JP3824674B2 - Printing proof creation method and apparatus - Google Patents

Description

残りの色（Ｙ色、Ｋ色等の１３色分）についての面積率ｃｉはゼロ値である。このようにして２８×２８ドット毎に面積率ｃｉを作成することで、１６００ＤＰＩの数え上げデータｐ（各要素値は面積率ｃｉで表される。）が作成される。
【００５７】
次に、カラー印刷物１２上に印刷された１６色のべた色を測色計により測定する処理（ステップＳ３）により予め測色しておいた色毎の測色値データＸｉ、Ｙｉ、Ｚｉ（ｉは、ＣＭＹＫの４版の場合には、２⁴ 色＝１６色）に対してステップＳ１２で数え上げた色毎の面積率ｃｉを重み係数として測色的データｑ（３刺激値データＸ、Ｙ、Ｚ）を（５）式に示すように求める（ステップＳ１３）。言い換えれば、測色値データＸｉ、Ｙｉ、Ｚｉを色毎の面積率ｃｉで加重平均して３刺激値データＸ、Ｙ、Ｚ（測色的データｑ）を求める。
【００５８】

このように、７８４（２８×２８）ドット毎の数え上げ処理（ステップＳ１２）と加重平均処理（ステップＳ１３）を４４８００ＤＰＩのビットマップデータｂ’ｊの全範囲で行うことにより、１６００ＤＰＩの測色的データｑが得られる。
【００５９】
次に、得られた１６００ＤＰＩの測色的データｑに図５に示すアンチエリアジングフィルタＡＦを使用したアンチエリアジングフィルタ処理を行い、アンチエリアジングフィルタ処理後のＤＰ３の解像度に等しい４００ＤＰＩの測色的データβ（３刺激値データＸ、Ｙ、Ｚ）を作成する（ステップＳ１４）。
【００６０】
ステップＳ１４のアンチエリアジングフィルタ処理過程は、ＤＰ３の解像度（この実施例では、４００ＤＰＩ）でカラー印刷プルーフＣＰｂを作成しようとするとき、このＤＰ３の解像度を原因とするエリアジング雑音（折り返し雑音）の発生を予め回避するために挿入した過程である。アンチエリアジングフィルタ処理を有効に行うためには、アンチエリアジングフィルタＡＦがかけられる原信号である画像データ（この場合、測色的データｑ）の解像度がＤＰ３の解像度（４００ＤＰＩ）より高い解像度になっていることが必要である。この実施例では、その解像度が１６００ＤＰＩに選択されている。
【００６１】
図５に示したアンチエリアジングフィルタＡＦのマトリクス（ここでは、要素数がｎ×ｎの正方マトリクス）の構成について考える。
【００６２】
解像度１６００ＤＰＩの画像データである測色的データｑを解像度４００ＤＰＩの画像データである測色的データβに変換するためには、４００ＤＰＩの１ドットが１６００ＤＰＩの１６ドットに対応することからアンチエリアジングの効果を考えない場合のフィルタの最小限の要素数は４×４である。
【００６３】
そして、エリアジング雑音をできるだけ小さくするためには、アンチエリアジングフィルタＡＦの要素数は大きければ大きいほど望ましいが、演算速度、ハードウェア等との関係で制限される。
【００６４】
一方、色情報はノイゲバウア方程式によって再現できることからも類推できるように、直流成分を含む比較的低周波の成分を通過させる必要があることから、直流成分の近傍ではできるだけ挿入損失が発生しないような周波数特性にする必要がある。したがって、マトリクスの中心の応答が０ｄＢになることが理想である。
【００６５】
また、モアレ等の干渉縞成分｛網周波数（スクリーン線数）成分の１／２以下の成分｝はアンチエリアジングフィルタ処理（ステップＳ１４）を行ってもすべて残すようにしたい。
【００６６】
さらに、アンチエリアジングフィルタＡＦの減衰特性が急峻であると、このアンチエリアジングフィルタ処理を行うことによる新たな偽模様が現れてしまうことも考慮しなければならない。
【００６７】
図５は、このような観点を総合して作成された要素数が９×９のアンチエリアジングフィルタＡＦの構成例を示している。なお、各要素をｄｉｊで表すとき、各要素ｄｉｊの値（フィルタ係数ともいう。）は全部加えて１．０にする必要性があることから、各要素ｄｉｊの実際の値は各要素ｄｃｉｊの総和（Σｄｃｉｊ）で割っておく。
【００６８】
このように構成したアンチエリアジングフィルタＡＦのフィルタ係数の配置は、図５から分かるように、中央部分から外方に向かうにしたがってほぼ釣り鐘状に単調減少的に減衰する周波数特性になっている。
【００６９】
図６は、このアンチエリアジングフィルタＡＦの周波数特性を示している。図６において、横軸は解像度を示し、ＤＰ３の解像度Ｒａ＝４００ＤＰＩを値１．０に規格化している。したがって、網周波数であるスクリーン線数１７５線は、値０．４４に規格化される。縦軸は応答を示し、図５中、中央の要素ｄ₅₅＝１２１を値１．０に規格化している。
【００７０】
図５例では、図６から分かるように、解像度１．０において、応答は約０．２３であり、解像度０．４４において、応答は、約０．７７である。
【００７１】
なお、種々の例を検討した結果、解像度が網周波数（スクリーン線数相当）のときに応答が０．５（５０％）以上で、解像度がカラーデジタルプリンタであるＤＰ３の解像度１．０であるときに応答が０．３（３０％）以下であれば、カラー印刷物１２に現れるモアレ等の干渉縞をカラー印刷プルーフＣＰｂで再現できることが分かり、かつエリアジング雑音が視認されない程度にできることが分かった。
【００７２】
以上の説明がアンチエリアジングフィルタＡＦのマトリクス（ここでは、要素数がｎ×ｎ（９×９）の正方マトリクス）の構成の説明である。
【００７３】
図７は、このアンチエリアジングフィルタ処理の説明に供される線図である。図７Ａに示すように、１６００ＤＰＩの測色的データｑの左上の９×９ドット分に対して図５に示した要素がｄｉｊで表される９×９のアンチエリアジングフィルタＡＦを対応させ、対応する各要素を掛算して、それらの総和を求めてアンチエリアジングフィルタ処理を行う。すなわち、測色的データｑの各要素をｅｉｊと表すとき、Σ（ｄｉｊ×ｅｉｊ）（９×９要素分）を求め、これを解像度４００ＤＰＩの測色的データβとする。なお、上述したようにアンチエリアジングフィルタＡＦの総和はΣｄｉｊ＝１に規格化しているが、小数を含む掛算は時間がかかるので、アンチエリアジングフィルタＡＦの各要素の値は図５に示した値をそのまま用いて、ｄ’ｉｊとするとき、Σ（ｄ’ｉｊ×ｅｉｊ）／Σｄ’ｉｊとしてアンチエリアジングフィルタ処理後の値を求めてもよい。
【００７４】
