in a hollow shape, and heaters 33 and 34 are incorporated therein. That is, the transfer material 11 holding the multicolor toner image is conveyed by the fixing roller 31 and the pressure roller 32, and heat and pressure are applied to fix the toner on the surface.
[0041]
After the toner image is fixed, the transfer material 11 is discharged to a discharge tray (not shown) by a discharge roller (not shown), and the image forming operation ends.
[0042]
The cleaning unit 29 cleans the toner remaining on the intermediate transfer member 27. The waste toner after the four-color multicolor toner image formed on the intermediate transfer member 27 is transferred to the transfer material 11 is: Stored in a cleaner container.
[0043]
In the image forming apparatus of FIG. 1, the density sensor 41 is disposed toward the intermediate transfer body 27 and measures the density of the toner patch formed on the surface of the intermediate transfer body 27.
[0044]
An example of the configuration of the density sensor 41 is shown in FIG.
[0045]
FIG. 2 is a diagram showing an example of the configuration of the concentration sensor of the present invention.
[0046]
Reference numeral 51 denotes an infrared light emitting element such as an LED, 52a and 52b denote photodiodes, a light receiving element such as Cds, and 64 denotes a single color toner gradation patch.
[0047]
The density sensor 41 includes an infrared light emitting element 51, light receiving elements 52a and 52b, an IC (not shown) that processes received light data, and a holder (not shown) that accommodates these.
[0048]
The light receiving element 52a detects the intensity of irregularly reflected light from the toner patch, and the light receiving element 52b detects the intensity of regular reflected light from the toner patch. By detecting both the regular reflection light intensity and the irregular reflection light intensity, the density of the toner patch from a high density to a low density can be detected. Further, a color difference from a predetermined paper can be output. An optical element (not shown) may be used for coupling the light emitting element 51 and the light receiving elements 52a and 52b.
[0049]
At this time, the gradation patch 64 is formed of a single color toner. This is because the density sensor 41 cannot distinguish the color of the toner on the intermediate transfer member 27.
[0050]
The detected density data is fed back to the density correction table for correcting the gradation-density characteristics of the image processing unit Q and each process condition of the image forming means P.
[0051]
In the image forming apparatus of FIG. 1, the color sensor 42 is disposed toward the image forming surface of the transfer material 11 downstream of the fixing device 30 in the transfer material conveyance path, and the fixing formed on the transfer material 11. The RGB output value of the color of the later mixed color patch pattern is detected. The color sensor 42 is very similar to the density sensor 41.
[0052]
FIG. 3A and FIG. 3B show an example of the configuration of the color sensor 42.
[0053]
FIG. 3A is a diagram showing an example of the configuration of the color sensor of the present invention, and FIG. 3B is a diagram showing a light receiving portion of the charge storage type sensor.
[0054]
53 is a white LED, 54a is a charge storage sensor with an RGB on-chip filter, 54b is a light receiving portion of the charge storage sensor 54a, and 65 is a mixed color patch.
[0055]
The color sensor 42 includes a white LED 53 and a charge storage type sensor 54a. The white LED 53 is incident on the transfer material 11 on which the patch 65 after fixing is formed at an angle of 45 degrees, and the intensity of diffuse reflected light in the 0 degree direction is detected by the charge storage sensor 54a with an RGB on-chip filter.
[0056]
The light receiving portion 54b of the charge storage type sensor 54a is a pixel independent of RGB. A photodiode can also be used as the charge storage type sensor. Several sets of three RGB pixels may be arranged. Further, the color sensor 42 may be configured such that the incident angle is 0 degree and the reflection angle is 45 degrees. Furthermore, you may comprise by LED which light-emits RGB3 color, and a sensor without a filter.
[0057]
Next, processing in the image processing unit Q will be described.
[0058]
The color image forming apparatus of the present embodiment has three types of image processing modes: a photo mode, a graphic mode, and a document mode.
[0059]
The user selects one of these from the printer driver according to the purpose of printing (graphic image such as photographic image, CG, document image mainly composed of characters).
[0060]
The color conversion table for each image processing mode is set as follows to suit the user's purpose.
[0061]
○ Photo mode
In the photo image, the gradation of the light color near the highlight is important.
○ Graphic mode
Since it is important for graphic images to have smooth gradation changes from light to highly saturated colors, emphasis is placed on overall gradation from highlights to shadows.
