JP3732376B2 - Image processing apparatus and image forming apparatus having the same - Google Patents

Description

【０１８５】
となる。ここで［ｎ／２］はｎ／２を超えない最大の整数を表し、ｎは奇数とする。
【０１８６】
この操作は要素がすべて１／ｎ² である荷重マトリクスによる空間フィルタリングである。近傍画素の範囲については、例えば図１４（ａ）のような３×３（ｎ＝３）画素程度の小さな範囲を用いる。なお、図１４（ｂ）は、平滑化処理を行う場合のフィルタ係数の一例を示している。
【０１８７】
以上のフィルタは移動平均法と呼ばれる方法を使用したものであるが、メディアンフィルタなどといったものも考えられる。このメディアンフィルタは、対象画像領域内の画素を濃度の高い順に並べて、その中央の画素の濃度を注目画素の濃度値とするフィルタであり、ノイズの除去などが可能なものである。これらの空間フィルタ処理により、画像入力装置１１０すなわちスキャナの多少のばらつきやノイズなどに影響されず、より正確な濃度ヒストグラムを作成することができる。なお、上記の空間フィルタ処理は、実施の形態１に示した入力階調補正処理部３１３に適用することも可能である。
【０１８８】
単色信号変換部３５２は、前記単色信号変換部５１と同様、ＲＧＢ信号からＣＭＹ系の単色信号を取り出すものである。
【０１８９】
ヒストグラム作成部３５３は、各画素の濃度とその度数（画素数）とにより濃度ヒストグラムを作成するものである。ヒストグラム作成部３５３は、濃度領域分割部３５３ａ、濃度領域作成部３５３ｂおよび第１〜第４の閾値設定部３５３ｅ〜３５３ｈを備えている。
【０１９０】
濃度領域分割部３５３ａは、入力された画像データの濃度ヒストグラムをヒストグラム作成部３５３が作成するに際して、画像データの種々の濃度を有する領域（以下、濃度領域と称する）を次のように分割するものである。なお、この分割機能は、任意に設定可能である。
【０１９１】
濃度ヒストグラムとしては、図６に示したように、通常２５６段階の濃度毎に各々の度数（画素数）を表したものが作成されるが、濃度領域分割部３５３ａは、例えば、図１５に示すように、２５６段階の濃度区分を３２分割（濃度区分：ａ１、ａ２、…、ａ３２）し、簡略化している。このように通常の濃度区分の数に対して、濃度区分の数を少なくすることにより、ハードウエアを大幅に簡略化することができる。なお、より正確な処理を行うならば、濃度区分を多くすること、即ち濃度領域の分割数を増やすことが好ましい。
【０１９２】
濃度領域を複数の濃度区分に分割する場合には、各濃度区分の幅、即ち各濃度区分における濃度値の幅を均等にする必要はなく、情報として相対的に重要な領域を細かく分割する。図１５に示す例では、低濃度値側の濃度区分と高濃度値側の濃度区分とを細かくし、中濃度値側の濃度区分を大きくしている。
【０１９３】
濃度ヒストグラムを作成する場合のその他の処理については、前述の実施の形態１の場合と同様である。
【０１９４】
第１〜第４の閾値設定部３５３ｅ〜３５３ｈは第１〜第４の閾値を設定するものである。
【０１９５】
第１の閾値は、実施の形態１の場合と同様、どの濃度値までを下地と判断するかについての判断基準となるものであり、下地と判断される濃度値の最大値を示している。
【０１９６】
第２の閾値は、実施の形態１の場合と同様、どれだけの度数（画素数）から下地と判断するかについての判断基準となるものであり、下地と判断される画素数の最小値を示している。
【０１９７】
なお、第１および第２閾値をＲＯＭ等に記憶させておき、必要に応じてスイッチ等により、メモリ等の記憶手段に格納される閾値を設定できるようにしておけば良い点、並びに図８及び図９に示した構成により使用者が任意に設定できるようにしても構わない点は前述の通りである。
【０１９８】
第３の閾値は、最低どの濃度値までを最大濃度と判断するかについての判断基準となるものであり、出力画像における原稿の最大濃度と判断される濃度値の最小値を示している。
【０１９９】
第４の閾値は、どれだけの度数から画像にとっての必要濃度と判断するか、即ちどれだけの度数から最大濃度として画像に表示すべきかということについての判断基準となるものであり、出力画像に最大濃度として表示する場合に必要な画素数の最小値を示している。
【０２００】
これら第３および第４閾値は調節可能であり、この調整を行うことにより、より広範囲な処理が可能となる。
【０２０１】
第３の閾値については、第１の閾値を決定する場合と同様に、予想される複数の値を予めＲＯＭ等に記憶させておき、必要に応じてスイッチ等により、メモリ等の記憶手段に格納される閾値を設定できるようにしておく。あるいは、図８に示したデジタルカラー複写機２の操作部より、使用者が任意に設定できるようにしてもよい。
【０２０２】
第４の閾値についても、予め予想される複数の値を予めＲＯＭ等に記憶させておき、例えば、デジタルカラー複写機２の原稿台１１１に載置された原稿のサイズを検知する信号や、操作部に設けられている用紙などの記録媒体選択ボタンからの検知信号を基に、メモリ等の記憶手段に格納される閾値を設定できるようにしておけばよい。あるいは、第２の閾値の設定の場合と同様に、図９に示すデジタルカラー複写機２の操作部より、使用者が任意に設定できるようにしても構わない。
【０２０３】
なお、図８、図９に示したデジタルカラー複写機２の操作部より第１〜第４の閾値を入力する場合には、例えば液晶パネルからなる表示部（図示せず）に、例えば「薄い色を選択して下さい」等のメッセージが表示され、使用者がそのメッセージに従って処理を行い、これによって対応する閾値が順次設定されるようにしてもよい。
【０２０４】
また、本デジタルカラー複写機２では、図８に示した操作部から誤った数値が入力されることによる誤動作を防ぐために、第１、第３の閾値については、各々上限値および下限値が決められており、これらの範囲外の数値、例えば、下地の濃度としてはありえない高い数値や、最大濃度としては低すぎる数値については禁則処理がなされ、エラーメッセージが表示されるようになっている。
【０２０５】
濃度領域作成部３５３ｂは、下地濃度判別領域作成部３５３ｃと最大濃度判別領域作成部３５３ｄとからなる。
【０２０６】
下地濃度判別領域作成部３５３ｃは、前記第１の閾値に基づいて下地濃度判別対象となる濃度領域、即ち、下地濃度判別領域（濃度が図１５に示す第１の閾値以下の領域）を選択するものである。
【０２０７】
最大濃度判別領域作成部３５３ｄは、前記第３の閾値に基づいて最大濃度判別対象となる濃度領域、即ち最大濃度判別領域（濃度が図１５に示す第３の閾値以上の領域）を選択するものである。
【０２０８】
濃度区分抽出部３５４は、ヒストグラム作成部３５３にて作成された濃度ヒストグラムの各濃度区分の度数（画素数）を、第２の閾値設定部３５３ｆにて設定された第２の閾値と比較することにより、下地と判別される濃度区分（下地として考え得る可能性がある領域：図１５における低濃度側の斜線領域）を抽出するとともに、第４の閾値設定部３５３ｈにて設定された第４の閾値と比較することにより、最大濃度と判別される濃度区分（最大濃度として考え得る可能性がある領域：図１５における高濃度側の斜線領域）を抽出するものである。
【０２０９】
したがって、図１５に示す濃度ヒストグラムにおいて、濃度値が第１の閾値以下であり、かつ度数（画素数）が第２の閾値以上のものが、原稿画像の下地と考え得る可能性のある領域と判断される。また、濃度値が第３の閾値以上であり、かつ度数（画素数）が第４の閾値以上のものが原稿画像の最大濃度と考え得る可能性のある領域と判断される。
【０２１０】
さらに、濃度区分抽出部３５４は、下地と考え得る可能性がある領域の中で、最も下地として判断するにふさわしい濃度区分を選択する。選択される濃度区分は、第１の閾値以下で、かつ第２の閾値以上を満たすもののうち、最も第１の閾値に近いもの、つまり濃度値が最も高いものである。
【０２１１】
上記下地と判断される濃度区分を選択する方法としては、低濃度側、または第１の閾値の高濃度側から、順次、各濃度区分の度数と第２の閾値とを比較して行うことができる。なお、この場合にも、前述のように、第１の閾値の高濃度側から比較するのが好ましい。
【０２１２】
同様にして、濃度区分抽出部３５４は、原稿の最大濃度と考え得る領域の中で、最大濃度の濃度区分を選択する。選択される濃度区分は、第３の閾値以上で、かつ第４の閾値以上を満たすもののうち、最も濃度値が最も高いものである。
【０２１３】
上記原稿の最大濃度と判断される濃度区分を選択する場合も、同様に、高濃度側から比較することにより、容易にかつ速やかに上記条件を充たす最も高い濃度区分を選択することができる。
【０２１４】
図１５の例では、濃度区分αが下地、濃度区分βが最大濃度値（図１５の白ぬきの領域）と判断され、これらが、濃度区分抽出部３５４により、それぞれの区分の濃度値を第１の基準値、第２の基準値として設定される。
【０２１５】
濃度補正曲線作成部３５５は、上記第１の基準値と第２の基準値とに基づいて、濃度補正曲線を作成するものである。この濃度補正曲線の一例を図１６に示す。
【０２１６】
濃度補正曲線の作成の際には、まず、図１６に示す予め基準濃度補正曲線を設定する。さらに、同図に示すように、前記基準濃度曲線に予め等間隔の補正するポイント、即ち補正ポイント（所定の入力濃度値）を設定する。
【０２１７】
つぎに、原稿画像の下地から得られた第１の基準値の濃度値を、作成する濃度補正曲線の始点（低濃度側の端部）とする。この場合、もし第１の基準値が得られていなければ、入力濃度値０の点を始点とする。
【０２１８】
また、原稿画像の最大濃度から得られた第２の基準値の濃度値を、作成する濃度補正曲線の終点とする。この場合、もし第２の基準値が得られていなければ、第３の閾値の値を濃度補正曲線の終点とする。
【０２１９】
次に、上記のようにして決定した始点（第１の基準値）を濃度値０とし、前記基準濃度曲線の補正ポイントにおいて、濃度値が高い側でかつ上記始点に最も近い補正ポイントａと上記始点とを直線で結ぶ。同様にして、決定された終点を濃度値２５５とし、前記基準濃度曲線の補正ポイントにおいて、濃度値が低い側でかつ上記終点に最も近い補正ポイントｂと終点とを直線で結ぶ。このような処理により濃度補正曲線を得る。
【０２２０】
なお、ここでは、始点および終点と補正ポイントとを直線により結ぶものとしているが、これに限定されることなく、他の適切な例えば曲線により結ぶものとしてもよい。
【０２２１】
このようにして、各入力画像に対する濃度補正曲線を作成し、この濃度補正曲線に基づいて画像を補正することにより、最適な画像を形成することができる。即ち、本スキャンが開始されると、作成された濃度補正曲線に基づいて、例えば、図１６に示す始点（第１の基準値）以下であり、かつ終点（第２の基準値）以上の濃度が濃度補正曲線作成部３５５により除去され、各入力値に対する濃度値が補正された最適な画像が出力される。また、上記のようにして濃度補正曲線を得る構成により、ハードウエアを大幅に簡略化することができる。
【０２２２】
補正値設定部３５６は、濃度補正曲線作成部３５５が濃度補正曲線を作成する際に使用する始点（第１の基準値）および終点（第２の基準値）を、手動調整により低濃度側および高濃度側に任意に設定可能とするものである。
【０２２３】
即ち、場合によっては、使用者が、自動露光調整機能によるものではなく、自分で調整した好みの画像を出力したいということが生じ得る。その場合には、作成された濃度補正曲線を基準に、始点（第１の基準値）および終点（第２の基準値）の値を、補正値設定部３５６を操作することにより、手動で調整できるようにしてもよい。この場合、補正値設定部３５６は、例えばデジタルカラー複写機２の操作部に設けられた、図８に示した形態の露光調整ボタンを有する。これにより、使用者の好みに応じて低濃度、高濃度を調節でき、使用者の好みに応じて調整された画像を出力することが可能となる。
【０２２４】
この手動による濃度補正曲線の調整を行う補正値設定部３５６は、次のような構成とすることができる。例えば、濃度補正曲線作成時における始点（第１の基準値）、終点（第２の基準値）を、例えば上記露光調整ボタンを操作することにより、ある一定値ごとに低濃度側および高濃度側にずらせるようにしておけばよい。このような構成により、手動の濃度補正を容易に行うことができる。
【０２２５】
信号変換部３５７は、前記単色信号をＫ信号に変換するものである。
【０２２６】
上記の入力階調補正部３３１の各部の処理を行うためのプログラムは、図１９に示すＲＯＭ５８に記憶されており、ＣＰＵ５９がそのプログラムを実行するようになっている。なお、同図においては、記載の簡略化のため、補正値設定部３５６へのアクセスを濃度補正曲線作成部３５５により代表させている。
【０２２７】
次に、上記入力階調補正部３３１による入力階調補正処理を図１７のフローチャートに基づいて説明する。
【０２２８】
コピースタートボタンが操作されたとき、自動露光モードが設定されていると（Ｓ２１）、まず画像入力装置１１０によるプレスキャンが行われる（Ｓ２２）。なお、自動露光調整モード設定ボタンは、デジタルカラー複写機２の例えば操作部（図示せず）に設けられている。また、Ｓ２１において自動露光モードが設定されていないときには、通常のコピー動作が行われる（Ｓ３５）。
【０２２９】
次に、画像入力装置１１０にて読み取られた原稿の全画素のＲＧＢ信号に対して、フィルタ処理部３５１により前述のフィルタ処理が行われる（Ｓ２３）。
【０２３０】
次に、単色信号変換部３５２により単色信号（例えば、Ｍ信号）が選択される（Ｓ２４）。
【０２３１】
次に、下地及び最大濃度を抽出するにあたり、手動モードによる濃度領域の設定が選択されているか否が判断される（Ｓ２５）。なお、この判断は、ＣＰＵ５９にて行われる。
【０２３２】
下地及び最大濃度を抽出する際の濃度領域の選定にあたっては、第１の閾値（下地の選択に使用）並びに第３の閾値（最大濃度の選択に使用）が予め設定されているが、手動モードによる設定が選択されている場合には、それによる濃度領域の設定が各々なされる（Ｓ２６）。
【０２３３】
次に、Ｓ２３にてフィルタ処理され、Ｓ２４にて選択された単色信号を用いて、ヒストグラム作成部３５３により、前述のようにして例えば図１５に示す濃度ヒストグラムが作成される（Ｓ２７）。
【０２３４】
次に、ヒストグラム作成部３５３にて作成された濃度ヒストグラムに基づき、最終的に、濃度区分抽出部３５４により、第２の閾値を用いて下地（第１の基準値）が判別され（Ｓ２８）、第４の閾値を用いて最大濃度（第２の基準値）が判別される（Ｓ２９）。
【０２３５】
次に、Ｓ２８で抽出された下地の濃度値とＳ２９で抽出された最大濃度の濃度値が、それぞれ第１の基準値と第２の基準値として設定される（Ｓ３０）。なお、これら第１および第２の基準値も、前述のように、手動により任意に設定可能である。
【０２３６】
次に、濃度補正曲線作成部３５５により、上記の第１と第２の基準値に基づいて、図１６に示したように、濃度補正曲線が作成され（Ｓ３１）、この濃度補正曲線を用いて画像データが補正され、その画像が出力される（Ｓ３２）。
【０２３７】
出力された上記画像に対しては、さらに濃度調整を行うか否かの判断がなされ（Ｓ３３）、さらに濃度調整が選択されると、手動モードによる濃度設定が行われた後（Ｓ３４）、Ｓ２８に戻ってそれ以下の処理を繰り返す。
【０２３８】
即ち、Ｓ２８において下地を抽出するにあたっては第２の閾値が、Ｓ２９にて最大濃度を抽出するにあたっては第４の閾値が、それぞれ予め設定されているものの、これらの値は手動により設定することも可能である。そこで、さらに濃度調整を行う場合は、Ｓ３４にて手動モードにより第２及び第４の閾値の設定がなされ、Ｓ２８からＳ３２の処理が再度行われる。なお、Ｓ３３にて濃度調整を行う必要がないと判断された場合には、この時点で一連の処理を終了する。
【０２３９】
上記の動作では、Ｓ３３にて濃度調整を行う場合、手動モードにて、Ｓ２８での下地及びＳ２９での最大濃度を判断するための第２の閾値及び第４の閾値の値を変えるようにしているが、図１８に示すように、Ｓ３４からＳ３０に戻り、前記の第１及び第２の基準値を変えるようにしてもよい。なお、同図での各処理については、図１７において説明したものと同様である。
【０２４０】
以上の説明では、単色信号がＣＭＹ系の信号である場合について例示している。一方、単色信号がＲＧＢ系である場合には、下地と考え得る可能性のある領域（複数の濃度区分）は、作成されたヒストグラムにおいて、濃度値が第１の閾値以上であり、度数（画素数）が第２の閾値以上のものである。また、原稿の最大濃度と考え得る可能性のある領域（複数の濃度区分）は、作成されたヒストグラムにおいて、濃度値が第３の閾値以下であり、度数（画素数）が第４の閾値以上のものである。
【０２４１】
また、単色信号がＲＧＢ系である場合において、原稿の下地と考え得る領域のうちで、最も下地として判断するにふさわしい区分値（第１の基準値）は、第１の閾値以上であり、かつ第２の閾値以上を満たすもののうち、最も第１の閾値に近いもの、つまり濃度値が最も低い区分値である。
【０２４２】
また、原稿の最大濃度と考え得る領域のうちで、最も原稿の最大濃度として判断するにふさわしい区分値（第２の基準値）は、第３の閾値以下であり、かつ第４の閾値以上を満たすもののうち、最も第３の閾値に遠いもの、つまり濃度値が最も低い区分値である。その他の処理においてはＣＭＹ系の単色信号である場合と同様に行えばよい。上記の点は、次の実施の形態３の構成においても同様である。
【０２４３】
また、上記の説明では、濃度補正曲線を得るために、デジタルカラー複写機２がプレスキャンを行う方式について例示している。しかしながら、これに限定されることなく、入力画像データを二つに分離し、一方を一旦画像メモリ等の記憶手段に記憶しておき、他方を用いて濃度補正曲線を求め、前記記憶手段から入力画像データを読み出して画像を出力する方式としてもよい。
【０２４４】
また、本デジタルカラー複写機２も、画像入力装置から情報を入力して、所定の画像処理を行い、その結果を出力する画像形成装置、例えば、インクジェット記録方式や昇華型の記録方式を用いた画像形成装置にも適用可能であるのは勿論である。この点も、次の実施の形態３の構成において、同様である。
【０２４５】
〔実施の形態３〕
本発明の実施の他の形態を図２０ないし図２６に基づいて説明すれば以下の通りである。なお、前記の実施の形態に示した手段と同一の機能を有する手段には同一の符号を付記し、その説明を省略する。
【０２４６】
本デジタルカラー複写機３は、図３に示した画像処理装置３６０を備え、図４に示した構成により自動露光調整モードを実行するようになっている。この画像処理装置３６０は、図３および図４に示す、前記入力階調補正部３１３に代わる入力階調補正部３７１を備えている。
【０２４７】
次に、上記入力階調補正部３７１での入力階調補正処理（自動露光調整）について説明する。なお、ここでは、ＣＭＹより選択された単色信号を用いて処理を行う場合について説明する。
【０２４８】
入力階調補正部３７１は、図２０に示すように、単色信号変換部３６１、ヒストグラム作成部（ヒストグラム作成手段）３６２、組合せ濃度区分抽出部（組合せ濃度区分抽出手段、濃度補正手段）３６３、第２の閾値設定部３６４、下地濃度区分抽出部（下地濃度区分抽出手段、濃度補正手段）３６５、濃度補正曲線作成部（濃度補正曲線作成手段、濃度補正手段）３６６、濃度補正量作成部（濃度補正量作成手段、濃度補正手段）３６７、濃度補正量調整部３６８および信号変換部３６９を備えている。
【０２４９】
単色信号変換部３６１は、前記単色信号変換部５１と同様、ＲＧＢ信号からＣＭＹ系の単色信号を取り出すものである。
【０２５０】
ヒストグラム作成部３６２は、各画素の濃度とその度数（画素数）とにより濃度ヒストグラムを作成するものである。ヒストグラム作成部３６２は、濃度領域分割部３６２ａ、下地濃度判別領域作成部（下地濃度判別領域作成手段）３６２ｂおよび第１の閾値設定部３６２ｃを備えている。
【０２５１】
濃度領域分割部３６２ａは、入力された画像データの濃度ヒストグラムをヒストグラム作成部３５３が作成するに際して、画像データの種々の濃度を有する領域（以下、濃度領域と称する）を次のように分割するものである。なお、この分割機能は、任意に設定可能である。
【０２５２】
濃度ヒストグラムとしては、図６に示したように、通常２５６段階の濃度毎に各々の度数（画素数）を表したものが作成されるが、濃度領域分割部３６２ａは、例えば、図２１に示すように、２５６段階の濃度区分を３２分割（濃度区分：ａ１、ａ２、…、ａ３２）し、簡略化している。このように通常の濃度区分の数に対して、濃度区分の数を少なくすることにより、ハードウェアを大幅に簡略化することができる。
【０２５３】
濃度領域を複数の濃度区分に分割する場合には、各濃度区分の幅、即ち各濃度区分における濃度値の幅を均等にする必要はなく、下地側の濃度領域では、細かくかつ均等幅に分割する。図２１に示す例では、下地の濃度領域になると考えられる低濃度値側の濃度区分を細かくし、高濃度側の濃度区分を大きくしている。
【０２５４】
