JP2004328481A - Image reader and image reading method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To reduce an influence on image data caused due to variation in the temporal change of light quantity distribution in a main scan direction of a light source and to reduce an influence on compensated image data caused due to the dirt of a concentration reference member, etc. <P>SOLUTION: This image reader is constituted of: a reading means for reading an image of an original by feeding the original to a prescribed reading position; a shading compensation board arranged outside a reading area for reading the original; and a platen roller arranged on the prescribed reading position. The image reader detects the dirt of the platen roller by reading the platen roller on the prescribed reading position by the reading means before reading the image of the original by the reading means and selects one of a plurality of compensation means for compensating the temporal variation of the light source according to a detection result of the dirt. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

Ｐ_０（ｊ）は、複数原稿の読取開始時に（シェーディング補正用の基準データを読み取ったときと同時期に）プラテンローラ５１１を読み取ったデータである。それに対して、Ｐ（ｊ）は、各原稿を読み取る直前に（原稿と原稿の間などに）プラテンローラ５１１を読み取ったデータである。
【００３５】
原稿を読み取って得られたデータはシェーディング補正に加えて、さらに上式の変化を補うように補正を加える。すなわち、原稿の読み取りデータをシェーディング補正して、なおかつ、次式の補正係数を画素毎に乗ずる。
【００３６】
【外２】

こうすることによって、ランプが光量変化したにもかかわらず濃度の均一性を保つことができる（図４（ｄ））。
【００３７】
以上のように、配光補正を行うには、複数原稿の読み取り開始時のプラテンローラの読み取り値、および原稿間での読み取りの時におけるプラテンローラの読み取り値を画素毎に制御部のメモリに記憶しておかなければならない。例えば、６００ｄｐｉの解像度で、最も大きな読み取り原稿サイズがＡ３であった場合、主走査方向の画素数は
【外３】

となる。制御部は、読み取り前・読み取り途中の値を記憶しておかないために、少なくとも１４０００画素の情報を記憶しておかなければならなく、メモリ量を非常に多く要するという問題がある。
【００３８】
そこで、主走査方向におけるプラテンローラ全体のデータを記憶しておくのではなく、主走査方向をいくつかの領域に分けて、その領域内の補正係数は直線的に変化すると仮定して、記憶する情報の量を低減する方法を採用してもよい。
【００３９】
図５（ａ）（ｂ）（ｃ）は、横軸が主走査方向、縦軸がプラテンローラ読み取りの変化を表している。図５（ａ）は、主走査方向におけるＣＣＤの全ての画素に対するプラテンローラ読み取りの変化を表している。これに対して図５（ｂ）は、主走査方向を１２の領域に分割して、その領域の境界にプラテンローラ読み取りの変化値を置き、その間を直線的に近似することによって、メモリに記憶するデータ量を低減している。
【００４０】
この補正方法を採用したとして、複数原稿の読取開始時（シェーディング補正用の基準データを読み取ったときと同時期）のプラテンローラの読み取り値が図６の読み取り領域Ａのところでプラテンローラの汚れを読み取ってしまい、主走査方向のほかの箇所の読み取り値よりも小さかったとする。原稿と原稿の間で読み取ったプラテンローラの読み取り値は全体的な読み取りのレベルは下がるけれども主走査方向に対して一様になっているとするとしても、その際には、Ｐ（ｊ）がＰ_０（ｊ）になるように補正されるので、図６（ａ）の読み取り領域Ａでは主走査方向の他の箇所よりも補正量が少なくなり、主走査方向のＡ付近において画像が暗くなってしまう（図６（ｂ））。逆にプラテンローラの読み取り値が他よりも大きな場合には（図７（ａ））、主走査方向のＡ付近において画像が明るくなってしまう（図７（ｂ））。
【００４１】
このようにして、複数原稿の読取開始時（シェーディング補正用の基準データを読み取ったときと同時期）にプラテンローラの汚れを読み取ってしまうと、基準がずれてしまうために、補正を施す画像データ全てに対して影響を及ぼすことになる。
【００４２】
