JP2004023349A - Image reader and image processing apparatus equipped therewith - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image reader provided with a low-cost means capable of outputting a digital image signal maintaining a wide dynamic range without employing a conventional system in which gain adjustment of a variable gain is wholly used. <P>SOLUTION: A CPU 29 sets one main scanning time of a length capable of obtaining a CCD output of an S/N corresponding to a color or monochrome mode selected by an operation unit 38 in a driving circuit 21 of a CCD 9, and changes a preset value of a reference voltage in an A/D conversion circuit 26 so as to correspond to the output mode in order to maintain the wide dynamic range even depending on a change in CCD output generated by a change in output mode. Since the preset value of the reference voltage is changed in proportion to the one main scanning time, a means can be simplified. <P>COPYRIGHT: (C)2004,JPO

Description

【００２２】
なお、［表１］において、Ｆ１，Ｎ１，Ｎ２は任意の数値である。この実施例の特徴はクロック周波数を不変として、１主走査期間の駆動クロック数を選択モードにより変化させる。
【００２３】
【表２】

【００２４】
なお、［表２］において、Ｆ１，Ｆ２，Ｎ１は任意の数値である。この実施例の特徴はクロック周波数を選択モードにより変化させ、１主走査期間の駆動クロック数を不変とする。この方式では、クロック周波数を変更することになるので、駆動回路２１内部にＰＬＬ回路を必要とする。
上記した設定値Ｆ１，Ｆ２，Ｎ１，Ｎ２はその都度ＣＰＵ２９が、実施装置に合った計算式で算出しても良いし、予めメモリに格納しておいた値を用いても良い。
ＣＰＵ２９は、ＣＣＤ９の駆動条件を設定した後に、Ａ／Ｄ変換回路２６に用いる基準（リファレンス）電圧として、選択された出力モードに対応した電圧値をＤ／Ａ変換回路３１を介して設定する（Ｓ１４）。
カラー出力／モノクロ出力の各モード選択時に設定する基準（リファレンス）電圧値の条件は、カラー出力モード時の基準電圧値をモノクロ出力時に比べて大きくするようにし、例えば［表３］の形態で実施し得る。
【００２５】
【表３】

【００２６】
なお、［表３］において、ＣＰＵ２９がＤ／Ａ変換回路３１に設定する値Ｓ１，Ｓ２は、いずれの出力モードを選択した場合にも（つまり、１主走査期間（光蓄積時間）を出力モードに適した条件に変更して駆動しても）、所定の広ダイナミックレンジを保つことを可能にするための値とし、その都度ＣＰＵ２９が、実施装置に合った計算式で算出しても良いし、予めメモリに格納しておいた値を用いても良い。上記のようにして基準（リファレンス）電圧値を求める際に、選択したモードの適合値のみを求め、求めた値を設定するという方式によっても良いが、図１１に示すように、Ｄ／Ａ変換回路３１は多出力をもち、出力はセレクタ３３に入力される。ＣＰＵ２９は出力モードを示す信号をセレクタ３３に入力し、Ｄ／Ａ変換回路３１の一方の出力モードの基準電圧を選択する。
Ａ／Ｄ変換回路２６に基準電圧を設定した後、画像読み取り装置は読み取り動作を開始し、ランプを点灯から始まる一連の画像を読み取り処理を行なうための動作を行う（Ｓ１５）。
【００２７】
上記した実施形態において、各出力動作モードにおけるＣＣＤ９の駆動条件と駆動条件に対応するＡ／Ｄ変換回路２６に用いる基準電圧は、それぞれ個別に用意した設定値を用いるという形態で実施し得るものを想定したが、次の実施形態では、相互関係を考慮して設定を行うようにするものである。
ＣＣＤ９の出力は光蓄積時間（１主走査時間）に比例するので、Ａ／Ｄ変換回路２６に用いる基準電圧を光蓄積時間（１主走査時間）に比例させて変化させることにより対応することができる。このようにしても、光源４の光量、ＣＣＤ９のセンサ感度、メカ寸法のバラツキ等を考慮した時に必要なゲインアンプ２４のゲイン可変範囲は光蓄積時間が変わっても、同じ可変範囲で対応できる。
本実施形態の設定方法は、前述のＳ１，Ｓ２（［表３］参照）をＮ１，Ｎ２（［表１］参照）或いはＦ１，Ｆ２（［表２］参照）と関連つけて決定することで実現できる。
即ち、次の各式により決定する。
Ｎ１／Ｆ１／ｆ（Ｓ１）＝Ｎ２／Ｆ１／ｆ（Ｓ２）：駆動クロック数変化方式（［表１］参照）の場合
或いは、
Ｎ１／Ｆ１／ｆ（Ｓ１）＝Ｎ１／Ｆ２／ｆ（Ｓ２）：クロック周波数変化方式（［表２］参照）の場合
但し、上記各式においてｆ（Ｓ）は、Ｄ／Ａ変換器３１に設定値Ｓを設定した時の出力値（Ａ／Ｄ変換回路２６の基準電圧）である。
【００２８】
次に示す実施形態は、Ａ／Ｄ変換回路２６の基準電圧をカラー出力／モノクロ出力の各モードに適した設定にする際に、画像読み取り装置の各機械間のバラツキの補正を加味した設定を行うようにすることを可能にするものである。
原稿を読み取ったデジタル画像データはシェーディングデータ保存回路３５に保存されている基準白板データを用いてシェーディング補正されるので、補正後のデジタル画像データの大きさは基準白板データに依存することになる。このため、基準白板データと基準濃度の原稿を読み取ったデジタル画像データの比が一定値に規格化されていないと、同じ濃度の原稿を読み取った場合でも補正後のデジタル画像データは機械間でバラツキを持つことになる。このバラツキをＡ／Ｄ変換回路２６の基準電圧の設定値を変更することにより補正可能とする。
このような補正を加味してカラー出力／モノクロ出力の各出力モードに対応する基準電圧設定を行うため、まず現行出力モードの１主走査時間（読み取り時間）の設定で基準白板読み取り時、原稿読み取り時のＡ／Ｄ変換回路２６の出力が規定の比率になる様な基準電圧値を求め、主走査時間変更時には、基準白板読み取り時、原稿読み取り時の各基準電圧をそれぞれ変更する方法を採用することにより目的の動作を実現する。
【００２９】
図１２は、本実施形態の動作を実現するために使用される基準電圧の設定値の保存処理に関するフローチャートを示す。なお、本例は、１主走査時間をｔ１，ｔ２に切り替える場合の例である。
図１２を参照すると、先ず１主走査時間ｔ１の場合にＤ／Ａ変換回路３１にゲインＶｇ、基準白板読み取り用上側基準電圧Ｖｒｅｆｗ、原稿読み取り用上側基準電圧Ｖｒｅｆｄ、下側基準電圧Ｖｒｅｆｂ、オフセットレベルＶｏｆに対応するデフォルト値を設定する（Ｓ２１）。
次に、基準濃度の原稿をコンタクトガラス２上にセットし、キャリッジを基準濃度原稿読み取り位置に移動させる（Ｓ２２）。このとき、Ａ／Ｄ変換回路２６の上側基準電圧は、Ｖｒｅｆｄ（原稿読み取り用）が選択されるようにセレクタ３２へのＷＴＧＴ信号を操作する。
ＣＰＵ２９は、オフセットレベル検出回路２７の値を参照しながら、オフセットレベルが所定値になる様にＤ／Ａ変換回路３１のＶｏｆ用設定値：Ｓｏｆを調整する（Ｓ２３）。また、コンタクトガラス２上に置かれた基準濃度原稿を読み取り、白ピーク検出回路３０の値を参照しながら、ピークデータ：Ｄｄｐが所定値になる様にＤ／Ａ変換回路３１のＶｇ用設定値：Ｓｇを調整する（Ｓ２４）。
この後、基準濃度原稿読み取り時の特定画素の値：Ｄｄを取り出し（Ｓ２５）、キャリッジを基準白板３の読み取り位置に移動させ、セレクタ３２によりＡ／Ｄ変換回路２６の上側基準電圧をＶｒｅｆｗ（基準白板読み取り用）に切り替える（Ｓ２６）。
【００３０】
次に基準白板３を読み取り、上記と同じ特定画素の値：Ｄｗを取り出す。この基準白板３を読み取った値：Ｄｗが基準濃度原稿を読み取った値：Ｄｄに対して公差Ａ以内に入っているか否か判断する（Ｓ２８）。ここで、公差Ａ以内に入っていない場合、ＣＰＵ２９はＡ／Ｄ変換回路２６のＶｒｅｆｗを変えるためにＤ／Ａ変換回路３１の設定値Ｓｒｅｆｗを変更して（Ｓ２９）、再度基準白板３を読み取り、Ｄｄに対して公差Ａ以内に入るまで、ステップＳ２７〜２９を繰り返す。
基準白板３を読み取った値：Ｄｗが基準濃度原稿を読み取った値：Ｄｄに対して公差Ａ以内に入った場合（Ｓ２８−ＹＥＳ）、そのときのＶｒｅｆｗに対応するＤ／Ａ変換回路３１の設定値をＳｒｅｆｗ１とする（Ｓ３０）。
次いで、１主走査時間ｔ２にした時にＡ／Ｄ変換回路２６で用いる基準白板読み取り用上側基準電圧Ｖｒｅｆｗ、原稿読み取り用上側基準電圧Ｖｒｅｆｄに対応するＤ／Ａ変換回路３１の設定値：Ｓｒｅｆｄ２、Ｓｒｅｆｗ２を求める（Ｓ３１）。Ｓｒｅｆｄ２、Ｓｒｅｆｗ２は以下の関数に従って求める。
Ｓｒｅｆｄ２＝ｆ（Ｓｒｅｆｄ１，ｔ１，ｔ２）
Ｓｒｅｆｗ２＝ｇ（Ｓｒｅｆｗ１，ｔ１，ｔ２）
上記関数において、ｆ（Ｓｒｅｆｄ，ｔ）、ｇ（Ｓｒｅｆｗ，ｔ）は、１主走査時間とＤ／Ａ変換回路３１の設定値に対する関数式である。
（上側基準電圧―下側基準電圧）を１主走査時間に比例させる様に設計する場合は、以下のように関数式が定まる。
（Ｖｒｅｆｗ１−Ｖｒｅｆｂ）×ｔ２＝（Ｖｒｅｆｗ２−Ｖｒｅｆｂ）×ｔ１
∴　Ｖｒｅｆｗ２＝（（Ｖｒｅｆｗ１−Ｖｒｅｆｂ）×ｔ２／ｔ１）＋Ｖｒｅｆｂ
仮に、Ｖｒｅｆ＊＝α・Ｓｒｅｆ＊＋β　（＊はｄまたはｗまたはｂ）
の関係である場合、