○ Document mode
Since document images are important for reproducibility of characters with high saturation and density, focus on the gradation of shadows.
In addition, if a halftone table such as dither is used with a high number of lines, sufficient resolution can be obtained, but the gradation is sacrificed. If a table with a low number of lines is used, sufficient gradation is obtained. The resolution is sacrificed. Therefore, the halftone table for each image processing mode is set as follows to meet the user's purpose.
[0062]
○ Photo mode
Since both gradation and resolution are required to some extent, a medium number of lines is used.
[0063]
○ Graphic mode
Since gradation is important, the one with a low number of lines is used.
[0064]
○ Document mode
Since the resolution is important, the one with a high number of lines is used.
[0065]
FIG. 4 is a diagram illustrating an example of processing in the image processing unit of the image forming apparatus.
[0066]
131 is a color conversion processing unit that is a correction unit, 132 is a density correction processing unit that is a correction unit, 133 is a halftone processing unit that is a correction unit, 134 is a PWM processing unit, and 139, 143, and 147 are selectors. is there.
[0067]
m1 is a nonvolatile memory such as a ROM, m2 is a writable memory such as a RAM, m3 is a nonvolatile memory such as a ROM, and Q is an image processing unit.
[0068]
The color conversion processing unit 131, the density correction processing unit 132, the halftone processing unit 133, the PWM processing unit 134, the selectors 139, 143, and 147, the memory m1, the memory m2, and the memory m3 constitute an image processing unit Q.
[0069]
The image processing unit Q defines image forming conditions for converting RGB signals into exposure times Tc, Tm, Ty, and Tk.
[0070]
The image forming condition is a condition on how to convert the RGB signal into exposure times Tc, Tm, Ty, Tk. Specifically, the color conversion processing unit 131, the density correction processing unit 132, and the halftone processing. This is a condition that is determined and corrected by what color conversion table, density correction table, and halftone table the conversion is performed by the unit 133 and how the conversion is performed by the PWM processing unit.
[0071]
X is an image mode designation signal indicating any one of “photo mode”, “graphic mode”, and “document mode” designated by the user, T136 is a color conversion table for photo mode, T137 is a color conversion table for graphic mode, and T138. Is a color conversion table for document mode.
[0072]
T140 is a density correction table for photo mode that is a correction table, T141 is a density correction table for graphic mode that is a correction table, and T142 is a density correction table for document mode that is a correction table. The density correction table for photo mode T140, the density correction table for graphic mode T141, and the density correction table for document mode T142 constitute a correction table for each image control mode.
[0073]
T144 is a halftone table for photo mode, T145 is a halftone table for graphic mode, T146 is a halftone table for document mode, T150 is a target table for photo mode, T151 is a target table for graphic mode, and T152 is a target table for document mode It is.
[0074]
The memory m1 stores in advance a photo mode color conversion table T136, a graphic mode color conversion table T137, and a document mode color conversion table T138.
[0075]
In the memory m2, a photo mode density correction table T140, a graphic mode density correction table T141, a document mode density correction table T142, a photo mode target table T150, a graphic mode target table T151, and a document mode target table T152 are stored in advance. Is stored. The density correction tables T140, T141, and T142 and the target tables T150, T151, and T152 may be stored in different memories.
[0076]
The memory m3 stores a photo mode halftone table T144, a graphic mode halftone table T145, and a document mode halftone table T146 in advance.
[0077]
The selector 139 selects one of the photo mode color conversion table T136, the graphic mode color conversion table T137, and the document mode color conversion table T138 in accordance with the content specified by the image mode specifying signal X, and a color conversion processing unit. 131 is loaded.
[0078]
The color conversion processing unit 131 converts an image signal (RGB signal) sent from a host computer or the like into a CMYK signal that is a toner color material color of the image forming apparatus.
[0079]
The selector 143 selects one of the photo mode density correction table T140, the graphic mode density correction table T141, and the document mode density correction table T142 in accordance with the contents designated by the image mode designation signal X, and the density correction processing unit. 132.
[0080]
The density correction processing unit 132 uses the density correction table for correcting the tone-density characteristics unique to each image forming apparatus, and C′M′Y′K ′ obtained by adding the correction of the tone-density characteristics to the CMYK signal. Convert to signal.