濃度ヒストグラムを作成する際には、原稿画像のプレスキャンを行う。そして、プレスキャンにより読みとられた各画素の濃度値がどの濃度区分の濃度値であるかに応じて、該当する濃度区分のヒストグラム度数を１加算していく。すなわち、ある濃度区分をａｉとすると、任意の濃度区分Ｄｉにおける度数Ｈｉは、Ｈｉ＝Σｈｊ（ｈｊは濃度区分Ｄｉに含まれている２５６段階の度数）として求めればよい。
【０２５５】
第１の閾値設定部３６２ｃは、濃度領域分割部３６２ａが使用する第１の閾値を設定するものである。この第１の閾値は、どの濃度値までを下地と判断するかについての判断基準となるものであり、下地と判断される濃度値の最大値を示している。
【０２５６】
下地濃度判別領域作成部３６２ｃは、前記第１の閾値に基づいて下地濃度判別対象となる濃度領域（濃度が図２１に示す第１の閾値以下の領域：下地として考え得る可能性がある領域）を選択するものである。
【０２５７】
第２の閾値設定部３６４は組合せ濃度区分抽出部３６３で使用される第２の閾値を設定するものである。この第２の閾値は、下地濃度領域における下記の組合せ濃度区分の総度数が、どれだけの度数から下地と判断するかについての判断基準となるものであり、下地と判断される組合せ濃度区分における総画素数の最小値を示すものである。
【０２５８】
組合せ濃度区分抽出部３６３は、ヒストグラム作成部３６２により作成された濃度ヒストグラムにおいて、複数の濃度区分の組み合わせを設定し、この組合せ濃度区分における総度数（総画素数）を上記の第２の閾値と比較することにより、総度数が第２の閾値以上となる組合せ濃度区分を抽出するものである。
【０２５９】
即ち、組合せ濃度区分抽出部３６３は、下地濃度判別領域作成部３６２ｂにて選択された領域内において、ヒストグラムの度数を用いて、注目する濃度区分を中心としてその前後の濃度区分の組合せを組合せ濃度区分として抽出する。
【０２６０】
例えば、図２１において、注目する濃度区分の区分値をＨｉとすると、前後の濃度区分の区分値はＨｉ−１、Ｈｉ＋１となる。この場合、これらの度数をそれぞれＰ（Ｈ）、Ｐ（Ｈｉ−１）、Ｐ（Ｈｉ＋１）とすると、下地判定の総度数Ｐ（Ｈ）は、
Ｐ（Ｈ）＝Ｐ（Ｈｉ−１）＋Ｐ（Ｈｉ）＋Ｐ（Ｈｉ＋１）となる。
【０２６１】
濃度区分の組合せとしては、図２１に示すように、注目する濃度区分を中心に、低濃度側および高濃度側へ同区分数を組合せる。組合せる数としては濃度区分幅によるが、濃度区分幅が小さくなるほど、組合せる濃度区分数は多く必要になる。
【０２６２】
なお、第１および第２閾値をＲＯＭ等に記憶させておき、必要に応じてスイッチ等により、メモリ等の記憶手段に格納される閾値を設定できるようにしておけば良い点、並びに図８及び図９に示した構成により使用者が任意に設定できるようにしても構わない点は前述の通りである。このような構成により、どの濃度値までを下地と判断するかの第１の閾値を調整することが容易に可能となり、これにより注目するどんな濃度の下地に対しても下地の除去あるいは下地の出力が可能となる。また、どの度数まで下地と判断するかの第２の閾値を調整することが容易に可能であり、これにより注目するどんな大きさの下地に対しても下地の除去あるいは下地の出力が可能となる。
【０２６３】
なお、図８、図９に示したデジタルカラー複写機３の操作部より第１、第２の閾値を入力する場合には、例えば液晶パネルからなる表示部（図示せず）に、例えば「薄い色を選択して下さい」等のメッセージが表示され、使用者がそのメッセージに従って処理を行い、これによって対応する閾値が順次設定されるようにしてもよい。
【０２６４】
また、本デジタルカラー複写機３では、図８に示した操作部から誤った数値が入力されることによる誤動作を防ぐために、第１の閾値については、上限値および下限値が決められており、これらの範囲外の数値、例えば、下地の濃度としてはありえない高い数値については禁則処理がなされ、エラーメッセージが表示されるようになっている。
【０２６５】
下地濃度区分抽出部３６５は、組合せ濃度区分抽出部３６３により抽出された組合せ濃度区分のうちの最大濃度の濃度区分を下地濃度と判断するものである。
【０２６６】
この場合、下地濃度区分抽出部３６５は、まず、組合せ濃度区分抽出部３６３により抽出された組合せ濃度区分のうちの最大濃度の組合せ濃度区分を選択する。つぎに、下地濃度区分抽出部３６５は、選択された組合せ濃度区分のうちの最大濃度の濃度区分を下地（下地濃度）と判断する。この下地は、図２１に示すものでは、網目によって示された濃度区分である。即ち、この下地の判断は、第１の閾値以下、かつ第２の閾値以上を満たす組合せ濃度区分のうちの最も濃度の高い濃度区分に対して行われる。これにより、下地として考え得る領域の中で、最も下地として判断するにふさわしい濃度区分が下地として選択される。
【０２６７】
下地濃度区分抽出部３６５において、下地となる組合せ濃度区分を抽出する際には、低濃度側または高濃度側（第１の閾値側）から、順次各組合せ濃度区分の総度数と第２の閾値とを比較してもよいが、この処理は、第１の閾値の高濃度側から行うのが好ましい。これにより、容易にかつ速やかに下地となる組合せ濃度区分を抽出することができる。
【０２６８】
さらに、下地濃度区分抽出部３６５は、上記のようにして下地と判断した濃度区分の濃度を基準値として設定する。
【０２６９】
濃度補正量作成部３６７は、予め用意された基準濃度補正量線から上記基準値に基づいて、例えば図２２に示す濃度補正量線を作成するとともに、これら基準濃度補正量線と濃度補正量線とに基づいて、濃度補正曲線を作成するための補正量を求めるものである。
【０２７０】
上記基準濃度補正量線は、本実施の形態において、縦軸に補正量、横軸に入力濃度値を設定した座標において、補正量２５５と入力濃度値２５５との交点と原点Ｏとを結んだ直線となっている。
【０２７１】
この基準濃度補正量線は、基準濃度補正曲線を作成するための補正量を決めるものであり、一つの基準となるものである。基準濃度補正量線は、作成する基準濃度補正曲線の形状、例えばその基準濃度補正曲線が適用される文字や写真等のモードによって異なる形状に応じて、その形状に合うものが選択される。
【０２７２】
濃度補正量作成部３６７により作成される濃度補正量線は、下地と判断された上記基準値の濃度値が始点（低濃度側の端部）となり、予め用意された基準濃度補正量線の終点が終点となる。そして、これら始点と終点とをつなぐ形で濃度補正量線が形成される。
【０２７３】
なお、図２２に示した例では、基準濃度補正量線および濃度補正量線が直線となっているが、これらは他の適切な曲線であってもよい。
【０２７４】
濃度補正量作成部３６７は、上記の基準濃度補正量線と濃度補正量線との差により補正量を求めるものである。なお、基準濃度補正量線は、前述のようにして作成されたものである。
【０２７５】
濃度補正曲線作成部３６６は、濃度補正量作成部３６７にて作成された補正量により、例えば図２３に示すように、予め用意された基準濃度補正曲線を補正し、濃度補正曲線を作成するものである。
【０２７６】
濃度補正曲線は、前記基準値の濃度値を始点（低濃度側の端部）として作成される。もし、下地濃度区分抽出部３６５において、該当する下地（基準値）が得られなかった場合、基準濃度補正曲線の補正が行われず、濃度補正曲線は基準濃度補正曲線と同じものになる。
【０２７７】
そして、基準濃度補正曲線に設定した各補正ポイントに対応する前記補正量を、各補正ポイントに適用して基準濃度補正曲線を補正することにより、即ち基準濃度補正曲線の各濃度値に対応する前記補正量を、各濃度値に適用して基準濃度補正曲線を補正することにより、前記濃度補正曲線が作成される。基準濃度補正曲線の補正は、その全ての濃度値に対して行われることが好ましいものの、図２３に示したように、基準濃度補正曲線上に分散した状態で予め設定された補正するポイントについて補正を行うことにより、濃度補正曲線を得るようにしてもよい。
【０２７８】
なお、図２２および図２３による説明では、基準濃度補正曲線の補正が補正量の減算により行われるものとなっているが、基準濃度補正曲線の形状によっては、補正が加算、あるいは加算および減算により行われるものであってもよい。
【０２７９】
上記のようにして、各入力画像に対する濃度補正曲線が作成されることにより、デジタルカラー複写機３においては、最適な画像を得ることができる。即ち、本スキャンが開始されると、作成された濃度補正曲線に基づいて、例えば、図２３に示す始点（基準値）以下の濃度が濃度補正曲線作成部３６６により除去され、各入力値に対する濃度値が補正された最適な画像が出力される。また、上記のようにして濃度補正曲線を得る構成により、ハードウェアを大幅に簡略化することができる。
【０２８０】
濃度補正量調整部３６８は、濃度補正量曲線の始点（基準値）を手動により低濃度側および高濃度側に調整することにより、濃度の補正量を調整するものである。
【０２８１】
即ち、場合によっては、使用者が、自動露光調整機能によるものではなく、自分で調整した好みの画像を出力したいということが生じ得る。この場合には、作成された濃度補正曲線を基準に、始点（基準値）を、濃度補正量調整部３６８を操作することにより、手動で調整できるようにしてもよい。この場合、濃度補正量調整部３６８は、例えばデジタルカラー複写機３の操作部に設けられた、図８に示した形態の露光調整ボタンを有する。
【０２８２】
例えば、濃度補正曲線作成時における始点（基準値）を、上記露光調整ボタンを操作することにより、ある一定値ごとに低濃度側および高濃度側にずらせるようにしておけばよい。このような構成により、手動の濃度補正を容易に行うことができる。
【０２８３】
信号変換部３６９は、前記単色信号をＫ信号に変換するものである。
【０２８４】
上記の入力階調補正部３７１の各部の処理を行うためのプログラムは、図２６に示すＲＯＭ５８に記憶されており、ＣＰＵ５９がそのプログラムを実行するようになっている。なお、同図においては、記載の簡略化のため、濃度補正量調整部３６８および濃度補正量作成部３６７へのアクセスを濃度補正曲線作成部３６６により代表させている。
【０２８５】
次に、上記入力階調補正部３７１による入力階調補正処理を図２４のフローチャートに基づいて説明する。
【０２８６】
コピースタートボタンが操作されたとき、自動露光モードが設定されていると（Ｓ４１）、まず画像入力装置１１０によるプレスキャンが行われる（Ｓ４２）。なお、自動露光調整モード設定ボタンは、デジタルカラー複写機３の例えば操作部（図示せず）に設けられている。また、Ｓ４１において自動露光モードが設定されていないときには、通常のコピー動作が行われる（Ｓ５４）。
次に、単色信号変換部３５２により単色信号（例えば、Ｍ信号）が選択される（Ｓ４３）。
【０２８７】
次に、単色信号変換部３５２により単色信号（例えば、Ｍ信号）が選択される（Ｓ４３）。
【０２８８】
次に、下地及び最大濃度を抽出するにあたり、手動モードによる濃度領域の設定が選択されているか否が判断される（Ｓ４４）。なお、この判断は、ＣＰＵ５９にて行われる。
【０２８９】
下地濃度を抽出する際の濃度領域の選定にあたっては、第１の閾値（下地の選択に使用）が予め設定されているが、手動モードによる設定が選択されている場合には、それによる濃度領域の設定がなされる（Ｓ４５）。
【０２９０】
次に、Ｓ４３にて選択された単色信号を用いて、ヒストグラム作成部３６２により、前述のようにして例えば図２１に示す濃度ヒストグラムが作成される（Ｓ４６）。
【０２９１】
次に、組合せ濃度区分抽出部３６３は、ヒストグラム作成部３６２の下地濃度判別領域作成部３６２ｂにて選択された領域（下地として考え得る可能性がある領域）内において、第２の閾値設定部３６４にて設定された第２の閾値に基づき、下地の候補となる組合せ濃度区分を抽出する（Ｓ４７）。
【０２９２】
次に、下地濃度区分抽出部３６５は、組合せ濃度区分抽出部３６３により抽出された組合せ濃度区分のうちの最大濃度の組合せ濃度区分を選択し、選択した組合せ濃度区分のうちの最大濃度の濃度区分を下地として抽出する。そして、その濃度区分の濃度を基準値として設定する（Ｓ４８）。
【０２９３】
次に、濃度補正量作成部３６７は、予め用意された基準濃度補正量線から上記基準値に基づいて、例えば図２２に示す濃度補正量線を作成するとともに、これら基準濃度補正量線と濃度補正量線とに基づいて、濃度補正曲線を作成するための補正量を求める（Ｓ４９）。
【０２９４】
濃度補正曲線作成部３６６は、濃度補正量作成部３６７にて作成された補正量により、例えば図２３に示すように、予め用意された基準濃度補正曲線を補正し、濃度補正曲線を作成する（Ｓ５０）。
【０２９５】
そして、作成された濃度補正曲線を用いて画像データが補正され、その画像がが出力される（Ｓ５１）。
【０２９６】
出力された上記画像に対しては、さらに濃度調整を行うか否かの判断がなされ（Ｓ５３）、濃度調整が選択されると、手動モードによる濃度設定が行われた後（Ｓ５３）、Ｓ４７に戻ってそれ以下の処理を繰り返す。
【０２９７】
即ち、Ｓ４８において下地を抽出するにあたっては第２の閾値が予め設定されているものの、これらの値は手動により設定することも可能である。そこで、さらに濃度調整を行う場合は、Ｓ５３にて手動モードにより第２の閾値の設定がなされ、Ｓ４７からＳ５１の処理が再度行われる。なお、Ｓ５２にて濃度調整を行う必要がないと判断された場合には、この時点で一連の処理を終了する。
【０２９８】
上記の動作では、Ｓ５２にて濃度調整を行う場合、手動モードにて、Ｓ４７での下地を判断するための第２の閾値の値を変えるようにしているが、図２５に示すように、Ｓ５３からＳ４９に戻り、前記の基準値を変えるようにしてもよい。なお、同図での各処理については、図２４において説明したものと同様である。
【０２９９】
以上のように、本実施の形態のデジタルカラー複写機３における入力階調補正部３７１の処理では、画像の下地を判別する場合に、複数の濃度区分を組合せたもの、即ち組合せ濃度区分を設定し、個々の濃度区分ではなく、この組合せ濃度区分と第２の閾値とを比較することにより、下地を判別するようにしている。
【０３００】
したがって、ハード（スキャナ）の精度が悪い場合、画像データにノイズが混入した場合、あるいは画像を読み込む際に機械的振動が生じた場合にも、これらの影響を抑制して、下地について常に均一な判別を行うことができる。即ち、本実施の形態の構成では、実施の形態２に示した空間フィルタ処理を行うのではなく、組合せ濃度区分を設定することにより、画像データに混入するノイズを除去している。これにより、例えば同じ入力画像に対しては、常に同じ処理を行なうことが可能となり、良質の画像を得ることができる。
【０３０１】
以上の説明では、単色信号がＣＭＹ系の信号である場合について例示している。一方、単色信号がＲＧＢ系である場合には、下地と考え得る可能性のある領域（濃度区分）は、作成されたヒストグラムにおいて、濃度値が第１の閾値以上であり、度数（画素数）が第２の閾値以上のものである。
【０３０２】
また、選択された組合せ濃度区分の中で下地として最もふさわしい濃度区分は、組合せ濃度区分において最も濃度の低い区分が選択される。その他の処理においてはＣＭＹ系の単色信号であった場合と同様に行えばよい。
【０３０３】
本発明の画像処理装置は、入力されたデジタル画像の各画素の濃度に基づいて濃度ヒストグラムを作成するヒストグラム作成手段と、前記濃度ヒストグラムに基づき、前記デジタル画像の下地となる領域の濃度を補正する濃度補正手段とを備えている画像処理装置において、前記ヒストグラム作成手段は、デジタル画像の画素の濃度範囲を複数の濃度区分に分割する濃度領域分割手段と、デジタル画像の画素の濃度範囲を複数の濃度区分に分割する濃度領域分割手段と、作成された濃度ヒストグラムの複数の濃度区分を予め設定された第１の閾値に基づいて区分けし、区分けされた低濃度側の領域を下地濃度判別領域として設定する下地濃度判別領域作成手段とを備え、前記濃度補正手段は、前記下地濃度判別領域の濃度区分の中から画素数が予め設定された第２の閾値以上のものを抽出するとともに、抽出された濃度区分の中で第１の閾値に最も近い濃度区分を画像の下地として判別する濃度区分抽出手段を備えていることを特徴としている。
【０３０４】
上記の画像処理装置において、前記濃度区分抽出手段は、下地となる各濃度区分の判別動作を高濃度側から低濃度側に向かって行う構成としてもよい。
【０３０５】
また、上記の画像処理装置において、前記ヒストグラム作成手段は、各濃度区分に振り分けられる画素数を加算し、この加算した画素数を濃度区分幅で除算して各濃度区分の画素数とする構成としてもよい。
【０３０６】
また、上記の画像処理装置において、前記ヒストグラム作成手段は、下地濃度判別領域における各濃度区分の分割間隔を変更可能である構成としてもよい。
【０３０７】
また、本発明の画像処理方法は、入力されたデジタル画像の各画素の濃度に基づいて濃度ヒストグラムを作成し、作成された濃度ヒストグラムに基づき、前記デジタル画像の下地となる領域の濃度を補正する画像処理方法において、前記濃度ヒストグラムの複数の濃度区分を予め設定された第１の閾値に基づいて区分けし、区分した低濃度側の領域を下地濃度判別領域として設定し、この下地濃度判別領域の濃度区分の中から画素数が予め設定された第２の閾値以上のものを抽出し、抽出した濃度区分の中で第１の閾値に最も近い濃度区分を画像の下地として設定する構成としてもよい。
【０３０８】
上記の画像処理方法は、前記下地濃度判別領域における各濃度区分の分割間隔を他領域における各濃度区分の分割間隔よりも細かくする構成としてもよい。
【０３０９】
【発明の効果】
本発明の画像処理装置は、以上のように、ヒストグラム作成手段は、デジタル画像の画素の濃度範囲を複数の濃度区分に分割する濃度領域分割手段と、これら複数の濃度区分に分割された全濃度範囲を、予め定められた第１の閾値に基づいて区分けすることにより所定濃度区分群からなる所定濃度領域を作成する所定濃度領域作成手段とを有する一方、上記所定濃度領域作成手段にて作成された所定濃度領域における各濃度区分の画素数を予め設定された第２の閾値と比較してこの第２の閾値以上の濃度区分を抽出する濃度区分抽出手段を備え、かつこの濃度区分抽出手段は、抽出された濃度区分の中で第１の閾値に近い濃度区分を画像の下地として判別して上記濃度補正手段に出力するものである。
【０３１０】
それゆえ、ヒストグラム作成手段は、濃度領域分割手段と所定濃度領域作成手段とを有しているので、ヒストグラム作成に際して、先ず、濃度領域分割手段が、デジタル画像の画素の濃度範囲を複数の濃度区分に分割した後、所定濃度領域作成手段が、これら複数の濃度区分に分割された全濃度範囲を、予め定められた第１の閾値に基づいて区分けすることにより所定濃度区分群からなる所定濃度領域を作成する。
【０３１１】
したがって、第１の閾値を適切に設定しておくことによって、画像の下地と見なすときの最大濃度を決定することができ、画像を下地判断濃度領域である所定濃度領域とそれ以外とに区分けすることができる。
【０３１２】
次いで、下地の濃度として採用するために、所定濃度領域の中で、各濃度区分の画素数の多いものが下地の濃度として選択されることになるが、その基準として第２の閾値が予め設定される。したがって、この第２の閾値は、ある画像が与えられたときに、画像全体の下地濃度を判断するに際して、その濃度の分布量つまり画素数が多いものを選ぶための基準となる。
【０３１３】
また、濃度区分抽出手段は、これら抽出された第２の閾値以上の濃度区分の中で第１の閾値に近い濃度区分を画像の下地として判別して濃度補正手段に出力するので、画像の下地としては、下地として考えられる濃度の最大値として設定した第１の閾値による濃度よりも小さく、かつ、画像全体としてその第１の閾値による濃度に近いものが判別される。そして、この選ばれた画像の下地が濃度補正手段に出力されることによって、濃度補正手段はその後、下地の除去やその下地の濃度を補正して出力する等、各種の画像出力のための補正処理を行うことができる。
【０３１４】
この結果、対象画像における画素濃度の濃度ヒストグラムを作成して簡易に画像の下地を判別し、濃度条件の異なる種々の原稿に応じた適切な濃度制御を的確かつ効率良く行い得る画像処理装置を提供することができるという効果を奏する。
【０３１５】
上記の画像処理装置において、前記濃度区分抽出手段は、作成された所定濃度領域を第１の閾値に近い高濃度側から低濃度側に向かって順次、各濃度区分の画素数と第２の閾値とを比較し、第２の閾値以上の最初の濃度区分を画像の下地と判定する構成としてもよい。
【０３１６】
上記の構成によれば、簡易な方法で速やかに、目的とする第１の閾値に近い濃度の下地の判断を行うことができるという効果を奏する。
【０３１７】
上記の画像処理装置において、前記濃度領域分割手段は、各濃度区分に振り分けられる画素数を加算し、この加算した画素数を濃度区分幅で除算して各濃度区分の画素数とする構成としてもよい。
【０３１８】
上記の構成によれば、このようにして求めた画素数は、その濃度区分に含まれる画素数の平均値として求まることになる。この結果、濃度区分の幅が種々異なる場合でも、各濃度区分の画素数の絶対比較が可能となるので、精度良く下地の判別を行うことができるという効果を奏する。
【０３１９】
上記の画像処理装置において、前記濃度領域分割手段は、所定濃度領域における各濃度区分の分割間隔を変更可能に設けられている構成としてもよい。
【０３２０】