この場合、アンチエリアジングフィルタ処理では、解像度１６００ＤＰＩの測色的データｑを解像度４００ＤＰＩの測色的データβに変換するのであるから、測色的データｑに対する２回目のアンチエリアジングフィルタ処理は、図７Ｂに示すように、アンチエリアジングフィルタＡＦを測色的データｑの４ドット分を、例えば、右側にずらして行えばよい。以下、同様にして４ドット分ずつずらしてアンチエリアジングフィルタ処理を行い、アンチエリアジングフィルタＡＦの右端が測色的データｑの右端に等しい位置でアンチエリアジングフィルタ処理を行った後には、図７Ｂに示す、上から５番面の要素ｅ₅₁にアンチエリアジングフィルタＡＦの要素ｄ₁₁を対応させて行い、以下同様にして要素ｅ_16001600と要素ｄ₉₉とが対応するまで４ドットずつずらしてアンチエリアジングフィルタ処理を行うことで、１６００ＤＰＩの測色的データｑの解像度を低下させて４００ＤＰＩの測色的データβを得ることができる。アンチエリアジングフィルタ処理は、カラー印刷物１２の印刷網に特有の空間周波数応答を保存したまま、ＤＰ３に固有の空間周波数応答を遮断するフィルタ処理であるともいえる。
【００７５】
次に、ステップＳ８で作成した測色的データβとステップＳ２１で作成しておいた測色的データαとから、ステップＳ８の像構造シミュレーション処理を実行したことによる色ずれ量を補正するための色ずれ量補正データγを作成する（ステップＳ２５）。出力端５３に現れる色ずれ量補正データγは、各測色的データの差β−α（＝γ）または各測色的データの比（α／β）（＝γ）とする簡単な数学的演算で得られる。
【００７６】
色ずれ量補正データγを図１に示す入力端５４から供給することで、色ずれ量補正ＬＵＴ２１を作成することができる。
【００７７】
以上が像構造シミュレーション処理（ステップＳ８）を実行することにより発生する色ずれ量を補正するための色ずれ量補正ＬＵＴ２１の作成についての説明である。
【００７８】
図８は、カラー印刷物１２の色再現範囲より狭い色再現範囲を有するＤＰ３を使用することにより発生する色ずれ量補正ＬＵＴ２２の作成に供される図である。
【００７９】
この場合、入力端５１に供給される網点面積率データａｊが像構造シミュレーション処理（ステップＳ８）によって測色的データβに変換され、この像構造シミュレーション処理を原因とする色ずれ量が色ずれ量補正ＬＵＴ２１で補正された測色的補正データδ（例えば、δ＝β−γ＝α、δ＝β×γ＝α）が得られる。
【００８０】
この測色的補正データδは、共通色空間データであり、例えば、３刺激値データＸ、Ｙ、Ｚであるので、これが、ＬＵＴ２３でＤＰ３に固有の色空間データ、この場合、ＲＧＢデータに変換される。このようにして作成されたＲＧＢデータをもとにＤＰ３でハードコピーである予備的印刷プルーフＣＰａを作成する。
【００８１】
次にこの予備的印刷プルーフＣＰａを測色計で測定して測色データζを得る（ステップＳ２６）。次いで、この測色データζと測色的データδとからＤＰ３を使用したことによる色ずれ量補正を行うための色ずれ量補正データηを作成する（ステップＳ２７）。出力端５５に現れる色ずれ量補正データηも、色ずれ量補正データγと同様に、データの差δ−ζ（＝η）または各測色的データの比（ζ／δ）（＝η）とする簡単な数学的演算で得られる。
【００８２】
色ずれ量補正データηを図１に示す入力端５６から供給することで、色ずれ量補正ＬＵＴ２２を作成することができる。
【００８３】
このような準備のもとで、図１においてカラー印刷プルーフＣＰｂを作成する際には、まず、像構造シミュレーション処理（ステップＳ８）で発生する色ずれ量を色ずれ量補正ＬＵＴ２１で補正して測色的データδを得、次に、ＤＰ３を利用することにより発生する色ずれ量を色ずれ量補正ＬＵＴ２２により補正して測色的データθを得る。この場合、色ずれの無い測色的データθを得ることができる。
【００８４】
ところで、図１に示すカラー印刷システム１１においては、カラー印刷物１２として、ユーザが指定した特定の印刷用紙および印刷用インクが用いられる。この場合、前記印刷用紙は、その種類によって表面の光沢、ザラツキ状態、あるいは、インク乗りの良し悪し等が異なっている。また、前記印刷用インクの場合も、選択された印刷用紙に応じて印刷状態が異なる場合がある。一方、カラー印刷プルーフＣＰｂを作成するＤＰ３では、通常、印刷用紙および印刷用インクの種類が制限されており、カラー印刷システム１１における記録媒体と同一の記録媒体でカラー印刷プルーフＣＰｂを作成することは事実上不可能である。
【００８５】
そこで、本実施例では、まず、像構造シミュレーション（ステップＳ８）において、網点面積率データａｊをビットマップ展開（ステップＳ２２）する際、図３に示すように、閾値マトリクス２４を印刷用紙および印刷用インクに応じて調整するようにしている。
【００８６】
すなわち、印刷用紙に対する印刷用インクの乗りの良し悪しは、使用する印刷用紙の表面特性および／または印刷用インクの種類に依存している。そして、この良し悪しの結果は、カラー印刷物１２を構成する画素レベルの微視的な振る舞いとして視認される。そこで、前記印刷用インクの乗りの良し悪しを、図９に示すように、印刷用紙と印刷用インクとの組み合わせに対するパラメータとして設定しておく。この場合、前記パラメータは、実験的に求められるものであり、次に示す乱数ＲＮのばらつき範囲を規制する標準偏差ＳＤとして標準偏差ＬＵＴ２８に格納される。なお、図９に示す標準偏差ＳＤは、網点面積率データａｊが０〜２５５の値を取るものとした場合の値であり、前記網点面積率データａｊを０〜１００％の値とした場合には、ＳＤ／２．５５の値に設定されることになる。
【００８７】
印刷用紙および印刷用インクからなる印刷条件が特定されると、標準偏差ＬＵＴ２８から該当するパラメータである標準偏差ＳＤが選択され、乱数発生器３０に供給される。乱数発生器３０は、前記標準偏差ＳＤに従ったばらつき範囲からなる平均値が０の乱数ＲＮを生成し、閾値マトリクス２４に加算する。この場合、前記閾値マトリクス２４を構成する閾値Ｔ（ｉ，ｊ）は、
Ｔ（ｉ，ｊ）＝Ｔ（ｉ，ｊ）＋ＲＮ（ＳＤ） …（６）
として修正され、網点面積率データａｊと比較される（ステップＳ１０）。この結果、印刷用インクの乗りの良し悪しが加味されたビットマップデータｂ’ｊ
を得ることができる。
【００８８】
また、本実施例では、前記のようにして印刷用インクの乗りの良し悪しが加味されたビットマップデータｂ’ｊを生成した後、数え上げ処理（ステップＳ１２）、加重平均処理（ステップＳ１３）、アンチエリアジングフィルタ処理（ステップＳ１４）、色ずれ量補正ＬＵＴ２１、２２による色補正処理を行い、さらに、印刷用紙の種類に応じた大域的な補正処理を印刷用紙補正ＬＵＴ２６を用いて行っている。
【００８９】
すなわち、カラー印刷物１２の仕上がり感は、印刷用紙の表面における光の散乱の相違（例えば、ザラツキ感、光沢感等として認識される。）や、用紙の部分的な厚みの相違による濃度分布の変動により異なる。そこで、これらの印刷用紙に依存する仕上がり感を再現するための補正データを予め測定によって求めておき、印刷用紙補正ＬＵＴ２６に設定しておく。なお、この仕上がり感は、カラー印刷物１２の全体に略均等に広がる比較的大きい領域でのザラツキ感として認識されるものであるため、網展開処理後のデータに対して処理を行うことで再現することができる。