[0081]
The selector 147 selects one of the photo mode halftone table T144, the graphic mode halftone table T145, and the document mode halftone table T146 in accordance with the content designated by the image mode designation signal X, and selects a halftone processing unit. Load to 133.
[0082]
The halftone processing unit 133 performs halftone processing and converts the C′M′Y′K ′ signal into a C ″ M ″ Y ″ K ″ signal.
[0083]
Further, a PWM (Pulse Width Modulation) processing unit 134 converts the exposure times Tc, Tm, Ty, and Tk of the scanner units 24C to 24K corresponding to the C ″ M ″ Y ″ K ″ signal.
[0084]
Next, the gradation-density characteristic control of the present invention will be described.
[0085]
In the gradation-density characteristic control, the density correction tables T140, T141, and T142 are updated using the target tables T150, T151, and T152.
[0086]
For gradation-density characteristic control, gradation-density characteristic control using only the density sensor 41 (hereinafter referred to as single color control) and gradation-density characteristic control using the color sensor 42 and the density sensor 41 ( Hereinafter, it is referred to as mixed color single color control).
[0087]
The single color control is a control for updating the density correction tables T140, T141, and T142 for each color so that the density correction tables T140, T141, and T142 coincide with the target tables T150, T151, and T152. First, the color mixture is adjusted (target tables T150, T151, and T152 are updated), and then the single color control is performed based on the adjustment.
[0088]
FIG. 5 is a flowchart showing gradation-density characteristic control combining single color control and mixed color single color control.
[0089]
Since the mixed color single color control consumes the transfer material 11 in the process of adjusting the mixed color, it is necessary to limit the number of times of execution compared to the single color control.
[0090]
Therefore, in this embodiment, gradation-density characteristic control is performed as shown in FIG.
[0091]
When the cartridge is replaced, first, in step S101, single color control and mixed color single color control are performed (hereinafter, this single color control and mixed color single color control are referred to as cartridge replacement mode control).
[0092]
Thereafter, in S102 to S104, the monochromatic control is performed a predetermined number of times A. Thereafter, in step S105, mixed color single color control is performed. And it returns to S102 again.
[0093]
Note that tone-density characteristic control is generally performed intermittently between normal print operations, except for the cartridge replacement mode control S101. That is, after printing a predetermined number of sheets, single color control (S102), after further printing a predetermined number of sheets, single color control (S103),..., After printing a predetermined number of sheets, single color control (S104), mixed color single color control (S105) Further, after printing a predetermined number of sheets, monochrome control (S102) is performed. Thus, appropriate density correction tables T140, T141, and T142 can always be provided.
[0094]
In addition, the implementation timing may be automatically implemented at a predetermined timing which is detected in advance by detecting environmental fluctuations, or when the user desires to carry out the control, it may be implemented manually by the user. Also good.
[0095]
Next, single color control and mixed color single color control will be described.
[0096]
First, the case of control in the cartridge exchange mode will be described.
[0097]
When a new cartridge is used, that is, when the image forming apparatus is first installed or when the cartridge is replaced, the cartridge replacement mode is entered.
[0098]
Control of the cartridge exchange mode will be described with reference to FIGS.
[0099]
FIG. 6 is a flowchart showing the control of the cartridge replacement mode of the present invention, FIG. 7 is a diagram showing the gradation-density curve of the default target table of the present invention, and FIG. 8 is formed on the intermediate transfer member of the present invention. FIG. 9 is a diagram showing the single color control of the present invention, FIG. 10 is a diagram showing the mixed color patch pattern formed on the transfer material of the present invention, and FIG. 11 is the mixed color single color control of the present invention. FIG. 12 is a diagram showing the gradation-density curve of the target table of the present invention.
[0100]
In the control of the cartridge exchange mode, the density correction table is updated by performing single color control and mixed color single color control for all image modes. In this embodiment, the density correction table is updated in the order of photo mode, graphic mode, and document mode.
[0101]
The density correction table corresponds to the gradation-density curve, and when the density correction table is updated, the gradation-density curve corresponding to the density correction table is determined.
[0102]
How to update the density correction table is determined by the target table.
[0103]
The target table is determined by a control means such as a CPU (not shown) so as to place importance on appropriate gradation for each mode in consideration of various conditions and so that process gray matches black. .