上記の構成によれば、各濃度区分の幅を細かく設定することができるので、より正確に画像の下地判別を行うことができるという効果を奏する。
【０３２１】
上記の画像処理装置において、前記濃度補正手段は、画像の下地を判別した結果に基づいて補正を行うべく、各濃度区分についての種々の補正量を格納した複数の濃度補正量テーブルから一つを選択して補正する濃度補正量テーブル選択手段を備えている構成としてもよい。
【０３２２】
上記の構成によれば、各濃度区分についての種々の補正量を格納した複数の濃度補正量テーブルを用いるので、処理速度を短縮しかつ回路規模を小さくすることができるという効果を奏する。
【０３２３】
上記の画像処理装置において、前記濃度補正手段は、濃度補正量テーブルに対して各濃度区分についての種々の補正量を任意に調節できる濃度補正量調節手段を有している構成としてもよい。
【０３２４】
上記の構成によれば、選択された濃度補正量テーブルに対して任意に調節できることにより、使用者の好みにあった出力画像を得ることができるという効果を奏する。
【０３２５】
上記の画像処理方法は、濃度ヒストグラムの全濃度領域から予め定められた第１の閾値に基づいて所定濃度領域を作成し、その所定濃度領域の複数分割された各濃度区分における、第２の閾値以上の画素数を有する濃度区分の中で第１の閾値に近い濃度区分を画像の下地として判別する構成としてもよい。
【０３２６】
上記の構成によれば、対象画像における画素濃度の濃度ヒストグラムを作成して簡易に画像の下地を判別し、濃度条件の異なる種々の原稿に応じた適切な濃度制御を的確かつ効率良く行い得る画像処理方法を提供することができるという効果を奏する。
【０３２７】
上記の画像処理方法は、前記所定濃度領域における各濃度区分の分割間隔が他領域における各濃度区分の分割間隔よりも細かく分けられている構成としてもよい。
【０３２８】
上記の構成によれば、各濃度区分の幅を細かく設定することにより、より正確に画像の下地判別を行うことができるという効果を奏する。
【０３２９】
また、本発明の画像処理装置は、入力されたデジタル画像の各画素の濃度に基づいて濃度ヒストグラムを作成するヒストグラム作成手段と、前記濃度ヒストグラムに基づき、前記デジタル画像の濃度を補正する濃度補正手段とを備えている画像処理装置において、前記ヒストグラム作成手段の処理に先立ち、前記デジタル画像に、デジタル画像の各画素の濃度に基づいて、前記各画素の濃度を補正する空間フィルタ処理を施すフィルタ処理手段を備えている構成である。
【０３３０】
上記の構成によれば、ヒストグラム作成手段の処理に先立ち、デジタル画像に、デジタル画像の各画素の濃度に基づいて、前記各画素の濃度を補正する空間フィルタ処理が施される。こ空間フィルタ処理は、画像データに混入したノイズや、画像を読み込む際の機械的振動等により生じた画像データのばらつきを除去するためのものである。
【０３３１】
したがって、上記空間フィルタ処理を施すことにより、ハード（スキャナ）の精度が悪い場合、画像データにノイズが混入した場合、あるいは画像を読み込む際に機械的振動が生じた場合にも、これらの影響が抑制され、原稿画像に沿った濃度ヒストグラムを作成することができる。これにより、濃度補正手段による画像濃度の補正を適切に行うことができ、良好な画像を得ることができる。
【０３３２】
また、本発明の画像処理装置は、入力されたデジタル画像の各画素の濃度に基づいて濃度ヒストグラムを作成するヒストグラム作成手段と、前記濃度ヒストグラムに基づき、前記デジタル画像の濃度を補正する濃度補正手段とを備えている画像処理装置において、前記ヒストグラム作成手段は、デジタル画像の画素の濃度範囲を複数の濃度区分に分割する濃度領域分割手段を備え、さらに、作成した濃度ヒストグラムの濃度区分から、下地と判別できる濃度区分を抽出し、その濃度を第１の基準値として設定するとともに、最大濃度と判別できる濃度区分を抽出し、その濃度を第２の基準値として設定する基準値設定動作を行うものであり、前記濃度補正手段は、第１の基準値から低濃度側の画像濃度を濃度０に補正し、第２の基準値から高濃度側の画像濃度を最高濃度に補正する構成である。
【０３３３】
上記の構成によれば、ヒストグラム作成手段は、作成した濃度ヒストグラムの濃度区分から、下地と判別できる濃度区分を抽出し、その濃度を第１の基準値として設定するとともに、最大濃度と判別できる濃度区分を抽出し、その濃度を第２の基準値として設定する。そして、濃度補正手段は、第１の基準値から低濃度側の画像濃度を濃度０に補正し、第２の基準値から高濃度側の画像濃度を最高濃度に補正する。
【０３３４】
これにより、入力された画像データに対する濃度補正を簡単かつ良好に行うことができる。
【０３３５】
また、本発明の画像処理装置は、入力されたデジタル画像の各画素の濃度に基づいて濃度ヒストグラムを作成するヒストグラム作成手段と、前記濃度ヒストグラムに基づき、前記デジタル画像の濃度を補正する濃度補正手段とを備えている画像処理装置において、前記ヒストグラム作成手段は、デジタル画像の画素の濃度範囲を複数の濃度区分に分割する濃度領域分割手段を備え、さらに、作成した濃度ヒストグラムの濃度区分から、下地と判別できる濃度区分を抽出し、その濃度を第１の基準値として設定するとともに、最大濃度と判別できる濃度区分を抽出し、その濃度を第２の基準値として設定する基準値設定動作を行うものであり、前記濃度補正手段は、予め設定された基準濃度補正曲線を有し、この基準濃度補正曲線上の所定の補正ポイントと前記第１の基準値および第２の基準値とを結ぶことにより、前記デジタル画像の濃度を補正するための濃度補正曲線を作成する構成である。
【０３３６】
上記の構成によれば、ヒストグラム作成手段は、作成した濃度ヒストグラムの濃度区分から、下地と判別できる濃度区分を抽出し、その濃度を第１の基準値として設定するとともに、最大濃度と判別できる濃度区分を抽出し、その濃度を第２の基準値として設定する基準値設定動作を行う。そして、濃度補正手段は、予め設定された基準濃度補正曲線を有し、この基準濃度補正曲線上の所定の補正ポイントと前記第１の基準値および第２の基準値とを結ぶことにより、デジタル画像の濃度を補正するための濃度補正曲線を作成する。
【０３３７】
これにより、入力されたデジタル画像の濃度を補正するための濃度補正曲線を、簡単かつ迅速に作成することができる。
【０３３８】
上記の画像処理装置において、前記ヒストグラム作成手段は、前記基準値設定動作を行うものとして、作成された濃度ヒストグラムの複数の濃度区分を予め設定された低濃度側閾値に基づいて区分けし、区分けされた低濃度側の領域を第１の濃度領域として選択するとともに、前記複数の濃度区分を予め設定された高濃度側閾値に基づいて区分けし、区分けされた高濃度側の領域を第２の濃度領域として選択する濃度領域作成手段と、前記第１の濃度領域から画像の下地と判別できる濃度区分を抽出し、その濃度を第１の基準値として設定し、前記第２の濃度領域から画像の最大濃度と判別できる濃度区分を抽出し、その濃度を第２の基準値として設定する濃度区分抽出手段とを備えている構成としてもよい。
【０３３９】
上記の構成によれば、ヒストグラム作成手段における第１および第２の基準値設定動作を、濃度領域作成手段と濃度区分抽出手段とにより適切に行うことができる。
【０３４０】
上記の画像処理装置において、前記基準濃度補正曲線上には予め複数の補正ポイントが分散して設定され、前記濃度補正手段は、前記第１の基準点を濃度補正曲線の始点とするとともに、この始点よりも濃度値が高くかつ始点に最も近い前記補正ポイントと始点とを結ぶことにより、濃度補正曲線を作成するものである構成としてもよい。
【０３４１】
上記の構成によれば、簡易な方法で速やかに下地濃度を設定すること、即ち下地濃度を除去する濃度補正曲線を作成することができる。また、入力画像データに対する濃度補正の処理速度を高め、かつ濃度補正のための回路規模を小さくして、ハードウエアを大幅に簡略化することができる。
【０３４２】
上記の画像処理装置において、前記基準濃度補正曲線上には予め複数の補正ポイントが分散して設定され、前記濃度補正手段は、前記第２の基準点を濃度補正曲線の終点とするとともに、この終点よりも濃度値が低くかつ終点に最も近い前記補正ポイントと終点とを結ぶことにより、濃度補正曲線を作成するものである構成としてもよい。
【０３４３】
上記の構成によれば、簡易な方法で速やかに最大濃度を設定することができ、階調の再現性を大きくし、各入力画像に対して最適かつ高精度の濃度補正曲線を作成することができる。また、入力画像データに対する濃度補正の処理速度を高め、かつ濃度補正のための回路規模を小さくして、ハードウエアを大幅に簡略化することができる。
【０３４４】
本発明の画像処理装置は、入力されたデジタル画像の各画素の濃度に基づいて濃度ヒストグラムを作成するヒストグラム作成手段と、前記濃度ヒストグラムに基づき、前記デジタル画像の下地となる領域の濃度を補正する濃度補正手段とを備えている画像処理装置において、前記ヒストグラム作成手段は、作成された濃度ヒストグラムの複数の濃度区分を予め設定された第１の閾値に基づいて区分けし、区分けされた低濃度側の領域を下地濃度判別領域として設定する下地濃度判別領域作成手段を備え、前記濃度補正手段は、前記下地濃度判別領域において連続する複数の濃度区分からなる組合せ濃度区分を順次抽出する組合せ濃度区分抽出手段と、前記組合せ濃度区分抽出手段により抽出された組合せ濃度区分の中から総画素数が予め設定された第２の閾値以上のものを抽出し、そのうちの第１の閾値に最も近い組合せ濃度区分における所定の濃度区分を下地と判別する下地濃度区分抽出手段とを備えている構成である。
【０３４５】
上記の構成によれば、ヒストグラム作成手段の下地濃度判別領域作成手段は、作成された濃度ヒストグラムの複数の濃度区分を予め設定された第１の閾値に基づいて区分けし、区分けされた低濃度側の領域を下地濃度判別領域として設定する。濃度補正手段は、前記下地濃度判別領域において連続する複数の濃度区分からなる組合せ濃度区分を順次抽出する。下地濃度区分抽出手段は、組合せ濃度区分抽出手段により抽出された組合せ濃度区分の中から総画素数が予め設定された第２の閾値以上のものを抽出し、そのうちの第１の閾値に最も近い組合せ濃度区分における所定の濃度区分を下地と判別する。そして、濃度補正手段は、下地と判別された濃度区分の濃度に基づいて、デジタル画像の下地となる領域の濃度を補正する。
【０３４６】
このような構成により、ハードウェア（スキャナ）の精度が悪い場合、画像データにノイズが混入した場合、あるいは画像を読み込む際に機械的振動が生じた場合にも、これらの影響を抑制し、入力画像における下地の判別を正確に行うことができる。これにより、濃度補正手段による画像濃度の補正を適切に行うことができ、同様の入力画像に対しては常に均一な処理を行なうことが可能となる。この結果、入力画像に対して最適な階調処理を施し、良好な画像を出力することができる。
【０３４７】
上記の画像処理装置において、前記組合せ濃度区分抽出手段は、前記組合せ濃度区分の抽出動作を、前記下地濃度判別領域の高濃度側から低濃度側へ行うものであり、前記下地濃度区分抽出手段は、第２の閾値以上の最初の組合せ濃度区分を下地と判別される濃度区分を含む組合せ濃度区分として選択する構成としてもよい。
【０３４８】
上記の構成によれば、組合せ濃度区分抽出手段は、組合せ濃度区分の抽出動作を、下地濃度判別領域の高濃度側（第１の閾値側）から低濃度側へ行う。そして、下地濃度区分抽出手段は、第２の閾値以上の最初の組合せ濃度区分を下地と判別される濃度区分を含む組合せ濃度区分として選択する。
【０３４９】
これにより、簡単かつ速やかに下地となる濃度区分を抽出することができ、装置の処理速度を高めることができる。
【０３５０】
上記の画像処理装置において、前記下地濃度区分抽出手段は、第２の閾値以上の組合せ濃度区分のうちの最大濃度を示す濃度区分を下地と判別する構成としてもよい。
【０３５１】
上記の構成によれば、下地の濃度値を適切なものに設定することができる。
【０３５２】
上記の画像処理装置において、前記組合せ濃度区分抽出手段は、注目する濃度区分にその濃度区分の高濃度側と低濃度側の濃度区分をそれぞれ同数加えて組合せ濃度区分とする構成であってもよい。
【０３５３】
上記の構成によれば、注目する濃度区分にその濃度区分の高濃度側と低濃度側の濃度区分をそれぞれ同数加えて組合せ濃度区分が設定されるので、組合せ濃度区分は下地となる濃度区分を抽出する上で適切なものとなり、これにより下地の判別を正確に行うことができる。
【０３５４】
上記の画像処理装置において、前記濃度補正手段は、下地と判別された濃度区分の濃度を基準値とし、この基準値が、予め設定された基準濃度補正量線における低濃度側の始点となるように、基準濃度補正量線を補正して濃度補正量線を作成し、これら基準濃度補正量線と濃度補正量線との差分により濃度補正曲線の補正量を求める濃度補正量作成手段と、前記補正量に基づいて前記デジタル画像の濃度を補正するための濃度補正曲線を作成する濃度補正曲線作成手段とを備えている構成としてもよい。
【０３５５】
上記の構成によれば、濃度補正手段の濃度補正量作成手段は、下地と判別された濃度区分の濃度を基準値とし、この基準値が、予め設定された基準濃度補正量線における低濃度側の始点となるように、基準濃度補正量線を補正して濃度補正量線を作成し、これら基準濃度補正量線と濃度補正量線との差分により濃度補正曲線の補正量を求める。そして、濃度補正曲線作成手段は、前記補正量に基づいてデジタル画像の濃度を補正するための濃度補正曲線を作成し、濃度補正手段は、この濃度補正曲線に基づいてデジタル画像の下地となる領域の濃度を補正する。
【０３５６】
上記の構成によれば、各入力画像に対して最適な濃度補正曲線を精度良く作成することができる。また、上記のようにして濃度補正曲線を作成することにより、装置の処理速度を高め、かつ回路規模を小さくしてハードウェアを大幅に簡略化することができる。
【０３５７】
本発明の画像形成装置は、上記の画像処理装置を備えているものである。
【０３５８】
それゆえ、例えば、複写機やファクシミリ等の画像形成装置に、本発明の画像処理装置を搭載することにより、対象画像における画素濃度の濃度ヒストグラムを作成して簡易に画像の下地を判別し、濃度条件の異なる種々の原稿に応じた適切な濃度制御を的確かつ効率良く行い得る画像形成装置を提供することができるという効果を奏する。
【図面の簡単な説明】
【図１】本発明における画像処理装置の実施の一形態を示すものであり、入力階調補正部のブロック図である。
【図２】上記画像処理装置を備えた画像形成装置としてのデジタルカラー複写機を示す構造図である。
【図３】上記画像処理装置において通常の画像処理を行う場合に使用される部分を示すブロック図である。
【図４】上記画像処理装置において下地判別を行う場合に使用される部分を示すブロック図である。
【図５】上記画像処理装置による画像処理方法の流れを示すフローチャートである。
【図６】上記画像処理装置により画像処理を行う場合に、画素の濃度領域を２５６段階に区分したときに作成される濃度ヒストグラムの一例を示す図である。
【図７】上記画像処理装置により、下地判別を行う場合に、画素の濃度領域を１６個の濃度区分に分割した状態の濃度ヒストグラムを示す説明図である。
【図８】上記画像処理装置にて濃度ヒストグラムを作成する際に、第１の閾値を任意に設定するためのデジタルカラー複写機の操作部の構成を示す説明図である。
【図９】上記画像処理装置にて濃度ヒストグラムを作成する際に、第２の閾値を任意に設定するためのデジタルカラー複写機の操作部の構成を示す説明図である。
【図１０】上記画像処理装置の濃度補正手段にて使用される、補正量を格納した濃度補正量テーブルを示す説明図である。
【図１１】上記濃度補正手段にて濃度補正量テーブルを用いて補正された状態を示すものであり、基準濃度補正曲線に対して補正された濃度補正曲線を示す説明図である。
【図１２】図１に示した入力階調補正部について、ＣＰＵおよびＲＯＭまでを含んだ構成を示すブロック図である。
【図１３】本発明における画像処理装置の実施の他の形態を示すものであり、入力階調補正部の構成を示すブロック図である。
【図１４】図１４（ａ）は、図１３に示したフィルタ処理部の動作の説明に使用される近傍画素の範囲の説明図、図１４（ｂ）は、フィルタ処理部が平滑化処理を行う場合のフィルタ係数の一例を示す説明図である。
【図１５】図１３に示したヒストグラム作成部で作成される濃度ヒストグラムの一例と下地および最大濃度の選択例とを示す説明図である。
【図１６】図１３に示した濃度補正曲線作成部で作成される濃度補正曲線の一例を示す説明図である。
【図１７】図１３に示した入力階調補正部を有する画像処理装置の画像処理動作の一例を示すフローチャートである。
【図１８】図１７のフローチャートに示した画像処理動作の他の例を示すフローチャートである。
【図１９】図１３に示した入力階調補正部について、ＣＰＵおよびＲＯＭまでを含んだ構成を示すブロック図である。
【図２０】本発明における画像処理装置の実施のさらに他の形態を示すものであり、入力階調補正部の構成を示すブロック図である。
【図２１】図２０に示したヒストグラム作成部で作成される濃度ヒストグラムの一例と下地の選択例とを示す説明図である。
【図２２】図２０に示した濃度補正量作成部で作成される補正量の一例を示す説明図である。
【図２３】図２０に示した濃度補正曲線作成部で作成される濃度補正曲線の一例を示す説明図である。
【図２４】図２０に示した入力階調補正部を有する画像処理装置の画像処理動作の一例を示すフローチャートである。
【図２５】図２４のフローチャートに示した画像処理動作の他の例を示すフローチャートである。
【図２６】図２０に示した入力階調補正部について、ＣＰＵおよびＲＯＭまでを含んだ構成を示すブロック図である。
【符号の説明】
１ デジタルカラー複写機（画像形成装置）
２ デジタルカラー複写機（画像形成装置）
３ デジタルカラー複写機（画像形成装置）
５２ ヒストグラム作成部（ヒストグラム作成手段）
５２ａ 濃度領域分割部（濃度領域分割手段）
５２ｂ 濃度領域作成部（所定濃度領域作成手段）
５２ｃ 第１の閾値設定部
５２ｄ 第２の閾値設定部
５３ 濃度区分抽出部（濃度区分抽出手段）
５４ 濃度補正部（濃度補正手段）
５５ 濃度補正量調節部（濃度補正量調節手段、濃度補正手段）
５６ 濃度補正量テーブル選択部（濃度補正量テーブル選択手段、濃度補正手段）
８１ 濃度補正量テーブル
１１０ 画像入力装置（画像入力手段）
２１０ 画像形成部
３１０ 画像処理装置
３１３ 入力階調補正部
３３０ 画像処理装置
３３１ 入力階調補正部
３５１ フィルタ処理部（フィルタ処理手段）
３５３ ヒストグラム作成部（ヒストグラム作成手段）
３５３ａ 濃度領域分割部（濃度領域分割手段）
３５３ｂ 濃度領域作成部（濃度領域作成手段）
３５３ｃ 下地濃度判別領域作成部
３５３ｄ 最大濃度判別領域作成部
３５３ｅ 第１の閾値設定部
３５３ｆ 第２の閾値設定部
３５３ｇ 第３の閾値設定部
３５３ｈ 第４の閾値設定部
３５４ 濃度区分抽出部（濃度補正手段、濃度区分抽出手段）
３５５ 濃度補正曲線作成部（濃度補正手段）
３５６ 補正値設定部
３６０ 画像処理装置
３６２ ヒストグラム作成部（ヒストグラム作成手段）
３６２ａ 濃度領域分割部（濃度領域分割手段）
３６２ｂ 下地濃度判別領域作成部（下地濃度判別領域作成手段）
３６２ｃ 第１の閾値設定部
３６３ 組合せ濃度区分抽出部（組合せ濃度区分抽出手段、濃度補正手段）
３６４ 第２の閾値設定部
３６５ 下地濃度区分抽出部（下地濃度区分抽出手段、濃度補正手段）
３６６ 濃度補正曲線作成部（濃度補正量作成手段、濃度補正手段）
３６７ 濃度補正量作成部（濃度補正曲線作成手段、濃度補正手段）
３６８ 濃度補正量調整部
３７１ 入力階調補正部[0001]
BACKGROUND OF THE INVENTION
The present invention provides an image processing apparatus that creates a density histogram from the density of each pixel in an input digital image, and performs density correction processing of the digital image based on the result of the created density histogram, and image formation provided with the image processing apparatus In particular, the present invention relates to an apparatus and an image processing method, in which a background of an image is determined from a density histogram of pixel density of a target image, and an optimal density correction curve is created based on the determination result.