【００９０】
前記印刷用紙補正ＬＵＴ２６の作成方法としては、例えば、１６００ＤＰＩの解像度で網点面積率が１００％となる、いわゆるべた濃度のカラー印刷物１２を所定の印刷用紙上に作成し、一定領域内の各画素毎の濃度を測定して測色値データＹ（ｉ，ｊ）を求める。例えば、コート紙、アート紙の場合、３ｍｍ四方で１８９×１８９画素、上質紙の場合、１ｃｍ四方で６３０×６３０画素の濃度を測定し、測定値のマトリクスを作成する。次に、前記一定領域内の各画素毎の濃度の平均値を求め、前記各画素の測定値と前記平均値との比率を求め、これを補正データＭＹ（ｉ，ｊ）とする。なお、（ｉ，ｊ）は、例えば、コート紙の場合、（０，０）〜（１８８，１８８）の値に設定するものとする。これらの補正データＭＹ（ｉ，ｊ）は、印刷用紙毎に設定され、印刷用紙補正ＬＵＴ２６に格納される。
【００９１】
そこで、色ずれ量補正ＬＵＴ２１、２２によって色ずれ量が補正された測色的データθ（＝Ｘ（ｉ，ｊ）、Ｙ（ｉ，ｊ）、Ｚ（ｉ，ｊ））は、印刷用紙に応じて選択された前記印刷用紙補正ＬＵＴ２６により、次の（７）式のように補正される。
【００９２】
Ｘ’（ｉ，ｊ）＝Ｘ（ｉ，ｊ）・ＭＹ（ｉ，ｊ）
Ｙ’（ｉ，ｊ）＝Ｙ（ｉ，ｊ）・ＭＹ（ｉ，ｊ）
Ｚ’（ｉ，ｊ）＝Ｚ（ｉ，ｊ）・ＭＹ（ｉ，ｊ） …（７）
この結果、印刷用紙に応じた仕上がり感を備えた測色的データθ’（＝Ｘ’（ｉ，ｊ）、Ｙ’（ｉ，ｊ）、Ｚ’（ｉ，ｊ））を得ることができる。なお、前記（７）式において、補正データＭＹ（ｉ，ｊ）は、色の明るさを示す刺激値データＹに対するものを代表値として設定しているが、各刺激値データＸ、Ｙ、Ｚ毎に設定するようにしてもよい。
【００９３】
以上のようにして補正された測色的データθ’は、ＬＵＴ２３でＲＧＢデータに変換される。このＲＧＢデータによりＤＰ３で作成されたハードコピー上の画像、すなわち、カラー印刷プルーフＣＰｂは、カラー印刷物１２と色が一致し、かつ、網点画像の像構造も再現し得る。すなわち、カラー印刷プルーフＣＰｂ上には、カラー印刷物１２上に現れるのとほぼ等しいモアレ、ローゼット等の干渉縞、すなわち、像構造が忠実に再現される。また、印刷用紙および印刷用インクに対応した仕上がり感も再現されることになる。
【００９４】
この場合、ＤＰ３の解像度が４００ＤＰＩと比較的低い値であるにもかかわらず、２０００ＤＰＩ（この実施例では１６００ＤＰＩと仮定している。）の解像度を有するカラー印刷機で作成されたカラー印刷物１２上に現れるのとほぼ等しいモアレ、ローゼット等の干渉縞をカラー印刷プルーフＣＰｂ上に再現することができるとともに、色再現予測処理および色ずれ量補正処理により色も忠実に再現できるので、カラー印刷プルーフＣＰｂを簡易かつ廉価に作成することができる。
【００９５】
また、アンチエリアジングフィルタ処理をかけているので、ＤＰ３の解像度を原因として発生するエリアジング雑音（画像上ではビートによる偽模様とも呼ばれる。）、言い換えれば、ＤＰ３を使用することによる網周期とプリンタの解像度（ＤＰ３の解像度）との干渉に基づく偽の像構造をも取り除くことができる。
【００９６】
なお、上述の実施例においては、画像出力装置としてＤＰ３を使用しているが、これにかぎらず、ＤＰ３に代替してビットマップメモリとビットマップディスプレイを有するカラーモニタを利用できることはもちろんである。
【００９７】
【発明の効果】
以上説明したように、この発明によれば、カラー印刷物に使用される印刷用紙および／または印刷用インクの種類に応じて閾値マトリクスを修正し、あるいは、ビットマップデータに展開された後のデータを前記印刷用紙に応じて補正することにより、印刷時の仕上がり感と同等の状態からなるカラー印刷プルーフを比較的廉価な低解像度の画像出力装置で忠実かつ簡易に得ることができる。
【図面の簡単な説明】
【図１】この発明の一実施例の処理フローを含み、全体としては、カラー印刷物に対応するカラー印刷プルーフを作成する工程の説明に供されるフロー図である。
【図２】図１の処理フロー中、カラー印刷物を作成する際の一般的なビットマップデータを作成する際の説明に供される線図である。
【図３】像構造シミュレーションによる色ずれ量補正データを作成する説明に供される線図である。
【図４】図４Ａおよび図４Ｂは、図１の処理フロー中、カラー印刷プルーフを作成する際の比較的高解像度のビットマップデータから平均測色値データを作成する際の説明に供される線図である。
【図５】アンチエリアジングフィルタの構成を示す線図である。
【図６】アンチエリアジングフィルタの周波数応答を示す線図である。
【図７】図７Ａおよび図７Ｂは、測色値データに対してアンチエリアジングフィルタをかける際の説明に供される線図である。
【図８】カラープリンタを使用することに伴う色ずれ量補正データを作成する説明に供される線図である。
【図９】閾値マトリクスを修正するために設定される記録媒体に応じた標準偏差ＬＵＴの説明図である。
【図１０】従来の技術の説明に供されるフロー図である。
【符号の説明】
２…画像原稿 ３…カラープリンタ
１１…カラー印刷システム １２…カラー印刷物
２１、２２…色ずれ量補正ＬＵＴ ２６…印刷用紙補正ＬＵＴ
２８…標準偏差ＬＵＴ ３０…乱数発生器
ａｊ…網点面積率データ ｂｊ…ビットマップデータ
ｃｉ…面積率 ＣＰｂ…カラー印刷プルーフ[0001]
[Industrial application fields]
The present invention provides a density gradation when a color printing proof (also referred to as a color printing proof) for proofreading is created before a color print using a halftone image is created by a color printing machine using a rotary press or the like. The present invention relates to a method and apparatus for creating a color printing proof with a color printer that forms an image for each pixel on a sheet by a method or a color monitor that forms an image for each pixel on a display by a luminance modulation method.
