JP3938283B2 - Image processing apparatus, image reading apparatus, image forming apparatus, and image processing method - Google Patents

Description

【００２８】
データライン入れ替え回路の動作を制御する上記した制御信号生成回路による動作を以下に示す。
上記したように、データライン入れ替え回路は、Ａ／Ｄ変換により起きる擬似輪郭の発生の抑制を図るので、原稿画像データに対して有効に働くことになるが、ゲイン調整やシェーディング補正等の各種の調整を行うために読み取られるデータに対しては、画像データへノイズを重畳する必要がなく、読み取ったデータを加工せずにそのまま用いる方が良い。
従って、データライン入れ替え回路を動作させる場合を原稿画像データのみに限るようにして、原稿画像以外の基準白板を読み取る場合に入れ替え動作をさせずに、通常の動作を行うようにする。
図５及び図６は、制御信号生成回路の制御動作を説明するタイミングチャートであり、図５は擬似輪郭を抑制するモードONにおける動作を示し、図６は、同モードOFFにおける動作を示す。
擬似輪郭を抑制するモードONの場合、図５に示されるように、外部からのスイッチ等の設定で、Change_enがLowになる。XSSCANは、スキャナ部３が原稿領域外に配置された基準白板を読み取るときにHighに、また原稿を読み取るときにLowなる。したがって、ＮＯＲ回路４５の出力は、スキャナ部３が基準白板を読み取っているときはLowに、原稿を読み取るときはHighになる。よって、データライン入れ替え回路（図３）は、バッファＩＣ（２）４２のイネーブル信号がLow、バッファＩＣ（３）４３のイネーブル信号がHighとなり、バッファＩＣ（３）４３はHighインピーダンス状態となり、バッファ動作を行なわず、バッファＩＣ（２）４２がバッファ動作を行い、このときは通常モードで動作する。また原稿を読み取るときには、各バッファＩＣのイネーブル信号が通常モード時のイネーブル信号のLow、Highをそれぞれ逆にするので、通常モードからデータの入れ替えモードの動作に変わる。
他方、擬似輪郭を抑制するモードOFF場合、図６に示されるように、外部からのスイッチ等の設定で、Change_enがHighになるので、XSSCANのいかんに係わらず、ＮＯＲ回路４５の出力は常にLowであるから、バッファＩＣ（２）４２のイネーブル端子には常にLowレベルの信号が入力され、バッファＩＣ（３）４３のイネーブル端子には常にHighレベルの信号が入力される。その結果、バッファＩＣ（３）４３はHighインピーダンス状態となり、バッファ動作を行なわず、バッファＩＣ（２）４２がバッファ動作を行う。したがって、通常モードで動作する。
このように、ゲイン調整やシェーディング補正を行うために、基準白板を読み取る場合には、［表１］の状態２，３，４のいずれかの状態をつくり、ノイズ重畳機能であるデータラインの入れ替え機能を働かせる必要がないので、入れ替えを行わずに、画像データ読み取り時にのみノイズ重畳機能であるデータラインの入れ替えを行うことを可能とする。
【００２９】
「ゲイン調整、地肌除去、シェーディング処理部３７における各処理」
上記した動作を行った後にノイズ重畳処理部３５から出力される画像データを用いてゲイン調整、地肌除去、シェーディングデータ生成およびシェーディング処理を行う。
基準白板読み取り時には、ノイズを重畳していないデータをメモリ部３６に保存する。保存したデータに関して着目画素およびその周囲のｍ×ｍのエリアのデータを用いて、平均化処理を行う。
図５はラインメモリを利用して読み取り画像データを操作することにより行われる基準白板読み取りデータの平均化処理を説明するための概念図である。
図５を参照して、以下に平均化処理操作に関し説明すると、まず、基準白板データが保存されているメモリの２ライン目の２画素目（図５に“処理中心着目画素ｉ”として示す）に着目し、その画素からｍ×ｍエリアでの平均化処理を行い処理後のデータを後段のシェーディングデータ生成ブロック（図６参照）へ転送していく。ただし、基準白板データの平均化処理では、１画素目と最終画素、１ライン目、最終ラインのデータに関しては処理を行わずに１画素目は２画素目と同一のデータ、最終画素は最終画素−１番目と同一のデータを用いる。
次に、シェーディングデータを生成する。
図６は、上記で得たエリアでの基準白板データの平均化処理後のデータを操作することにより行われるシェーディングデータ等の生成過程を説明するための概念図である。同図にしめすように、エリアでの基準白板データの平均化処理後のデータが保存されているメモリの複数ラインの平均化した白板データを今度は副走査方向に各画素毎に平均化処理を行い、画素毎のシェーディングデータを生成し、また画素毎のシェーディングデータに基づいてピーク値を検出する。
【００３０】
基準白板読み取り時に行う基準白板データの平均化処理及びシェーディングデータ生成処理の詳細を以下に説明する。
基準白板データの平均化処理は、処理中心着目画素ｉに対して３画素×３画素エリアとして、周囲画素のデータを用いた場合、次式により表せる。
【００３１】
【数１】

【００３２】
上記式（３）において、data_av (i）が平均化処理を行った後の画像データ、data_mem(i,j)が基準白板データを保存しているメモリでのデジタル画像データ、w(k,l)がノイズ除去のための重み、Kは係数である。
重みw(k,l)は、ノイズ除去の平均化処理の一つとして単純平均化処理を行う場合、次の行列（１）の重み行列を用いる。この時、K=1/9となる。
【００３３】
【数２】

【００３４】
行列（１）の場合、画像のエッジ部分の情報も損なわれるため、各画素に重み付けを行いエッジ部分の情報の損失を少なくする局所平均加重平均処理を行う場合、次の行列（２）の重み行列を用いる。この時、K=1となる。
【００３５】
【数３】

【００３６】
このようにノイズ除去のための重み行列と係数を変更することでノイズ除去の特性を変更することが可能となる。
【００３７】
上記のように平均化処理を行った基準白板データを基にして、シェーディングデータを作成するために副走査方向に平均化処理を行いシェーディングデータ：data_sh(i)を次式により生成する。
data_sh(i)＝Σdata_av (i）／N_sh・・・式（４）
N_sh：シェーディングデータ生成に用いたライン数
生成したシェーディングデータdata_sh(i)を用いてゲイン調整およびシェーディング処理を行う。
ゲイン調整値は、生成したシェーディングデータdata_sh(i)からピーク値：Data_Pを検出し、検出したピーク値Data_Pと予め定められた所定値を持つ出力白レベル目標値とからゲイン調整でのゲイン値：GAINを次式により決定する。
GAIN＝（目標白レベル）／Data_P・・・式（５）
決定したゲイン値GAINとシェーディングデータdata_sh(i)とからノイズ入れ替え機能によりノイズを重畳したデータにたいしてゲイン調整とシェーディング処理を行う。
【００３８】
ゲイン調整とシェーディング処理は、上述の通りの順序で処理がなされてきたので、式（２）に示される黒レベル調整後の画像データ：Data_b(i)に対してノイズ重畳を行ったデータData_n(i)に対して次式に従う処理を行い、次段の画像処理部へデータData_out(i)として次式により出力されることになる。
Data_out(i) ＝ Data_ｎ(i)×GAIN×｛Data_P/Data_sh(i)｝・・・式（６）
上記のように、ゲイン調整処理部とシェーディング処理部をノイズ重畳処理部３５の後段に設けたことにより、ノイズ重畳処理部３５によりノイズが重畳されて画像データの疑似輪郭の発生を抑制したデータに対してゲイン調整およびシェーディング処理を行うことになるので、抑制処理をしないデータに対してゲイン調整およびシェーディング処理を行うと、疑似輪郭の発生を助長することがある従来の問題点（［従来の技術］の項、参照）を解決することが可能となる。