[0002]
[Prior art]
In addition to the conventional analog type, digital type image forming apparatuses such as electronic copying machines have been widely used. Under such circumstances, there is an automatic exposure function, which is a general function in an analog copying machine, that is, a method of obtaining the optimum image quality by detecting the density of an original with an original density sensor and changing the brightness of an exposure lamp. Are known.
[0003]
On the other hand, in a digital copying machine, as a conventional method for realizing the above automatic exposure function, a density histogram is used in Japanese Patent Publication No. 3-30143, Japanese Patent Laid-Open No. 8-204963, or Japanese Patent Laid-Open No. 9-43915. The proposed automatic density adjustment has been proposed.
[0004]
In the above Japanese Patent Publication No. 3-30143, a density histogram is created by sampling at a constant period and also by sampling at an extreme value, and comparing the density histogram pattern with ROM (Read Only Memory) data. Thus, the type of each original such as a white background original, a color background original, or a white pencil original is discriminated and an image density control signal is output.
[0005]
In Japanese Patent Laid-Open No. 8-204963, two peak positions of white and black are determined from the created density histogram to determine a reference value, and further, the type of image is determined from the density histogram to determine the reference value. Correction is performed, and gradation correction is performed using the corrected reference value.
[0006]
Further, in Japanese Patent Application Laid-Open No. 9-43915, in an automatic density adjustment method for obtaining a density correction reference value by referring to the density histogram values, the density histogram is applied only to the document area even when the document cover is open. Is described, and automatic density adjustment is performed without being affected by the data outside the document.
[0007]
[Problems to be solved by the invention]
However, the conventional image processing apparatus, the image forming apparatus including the image processing apparatus, and the image processing method have the following problems and cannot be said to be sufficient.
[0008]
That is, in Japanese Patent Publication No. 3-30143, since the ROM data is used to discriminate the type of the document, it is necessary to store data corresponding to the data beforehand in order to make a detailed discrimination. Capacity increases. Further, there is a problem that a special image is determined to be indistinguishable and the application range is limited.
[0009]
The techniques of Japanese Patent Application Laid-Open Nos. 8-204963 and 9-43915 use a method for obtaining a reference value for gradation correction from a density histogram of a target image. For this reason, it is impossible to determine whether the target image is a photograph or a character, a photograph and a character are mixed, or there are a plurality of backgrounds. If it is not represented faithfully, an optimal correction reference value cannot be calculated, and there is a problem that automatic density adjustment is impossible or a defective image is output.
[0010]
Furthermore, Japanese Patent Application Laid-Open No. 9-43915 has a problem in that different processes are performed depending on opening and closing of the document cover, and the process becomes complicated.
[0011]
Furthermore, many conventional digital image processing apparatuses incorporate a manual density adjusting device. In this case, the user makes a trial copy and adjusts it to the optimum density, or makes adjustments depending on experience, but in any case, it is impossible to prevent useless copying. ing.
[0012]
The present invention has been made in view of the above-described conventional problems, and an object of the present invention is to create a density histogram of pixel density in a target image, easily determine the background of the image, and various originals having different density conditions. It is an object of the present invention to provide an image processing apparatus, an image forming apparatus including the image processing apparatus, and an image processing method capable of accurately and efficiently performing appropriate density control according to the above.
[0013]
[Means for Solving the Problems]
In order to solve the above problems, the image processing apparatus of the invention creates a density histogram from the density of each pixel of the input digital image, and the density of the digital image based on the result of the histogram creation means In the image processing apparatus having the density correction means for correcting the density, the histogram creation means is divided into density area dividing means for dividing the density range of the pixel of the digital image into a plurality of density sections, and the plurality of density sections. A predetermined density area creating means for creating a predetermined density area consisting of a predetermined density classification group by dividing the entire density range based on a predetermined first threshold; The number of pixels of each density section in the created predetermined density area is compared with a second threshold value set in advance, and the density is equal to or higher than the second threshold value. A density category extracting means for extracting a category is provided, and the density category extracting means discriminates a density category that is close to the first threshold among the extracted density categories as the background of the image, and outputs it to the density correction means. It is characterized by that.
[0014]
According to the above configuration, the histogram creating means creates a density histogram from the density of each pixel of the digital image. Further, the density correction unit corrects the density of the digital image based on the result of the histogram creation unit.
[0015]
Here, since the histogram creating means includes the density area dividing means and the predetermined density area creating means, when creating the histogram, the density area dividing means first sorts the density range of the pixel of the digital image into a plurality of density sections. Then, the predetermined density area creating means divides the entire density range divided into the plurality of density sections based on a predetermined first threshold value, thereby forming a predetermined density area consisting of a predetermined density section group. Create
[0016]
Therefore, by appropriately setting the first threshold value, the maximum density when it is regarded as the background of the image can be determined, and the image is divided into the predetermined density area which is the background determination density area and the other areas. be able to.
[0017]
Next, in this predetermined density region, the density category extraction means compares the number of pixels of each density category in the predetermined density region created by the predetermined density region creation means with a second threshold value set in advance. A density category that is equal to or greater than the threshold is extracted.
[0018]
In other words, in order to adopt as the background density, a predetermined density area having a large number of pixels in each density section is selected as the background density, and the second threshold is set in advance as the reference. Is done. Therefore, the second threshold value is a reference for selecting a density distribution amount, that is, a pixel having a large number of pixels when determining the background density of the entire image when a certain image is given.
[0019]
Next, the density category extracting unit discriminates a density category close to the first threshold value among the extracted density categories equal to or higher than the second threshold value, and outputs it to the density correction unit.
[0020]
Therefore, the background of the image is determined to be smaller than the density based on the first threshold set as the maximum density value considered as the background, and the image as a whole is close to the density based on the first threshold. Then, the background of the selected image is output to the density correction unit, so that the density correction unit subsequently performs correction for various image outputs such as removal of the background and correction of the density of the background. Processing can be performed.
[0021]
As a result, an image processing apparatus capable of accurately and efficiently performing appropriate density control according to various originals with different density conditions by creating a density histogram of the pixel density in the target image and easily determining the background of the image. can do.
[0022]
In the above-described image processing apparatus, the density category extracting unit sequentially creates the predetermined density region from the high density side close to the first threshold value toward the low density side, and the number of pixels of each density category and the second threshold value. And the first density section equal to or higher than the second threshold value may be determined as the background of the image.
[0023]
According to the above configuration, the density category extraction unit sequentially creates the predetermined density area from the high density side close to the first threshold value toward the low density side, and the number of pixels of each density category and the second threshold value. And the first density section equal to or higher than the second threshold is determined as the background of the image.
[0024]
Therefore, it is possible to quickly determine a background having a density close to the target first threshold by a simple method.
[0025]
In the above-described image processing apparatus, the density correction unit is configured to perform one correction from a plurality of density correction amount tables storing various correction amounts for each density category in order to perform correction based on the result of determining the background of the image. A configuration may be provided that includes density correction amount table selection means for selecting and correcting.
[0026]
According to the above configuration, when the density correction unit performs correction based on the result of determining the background of the image, the density correction amount table selection unit provided in the density correction unit performs various corrections for each density category. One of the plurality of density correction amount tables storing the amount is selected and corrected.
[0027]
As a result, since a plurality of density correction amount tables storing various correction amounts for each density category are used, the processing speed can be shortened and the circuit scale can be reduced.
[0028]
In the above-described image processing apparatus, the density correction unit may include a density correction amount adjusting unit that can arbitrarily adjust various correction amounts for each density category with respect to the density correction amount table.
[0029]
According to the above configuration, the density correction unit has the density correction amount adjustment unit that can arbitrarily adjust various correction amounts for each density category with respect to the density correction amount table.
[0030]
For this reason, it is possible to arbitrarily adjust the selected density correction amount table, so that an output image suitable for the user can be obtained.
[0031]
In order to solve the above problems, the image processing method of the present invention creates a density histogram from the density of each pixel in a digital image, and performs density correction processing of the digital image based on the result of the created density histogram In the processing method, a predetermined density area is created based on a predetermined first threshold value from all density areas of the density histogram, and a predetermined threshold area is equal to or greater than a second threshold value in each of the divided density sections of the predetermined density area. In this configuration, a density section close to the first threshold value among the density sections having the number of pixels is determined as the background of the image.
[0032]
According to the above configuration, a density histogram is created from the density of each pixel in the digital image, and density correction processing of the digital image is performed based on the result of the created density histogram.
[0033]
Here, a predetermined density area is created from all density areas of the density histogram based on a predetermined first threshold value, and the number of pixels equal to or larger than the second threshold value in each of the plurality of divided density sections of the predetermined density area. Among the density sections having, the density section close to the first threshold is determined as the background of the image.
[0034]
As a result, a density histogram of the pixel density in the target image can be created to easily determine the background of the image, and an image processing method capable of accurately and efficiently performing appropriate density control according to various originals with different density conditions is provided. can do.
[0035]
The above image processing method may be configured such that the division interval of each density section in the predetermined density area is divided more finely than the division interval of each density section in another area. Good .
[0036]
According to the above configuration, the division interval of each density section in the predetermined density area is divided more finely than the division interval of each density section in the other area.
[0037]
For this reason, it is possible to more accurately determine the background of the image by finely setting the width of each density section.
[0038]
The image processing apparatus according to the present invention includes a histogram creating unit that creates a density histogram based on the density of each pixel of the input digital image, and a density correction unit that corrects the density of the digital image based on the density histogram. In the image processing apparatus comprising: a filter process for performing a spatial filter process for correcting the density of each pixel on the digital image based on the density of each pixel of the digital image prior to the process of the histogram creating unit It is characterized by having means.
[0039]
According to the above configuration, prior to the processing of the histogram creation means, the digital image is subjected to the spatial filter processing for correcting the density of each pixel based on the density of each pixel of the digital image. This spatial filter processing is for removing variations in image data caused by noise mixed in image data, mechanical vibrations when reading an image, or the like.
[0040]
Therefore, by performing the above spatial filter processing, these effects are also affected when the accuracy of the hardware (scanner) is poor, when noise is mixed in the image data, or when mechanical vibration occurs when the image is read. The density histogram along the original image is suppressed. Thereby, the correction of the image density by the density correction means can be performed appropriately, and a good image can be obtained.
[0041]
The image processing apparatus according to the present invention includes a histogram creating unit that creates a density histogram based on the density of each pixel of the input digital image, and a density correction unit that corrects the density of the digital image based on the density histogram. In the image processing apparatus, the histogram creating means includes density region dividing means for dividing the density range of the pixel of the digital image into a plurality of density sections. Is extracted as a first reference value, and a density category that can be determined as the maximum density is extracted, and a reference value setting operation is performed to set the concentration as a second reference value. The density correction means corrects the image density on the low density side from the first reference value to 0, and increases the density from the second reference value. It is characterized in that to correct the image density in degrees side to the highest concentration.
[0042]
According to the above configuration, the histogram creating means extracts a density section that can be determined as the background from the density sections of the generated density histogram, sets the density as the first reference value, and sets the density that can be determined as the maximum density. A category is extracted, and its concentration is set as the second reference value. Then, the density correction unit corrects the image density on the low density side from the first reference value to 0, and corrects the image density on the high density side from the second reference value to the maximum density.
[0043]
Thereby, it is possible to easily and satisfactorily perform density correction on the input image data.
[0044]
The image processing apparatus according to the present invention includes a histogram creating unit that creates a density histogram based on the density of each pixel of the input digital image, and a density correction unit that corrects the density of the digital image based on the density histogram. In the image processing apparatus, the histogram creating means includes density region dividing means for dividing the density range of the pixel of the digital image into a plurality of density sections. Is extracted as a first reference value, and a density category that can be determined as the maximum density is extracted, and a reference value setting operation is performed to set the concentration as a second reference value. The density correction means has a preset reference density correction curve, and a predetermined correction on the reference density correction curve. By connecting the said a point first reference value and second reference value, and characterized in that to create a density correction curves for correcting the density of the digital image.
[0045]
According to the above configuration, the histogram creating means extracts a density section that can be determined as the background from the density sections of the generated density histogram, sets the density as the first reference value, and sets the density that can be determined as the maximum density. A reference value setting operation is performed to extract the classification and set the density as the second reference value. The density correction means has a preset reference density correction curve, and connects the predetermined correction point on the reference density correction curve with the first reference value and the second reference value, thereby digitally A density correction curve for correcting the image density is created.
[0046]
Thereby, a density correction curve for correcting the density of the input digital image can be created easily and quickly.
[0047]
In the above image processing apparatus, as the reference value setting operation, the histogram creating means divides a plurality of density sections of the created density histogram based on a preset low density side threshold value, and performs the classification. The low density side area is selected as the first density area, the plurality of density categories are classified based on a preset high density side threshold value, and the classified high density side area is selected as the second density area. A density area creating means for selecting an area, wherein the density correction means extracts a density category that can be distinguished from the background of the image from the first density area, sets the density as a first reference value, and A configuration may be provided that includes a density category extraction unit that extracts a density category that can be determined as the maximum density of the image from the second density region, and sets the density as a second reference value.
[0048]
According to the above configuration, the first and second reference value setting operations in the histogram creating unit can be appropriately performed by the density region creating unit and the density category extracting unit.
[0049]
In the above image processing apparatus, a plurality of correction points are set in advance on the reference density correction curve, and the density correction unit uses the first reference point as the start point of the density correction curve. The density correction curve may be created by connecting the correction point having a density value higher than the start point and closest to the start point.
[0050]
According to the above configuration, it is possible to quickly set the background density by a simple method, that is, to create a density correction curve for removing the background density. In addition, the hardware can be greatly simplified by increasing the density correction processing speed for the input image data and reducing the circuit scale for density correction.
[0051]
In the image processing apparatus, a plurality of correction points are set in advance on the reference density correction curve, and the density correction unit sets the second reference point as an end point of the density correction curve. The density correction curve may be created by connecting the correction point having a density value lower than the end point and closest to the end point.
[0052]
According to the above configuration, the maximum density can be quickly set by a simple method, the gradation reproducibility can be increased, and an optimum and highly accurate density correction curve can be created for each input image. it can. In addition, the hardware can be greatly simplified by increasing the density correction processing speed for the input image data and reducing the circuit scale for density correction.
[0053]
The image processing apparatus according to the present invention also includes a histogram creating unit that creates a density histogram based on the density of each pixel of the input digital image, and a density of a region serving as a background of the digital image based on the density histogram. In the image processing apparatus including the density correcting unit for correcting, the histogram generating unit includes a density region dividing unit that divides the density range of the pixel of the digital image into a plurality of density sections, and a plurality of the generated density histograms. A density-classifying area creating unit configured to classify the density classification based on a first threshold value set in advance, and to set the classified low-density side area as a background density-determining area; A combination density category extracting means for sequentially extracting a combination density category consisting of a plurality of density categories that are continuous in the background density discrimination region; The combination density categories extracted by the combination density category extraction means are extracted from the combination density categories having a total number of pixels equal to or greater than a preset second threshold value, and a predetermined density value in a combination density category closest to the first threshold value is extracted. The present invention is characterized by comprising background density category extraction means for discriminating the density category from the background.
[0054]
According to the above configuration, the background density determination area creating unit of the histogram creating unit classifies the plurality of density categories of the created density histogram based on the first threshold value set in advance, and the classified low density side Is set as a background density discrimination area. The density correction means sequentially extracts a combination density section composed of a plurality of continuous density sections in the background density determination area. The background density category extraction unit extracts a combination density category extracted by the combination density category extraction unit that has a total number of pixels equal to or greater than a preset second threshold value, and is closest to the first threshold value. A predetermined density section in the combination density section is determined as the background. Then, the density correction unit corrects the density of the area serving as the background of the digital image based on the density of the density category determined as the background.
[0055]
With this configuration, even if the hardware (scanner) accuracy is poor, noise is mixed in the image data, or mechanical vibration occurs when reading the image, these effects are suppressed and input It is possible to accurately determine the background in the image. As a result, the image density can be appropriately corrected by the density correction means, and uniform processing can always be performed on similar input images. As a result, it is possible to perform optimum gradation processing on the input image and output a good image.
[0056]
In the above image processing apparatus, the combination density category extraction unit performs the operation of extracting the combination density category from the high density side to the low density side of the background density determination region, and the background density category extraction unit includes: The first combination density section that is equal to or higher than the second threshold may be selected as a combination density section including a density section that is determined to be the background.
[0057]
According to the above configuration, the combination density category extraction unit performs the combination density category extraction operation from the high density side (first threshold side) to the low density side of the background density determination region. Then, the background density category extraction means selects the first combination density category equal to or higher than the second threshold as the combination density category including the density category that is determined as the background.
[0058]
As a result, it is possible to easily and quickly extract a density section as a base, and to increase the processing speed of the apparatus.
[0059]
In the above image processing apparatus, the background density category extraction unit may be configured to determine a density category indicating the maximum density among the combination density categories equal to or higher than the second threshold as the background.
[0060]
According to the above configuration, the background density value is appropriately set. thing Can be set to
[0061]
In the above-described image processing apparatus, the combination density category extraction unit may be configured to add the same number of density categories on the high density side and the low density side of the density category to the density category of interest to form a combination density category. .
[0062]
According to the above configuration, since the combination density category is set by adding the same number of high density side and low density side density categories to the density category of interest, the combination density category is the background density category. This is appropriate for extraction, and this makes it possible to accurately determine the background.
[0063]
In the above-described image processing apparatus, the density correction unit uses the density of the density classification determined as the background as a reference value, and this reference value is a starting point on the low density side in a preset reference density correction amount line. A density correction amount creating means for correcting a reference density correction amount line to create a density correction amount line, and obtaining a correction amount of a density correction curve based on a difference between the reference density correction amount line and the density correction amount line; A density correction curve creating means for creating a density correction curve for correcting the density of the digital image based on the correction amount may be provided.
[0064]
According to the above configuration, the density correction amount creating means of the density correction means uses the density of the density classification determined as the background as a reference value, and this reference value is the lower density side in the preset reference density correction amount line. The density correction amount line is created by correcting the reference density correction amount line so as to be the starting point of the image, and the correction amount of the density correction curve is obtained from the difference between the reference density correction amount line and the density correction amount line. Then, the density correction curve creating means creates a density correction curve for correcting the density of the digital image based on the correction amount, and the density correcting means is a region serving as a background of the digital image based on the density correction curve. Correct the density.
[0065]
According to the above configuration, it is possible to accurately create an optimum density correction curve for each input image. Also, by creating the density correction curve as described above, the processing speed of the apparatus can be increased, and the hardware can be greatly simplified by reducing the circuit scale.
[0066]
In the above image processing apparatus, the density region dividing unit may add the number of pixels allocated to each density section, and divide the added number of pixels by the density section width to obtain the number of pixels of each density section. Good.
[0067]
According to the above configuration, the density area dividing unit adds the number of pixels allocated to each density section, and divides the added number of pixels by the density section width to obtain the number of pixels in each density section.
[0068]
Therefore, the number of pixels obtained in this way is obtained as an average value of the number of pixels included in the density category.
[0069]
As a result, even if the widths of the density sections are different, absolute comparison of the number of pixels in each density section is possible, so that the background can be discriminated with high accuracy.
[0070]
In the above-described image processing apparatus, the density area dividing unit may be configured to be capable of changing a division interval of each density section in a predetermined density area.
[0071]
According to the above configuration, the density area dividing means can change the division interval of each density section in the predetermined density area.
[0072]
For this reason, since the width of each density section can be set finely, the background of the image can be determined more accurately.
[0073]
The image forming apparatus of the present invention can be configured to include the above-described image processing apparatus.
[0074]
According to the above configuration, for example, by installing the image processing apparatus of the present invention in an image forming apparatus such as a copying machine or a facsimile, a density histogram of the pixel density in the target image can be created to easily apply the background of the image. It is possible to provide an image forming apparatus capable of accurately and efficiently performing appropriate density control according to various originals having different density conditions.
[0075]
DETAILED DESCRIPTION OF THE INVENTION
[Embodiment 1]
An embodiment of the present invention will be described below with reference to FIGS.
[0076]
As shown in FIG. 2, the digital color copying machine 1 as the image forming apparatus of the present embodiment is provided with a document table 111 and an operation unit (not shown) on the upper surface of the main body of the digital color copying machine. In this configuration, an image input device 110 and an image forming unit 210 as image input means are provided inside one main body.
[0077]
A double-sided automatic document feeder (RADF) 112 is supported on the upper surface of the document table 111 so as to be openable and closable with respect to the document table 111 and has a predetermined positional relationship with respect to the surface of the document table 111. It is installed.