[0002]
[Prior art]
Conventionally, a color printing proof for proofreading a color or the like has been created by a color printer before creating a color printed product using a halftone dot image as a product by a color printer.
[0003]
In order to create a color printing proof, a color printer is used because the color printer has a relatively simple configuration and is inexpensive, and, as is well known, in a color printer, a plate-making film related to a color printing machine is used. This is because there is no need to create a printing plate (PS plate) or the like, and a hard copy in which an image is formed on a sheet can be easily created in a short time.
[0004]
FIG. 10 shows a flow of a conventional method for creating a color printing proof.
[0005]
First, an image on the image original 2 is read by an image reading device such as a color scanner having a CCD area sensor or the like, and gradation image data Ia for each color of R (red), G (green), and B (blue) is obtained. It is created (step S1).
[0006]
Next, the RGB gradation image data Ia is converted into four halftone dot area ratio data (halftone%) for each color of C (cyan), M (magenta), Y (yellow), and K (black) by color conversion processing. It is also referred to as data.) Aj (j = 0 to 3: 0 is C color, 1 is M color, 2 is Y color, 3 is K color respectively) (step S2). This conversion can be performed in various ways depending on the relationship with the color printer.
[0007]
The image on the color print produced by this color printing machine is a halftone dot image. Therefore, when actually producing a color print, the dot area ratio data aj after color conversion processing is developed into bitmap data. On the basis of this, a plate making film or the like is created. However, an automatic processor (automatic machine) or the like is required, and the steps after the plate making film creation processing step are considerably complicated.
[0008]
Therefore, a color printer (hereinafter also referred to as a color digital printer, also referred to as DP) 3 is used for the reason described above in order to easily create a color printing proof CPa. DP3 forms an image on a donor film by digitally controlling the emission intensity and time of an LED (light emitting diode) or laser corresponding to the three primary colors for each pixel by a density gradation method, and this is received on an image receiving sheet. The image is formed on the sheet, and an image is formed on the sheet, which is considerably cheaper than a color printing machine that makes a printing plate and prints using it. In addition, the volume is small and the weight is light.
[0009]
Therefore, in order to use DP3, the CMYK 4th halftone dot area ratio data aj created in step S2 is temporarily image data (also referred to as common color space data) that is not dependent on a device. It is necessary to convert to tristimulus value data X, Y, and Z.
[0010]
Therefore, image data processing for converting the dot area ratio data aj of the CMYK4 version into the tristimulus value data X, Y, Z is performed (step S4). As this image data processing, for example, processing using the Neugebauer equation is employed.
[0011]
In this case, colorimetric value data Xi, Yi, Zi for each color of the printing ink is previously measured by a colorimeter (in the case of the 4th edition of CMYK, i is 2).^FourCorresponding to color = 16 colors, i = 0-15. ) Is measured (step S3). In this measurement, first, each of the 16 colors is printed in advance on a printing paper when a color printed material is created by a color printer (usually referred to as solid printing). The 16 colors specifically correspond to the presence / absence of each of the C color, M color, Y color, and K color, and 2 in total.^FourColor = 16 colors.
[0012]
That is, W (white) color, which is the background color of the printing paper when nothing is printed, each color of only C, M, Y as primary colors, K (black) color, and other mixed colors such as C + M, C + Y, C + K, There are a total of 16 colors including M + Y, M + K, Y + K, C + M + Y, C + M + K, C + Y + K, M + Y + K, and C + M + Y + K. These reflected colors formed on the printing paper are measured with a colorimeter, for example, a spectrometer, to obtain colorimetric value data Xi, Yi, Zi.
[0013]
In the processing using the Neugebauer equation, as shown in the following equation (1), the halftone dot area rate data bi (i = 0 to 15) is multiplied as each coefficient of the colorimetric value data Xi, Yi, and Zi. Tristimulus value data X, Y, and Z after image data processing are created (step S4).
[0014]
X = Σbi · Xi
Y = Σbi · Yi
Z = Σbi · Zi (1)
Here, the halftone dot area ratio data bi of the 16 basic colors as the coefficients is obtained from the halftone dot area ratio data aj by the probability calculation shown in the following equation (2).
[0015]
b0 = (1-c) (1-m) (1-y) (1-k)
b1 = c. (1-m) (1-y) (1-k)
b2 = (1-c) .m. (1-y) (1-k)
b3 = c.m. (1-y) (1-k)
b4 = (1-c) (1-m) .y. (1-k)
b5 = c. (1-m) .y. (1-k)
b6 = (1-c) .m.y. (1-k)
b7 = c.m.y. (1-k)
b8 = (1-c) (1-m) (1-y) · k
b9 = c. (1-m) (1-y) .k
b10 = (1-c) · m · (1-y) · k
b11 = c · m · (1-y) · k
b12 = (1-c) (1-m) · y · k
b13 = c · (1−m) · y · k
b14 = (1-c) · m · y · k
b15 = c · m · y · k (2)
In equation (2), the dot area ratio data aj (j = 0 to 3) are set as a0 = c, a1 = m, a2 = y, and a3 = k so that an intuitive understanding can be easily obtained. In this case, c, m, y, and k are halftone dot area ratio data. In the equation (2), for example, b3 is C + M color area ratio data, which is the probability c that the C version exists, the probability m that the M version exists, and the probability that the Y version does not exist (1 -Y) and the probability that the K version does not exist (1-k) is multiplied by probability calculation. Therefore, the Neugebauer equation shown in equation (1) can be understood as an equation based on probability theory.
[0016]
Tristimulus value data X, Y, Z after image data processing created based on the equation (1) is supplied to DP3, and DP3 uses the tristimulus value data X, Y, Z as a lookup table (LUT). Color printing proof CPa, which is a hard copy in which an image is formed on a sheet after being converted into data for each of the three primary colors relating to the LED or the like (image data dependent on a device, also called intrinsic color space data). Create
[0017]
By the way, as described above, when the tristimulus value data X, Y, and Z for DP3 are created using the Neugebauer equation, the color of the image formed on the color printed matter created by the color printer Since the colorimetric value measured by the colorimeter is used, the color of the color printed matter can be faithfully reproduced in the image on the hard copy. However, the recording medium made of printing paper and printing ink used in DP3 is usually different from the recording medium used in an actual color printing machine, and therefore, the same finishing feeling as in printing is obtained. It could not be reproduced on CPa.
[0018]
That is, there are various types of paper used for printing, such as high-quality paper, art paper, and coated paper, depending on the application, and the surface condition and the quality of printing ink are different. In addition, there are various types of printing inks, and the finished feeling varies depending on the relationship with the printing paper. The user designates the recording medium according to the print contents and performs printing, and it is extremely important to create the color print proof CPa in consideration of these factors.
[0019]
[Problems to be solved by the invention]
The present invention has been made in view of the above points, and provides a method and apparatus capable of creating a faithful color printing proof according to a recording medium made of printing paper or printing ink used for printing. The purpose is to do.