[0104]
In this embodiment, in the cartridge replacement mode, the image forming means P sequentially forms patches for all image processing modes, and a control means such as a CPU (not shown) controls the density for all image processing modes. Create a correction table.
[0105]
First, update of the density correction table in the photo mode will be described.
[0106]
As shown in FIG. 6, in S111 to S114, the density correction table T140 is updated (monochromatic control) so that appropriate gradation is emphasized for each mode with respect to the default target table, and S115 to S117. Then, the target table T150 is updated so that the process gray matches black (adjustment for mixed color in mixed color single color control), and in S118, the updated target table T150 has an appropriate gradation for each mode. The density correction table T140 is updated again so as to be emphasized (single color control of mixed color single color control).
[0107]
First, the photographic mode is designated by the image mode designation signal X, and the photographic mode color conversion table T136 is loaded into the color conversion processing unit 131, and the photographic mode halftone table T144 is loaded into the halftone processing unit 133 (S111).
[0108]
Next, in S112, a predetermined default target table is set as a target table of gradation-density characteristics of each color of C, M, Y, and K.
[0109]
In this embodiment, common to each image mode, as shown in FIG. 7, a target table corresponding to a gradation-density curve 300 in which the output density is linear with respect to the input gradation degree is used. The default target table is set in consideration of the characteristics of the image forming apparatus, and different target tables may be prepared for each image mode, or the same target table may be prepared for all image modes.
[0110]
The density correction processing unit 132 is loaded with a so-called through table that does not change the input value.
[0111]
Next, a single color patch pattern is formed on the intermediate transfer member 27 and read by the density sensor 41 (S113 in FIG. 6).
[0112]
FIG. 8 shows an example of a single-color patch pattern formed on the intermediate transfer member.
[0113]
Unfixed K toner single-color gradation patches are arranged, and thereafter, C, M, and Y toner single-color gradation patches (not shown) are continuously formed. In this embodiment, eight single color patches of C, M, Y, and K are formed. Table 1 shows the C, M, Y, and K gradation levels of the single color patch to be formed.
[0114]
Table 1 is a table showing the contents of the single-color patch pattern formed on the intermediate transfer member of the present invention.
[0115]
[Table 1]

The image forming means P of this embodiment forms patches with different gradations for each image processing mode.
[0116]
Here, since the photographic mode places importance on the gradation of highlights, as shown in the column of photographic mode in Table 1, a single color patch centered on a highlight of 10h to 70h, and a single color patch of FFh as a maximum value. To form a single color patch pattern.
[0117]
The density of the monochrome patch pattern formed on the intermediate transfer member 27 is detected by the density sensor 41, and a gradation-density curve is generated by interpolation from the detected density. When the density detection result is as shown by the black circle in FIG. 9, the gradation-density curve 100 is generated by interpolation such as linear interpolation.
[0118]
Then, based on the gradation-density curve 300 of the set default target table, a gradation-density curve 200 having a reverse characteristic of the gradation-density curve 100 is calculated, and a density correction table corresponding thereto is obtained. Then, it is updated as the density correction table T140 for the input image data (S114 in FIG. 6).
[0119]
By converting the input image data using the density correction table T140, the relationship between the input gradation level and the output density becomes a gradation-density curve 300.
[0120]
Next, mixed color single color control is performed.
[0121]
First, adjustment for mixed colors in mixed color single color control is performed.
[0122]
In S115, using the density correction table T140 that defines the gradation-density curve 200 generated in S114, a mixed color patch pattern including a CMY mixed color patch and a black (K) patch is formed on the transfer material 11, and the color sensor. Detect at 42.
[0123]
Table 2 shows the contents of each patch.
[0124]
Table 2 is a table showing the contents of the mixed color patch pattern formed on the transfer material of the present invention.
[0125]
[Table 2]

As shown in Table 2, the mixed color patch pattern includes C, M, and Y process gray patch numbers. 1-No. 6 and K patch nos. It consists of seven.
[0126]
C₀₀~ C₀₅, M₀₀~ M₀₅, Y₀₀~ Y₀₅Is a certain reference value C₀, M₀, Y₀To a value obtained by changing only a specific color by a predetermined change amount ± α. In this embodiment, the value of α is the same for C, M, and Y, but may be different for each color.
[0127]
The patch No. 7 is a single color patch of K, which is a predetermined value K₀Formed with.