[0078]
The double-sided automatic document feeder 112 first transports a document so that one side of the document faces the image input device 110 at a predetermined position on the document table 111, and after image reading on this one side is completed. The document is reversed and conveyed toward the document table 111 so that the other side faces the image input device 110 at a predetermined position on the document table 111. The double-sided automatic document feeder 112 discharges the original after one-sided image reading for one original is completed, and executes a double-sided conveyance operation for the next original.
[0079]
The operations of conveying the document and turning the front and back are controlled in relation to the operation of the entire digital color copying machine 1.
[0080]
Next, the image input device 110 is disposed below the document table 111 in order to read an image of the document conveyed on the document table 111 by the double-sided automatic document feeder 112. The image input device 110 includes a first scanning unit 113 and a second scanning unit 114 that reciprocate in parallel along the lower surface of the document table 111, an optical lens 115, and a CCD (Charge Coupled Device) that is a photoelectric conversion element. ) Line sensor 116.
[0081]
The first scanning unit 113 includes an exposure lamp that exposes the surface of the document image, and a first mirror that deflects a reflected light image from the document in a predetermined direction. And reciprocating in parallel at a predetermined scanning speed while maintaining a certain distance. The second scanning unit 114 includes second and third mirrors that deflect the reflected light image from the original deflected by the first mirror of the first scanning unit 113 further in a predetermined direction. The reciprocating unit 113 is reciprocated in parallel while maintaining a constant speed relationship.
[0082]
The optical lens 115 reduces the reflected light image from the original deflected by the third mirror of the second scanning unit 114 and forms the reduced light image at a predetermined position on the CCD line sensor 116. .
[0083]
The CCD line sensor 116 sequentially photoelectrically converts the formed light image and outputs it as an electrical signal. The above-mentioned CCD line sensor 116 reads a black and white image or a color image, and outputs a line data that is color-separated into R (red), G (green), and B (blue) color components, and is a three-line color CCD. It is. The document image information converted into an electrical signal by the CCD line sensor 116 is further transferred to an image processing device 310 (to be described later) and subjected to predetermined image data processing.
[0084]
Next, the configuration of the image forming unit 210 and the configuration of each unit related to the image forming unit 210 will be described.
[0085]
Below the image forming unit 210, a paper feed mechanism 211 that separates sheets (recording media) P stacked and accommodated in a paper tray one by one and supplies them to the image forming unit 210 is provided. The sheets P separated and supplied one by one are transported to the image forming unit 210 with timing controlled by a pair of registration rollers 212 arranged in front of the image forming unit 210. Further, the paper P on which an image is formed on one side is re-supplied and conveyed to the image forming unit 210 in synchronization with the image formation of the image forming unit 210.
[0086]
A transfer conveyance belt mechanism 213 is arranged below the image forming unit 210.
[0087]
The transfer conveyance belt mechanism 213 is configured to convey the paper P by electrostatically adsorbing the transfer conveyance belt 216 stretched between the driving roller 214 and the driven roller 215 so as to extend substantially in parallel. A pattern image detection unit 232 is provided adjacent to the lower side of the transfer conveyance belt 216.
[0088]
Further, a fixing device 217 for fixing the toner image transferred and formed on the paper P onto the paper P is disposed on the downstream side of the transfer and transport belt mechanism 213 in the paper transport path. The paper P that has passed through the nip between the pair of fixing rollers of the fixing device 217 is discharged onto a paper discharge tray 220 attached to the outer wall of the copier body 1 by a discharge roller 219 through a conveyance direction switching gate 218. The
[0089]
The switching gate 218 selects a conveyance path of the paper P after fixing between a path for discharging the paper P to the main body of the digital color copying machine 1 and a path for resupplying the paper P toward the image forming unit 210. It is to switch automatically. The paper P whose transport direction has been switched again toward the image forming unit 210 by the switching gate 218 is turned upside down via the switchback transport path 221 and then supplied again to the image forming unit 210.
[0090]
In addition, the first image forming station Pa, the second image forming station Pb, the third image forming station Pc, and the first image forming station Pa are adjacent to the transfer conveying belt 216 above the transfer conveying belt 216 in the image forming unit 210. Four image forming stations Pd are arranged in order from the upstream side of the sheet conveyance path.
[0091]
The transfer conveyance belt 216 is driven in the direction of arrow Z in FIG. 2 by the driving roller 214, holds the paper P fed through the paper feed mechanism 211 as described above, and feeds the paper P to the image forming stations Pa to Pd. And sequentially.
[0092]
Each of the image forming stations Pa to Pd has substantially the same configuration. Each of the image forming stations Pa, Pb, Pc, and Pd includes photosensitive drums 222a, 222b, 222c, and 222d that are rotationally driven in the direction of arrow F shown in FIG.
[0093]
Around each of the photosensitive drums 222a to 222d, there are chargers 223a, 223b, 223c, and 223d for uniformly charging the photosensitive drums 222a to 222d, and electrostatic latent images formed on the photosensitive drums 222a to 222d. Developing devices 224a, 224b, 224c, and 224d for developing the images, transfer dischargers 225a, 225b, 225c, and 225d for transferring the developed toner images on the photosensitive drums 222a to 222d to the paper P, and photosensitive members Cleaning devices 226a, 226b, 226c, and 226d that remove toner remaining on the drums 222a to 222d are sequentially arranged along the rotation direction of the photosensitive drums 222a to 222d.
[0094]
Laser beam scanner units (hereinafter referred to as “LSU”) 227a, 227b, 227c, and 227d are provided above the respective photosensitive drums 222a to 222d. LSUs 227a to 227d are semiconductor laser elements (not shown) that emit light modulated according to image data, polygon mirrors (deflecting devices) 240a to 240d for deflecting a laser beam from the semiconductor laser elements in the main scanning direction, It comprises f-θ lenses 241a to 241d, mirrors 242a to 242d, 243a to 243d, and the like for imaging the laser beams deflected by the polygon mirrors 240a to 240d on the surfaces of the photosensitive drums 222a to 222d.
[0095]
A pixel signal corresponding to a black (K) color component image of a color original image is input to the LSU 227a. Similarly, a pixel signal corresponding to the yellow (Y) color component image of the color document image is displayed in LSU 227b, a pixel signal corresponding to the magenta (M) color component image of the color document image is stored in LSU 227b, and LSU 227d. The pixel signals corresponding to the cyan (C) color component image of the color original image are respectively input.
[0096]
As a result, electrostatic latent images corresponding to the color-converted document image information are formed on the respective photosensitive drums 222a to 222d.
[0097]
The developing device 224a contains black toner, the developing device 224b contains yellow toner, the developing device 224c contains magenta toner, and the developing device 224d contains cyan toner. The electrostatic latent images on the photosensitive drums 222a to 222d are developed with the toners of these colors. Thus, the document image information color-converted by the image forming unit 210 is reproduced as a toner image of each color.
[0098]
Further, a paper suction (brush) charger 228 is provided between the first image forming station Pa and the paper feed mechanism 211, and the suction charger 228 charges the surface of the transfer conveyance belt 216. Let As a result, the paper P supplied from the paper feed mechanism 211 is transported without shifting between the first image forming station Pa and the fourth image forming station Pd in a state in which the paper P is reliably adsorbed on the transfer transport belt 216. Is done.
[0099]
On the other hand, a discharger 229 for neutralization is provided almost directly above the drive roller 214 between the fourth image forming station Pd and the fixing device 217. An AC voltage for separating the sheet P electrostatically attracted to the transport belt 216 from the transfer transport belt 216 is applied to the discharger 229 for discharging.
[0100]
In the digital color copying machine 1 configured as described above, cut sheet-like paper is used as the paper P. When the paper P is fed from the paper feed cassette and supplied into the guide of the paper feed conveyance path of the paper feed mechanism 211, the leading end of the paper P is detected by a sensor (not shown) and output from this sensor. Is temporarily stopped by the pair of registration rollers 212 based on the detected signal.
[0101]
Then, the paper P is fed onto the transfer conveyance belt 216 rotating in the direction of the arrow Z shown in FIG. 2 in time with each of the image forming stations Pa to Pd. At this time, the transfer conveyance belt 216 is charged by the suction charger 228 as described above, so that the sheet P is stably conveyed and supplied while passing through the image forming stations Pa to Pd. The
[0102]
In each of the image forming stations Pa to Pd, toner images of respective colors are formed and superimposed on the support surface of the paper P that is electrostatically attracted and transported by the transfer transport belt 216. When the transfer of the image by the fourth image forming station Pd is completed, the sheet P is sequentially peeled off from the transfer conveyance belt 216 by the discharger 229 for discharging from the leading end portion thereof and guided to the fixing device 217. Finally, the paper P on which the toner image is fixed is discharged from a paper discharge port (not shown) onto the paper discharge tray 220.
[0103]
In the above description, optical writing is performed on the photosensitive drums 222a to 222d by performing exposure by scanning the laser beams with the LSUs 227a to 227d. However, a writing optical system (LED (Light Emitting Diode) head) including a light emitting diode array and an imaging lens array may be used instead of the LSUs 227a to 227d. LED heads are smaller than LSUs and have no moving parts and are silent. Therefore, it can be suitably used in an image forming apparatus such as a tandem digital color copying machine 1 that requires a plurality of optical writing units.
[0104]
Next, the configuration of the image processing apparatus 310 will be described with reference to FIG.
As shown in the figure, in the image input device 110, a reflected light image from a document is read as an RGB analog signal by the CCD line sensor 116, and first converted into a digital signal by an A / D converter (analog / digital) 311. Converted. Then, the shading correction unit 312 performs shading correction for removing various distortions generated in the illumination system, the imaging system, and the imaging system of the image input device 110. Thereafter, the input tone correction unit 313 performs input tone correction processing for converting the RGB reflectance signal into a signal that can be easily handled by the image processing system, such as a density signal, at the same time as adjusting the color balance. In this input tone correction process, a density histogram is created from the density of each pixel of the digital image, and the density of the input image original is corrected based on the result.
[0105]
Next, the color correction unit 314 removes color turbidity based on the spectral characteristics of C (cyan), M (magenta), and Y (yellow) color materials including unnecessary absorption components in order to achieve faithful color reproduction. Color correction processing is performed. The black generation / under color removal unit 315 generates a new CMY by subtracting the K signal obtained by black generation from the original CMY signal and the black generation that generates the black (K) signal from the CMY three-color signal after color correction. A lower color removal process for generating a signal is performed, and the CMY three-color signal is converted into a CMYK four-color signal.
[0106]
Next, the spatial filter processing unit 316 performs spatial filter processing using a digital filter on the obtained image signal, and corrects the spatial frequency characteristics to prevent blurring and graininess of the output image. The The output tone correction unit 317 performs output tone correction processing for converting a signal such as a density signal into a halftone dot area ratio that is a characteristic value of the image forming unit 210, and finally divides the image into pixels. Gradation reproduction processing (halftone generation processing) is performed so that each gradation can be reproduced.
[0107]
In addition, after the above-described color correction processing, in order to improve the reproducibility of black characters or color characters particularly in a character and photo mixed document, the region separation processing unit 319 extracts it as black characters (including color characters in some cases). The enhancement amount of the high frequency of the image region is increased by the sharpness enhancement processing in the spatial filter processing unit 316. At the same time, in the halftone generation process, a binarization process or a multi-value process on a high resolution screen suitable for high frequency reproduction is selected.
[0108]
On the other hand, with respect to the region determined to be a photograph by the region separation processing unit 319, the spatial filter processing unit 316 performs low-pass filter processing for removing the input halftone component. At the same time, in the halftone generation process, a binarization process or a multi-value process is performed on the screen with an emphasis on gradation reproducibility.
[0109]
The image data subjected to the above-described processes is temporarily stored in a storage unit (not shown), read out at a predetermined timing, and output to the image forming unit 210.
[0110]
Here, the characteristic automatic exposure adjustment of the present embodiment is performed by the input tone correction unit 313 described above.
[0111]
That is, when the automatic exposure adjustment mode is selected, as shown in FIG. 4, the input tone correction unit 313 performs automatic exposure adjustment using a single color signal selected from RGB or CMY from RGB image input signals. Done. The processed monochromatic signal is converted into a K signal, and further subjected to region separation processing, spatial filter processing, output tone correction processing, and tone reproduction processing (halftone generation processing) and output. During the automatic exposure adjustment, the processing of the color correction unit 314 and the black generation / under color removal unit 315 shown in FIG. 3 is excluded.
[0112]
Hereinafter, the input tone correction processing (automatic exposure adjustment) in the input tone correction unit 313 according to the present embodiment will be described in detail. In the following description, a case where processing is performed using a single color signal selected from CMY will be described.
[0113]
First, as shown in FIG. 1, the input tone correction unit 313 includes a monochrome signal conversion unit 51 that extracts a CMY single-color signal from RGB signals, and a histogram creation unit 52 that creates a density histogram based on the density of each pixel in the digital image. By comparing the number of pixels of each density section of the created density histogram with the second threshold value preset by the second threshold value setting section 52d in the histogram creation section 52, the density section determined as the background is extracted. The density section extraction section 53, a density correction section 54 that corrects a reference density correction curve based on the result of the density section extraction section 53, and a signal conversion section 57 that converts the monochromatic signal into a K signal.
[0114]
The reference density correction curve defines input / output characteristics of the input tone correction unit 313 and is set based on the specifications of the digital color copying machine 1 so as to obtain target input / output characteristics. It is.
[0115]
The histogram creating unit 52 further selects a target density region based on the first threshold value preset by the density region dividing unit 52a and the first threshold value setting unit 52c for dividing the density region. It is composed of a density area creating section 52b as density area creating means and the above-described second threshold value setting section 52d. The density area dividing unit 52a is further provided with a function of dividing the density area into arbitrary sections.
[0116]
The density correction unit 54 is provided with a density correction amount adjustment unit 55 that can manually change the correction amount for the reference density correction curve, and the density classification extraction unit 53 and the manual density correction amount adjustment unit 55. A density correction amount table selection unit 56 is provided for selecting a density correction amount table for correcting the reference density correction curve based on the above result.
[0117]
A program for performing processing of each unit of the input tone correction unit 313 is stored in the ROM 58 shown in FIG. 12, and the CPU 59 executes the program. In the figure, for simplicity of description, access to the density correction amount adjusting unit 55 and the density correction amount table selecting unit 56 is represented by the density correction unit 54.
[0118]
The input tone correction processing of the present embodiment having the above configuration will be described based on the flowchart shown in FIG.
[0119]
First, the automatic exposure mode is set first (S1). The automatic exposure mode can be set, for example, by pressing an automatic exposure mode setting button on an operation unit (not shown) of the digital color copying machine 1. When the automatic exposure mode is not set, a normal copy operation is performed (S14).
[0120]
When the automatic exposure mode is set, pre-scanning is performed (S2), and a monochrome signal such as an M signal is selected from the RGB signals of all pixels of the original read by the pre-scanning (S3), and the density is manually adjusted. After determining whether or not to set the area (S4), a density histogram of the monochrome signal is formed (S6). Normally, the density histogram shows the number of pixels for each of 256 levels of density, and the one shown in FIG. 6 is created. In this embodiment, for example, as shown in FIG. It is simplified by dividing (density classification: a1, a2,... A16). This greatly simplifies the hardware.
[0121]
When more accurate processing is performed, in S4, the setting shifts to the setting in the manual mode (S5), and the number of divisions can be increased.
[0122]
As a method of dividing, it is not necessary to make the density divisions equal, and more detailed information is required. For example, in FIG. 7, the density section of the low density value is taken finely, and the density section of the high density value is large. The density value of the pixel read out by the pre-scan is incremented by 1 for the number of histogram pixels in the corresponding density category, depending on which category the density value is. If the width of the density section is not constant, the average value is taken so that there is no difference due to the width of the density section. That is, when a certain density section is ai and the density section width is bi, the number of pixels Hi in an arbitrary density section Di is
Hi = Σhj / bi (hj is the number of pixels in 256 levels included in the density category)
As long as you ask.
[0123]
The background determination of the image is performed using the density histogram thus created. That is, feature data extraction (background selection) shown in the flowchart of FIG. 5 is performed (S7).
[0124]
In order to determine the background, up to which density value is determined as the background, that is, the maximum density value determined as the background is set in advance as the first threshold value. The background density refers to the density of the original sheet of the original or the density of the background portion that is not related to the original image. In addition, the minimum value of the number of pixels determined to be the background, that is, the number of pixels determined to be the background, is set in advance as the second threshold value. The two first threshold values and the second threshold value serve as a reference, and by adjusting the threshold values, a wider range of processing can be performed. As for the first threshold value and the second threshold value, a plurality of expected values can be stored in a ROM or the like in advance, and values stored in a storage unit such as a memory can be set by a switch or the like as necessary. You should do so. However, the present invention is not necessarily limited to this, and the user may arbitrarily set as described below.
[0125]
For example, as shown in FIG. 8, the first threshold value setting unit 52c displays 256 levels of density bands on the display unit 60 such as a liquid crystal display panel in the operation unit of the digital color copying machine 1, When the instruction unit 61 is moved by the position setting unit 63 such as the two button instruction units 62 and 62 capable of moving the left and right 61 and a predetermined density is selected and the determination button 64 is pressed, the selected density is adopted. The density value may be stored in the storage means. The numerical value display unit 65 shown in the figure displays the density at the position of the instruction unit 61 as a numerical value.
[0126]
Accordingly, it is possible to easily adjust the reference value for determining which density value is the background, and it is possible to remove the background or output the background for any background of interest.
[0127]
Although the above description shows an example of displaying a density band of 256 gradations, the present invention is not limited to this, and it may display a density for each predetermined step. The operation of 61 may be performed by a mouse (not shown) instead of the two button instruction units 62 and 62 that can move the instruction unit 61 left and right.
[0128]
Similarly, when adjusting the second threshold value, as shown in FIG. 9, the size of the background to be removed is displayed on the display unit 70 in the operation unit of the digital color copying machine 1 as the second threshold value setting unit 52d. A band representing is displayed. In the figure, for example, the minimum size is a postcard and the maximum size is set to A3. In the same manner as described above, a position setting unit 73 including two setting buttons 72 and 72 or a mouse (not shown) is used to move the instruction unit 71 and determine with the determination button 74 to select the size of the background.
[0129]
When the background size is selected, the number of pixels corresponding to the selected background size is stored in the storage means. In this way, it is possible to easily adjust the reference value for determining which pixel value is the background, and it is possible to remove the background or output the background for any size of the background of interest. Become.
[0130]
Specifically, for example, in the created density histogram shown in FIG. 7, a density value that is less than or equal to the first threshold value and a pixel number that is greater than or equal to the second threshold value may be considered as the background. It is judged.
[0131]
Next, the density category most suitable for determining the background is selected from the areas that can be considered as the background. That is, the selected density category is the one that is equal to or lower than the first threshold value and that satisfies the second threshold value and is closest to the first threshold value, that is, the highest density value in the region that can be considered as the background. A category is selected. This is because it corresponds to the case where a plurality of originals or backgrounds exist, and by determining the background with the highest density, it is possible to remove the background with lower density than that.
[0132]
As a method of selecting the density category determined as the background, the number of pixels in each density category is sequentially compared with the second threshold value from either the low density side or the high density side of the first threshold value. However, it is preferable to compare from the high concentration side of the first threshold value.
[0133]
The reason is that the highest density category satisfying the above conditions can be selected easily and quickly by comparing from the higher density side of the first threshold.
[0134]
The above is the feature data extraction (background selection) process in the flowchart shown in FIG. 5 (S7).
[0135]
When the density classification is determined in this way, the density correction amount table is also determined and selected (S8).
[0136]
In the density correction amount table 81..., For example, as shown in FIG. 10, the density correction amount corresponding to a predetermined input density value is set for each segment value as a table. Then, the density correction amount table 81... Corresponding to the background and the selected segment value is selected. Here, the density correction amount indicates a correction amount for a reference density correction curve shown below. Further, in the figure, “*” added to the section value and not numbered are tables used when the correction amount table is manually selected. In addition, the said division | segmentation value is a code | symbol attached | subjected to them, in order to identify each density | concentration division.
[0137]
As shown in the flowchart of FIG. 5, when the above-described density correction amount table 81 is selected, correction by the density correction amount table 81 is performed (S9), and a density correction curve is created (S10). ).
[0138]
Here, a reference density correction curve for correcting the density correction amount table 81... Is prepared in advance as a table “4”. When it is determined that there is no background, that is, when the number of pixels is not satisfied in the above-described area that can be a background, the reference density correction curve is directly used as a density correction curve and an image is output. For the density classification determined as the background, the above-described density correction amount table 81 is prepared for each appropriate reference density correction curve. As a result, when the density category to be the background is determined by the above-described density histogram, the density correction amount table 81... For the determined density category is selected.
[0139]
The correction for the reference density correction curve by the density correction amount table 81... Is performed as shown in FIG. In the figure, the solid line represents the reference density correction curve, the arrow portion represents the above-described density correction amount, and the broken line represents the density correction curve. The density value to be corrected is set at regular intervals. This greatly simplifies the hardware.
[0140]
In addition, adjustment with other image quality adjustment processing such as sharpness, brightness, and saturation can be simplified. If it is necessary to create a more accurate density correction amount table 81..., It is possible to increase the number of density sections and set a correction amount suitable for each. A density correction curve is created by connecting the corrected values by the density correction amount table 81.