となる。
同様に、

となる。
処理フローでは、上記のようにして求めたＤ／Ａ変換回路３１の設定値：Ｓｒｅｆｗ１，Ｓｒｅｆｗ２，Ｓｒｅｆｄ２をＣＰＵ２９制御下の不揮発性メモリに保存し（Ｓ３２）、この処理フローを終える。
【００３１】
次に、上記した基準電圧の設定値の保存処理により１主走査時間を変更した場合に使用するＤ／Ａ変換回路３１の設定値を不揮発性メモリに格納した後、該メモリに格納された設定値をＤ／Ａ変換回路３１に設定し、読み取りを実行する際の処理動作に関する実施形態を示す。
図１３は、Ｄ／Ａ変換回路３１の設定値を反映した読み取り動作のフローチャートを示す。
図１３を参照すると、先ず、画像読み取り装置の電源がＯＮされたことを確認して（Ｓ４１−ＹＥＳ）、Ｄ／Ａ変換器３１に対して各種デフォルト値を設定する。ここでは、ゲインＶｇ、オフセットＶｏｆ、Ａ／Ｄ変換回路２６の基準（リファレンス）電圧関連等のデフォルト値を設定する。Ａ／Ｄ変換回路２６の上側基準電圧の設定値は、例えばデフォルト設定において読み取り時間（１主走査時間）をｔ１とした場合、不揮発性メモリに格納しておいた、Ｓｒｅｆｗ１，Ｓｒｅｆｄ１を設定する（Ｓ４１）。
次いで、デフォルト設定で始動させ、オフセットレベル検出回路２７の値を参照しながら、オフセットレベルが所定値になる様に、また、白ピーク検出回路３０の値を参照しながら、ピーク値が所定値になる様に、オフセット調整、ゲイン調整等のセットアップ動作を行なう（Ｓ４３）。
【００３２】
ここで、読み取り要求を待ち、要求があった場合に（Ｓ４４−ＹＥＳ）、１主走査時間の変更があったかをチェックして、１主走査時間の変更の指示があった場合に（Ｓ４５−ＹＥＳ）、Ｄ／Ａ変換器３１に対し指示する基準白板、原稿読み取り用の基準電圧設定値Ｓｒｅｆｗ、Ｓｒｅｆｄを下記［表４］で示される様に、不揮発性メモリから読み出して変更する（Ｓ４６）。
この例ではＳｒｅｆｗ１，Ｓｒｅｆｄ１１が先ず設定されていたので、Ｓｒｅｆｗ２，Ｓｒｅｆｄ１２に変更する。なお、ここでは、下側基準電圧Ｖｒｅｆｂに対する設定値Ｓｒｅｆｂは固定のままとする。
【００３３】
【表４】