複数原稿の読取開始時にプラテンローラを読み取ったときには汚れを読み取らず、原稿と原稿の間でプラテンローラの汚れを読み取ってしまうときも同様である。原稿間でプラテンローラの汚れを読み取る際に、主走査方向の他の箇所の読み取り値よりも小さかったとする（図８）。このとき、Ｐ（ｊ）がＰ_０（ｊ）になるように補正される。したがって、図８（ａ）の読み取り領域Ｂでは、主走査方向の他の箇所よりも過剰に補正され、主走査方向のＢ付近において画像が明るくなってしまう（図８（ｂ））。逆に、プラテンローラの読み取り値が他よりも大きな場合には（図９（ａ））、主走査方向のＢ付近において画像が暗くなってしまう（図９（ｂ））。
【００４３】
原稿と原稿の合間にプラテンローラの汚れを読み取ってしまった場合には、そのデータを使って補正を施す画像のみが影響を受けることになる。
【００４４】
以上をまとめると、配光補正を適用したときに、原稿読み取り前にプラテンローラの汚れを読み取ってしまった場合には、それ以降補整する画像全ての画像が部分的に明るくなったり暗くなったり、影響を受けてしまう。原稿と原稿の合間にプラテンローラの汚れを読み取ってしまった場合には、そのデータを使って補正を施す画像のみが、部分的に明るくなったり暗くなったり影響を受けてしまう。
【００４５】
次に、光量変動補正の補正方法について、図４および図５を用いて説明する。ランプの連続点灯による光量劣化を補正することについては、前述した配光補正と同じであるが、その補正する手法が異なる。
【００４６】
光量変動補正方法の詳細は、図５（ｃ）を用いて説明する。図５（ｃ）の点線（曲線）はプラテンローラの読み取りデータを示し、直線は主走査方向の読み取り領域データにおける平均化したデータを示している。ランプの光量劣化による主走査方向に対する変化プラテンローラ読み取りの変化が主走査方向に対して変化が少なかった場合には、主走査方向に対する変化は一様であるとして、補正を実行する。例えば、プラテンローラを読み取ったデータとして、図５（ｂ）におけるプラテンローラ読み取りのデータを用いて説明する。
【００４７】
光量変動補正を実行する場合、光量変動補正の補正係数が次式で表される。
【００４８】
【外４】

【００４９】
この補正係数によって、原稿を読み取って画像データ補正する際に、例えばプラテンローラの読み取りのうちの１カ所で汚れを読み取ってしまったとしも、補正後の画像データへ与える影響は平均を取ることによって低減される。上記補正係数の例では、汚れの影響は１／１２までに低減されることになる。光量変動補正は、配光補正と同様に汚れの影響を受けることに変わりないが、その影響はプラテンローラの読み取り値の平均を取ることによって低減され、すなわち、汚れには比較的強い補正方法と言うことができる。ここでは、主走査方向の領域を１２に分割したが、これに限定されるものではない。
【００５０】
以上を踏まえると、配光補正と光量変動補正の関係は、画質は配光補正のほうが良く、プラテンローラの汚れによる影響は光量変動補正の方が優れており、相補う関係にある（図１０参照）。
【００５１】
本発明の特徴を示す読み取り処理について図１１を用いて説明する。この読み取り処理は、不図示の制御部が所定のプログラムを動作させることによって実行される。オペレータなどによる操作部のスタートキーの押下によって、原稿の読み取り処理が開始される。まず、第１ミラーユニット５０４をシェーディング補正板が読み取れる位置（シェーディング補正板の下）に移動し、シェーディング補正板の読み取りを実行する（Ｓ１０１）。そして、読み取られた画像データに対して、シェーディング補正を行えるように基準データを作成する。それに続いて、第１ミラーユニット５０４を移動させ、プラテンローラ５１１の読み取りを実行する（Ｓ１０２）。
【００５２】
次に、原稿読み取り前に、プラテンローラを読み取って、得られた読み取りデータをもとにして汚れ検知処理を実行し、プラテンローラに汚れ等があるかどうかを判定する（Ｓ１０３、Ｓ１０４）。読み取った画像データの画質を向上させたいために、出来る限り補正方法は前述した配光補正を利用したい。しかし、配光補正は光量変動補正に比べて、プラテンローラの汚れの影響を受けやすい。その点を考慮して、プラテンローラに汚れがあるかどうかを調べるために汚れ検知処理を実行する。
【００５３】
Ｓ１０４で、プラテンローラの汚れを検知しない場合には、配光補正（第１の補正方法）を選択する。一方、プラテンローラの汚れを検知する場合には、読み取られるすべての原稿の画像にその影響が及んでしまうために、画質を犠牲にしても汚れに強い補正方法である光量変動補正（第２の補正方法）を選択する。なお、補正方法はできるだけ配光補正を選択したいので、プラテンローラで汚れを検知したら、汚れ検知処理を所定回数実行して汚れを回避できる可能性を探っても良い。その際、汚れ検知処理のためにプラテンローラを読み取る際には、プラテンローラを回転させるようにした方がよい。
【００５４】
ここで、汚れ検知方法処理の一例を紹介する。汚れのないプラテンローラは濃度が一様であるため、プラテンローラの読み取り値は主走査方向に対して一様になる。あらかじめローラの読み取りレベルの値、そのばらつき状態がわかっている場合には、読み取りレベルがある領域（図１２の２εの領域）に入っていれば汚れがないと判断し、入っていない箇所があれば（図１２の読み取り領域Ｃ）汚れがあると判断する。
【００５５】
詳細には、プラテンローラの読み取り値が主走査方向に対して一様にならないような場合には、隣接する読み取りデータの変化がある一定値を超えるようであれば、汚れがあると判断する。さらに、図１３を例に説明すると、ｉとｉ＋１（ｉ＝１・・・１１）を比較し、その差が所定値以上になる箇所に基づいて、汚れのある箇所を特定する。この例では、６と７、７と８の差が所定値以上になるので、７の箇所を汚れと判断する。なお、ここで紹介した汚れの検知方法は一例であり、これに限定するものではない。