[0141]
Next, the above-described original scanning is started, and based on the created density correction curve, for example, the density (background) below X3 shown in the figure is removed, and the optimum density value is corrected for each input value. An image is output (S11 shown in FIG. 5).
[0142]
By the way, depending on the case, there may occur a situation where the user wants to output a favorite image, that is, manually adjusts the density (S12).
[0143]
In that case, the density correction amount table 81... Is set on the basis of the created density correction curve, for example, an exposure adjustment button provided on the operation unit of the digital color copying machine 1 is manually set to low density and high density. By adjusting and setting (S13), it becomes possible to output a favorite image.
[0144]
The manual adjustment method of the density correction amount table 81 is as follows.
[0145]
In contrast to the above-described density correction amount table 81 set for each segment value, the density correction amount table 81... Is prepared by the number of manual adjustment steps. That is, when manual adjustment is performed, these density correction amount tables 81 are selected, the reference density correction curve is corrected, and a density correction curve is created. However, although the density correction amount table 81 set for manual adjustment may be newly set for the density correction amount table 81 set for each section value, hardware simplification is possible. Therefore, the density correction amount table 81... Set for each segment value is used. By this manual density correction curve selection, an image can be output more optimally and easily.
[0146]
According to the above method, for example, a dark blue background in a newspaper can be removed and copied, while the dark blue background can be output to be copied like a newspaper.
[0147]
By the way, the above description is the contents when the monochromatic signal is a CMY signal.
[0148]
On the other hand, when the monochrome signal is an RGB single-color signal, it is considered that there is a possibility that it can be considered as the background. In the created density histogram, the density value is equal to or higher than the first threshold value. Yes, the number of pixels is greater than or equal to the second threshold. In addition, among the areas that can be considered as the background, the density category selected as the most suitable to be determined as the background is the first threshold value that is equal to or higher than the first threshold value and satisfies the second threshold value or higher. A density section having the lowest density value is selected from the closest areas, that is, the area that can be considered as the background. Other processes may be performed in the same manner as in the case of CMY monochromatic signals.
[0149]
In this embodiment, the pre-scan method has been described. However, the present invention is not limited to this, and the input data is separated into two, and one is temporarily stored in a storage means such as an image memory. Alternatively, a method may be used in which the density correction curve is obtained by performing the automatic density adjustment of the present embodiment using the other data, the input data is read from the storage means, and the image is output.
[0150]
In this embodiment, the digital color copying machine 1 using an electrophotographic process is described as an example. However, the present invention is not limited to the digital color copying machine 1, and information from an image input unit is used. Of course, the present invention can also be applied to an image forming apparatus that performs predetermined image processing, inputs the result, and outputs the result, for example, an image forming apparatus using an inkjet recording method or a sublimation recording method.
[0151]
As described above, in the image processing apparatus 310 according to the present embodiment, the analog image input from the image input apparatus 110 is converted into a digital image. Then, the histogram creation unit 52 creates a density histogram from the density of each pixel of the digital image.
[0152]
Further, the density correction unit 54 corrects the density of the digital image based on the result of the histogram creation unit 52.
[0153]
Here, since the histogram creating unit 52 includes the density region dividing unit 52a and the density region creating unit 52b, when creating the histogram, the density region dividing unit 52a first selects a plurality of density ranges of the pixels of the digital image. After being divided into a plurality of density sections, the density area creating unit 52b divides the entire density range divided into the plurality of density sections based on a predetermined first threshold value, thereby forming a predetermined density section group. A predetermined density region is created.
[0154]
Therefore, by appropriately setting the first threshold value, the maximum density when it is regarded as the background of the image can be determined, and the image is divided into the predetermined density area which is the background determination density area and the other areas. be able to.
[0155]
Next, in this predetermined density region, the density category extraction unit 53 compares the number of pixels of each density category in the predetermined density region created by the density region creation unit 52b with a preset second threshold value. Extract density categories that are greater than or equal to the threshold of 2.
[0156]
In other words, in order to adopt as the background density, a predetermined density area having a large number of pixels in each density section is selected as the background density, and the second threshold is set in advance as the reference. Is done. Therefore, the second threshold value is a reference for selecting a density distribution amount, that is, a pixel having a large number of pixels when determining the background density of the entire image when a certain image is given.
[0157]
Further, the density category extraction unit 53 discriminates a density category close to the first threshold value among the extracted density categories equal to or higher than the second threshold value, and outputs it to the density correction unit 54.
[0158]
Therefore, the background of the image is determined to be smaller than the density based on the first threshold set as the maximum density value considered as the background, and the image as a whole is close to the density based on the first threshold. The background of the selected image is output to the density correction unit 54 so that the density correction unit 54 can output various images such as removing the background and correcting the density of the background. Correction processing can be performed.
[0159]
As a result, an image processing apparatus 310 that can create a density histogram of pixel density in the target image, easily determine the background of the image, and accurately and efficiently perform appropriate density control according to various originals with different density conditions. Can be provided.
[0160]
Further, in the image processing apparatus 310 according to the present embodiment, the density category extraction unit 53 sequentially creates the created predetermined density area from the high density side close to the first threshold value toward the low density side. The number and the second threshold value are compared, and the first density section equal to or higher than the second threshold value is determined as the background of the image.
[0161]
Therefore, it is possible to quickly determine a background having a density close to the target first threshold by a simple method.
[0162]
Further, in the image processing apparatus 310 according to the present embodiment, the density region dividing unit 52a adds the number of pixels included in each density section, and divides the added number of pixels by the density section width to thereby obtain the pixels of each density section. It is a number.
[0163]
Therefore, the number of pixels obtained in this way is obtained as an average value of the number of pixels included in the density category.
[0164]
As a result, even if the widths of the density sections are different, absolute comparison of the number of pixels in each density section is possible, so that the background can be discriminated with high accuracy.
[0165]
Further, in the image processing apparatus 310 of the present embodiment, the density area dividing unit 52a can change the division interval of each density section in the predetermined density area.
[0166]
For this reason, since the width of each density section can be set finely, the background of the image can be determined more accurately.
[0167]
In the image processing apparatus 310 of the present embodiment, when the density correction unit 54 performs correction based on the result of determining the background of the image, the density correction amount table selection unit 56 provided in the density correction unit 54 Then, one of the plurality of density correction amount tables 81... Storing various correction amounts for each density category is selected and corrected.
[0168]
As a result, since a plurality of density correction amount tables 81... Storing various correction amounts for each density category are used, the processing speed can be shortened and the circuit scale can be reduced.
[0169]
Further, in the image processing apparatus 310 of the present embodiment, the density correction unit 54 has a density correction amount adjustment unit 55 that can arbitrarily adjust various correction amounts for each density category with respect to the density correction amount table 81. is doing.
[0170]
For this reason, it is possible to arbitrarily adjust the selected density correction amount table 81 to obtain an output image that suits the user's preference.
[0171]
The digital color copying machine 1 according to the present embodiment includes the image processing apparatus 310 according to the present embodiment.
[0172]
For this reason, by installing the image processing apparatus 310 according to the present embodiment in an image forming apparatus such as a copying machine such as the digital color copying machine 1 or a facsimile, a density histogram of the pixel density in the target image can be created easily. It is possible to provide an image forming apparatus capable of accurately and efficiently performing appropriate density control according to various originals having different density conditions by determining the background of the image.
[0173]
In the image processing method of the present embodiment, a density histogram is created from the density of each pixel in the digital image, and the density correction process of the digital image is performed based on the created density histogram result.
[0174]
Here, a predetermined density area is created from all density areas of the density histogram based on a predetermined first threshold value, and the number of pixels equal to or larger than the second threshold value in each of the plurality of divided density sections of the predetermined density area. Among the density sections having, the density section close to the first threshold is determined as the background of the image.
[0175]
As a result, a density histogram of the pixel density in the target image can be created to easily determine the background of the image, and an image processing method capable of accurately and efficiently performing appropriate density control according to various originals with different density conditions is provided. can do.
[0176]
Further, in the image processing method of the present embodiment, the division interval of each density section in the predetermined density area is divided more finely than the division interval of each density section in the other areas.
[0177]
For this reason, it is possible to more accurately determine the background of the image by finely setting the width of each density section.
[0178]
[Embodiment 2]
The following will describe another embodiment of the present invention with reference to FIGS. In addition, the same code | symbol is attached | subjected to the means which has the same function as the means shown to the said embodiment, and the description is abbreviate | omitted.
[0179]
The digital color copying machine 2 includes the image processing apparatus 330 shown in FIG. 3, and executes the automatic exposure adjustment mode with the configuration shown in FIG. The image processing apparatus 330 includes an input tone correction unit 331 instead of the input tone correction unit 313 shown in FIGS. 3 and 4.
[0180]
Next, input tone correction processing (automatic exposure adjustment) in the input tone correction unit 331 will be described. Here, a case will be described in which processing is performed using a monochromatic signal selected from CMY.
[0181]
As shown in FIG. 13, the input tone correction unit 331 includes a filter processing unit (filter processing unit) 351, a monochrome signal conversion unit 352, a histogram generation unit (histogram generation unit) 353, and a density category extraction unit (density correction unit, A density classification extraction unit) 354, a density correction curve creation unit (density correction unit) 355, a correction value setting unit 356, and a signal conversion unit 357;
[0182]
The filter processing unit 351 performs filter processing for removing noise and data variations on the image data input from the scanner, that is, the image input device 110 during pre-scanning. Hereinafter, an example of filter processing (smoothing filter) in the filter processing unit 351 will be described.
[0183]
Variance is σ ² The variance of the mean value of n samples taken independently of the distribution of ² / N. Therefore, by setting the average density of pixels in the vicinity of the pixel A (i, j) in the input image to the value of B (i, j) below, density variation due to noise or the like can be reduced. That is, if the (n × n) size is used as the range of the neighboring pixels of the pixel A (i, j),
[0184]
[Expression 1]

[0185]
It becomes. Here, [n / 2] represents the maximum integer not exceeding n / 2, and n is an odd number.
[0186]
This operation is all 1 / n elements ² It is spatial filtering by the load matrix which is. For the range of neighboring pixels, for example, a small range of about 3 × 3 (n = 3) pixels as shown in FIG. FIG. 14B shows an example of the filter coefficient when the smoothing process is performed.
[0187]
The above filter uses a method called a moving average method, but a median filter or the like is also conceivable. This median filter is a filter that arranges the pixels in the target image area in descending order of density and uses the density of the center pixel as the density value of the pixel of interest, and can remove noise and the like. By these spatial filter processes, it is possible to create a more accurate density histogram without being affected by some variation or noise of the image input apparatus 110, that is, the scanner. Note that the above spatial filter processing can also be applied to the input tone correction processing unit 313 described in Embodiment 1.
[0188]
Similar to the single color signal conversion unit 51, the single color signal conversion unit 352 extracts a CMY single color signal from the RGB signals.
[0189]
The histogram creation unit 353 creates a density histogram based on the density of each pixel and its frequency (number of pixels). The histogram creating unit 353 includes a density region dividing unit 353a, a density region creating unit 353b, and first to fourth threshold setting units 353e to 353h.
[0190]
The density region dividing unit 353a divides regions having various densities of image data (hereinafter referred to as density regions) as follows when the histogram creation unit 353 creates a density histogram of input image data. It is. This division function can be arbitrarily set.
[0191]
As the density histogram, as shown in FIG. 6, one that represents each frequency (number of pixels) is usually created for every 256 levels of density. The density area dividing unit 353 a is, for example, shown in FIG. 15. As described above, the 256-level density division is divided into 32 (density division: a1, a2,..., A32) for simplification. Thus, the hardware can be greatly simplified by reducing the number of density sections with respect to the normal number of density sections. If more accurate processing is performed, it is preferable to increase the number of density sections, that is, increase the number of density area divisions.
[0192]
When the density area is divided into a plurality of density sections, it is not necessary to equalize the width of each density section, that is, the width of the density value in each density section, and a relatively important area as information is finely divided. In the example shown in FIG. 15, the density section on the low density value side and the density section on the high density value side are made finer, and the density section on the medium density value side is enlarged.
[0193]
Other processes for creating the density histogram are the same as those in the first embodiment.
[0194]
The first to fourth threshold setting units 353e to 353h set the first to fourth thresholds.
[0195]
As in the case of the first embodiment, the first threshold value is a criterion for determining up to which density value the background is determined, and indicates the maximum density value determined as the background.
[0196]
Similar to the case of the first embodiment, the second threshold value is a criterion for determining how many times (number of pixels) the background is determined. Show.
[0197]
The first and second threshold values may be stored in a ROM or the like, and the threshold value stored in the storage means such as a memory may be set by a switch or the like as necessary. As described above, the user may arbitrarily set the configuration shown in FIG.
[0198]
The third threshold value is a criterion for determining the lowest density value to be determined as the maximum density, and indicates the minimum density value determined as the maximum density of the document in the output image.
[0199]
The fourth threshold is a criterion for determining from what frequency the image is necessary density for the image, that is, from what frequency is to be displayed on the image as the maximum density. The minimum value of the number of pixels necessary for displaying as the maximum density is shown.
[0200]
These third and fourth threshold values can be adjusted, and by performing this adjustment, a wider range of processing becomes possible.
[0201]
As for the third threshold value, as in the case of determining the first threshold value, a plurality of predicted values are stored in advance in a ROM or the like, and stored in a storage means such as a memory by a switch or the like as necessary. The threshold to be set can be set. Alternatively, the user may arbitrarily set it from the operation unit of the digital color copying machine 2 shown in FIG.
[0202]
Also for the fourth threshold, a plurality of values predicted in advance are stored in a ROM or the like in advance, for example, a signal for detecting the size of the document placed on the document table 111 of the digital color copying machine 2, The threshold stored in the storage means such as a memory may be set based on a detection signal from a recording medium selection button such as a sheet provided in the section. Alternatively, as in the case of setting the second threshold value, the user may arbitrarily set the value from the operation unit of the digital color copying machine 2 shown in FIG.
[0203]
When the first to fourth threshold values are input from the operation unit of the digital color copying machine 2 shown in FIGS. 8 and 9, for example, “light” is displayed on a display unit (not shown) including a liquid crystal panel. A message such as “Please select a color” may be displayed, and the user may perform processing according to the message, thereby sequentially setting corresponding threshold values.
[0204]
In the digital color copying machine 2, an upper limit value and a lower limit value are determined for the first and third threshold values in order to prevent malfunction due to an incorrect numerical value input from the operation unit shown in FIG. For example, a numerical value outside these ranges, for example, a numerical value that is not possible as the background density or a numerical value that is too low as the maximum density, is prohibited and an error message is displayed.
[0205]
The density region creation unit 353b includes a background density determination region creation unit 353c and a maximum density determination region creation unit 353d.
[0206]
Based on the first threshold value, the background density determination area creation unit 353c selects a density area that is a background density determination target, that is, a background density determination area (area whose density is equal to or lower than the first threshold value shown in FIG. 15). Is.
[0207]
The maximum density discriminating area creating unit 353d selects a density area as a maximum density discriminating object based on the third threshold value, that is, a maximum density discriminating area (area having a density equal to or higher than the third threshold value shown in FIG. It is.
[0208]
The density category extraction unit 354 compares the frequency (number of pixels) of each density category of the density histogram created by the histogram creation unit 353 with the second threshold value set by the second threshold value setting unit 353f. Thus, the density classification (area that can be considered as the background: the hatched area on the low density side in FIG. 15) is extracted and the fourth threshold set by the fourth threshold setting unit 353h is extracted. By comparing with the threshold value, the density classification (area that can be considered as the maximum density: the hatched area on the high density side in FIG. 15) is extracted.
[0209]
Therefore, in the density histogram shown in FIG. 15, areas whose density values are equal to or smaller than the first threshold and whose frequency (number of pixels) is equal to or larger than the second threshold are areas that can be considered as the background of the document image. To be judged. A region having a density value equal to or higher than the third threshold value and a frequency (number of pixels) equal to or higher than the fourth threshold value is determined to be an area that can be considered as the maximum density of the document image.
[0210]
Further, the density category extraction unit 354 selects a density category that is most suitable to be determined as the background from among the regions that can be considered as the background. The selected density category is the one closest to the first threshold, that is, the one having the highest density value among those that are equal to or lower than the first threshold and satisfy the second threshold or higher.
[0211]
As a method of selecting the density category determined as the background, the frequency of each density category and the second threshold value are sequentially compared from the low density side or the high density side of the first threshold value. it can. Also in this case, as described above, it is preferable to compare from the high density side of the first threshold value.
[0212]
Similarly, the density category extraction unit 354 selects the density category having the maximum density in the region that can be considered as the maximum density of the document. The selected density category has the highest density value among those that are equal to or higher than the third threshold and satisfy the fourth threshold.
[0213]
Similarly, when selecting the density category determined to be the maximum density of the original, the highest density category satisfying the above condition can be selected easily and quickly by comparing from the high density side.
[0214]
In the example of FIG. 15, it is determined that the density category α is the background and the density category β is the maximum density value (the white area in FIG. 15). The first reference value and the second reference value are set.
[0215]
The density correction curve creation unit 355 creates a density correction curve based on the first reference value and the second reference value. An example of this density correction curve is shown in FIG.
[0216]
When creating a density correction curve, first, a reference density correction curve shown in FIG. 16 is set in advance. Further, as shown in the figure, points to be corrected at equal intervals, that is, correction points (predetermined input density values) are set in advance in the reference density curve.
[0217]
Next, the density value of the first reference value obtained from the background of the document image is used as the starting point (end on the low density side) of the density correction curve to be created. In this case, if the first reference value is not obtained, the point of the input density value 0 is set as the starting point.
[0218]
Further, the density value of the second reference value obtained from the maximum density of the document image is set as the end point of the density correction curve to be created. In this case, if the second reference value is not obtained, the third threshold value is set as the end point of the density correction curve.
[0219]
Next, the start point (first reference value) determined as described above is set to a density value of 0, and the correction point a closest to the start point on the higher density value side of the correction point of the reference density curve and the above point Connect the start point with a straight line. Similarly, the determined end point is set to a density value 255, and the correction point b on the side where the density value is low and closest to the end point is connected by a straight line at the correction point of the reference density curve. A density correction curve is obtained by such processing.
[0220]
Here, the start point, the end point, and the correction point are connected by a straight line, but the present invention is not limited to this, and may be connected by another appropriate curve, for example.
[0221]
In this way, an optimum image can be formed by creating a density correction curve for each input image and correcting the image based on the density correction curve. That is, when the main scan is started, based on the created density correction curve, for example, the density is equal to or lower than the start point (first reference value) and equal to or higher than the end point (second reference value) shown in FIG. Are removed by the density correction curve creation unit 355, and an optimum image in which the density value for each input value is corrected is output. Further, the hardware can be greatly simplified by the configuration for obtaining the density correction curve as described above.
[0222]
The correction value setting unit 356 manually sets the start point (first reference value) and end point (second reference value) used when the density correction curve creation unit 355 creates the density correction curve, It can be arbitrarily set on the high concentration side.
[0223]
That is, in some cases, the user may want to output a favorite image adjusted by himself / herself, not by the automatic exposure adjustment function. In that case, the start point (first reference value) and end point (second reference value) values are manually adjusted by operating the correction value setting unit 356 with reference to the created density correction curve. You may be able to do it. In this case, the correction value setting unit 356 has an exposure adjustment button of the form shown in FIG. 8 provided in the operation unit of the digital color copying machine 2, for example. Thereby, the low density and the high density can be adjusted according to the user's preference, and an image adjusted according to the user's preference can be output.
[0224]
The correction value setting unit 356 for manually adjusting the density correction curve can be configured as follows. For example, the start point (first reference value) and the end point (second reference value) at the time of density correction curve creation are set to the low density side and the high density side for each certain value by, for example, operating the exposure adjustment button. You can make them drift. With such a configuration, manual density correction can be easily performed.
[0225]
The signal conversion unit 357 converts the monochromatic signal into a K signal.
[0226]
A program for performing processing of each unit of the input tone correction unit 331 is stored in the ROM 58 shown in FIG. 19, and the CPU 59 executes the program. In the figure, for simplicity of description, access to the correction value setting unit 356 is represented by the density correction curve creation unit 355.
[0227]
Next, input tone correction processing by the input tone correction unit 331 will be described with reference to the flowchart of FIG.
[0228]
If the automatic exposure mode is set when the copy start button is operated (S21), pre-scanning is first performed by the image input device 110 (S22). The automatic exposure adjustment mode setting button is provided on, for example, an operation unit (not shown) of the digital color copying machine 2. In S21, the automatic exposure mode is set. Not in Sometimes a normal copy operation is performed (S35).
[0229]
Next, the filter processing unit 351 performs the above-described filter processing on the RGB signals of all the pixels of the document read by the image input device 110 (S23).
[0230]
Next, a monochrome signal (for example, M signal) is selected by the monochrome signal conversion unit 352 (S24).
[0231]
Next, when extracting the background and the maximum density, it is determined whether or not the density area setting in the manual mode is selected (S25). This determination is made by the CPU 59.
[0232]
In selecting the density region for extracting the background and the maximum density, the first threshold (used for selecting the background) and the third threshold (used for selecting the maximum density) are set in advance. When the setting by is selected, the density area is set by each (S26).
[0233]
Next, for example, a density histogram shown in FIG. 15 is created as described above by the histogram creation unit 353 using the monochromatic signal filtered in S23 and selected in S24 (S27).
[0234]
Next, based on the density histogram created by the histogram creation unit 353, the background (first reference value) is finally determined by the density category extraction unit 354 using the second threshold (S28). The maximum density (second reference value) is determined using the fourth threshold value (S29).