【００３９】
上記では、地肌除去処理を行わない場合の画像データData_out(i)を出力するまでの処理を示したが、次に、地肌除去処理を行う場合の処理を以下に説明する。
地肌除去処理を行う場合は、上記したData_out(i)を出力するまでの処理を行って式（６）により得たデータを基準白板読取データを保存する際に使用したメモリ部３６に保存する。一方、地肌を読み取ることが可能な原稿部分について、シェーディングデータ生成及びゲイン調整時に行った上記の処理と同様に読み取り画像データのエリアでの平均化処理、副走査方向の平均化処理、ピーク検出処理を行い、地肌レベルのピーク値を検出する（図５、図６参照）。検出した地肌ピーク値Data_P_AEと予め定められた所定値を持つ地肌除去処理時の出力目標値をもとに求められる地肌除去係数値：地肌除去目標出力値/Data_P_AEを用いると地肌除去を行うことができる。地肌除去後のデータData_out'(i)は次式により出力されることになる。
Data_out'(i) ＝ Data_n(i)×GAIN×｛Data_P／Data_sh(i)｝×｛地肌除去目標出力値／Data_P_AE｝・・・式（７）
上記のようにして次段の画像処理部へ出力される地肌除去後のデータData_out'(i)は、地肌除去を行わない先の例と同様に、式（７）に示すように、もとの読取データに対し何らかの係数を乗じていく形となっている。このためにＡ／Ｄ変換時に生じたアナログデータとの差が広がり、Ａ／Ｄ変換時に生じた擬似輪郭を強調する可能性があるが、本実施例では、Ａ／Ｄ変換後のデータに対し、ノイズ成分を重畳し擬似輪郭の発生を抑制し、地肌除去の係数を乗じる処理をノイズ重畳処理の後段で行うようにしたので、疑似輪郭の発生を助長することがない。
【００４０】
【発明の効果】
（１） 請求項１の発明に対応する効果
Ａ／Ｄ変換手段により変換された（Ｎ＋ｎ）ビット階調のデジタル画像データを入力とし、該データのＭＳＢから（Ｎ）ビット目のデータを高周波ノイズ成分を含むＬＳＢのデータに入れ替えたデジタル画像データの上位（Ｎ）ビットを出力するデータ入れ替え手段を設けたことにより、Ａ／Ｄ変換の過程で起こりうる疑似輪郭の発生を簡単に抑制することができ、高画質の画像データの提供を可能にし、回路の大規模化及び複雑化を招くことのない回路設計を可能とする。
（２） 請求項２の発明に対応する効果
上記（１）の効果に加え、データに対し係数を乗じていく形をとるためにＡ／Ｄ変換時に生じた擬似輪郭を強調する可能性があるゲイン調整手段をデータ入れ替え手段の後段に設けるようにしたことにより、疑似輪郭の発生を助長することがなく、所期の抑制効果を発揮することが可能となる。
（３） 請求項３の発明に対応する効果
上記（１）、（２）の効果に加え、データ入れ替え手段の作動／不作動を制御する手段を備えたことにより、データの入れ替えの必要がないデータにも対応でき、装置のパフォーマンスを向上させることが可能となる。
（４） 請求項４の発明に対応する効果
請求項１〜３記載の画像処理装置を備えた画像形成装置おいて上記（１）〜（３）の効果を実現することにより、画像形成装置の性能を向上させることが可能となる。
【００４１】
（５） 請求項５の発明に対応する効果
イメージセンサ出力信号のアナログ処理手段から出力されるアナログ画像データをＡ／Ｄ変換手段により（Ｎ＋ｎ）ビット階調のデジタル画像データに変換し、該デジタル画像データのＭＳＢから（Ｎ）ビット目のデータを高周波ノイズ成分を含むＬＳＢのデータに入れ替えたデジタル画像データの上位（Ｎ）ビットを出力するデータ入れ替え手段を設けたことにより、Ａ／Ｄ変換の過程で起こりうる疑似輪郭の発生を簡単に抑制することができ、イメージセンサで読み取った画像データを高画質のデジタルデータとして提供することを可能にし、回路の大規模化及び複雑化を招くことのない回路設計を可能とする。
（６） 請求項６，７の発明に対応する効果
上記（５）の効果に加え、データに対し係数を乗じていく形をとるためにＡ／Ｄ変換時に生じた擬似輪郭を強調する可能性がある、白レベル調整、地肌除去、シェーディング処理といった処理を含むゲイン調整処理をデータ入れ替え処理の後に行うようにしたことにより、疑似輪郭の発生を助長することがなく、所期の抑制効果を発揮することが可能となる。
（７） 請求項８の発明に対応する効果
上記（５）、（６）の効果に加え、データ入れ替え手段の作動／不作動を制御する手段を備えたことにより、データの入れ替えの必要がないデータの読み取りにも対応でき、装置のパフォーマンスを向上させることが可能となる。
（８） 請求項９の発明に対応する効果
上記（７）の効果に加え、原稿画像読み取り時にデータ入れ替え手段を作動させ、シェーディングデータ読み取り時に不作動とする制御動作を行う手段を備えたことにより、それぞれの読み取りに最適なモードで読み取りデータの処理が可能となり、装置のパフォーマンスを向上させることができる。
（９） 請求項１０の発明に対応する効果
請求項５〜９記載の画像読み取り装置を備えた複写機、ファクシミリ等の画像形成装置おいて上記（５）〜（８）の効果を実現することにより、該画像形成装置の性能を向上させることが可能となる。
【００４２】
（１０） 請求項１１の発明に対応する効果
Ａ／Ｄ変換処理により変換された（Ｎ＋ｎ）ビット階調のデジタル画像データを入力とし、該データのＭＳＢから（Ｎ）ビット目のデータをＬＳＢのデータに入れ替えたデジタル画像データの上位（Ｎ）ビットを出力するデータ入れ替え処理を行うことにより、Ａ／Ｄ変換の過程で起こりうる疑似輪郭の発生を簡単かつ低コストに抑制することができ、高画質の画像データを提供することが可能となる。
（１１） 請求項１２の発明に対応する効果
イメージセンサ出力信号をアナログ処理し、出力されるアナログ画像データをＡ／Ｄ変換する処理の過程で上記（１０）の効果を実現することにより、イメージセンサで読み取った画像データを高画質のデジタルデータとして出力することが可能となる。
（１２） 請求項１３，１４の発明に対応する効果
上記（１０）、（１１）の効果に加え、データに対し係数を乗じていく形をとるためにＡ／Ｄ変換時に生じた擬似輪郭を強調する可能性がある、白レベル調整、地肌除去、シェーディング処理といった処理を含むゲイン調整処理をデータ入れ替え処理の後に行うようにしたことにより、疑似輪郭の発生を助長することがなく、所期の抑制効果を発揮することが可能となる。
（１３） 請求項１５の発明に対応する効果
上記（１１）、（１２）の効果に加え、原稿画像読み取り時にデータの入れ替えを行い、シェーディングデータ読み取り時にデータの入れ替えを行わないように動作を制御することにより、それぞれの読み取りに最適なモードで読み取りデータの処理が可能となり、イメージセンサで読み取った画像データをデジタル出力する処理のパフォーマンスを向上させることができる。
【図面の簡単な説明】
【図１】 本発明の実施例に係わるＤＰＰＣの全体構成を概略図として示す。
【図２】 ＤＰＰＣの制御部における読み取り画像データ処理に関わる回路部の概要をブロック図にて示す。
【図３】 読み取り画像データ処理回路（図２）におけるデータライン入れ替え回路を示す。
【図４】 データライン入れ替え回路（図３）の動作を制御する制御信号生成回路の１例を示す。
【図５】 擬似輪郭を抑制するモードONにおける制御信号生成回路の制御動作を説明するタイミングチャートである。
【図６】 擬似輪郭を抑制するモードOFFおける制御信号生成回路の制御動作を説明するタイミングチャートである。
【図７】 基準白板読み取りデータの平均化処理を説明するための概念図である。
【図８】 基準白板平均化データからシェーディングデータ等を生成する過程を説明するための概念図である。
【図９】 アナログ画像信号の量子化により起きる擬似輪郭の発生原理を説明する図である。
【符号の説明】
１…ＤＰＰＣ（デジタル複写機）、 ３…スキャナ部、