【００３４】
ステップＳ４５で、１主走査時間の変更の指示がなかった場合には、基準白板、原稿読み取り用の基準電圧設定値Ｓｒｅｆｗ、Ｓｒｅｆｄを変更するステップＳ４６をパスする。
次いで、上記のフローを経て設定された条件に従って、原稿１（基準白板３）の読み取りを実行して（Ｓ４７）、次の読み取り要求を待つ（Ｓ４４）。
以上の様に、１主走査時間の変更があった場合は基準白板、原稿読み取り用の基準電圧設定値Ｓｒｅｆｗ、Ｓｒｅｆｄを同じ割合で変更する。
また、上記でＳｒｅｆｄ２＝ｆ（Ｓｒｅｆｄ１，ｔ１，ｔ２）、Ｓｒｅｆｗ２＝ｇ（Ｓｒｅｆｗ１，ｔ１，ｔ２）の関数式の例を示したが、回路構成、設計思想によりのこの関数式は異なってくるが、基準白板／原稿読み取り時の基準電圧の比が一定であれば問題無い。
更に、上記実施形態では比例関係を保った基準電圧の設定値を一旦メモリに入れる方式であったが、１主走査時間の変更があった場合にその都度、計算をし直してＤ／Ａ変換器３１に設定する方式であっても構わない。
【００３５】
また、上述した実施形態に示す画像読み取り装置は、スキャナ、複写機、ファクシミリ等の画像処理装置の画像読み取り部として装備することにより該画像処理装置を構成し得る。スキャナ、複写機、ファクシミリ等の画像処理装置を構成するときには、各画像処理装置の仕様に従って、当該画像読み取り装置の入力側には読み取り対象を供給する装置（例えばＡＤＦ：オートドキュメントフィーダ）、を、又出力側に読み取りデータを利用形態に適したデータに変換・処理するデータ処理装置や処理後のデータを用いて各種の出力を行う出力装置（例えば、画像形成装置）を組み合わせる必要がある。なお、スキャナ、複写機、ファクシミリ等の画像処理装置を構成するために当該画像読み取り装置の入力側、出力側に装備するこれらの装置については、既存の技術を適用することにより、実施することが可能である。
【００３６】
【発明の効果】
（１）　請求項１の発明に対応する効果
出力モードに対応したＳ／ＮのＣＣＤ出力を得るために読み取り時間（１主走査時間）を変更する場合に、Ａ／Ｄ変換手段に用いるリファレンス値をＣＣＤの１主走査時間を設定する手段により設定された１主走査時間に応じて調整するようにしたので、可変範囲が割合狭いゲインアンプ（低コストのアンプ）を用いた構成でも、簡易な方式によりＡ／Ｄ変換手段の性能を充分に引き出して使用することが可能になる。即ち、デジタル出力信号の広ダイナミックレンジを確保でき（実効的な階調数が確保でき）、その結果、シェーディング補正演算結果の丸め込み量も小さくすることが可能で、ガサツキ感の無い綺麗な画像を得ることができる。
（２）　請求項２，３の発明に対応する効果
上記（１）の効果に加えて、読み取り時間（１主走査時間）として画像信号出力の用途に適応する値を設定するようにしたので、目的に合った画像を取り出すことができる。また、カラー出力用途の場合には、より高画質の信号出力が得られ、モノクロ出力用途の場合には、読み取り処理の高生産性を図ることができる。
【００３７】
（３）　請求項４の発明に対応する効果
上記（１）、（２）の効果に加えて、リファレンス値を１主走査時間に比例させて変更するようにしたことにより、例えばゲインアンプのゲイン可変範囲が最小ですむ等、制御手段を簡易な手段で実現することが可能になる。
（４）　請求項５の発明に対応する効果
上記（１）〜（３）の効果に加えて、読み取り対象を濃度基準部材及び原稿とする場合、Ａ／Ｄ変換手段に用いるリファレンス値を濃度基準部材及び原稿画像に対するリファレンス値を同じ割合で変更するようにしたことにより、変更前後での画像濃度および画像読み取り装置毎の濃度バラツキを無くすことが可能になる。
（５）　請求項６の発明に対応する効果
上記（１）〜（４）の効果に加えて、Ａ／Ｄ変換手段に用いるリファレンス値をそれぞれの設定条件に対応して予め記憶部に格納しておいた数値を選択して適用するようにしたことにより、画像読み取り装置の電源をＯＦＦ／ＯＮしても同じ設定値を再度使用することが可能になる。
（６）　請求項７の発明に対応する効果
上記（１）〜（５）の効果を複写機、ファクシミリ、スキャナ、及び上記の複合機、或いは画像データを蓄積するファイリング装置等の画像読み取り装置を装備した画像処理装置において実現することができ、画像処理装置の処理性能を向上させることが可能となる。
【図面の簡単な説明】
【図１】本発明の実施形態に係る画像読み取り装置の概略構成を示す。
【図２】本発明の実施形態に係る画像読み取り回路の概略ブロック図を示す。
【図３】ゲインアンプの特性を表すグラフで、ゲイン制御量（Ｖｇ）とゲインの関係を示す。
【図４】オフセット設定回路の特性を表すグラフで、オフセット制御量（Ｖｏｆ）とオフセット量の関係を示す。
【図５】図２に示されるＡ／Ｄ変換回路をより詳細に示す図であ。
【図６】Ｄ／Ａ変換回路出力を分圧する方式の電圧設定回路の他の実施形態を示す。
【図７】カラー出力選択時、モノクロ出力選択時のＣＣＤの駆動タイミングの１例を表すチャートである。
【図８】１主走査期間のクロック数を変更するこの実施形態のＣＣＤ出力モードの動作を説明するための図である。
【図９】副走査方向の白基準板読み取りゲート信号を示すタイミングチャートを示す。
【図１０】本発明に係わる画像読み取り装置の読み取り動作のフローチャートを示す。
【図１１】多出力のＤ／Ａ変換回路によるリファレンス電圧設定回路の一例を示す。
【図１２】Ａ／Ｄ変換回路に使用される基準電圧の設定値の保存処理に関するフローチャートを示す。
【図１３】Ｄ／Ａ変換回路による設定値を反映した読み取り動作のフローチャートを示す。
【符号の説明】
１…原稿、　　　　　　　　　　　２…コンタクトガラス、
３…白基準板、　　　　　　　　　４…光源、
９…ＣＣＤラインイメージセンサ、
１０…読み取り基板、　　　　　　１１…画像処理基板、
２１…駆動回路、　　　　　　　　２６…Ａ／Ｄ変換回路、
２９…ＣＰＵ、　　　　　　　　　　３１…Ｄ／Ａ変換回路、
３４…シェーディング補正回路、　３５…シェーディングデータ保存回路、
３８…操作部。[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an image reading device and an image processing device (scanner, digital copier, digital facsimile, etc.) equipped with the image reading device, and more particularly, to one main scanning of a line image sensor (CCD: Charge Coupled Device). The present invention relates to an image reading apparatus provided with an adjusting means capable of variably setting a time and maintaining a wide dynamic range even when the setting of one main scanning time is changed, and an image processing apparatus equipped with the image reading apparatus.
[0002]
[Prior art]
2. Description of the Related Art Conventionally, an image reading device provided in a scanner, a copying machine, or the like has a line image sensor (CCD), and converts a target image into a time-series electric signal by a line scanning method using the CCD. In such an image reading apparatus, a digital signal is obtained by inputting an analog image signal from a line sensor that has read an image to an A / D conversion circuit. At this time, in order to fully utilize and use the performance of the A / D conversion circuit, the analog image signal has a wide dynamic range that does not exceed the reference voltage of the A / D conversion circuit. It is desirable to enter In the prior art, a wide dynamic range can be obtained for the input to the A / D conversion circuit by performing analog signal processing such as clamp correction and sample hold on the output of the CCD line sensor, and then adjusting the gain through a variable amplifier. A value is used (see, for example, JP-A-6-105135).
In the case of this conventional method, the CCD output is amplified by a variable amplifier so as to match a predetermined input range of the A / D conversion circuit, so that the gain adjustment range of this amplifier depends on the CCD output. Also, since this CCD output originally has variations due to variations in the light source light amount, line sensor sensitivity, mechanical dimensions, etc., in the conventional method, the variable amplifier uses a variable amplifier from the minimum to the maximum in consideration of these factors. It was necessary to have a wide variable range that could cover the entire range. Such an amplifier design is technically difficult, and the cost cannot be avoided.
[0003]
By the way, when an image forming apparatus having a full-color output function and a monochrome output function (for example, a printer installed in a copying machine or the like) is considered, the full-color output is compared with the monochrome output to generate an image signal used for image formation. High S / N is required. In this case, since the characteristics of the CCD, the CCD output signal processing circuit, and the reading illumination system are common, in order to obtain a high S / N image signal when the operation mode using the full color output function is selected, the light accumulation time of the CCD is required. Can be dealt with by increasing the output voltage and increasing the output voltage. On the other hand, when the operation mode using the monochrome output function is selected, the S / N is also required. However, usually, productivity such as how many documents can be read per unit time is emphasized. In order to achieve both, there is an idea that the light accumulation time of the CCD is changed when the operation mode of each of the full-color output and the monochrome output is selected.
[0004]
[Problems to be solved by the invention]
However, when such a measure is taken, it is necessary to stabilize the CCD output that changes due to the mode change, and if this is performed by adjusting the gain of the amplifier, the gain variable range of the variable amplifier will have the aforementioned CCD output variation. In addition to the factors, the light accumulation time must be taken into account. In particular, an IC contained in one package is used in a circuit for performing processing until the output of a line sensor is input to an A / D conversion circuit as in the cited conventional example (Japanese Patent Laid-Open No. 6-105135). In this case, since the variable gain range of the amplifier is limited, it is necessary to add an external amplifier when a wider variable gain range is required.
The present invention has been made in view of the above-described problems of the related art, and has as its object to switch one main scanning time by mode setting, drive a sensor pixel according to the switched setting condition, and read a read image signal. In an image reading apparatus that obtains a digital signal output by using a line image sensor that detects (changes the S / N of a detected image signal), even when the line image sensor is operated by switching one main scanning time by mode setting, Equipped with a simple and low-cost means that can obtain a digital image signal output with a wide dynamic range, without using the conventional method that had been solved by fully adopting the gain adjustment of the amplifier. Provided is an image reading device and an image processing device (scanner, copier, facsimile, etc.) provided with the image reading device. Lies in the fact.
[0005]
[Means for Solving the Problems]
A first main scanning time setting means for variably setting one main scanning time, a line image sensor for driving a sensor pixel according to the set one main scanning time and detecting an image signal to be read, An image reading apparatus having A / D conversion means for converting an analog image signal detected by the line image sensor into a digital signal based on a variable reference value, wherein the reference value used for the A / D conversion means is set to An image reading apparatus comprising: means for changing in accordance with one main scanning time set by one main scanning time setting means.
[0006]
According to a second aspect of the present invention, in the image reading apparatus according to the first aspect, the one main scanning time can be set in the one main scanning time setting means so as to be suitable for the purpose of outputting a read image signal. It is assumed that.
[0007]
According to a third aspect of the present invention, in the image reading apparatus according to the second aspect, the read image signal output is used for color and monochrome, one main scanning time is long for color, and one main scan for monochrome. The feature is that the time is reduced.
[0008]
According to a fourth aspect of the present invention, in the image reading apparatus according to any one of the first to third aspects, the means for changing a reference value used in the A / D conversion means makes the reference value proportional to one main scanning time. It is characterized in that it is changed by changing.