[0235]
Next, the background density value extracted in S28 and the maximum density value extracted in S29 are set as a first reference value and a second reference value, respectively (S30). Note that the first and second reference values can also be arbitrarily set manually as described above.
[0236]
Next, the density correction curve creation unit 355 creates a density correction curve based on the first and second reference values as shown in FIG. 16 (S31), and uses this density correction curve. The image data is corrected and the image is output (S32).
[0237]
It is determined whether or not to further adjust the density of the output image (S33). When the density adjustment is further selected, the density is set in the manual mode (S34) and then S28. Return to, and repeat the process below.
[0238]
That is, the second threshold value is set in advance in S28 and the fourth threshold value is set in advance in S29 to extract the maximum density, but these values may be set manually. Is possible. Therefore, when further density adjustment is performed, the second and fourth threshold values are set in the manual mode in S34, and the processing from S28 to S32 is performed again. If it is determined in S33 that it is not necessary to perform density adjustment, the series of processing is terminated at this point.
[0239]
In the above operation, when the density adjustment is performed in S33, the values of the second threshold value and the fourth threshold value for determining the background in S28 and the maximum density in S29 are changed in the manual mode. However, as shown in FIG. 18, the process may return from S34 to S30, and the first and second reference values may be changed. In addition, each process in the same figure is the same as what was demonstrated in FIG.
[0240]
In the above description, the case where the monochromatic signal is a CMY signal is illustrated. On the other hand, when the monochrome signal is an RGB system, an area (a plurality of density categories) that may be considered as the background has a density value equal to or higher than the first threshold in the created histogram, and the frequency (pixel Number) is greater than or equal to the second threshold. An area (a plurality of density categories) that can be considered as the maximum density of the document has a density value equal to or lower than the third threshold and a frequency (number of pixels) equal to or higher than the fourth threshold in the created histogram. belongs to.
[0241]
In the case where the monochrome signal is an RGB system, the segment value (first reference value) that is most suitable to be determined as the background among the regions that can be considered as the background of the document is equal to or greater than the first threshold value, and Among those satisfying the second threshold or more, the one closest to the first threshold, that is, the division value having the lowest density value.
[0242]
In addition, among the areas that can be considered as the maximum density of the document, the segment value (second reference value) that is most suitable for determining the maximum density of the document is equal to or less than the third threshold and equal to or greater than the fourth threshold. Among those satisfying, the one farthest from the third threshold value, that is, the division value having the lowest density value. Other processing may be performed in the same manner as in the case of a CMY monochromatic signal. The above point is the same in the configuration of the third embodiment.
[0243]
In the above description, the digital color copying machine 2 performs a prescan in order to obtain a density correction curve. However, the present invention is not limited to this, and the input image data is divided into two, one is temporarily stored in a storage means such as an image memory, and a density correction curve is obtained using the other, and input from the storage means. A method of reading out image data and outputting an image may be used.
[0244]
The digital color copying machine 2 also uses an image forming apparatus that inputs information from the image input apparatus, performs predetermined image processing, and outputs the result, for example, an ink jet recording system or a sublimation recording system. Of course, the present invention can also be applied to an image forming apparatus. This also applies to the configuration of the third embodiment described below.
[0245]
[Embodiment 3]
The following will describe another embodiment of the present invention with reference to FIGS. In addition, the same code | symbol is attached | subjected to the means which has the same function as the means shown to the said embodiment, and the description is abbreviate | omitted.
[0246]
The digital color copying machine 3 includes the image processing apparatus 360 shown in FIG. 3, and executes the automatic exposure adjustment mode with the configuration shown in FIG. The image processing apparatus 360 includes an input tone correction unit 371 in place of the input tone correction unit 313 shown in FIGS. 3 and 4.
[0247]
Next, input tone correction processing (automatic exposure adjustment) in the input tone correction unit 371 will be described. Here, a case will be described in which processing is performed using a monochromatic signal selected from CMY.
[0248]
As shown in FIG. 20, the input tone correction unit 371 includes a monochrome signal conversion unit 361, a histogram creation unit (histogram creation unit) 362, a combination density category extraction unit (combination density category extraction unit, density correction unit) 363, 2 threshold setting unit 364, background density category extraction unit (background density category extraction unit, density correction unit) 365, density correction curve creation unit (density correction curve creation unit, density correction unit) 366, density correction amount creation unit (density) Correction amount creation means, density correction means) 367, density correction amount adjustment section 368, and signal conversion section 369.
[0249]
Similar to the single color signal conversion unit 51, the single color signal conversion unit 361 extracts a CMY single color signal from the RGB signals.
[0250]
The histogram creation unit 362 creates a density histogram based on the density of each pixel and its frequency (number of pixels). The histogram creating unit 362 includes a density region dividing unit 362a, a background density determining region creating unit (background density determining region creating unit) 362b, and a first threshold setting unit 362c.
[0251]
The density region dividing unit 362a divides regions having various densities of image data (hereinafter referred to as density regions) as follows when the histogram creating unit 353 creates a density histogram of input image data. It is. This division function can be arbitrarily set.
[0252]
As the density histogram, as shown in FIG. 6, one representing each frequency (number of pixels) is usually created for each density in 256 levels. The density region dividing unit 362 a is, for example, shown in FIG. 21. As described above, the 256-level density division is divided into 32 (density division: a1, a2,..., A32) for simplification. Thus, the hardware can be greatly simplified by reducing the number of density sections relative to the number of normal density sections.
[0253]
When dividing a density area into a plurality of density sections, it is not necessary to equalize the width of each density section, that is, the width of the density value in each density section. To do. In the example shown in FIG. 21, the density section on the low density value side, which is considered to be the background density area, is made finer and the density section on the high density side is made larger.
[0254]
When creating a density histogram, a document image is pre-scanned. Then, 1 is added to the histogram frequency of the corresponding density section according to which density section the density value of each pixel read by the pre-scan is. That is, assuming that a certain density category is ai, the frequency Hi in any density category Di may be obtained as Hi = Σhj (hj is a 256-level frequency included in the density category Di).
[0255]
The first threshold setting unit 362c sets a first threshold used by the density region dividing unit 362a. The first threshold value is a criterion for determining up to which density value the background is determined, and indicates the maximum density value determined as the background.
[0256]
The background density determination area creating unit 362c is a density area that is a background density determination target based on the first threshold (area where the density is equal to or lower than the first threshold shown in FIG. 21: an area that can be considered as the background). Is to select.
[0257]
The second threshold value setting unit 364 sets a second threshold value used by the combination density category extraction unit 363. This second threshold value is a criterion for determining from what frequency the total frequency of the following combination density classification in the background density area is determined as the background, and in the combination density classification determined as the background. It shows the minimum value of the total number of pixels.
[0258]
The combination density category extraction unit 363 sets a combination of a plurality of density categories in the density histogram created by the histogram creation unit 362, and sets the total frequency (total number of pixels) in the combination density category as the second threshold value. By comparison, a combination density category whose total frequency is equal to or greater than the second threshold is extracted.
[0259]
That is, the combination density category extraction unit 363 uses the histogram frequency in the region selected by the background density determination region creation unit 362b, and combines the density groups before and after the target density category as a combination density. Extract as a category.
[0260]
For example, in FIG. 21, if the value of the concentration category of interest is Hi, the value of the previous and subsequent concentration categories is Hi-1 and Hi + 1. In this case, assuming that these frequencies are P (H), P (Hi-1), and P (Hi + 1), respectively, the total number P (H) of the background determination is
P (H) = P (Hi-1) + P (Hi) + P (Hi + 1).
[0261]
As the combination of the density sections, as shown in FIG. 21, the same number of sections is combined on the low density side and the high density side with the focused density section as the center. Although the number of combinations depends on the density section width, the smaller the density section width, the greater the number of density sections to be combined.
[0262]
The first and second threshold values may be stored in a ROM or the like, and the threshold value stored in the storage means such as a memory may be set by a switch or the like as necessary. As described above, the user may arbitrarily set the configuration shown in FIG. With such a configuration, it is possible to easily adjust the first threshold value to determine which density value is the background, thereby removing the background or outputting the background for any background of interest. Is possible. In addition, it is possible to easily adjust the second threshold value to determine how many times the background is determined. This makes it possible to remove the background or output the background for any size of the background of interest. .
[0263]
When the first and second threshold values are input from the operation unit of the digital color copying machine 3 shown in FIGS. 8 and 9, for example, “light” is displayed on a display unit (not shown) made of a liquid crystal panel, for example. A message such as “Please select a color” may be displayed, and the user may perform processing according to the message, thereby sequentially setting corresponding threshold values.
[0264]
In the digital color copying machine 3, an upper limit value and a lower limit value are determined for the first threshold value in order to prevent malfunction due to an incorrect numerical value input from the operation unit shown in FIG. A numerical value outside these ranges, for example, a high value that is impossible as the background density, is subjected to prohibition processing and an error message is displayed.
[0265]
The background density category extraction unit 365 determines the density category of the maximum density among the combination density categories extracted by the combination density category extraction unit 363 as the background density.
[0266]
In this case, the background density category extraction unit 365 first selects the combination density category having the maximum density among the combination density categories extracted by the combination density category extraction unit 363. Next, the background density category extraction unit 365 determines the density category of the maximum density among the selected combination density categories as the background (background density). In FIG. 21, the background is a density section indicated by a mesh. That is, the background determination is performed for the density category having the highest density among the combination density categories that satisfy the first threshold value or less and satisfy the second threshold value or more. As a result, among the regions that can be considered as the background, the density classification that is most appropriate to be determined as the background is selected as the background.
[0267]
When the background density category extraction unit 365 extracts the combination density category to be the background, the total frequency of each combination density category and the second threshold value are sequentially applied from the low density side or the high density side (first threshold side). However, this process is preferably performed from the high density side of the first threshold. Thereby, it is possible to easily and quickly extract a combination density category as a base.
[0268]
Further, the background density category extraction unit 365 sets the density of the density category determined as the background as described above as a reference value.
[0269]
The density correction amount creation unit 367 creates, for example, a density correction amount line shown in FIG. 22 based on the reference value from a reference density correction amount line prepared in advance, and these reference density correction amount line and density correction amount line. Based on the above, a correction amount for creating a density correction curve is obtained.
[0270]
In the present embodiment, the reference density correction amount line connects the intersection point of the correction amount 255 and the input density value 255 with the origin O in the coordinates where the vertical axis indicates the correction amount and the horizontal axis indicates the input density value. It is a straight line.
[0271]
This reference density correction amount line determines a correction amount for creating a reference density correction curve and serves as one reference. The reference density correction amount line is selected according to the shape of the reference density correction curve to be created, for example, the shape that differs depending on the mode of the character or photograph to which the reference density correction curve is applied.
[0272]
In the density correction amount line created by the density correction amount creating unit 367, the density value of the reference value determined as the background is the starting point (the end on the low density side), and the end point of the reference density correction amount line prepared in advance. Is the end point. A density correction amount line is formed by connecting the start point and the end point.
[0273]
In the example shown in FIG. 22, the reference density correction amount line and the density correction amount line are straight lines, but these may be other appropriate curves.
[0274]
The density correction amount creating unit 367 obtains a correction amount based on the difference between the reference density correction amount line and the density correction amount line. The reference density correction amount line is created as described above.
[0275]
The density correction curve creation unit 366 creates a density correction curve by correcting a reference density correction curve prepared in advance with the correction amount created by the density correction amount creation unit 367, for example, as shown in FIG. It is.
[0276]
The density correction curve is created with the density value of the reference value as a starting point (end on the low density side). If the corresponding background (reference value) is not obtained in the background density category extraction unit 365, the reference density correction curve is not corrected, and the density correction curve is the same as the reference density correction curve.
[0277]
Then, the correction amount corresponding to each correction point set in the reference density correction curve is applied to each correction point to correct the reference density correction curve, that is, the density value corresponding to each density value of the reference density correction curve. The density correction curve is created by correcting the reference density correction curve by applying the correction amount to each density value. Although the correction of the reference density correction curve is preferably performed for all of the density values, as shown in FIG. 23, correction is performed with respect to preset correction points in a dispersed state on the reference density correction curve. The density correction curve may be obtained by performing the above.
[0278]
In the description with reference to FIGS. 22 and 23, the correction of the reference density correction curve is performed by subtraction of the correction amount. However, depending on the shape of the reference density correction curve, the correction is performed by addition, or by addition and subtraction. It may be performed.
[0279]
As described above, by creating a density correction curve for each input image, the digital color copying machine 3 can obtain an optimum image. That is, when the main scan is started, based on the created density correction curve, for example, the density below the start point (reference value) shown in FIG. 23 is removed by the density correction curve creating unit 366, and the density for each input value is determined. An optimal image whose value is corrected is output. Further, the hardware can be greatly simplified by the configuration for obtaining the density correction curve as described above.
[0280]
The density correction amount adjustment unit 368 adjusts the density correction amount by manually adjusting the start point (reference value) of the density correction amount curve to the low density side and the high density side.
[0281]
That is, in some cases, the user may want to output a favorite image adjusted by himself / herself, not by the automatic exposure adjustment function. In this case, the start point (reference value) may be manually adjusted by operating the density correction amount adjustment unit 368 with reference to the created density correction curve. In this case, the density correction amount adjustment unit 368 has an exposure adjustment button of the form shown in FIG. 8 provided in the operation unit of the digital color copying machine 3, for example.
[0282]
For example, the starting point (reference value) at the time of density correction curve creation may be shifted to the low density side and the high density side for each certain value by operating the exposure adjustment button. With such a configuration, manual density correction can be easily performed.
[0283]
The signal converter 369 converts the monochrome signal into a K signal.
[0284]
A program for performing processing of each unit of the input tone correction unit 371 is stored in the ROM 58 shown in FIG. 26, and the CPU 59 executes the program. In the figure, for the sake of simplicity, the density correction curve creation unit 366 represents access to the density correction amount adjustment unit 368 and the density correction amount creation unit 367.
[0285]
Next, input tone correction processing by the input tone correction unit 371 will be described with reference to the flowchart of FIG.
[0286]
If the automatic exposure mode is set when the copy start button is operated (S41), prescanning is first performed by the image input device 110 (S42). The automatic exposure adjustment mode setting button is provided on, for example, an operation unit (not shown) of the digital color copying machine 3. In S41, the automatic exposure mode is set. Not in Sometimes, a normal copy operation is performed (S54).
Next, a monochrome signal (for example, M signal) is selected by the monochrome signal conversion unit 352 (S43).
[0287]
Next, a monochrome signal (for example, M signal) is selected by the monochrome signal conversion unit 352 (S43).
[0288]
Next, when extracting the background and maximum density, it is determined whether or not the density area setting in the manual mode is selected (S44). This determination is made by the CPU 59.
[0289]
In the selection of the density area when extracting the background density, the first threshold (used for selection of the background) is set in advance. If the setting in the manual mode is selected, the density area based on the first threshold value is used. Is set (S45).
[0290]
Next, for example, the density histogram shown in FIG. 21 is created by the histogram creating unit 362 using the single color signal selected in S43 as described above (S46).
[0291]
Next, the combination density category extraction unit 363 includes a second threshold setting unit 364 in the region selected by the background density determination region creation unit 362b of the histogram creation unit 362 (a region that can be considered as a background). Based on the second threshold value set in (2), a combination density category as a background candidate is extracted (S47).
[0292]
Next, the background density category extraction unit 365 selects the maximum density combination density category among the combination density categories extracted by the combination density category extraction unit 363, and selects the maximum density category among the selected combination density categories. Is extracted as a base. Then, the density of the density category is set as a reference value (S48).
[0293]
Next, the density correction amount creation unit 367 creates, for example, a density correction amount line shown in FIG. 22 based on the reference value from a reference density correction amount line prepared in advance, and these reference density correction amount line and density A correction amount for creating a density correction curve is obtained based on the correction amount line (S49).
[0294]
The density correction curve creation unit 366 corrects a reference density correction curve prepared in advance with the correction amount created by the density correction amount creation unit 367, for example, and creates a density correction curve (see FIG. 23). S50).
[0295]
Then, the image data is corrected using the created density correction curve, and the image is output (S51).
[0296]
It is determined whether or not density adjustment is further performed on the output image (S53). When density adjustment is selected, density setting in the manual mode is performed (S53), and then S47 is performed. Go back and repeat the process below.
[0297]
That is, when extracting the background in S48, the second threshold value is set in advance, but these values can also be set manually. Therefore, when further density adjustment is performed, the second threshold value is set in the manual mode in S53, and the processing from S47 to S51 is performed again. If it is determined in S52 that it is not necessary to adjust the density, a series of processing ends at this point.
[0298]
In the above operation, when the density adjustment is performed in S52, the second threshold value for determining the background in S47 is changed in the manual mode. However, as shown in FIG. From S49, the reference value may be changed. In addition, each process in the same figure is the same as what was demonstrated in FIG.
[0299]
As described above, in the processing of the input tone correction unit 371 in the digital color copying machine 3 of the present embodiment, a combination of a plurality of density categories, that is, a combination density category is set when determining the background of an image. However, the background is discriminated by comparing this combination density section with the second threshold value instead of the individual density sections.
[0300]
Therefore, even if the hardware (scanner) accuracy is poor, noise is mixed in the image data, or mechanical vibration occurs when the image is read, these effects are suppressed and the background is always uniform. A determination can be made. In other words, in the configuration of the present embodiment, the noise mixed in the image data is removed by setting the combination density category instead of performing the spatial filter processing shown in the second embodiment. Thereby, for example, the same processing can always be performed on the same input image, and a high-quality image can be obtained.
[0301]
In the above description, the case where the monochromatic signal is a CMY signal is illustrated. On the other hand, when the monochrome signal is an RGB system, the area (density classification) that may be considered as the background has a density value equal to or higher than the first threshold in the created histogram, and the frequency (number of pixels). Is greater than or equal to the second threshold.
[0302]
Also, the density group that is most suitable as the background among the selected combination density categories is selected as the lowest density in the combination density category. Other processes may be performed in the same manner as in the case of a CMY monochromatic signal.
[0303]
The image processing apparatus of the present invention corrects the density of a region serving as a background of the digital image based on the density histogram, and a histogram creation unit that creates a density histogram based on the density of each pixel of the input digital image. In the image processing apparatus including the density correction unit, the histogram creation unit includes a density region dividing unit that divides the density range of the pixel of the digital image into a plurality of density categories, and a plurality of density ranges of the pixel of the digital image. A density area dividing means for dividing into density sections, and a plurality of density sections of the created density histogram are classified based on a preset first threshold, and the divided low density side area is used as a background density determination area A background density determination area creating means for setting, wherein the density correction means is configured to select the number of pixels from the density classification of the background density determination area. Containing a density category extracting means for extracting a density category that is equal to or higher than a preset second threshold and discriminating a density category that is closest to the first threshold among the extracted density categories as a background of the image. It is a feature.
[0304]
In the above-described image processing apparatus, the density category extraction unit may perform a discrimination operation for each density category as a background from the high density side toward the low density side.
[0305]
Further, in the above image processing apparatus, the histogram creation means adds the number of pixels allocated to each density section, and divides the added number of pixels by the density section width to obtain the number of pixels of each density section. Also good.
[0306]
Further, in the above image processing apparatus, the histogram creating means may be configured to be able to change a division interval of each density section in the background density determination region.
[0307]
In the image processing method of the present invention, a density histogram is created based on the density of each pixel of the input digital image, and the density of a region serving as a background of the digital image is corrected based on the created density histogram. In the image processing method, a plurality of density sections of the density histogram are classified based on a first threshold value set in advance, and the divided low density side area is set as a background density determination area. A configuration may be adopted in which pixels having a number of pixels equal to or greater than a preset second threshold value are extracted from the density segments, and the density segment closest to the first threshold value among the extracted density segments is set as the background of the image. .
[0308]
The image processing method may be configured such that the division interval of each density section in the background density determination region is finer than the division interval of each density section in another region.
[0309]
【The invention's effect】
In the image processing apparatus of the present invention, as described above, the histogram creating means includes density area dividing means for dividing the density range of the pixel of the digital image into a plurality of density sections, and the total density divided into the plurality of density sections. A predetermined density area creating means for creating a predetermined density area composed of a predetermined density classification group by dividing the range based on a predetermined first threshold, and created by the predetermined density area creating means; A density section extracting means for comparing the number of pixels of each density section in the predetermined density area with a second threshold value set in advance and extracting a density section equal to or higher than the second threshold; Among the extracted density sections, the density section close to the first threshold value is determined as the background of the image and is output to the density correction means.
[0310]
Therefore, since the histogram creating means has the density area dividing means and the predetermined density area creating means, when creating the histogram, the density area dividing means first sorts the density range of the pixels of the digital image into a plurality of density sections. Then, the predetermined density area creating means divides the entire density range divided into the plurality of density sections based on a predetermined first threshold value to thereby form a predetermined density area consisting of a predetermined density section group. Create
[0311]
Therefore, by appropriately setting the first threshold value, the maximum density when it is regarded as the background of the image can be determined, and the image is divided into the predetermined density area which is the background determination density area and the other areas. be able to.
[0312]
Next, in order to adopt as the background density, a predetermined density area having a large number of pixels in each density section is selected as the background density, and the second threshold is set in advance as the reference. Is done. Therefore, the second threshold value is a reference for selecting a density distribution amount, that is, a pixel having a large number of pixels when determining the background density of the entire image when a certain image is given.