[0128]
The predetermined reference value C₀, M₀, Y₀If the density characteristic of K is adjusted to the state of the gradation-density curve 300, and C, M, and Y are in the state of a typical gradation-density curve, C₀, M₀, Y₀If you mix the values of K, K₀Is a value that is almost the same color as.
[0129]
On the transfer material 11, as shown in FIG. 1 to patch no. 7 is formed, and after passing through the fixing device 30, the mixed color patch pattern is detected by the color sensor 42 and RGB values are output.
[0130]
Next, in S116 of FIG. 6, from the RGB output value of the sensor, K₀C that matches the color of the patch₀', M₀', Y₀The value of ′ (gradation degree) is calculated.
[0131]
Hereinafter, C₀', M₀', Y₀A method of calculating the value of '(gradation degree) will be described.
[0132]
The RGB output value of each patch of the mixed color patch pattern is set to the patch No. 1 = (r₀₀, G₀₀, B₀₀), Patch No. 2 = (r₀₁, G₀₁, B₀₁), ..., Patch No. 6 = (r₀₅, G₀₅, B₀₅) And patch no. The RGB output value of the 7 K patch (r_k0, G_k0, B_k0).
[0133]
First, R output of RGB output will be described.
[0134]
Table 3 is a table showing the contents of the mixed color patch pattern formed on the transfer material 11 and the target variable R.
[0135]
[Table 3]

Here, as shown in Table 3, the coefficient r of the following multiple regression equation is used, where C, M, and Y gradations are explanatory variables and R is a target variable._c0, R_c1, R_c2, R_c3Ask for.
[0136]
R = r_c1× C + r_c2× M + r_c3× Y + r_c0
Coefficient r_c0, R_c1, R_c2, R_c3Is obtained as follows.
[0137]
[Expression 1]

However,
[0138]
[Expression 2]

Then,
[0139]
[Equation 3]

At r_c1, R_c2, R_c3Is obtained.
[0140]
further,
[0141]
[Expression 4]

At r_c0Is obtained.
[0142]
Next, the coefficients of the following multiple regression equations can be obtained for the G output and B output of RGB output as well as the R output.
G = g_c1× C + g_c2× M + g_c3× Y + g_c0
B = b_c1× C + b_c2× M + b_c3× Y + b_c0
Here, the output value of K (r_k0, G_k0, B_k0) For C, M, and Y₀', M₀', Y₀Substituting it into the above equation as ′) and writing it as a matrix,
[0143]
[Equation 5]

And
[0144]
[Formula 6]

(C₀', M₀', Y₀′) Is obtained.
[0145]
This (C₀', M₀', Y₀′) Shows the chromaticity of the process gray and No. This is the amount (gradation) of cyan, magenta, and yellow that matches the chromaticity of the K patch of 7.
[0146]
That is, this (C₀', M₀', Y₀The color of process gray created by ′) is K₀Match the color of.
[0147]
In this way, the predetermined value K₀C that matches the chromaticity of₀', M₀', Y₀The value of ′ can be calculated.
[0148]
Next, in the same manner, 1 (C₁₀, M₁₀, Y₁₀) -No. 6 (C₁₅, M₁₅, Y₁₅) And No. 7 (K₁) To form a mixed color patch pattern₁Matching C₁', M₁', Y₁'Can be obtained.
[0149]
In addition, K₂Matching C₂', M₂', Y₂', K₃Matching C₃', M₃', Y₃', ..., K_NMatching C_N', M_N', Y_N'Can be obtained.
[0150]
That is, K_NA predetermined reference value (C for the gradation of (N = 0, 1, 2,..., N))_N, M_N, Y_N) (N = 0, 1, 2,..., N), C_N0~ C_N5, M_N0~ M_N5, Y_N0~ Y_N5Patch No. 1-No. 6 and K_NNo. of No. 7 and K_N(C_N', M_N', Y_N′) Can be obtained.
[0151]
In this embodiment, n = 7.
[0152]
K₀~ K₇Table 4 shows the values.
[0153]
Table 4 shows K formed on the transfer material of the present invention.₀~ K₇Is a table summarizing the contents of the patch.
[0154]
[Table 4]

The image forming means P of this embodiment forms patches with different gradations for each image processing mode.
[0155]
Similar to the pattern read by the density sensor 41, in the photographic mode, the highlight is formed as shown in the photographic mode column of Table 4.