５…ＡＤＦ（Automatic Document Feeder)ユニット、
４…プリンタ部、 ６…コンタクトガラス、
７…制御部、 １０…ＣＣＤイメージセンサ、
１１…感光ドラム、 １４…光書き込み部、
３２ｅ，３２ｏ…Ａ／Ｄ変換器、 ３３…デジタル信号補正部、
３４…オフセット除去処理部、 ３５…ノイズ重畳処理部、
３７…ゲイン調整処理、地肌除去処理、シェーディング処理部、
４１…バッファＩＣ（１）、 ４２…バッファＩＣ（２）、
４３…バッファＩＣ（３）、 ４４…インバータ、
４５…ＮＯＲ回路。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to image data processing that can be applied to a digital copying machine or the like that digitally processes an image read from a document and forms an image based on the digital data. More specifically, the present invention occurs with A / D conversion. The present invention relates to a process for suppressing generation of pseudo contours.
[0002]
[Prior art]
In the currently popular digital copying machine, the image data of the original read by the image sensor is digitally converted using an A / D converter, and the converted digital data is subjected to digital processing such as shading processing. The processed digital image data is sent to the image forming unit for use in image formation, or stored in a storage means for later use, and is also used for enlargement / reduction, aggregation / division image processing, etc. Realizes functions unique to data.
A problem that occurs in such an image processing apparatus that involves A / D conversion is the generation of pseudo contours caused by quantization of image data. This is because when the analog output value of an image sensor that reads an image is processed by an A / D converter, the converted digital image data becomes a discrete value corresponding to the number of gradations of the A / D converter. The change is at least 1 digit step. FIG. 9 shows this state. Referring to FIG. 9, when the analog image data of the image sensor output shown in (A) is A / D converted, the converted digital image data has discrete values that change in steps of 1 digit as shown in (B). That is, analog data that is a continuous amount concentrates on a specific level of digital data that is a discrete value. Further, if the digital data is corrected by digital operations such as gain calculation and rounding, the gradation level may be further concentrated on a specific level. That is, when coefficient multiplication in gain calculation and rounding in digital calculation are performed, the density change of image data becomes a density change in steps of (1 × α) digits or more as shown in FIG. If α is larger, the density change step becomes larger accordingly.
For example, this has a large effect on image data whose density change changes gently in a photographic image or the like, and the digital image data after gain calculation has a large width and a density change of (1 × α) digit or more. There is a possibility that a step changes in a stepped manner and a pseudo contour is generated.
[0003]
[Problems to be solved by the invention]
By the way, with respect to the generation of pseudo contours, a 1-bit random number generator is conventionally installed for data that has been concentrated at a specific level during conversion to digital data, and the noise component from the random number generator is included in the data. In order to prevent the occurrence of data concentration on a specific level by superimposing, it has been proposed to suppress the occurrence thereof.
However, in the above-described method, a 1-bit random number generator is specially installed in order to generate noise, thereby increasing the scale and complexity of the circuit and increasing the cost.