【００５６】
Ｓ１０６で光量変動補正が選択された場合、プラテンローラを読み取って得られた基準データに汚れが含まれているために、それ以降の連続した原稿を読み取る際には、配光補正をすることはなく、原稿束の読み取りが終了するまで光量変動補正を行うことになる。
【００５７】
Ｓ１０６で光量変動補正（第２の補正方法）が選択された場合、原稿を読み取って得られたデータを光量変動補正する（Ｓ１２１）。次に、読み取っていない原稿があるかどうかを判定する（Ｓ１２２）。読み取っていない原稿がある場合は、プラテンローラを読み取って光量変動補正の準備をする（Ｓ１２３）。実際には光量変動補正係数を求める。Ｓ１２２で読み取っていない原稿がなくなったら、読み取りが終了する（Ｓ１３１）。
【００５８】
原稿読み取り前にプラテンローラを読み取って汚れ検知処理を実行し、汚れがないと判定された場合には、補正方法として配光補正（第１の補正方法）を選択する（Ｓ１０５）。そして、原稿の読み取りを行い、読み取ったデータに対して配光補正を行う（Ｓ１１１）。次に、読み取っていない原稿があるかどうかを判定する（Ｓ１１２）。読み取っていない原稿がある場合は、プラテンローラを読み取って光量変動補正の準備をする（Ｓ１１３）。
【００５９】
原稿と原稿の合間で読み取ったプラテンローラに汚れがあっても、原稿読み取り前にプラテンローラに汚れがあったときと画像に現れる現象は異なるが、画像に影響を及ぼしてしまうためにプラテンローラの汚れがあるかどうか調べる必要がある。プラテンローラで読み取られたデータをもとにして、汚れがあるかどうかを判定する（Ｓ１１４）。その結果、Ｓ１０４と同様にして、汚れがなければ汚れによる影響はないので補正方法は配光補正を選択し、汚れがあれば汚れの影響を回避するために光量変動補正を選択するように切り替える。なお、原稿読み取り前のプラテンローラに汚れを検知した時と同様にして、汚れを検知したら再度プラテンローラを読み取るリトライ行為を行って汚れを回避できる可能性を探っても良い。このように補正の方法を決定し、原稿を読み取り（Ｓ１１１）、さらに原稿があるならプラテンローラを読み取って、汚れ検知を行い、その結果に従って補正方法を決めることを読み取る原稿がなくなるまで繰り返し、原稿の読み取りを終了する（Ｓ１３１）。
【００６０】
上述の実施例では、原稿を読み取るたびプラテンローラを読み取って補正の方法を決めているが、所定枚数毎にプラテンローラを読み取って補正の方法を変更しても良く、そのタイミングを限定するものではない。
【００６１】
実際のプラテンローラの汚れは非常に少なく、プラテンローラを読み取ったときに、汚れはあったとしても１カ所で、リトライ行為によってほとんど回避することができるので、プラテンローラの汚れを検知することによって汚れの影響を受けず、従来よりも画質を向上させることが可能になる。
【００６２】
【発明の効果】
以上説明したように、本発明によれば、プラテンローラの汚れを検出し、適切に画像補正方法を切り替えることにより、画質を向上させつつ、画像補正による汚れの影響を抑えることが可能になる。
【図面の簡単な説明】
【図１】画像読み取り装置の構成を示す図
【図２】画像読み取り部を上から見た図
【図３】画像処理部のブロック図
【図４】ＣＣＤで読み取られたデータの一例を示す図
【図５】プラテンローラを読み取ったデータの一例を示す図
【図６】複数の原稿読み取り前にプラテンローラの汚れを読み取って得られたデータとそのデータを基準にして原稿画像データを補正した場合における補正後のデータの一例を示す図
【図７】複数の原稿読み取り前にプラテンローラの汚れを読み取って得られたデータとそのデータを基準にして原稿画像データを補正した場合における補正後のデータの一例を示す図
【図８】原稿と原稿の間でプラテンローラの汚れを読み取って得られたデータとそのデータを基準にして原稿画像データを補正した場合における補正後のデータの一例を示す図
【図９】原稿と原稿の間でプラテンローラの汚れを読み取って得られたデータとそのデータを基準にして原稿画像データを補正した場合における補正後のデータの一例を示す図
【図１０】配光補正と光量変動補正を比較したテーブル
【図１１】本発明の実施の形態に係る読み取り処理を示すフローチャート
【図１２】プラテンローラの汚れ検知処理を示す図
【図１３】プラテンローラの汚れ検知処理を示す図
【符号の説明】
５００ 画像読み取り装置
５０１ 原稿搬送部
５０２ 画像読み取り部
５０３ 第１ミラーユニット
５０４ 第２ミラーユニット
５０５ 原稿
５０６ レンズ
５０７ ＣＣＤ
５０８ 原稿載置台
５０９ 排紙トレイ
５１０ シェーディング補正板
５１１ プラテンローラ
５１２ ガラス台
５１３ ガラス台
５２４ 光
６００ 画像処理部
６２０ 増幅器
６２１ Ａ／Ｄ変換器
６２２ シェーディング補正部
６２３ 汚れ検知部
６２５ 第１の補正部（配光補正部）
６２６ 第２の補正部（光量変動補正部）[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an image reading technique in a copying machine, a scanner, a facsimile apparatus, and the like, and more particularly to a technique for correcting shading due to fluctuations in light amount and light distribution of a light source when performing continuous reading of a document.