[0020]
[Means for Solving the Problems]
  This invention,networkIn a printing proof creation method, the point area ratio data is developed into bitmap data by comparing with predetermined threshold data, and a print proof of a color printed matter created based on the bitmap data is created via an image output device. There,
  A first step of setting standard deviation data according to a feeling of finishing of an image by a recording medium comprising printing paper and / or printing ink constituting the color printed matter;
  A second step of adjusting the threshold data by applying a random number having a standard deviation according to the standard deviation data to predetermined threshold data;
  A third step of developing the dot area ratio data into bitmap data using the adjusted threshold data;
  A fourth step of creating a print proof based on the bitmap data;
  It is characterized by having.
[0021]
  Further, the present invention develops bitmap area data by comparing the dot area ratio data with predetermined threshold data, and prints a print proof of a color print produced based on the bitmap data via an image output device. A print proof creation method to create,
  Printing paper constituting the color printed matterThe ratio of the density value of each pixel of the color printed matter formed in a certain area of the image and the average value of the density values of the pixels is the ratio of the printing paper.Correction dataAsA first step to set,
  A second step of developing the dot area ratio data into bitmap data using threshold data;
  Using the correction data, the bitmap dataTFirst to correct3Steps,
  Said3Corrected in stepbitmapBased on dataAndCreate a print proof4Steps,
  It is characterized by having.
[0022]
  Further, the present invention develops bitmap area data by comparing the dot area ratio data with predetermined threshold data, and prints a print proof of a color print produced based on the bitmap data via an image output device. A printing proof creation device for creating,
  By a recording medium comprising printing paper and / or printing ink constituting the color printed matter.RuStandard deviation data holding means for holding standard deviation data corresponding to the finished image,
  Random number generating means for generating a random number having a standard deviation according to the standard deviation data;
  Threshold data holding means for holding threshold data;
  Depending on the printing paper and / or the printing inkThe standard deviation data is selected, the standard deviation of the random number is controlled according to the standard deviation data, and the threshold data is corrected by the random number.Threshold data correction means;
  And creating the print proof by developing the dot area ratio data into bitmap data using the corrected threshold dataIt is characterized by that.
[0023]
  Further, according to the present invention, the halftone dot area ratio data is developed into bitmap data by comparing with predetermined threshold data, and a print proof of the color printed matter created based on the bitmap data is sent via the image output device. A printing proof creation device for creating,
  Printing paper constituting the color printed matterThe ratio of the density value of each pixel of the color printed matter formed in a certain area of the image and the average value of the density values of the pixels is the ratio of the printing paper.Correction dataAsCorrection data holding means to holdWhen,
  Threshold data holding means for holding threshold data;
  Select the correction data according to the printing paper,According to the correction dataCorrect the bitmap dataBitmap data correction means;
  And developing the halftone dot area ratio data into the bitmap data using the threshold data, and correcting the bitmap data with the correction data to create a print proofIt is characterized by that.
[0024]
[Action]
According to the present invention, the microscopic value corresponding to the printing paper and / or printing ink is obtained by correcting the threshold data using a predetermined parameter set according to the type of printing paper and / or printing ink. A color printing proof having a realistic finish can be obtained. Further, by applying correction data for reproducing the surface state of the printing paper to the image data, it is possible to obtain a color printing proof having a global finish feeling corresponding to the printing paper.
[0025]
【Example】
Hereinafter, an embodiment of the present invention will be described with reference to the drawings. In the drawings to be referred to below, the same reference numerals are given to the components corresponding to those shown in FIG. 10, and the description thereof is omitted as appropriate.
[0026]
FIG. 1 shows a processing flow for creating a color print proof CPb according to this embodiment by a color digital printer (DP) 3 for a color print 12 produced by a general color printing system 11.
[0027]
First, the contents of a general color printing system 11 will be described.
[0028]
In a general color printing system 11, an image on an image original 2 is read by an image reading device such as a color scanner having a CCD area sensor or the like, and each color of R (red), G (green), and B (blue) is read. Gradation image data Ia is created (step S1). In this case, for example, about 400 DPI (Dot Per Inch) is selected as the resolution of the CCD area sensor or the like. Here, 1 dot (dot) means a pixel by a density gradation method (also referred to as a continuous tone method) corresponding to one pixel and having a gradation of 256 or the like.
[0029]
Next, each pixel data constituting the RGB gradation image data Ia is converted into four halftone dots for each color of C (cyan), M (magenta), Y (yellow), and K (black) by color conversion processing. The area ratio data (also referred to as halftone data) aj is converted (step S2). This conversion can be performed in various ways depending on the relationship with a color printer described later. In the case where UCR (Under Color Removal) processing is not performed, RGB gradation image data Ia may be converted into halftone dot area ratio data aj of C, M, and Y. In addition, for example, when there is no Y color on the color printed matter 12, it is needless to say that it is only necessary to convert it into C and M halftone dot area ratio data aj.
[0030]
Next, with respect to the CMYK4 plate halftone dot area ratio data aj created for each pixel, the resolution is about 2000 DPI (here, 1600 DPI for ease of understanding) for each of the CMYK4 plates. Referring to four threshold matrixes (also referred to as threshold templates) 14 having desired halftone angles and screen line numbers, the threshold values in each element of the threshold matrix 14 are compared with the values of the dot area ratio data aj. , Converted into binary data having a value “0” or a value “1”, that is, bitmap data bj (step S5). In general, the screen angle has an angle difference of 45 ° or the like between the threshold matrix 14 for the Y plate and the threshold matrix 14 for the M plate. In practice, the screen angle is, for example, CMYK. The 4th edition has an angular difference of 75 °, 45 °, 0 °, 15 °, etc. with respect to the reference. The number of screen lines is 175 lines in this embodiment.
[0031]
FIG. 2 is a diagram schematically illustrating the threshold matrix 14 and the like in order to explain in detail the bitmap development process in step S5.
[0032]
In FIG. 2, the two diagrams drawn at the top represent that one dot of the dot area ratio data aj of 400 DPI is converted to 16 dots of the bitmap data bj of 1600 DPI.
[0033]
One dot of the halftone dot area ratio data aj is, for example, the C plate, and the value of the halftone dot area ratio data aj is represented by 256 gradations, and aj = 77 (corresponding to 30% in% display). If there is, this and the threshold matrix 14 for the C plate are referred to. In the threshold value matrix 14, for example, threshold values T as shown in FIG. 2 are spirally arranged in the elements of the matrix. The threshold value matrix 14 is virtually set because it is not directly related to the present invention and will not be described in detail. For example, 8 bits of 0, 1, 2,. A threshold matrix corresponding to one halftone dot in which the gradation threshold T is spirally arranged from the center, or a so-called supercell (for example, one threshold matrix corresponding to nine halftone dots), respectively. A part to be extracted is reconstructed.
[0034]
As is well known, the development to the bitmap data bj, that is, binary data conversion, is performed as shown in the following equations (3) and (4).
[0035]
aj ≧ T → 1 (3)
aj <T → 0 (4)
In this way, the bitmap data bj for the one pixel of the C plate shown in the lowermost row of FIG. 2 (pixels with halftone dot area ratio data aj of aj = 77) is created. As described above, the threshold matrix 14 for M, Y, and K has a predetermined selectable halftone angle with respect to the threshold matrix 14 for C plate.
[0036]
Next, based on the bitmap data bj created in this way, as shown in FIG. 1, processing by a photosetting machine, an automatic developing machine or the like is performed (step S6), and the 4th version having a halftone image as a composition A plate making film 16 and a PS plate 17 as a printing plate are prepared.