The present invention has been made in view of the above-described problems in the prior art that have been taken in order to suppress the occurrence of pseudo contours that occur when analog image data is A / D converted. Image processing apparatus, image reading apparatus (scanner, etc.), image forming apparatus (copier, facsimile, etc.) that can suppress the occurrence of pseudo contours using simple means that do not cause an increase in scale and complexity And an image processing method capable of suppressing the generation of pseudo contours by a simple method without causing an increase in the scale and complexity of a circuit.
[0004]
[Means for Solving the Problems]
According to the first aspect of the present invention, in the image processing apparatus having at least A / D conversion means for converting analog image data into digital image data, the A / D conversion means converts the analog image data into digital of (N + n) bit gradation. (N + n) bit gradation digital image data converted by the A / D conversion means, and the (N) bit data from the MSB to LSB data. An image processing apparatus comprising data replacement means for outputting upper (N) bits of replaced digital image data.
[0005]
According to a second aspect of the present invention, in the image processing apparatus according to the first aspect of the present invention, the image processing apparatus further comprises means for adjusting a gain to adjust the image data to a predetermined reference value, and the gain adjusting means is provided after the data exchanging means. It is characterized in that it is provided.
[0006]
According to a third aspect of the present invention, in the image processing apparatus according to the first or second aspect, the image processing apparatus further comprises means for controlling operation / non-operation of the data exchange means.
[0007]
According to a fourth aspect of the present invention, there is provided an image forming apparatus comprising the image processing apparatus according to any one of the first to third aspects.
[0008]
The invention of claim 5 includes at least an image sensor, analog processing means for analog processing of an output signal of the image sensor and outputting analog image data, and A / D conversion means for converting the analog image data into digital image data. In the image reading apparatus, the A / D conversion means is means for converting analog image data into digital image data of (N + n) bit gradation, and the (N + n) bit gradation converted by the A / D conversion means. The digital image data is input, and data replacement means for outputting the upper (N) bits of the digital data obtained by replacing the (N) bit data from the MSB of the data with the LSB data is provided. An image reading apparatus.
[0009]
According to a sixth aspect of the present invention, in the image reading apparatus according to the fifth aspect, the image reading apparatus further comprises means for adjusting a gain to adjust the image data to a predetermined reference value, and the gain adjusting means is provided at a subsequent stage of the data replacing means. It is characterized in that it is provided.
[0010]
According to a seventh aspect of the present invention, in the image reading apparatus according to the sixth aspect, the gain adjusting means includes at least one of white level adjustment, background removal, and shading processing.
[0011]
According to an eighth aspect of the present invention, in the image reading apparatus according to any one of the fifth to seventh aspects, a means for controlling the operation / non-operation of the data exchange means is provided.
[0012]
According to a ninth aspect of the present invention, in the image reading apparatus according to the eighth aspect, the means for controlling the operation / non-operation of the data exchanging means operates the data exchanging means at the time of reading the original image and is not effective at the time of reading shading data. It is characterized by performing a control operation to be activated.
[0013]
A tenth aspect of the invention includes the image reading device according to any one of the fifth to ninth aspects, and means for forming an image based on image data output from the image reading device. An image forming apparatus.
[0014]
According to an eleventh aspect of the present invention, in the image processing method including at least a conversion process step of converting analog image data into digital image data, the A / D conversion step converts the analog image data into digital image data of (N + n) bit gradation. This is a step of conversion, and data exchange for outputting the upper (N) bits of the digital image data obtained by replacing the (N) -th bit data with the LSB data from the MSB of the converted (N + n) -bit gradation digital image data An image processing method characterized in that a process is provided.
[0015]
According to a twelfth aspect of the present invention, in the image processing method according to the eleventh aspect, an analog processing is performed on the output signal of the image sensor before the conversion processing step.
[0016]
According to a thirteenth aspect of the present invention, in the image processing method according to the eleventh or twelfth aspect of the present invention, a gain adjustment step for adjusting the image data to a predetermined reference value is provided, and the gain adjustment step is the data replacement step. It is a method characterized by being performed after.
[0017]
According to a fourteenth aspect of the present invention, in the image processing method according to the thirteenth aspect, the gain adjustment step is a step for performing at least one of white level adjustment, background removal, and shading processing. Is the method.
[0018]
A fifteenth aspect of the present invention is the image processing method according to any one of the twelfth to fourteenth aspects, further comprising a step of controlling operation / non-operation of the data replacement step, and data is read at the time of reading a document image by the control step. This is a method characterized in that the data is not replaced when the shading data is read.
[0019]
DETAILED DESCRIPTION OF THE INVENTION
The present invention will be described based on the following examples shown with the accompanying drawings. The following embodiment shows an application example to a DPPC (Digital Plane Paper Copy-machine, so-called digital copying machine) as an image forming apparatus having an image processing apparatus and an image reading apparatus.
FIG. 1 is a schematic diagram showing the overall configuration of a DPPC according to an embodiment of the present invention.
The configuration of the DPPC of this embodiment will be described with reference to FIG. 1. The apparatus main body 2 of the DPPC 1 includes a scanner unit 3 as an image reading unit and a printer unit 4 as an image printing unit. An ADF (Automatic Document Feeder) unit 5 which is a document feeding mechanism is connected.
The scanner unit 3 includes a contact glass 6 on which a document is placed. A first traveling mirror 8 that deflects an optical path at a right angle is provided at a position facing the document surface with the contact glass 6 interposed therebetween. A second traveling mirror 9 that reverses the reflected light path from the traveling mirror 8 is provided. Further, a CCD (Charge Coupled Device) sensor 10 as an image sensor for photoelectrically converting image data via an imaging lens is installed on the reflected light path from the second traveling mirror 9. The scanner unit 3 reads a reference white plate (not shown) in addition to the original. The read reference white plate data is used for white level adjustment of the read image data and generation of shading data.
[0020]
The image data read by the CCD sensor 10 is input to a control unit 7 which is a processing means for image data. The control unit 7 performs digital processing such as A / D conversion on the input image data, and outputs a laser beam output device ( The optical output of a laser diode (LD) or the like is modulated by image data) and output to an optical writing unit 14 having a polygon mirror.
The printer unit 4 includes a photosensitive drum 11. A toner cleaner 12, a charger 13, a developing device 15, and a transfer device 16 are sequentially arranged on the outer periphery of the photosensitive drum 11 so as to face the drum surface.
The photosensitive drum 11 provided in the printer unit 4 is charged by the charger 13, and the charged photosensitive drum 11 is irradiated with laser light for carrying image information from the writing unit 14, thereby forming an electrostatic latent image on the surface of the photosensitive drum 11. To do.