[0002]
[Prior art]
2. Description of the Related Art There is generally known a method of automatically supplying a document and reading an image while moving the document while fixing a reading unit (“flow reading method”). A brief reading method will be briefly described. When the operator places a document on the ADF and issues a reading start command, the reading side moves to a certain position and stops, the reading sensor reads the main scanning direction one-dimensionally, and the ADF moves the document in a sub-scanning direction orthogonal to the scanning direction. To read the image of the entire document.
[0003]
This skip-reading method can save the work of placing and replacing the originals by the operator, and thus can reduce the time when continuously reading many originals.
[0004]
However, when a plurality of continuous documents (images) are read, there is a problem that the absolute light amount of the lamp changes over time (a problem that the light amount of the lamp decreases over time). In order to solve this problem, a density reference plate is provided at a position where the document is read and at a position outside the reading area of the document, and the document read data is corrected based on the read data obtained from the density reference plate. (For example, see Patent Document 1).
[0005]
[Patent Document 1]
JP 2001-094737 A
[0006]
[Problems to be solved by the invention]
However, when the rate of change in the temporal change in the light intensity of the lamp differs depending on the position in the main scanning direction, that is, the light intensity of the lamp in the main scanning direction from the initial stage of lamp lighting (at the start of reading of a continuous document) When the distribution changes, the brightness of the read image changes (in many cases, the brightness decreases), and in the case of a color image, the saturation and chromaticity also change. As a result, the difference between the actual document and the read document increases, and the performance of the image reading apparatus is significantly impaired.
[0007]
In order not to lower the performance of the image reading device, it is necessary to perform correction so as to suppress the influence of variation due to a temporal change in the light amount distribution of the lamp in the main scanning direction. Therefore, when reading a plurality of documents continuously, the density reference member disposed in the document reading area at the reading position is used over the area in the main scanning direction by using the space between the documents (when the document is not read). A method is conceivable in which reading is performed and correction is performed based on the reference data. However, this method has a problem in that, when dirt or the like is attached to the density reference member, the read image data is strongly affected by the dirt.
[0008]
SUMMARY OF THE INVENTION It is an object of the present invention to reduce the influence on the image data due to the variation in the temporal change of the light amount distribution in the main scanning direction, and to reduce the influence on the corrected image data due to contamination of the density reference member.
[0009]
[Means for Solving the Problems]
In order to solve the above-described problems, the present invention provides a conveying unit that conveys an original to a reading position, a reading unit that reads the original conveyed by the conveying unit, and a correction unit that corrects image data of the original read by the reading unit. Detecting a stain on the density reference member by reading the density reference member at the reading position with the reading unit before reading the document with the reading unit. And a selecting step of selecting one correction means from the plurality of correction means according to a detection result of the detection step.
[0010]
Further, in the selection step, when the contamination of the density reference member is detected in the detection step, the second correction unit is selected, and in the detection step, the contamination of the concentration reference member is not detected. Is characterized in that the first correction means is selected.
[0011]
Further, the plurality of correction units obtain a correction value for each pixel of the reading unit from the data read from the density reference member, and correct the image data of the original read by the reading unit based on the correction value. A first correction means, and a second correction means for obtaining an average value from the data read from the density reference member and correcting the image data of the original read by the reading means based on the average value. Features.
[0012]
Further, in the detecting step, a process of detecting contamination of the density reference member is performed a predetermined number of times.
[0013]
The present invention also provides a conveying unit for conveying a document to a reading position, a reading unit for reading the document conveyed by the conveying unit, a first density reference member disposed outside a reading area for reading the document, A second density reference member disposed at the reading position, a plurality of correction units for correcting image data of the document read by the reading unit, and a second density reference member at the reading position before reading the document by the reading unit. Detecting means for detecting contamination of the second density reference member by reading the density reference member by the reading means, and selecting one correction means from the plurality of correction means according to the detection result of the detection means. It is characterized by having a selecting means to perform.
[0014]
Further, when the detecting means detects the contamination of the second density reference member, the selecting means selects the second correction means, and the detecting means detects the contamination of the second density reference member. If no is detected, the first correction means is selected.
[0015]
Further, the plurality of correction units determine a correction value for each pixel of the reading unit from data read from the second density reference member, and based on the correction values, image data of the original read by the reading unit. A second correction means for calculating an average value from data read from the second density reference member, and correcting the image data of the document read by the reading means based on the average value. It is characterized by comprising correction means.
[0016]
Further, the detection means executes a process of detecting contamination of the second density reference member a predetermined number of times.
[0017]
Also, the present invention provides a conveying unit for conveying a document to a reading position, a reading unit for reading the document conveyed by the conveying unit, a density reference member disposed at the reading position, and a document read by the reading unit. A plurality of correction means for correcting the image data, a detection means for detecting dirt on the density reference member by reading the density reference member at the reading position by the reading means before reading the original by the reading means; And a selecting means for selecting one correcting means from the plurality of correcting means in accordance with a detection result of the detecting means.