[0009]
According to a fifth aspect of the present invention, in the image reading device according to any one of the first to fourth aspects, when the reading target is a density reference member and a document, a reference value used for the A / D conversion unit is changed. The means is characterized in that reference values for the density reference member and the document image are changed at the same ratio.
[0010]
According to a sixth aspect of the present invention, in the image reading apparatus according to any one of the first to fifth aspects, a reference value used for the A / D conversion unit is stored in a storage unit in advance corresponding to each set condition. It is characterized in that the set numerical value is selected and applied.
[0011]
According to a seventh aspect of the present invention, there is provided an image processing apparatus including the image reading device according to any one of the first to sixth aspects.
[0012]
BEST MODE FOR CARRYING OUT THE INVENTION
The present invention will be described based on the following embodiments shown in the accompanying drawings.
FIG. 1 shows a schematic configuration of an image reading apparatus according to an embodiment of the present invention.
In the image reading apparatus shown in FIG. 1, a contact glass 2 and a white reference plate 3 are arranged at the top of the apparatus. The contact glass 2 is set when reading the original 1. The original 1 is suppressed from floating above the contact glass 2 by an original pressing plate called a pressure plate (not shown) from above. Of course, a known ADF (automatic document feeder) may be provided to automatically carry and supply the document set on the tray. The white reference plate 3 is moved in a main scanning direction (a line direction of a line image sensor described later and a direction perpendicular to the surface of FIG. 1) for obtaining correction data used for shading correction (see a shading data storage circuit 35 described later) and the like. This is a substantially white member having a uniform density as the provided density reference member.
The illumination light from the light source 4 irradiates the white reference plate 3 or the original placing surface of the contact glass 2 at a predetermined angle, and the reflected light from the original 1 or the white reference plate 3 carries image information of the surface. Obtained as reading light. The reflected light from the white reference plate 3 or the original 1 is guided to the imaging lens 8 by three mirrors, that is, the first mirror 5, the second mirror 6, and the third mirror 7, and the photoelectric conversion element is formed by the imaging lens 8. The light enters a light receiving surface of a line image sensor (here, a CCD is used as a sensor) 9 as an image sensor and forms an image.
In order to scan the reading surfaces of the original 1 and the white reference plate 3 with the illumination light from the light source (lamp) 4, the light source 4 and the first mirror 5, and the second mirror 6 and the third mirror 7 are each provided with a carriage (not shown). ) To form a first traveling body 12 and a second traveling body 13, and each of the traveling bodies 12 and 13 is driven by a motor 14 so that the distance between the reading surface and the CCD 9 is kept constant while maintaining a constant distance between the reading surface and the CCD 9. (In the direction of the arrow shown).
The CCD 9 outputs an analog image signal corresponding to the amount of incident light, converts this output into a digital signal by the reading substrate 10, and passes the image data to the image processing substrate 11.
[0013]
FIG. 2 is a schematic block diagram of the image reading circuit according to the embodiment of the present invention.
In FIG. 2, an analog image signal obtained by reading a document surface and converted by a CCD (line image sensor) 9 is output from an image processing circuit 36 as, for example, image forming data used for image formation by a plotter (not shown). 1 shows an operation of each processing circuit unit for image signals up to and an image reading circuit including a CPU 29 for controlling the operation in accordance with an operation mode instructed from the operation unit 38. The configuration and operation of the circuit will be described below with reference to FIG.
The operation unit 38 is provided for the user to input a desired operation mode. The operation mode includes a reading mode (ON / OFF of a background removal function or the like), an output mode (color output / monochrome output), a magnification, and the like. The present invention focuses on the output mode (color output / monochrome output), and information of any of the set output modes is transmitted to the CPU 29. The CPU 29 determines the timing for driving the CCD 9 based on the received output mode information. The drive circuit 21 of the CCD 9 includes an operation condition setting I / F section from the CPU 29, a timing generation section including a counter, and a driver section for driving a load. The CPU 29 sets driving conditions in the driving circuit 21, and the CCD 9 is driven according to a clock output from the driving circuit 21. The driven CCD 9 converts the reflected light from the original 1 into an analog image signal. The setting method of the driving conditions and the driving state according to the setting will be described later in detail with reference to FIG.
[0014]
The analog image signal output from the CCD 9 is driven by a buffer 22 and sampled and held by a sampling circuit 23 to remove high frequency components such as reset noise. A gain amplifier 24 capable of controlling the gain is provided downstream of the sampling circuit 23. This amplifier is an amplifier whose gain can be controlled by a voltage: Vg applied to its control terminal, and has a characteristic in which Vg versus gain has a substantially linear relationship as illustrated in FIG.
The offset setting circuit 25 provided next has a function of providing an offset to an image signal with a voltage: Vof applied to its control terminal, and has + and-offsets in proportion to Vof as illustrated in FIG. It has the property of providing an amount. Vg and Vof are voltages determined by the CPU 29 operating the D / A conversion circuit 31. For example, if the D / A conversion circuit 31 has 8 bits, the CPU 29 sets any value of 0￣255: S to the D / A conversion circuit 31, and the D / A conversion circuit 31 Output to control terminal.
[0015]
The A / D conversion circuit 26 converts the analog image signal after the offset setting into a digital signal. FIG. 5 is a diagram showing the A / D conversion circuit 26 in more detail. Referring to FIG. 5, the analog image signal is converted into a predetermined resolution (for example, based on an upper limit reference (voltage) value and a lower limit reference (voltage) value). 8 bits). Here, Vrefw or Vrefd is an upper limit reference value of the A / D conversion circuit 26, and Vrefb is a lower limit reference value, which are determined by the CPU 29 operating the D / A conversion circuit 31. At this time, if the input of the A / D conversion circuit 26 is Vin and the output is Dout,
Dout = (Vin−Vrefb) × 255 / (Vref * −Vrefb)
However, Vref *: Vrefw or Vrefd
The setting of Vrefw and Vrefd will be described. The outputs Vrefw and Vrefd of the D / A conversion circuit 31 are input to the selector 32. The selection operation is performed by a WTGT signal (white reference plate reading timing signal) so that Vrefd is input to the A / D conversion circuit 26. The output voltages from the D / A conversion circuit 31: Vg, Vof, Vrefb, and Vrefw / Vrefd are respectively set directly as shown in FIG. 2 by the gain amplifier 24, the offset setting circuit 25, and the A / D conversion circuit 26 (selector). 32), but as shown in FIG. 6, the output voltage of the D / A conversion circuit 31 may be divided and finely controlled. However, in this case, since the variable range becomes narrow, it is necessary to consider the resistance constant.
[0016]
The digital image signal from the A / D conversion circuit 26 is input to an offset level detection circuit 27 and an offset level subtraction circuit 28.
The offset level detection circuit 27 has a function of capturing and storing the output of the A / D conversion circuit 26 corresponding to the OPB (Optical Black) pixel (black level signal output pixel) of the CCD 9.
FIG. 8 shows an example of the timing of each circuit output and control signal. In the figure, the output of the CCD 9, the output of the sampling circuit 23, and the output of the A / D conversion circuit 26 are respectively assigned to the output timings of an invalid pixel, an OPB pixel, and an effective pixel, and xopb and xlgate (effective pixel output is The line gate signal that is asserted to capture is shown. xopb is an offset level data range instruction signal which is designed to be asserted for a predetermined period at the timing of the output of the A / D conversion circuit 26 corresponding to OPB. It has been empirically known that the latter half of the OPB generally has less noise when used, and this is also illustrated here.