[0037]
Finally, using this PS plate 17, a color print 12 formed with a halftone image is created by a color printing machine having a rotary press or the like (step S7).
[0038]
In the halftone dot image on the color printed matter 12, interference fringes such as moire and rosette, which are not present in the image original 2 and are generated by using the threshold value matrix 14 having different halftone angles, so-called image structures appear, and the roughness is increased. A feeling of finish specific to printing paper and printing ink, such as feeling, glossiness, and color unevenness, occurs.
[0039]
The above is the description of the contents of the general color printing system 11.
[0040]
In the present invention, the finished feeling resulting from the recording medium of the color printed matter 12 created by the color printing system 11 is faithfully reproduced on the color printing proof CPb.
[0041]
Here, the image structure of the color printed matter 12 can be accurately reproduced by performing an image structure simulation process (step S8) described in detail later.
[0042]
By the way, since color misregistration occurs when the image structure is reproduced, a color misregistration amount correction look-up table (hereinafter referred to as LUT) 21 for correcting this is necessary, and the color reproduction range of DP3. And a color misregistration correction LUT 22 for correcting color misregistration caused by the fact that the color reproduction range of printing is different (usually, the color reproduction range of DP3 is narrower than the color reproduction range of printing). It is.
[0043]
The data corrected by the color misregistration amount correction LUTs 21 and 22 is the common color space data described in the section of the prior art, and the common color space data is corrected according to the printing paper described in detail later on the printing paper. After performing using the correction LUT 26, as described in the section of the prior art, it is converted into color space data specific to DP3 (in FIG. 1, it is represented by LUT indicated by reference numeral 23) and supplied to DP3. As a result, a color printing proof CPb that can faithfully reproduce the image structure and color can be created.
[0044]
Therefore, the creation of the color misregistration amount correction LUT 21 and the color misregistration amount correction LUT 22 will be described next.
[0045]
FIG. 3 shows a configuration for creating a color misregistration amount correction LUT 21 for correcting the color misregistration amount generated by the image structure simulation process (step S8).
[0046]
When creating the color misregistration correction LUT 21, first, a color reproduction prediction process (step S21) and an image structure simulation process (step S8) are performed.
[0047]
The color reproduction prediction process in step S21 corresponds to, for example, the process using the above-mentioned Neugebauer equation or the case where each halftone dot area data aj of the CMYK4 version is changed by a predetermined percentage (predetermined amount). A plurality of color samples on the printed color printed matter 12 are measured with a colorimeter, and color measurement data in the CIE color system, for example, tristimulus value data, for each color sample when changed by a predetermined percentage. Colorimetric value data Xi, Yi, Zi are obtained, colorimetric data between color samples when the predetermined percentage is changed are obtained by interpolation processing, and the colorimetric values measured by the colorimetry system and the interpolation processing are obtained. There is a process of having the obtained colorimetric data as a lookup table or a correction function using the halftone dot area ratio data aj as input data. In any case, at least the colorimetric value data Xi, Yi, Zi for each color by the colorimeter (i is 2 in the case of the 4th edition of CMYK).^FourIt is necessary to measure (color = 16 colors) (step S3 in FIG. 10).
[0048]
In this way, in the color reproduction prediction process in step S21, for example, the expression (1), the expression (2), and the colorimetric value data for the halftone dot area ratio data aj having the resolution of 400 DPI supplied from the input terminal 51 are used. Colorimetric data α is obtained using Xi, Yi, and Zi. Next, in the image structure simulation process in step S8, first, a bitmap development process peculiar to the image structure simulation process is performed (step S22).
[0049]
In this case, the threshold matrix 24 having a higher resolution than the threshold matrix 14 shown in FIG. 2 is selected in accordance with the screen line number and the screen angle under the same conditions as the printing supplied from the input end 52. This is for increasing the resolution of the bitmap data b'j. Since the screen line number and the screen angle related to the threshold matrix 24 are the same as those for printing in order to reproduce the moire and the like, the screen line number is set to 175 lines. As described above, the mesh angle is selected so that each of the CMYK plates has angles of 75 °, 45 °, 0 °, and 15 ° with respect to the reference.
[0050]
On the other hand, in order to increase the resolution, the threshold value matrix 24 having 256 elements × 256 = 65536 is used as the threshold value matrix 24 for creating halftone dots. For example, values 0, 1, 2,..., 255 are taken as threshold values in each element. The threshold value matrix 24 and the halftone dot area ratio data aj are compared to create bitmap data b'j (step S10).
[0051]
The resolution of the bitmap data b'j for the CMYK 4-version created in this way is 44800 (256 × 175) DPI.
[0052]
Next, the bitmap data b'j having 44800 DPI is converted into data having a resolution of 1600 DPI. For this purpose, a counting process may be performed in which 28 × 28 (784) dots of the bitmap data b′j are counted and converted into one dot of the counting data p (step S12).
[0053]
In order to explain the counting process in step S12 in an easy-to-understand manner, an example of 28 × 28 dots of the C version bitmap data b′j is shown in FIG. 4A, and 28 × 28 dots of the M version bitmap data b′j. An example of minutes is shown in FIG. 4B. In FIG. 4A and FIG. 4B, it is assumed that the values of elements not shown are all “0”. Further, it is assumed that the remaining elements of the Y version and K version bitmap data b'j are all the value "0".
[0054]
Therefore, for 28 × 28 dots, bitmap data b′j for the CMYK 4th edition (here, it is needless to say that the bitmap data b′j for the 2nd edition of the C edition and the M edition may be used) at the same time. Refer to each color (2 because the version number is 4)^FourA process of counting the area ratio ci for each color) is performed.
[0055]
In the pixels shown in FIGS. 4A and 4B (corresponding to 28 × 28 dots), the area ratio ci for each color is calculated as follows.
[0056]

The area ratio ci for the remaining colors (13 colors such as Y color and K color) is zero. By creating the area ratio ci for each 28 × 28 dots in this way, 1600 DPI counting data p (each element value is represented by the area ratio ci) is created.
[0057]
Next, the colorimetric value data Xi, Yi, Zi (i) for each color measured in advance by the process (step S3) of measuring the 16 solid colors printed on the color printed matter 12 with the colorimeter. Is 2 for the 4th edition of CMYK^FourThe colorimetric data q (tristimulus value data X, Y, Z) is obtained as shown in the equation (5) by using the area ratio ci for each color counted in step S12 for color = 16 colors) as a weighting factor ( Step S13). In other words, the colorimetric value data Xi, Yi, Zi are weighted and averaged by the area ratio ci for each color to obtain tristimulus value data X, Y, Z (colorimetric data q).
[0058]

In this way, by performing the counting process (step S12) and the weighted average process (step S13) for each of 784 (28 × 28) dots in the entire range of the bitmap data b′j of 44800 DPI, 1600 DPI colorimetric data is obtained. q is obtained.
[0059]
Next, anti-aliasing filter processing using the anti-aliasing filter AF shown in FIG. 5 is performed on the obtained 1600 DPI colorimetric data q, and 400 DPI color measurement equal to the resolution of DP3 after the anti-aliasing filter processing is performed. Target data β (tristimulus value data X, Y, Z) is created (step S14).