[0018]
Further, the selection means selects the second correction means when the detection means detects the contamination of the density reference member, and when the detection means does not detect the contamination of the concentration reference member. Is characterized in that the first correction means is selected.
[0019]
Further, the plurality of correction units obtain a correction value for each pixel of the reading unit from the data read from the density reference member, and correct the image data of the original read by the reading unit based on the correction value. A first correction means, and a second correction means for obtaining an average value from the data read from the density reference member and correcting the image data of the original read by the reading means based on the average value. Features.
[0020]
Further, the detection means executes a process of detecting contamination of the density reference member a predetermined number of times.
[0021]
BEST MODE FOR CARRYING OUT THE INVENTION
An embodiment of the present invention will be described below with reference to the drawings.
[0022]
FIG. 1 shows the configuration of the image reading device 500. The image reading device 500 includes a document conveying unit 501 and an image reading unit 502. Note that the image reading device 500 can be used as a copier by connecting to a printer device.
[0023]
The document transport unit 501 includes a document table 508, a white platen roller 511, a paper discharge tray 509, and a plurality of drivable transport rollers for transporting the document. The plurality of documents 505 placed on the document table 508 are separated and fed one by one by driving a transport roller, and are transported to a predetermined reading position. Then, the document is read at a predetermined reading position while the document is being conveyed, and is discharged to a discharge tray 509.
[0024]
The image reading unit 502 includes a first mirror unit 503, a second mirror unit 504, a lens 506, a reading element (hereinafter, referred to as a CCD) 507, a white shading correction plate (first density reference plate) 510, and a glass table 512. , 513. The second mirror unit 504 includes a light source for irradiating the document. The document conveyed by the document conveying unit 501 is scanned at a predetermined reading position while being conveyed at a predetermined speed. At this time, the document is illuminated by a light source at a predetermined reading position. The light reflected from the document is guided to the CCD 507 via the first mirror unit 503, the second mirror unit 504, and the lens 506. This reading method is hereinafter referred to as “flow reading method”.
[0025]
FIG. 2 is a diagram of the image reading unit 502 viewed from above. The arrow direction shown in FIG. 2 is a direction orthogonal to the direction in which the document is transported by the document transport unit 501, and the direction is hereinafter referred to as the main scanning direction.
[0026]
FIG. 3 is a block diagram of the image processing unit 600. The image processing section 600 performs the following predetermined processing on the data read by the CCD 507 shown in FIG. The light 524 that illuminates the original and is reflected is converted from the light into an analog electric signal by the CCD 507. Then, the analog electric signal is amplified by the amplifier 620, and the analog electric signal is converted into a digital signal by the A / D converter 621. The converted digital signal is subjected to shading correction by a shading correction unit 622.
[0027]
Shading correction is performed to correct non-uniformities such as uneven distribution of light in the main scanning direction when the lamp is turned on and unevenness in the amount of light attenuation in the main scanning direction of the lens. Is FIG. 4A is an example of data when the shading correction plate 510 is read by the CCD 507. In FIG. 4, the horizontal axis represents the main scanning direction, and the vertical axis represents the output level read by the CCD. In order to correct variations in the main scanning direction as shown in FIG. 4B, the gain / offset is adjusted so that the output of the shading correction plate 510 becomes uniform in the main scanning direction.
[0028]
Reading of the reference data for shading correction is performed only once before starting reading of the first document when reading a plurality of documents continuously. If the image data of a subsequent document is corrected using the shading correction reference data before the first document is read, the light intensity of the read image is corrected due to the temporal change in the light intensity of the lamp. It has the effect of change. In the case where the temporal change of the light amount of the lamp is different in the main scanning direction, especially in a color image, the difference between the saturation and the chromaticity between the original and the read image data is large, and the performance as the reading device is impaired. .
[0029]
Image data that has been subjected to shading correction as a countermeasure is subjected to image correction by the first correction unit 625 or the second correction unit 626 based on reference data obtained by reading the platen roller 511.
[0030]
Whether the image correction is performed by the first correction method by the first correction unit 625 or by the second correction method by the second correction unit 626 is selected by a control unit (not illustrated). The selection by the control unit is controlled based on the determination result of the dirt detection unit 623 located at the previous stage of the first correction unit 625 or the second correction unit 626. The dirt detection unit 623 detects whether the platen roller 511 is dirty based on data obtained by reading the platen roller 511 before reading the document.
[0031]
When the dirt detection unit 623 does not detect dirt, the first correction unit 625 uses the first correction method. When the dirt detection unit 626 detects dirt, the second correction unit 626 uses the second correction method. Execute image correction. The first correction method and the second correction method will be described in detail below.
[0032]
Here, the first correction unit 625 and the second correction unit 626 are described as separate blocks, but a portion shared during correction may be shared. First, the first correction method will be described with reference to FIGS. Note that the first correction method is hereinafter referred to as light distribution correction.
[0033]
If the lamp is continuously turned on in order to continuously read a plurality of documents set on the document table, the absolute light amount of the lamp changes. Further, if the amount of change differs depending on the position in the main scanning direction, even if shading correction is performed, it will not be uniform in the main scanning direction as shown in FIG. It is necessary to calculate how much the light amount of the lamp has changed from the reading value of the platen roller 511 and correct it. Light distribution correction is one of the correction methods. The change in the light amount of the lamp is represented by the following equation.