As shown in FIG. 8, the offset level is detected by the offset level detection circuit 27 based on the OPB pixel signal output from the A / D conversion circuit 26 while the xopb signal is asserted. The offset level detected and stored at this time is an average value obtained by taking in a plurality of pixel outputs, and for each output system of the CCD 9 (not shown, for example, two-system output of even-numbered pixels and odd-numbered pixels). Etc.). The offset level subtraction circuit 28 is a circuit that subtracts the offset level value stored in the offset level detection circuit 27 from the input output value of the A / D conversion circuit 26 to perform black level correction.
[0017]
The next white peak detection circuit 30 calculates the peak value of the digital image signal input within a range in which the xlgate signal, the WTGT signal, and the SMPL signal (control signal for sampling the CCD output obtained by reading the white reference plate) are asserted. Is a circuit that detects and saves. FIG. 9 is a timing chart showing the relationship between the WTGT signal, which is a signal in the sub-scanning direction (a direction orthogonal to the main line scanning direction), and the SMPL signal. WTGT is a signal that is asserted when the CCD 9 reads the reference white plate 3 and is used as a switching signal for the selector 32. The selector 32 selects Vrefw when WTGT is asserted, and selects Vrefd when WTGT is negated and inputs the same to the A / D conversion circuit 26. The SMPL is asserted for a whole or a part of the timing (WTGT) when the CCD 9 reads the reference white board 3 and indicates the timing of loading the reference white board data into the shading data FIFO of the shading data storage circuit 35.
As shown in FIG. 9, the WTGT signal is asserted, and a white peak value is detected from a plurality of lines obtained during an effective pixel output period (the xlgate signal period in FIG. 8) in which the white reference plate 3 is read.
The CPU 29 obtains the latest offset level value and peak value by accessing the offset level detection circuit 27 and the white peak detection circuit 30, obtains the adjustment values such as the gain of the gain amplifier 24 and the offset of the offset setting circuit 25, and gives the instruction. give.
The shading data storage circuit 35 is a circuit for sequentially storing values obtained by reading the white reference plate 3 while performing processing such as averaging for each pixel, and the shading correction circuit 34 includes digital image data obtained by reading an original image and shading data. This is a circuit for performing a correction operation with the reference whiteboard data stored in the storage circuit 35. Further, the CPU 29 can read the value of the specific pixel from the shading data storage circuit 35.
The image data after the shading correction is processed in accordance with a use form of the image data, for example, as write data when used for image formation by a plotter (not shown), or as binary data in the case of facsimile transmission. The processing is performed by the image processing circuit 36.
[0018]
Next, a method of setting driving conditions in the CCD 9 and an operation according to the setting will be described in detail. Here, the driving conditions of the CCD 9 changed according to the setting of the selected output mode (color output / monochrome output) and the reading operation at the time of setting the conditions will be described.
FIGS. 7A and 7B are charts showing an example of the drive timing of the CCD 9 when color output and monochrome output are selected. FIG. 7A shows the color output mode, and FIG. 7B shows the monochrome output mode. FIG. 7 shows a main scanning synchronization signal having a predetermined cycle, drive clocks 1 and 2, and a CCD output. Driven by a clock. A clock required for driving is prepared corresponding to the CCD 9 to be used. In this embodiment, the clocks for driving the respective pixels, such as the drive clocks 1 and 2, use the same frequency even in the color / monochrome output mode. That's where the numbers are different. The number of clocks in one main scanning period is set in the color output mode ≧ the monochrome output mode, and the setting of the number of clocks is changed when the mode is changed. By changing the setting of the number of clocks and making one main scanning period in the color output mode longer (tc ≧ tm in FIG. 7) than in the monochrome output, a large output can be obtained from the CCD 9. Things.
The operation in the CCD output mode of this embodiment in which the number of clocks in one main scanning period is changed will be additionally described with reference to FIG. The CCD 9 has a sensor unit that is physically shielded from light, called optical black (OPB), and then has a sensor unit that outputs a voltage called an effective pixel, which is proportional to the amount of incident light. FIG. 8 shows the relationship between the output of the CCD 9, the output of the sampling circuit 23, the output of the A / D conversion circuit 26, and xopb and xlgate in the main scanning direction. When the number of drive clocks in one main scanning period is set and operated, if the set number of drive clocks is equal to or more than the number of OPBs and valid pixels, invalid pixels (invalid pixels which are not proportional to the incident light amount indicated by X in the drawing) ) Is output. The data of the OPB section (indicated by O in the figure), the valid pixel section, and the invalid pixel section are repeatedly output every main scanning period.
In the color output mode (FIG. 7A), more drive clocks are input than in the monochrome output mode (FIG. 7B), so that the output of invalid pixels increases. When these analog image signals are converted into digital image signals as the output of the A / D conversion circuit 26, the result is that a predetermined delay occurs.
Further, as an embodiment different from the above-described embodiment (FIG. 7), the clocks required for driving the driving clocks 1, 2 and the like are set to the same number of clocks in one main scanning period even in the color / monochrome output mode. , The clock frequency can be changed. In this embodiment, when the mode is changed, the setting is changed such that the clock frequency is set in the color output mode ≦ the monochrome output mode. By changing the setting of the clock frequency and making one main scanning period in the color output mode longer than that in the monochrome output, a large output can be obtained from the CCD 9.
[0019]
Next, in the image reading apparatus capable of selecting the output mode (color output / monochrome output), a wide dynamic range can be maintained even when one main scanning period (light accumulation time) is changed according to the selection of the output mode. An embodiment of the present invention will be described.
In an image reading apparatus capable of selecting an output mode (full-color output / monochrome output), a higher S / N is required for full-color output than for monochrome output. Therefore, as described in the above embodiment, full-color output is required. At the time of mode selection, it is possible to cope with this by increasing the light accumulation time of the CCD 9 and increasing the output voltage. In this case, the size of the analog image signal differs depending on the full-color output / monochrome output. Conventionally, to maintain a wide dynamic range while keeping the reference voltage of the A / D conversion circuit constant, it is necessary to adjust the gain of the variable gain amplifier at the input stage of the A / D conversion. To cope with such a case, the gain variable range is required to be wider, which leads to an increase in the cost of the amplifier. Therefore, in the present embodiment, the output mode (color output / monochrome output) is selected as a means for obtaining a digital image signal output having a wide dynamic range even if the variable gain range of the variable gain amplifier is not wide. The present invention proposes an image reading apparatus using low-cost means capable of responding by changing the reference voltage of the A / D conversion circuit according to the above.
[0020]
FIG. 10 is a flowchart illustrating a reading operation of the image reading apparatus according to the present embodiment. Based on the flow of FIG. 10, the configuration and operation of the image reading apparatus of the present example that performs the reading operation by changing the reference voltage of the A / D conversion circuit according to the selection of the output mode (color output / monochrome output) will be described below. Will be described.
When the image reading apparatus is started, first, the operation unit 38 accepts a setting instruction of an output mode (color output / monochrome output) selected by a user's input operation (S11), and confirms that the start button has been pressed. At this point, the operation unit 38 transmits which output mode is selected to the CPU 29 (S12).
Next, the CPU 29 sets the driving conditions of the CCD 9 corresponding to the set output mode in the driving circuit 21 (S13).
The driving conditions set when selecting each mode of color output / monochrome output are such that one main scanning period (light accumulation time) in the color output mode is longer than that in the monochrome output, and the following [Table 1] and [Table 2] It can be implemented in two forms.
[0021]
[Table 1]