[0060]
The anti-aliasing filter processing process in step S14 is performed when the color printing proof CPb is created at the resolution of DP3 (400 DPI in this embodiment), and aliasing noise (folding noise) caused by the resolution of DP3 is generated. This is a process inserted to avoid the occurrence in advance. In order to effectively perform the anti-aliasing filter processing, the resolution of the image data (in this case, the calorimetric data q) that is the original signal to which the anti-aliasing filter AF is applied is higher than the resolution of DP3 (400 DPI). It is necessary to become. In this embodiment, the resolution is selected as 1600 DPI.
[0061]
Consider the configuration of the matrix of the anti-aliasing filter AF shown in FIG. 5 (here, a square matrix having n × n elements).
[0062]
In order to convert calorimetric data q, which is image data with a resolution of 1600 DPI, into calorimetric data β, which is image data with a resolution of 400 DPI, since one dot of 400 DPI corresponds to 16 dots of 1600 DPI, anti-aliasing When the effect is not considered, the minimum number of elements of the filter is 4 × 4.
[0063]
In order to minimize aliasing noise as much as possible, the larger the number of elements of the anti-aliasing filter AF, the better. However, the number of elements is limited in relation to the calculation speed and hardware.
[0064]
On the other hand, color information can be reproduced by the Neugebauer equation, and it is necessary to pass a relatively low-frequency component including a DC component, so that it can be inferred that the frequency at which insertion loss does not occur as close as possible to the DC component. It needs to be a characteristic. Therefore, it is ideal that the response at the center of the matrix is 0 dB.
[0065]
Further, it is desirable to leave all interference fringe components such as moire {components of half or less of the network frequency (number of screen lines) components] even after the anti-aliasing filter processing (step S14).
[0066]
Further, it must be taken into account that if the attenuation characteristic of the anti-aliasing filter AF is steep, a new false pattern appears due to this anti-aliasing filter processing.
[0067]
FIG. 5 shows a configuration example of the anti-aliasing filter AF having 9 × 9 elements created by combining these viewpoints. When each element is represented by dij, the value of each element dij (also referred to as a filter coefficient) needs to be added to 1.0, so the actual value of each element dij is the value of each element djij. Divide by the sum (Σdcij).
[0068]
As can be seen from FIG. 5, the arrangement of the filter coefficients of the anti-aliasing filter AF configured as described above has a frequency characteristic that attenuates in a monotonically decreasing manner in a bell shape as it goes outward from the central portion.
[0069]
FIG. 6 shows the frequency characteristics of the anti-aliasing filter AF. In FIG. 6, the horizontal axis indicates the resolution, and the resolution Ra = 400 DPI of DP3 is normalized to a value of 1.0. Therefore, the screen frequency of 175 lines, which is the network frequency, is normalized to a value of 0.44. The vertical axis shows the response, and in FIG.₅₅= 121 is normalized to a value of 1.0.
[0070]
In the example of FIG. 5, as can be seen from FIG. 6, at a resolution of 1.0, the response is about 0.23, and at a resolution of 0.44, the response is about 0.77.
[0071]
As a result of examining various examples, when the resolution is a network frequency (corresponding to the number of screen lines), the response is 0.5 (50%) or more, and the resolution is 1.0 of the color digital printer DP3. It was found that when the response is 0.3 (30%) or less, interference fringes such as moire appearing in the color printed matter 12 can be reproduced with the color printing proof CPb, and aliasing noise can be prevented from being visually recognized. .
[0072]
The above is the description of the configuration of the anti-aliasing filter AF matrix (here, a square matrix having n × n (9 × 9) elements).
[0073]
FIG. 7 is a diagram for explaining the anti-aliasing filter processing. As shown in FIG. 7A, the 9 × 9 antialiasing filter AF in which the element shown in FIG. 5 is represented by dij corresponds to 9 × 9 dots in the upper left of the 1600 DPI colorimetric data q, The corresponding elements are multiplied to obtain a sum of them, and anti-aliasing filter processing is performed. That is, when each element of the colorimetric data q is represented as eij, Σ (di × eij) (9 × 9 elements) is obtained, and this is used as the calorimetric data β with a resolution of 400 DPI. As described above, the sum of the anti-aliasing filter AF is standardized to Σdij = 1, but multiplication including decimals takes time, so the values of each element of the anti-aliasing filter AF are shown in FIG. When the value is used as it is and d′ ij, the value after anti-aliasing filter processing may be obtained as Σ (d′ ij × eij) / Σd′ij.
[0074]
In this case, in the anti-aliasing filter process, the calorimetric data q with a resolution of 1600 DPI is converted into the calorimetric data β with a resolution of 400 DPI. Therefore, the second anti-aliasing filter process for the calorimetric data q is As shown in FIG. 7B, the anti-aliasing filter AF may be shifted by shifting, for example, four dots of the calorimetric data q to the right side. Thereafter, after anti-aliasing filter processing is performed by shifting by four dots in the same manner, and after anti-aliasing filter processing is performed at a position where the right end of the anti-aliasing filter AF is equal to the right end of the colorimetric data q, Element e on the fifth surface from the top shown in 7B₅₁Element d of anti-aliasing filter AF₁₁In the same manner, element e_16001600And element d₉₉By performing anti-aliasing filter processing by shifting by 4 dots until and correspond to each other, the resolution of 1600 DPI colorimetric data q can be reduced to obtain 400 DPI colorimetric data β. It can be said that the anti-aliasing filter process is a filter process for cutting off the spatial frequency response unique to DP3 while preserving the spatial frequency response peculiar to the printing network of the color printed matter 12.
[0075]
Next, the amount of color misregistration due to the execution of the image structure simulation processing in step S8 is corrected from the calorimetric data β created in step S8 and the calorimetric data α created in step S21. Color misregistration correction data γ is created (step S25). The color misregistration correction data γ appearing at the output terminal 53 is a simple mathematical expression in which each colorimetric data difference β−α (= γ) or each colorimetric data ratio (α / β) (= γ). Obtained by calculation.
[0076]
By supplying the color misregistration amount correction data γ from the input terminal 54 shown in FIG. 1, the color misregistration amount correction LUT 21 can be created.
[0077]
This completes the description of the creation of the color misregistration amount correction LUT 21 for correcting the color misregistration amount generated by executing the image structure simulation process (step S8).
[0078]
FIG. 8 is a diagram which is used to create a color misregistration correction LUT 22 that is generated by using DP3 having a color reproduction range narrower than the color reproduction range of the color printed material 12.
[0079]
In this case, the dot area ratio data aj supplied to the input terminal 51 is converted into colorimetric data β by the image structure simulation process (step S8), and the color misregistration amount caused by this image structure simulation process is the color misregistration. Colorimetric correction data δ (for example, δ = β−γ = α, δ = β × γ = α) corrected by the amount correction LUT 21 is obtained.
[0080]
Since the colorimetric correction data δ is common color space data, for example, tristimulus value data X, Y, and Z, this is converted into color space data specific to DP3 in the LUT 23, in this case, RGB data. Is done. A preliminary print proof CPa, which is a hard copy, is created at DP3 based on the RGB data created in this way.