The developing device 15 stores toner, and attaches the toner to the surface of the photosensitive drum 11 on which the electrostatic latent image is formed, thereby revealing the electrostatic latent image as a toner image.
The paper feed unit is provided with a paper transport mechanism for sequentially transporting printing paper from the two types of cassettes, a large capacity paper cassette 19 and a cassette 17 for storing small-capacity paper of different sizes, to the paper discharge tray 18, respectively. 20 communicates with the gap between the photosensitive drum 11 and the transfer device 16 and the inside of the fixing device 21.
In the transfer device 16, the toner image formed on the photosensitive drum 11 is transferred to the printing paper conveyed by the paper conveyance mechanism.
The printing paper on which the toner image is transferred is conveyed to the fixing device 21 by the paper conveying mechanism, the toner image is fixed on the printing paper, and the printing paper on which the image data is printed is discharged to the paper discharge tray 18.
An operation panel (not shown) is provided on the upper surface of the apparatus body 2, and the operation panel has a function of displaying various data and a function of inputting various data.
[0021]
Here, the circuit configuration and operation will be described focusing on the correction processing applied to the read image data in the image data processing section of the control section 7 of the DPPC (FIG. 1).
FIG. 2 is a block diagram showing an outline of a processing circuit unit related to read image data processing of the control unit 7. Here, an image processing portion from A / D conversion of an analog image signal read by the CCD image sensor 10 until digital correction processing is performed on the converted digital data is shown.
An object of the present invention is to suppress the generation of pseudo contours (refer to the section of [Prior Art]) that occurs when analog image data is converted into digital data.
In response to this problem, noise components are superimposed on the image data that has been converted to digital data, thereby preventing concentration on a specific level of digital data and suppressing the occurrence of pseudo contours. In the present invention, when a noise component is superimposed, a high-frequency randomness caused by flickering of the original illumination light included in the LSB of the image data is not used without using a special method of installing a 1-bit random number generator as in the prior art. This problem is solved by using noise.
For this purpose, in this embodiment, analog image data is converted into digital image data of (N + n) -bit gradation, and the (N) -th bit from the MSB of the converted digital image data of (N + n) -bit gradation. Data replacement means for outputting the upper (N) bits of the digital data in which the data is replaced with the LSB data is provided, whereby the high frequency included in the LSB data of the (N + n) -bit gradation digital image data. The random noise is used as the lowest data of the image data output from the data switching means, and the generation of pseudo contours is suppressed.
[0022]
Referring to the circuit of the embodiment shown in FIG. 2, the analog image signal read from the original by the CCD image sensor 10 is first amplified by the fixed gain amplifiers 31e and 31o. Here, the output of the CCD is a two-signal system of even pixels and odd pixels, but it may be one system or four systems. When applying to a plurality of systems, it is desirable to apply the subsequent processing for each system.
The analog signals amplified by the fixed gain amplifiers 31e and 31o are converted into digital data by the A / D converters (A / DC) 32e and 32o. Here, as described above, the digital signals are corrected and finally output. When the data is (N) bit, A / D conversion is performed to digital data of (N + n) bit gradation.
Digital image data that is converted from an analog image signal and output is input to the digital signal correction unit 33 and subjected to various corrections. Here, after the black level adjustment processing is performed by the offset removal processing unit 34, the data is input to the noise superimposition processing unit 35 that replaces the data lines for noise superposition, and the data is replaced.
After that, the image data that is exchanged and output as (N) bit grayscale data passes through the memory 36 or directly to the processing unit 37 that performs each process of gain adjustment, background removal, and shading. After being input and processed, it is output to the subsequent image processing portion.
[0023]
Next, the processing of the image data in the digital signal correction unit 33 shown in FIG. 2 will be described in detail step by step.
“Black level adjustment processing in the offset removal processing unit 34”
A black level is detected from data in an OPB (OPtical Black) area in an invalid pixel area in one main scanning line of an image signal converted into (N + n) bit gradation digital data by the A / D converters 32e and 32o. . In this detection, an average value for several pixels in the above-described OPB portion is calculated, and this is set as the black level of the image data.
Black = (Σdata_opt) / N_opt (1)
Black: Black level of image data
data_opt: OPB area image data
N_opt: Number of pixels in the OPB area used for calculation
The black level is adjusted by subtracting the black level obtained from the above equation (1) from each image data.
Data_b (n) = Data_in (n) −Black (2)
Data_b (n): Data after black level adjustment
Data_in (n): A / D converter output data
[0024]
“Data Line Replacement Processing in Noise Superimposition Processing Unit 35”
FIG. 3 illustrates a data line replacement circuit.
A data line switching circuit is configured by using three buffer ICs (4 elements / 1 circuit) (1), (2), and (3) with an enable function. When a high level signal is input to the enable terminals of these buffer ICs, the output of the circuit is in a high impedance state and no buffer operation is performed. When a low level signal is input to the enable terminal, the circuit performs a normal buffer operation.
In this example, the digital image data of (N + n) bit gradation after black level adjustment is 8 bits, the upper 4 bits are input to the buffer IC (1) 41, the lower 4 bits are buffer IC (2) 42, and the buffer IC (3) 43, the data exchange mode and the normal mode are performed.
In the normal mode, the upper 2 bits of the input lower 4 bits are output by the buffer operation of the buffer IC (2) 42. In the data replacement mode, the input lower order by the buffer operation of the buffer IC (3) 43 The LSB in 4 bits is replaced and output. For this purpose, the input of the data line is the normal combination of the buffer IC (2) 42, while the input to the buffer IC (3) 43 is replaced with the LSB. This will be described with reference to the example of FIG. 3. As shown in the figure, using a buffer IC having a circuit having an enable function for every four elements, the 6th bit (Data 2) and the LSB of the upper 8 bits of the digital data of the 8 bit gradation data are used. The data is replaced with (Data0), and 6-bit gradation data (Data7, Data6, Data5, Data4, Data3 ′, Data2 ′) is output. In this case, the upper 4 bits of the 8 bit gradation data are buffer IC (1) 41, the buffer IC (2) 42 that buffers the lower 4 bits of the 8 bit gradation data without replacing them, and the upper 5 bits of the 8 bit gradation data. (Data2) and LSB (Data0) of 8-bit grayscale data are replaced to buffer the buffer IC (3) 43, and control signals are sent to the enable terminals of the buffer IC (2) 42 and the buffer IC (3) 43. By using it, it is possible to select whether or not to replace data, that is, normal / replacement operation. Since either the buffer IC (2) 42 or the buffer IC (3) 43 is selected and operated, an inverter 44 for inverting the control signal input to one enable terminal is provided.