[0022]
In Table 1, F1, N1, and N2 are arbitrary numerical values. The feature of this embodiment is that the clock frequency is not changed, and the number of driving clocks in one main scanning period is changed by the selection mode.
[0023]
[Table 2]

[0024]
In Table 2, F1, F2, and N1 are arbitrary numerical values. The feature of this embodiment is that the clock frequency is changed by the selection mode, and the number of driving clocks in one main scanning period is not changed. In this method, since the clock frequency is changed, a PLL circuit is required inside the drive circuit 21.
The above-described set values F1, F2, N1, and N2 may be calculated by the CPU 29 in each case using a calculation formula suitable for the embodiment, or may be a value stored in a memory in advance.
After setting the driving conditions of the CCD 9, the CPU 29 sets a voltage value corresponding to the selected output mode via the D / A conversion circuit 31 as a reference (reference) voltage used for the A / D conversion circuit 26 ( S14).
The condition of the reference (reference) voltage value set when each mode of the color output / monochrome output is selected is such that the reference voltage value in the color output mode is set to be larger than that in the monochrome output, and is implemented, for example, in the form of [Table 3]. I can do it.
[0025]
[Table 3]

[0026]
In Table 3, the values S1 and S2 set by the CPU 29 in the D / A conversion circuit 31 are the same regardless of which output mode is selected (that is, one main scanning period (light accumulation time) corresponds to the output mode). May be changed to a condition suitable for the operation), a value may be used to maintain a predetermined wide dynamic range, and each time, the CPU 29 may calculate the value using a calculation formula suitable for the apparatus. Alternatively, a value stored in a memory in advance may be used. When the reference voltage value is obtained as described above, a method may be used in which only the appropriate value of the selected mode is obtained and the obtained value is set. However, as shown in FIG. The circuit 31 has multiple outputs, and the output is input to the selector 33. The CPU 29 inputs a signal indicating the output mode to the selector 33 and selects a reference voltage for one output mode of the D / A conversion circuit 31.
After setting the reference voltage in the A / D conversion circuit 26, the image reading device starts a reading operation and performs an operation for reading a series of images starting from turning on a lamp (S15).
[0027]
In the above-described embodiment, the driving condition of the CCD 9 in each output operation mode and the reference voltage used for the A / D conversion circuit 26 corresponding to the driving condition can be implemented in such a manner that individually prepared set values are used. Although it is assumed, in the following embodiment, the setting is performed in consideration of the mutual relationship.
Since the output of the CCD 9 is proportional to the light accumulation time (one main scanning time), it can be dealt with by changing the reference voltage used for the A / D conversion circuit 26 in proportion to the light accumulation time (one main scanning time). it can. Even in this case, the gain variable range of the gain amplifier 24 necessary in consideration of the light amount of the light source 4, the sensor sensitivity of the CCD 9, the variation of the mechanical dimensions, and the like can be coped with the same variable range even if the light accumulation time changes.
The setting method of the present embodiment is determined by associating the aforementioned S1 and S2 (see [Table 3]) with N1 and N2 (see [Table 1]) or F1 and F2 (see [Table 2]). realizable.
That is, it is determined by the following equations.
N1 / F1 / f (S1) = N2 / F1 / f (S2): In the case of the driving clock number change method (see [Table 1])
Or,
N1 / F1 / f (S1) = N1 / F2 / f (S2): Clock frequency change method (see [Table 2])
In the above equations, f (S) is the output value (reference voltage of the A / D conversion circuit 26) when the set value S is set in the D / A converter 31.
[0028]
In the embodiment described below, when the reference voltage of the A / D conversion circuit 26 is set to be suitable for each mode of color output / monochrome output, the setting taking into account the variation between the machines of the image reading apparatus is taken into consideration. It is what makes it possible to do.
Since the digital image data obtained by reading the document is subjected to shading correction using the reference whiteboard data stored in the shading data storage circuit 35, the size of the corrected digital image data depends on the reference whiteboard data. For this reason, if the ratio between the reference whiteboard data and the digital image data obtained by reading the document of the reference density is not standardized to a constant value, the corrected digital image data varies among machines even when the document of the same density is read. Will have. This variation can be corrected by changing the set value of the reference voltage of the A / D conversion circuit 26.
In order to set the reference voltage corresponding to each output mode of color output / monochrome output in consideration of such correction, first, at the time of setting one main scanning time (reading time) in the current output mode, when reading the reference white board and reading the original. In this case, a reference voltage value is determined so that the output of the A / D conversion circuit 26 attains a specified ratio, and when the main scanning time is changed, each reference voltage is changed when reading the reference white board and when reading the original. This achieves the desired operation.
[0029]
FIG. 12 is a flowchart illustrating a process of storing the set value of the reference voltage used to implement the operation of the present embodiment. This example is an example in which one main scanning time is switched to t1 and t2.
Referring to FIG. 12, first, in the case of one main scanning time t1, the gain Vg, the reference white plate reading upper reference voltage Vrefw, the document reading upper reference voltage Vrefd, the lower reference voltage Vrefb, and the offset level are supplied to the D / A conversion circuit 31. A default value corresponding to Vof is set (S21).
Next, a document having the reference density is set on the contact glass 2, and the carriage is moved to the reference density document reading position (S22). At this time, the WTGT signal to the selector 32 is operated so that Vrefd (for reading the original) is selected as the upper reference voltage of the A / D conversion circuit 26.
The CPU 29 adjusts the Vof setting value: Sof of the D / A conversion circuit 31 while referring to the value of the offset level detection circuit 27 so that the offset level becomes a predetermined value (S23). Also, the reference density original placed on the contact glass 2 is read, and the Vg setting value of the D / A conversion circuit 31 is set so that the peak data: Ddp becomes a predetermined value while referring to the value of the white peak detection circuit 30. : Sg is adjusted (S24).
Thereafter, the value of the specific pixel: Dd at the time of reading the reference density document is taken out (S25), the carriage is moved to the reading position of the reference white plate 3, and the selector 32 sets the upper reference voltage of the A / D conversion circuit 26 to Vrefw (reference). (For reading a white board) (S26).
[0030]
Next, the reference white plate 3 is read, and the same specific pixel value: Dw as described above is extracted. It is determined whether the value read from the reference white plate 3: Dw falls within the tolerance A with respect to the value read from the reference density original: Dd (S28). If not within the tolerance A, the CPU 29 changes the set value Srefw of the D / A conversion circuit 31 to change Vrefw of the A / D conversion circuit 26 (S29), and reads the reference white board 3 again. , Dd are repeated within the tolerance A, steps S27 to S29 are repeated.
When the value read from the reference white plate 3: Dw falls within the tolerance A with respect to the value read from the reference density document: Dd (S28-YES), the setting of the D / A conversion circuit 31 corresponding to Vrefw at that time. The value is set to Srefw1 (S30).
Next, the set values of the D / A conversion circuit 31 corresponding to the reference white board reading upper reference voltage Vrefw and the document reading upper reference voltage Vrefd used in the A / D conversion circuit 26 at the time of one main scanning time t2: Srefd2, Srefw2. Is obtained (S31). Srefd2 and Srefw2 are obtained according to the following functions.
Srefd2 = f (Srefd1, t1, t2)
Srefw2 = g (Srefw1, t1, t2)
In the above function, f (Srefd, t) and g (Srefw, t) are function expressions for one main scanning time and the set value of the D / A conversion circuit 31.
When the design is made such that (upper reference voltage−lower reference voltage) is proportional to one main scanning time, a function formula is determined as follows.
(Vrefw1-Vrefb) × t2 = (Vrefw2-Vrefb) × t1
Ｖ Vrefw2 = ((Vrefw1-Vrefb) × t2 / t1) + Vrefb
Assuming that Vref * = α · Sref * + β (* is d or w or b)
If the relationship is