[0156]
Accordingly, it is possible to ensure that an appropriate gradation is emphasized for each mode.
[0157]
Next, (C_N', M_N', Y_N′) And a predetermined reference value (C_N, M_N, Y_N).
[0158]
Assume that the relationship of cyan becomes like a black circle in FIG.
[0159]
At this time, a curve 150 is created by linearly interpolating values between black circles, for example, and a corresponding color correction table is obtained.
[0160]
The gradation-density curve 300 in FIG. 9 corresponding to the original target table is multiplied by the curve 150 in FIG. 11 corresponding to the color correction table to generate a gradation-density curve 400 as shown in FIG. Then, a new cyan target table is obtained from the gradation-density curve 400. Specifically, the input gradation degree is converted into a table by the color correction table, and then converted according to the target table to generate a gradation-density curve 400 to obtain a new target table.
[0161]
Similarly, new target tables are obtained for magenta and yellow.
[0162]
Then, as shown in S117 of FIG. 6, the new target table is updated (stored in the memory m2 as the photo mode target table T150).
[0163]
Next, monochromatic control of mixed color monochromatic control is performed.
[0164]
Next, in S118, the monochrome correction is again performed using the cyan, magenta, and yellow target tables updated in S117, whereby the density correction table is updated again and stored in the memory m2 as the density correction table T140 for the photo mode. To do.
[0165]
This completes the gradation-density control for the photographic mode (S110 in FIG. 6).
[0166]
Subsequently, gradation-density control for graphic mode is performed.
[0167]
The gradation-density control for the graphic mode is performed in the same procedure as the gradation-density control for the photographic mode, and the details are omitted.
[0168]
However, during the gradation-density control for the graphic mode, the graphic mode color conversion table T137 is loaded into the color conversion processing unit 131, and the graphic mode halftone table T145 is loaded into the halftone processing unit 133.
[0169]
In addition, since the graphic mode emphasizes the overall gradation from highlight to shadow, the monochrome patches formed for reading by the density sensor 41 have the graphics shown in Table 1 as C, M, Y, and K gradations. Select evenly from highlight to shadow as shown in the mode column.
[0170]
Furthermore, a mixed color patch pattern formed for reading by the color sensor 42 is also (C_N, M_N, Y_N), K_NAs shown in the graphic mode column of Table 4, the values from highlight to shadow are selected equally.
[0171]
Further, the target table generated by the graphic mode gradation-density control is stored in the memory m2 as the graphic mode target table T151, and the density correction table is stored in the memory m2 as the graphic mode density correction table T141. (S120 in FIG. 6).
[0172]
When the gradation-density control for the graphic mode is finished, the gradation-density control for the document mode is finally performed.
[0173]
The gradation-density control for the document mode is also performed in the same procedure as the gradation-density control for the photographic mode, and the details are omitted.
[0174]
However, during the tone-density control for the document mode, the document mode color conversion table T138 is loaded into the color conversion processing unit 131, and the document mode halftone table T146 is loaded into the halftone processing unit 133.
[0175]
Further, since the document mode places importance on the gradation of shadows, the monochrome patches formed for reading by the density sensor 41 are shown in the document mode column of Table 1 as C, M, Y, and K gradations. First, select the shadow.
[0176]
Furthermore, a mixed color patch pattern formed for reading by the color sensor 42 is also (C_N, M_N, Y_N), K_NAs shown in Table 4, in the document mode column, a shadow is selected as the center.
[0177]
The target table generated by the document mode gradation-density control is stored in the memory m2 as the document mode target table T152, and the density correction table is stored in the memory m2 as the document mode density correction table T142. (S130 in FIG. 6).
[0178]
After the above gradation-density control is performed, the normal print state is entered (S140 in FIG. 6), and the cartridge replacement mode is completed.
[0179]
Next, gradation-density control during normal printing will be described with reference to FIG.
[0180]
In this embodiment, in gradation-density control during normal printing, the image forming means P forms a patch for the image processing mode designated by the user, and the control means such as a CPU (not shown) is controlled by the user. Update the density correction table for the specified image processing mode.
[0181]
The user designates in advance which image mode the gradation-density control is to be performed by setting the printer driver or the printer panel. At this time, a plurality of image modes can be designated.