[0025]
FIG. 4 shows an example of a control signal generation circuit that controls the operation of the data line switching circuit (FIG. 3).
In this embodiment, a gate control signal: XSSCAN indicating an image reading signal section and a switch signal: Change_en signal input from the outside as an ON / OFF signal of a switching function are used as a control signal, thereby generating a timing control signal. This operation control can be performed in a mode in which the replacement function set by a simple circuit configuration is operated without requiring the gate array.
In the circuit of FIG. 4, the Change_en signal and the gate signal of the image reading section: XSSCAN are input to the NOR circuit 45 and the output is used as a control signal and input to the enable terminals of the buffer IC (2) 42 and the buffer IC (3) 43. Thus, a data line replacement function and its timing control function are realized with a simple circuit configuration. Since any one of the buffer ICs is selected and operated, an inverter 44 for inverting the control signal input to one enable terminal is provided.
[0026]
When the operation of the data line switching circuit is controlled by the control signal generation circuit (FIG. 4), the switching function is turned ON / OFF according to the state of the input control signal Change_en and XSSCAN as shown in [Table 1] below. Take. As shown in the table, XSSCAN is Low when asserted (in the image area), High when negated, and Change_en is set by an external switch or the like, and here it is Low when the replacement function is set. As shown in [Table 1], a mode for suppressing pseudo contours is set by an external switch (Change_en = Low), that is, the replacement function is turned on only during a period during which an image area is scanned (state 1). I understand that.
[0027]
[Table 1]

[0028]
The operation of the control signal generation circuit that controls the operation of the data line replacement circuit will be described below.
As described above, since the data line replacement circuit suppresses the generation of the pseudo contour caused by the A / D conversion, it works effectively on the original image data. However, various data such as gain adjustment and shading correction can be used. For data read for adjustment, it is not necessary to superimpose noise on the image data, and it is better to use the read data as it is without processing.
Accordingly, the operation of the data line replacement circuit is limited to only the original image data, and the normal operation is performed without performing the replacement operation when the reference white plate other than the original image is read.
5 and 6 are timing charts for explaining the control operation of the control signal generation circuit. FIG. 5 shows the operation in the mode ON for suppressing the pseudo contour, and FIG. 6 shows the operation in the mode OFF.
In the case of the mode ON for suppressing the pseudo contour, as shown in FIG. 5, Change_en becomes Low by setting of an external switch or the like. XSSCAN becomes High when the scanner unit 3 reads the reference white plate arranged outside the document area, and becomes Low when the document is read. Therefore, the output of the NOR circuit 45 is low when the scanner unit 3 is reading the reference white plate, and is high when the document is read. Therefore, in the data line switching circuit (FIG. 3), the enable signal of the buffer IC (2) 42 is low, the enable signal of the buffer IC (3) 43 is high, the buffer IC (3) 43 is in a high impedance state, and the buffer The buffer IC (2) 42 performs the buffer operation without performing the operation, and at this time operates in the normal mode. When reading a document, the enable signal of each buffer IC reverses the low and high enable signals in the normal mode, so that the operation changes from the normal mode to the data replacement mode.
On the other hand, when the pseudo contour suppression mode is OFF, as shown in FIG. 6, Change_en is set to High by setting the external switch, etc., so the output of the NOR circuit 45 is always low regardless of XSSCAN. Therefore, a low level signal is always input to the enable terminal of the buffer IC (2) 42, and a high level signal is always input to the enable terminal of the buffer IC (3) 43. As a result, the buffer IC (3) 43 enters a high impedance state, and the buffer IC (2) 42 performs the buffer operation without performing the buffer operation. Therefore, it operates in the normal mode.
As described above, when the reference white plate is read in order to perform gain adjustment or shading correction, one of the states 2, 3, and 4 in [Table 1] is created, and the data line that is a noise superimposing function is replaced. Since it is not necessary to activate the function, it is possible to replace the data line which is the noise superimposing function only when reading the image data without performing the replacement.
[0029]
“Gain adjustment, background removal, and each process in the shading processing unit 37”
After performing the above-described operation, gain adjustment, background removal, shading data generation, and shading processing are performed using the image data output from the noise superimposing processing unit 35.
At the time of reading the reference white plate, data on which no noise is superimposed is stored in the memory unit 36. For the stored data, averaging processing is performed using the data of the pixel of interest and the surrounding m × m area.
FIG. 5 is a conceptual diagram for explaining the standard whiteboard read data averaging process performed by manipulating read image data using a line memory.
With reference to FIG. 5, the averaging processing operation will be described below. First, the second pixel on the second line of the memory in which the reference white board data is stored (shown as “processing center focused pixel i” in FIG. 5). Focusing on the above, an averaging process in the m × m area is performed from the pixel, and the processed data is transferred to the subsequent shading data generation block (see FIG. 6). However, in the averaging process of the reference white plate data, the first pixel and the last pixel, the first line, the data of the last line are not processed, the first pixel is the same data as the second pixel, and the last pixel is the last pixel. The same data as -1 is used.
Next, shading data is generated.
FIG. 6 is a conceptual diagram for explaining a generation process of shading data and the like performed by manipulating the data after the averaging process of the reference whiteboard data in the area obtained above. As shown in the figure, the averaged whiteboard data of multiple lines in the memory where the data after the averaging processing of the reference whiteboard data in the area is stored is now averaged for each pixel in the sub-scanning direction. And generating shading data for each pixel, and detecting a peak value based on the shading data for each pixel.
[0030]
Details of the averaging process of the reference white board data and the shading data generation process performed when reading the reference white board will be described below.
The averaging process of the reference white plate data can be expressed by the following equation when data of surrounding pixels is used as a 3 pixel × 3 pixel area for the processing center target pixel i.
[0031]
[Expression 1]

[0032]
In the above equation (3), data_av (i) is the image data after the averaging process, data_mem (i, j) is the digital image data in the memory storing the reference white board data, w (k, l ) Is a weight for noise removal, and K is a coefficient.
The weight w (k, l) uses the weight matrix of the following matrix (1) when performing a simple averaging process as one of the averaging processes for noise removal. At this time, K = 1/9.