[0313]
In addition, since the density category extraction unit discriminates a density category close to the first threshold value among the extracted density categories equal to or higher than the second threshold value as an image background, and outputs it to the density correction unit. Are determined to be smaller than the density based on the first threshold value set as the maximum density value considered as the background and close to the density based on the first threshold value for the entire image. Then, the background of the selected image is output to the density correction unit, so that the density correction unit subsequently performs correction for various image outputs such as removal of the background and correction of the density of the background. Processing can be performed.
[0314]
As a result, an image processing apparatus capable of accurately and efficiently performing appropriate density control according to various originals with different density conditions by creating a density histogram of the pixel density in the target image and easily determining the background of the image. There is an effect that can be done.
[0315]
In the above-described image processing apparatus, the density category extracting unit sequentially creates the predetermined density region from the high density side close to the first threshold value toward the low density side, and the number of pixels of each density category and the second threshold value. And the first density section equal to or higher than the second threshold value may be determined as the background of the image.
[0316]
According to said structure, there exists an effect that the judgment of the foundation | substrate of the density | concentration close | similar to the target 1st threshold value can be performed quickly with a simple method.
[0317]
In the above image processing apparatus, the density region dividing unit may add the number of pixels allocated to each density section, and divide the added number of pixels by the density section width to obtain the number of pixels of each density section. Good.
[0318]
According to the above configuration, the number of pixels obtained in this way is obtained as an average value of the number of pixels included in the density category. As a result, even when the density sections have different widths, absolute comparison of the number of pixels in each density section is possible, so that the background can be distinguished with high accuracy.
[0319]
In the above-described image processing apparatus, the density area dividing unit may be configured to be capable of changing a division interval of each density section in a predetermined density area.
[0320]
According to said structure, since the width | variety of each density | concentration division can be set finely, there exists an effect that the background determination of an image can be performed more correctly.
[0321]
In the above-described image processing apparatus, the density correction unit is configured to perform one correction from a plurality of density correction amount tables storing various correction amounts for each density category in order to perform correction based on the result of determining the background of the image. A configuration may be provided that includes density correction amount table selection means for selecting and correcting.
[0322]
According to the above configuration, since a plurality of density correction amount tables storing various correction amounts for each density category are used, the processing speed can be shortened and the circuit scale can be reduced.
[0323]
In the above-described image processing apparatus, the density correction unit may include a density correction amount adjusting unit that can arbitrarily adjust various correction amounts for each density category with respect to the density correction amount table.
[0324]
According to the above configuration, the selected density correction amount table can be arbitrarily adjusted, so that an output image suitable for the user's preference can be obtained.
[0325]
The image processing method described above creates a predetermined density region based on a predetermined first threshold value from all density regions of the density histogram, and the second threshold value in each of the plurality of divided density sections of the predetermined density region. A configuration in which a density section close to the first threshold value among the density sections having the number of pixels described above is determined as an image background.
[0326]
According to the above configuration, a density histogram of pixel density in the target image can be created to easily determine the background of the image, and appropriate density control according to various originals with different density conditions can be performed accurately and efficiently. There exists an effect that a processing method can be provided.
[0327]
The above image processing method may be configured such that the division interval of each density section in the predetermined density area is divided more finely than the division interval of each density section in another area.
[0328]
According to said structure, there exists an effect that the background determination of an image can be performed more correctly by setting the width | variety of each density | concentration division finely.
[0329]
The image processing apparatus according to the present invention includes a histogram creating unit that creates a density histogram based on the density of each pixel of the input digital image, and a density correction unit that corrects the density of the digital image based on the density histogram. In the image processing apparatus comprising: a filter process for performing a spatial filter process for correcting the density of each pixel on the digital image based on the density of each pixel of the digital image prior to the process of the histogram creating unit It is the structure provided with a means.
[0330]
According to the above configuration, prior to the processing of the histogram creating means, the digital image is subjected to the spatial filter processing for correcting the density of each pixel based on the density of each pixel of the digital image. This spatial filter processing is for removing variations in image data caused by noise mixed in image data, mechanical vibrations when reading an image, or the like.
[0331]
Therefore, by performing the above spatial filter processing, these effects are also affected when the accuracy of the hardware (scanner) is poor, when noise is mixed in the image data, or when mechanical vibration occurs when the image is read. The density histogram along the original image is suppressed. Thereby, the correction of the image density by the density correction means can be performed appropriately, and a good image can be obtained.
[0332]
The image processing apparatus according to the present invention includes a histogram creating unit that creates a density histogram based on the density of each pixel of the input digital image, and a density correction unit that corrects the density of the digital image based on the density histogram. In the image processing apparatus, the histogram creating means includes density region dividing means for dividing the density range of the pixel of the digital image into a plurality of density sections. Is extracted as a first reference value, and a density category that can be determined as the maximum density is extracted, and a reference value setting operation is performed to set the concentration as a second reference value. The density correction means corrects the image density on the low density side from the first reference value to 0, and increases the density from the second reference value. It is configured to correct the image density in degrees side to the highest concentration.
[0333]
According to the above configuration, the histogram creating means extracts a density section that can be determined as the background from the density sections of the generated density histogram, sets the density as the first reference value, and sets the density that can be determined as the maximum density. A category is extracted, and its concentration is set as the second reference value. Then, the density correction unit corrects the image density on the low density side from the first reference value to 0, and corrects the image density on the high density side from the second reference value to the maximum density.
[0334]
Thereby, it is possible to easily and satisfactorily perform density correction on the input image data.
[0335]
The image processing apparatus according to the present invention includes a histogram creating unit that creates a density histogram based on the density of each pixel of the input digital image, and a density correction unit that corrects the density of the digital image based on the density histogram. In the image processing apparatus, the histogram creating means includes density region dividing means for dividing the density range of the pixel of the digital image into a plurality of density sections. Is extracted as a first reference value, and a density category that can be determined as the maximum density is extracted, and a reference value setting operation is performed to set the concentration as a second reference value. The density correction means has a preset reference density correction curve, and a predetermined correction on the reference density correction curve. By connecting the said a point first reference value and second reference value, is configured to create a density correction curves for correcting the density of the digital image.
[0336]
According to the above configuration, the histogram creating means extracts a density section that can be determined as the background from the density sections of the generated density histogram, sets the density as the first reference value, and sets the density that can be determined as the maximum density. A reference value setting operation is performed to extract the classification and set the density as the second reference value. The density correction means has a preset reference density correction curve, and connects the predetermined correction point on the reference density correction curve with the first reference value and the second reference value, thereby digitally A density correction curve for correcting the image density is created.
[0337]
Thereby, a density correction curve for correcting the density of the input digital image can be created easily and quickly.
[0338]
In the above-described image processing apparatus, the histogram creation means performs the reference value setting operation, and divides a plurality of density sections of the created density histogram based on a preset low density side threshold value. The low density side area is selected as the first density area, the plurality of density categories are classified based on a preset high density side threshold value, and the classified high density side area is selected as the second density area. A density area creating means to select as an area, a density category that can be distinguished from the background of the image is extracted from the first density area, and the density is set as a first reference value; A configuration may be provided that includes a density category extraction unit that extracts a density category that can be distinguished from the maximum density and sets the density as a second reference value.
[0339]
According to the above configuration, the first and second reference value setting operations in the histogram creating unit can be appropriately performed by the density region creating unit and the density category extracting unit.
[0340]
In the above image processing apparatus, a plurality of correction points are set in advance on the reference density correction curve, and the density correction unit uses the first reference point as the start point of the density correction curve. The density correction curve may be created by connecting the correction point having a density value higher than the start point and closest to the start point.
[0341]
According to the above configuration, it is possible to quickly set the background density by a simple method, that is, to create a density correction curve for removing the background density. In addition, the hardware can be greatly simplified by increasing the density correction processing speed for the input image data and reducing the circuit scale for density correction.
[0342]
In the image processing apparatus, a plurality of correction points are set in advance on the reference density correction curve, and the density correction unit sets the second reference point as an end point of the density correction curve. The density correction curve may be created by connecting the correction point having a density value lower than the end point and closest to the end point.
[0343]
According to the above configuration, the maximum density can be quickly set by a simple method, the gradation reproducibility can be increased, and an optimum and highly accurate density correction curve can be created for each input image. it can. In addition, the hardware can be greatly simplified by increasing the density correction processing speed for the input image data and reducing the circuit scale for density correction.
[0344]
The image processing apparatus of the present invention corrects the density of a region serving as a background of the digital image based on the density histogram, and a histogram creation unit that creates a density histogram based on the density of each pixel of the input digital image. In the image processing apparatus including the density correction unit, the histogram creation unit classifies the plurality of density categories of the created density histogram based on a preset first threshold, and the classified low density side A background density discrimination area creating means for setting the above-mentioned area as a background density discrimination area, wherein the density correction means sequentially extracts a combination density category composed of a plurality of density zones that are continuous in the background density discrimination area. And the total number of pixels is preset from among the combination density categories extracted by the combination density category extraction means. Second extracting threshold or more those, a structure and a background density division extracting means for determining the predetermined density bins in combination closest concentration divided into a first threshold value of them as a base.
[0345]
According to the above configuration, the background density determination area creating unit of the histogram creating unit classifies the plurality of density categories of the created density histogram based on the first threshold value set in advance, and the classified low density side Is set as a background density discrimination area. The density correction means sequentially extracts a combination density section composed of a plurality of continuous density sections in the background density determination area. The background density category extraction unit extracts a combination density category extracted by the combination density category extraction unit that has a total number of pixels equal to or greater than a preset second threshold value, and is closest to the first threshold value. A predetermined density section in the combination density section is determined as the background. Then, the density correction unit corrects the density of the area serving as the background of the digital image based on the density of the density category determined as the background.
[0346]
With this configuration, even if the hardware (scanner) accuracy is poor, noise is mixed in the image data, or mechanical vibration occurs when reading the image, these effects are suppressed and input It is possible to accurately determine the background in the image. As a result, the image density can be appropriately corrected by the density correction means, and uniform processing can always be performed on similar input images. As a result, it is possible to perform optimum gradation processing on the input image and output a good image.
[0347]
In the above image processing apparatus, the combination density category extraction unit performs the operation of extracting the combination density category from the high density side to the low density side of the background density determination region, and the background density category extraction unit includes: The first combination density section that is equal to or higher than the second threshold may be selected as a combination density section including a density section that is determined to be the background.
[0348]
According to the above configuration, the combination density category extraction unit performs the combination density category extraction operation from the high density side (first threshold side) to the low density side of the background density determination region. Then, the background density category extraction means selects the first combination density category equal to or higher than the second threshold as the combination density category including the density category that is determined as the background.
[0349]
As a result, it is possible to easily and quickly extract a density section as a base, and to increase the processing speed of the apparatus.
[0350]
In the above image processing apparatus, the background density category extraction unit may be configured to determine a density category indicating the maximum density among the combination density categories equal to or higher than the second threshold as the background.
[0351]
According to said structure, the density | concentration value of a foundation | substrate can be set to an appropriate thing.
[0352]
In the above-described image processing apparatus, the combination density category extraction unit may be configured to add the same number of density categories on the high density side and the low density side of the density category to the density category of interest to form a combination density category. .
[0353]
According to the above configuration, since the combination density category is set by adding the same number of high density side and low density side density categories to the density category of interest, the combination density category is the background density category. This is appropriate for extraction, and this makes it possible to accurately determine the background.
[0354]
In the above-described image processing apparatus, the density correction unit uses the density of the density classification determined as the background as a reference value, and this reference value is a starting point on the low density side in a preset reference density correction amount line. A density correction amount creating means for correcting a reference density correction amount line to create a density correction amount line, and obtaining a correction amount of a density correction curve based on a difference between the reference density correction amount line and the density correction amount line; A density correction curve creating means for creating a density correction curve for correcting the density of the digital image based on the correction amount may be provided.
[0355]
According to the above configuration, the density correction amount creating means of the density correction means uses the density of the density classification determined as the background as a reference value, and this reference value is the lower density side in the preset reference density correction amount line. The density correction amount line is created by correcting the reference density correction amount line so as to be the starting point of the image, and the correction amount of the density correction curve is obtained from the difference between the reference density correction amount line and the density correction amount line. Then, the density correction curve creating means creates a density correction curve for correcting the density of the digital image based on the correction amount, and the density correcting means is a region serving as a background of the digital image based on the density correction curve. Correct the density.
[0356]
According to the above configuration, it is possible to accurately create an optimum density correction curve for each input image. Also, by creating the density correction curve as described above, the processing speed of the apparatus can be increased, and the hardware can be greatly simplified by reducing the circuit scale.
[0357]
An image forming apparatus of the present invention includes the above-described image processing apparatus.
[0358]
Therefore, for example, by installing the image processing apparatus of the present invention in an image forming apparatus such as a copying machine or a facsimile, a density histogram of pixel density in the target image can be created to easily determine the background of the image, There is an effect that it is possible to provide an image forming apparatus capable of accurately and efficiently performing appropriate density control according to various documents having different conditions.
[Brief description of the drawings]
FIG. 1 shows an embodiment of an image processing apparatus according to the present invention, and is a block diagram of an input tone correction unit.
FIG. 2 is a structural diagram showing a digital color copying machine as an image forming apparatus provided with the image processing apparatus.
FIG. 3 is a block diagram showing a portion used when normal image processing is performed in the image processing apparatus.
FIG. 4 is a block diagram illustrating a portion used when performing background determination in the image processing apparatus.
FIG. 5 is a flowchart showing a flow of an image processing method by the image processing apparatus.
FIG. 6 is a diagram illustrating an example of a density histogram created when a pixel density region is divided into 256 levels when image processing is performed by the image processing apparatus.
FIG. 7 is an explanatory diagram showing a density histogram in a state in which a density area of a pixel is divided into 16 density sections when background determination is performed by the image processing apparatus.
FIG. 8 is an explanatory diagram showing a configuration of an operation unit of a digital color copying machine for arbitrarily setting a first threshold when a density histogram is created by the image processing apparatus.
FIG. 9 is an explanatory diagram illustrating a configuration of an operation unit of a digital color copying machine for arbitrarily setting a second threshold value when a density histogram is created by the image processing apparatus.
FIG. 10 is an explanatory diagram showing a density correction amount table storing correction amounts used by the density correction means of the image processing apparatus.
FIG. 11 is a diagram illustrating a state corrected by the density correction unit using a density correction amount table, and is an explanatory diagram illustrating a density correction curve corrected with respect to a reference density correction curve.
12 is a block diagram illustrating a configuration including a CPU and a ROM with respect to the input tone correction unit illustrated in FIG. 1;
FIG. 13 is a block diagram showing another embodiment of the image processing apparatus according to the present invention and showing the configuration of an input tone correction unit.
14A is an explanatory diagram of a range of neighboring pixels used for explaining the operation of the filter processing unit shown in FIG. 13, and FIG. 14B is a diagram illustrating a smoothing process performed by the filter processing unit. It is explanatory drawing which shows an example of the filter coefficient in the case of performing.
15 is an explanatory diagram showing an example of a density histogram created by the histogram creating unit shown in FIG. 13 and an example of selection of background and maximum density.
16 is an explanatory diagram showing an example of a density correction curve created by the density correction curve creating unit shown in FIG. 13;
17 is a flowchart illustrating an example of an image processing operation of the image processing apparatus having the input tone correction unit illustrated in FIG.
FIG. 18 is a flowchart showing another example of the image processing operation shown in the flowchart of FIG.
FIG. 19 is a block diagram illustrating a configuration including a CPU and a ROM with respect to the input tone correction unit illustrated in FIG. 13;
FIG. 20 is a block diagram showing still another embodiment of the image processing apparatus according to the present invention and showing a configuration of an input tone correction unit.
FIG. 21 is an explanatory diagram showing an example of a density histogram created by the histogram creating unit shown in FIG. 20 and an example of selecting a background.
FIG. 22 is an explanatory diagram showing an example of a correction amount created by the density correction amount creation unit shown in FIG. 20;
FIG. 23 is an explanatory diagram showing an example of a density correction curve created by the density correction curve creating unit shown in FIG.
24 is a flowchart illustrating an example of an image processing operation of the image processing apparatus including the input tone correction unit illustrated in FIG.
FIG. 25 is a flowchart showing another example of the image processing operation shown in the flowchart of FIG. 24;
26 is a block diagram showing a configuration including a CPU and a ROM in the input tone correction unit shown in FIG.
[Explanation of symbols]
1 Digital color copier (image forming device)
2 Digital color copier (image forming device)
3 Digital color copier (image forming device)
52 Histogram creation unit (histogram creation means)
52a Density area dividing unit (density area dividing means)
52b Density area creation unit (predetermined density area creation means)
52c 1st threshold value setting part
52d 2nd threshold value setting part
53 Concentration classification extraction unit (concentration classification extraction means)
54 Density Correction Unit (Density Correction Means)
55 Density correction amount adjustment unit (density correction amount adjustment means, density correction means)
56 Density correction amount table selection unit (density correction amount table selection means, density correction means)
81 Density correction amount table
110 Image input device (image input means)
210 Image forming unit
310 Image processing apparatus
313 Input tone correction unit
330 Image processing apparatus
331 Input tone correction unit
351 Filter processing unit (filter processing means)
353 Histogram creation unit (histogram creation means)
353a Density area dividing unit (density area dividing means)
353b Density area creation unit (density area creation means)
353c Background density determination region creation unit
353d Maximum density discrimination area creation unit
353e first threshold value setting unit
353f Second threshold value setting unit
353g third threshold value setting unit
353h Fourth threshold setting unit
354 Density classification extraction unit (density correction means, density classification extraction means)
355 Density correction curve generator (density correction means)
356 Correction value setting section
360 Image processing apparatus
362 Histogram creation unit (histogram creation means)
362a Density area dividing unit (density area dividing means)
362b Background density determination area creation unit (background density determination area creation means)
362c first threshold value setting unit
363 Combination density category extraction unit (combination density category extraction means, density correction means)
364 Second threshold setting unit
365 Background density category extraction unit (background density category extraction means, density correction means)
366 Density correction curve creation unit (density correction amount creation means, density correction means)
367 Density correction amount creation unit (density correction curve creation means, density correction means)
368 Density correction amount adjustment unit
371 Input tone correction unit

Claims (7)

A histogram creating means for creating a density histogram based on the density of each pixel of the input digital image;
In an image processing apparatus comprising density correction means for correcting the density of a region serving as a background of the digital image based on the density histogram,
The histogram creating means classifies the density range of the pixel of the digital image into a plurality of density sections, and classifies the plurality of density sections of the created density histogram based on a preset first threshold. And a background density determination area creating means for setting the divided low density side area as a background density determination area,
The density correction means includes a combination density section extraction means for sequentially extracting a combination density section composed of a plurality of continuous density sections in the background density determination area, and a combination density section extracted by the combination density section extraction means. A background density category extracting means for extracting a pixel having a total number of pixels equal to or greater than a preset second threshold and determining a predetermined density category in the combination density category closest to the first threshold as a background;
The density correction means further uses the density of the density classification determined as the background as a reference value, and the reference density correction is performed so that the reference value becomes the starting point on the low density side in the preset reference density correction amount line. A density correction amount creating means for correcting a quantity line to create a density correction amount line, and obtaining a correction amount of a density correction curve based on a difference between the reference density correction amount line and the density correction amount line, and a preset reference density An image processing apparatus comprising density correction curve creating means for creating a density correction curve for correcting the density of the digital image by correcting the correction curve with the correction amount. The combination density category extraction means performs the extraction operation of the combination density category from the high density side to the low density side of the background density determination region, and the background density category extraction means has a second threshold value or more. The image processing apparatus according to claim 1, wherein the first combination density section is selected as a combination density section including a density section that is determined to be a background. 3. The image processing apparatus according to claim 1, wherein the background density category extraction unit is configured to determine, as a background, a density category indicating a maximum density among the combination density categories equal to or higher than the second threshold value. 4. . The combined concentration division extracting means, according to claim 1, characterized in that a combination density bins attention concentrations partitioned into a concentration section of the high concentration side and the low concentration side of the concentration divided by adding the same number respectively Image processing apparatus. A histogram creating means for creating a density histogram based on the density of each pixel of the input digital image;
In an image processing apparatus comprising density correction means for correcting the density of a region serving as a background of the digital image based on the density histogram,
The histogram creating means classifies the density range of the pixel of the digital image into a plurality of density sections, and classifies the plurality of density sections of the created density histogram based on a preset first threshold. And a background density determination area creating means for setting the divided low density side area as a background density determination area,
The density correction unit extracts a density section having a number of pixels equal to or greater than a preset second threshold value from density sections included in the background density determination area, and selects a density section closest to the first threshold value as the background section. And background density classification extracting means for determining
The density correction means further uses the density of the density classification determined as the background as a reference value, and the reference density correction is performed so that the reference value becomes the starting point on the low density side in the preset reference density correction amount line. A density correction amount creating means for correcting a quantity line to create a density correction amount line, and obtaining a correction amount of a density correction curve based on a difference between the reference density correction amount line and the density correction amount line, and a preset reference density An image processing apparatus comprising density correction curve creating means for creating a density correction curve for correcting the density of the digital image by correcting the correction curve with the correction amount. The image processing apparatus according to claim 1, wherein the density area dividing unit is provided so that a division interval of each density section in a predetermined density area can be changed. An image forming apparatus comprising the image processing apparatus according to claim 1 .

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