[0034]
[Outside 1]

P ₀ (J) is data obtained by reading the platen roller 511 at the start of reading a plurality of documents (at the same time as reading the reference data for shading correction). On the other hand, P (j) is data obtained by reading the platen roller 511 immediately before reading each document (eg, between documents).
[0035]
Data obtained by reading the document is corrected in addition to shading correction so as to compensate for the change in the above equation. That is, shading correction is performed on read data of a document, and a correction coefficient of the following equation is multiplied for each pixel.
[0036]
[Outside 2]

By doing so, it is possible to maintain the uniformity of the density despite the change in the light amount of the lamp (FIG. 4D).
[0037]
As described above, in order to perform the light distribution correction, the reading value of the platen roller at the start of reading a plurality of documents and the reading value of the platen roller at the time of reading between documents are stored in the memory of the control unit for each pixel. Must be kept. For example, if the largest read document size is A3 at a resolution of 600 dpi, the number of pixels in the main scanning direction is
[Outside 3]

It becomes. Since the control unit does not store the values before and during reading, it must store information of at least 14000 pixels, and there is a problem that a very large amount of memory is required.
[0038]
Therefore, instead of storing the data of the entire platen roller in the main scanning direction, the main scanning direction is divided into several regions, and the data is stored on the assumption that the correction coefficient in that region changes linearly. A method of reducing the amount of information may be employed.
[0039]
5A, 5B, and 5C, the horizontal axis represents the main scanning direction, and the vertical axis represents changes in platen roller reading. FIG. 5A illustrates a change in platen roller reading for all pixels of the CCD in the main scanning direction. On the other hand, in FIG. 5B, the main scanning direction is divided into twelve areas, the change value of the platen roller reading is set at the boundary of the area, and the area is linearly approximated, and stored in the memory. The amount of data to be processed has been reduced.
[0040]
Assuming that this correction method is adopted, when the reading value of the platen roller at the start of reading a plurality of originals (at the same time as when the reference data for shading correction is read) is the reading area A in FIG. It is assumed that the read value is smaller than the read value of another portion in the main scanning direction. Although the reading value of the platen roller read between the originals is lower than the overall reading level but is uniform in the main scanning direction, in this case, P (j) is P ₀ (J), the correction amount is smaller in the reading area A in FIG. 6A than in other parts in the main scanning direction, and the image becomes dark near A in the main scanning direction. (FIG. 6 (b)). Conversely, when the reading value of the platen roller is larger than the others (FIG. 7A), the image becomes bright near A in the main scanning direction (FIG. 7B).
[0041]
In this way, if the contamination of the platen roller is read at the start of reading a plurality of originals (at the same time as the reading of the reference data for shading correction), the reference is shifted. It will affect everything.
[0042]
The same applies to the case where the platen roller is read at the start of reading a plurality of documents, the dirt is not read, and the dirt on the platen roller is read between the documents. It is assumed that when reading the stain on the platen roller between the originals, the read value is smaller than the read value of another portion in the main scanning direction (FIG. 8). At this time, P (j) becomes P ₀ (J) is corrected. Therefore, in the reading area B in FIG. 8A, the correction is performed more excessively than in other parts in the main scanning direction, and the image becomes bright near B in the main scanning direction (FIG. 8B). Conversely, when the reading value of the platen roller is larger than the others (FIG. 9A), the image becomes dark near B in the main scanning direction (FIG. 9B).
[0043]
If a stain on the platen roller is read between documents, only the image to be corrected using the data is affected.
[0044]
In summary, when light distribution correction is applied, if the stain on the platen roller is read before reading the original, all the images to be corrected thereafter become partially bright or dark, Affected. If the stain on the platen roller is read between documents, only the image to be corrected using the data is partially or brightly affected.
[0045]
Next, a correction method of the light amount fluctuation correction will be described with reference to FIGS. The correction of the light quantity deterioration due to the continuous lighting of the lamp is the same as the light distribution correction described above, but the method of correction is different.
[0046]
The details of the light amount fluctuation correction method will be described with reference to FIG. The dotted line (curve) in FIG. 5C indicates the read data of the platen roller, and the straight line indicates the averaged data in the read area data in the main scanning direction. Change in the main scanning direction due to deterioration of the light amount of the lamp When the change in the reading of the platen roller is small in the main scanning direction, the correction is performed on the assumption that the change in the main scanning direction is uniform. For example, as the data obtained by reading the platen roller, a description will be given using the data obtained by reading the platen roller in FIG.
[0047]
When performing the light quantity fluctuation correction, the correction coefficient of the light quantity fluctuation correction is expressed by the following equation.
[0048]
[Outside 4]

[0049]
With this correction coefficient, when the original is read and the image data is corrected, for example, even if one of the platen rollers reads a stain, the influence on the corrected image data is averaged. Reduced. In the above example of the correction coefficient, the influence of dirt is reduced to 1/12. The light amount fluctuation correction is still affected by dirt like the light distribution correction, but the influence is reduced by averaging the reading values of the platen roller. I can say. Here, the area in the main scanning direction is divided into 12, but the present invention is not limited to this.