It becomes.
Similarly,

It becomes.
In the processing flow, the setting values: Srefw1, Srefw2, and Srefd2 of the D / A conversion circuit 31 obtained as described above are stored in the nonvolatile memory under the control of the CPU 29 (S32), and this processing flow ends.
[0031]
Next, after the set value of the D / A conversion circuit 31 used when one main scanning time is changed by the above-described reference voltage set value storage processing is stored in the non-volatile memory, the setting stored in the memory is stored. An embodiment relating to a processing operation when a value is set in the D / A conversion circuit 31 and reading is performed will be described.
FIG. 13 shows a flowchart of a reading operation in which the set value of the D / A conversion circuit 31 is reflected.
Referring to FIG. 13, first, it is confirmed that the power of the image reading apparatus is turned on (S41-YES), and various default values are set for the D / A converter 31. Here, default values such as a gain Vg, an offset Vof, and a reference (reference) voltage of the A / D conversion circuit 26 are set. As the set value of the upper reference voltage of the A / D conversion circuit 26, for example, when the reading time (1 main scanning time) is t1 in the default setting, Srefw1 and Srefd1 stored in the nonvolatile memory are set ( S41).
Next, starting with the default setting, the peak value is set to a predetermined value so that the offset level becomes a predetermined value while referring to the value of the offset level detection circuit 27 and the value of the white peak detection circuit 30 is referred to. Then, a setup operation such as offset adjustment and gain adjustment is performed (S43).
[0032]
Here, a reading request is waited. If there is a request (S44-YES), it is checked whether or not one main scanning time has been changed. If there is an instruction to change one main scanning time (S45-YES). ), The reference white plate and the reference voltage setting values Srefw and Srefd for reading the document to be instructed to the D / A converter 31 are read from the nonvolatile memory and changed as shown in Table 4 below (S46).
In this example, since Srefw1 and Srefd11 are set first, they are changed to Srefw2 and Srefd12. Here, the set value Srefb for the lower reference voltage Vrefb remains fixed.
[0033]
[Table 4]