[0033]
[Expression 2]

[0034]
In the case of the matrix (1), the information on the edge portion of the image is also lost. Therefore, when performing the local average weighted average processing that weights each pixel and reduces the loss of information on the edge portion, the weight of the following matrix (2) Use a matrix. At this time, K = 1.
[0035]
[Equation 3]

[0036]
In this way, it is possible to change the noise removal characteristics by changing the weight matrix and coefficient for noise removal.
[0037]
Based on the reference whiteboard data subjected to the averaging process as described above, the averaging process is performed in the sub-scanning direction to generate shading data, and shading data: data_sh (i) is generated by the following equation.
data_sh (i) = Σdata_av (i) / N_sh (4)
N_sh: Number of lines used to generate shading data
Gain adjustment and shading processing are performed using the generated shading data data_sh (i).
The gain adjustment value is obtained by detecting the peak value: Data_P from the generated shading data data_sh (i), and the gain value in gain adjustment from the detected peak value Data_P and the output white level target value having a predetermined value set in advance: GAIN is determined by the following formula.
GAIN = (target white level) / Data_P (5)
From the determined gain value GAIN and shading data data_sh (i), gain adjustment and shading processing are performed on the data on which noise is superimposed by the noise replacement function.
[0038]
Since the gain adjustment and the shading processing have been performed in the order as described above, the data Data_n () obtained by performing noise superimposition on the image data: Data_b (i) after the black level adjustment shown in Expression (2) The processing according to the following equation is performed on i) and is output as data Data_out (i) to the next-stage image processing unit according to the following equation.
Data_out (i) = Data_n (i) × GAIN × {Data_P / Data_sh (i)} (6)
As described above, the gain adjustment processing unit and the shading processing unit are provided in the subsequent stage of the noise superimposing processing unit 35, so that noise is superimposed by the noise superimposing processing unit 35 and the generation of the pseudo contour of the image data is suppressed. Since the gain adjustment and shading processing is performed on the data, if the gain adjustment and shading processing is performed on the data that is not subjected to the suppression processing, the conventional problem ([Prior Art ] Can be solved.
[0039]
In the above, the processing until the output of the image data Data_out (i) when the background removal processing is not performed has been described. Next, processing when the background removal processing is performed will be described below.
When performing the background removal processing, the processing up to the output of Data_out (i) described above is performed, and the data obtained by Expression (6) is stored in the memory unit 36 used when storing the reference whiteboard read data. On the other hand, with respect to the manuscript portion from which the background can be read, in the same manner as the above processing performed when generating shading data and gain adjustment, averaging processing in the area of the read image data, averaging processing in the sub-scanning direction, peak detection processing And the peak value of the background level is detected (see FIGS. 5 and 6). Using the detected background peak value Data_P_AE and the output target value at the time of background removal processing having a predetermined value determined in advance, the background removal coefficient value: background removal target output value / Data_P_AE can be used to perform background removal. it can. The data Data_out ′ (i) after the background removal is output by the following equation.
Data_out ′ (i) = Data_n (i) × GAIN × {Data_P / Data_sh (i)} × {background removal target output value / Data_P_AE} (7)
As described above, the data Data_out ′ (i) after background removal output to the image processing unit at the next stage as described above is similar to the previous example in which background removal is not performed, as shown in Expression (7). The read data is multiplied by some coefficient. For this reason, there is a possibility that the difference from the analog data generated at the time of A / D conversion is widened and the pseudo contour generated at the time of A / D conversion may be emphasized. Since the process of multiplying the noise component to suppress the generation of the pseudo contour and multiplying the background removal coefficient is performed after the noise superimposition process, the generation of the pseudo contour is not promoted.
[0040]
【The invention's effect】
(1) Effects corresponding to the invention of claim 1
Digital image data in which (N + n) -bit gradation digital image data converted by the A / D conversion means is input, and the MSB to (N) -bit data are replaced with LSB data including high-frequency noise components. By providing a data replacement means for outputting the upper (N) bits, it is possible to easily suppress the occurrence of pseudo contours that can occur during the A / D conversion process, and to provide high-quality image data. Therefore, it is possible to design a circuit without increasing the scale and complexity of the circuit.
(2) Effects corresponding to the invention of claim 2
In addition to the effect of (1) above, a gain adjusting means for enhancing the pseudo contour generated during the A / D conversion in order to multiply the data by a coefficient is provided at the subsequent stage of the data exchanging means. By doing so, it is possible to exhibit the expected suppression effect without promoting the generation of the pseudo contour.
(3) Effect corresponding to invention of Claim 3
In addition to the effects of (1) and (2) above, by providing means for controlling the operation / non-operation of the data exchange means, it is possible to deal with data that does not require data exchange and improve the performance of the apparatus. It becomes possible.
(4) Effect corresponding to invention of claim 4
By realizing the effects (1) to (3) in the image forming apparatus including the image processing apparatus according to any one of claims 1 to 3, it is possible to improve the performance of the image forming apparatus.
[0041]
(5) Effects corresponding to the invention of claim 5
The analog image data output from the analog processing means of the image sensor output signal is converted into digital image data of (N + n) bit gradation by the A / D conversion means, and the (N) bit data from the MSB of the digital image data By providing data replacement means that outputs the upper (N) bits of digital image data in which is replaced with LSB data containing high-frequency noise components, the occurrence of pseudo contours that can occur during the A / D conversion process is easily suppressed The image data read by the image sensor can be provided as high-quality digital data, and the circuit design without increasing the scale and complexity of the circuit is possible.
(6) Effects corresponding to the inventions of claims 6 and 7
In addition to the effect of (5) above, processing such as white level adjustment, background removal, and shading processing, which may emphasize the pseudo contour generated during A / D conversion in order to multiply the data by a coefficient. By performing the gain adjustment processing including “after” the data replacement processing, it is possible to exhibit the expected suppression effect without promoting the generation of the pseudo contour.
(7) Effect corresponding to invention of claim 8
In addition to the effects (5) and (6) above, by providing a means for controlling the operation / non-operation of the data exchange means, it is possible to cope with the reading of data that does not require data exchange, and to improve the performance of the apparatus. It becomes possible to improve.
(8) Effect corresponding to invention of Claim 9
In addition to the effect of (7) above, there is provided means for performing a control operation that activates the data exchange means when reading the original image and deactivates it when reading the shading data. Processing is possible, and the performance of the apparatus can be improved.