[0050]
Based on the above, the relationship between the light distribution correction and the light amount fluctuation correction is complementary in that the image quality is better in the light distribution correction and the light amount fluctuation correction is better in the effect of contamination of the platen roller (FIG. 10). reference).
[0051]
A reading process showing the features of the present invention will be described with reference to FIG. This reading process is executed by a control unit (not shown) operating a predetermined program. When the start key of the operation unit is pressed by an operator or the like, a document reading process is started. First, the first mirror unit 504 is moved to a position where the shading correction plate can be read (below the shading correction plate), and reading of the shading correction plate is performed (S101). Then, reference data is created so that shading correction can be performed on the read image data. Subsequently, the first mirror unit 504 is moved to read the platen roller 511 (S102).
[0052]
Next, before reading the original, the platen roller is read, and a dirt detection process is performed based on the obtained read data, and it is determined whether the platen roller has dirt or the like (S103, S104). In order to improve the image quality of the read image data, it is desirable to use the above-described light distribution correction as a correction method as much as possible. However, light distribution correction is more susceptible to contamination of the platen roller than light amount fluctuation correction. In consideration of this point, a stain detection process is performed to check whether or not the platen roller is stained.
[0053]
If no stain on the platen roller is detected in S104, light distribution correction (first correction method) is selected. On the other hand, when detecting contamination of the platen roller, the influence is exerted on the images of all the originals to be read. Correction method). Since it is desirable to select light distribution correction as the correction method, if dirt is detected by the platen roller, dirt detection processing may be performed a predetermined number of times to search for the possibility of avoiding dirt. At this time, when reading the platen roller for the dirt detection processing, it is better to rotate the platen roller.
[0054]
Here, an example of the stain detection method processing will be introduced. Since the platen roller without contamination has a uniform density, the reading value of the platen roller becomes uniform in the main scanning direction. If the value of the reading level of the roller and its variation state are known in advance, it is determined that there is no contamination if the reading level is in a certain area (the area of 2ε in FIG. 12). In this case, it is determined that there is contamination (read area C in FIG. 12).
[0055]
More specifically, when the read value of the platen roller does not become uniform in the main scanning direction, if a change in adjacent read data exceeds a certain value, it is determined that there is dirt. Further, referring to FIG. 13 as an example, i is compared with i + 1 (i = 1... 11), and a stained portion is specified based on a portion where the difference is equal to or more than a predetermined value. In this example, since the difference between 6 and 7, and the difference between 7 and 8 are equal to or larger than a predetermined value, the portion 7 is determined to be dirty. Note that the dirt detection method introduced here is an example, and the present invention is not limited to this.
[0056]
When the light amount fluctuation correction is selected in S106, since the reference data obtained by reading the platen roller includes dirt, the light distribution correction cannot be performed when reading a subsequent successive document. In other words, the light amount fluctuation correction is performed until the reading of the document bundle is completed.
[0057]
When the light amount fluctuation correction (second correction method) is selected in S106, the light amount fluctuation correction is performed on the data obtained by reading the original (S121). Next, it is determined whether there is a document that has not been read (S122). If there is a document that has not been read, the platen roller is read to prepare for light amount fluctuation correction (S123). Actually, a light quantity fluctuation correction coefficient is obtained. If there are no unread originals in S122, the reading ends (S131).
[0058]
Before the document is read, the platen roller is read to perform the dirt detection process. If it is determined that there is no dirt, light distribution correction (first correction method) is selected as a correction method (S105). Then, the original is read, and light distribution correction is performed on the read data (S111). Next, it is determined whether there is a document that has not been read (S112). If there is a document that has not been read, the platen roller is read to prepare for light amount fluctuation correction (S113).
[0059]
Even if there is dirt on the platen roller read between the originals, the phenomenon that appears on the image is different from that when the platen roller is dirty before the original is read.However, this affects the image, You need to check for dirt. Based on the data read by the platen roller, it is determined whether there is any dirt (S114). As a result, as in step S104, if there is no dirt, there is no influence of the dirt, so that the correction method is selected such that the light distribution correction is selected, and if there is dirt, the light amount variation correction is selected to avoid the influence of the dirt. . Note that, similarly to the case where dirt is detected on the platen roller before reading the document, if dirt is detected, a retry operation of reading the platen roller may be performed again to search for the possibility of avoiding dirt. In this manner, the correction method is determined, the original is read (S111), and if there is an original, the platen roller is read to detect dirt, and the correction method is determined in accordance with the result. Is completed (S131).
[0060]
In the above-described embodiment, the correction method is determined by reading the platen roller each time the document is read.However, the correction method may be changed by reading the platen roller every predetermined number of sheets, and the timing is not limited. Absent.
[0061]
The actual contamination of the platen roller is very small, and when the platen roller is read, even if there is any contamination, it can be almost avoided by retrying at one place. And the image quality can be improved more than before.
[0062]
【The invention's effect】
As described above, according to the present invention, it is possible to detect the stain on the platen roller and appropriately switch the image correction method, thereby improving the image quality and suppressing the influence of the stain due to the image correction.