[0034]
If there is no instruction to change one main scanning time in step S45, step S46 for changing the reference white plate and the reference voltage setting values Srefw and Srefd for reading the document is passed.
Next, the original 1 (reference white plate 3) is read according to the conditions set through the above flow (S47), and the next reading request is waited (S44).
As described above, when one main scanning time is changed, the reference white plate and the reference voltage setting values Srefw and Srefd for reading the original are changed at the same ratio.
In the above, the example of the function formula of Srefd2 = f (Srefd1, t1, t2) and Srefw2 = g (Srefw1, t1, t2) has been shown. However, this function formula differs depending on the circuit configuration and design concept. There is no problem if the ratio of the reference voltage to the reference white plate / document reading is constant.
Further, in the above-described embodiment, the method of temporarily storing the set value of the reference voltage maintaining the proportional relationship in the memory is used. However, every time the main scanning time is changed, the calculation is performed again and the D / A conversion is performed. The method set in the container 31 may be used.
[0035]
Further, the image reading apparatus shown in the above-described embodiment can be configured as an image reading unit of an image processing apparatus such as a scanner, a copying machine, a facsimile, etc. When configuring an image processing apparatus such as a scanner, a copying machine, a facsimile, etc., a device (for example, an ADF: an auto document feeder) for supplying a reading target to the input side of the image reading device according to the specifications of each image processing device In addition, it is necessary to combine a data processing device that converts and processes read data into data suitable for a use form and an output device (for example, an image forming device) that performs various outputs using the processed data on the output side. Note that these devices that are provided on the input side and the output side of the image reading device to configure an image processing device such as a scanner, a copier, and a facsimile can be implemented by applying existing technology. It is possible.
[0036]
【The invention's effect】
(1) Effects corresponding to the first aspect of the invention
When the reading time (one main scanning time) is changed to obtain the S / N CCD output corresponding to the output mode, the reference value used for the A / D conversion means is set by the means for setting the one main scanning time of the CCD. Since the adjustment is performed in accordance with the set one main scanning time, the performance of the A / D conversion means can be sufficiently improved by a simple method even in a configuration using a gain amplifier (a low-cost amplifier) having a narrow variable range. It can be pulled out and used. In other words, a wide dynamic range of the digital output signal can be secured (an effective number of gradations can be secured). As a result, the rounding amount of the shading correction calculation result can be reduced, and a clear image without rough feeling can be obtained. Obtainable.
(2) Effects corresponding to the inventions of claims 2 and 3
In addition to the effect (1), a value suitable for the purpose of image signal output is set as the reading time (one main scanning time), so that an image suitable for the purpose can be taken out. Further, in the case of color output use, a signal output with higher image quality can be obtained, and in the case of monochrome output use, high productivity of reading processing can be achieved.
[0037]
(3) Effects corresponding to the invention of claim 4
In addition to the above effects (1) and (2), by changing the reference value in proportion to one main scanning time, the control means can be simplified, for example, the gain variable range of the gain amplifier can be minimized. It can be realized by various means.
(4) Effects corresponding to the invention of claim 5
In addition to the effects of the above (1) to (3), when the reading target is the density reference member and the document, the reference value used for the A / D conversion means is changed at the same rate as the reference value for the density reference member and the document image. By doing so, it is possible to eliminate variations in image density before and after the change and in density of each image reading apparatus.
(5) Effects corresponding to the invention of claim 6
In addition to the effects of the above (1) to (4), the reference value used for the A / D conversion means is selected and applied to a numerical value stored in the storage unit in advance corresponding to each setting condition. Thus, the same setting value can be used again even when the power of the image reading apparatus is turned off / on.
(6) Effects corresponding to the invention of claim 7
The effects of the above (1) to (5) can be realized in an image processing apparatus equipped with an image reading device such as a copying machine, a facsimile, a scanner, and the above-described multifunction peripheral, or a filing device for storing image data. It is possible to improve the processing performance of the image processing device.
[Brief description of the drawings]
FIG. 1 shows a schematic configuration of an image reading apparatus according to an embodiment of the present invention.
FIG. 2 is a schematic block diagram of an image reading circuit according to the embodiment of the present invention.
FIG. 3 is a graph showing characteristics of a gain amplifier, showing a relationship between a gain control amount (Vg) and a gain.
FIG. 4 is a graph showing characteristics of an offset setting circuit, showing a relationship between an offset control amount (Vof) and an offset amount.
FIG. 5 is a diagram showing the A / D conversion circuit shown in FIG. 2 in more detail;
FIG. 6 shows another embodiment of a voltage setting circuit that divides the output of the D / A conversion circuit.
FIG. 7 is a chart showing an example of a CCD drive timing when a color output is selected and a monochrome output is selected.
FIG. 8 is a diagram for explaining an operation in a CCD output mode of this embodiment in which the number of clocks in one main scanning period is changed.
FIG. 9 is a timing chart showing a white reference plate reading gate signal in the sub-scanning direction.
FIG. 10 shows a flowchart of a reading operation of the image reading apparatus according to the present invention.
FIG. 11 illustrates an example of a reference voltage setting circuit including a multi-output D / A conversion circuit.
FIG. 12 is a flowchart illustrating a process of storing a set value of a reference voltage used in the A / D conversion circuit.
FIG. 13 shows a flowchart of a reading operation in which a set value is reflected by a D / A conversion circuit.
[Explanation of symbols]
1 ... manuscript, 2 ... contact glass,
3: white reference plate, 4: light source,
9 ... CCD line image sensor
10: read substrate, 11: image processing substrate,
21: drive circuit, 26: A / D conversion circuit,
29: CPU, 31: D / A conversion circuit,
34: shading correction circuit, 35: shading data storage circuit,
38 Operation unit.

Claims (7)

One main scanning time setting means for variably setting one main scanning time; a line image sensor for driving a sensor pixel in accordance with the set one main scanning time to detect an image signal to be read; An A / D conversion unit for converting the analog image signal into a digital signal based on a variable reference value, wherein the reference value used for the A / D conversion unit is set by the one main scanning time setting unit. An image reading apparatus, comprising: means for changing in accordance with one set main scanning time. 2. The image reading apparatus according to claim 1, wherein said one main scanning time setting means can set one main scanning time suitable for the purpose of outputting a read image signal. 3. The image reading apparatus according to claim 2, wherein the use of the read image signal output is color and monochrome, and one main scanning time is long in the case of color and one main scanning time is short in the case of monochrome. An image reading device characterized by the above-mentioned. 4. The image reading apparatus according to claim 1, wherein the means for changing a reference value used in the A / D conversion means changes the reference value in proportion to one main scanning time. An image reading device characterized by the above-mentioned. 5. The image reading device according to claim 1, wherein when the reading target is a density reference member and a document, the unit that changes a reference value used in the A / D conversion unit includes a density reference member and a document. An image reading apparatus, wherein a reference value for a document image is changed at the same ratio. 6. The image reading device according to claim 1, wherein a reference value used for the A / D conversion unit is selected from numerical values stored in a storage unit in advance corresponding to respective setting conditions. An image reading apparatus characterized by being applied. An image processing device comprising the image reading device according to claim 1.

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