[0182]
In the normal printing state S140, normal printing is performed. Then, the process proceeds to S212 to check the cartridge replacement and the number of printed sheets.
[0183]
In S212, it is determined whether any color cartridge has been replaced. When the cartridge is replaced, the environment changes greatly. Therefore, after the cartridge replacement mode S101 described with reference to FIGS. 6 to 12 is performed, the process returns to the normal print state S140. If the cartridge has not been replaced in S212, the process proceeds to S213.
[0184]
In S213, it is determined whether or not a predetermined number of sheets have been printed. If printing has been performed, the process proceeds to S214. If printing has not been performed, the process returns to the normal printing state S140.
[0185]
In S214 to S217, single color control is performed for the image mode designated by the user.
[0186]
In monochromatic control, first, an image mode designated by the user is designated by the image mode designation signal X, and a color conversion table and a dither table corresponding to the designated image mode are loaded into the color conversion processing unit 131 and the halftone processing unit 133, respectively. (S214).
[0187]
Next, a target table generated during the previous mixed color single color control is set as the target table of gradation-density characteristics, and a through table is set in the density correction table 132 as in the cartridge replacement mode ( S215).
[0188]
In S216, similarly to S113 in FIG. 6, a single-color patch pattern is formed on the intermediate transfer member 27 and is read by the density sensor 41. At this time, the single-color patch pattern corresponding to the image mode specified by the user is selected from the photo mode column, graphic mode column, and document mode column of Table 1.
[0189]
In S217, a tone-density curve is generated by interpolation from the detected density.
[0190]
Then, based on the gradation-density curve of the target table set in S215, the gradation-density curve having the inverse characteristic of the gradation-density curve generated in S217 is calculated, and a density correction table corresponding to this is calculated. The density correction table T140 for the input image data is updated.
[0191]
Next, in S218, it is determined whether or not monochrome control has been performed for all image modes designated by the user. If not, the process returns to S214 to perform monochromatic control for another image mode. If yes, go to S219.
[0192]
In S219, it is determined whether the single color control has been performed a predetermined number of times A from the previous color mixture single color control to the present. If the predetermined number of times A has not been performed, the process returns to the normal print state S140 again. If the specified number of times A has been performed, the process proceeds to S220 and the mixed color single color control is performed.
[0193]
Note that the control shown in FIG. 5 is enabled by S219.
[0194]
In S220 to S225 of FIG. 13, mixed color single color control is performed for the image mode designated by the user.
[0195]
First, adjustment for mixed colors in mixed color single color control is performed.
[0196]
In S220, the color conversion table and the dither table corresponding to the image mode designated by the user are loaded into the color conversion processing unit 131 and the halftone processing unit 133, respectively.
[0197]
In step S <b> 221, a density correction table corresponding to the image mode designated by the user is loaded into the density correction processing unit 132.
[0198]
In step S222, a mixed color patch pattern including a CMY mixed color patch and a black (K) patch is formed on the transfer material 11, detected by the color sensor 42, and an RGB value is output. At this time, the patch pattern corresponding to the user-specified image mode is selected from the photo mode column, graphic mode column, and document mode column of Table 4.
[0199]
Thereafter, in S223 to S224, processing similar to S116 to S117 in FIG. 6 is performed. However, when a new target table is created in S224, a gradation-density curve is generated by multiplying the target table generated by the previous mixed color single color control by a new color correction table, and a new one is obtained from this gradation-density curve. Find the target table.
[0200]
Then, the new target table is updated (saved in the memory m2).
[0201]
Next, monochromatic control of mixed color monochromatic control is performed.
[0202]
In S225, the density correction table is updated again by performing monochrome control again using the cyan, magenta, and yellow target tables updated in S224, and stored in the memory m2 as the density correction table for the image mode specified by the user. To do.
[0203]
In step S226, it is determined whether mixed color single color control has been performed for all image modes designated by the user. When mixed color single color control is performed in all image modes, the process returns to the normal print state S140. If mixed color single color control is not performed in all image modes, the process returns to S220 to perform mixed color single color control for the other image modes.
[0204]
In this embodiment, the target table is updated as described above with emphasis on accuracy. However, the density correction table is updated without updating the target table, and the color correction table 150 shown in FIG. You may take the structure to multiply.
[0205]
In this embodiment, three-dimensional linear interpolation is used to calculate the optimum C, M, and Y values. As an interpolation method, quadratic function approximation, cubic function approximation, or spline interpolation is used. A non-linear method may be used.