[Brief description of the drawings]
FIG. 1 is a diagram illustrating a configuration of an image reading apparatus.
FIG. 2 is a top view of an image reading unit.
FIG. 3 is a block diagram of an image processing unit.
FIG. 4 is a diagram showing an example of data read by a CCD.
FIG. 5 is a diagram showing an example of data read from a platen roller.
FIG. 6 is a diagram illustrating an example of data obtained by reading a stain on a platen roller before reading a plurality of originals and data after correction when original image data is corrected based on the data;
FIG. 7 is a diagram illustrating an example of data obtained by reading a stain on a platen roller before reading a plurality of originals and data after correction when original image data is corrected based on the data;
FIG. 8 is a diagram illustrating an example of data obtained by reading stains on a platen roller between originals and original data after correction of original image data based on the data;
FIG. 9 is a diagram illustrating an example of data obtained by reading stains on a platen roller between originals and original data after correction of original image data based on the data;
FIG. 10 is a table comparing light distribution correction and light amount fluctuation correction.
FIG. 11 is a flowchart showing a reading process according to the embodiment of the present invention.
FIG. 12 is a diagram showing a process for detecting contamination of the platen roller.
FIG. 13 is a diagram showing a process for detecting contamination of the platen roller.
[Explanation of symbols]
500 Image reading device
501 Document transport unit
502 Image reading unit
503 First mirror unit
504 Second mirror unit
505 manuscript
506 lens
507 CCD
508 Document Placement Table
509 Output tray
510 Shading correction plate
511 Platen roller
512 glass stand
513 glass stand
524 light
600 Image processing unit
620 amplifier
621 A / D converter
622 Shading correction unit
623 Soil detector
625 First Correction Unit (Light Distribution Correction Unit)
626 Second correction unit (light amount fluctuation correction unit)

Claims (12)

A transport unit that transports the original to a reading position; a reading unit that reads the original transported by the transport unit; and an image reading method that includes a plurality of correction units that correct image data of the original read by the reading unit.
A detection step of detecting a stain on the density reference member by reading the density reference member at the reading position by the reading unit before reading the document by the reading unit;
An image reading method, comprising: a selection step of selecting one correction unit from the plurality of correction units according to a detection result of the detection step. The selecting step includes selecting the second correction unit when detecting the contamination of the density reference member in the detection step, and selecting the second correction unit when detecting no contamination of the concentration reference member in the detection step. 2. The image reading method according to claim 1, wherein the first correction unit is selected. A first correction unit that obtains a correction value for each pixel of the reading unit from data read from the density reference member, and corrects image data of a document read by the reading unit based on the correction value; Correction means, and a second correction means for obtaining an average value from data read from the density reference member, and correcting the image data of the document read by the reading means based on the average value. 3. The image reading method according to claim 2, wherein: 3. The image reading method according to claim 2, wherein the detecting step performs a process of detecting a stain on the density reference member a predetermined number of times. Conveying means for conveying the original to the reading position;
Reading means for reading the original conveyed by the conveying means,
A first density reference member disposed outside a reading area for reading a document,
A second density reference member disposed at the reading position;
A plurality of correction means for correcting the image data of the document read by the reading means,
Detecting means for detecting dirt on the second density reference member by reading the second density reference member at the reading position with the reading means before reading the document with the reading means;
An image reading apparatus comprising: a selection unit that selects one correction unit from the plurality of correction units in accordance with a detection result of the detection unit. The selection means selects the second correction means when the detection means detects contamination of the second density reference member, and detects the contamination of the second density reference member by the detection means. 6. The image reading apparatus according to claim 5, wherein the first correction unit is selected when the correction is not performed. The plurality of correction units determine a correction value for each pixel of the reading unit from data read from the second density reference member, and corrects image data of a document read by the reading unit based on the correction values. First correcting means for calculating an average value from data read from the second density reference member, and correcting the image data of the document read by the reading means based on the average value. 7. The image reading device according to claim 6, comprising: The image reading apparatus according to claim 6, wherein the detection unit executes a process of detecting dirt on the second density reference member a predetermined number of times. Conveying means for conveying the original to the reading position;
Reading means for reading the original conveyed by the conveying means,
A density reference member disposed at the reading position;
A plurality of correction means for correcting the image data of the document read by the reading means,
Detecting means for detecting dirt on the density reference member by reading the density reference member at the reading position with the reading means before reading the document with the reading means;
An image reading apparatus comprising: a selection unit that selects one correction unit from the plurality of correction units in accordance with a detection result of the detection unit. The selection unit selects the second correction unit when the detection unit detects the contamination of the density reference member, and selects the second correction unit when the detection unit does not detect the contamination of the concentration reference member. 10. The image reading apparatus according to claim 9, wherein the first correction unit is selected. A first correction unit that obtains a correction value for each pixel of the reading unit from data read from the density reference member, and corrects image data of a document read by the reading unit based on the correction value; Correction means, and a second correction means for obtaining an average value from data read from the density reference member, and correcting the image data of the document read by the reading means based on the average value. The image reading device according to claim 10, wherein: The image reading apparatus according to claim 10, wherein the detection unit executes a process of detecting contamination of the density reference member a predetermined number of times.

Images