(9) Effects corresponding to the invention of claim 10
A performance of the image forming apparatus is improved by realizing the effects (5) to (8) in an image forming apparatus such as a copying machine or a facsimile provided with the image reading apparatus according to claim 5. Is possible.
[0042]
(10) Effect corresponding to invention of claim 11
Higher (N) digital image data obtained by inputting digital image data of (N + n) -bit gradation converted by A / D conversion processing and replacing the (N) -th bit data from the MSB of the data to LSB data By performing data exchange processing that outputs bits, it is possible to easily and inexpensively suppress the occurrence of pseudo contours that can occur during the A / D conversion process, and to provide high-quality image data. .
(11) Effect corresponding to invention of claim 12
By realizing the effect of (10) above in the process of analog processing of the image sensor output signal and A / D conversion of the output analog image data, the image data read by the image sensor is converted into high-quality digital data. Can be output.
(12) Effects corresponding to the inventions of claims 13 and 14
In addition to the effects of (10) and (11) above, there is a possibility of emphasizing the pseudo contour generated at the time of A / D conversion to take the form of multiplying the data by a coefficient, white level adjustment, background removal, Since the gain adjustment process including the process such as the shading process is performed after the data replacement process, the expected suppression effect can be exhibited without promoting the generation of the pseudo contour.
(13) Effect corresponding to invention of claim 15
In addition to the effects of (11) and (12) above, by switching the data when reading the original image and controlling the operation so that the data is not replaced when reading the shading data, the mode is optimal for each reading. The read data can be processed, and the performance of the process of digitally outputting the image data read by the image sensor can be improved.
[Brief description of the drawings]
FIG. 1 is a schematic diagram showing the overall configuration of a DPPC according to an embodiment of the present invention.
FIG. 2 is a block diagram showing an outline of a circuit unit related to read image data processing in a DPPC control unit.
FIG. 3 shows a data line replacement circuit in a read image data processing circuit (FIG. 2).
FIG. 4 shows an example of a control signal generation circuit for controlling the operation of the data line switching circuit (FIG. 3).
FIG. 5 is a timing chart for explaining the control operation of the control signal generation circuit in the mode ON for suppressing the pseudo contour.
FIG. 6 is a timing chart for explaining the control operation of the control signal generation circuit in the mode OFF for suppressing the pseudo contour.
FIG. 7 is a conceptual diagram for explaining averaging processing of reference white board reading data.
FIG. 8 is a conceptual diagram for explaining a process of generating shading data and the like from reference whiteboard averaged data.
FIG. 9 is a diagram for explaining the principle of generation of a pseudo contour caused by quantization of an analog image signal.
[Explanation of symbols]
1 ... DPPC (digital copier), 3 ... scanner,
5 ... ADF (Automatic Document Feeder) unit,
4 ... Printer part, 6 ... Contact glass,
7 ... Control unit, 10 ... CCD image sensor,
11 ... photosensitive drum, 14 ... light writing section,
32e, 32o ... A / D converter, 33 ... digital signal correction unit,
34 ... Offset removal processing unit, 35 ... Noise superimposition processing unit,
37: Gain adjustment processing, background removal processing, shading processing section,
41: Buffer IC (1), 42: Buffer IC (2),
43 ... Buffer IC (3), 44 ... Inverter,
45: NOR circuit.

Claims (15)

In an image processing apparatus having at least A / D conversion means for converting analog image data into digital image data, the A / D conversion means is means for converting the analog image data into digital image data of (N + n) bit gradation. Yes, digital image data of (N + n) -bit gradation converted by the A / D conversion means is input, and the higher order of the digital image data obtained by replacing the (N) -bit data with LSB data from the MSB of the data (N) An image processing apparatus provided with data replacement means for outputting bits. 2. The image processing apparatus according to claim 1, further comprising means for adjusting a gain to adjust the image data to a predetermined reference value, wherein the gain adjusting means is provided at a subsequent stage of the data replacing means. An image processing apparatus. 3. The image processing apparatus according to claim 1, further comprising means for controlling operation / non-operation of the data exchange means. An image forming apparatus comprising the image processing apparatus according to claim 1. An image reading apparatus comprising at least an image sensor, analog processing means for analogly processing an output signal of the image sensor and outputting analog image data, and A / D conversion means for converting the analog image data into digital image data. / D conversion means is means for converting analog image data to digital image data of (N + n) bit gradation, and the digital image data of (N + n) bit gradation converted by the A / D conversion means is input. An image reading apparatus comprising: a data switching means for outputting upper (N) bits of the digital data obtained by replacing the (N) bit data from the MSB of the data with LSB data. 6. The image reading apparatus according to claim 5, further comprising means for adjusting a gain for adjusting the image data to a predetermined reference value, wherein the gain adjusting means is provided at a subsequent stage of the data replacement means. Image reading device. 7. The image reading apparatus according to claim 6, wherein the gain adjusting means includes at least one of white level adjustment, background removal, and shading processing. 8. The image reading apparatus according to claim 5, further comprising means for controlling operation / inactivation of the data exchange means. 9. The image reading apparatus according to claim 8, wherein the means for controlling the operation / non-operation of the data exchanging means performs a control operation of operating the data exchanging means when reading a document image and disabling the shading data. An image reading apparatus. An image forming apparatus comprising: the image reading apparatus according to claim 5; and means for forming an image based on image data output from the image reading apparatus. In the image processing method including at least a conversion processing step of converting analog image data into digital image data, the A / D conversion step is a step of converting analog image data into digital image data of (N + n) -bit gradation, A data replacement step of outputting the upper (N) bits of the digital image data obtained by replacing the (N) -th bit data with the LSB data from the MSB of the (N + n) -bit gradation digital image data is provided. An image processing method. 12. The image processing method according to claim 11, further comprising the step of analog processing of an output signal of the image sensor before the conversion processing step. 13. The image processing method according to claim 11 or 12, wherein a gain adjustment step for adjusting the image data to a predetermined reference value is provided, and the gain adjustment step is performed after the data replacement step. An image processing method characterized by the above. 14. The image processing method according to claim 13, wherein the gain adjustment step is a step for performing at least one of white level adjustment, background removal, and shading processing. 15. The image processing method according to claim 12, further comprising a step of controlling operation / non-operation of the data exchange step, wherein the data is exchanged at the time of reading a document image by the control step, and shading data is provided. An image processing method characterized in that data is not exchanged at the time of reading.

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