[0206]
Furthermore, in this embodiment, the color sensor 42 is RGB output, but it may output chromaticity such as L * a * b *, L * c * h *, and XYZ.
[0207]
Further, in this embodiment, the CMY mixed color patch is a patch that has substantially the same color as the black (K) patch if C, M, and Y are in a typical tone-density curve state. The color sensor 42 measures the L * a * b * value of the CMY mixed color patch, and the mixed color of C, M, Y becomes an achromatic color with the achromatic axis of a = 0, b = 0 as a target, for example. An optimum gradation may be calculated and fed back to the single color control.
[0208]
【The invention's effect】
As described above, according to the configuration of the present invention, when the C-, M-, Y-gradation-density characteristics and the K-gradation-density characteristics are matched using the output value of the color sensor, It is possible to provide an image forming apparatus that can perform gradation-density control optimal for an image mode and can always reproduce a user-desired color even when environmental fluctuation occurs.
[Brief description of the drawings]
FIG. 1 is a configuration diagram showing a color image forming apparatus of the present invention.
FIG. 2 is a diagram showing an example of the configuration of a concentration sensor according to the present invention.
FIG. 3A is a diagram showing an example of the configuration of a color sensor of the present invention, and FIG. 3B is a diagram showing a light receiving part of a charge storage type sensor.
FIG. 4 is a diagram illustrating an example of processing in an image processing unit of the image forming apparatus.
FIG. 5 is a flowchart showing tone-density characteristic control combining single color control and mixed color single color control of the present invention.
FIG. 6 is a flowchart showing control of a cartridge replacement mode according to the present invention.
FIG. 7 is a diagram showing a gradation-density curve of a default target table of the present invention.
FIG. 8 is a diagram showing a patch pattern formed on the intermediate transfer member of the present invention.
FIG. 9 is a diagram illustrating monochromatic control according to the present invention.
FIG. 10 is a view showing a mixed color patch pattern formed on the transfer material of the present invention.
FIG. 11 is a diagram illustrating adjustment of mixed colors in mixed color single color control according to the present invention.
FIG. 12 is a diagram showing gradation-density characteristics of the target table of the present invention.
FIG. 13 is a flowchart showing details of control of gradation-density characteristics during normal printing according to the present invention.
[Explanation of symbols]
11 Transfer material
21a, 21b Paper feed unit
22Y-22K Photosensitive drum
23Y-23K injection charging means
24Y-24K Scanner section
25Y-25K toner cartridge
26Y-26K developing means
27 Intermediate transfer member
28a, 28b Transfer roller
29 Cleaning means
30 Fixing device
31 Fixing roller
32 Pressure roller
33, 34 Heater
41 Concentration sensor
42 Color sensor
51 Infrared light emitting device
52a, 52b Light receiving element
53 White light emitting device
54a Charge accumulation type sensor with RGB on-chip filter
54b Photodetector
P Image forming means
Q Image processing unit

Claims (7)

Image forming means for forming a patch on a transfer material, chromaticity detection means for detecting the chromaticity of the patch, control means for creating a correction table based on the chromaticity, and conversion of image data by the correction table Thus, in an image forming apparatus having a correction unit that corrects an image forming condition,
The image forming apparatus, wherein the control unit creates the correction table for each image processing mode. The image forming apparatus according to claim 1, wherein the image forming unit forms a patch for each image processing mode, and the control unit creates the correction table for each image processing mode. The image forming apparatus according to claim 1, wherein the image forming unit forms patch patterns having different gradations for each image processing mode. The image forming apparatus according to claim 1, wherein the image forming unit sequentially forms patches for all image processing modes. The image forming apparatus according to claim 1, wherein the image forming unit forms a patch for an image processing mode designated by a user. The image forming unit forms a mixed color patch and a black patch, and the control unit determines, from the chromaticity of the mixed color patch and the black patch, cyan for creating a process gray having a chromaticity close to the black patch, 3. The image forming apparatus according to claim 1, wherein the amount of magenta and yellow is calculated, and the correction table is created so that process gray matches black. 7. The image forming apparatus according to claim 6, wherein the color mixture patch is formed by changing the amounts of cyan, magenta, and yellow by a predetermined change amount from a predetermined reference value.

Images