[0081]
Next, this preliminary printing proof CPa is measured with a colorimeter to obtain colorimetric data ζ (step S26). Next, color misregistration amount correction data η for correcting the color misregistration amount by using DP3 is created from the calorimetric data ζ and the calorimetric data δ (step S27). Similarly to the color misregistration amount correction data γ, the color misregistration amount correction data η appearing at the output terminal 55 is also the data difference δ−ζ (= η) or the ratio (ζ / δ) (= η) of each colorimetric data. It can be obtained by a simple mathematical operation.
[0082]
By supplying the color misregistration amount correction data η from the input terminal 56 shown in FIG. 1, the color misregistration amount correction LUT 22 can be created.
[0083]
With this preparation, when creating the color print proof CPb in FIG. 1, first, the color misregistration amount generated in the image structure simulation process (step S8) is corrected by the color misregistration amount correction LUT 21 and measured. The color data δ is obtained, and then the color misregistration amount generated by using DP3 is corrected by the color misregistration amount correction LUT 22 to obtain colorimetric data θ. In this case, colorimetric data θ without color misregistration can be obtained.
[0084]
By the way, in the color printing system 11 shown in FIG. 1, a specific printing paper and printing ink designated by the user are used as the color printed matter 12. In this case, the printing paper has different surface gloss, roughness, or good or bad ink riding depending on the type. In the case of the printing ink, the printing state may differ depending on the selected printing paper. On the other hand, in DP3 for creating a color printing proof CPb, the types of printing paper and printing ink are usually limited, and creating a color printing proof CPb with the same recording medium as in the color printing system 11 is not possible. Virtually impossible.
[0085]
Therefore, in the present embodiment, first, when the halftone dot area ratio data aj is developed as a bitmap (step S22) in the image structure simulation (step S8), the threshold matrix 24 is printed on the printing paper and the printing as shown in FIG. The ink is adjusted according to the ink used.
[0086]
That is, whether the printing ink is applied to the printing paper depends on the surface characteristics of the printing paper to be used and / or the type of printing ink. This good / bad result is visually recognized as a microscopic behavior at the pixel level constituting the color print 12. Therefore, whether the printing ink is applied or not is set as a parameter for a combination of printing paper and printing ink, as shown in FIG. In this case, the parameter is obtained experimentally and is stored in the standard deviation LUT 28 as a standard deviation SD that regulates the variation range of the random number RN shown below. The standard deviation SD shown in FIG. 9 is a value when the halftone dot area ratio data aj takes a value of 0 to 255, and the halftone dot area ratio data aj is set to a value of 0 to 100%. In this case, the value is set to SD / 2.55.
[0087]
When a printing condition consisting of printing paper and printing ink is specified, the standard deviation SD, which is a corresponding parameter, is selected from the standard deviation LUT 28 and supplied to the random number generator 30. The random number generator 30 generates a random number RN having an average value of 0 having a variation range according to the standard deviation SD, and adds the random number RN to the threshold value matrix 24. In this case, the threshold value T (i, j) constituting the threshold value matrix 24 is
T (i, j) = T (i, j) + RN (SD) (6)
And is compared with the dot area ratio data aj (step S10). As a result, the bitmap data b'j that takes into account whether the printing ink is loaded or not is added.
Can be obtained.
[0088]
Further, in the present embodiment, after generating the bitmap data b′j in consideration of whether or not the printing ink is loaded as described above, the counting process (step S12), the weighted average process (step S13), Anti-aliasing filter processing (step S14), color correction processing using the color misregistration correction LUTs 21 and 22, and global correction processing corresponding to the type of printing paper are performed using the printing paper correction LUT 26.
[0089]
That is, the finished feeling of the color printed matter 12 is a variation in density distribution due to a difference in light scattering on the surface of the printing paper (for example, recognized as a rough feeling, a glossy feeling, etc.) or a difference in partial thickness of the paper. Varies by Therefore, correction data for reproducing the finished feeling depending on the printing paper is obtained in advance by measurement and set in the printing paper correction LUT 26. This finished feeling is recognized as a rough feeling in a relatively large area that spreads almost uniformly over the entire color printed matter 12, and is thus reproduced by processing the data after the network expansion processing. be able to.
[0090]
As a method for creating the printing paper correction LUT 26, for example, a so-called solid color print 12 having a halftone dot area ratio of 100% at a resolution of 1600 DPI is created on a predetermined printing paper, and each pixel in a fixed area is created. The density of each color is measured to obtain colorimetric value data Y (i, j). For example, in the case of coated paper and art paper, a density of 189 × 189 pixels is measured in 3 mm square, and in the case of high-quality paper, a density of 630 × 630 pixels is measured in 1 cm square, and a measurement value matrix is created. Next, an average value of density for each pixel in the fixed region is obtained, and a ratio between the measured value of each pixel and the average value is obtained, and this is used as correction data MY (i, j). Note that (i, j) is set to a value of (0, 0) to (188, 188) in the case of coated paper, for example. These correction data MY (i, j) are set for each printing paper and stored in the printing paper correction LUT 26.
[0091]
Therefore, the colorimetric data θ (= X (i, j), Y (i, j), Z (i, j)) whose color misregistration amount is corrected by the color misregistration amount correction LUTs 21 and 22 is printed on the printing paper. The printing paper correction LUT 26 selected accordingly is corrected as shown in the following equation (7).
[0092]
X ′ (i, j) = X (i, j) · MY (i, j)
Y ′ (i, j) = Y (i, j) · MY (i, j)
Z '(i, j) = Z (i, j) .MY (i, j) (7)
As a result, colorimetric data θ ′ (= X ′ (i, j), Y ′ (i, j), Z ′ (i, j)) having a finished feeling corresponding to the printing paper can be obtained. . In the equation (7), the correction data MY (i, j) is set as a representative value for the stimulus value data Y indicating the brightness of the color. However, each of the stimulus value data X, Y, Z You may make it set for every.
[0093]
The calorimetric data θ ′ corrected as described above is converted into RGB data by the LUT 23. The image on the hard copy created by DP3 using this RGB data, that is, the color printing proof CPb, matches the color of the color printed matter 12, and can reproduce the image structure of the halftone image. That is, on the color printing proof CPb, interference fringes such as moire and rosette, that is, the image structure, which is almost the same as that appearing on the color printed matter 12, is faithfully reproduced. In addition, a finished feeling corresponding to printing paper and printing ink is also reproduced.
[0094]
In this case, even though the resolution of DP3 is a relatively low value of 400 DPI, the color print 12 produced by a color printing machine having a resolution of 2000 DPI (in this example, 1600 DPI) is used. Interference fringes such as moire and rosette that are almost the same as appearing can be reproduced on the color printing proof CPb, and color can also be faithfully reproduced by color reproduction prediction processing and color misregistration correction processing. It can be created easily and inexpensively.
[0095]
Further, since anti-aliasing filter processing is applied, aliasing noise (also referred to as a false pattern due to beats on the image) generated due to the resolution of DP3, in other words, the network period and printer by using DP3. The false image structure based on the interference with the resolution (DP3 resolution) can also be removed.
[0096]
In the above-described embodiment, DP3 is used as an image output device. However, it is needless to say that a color monitor having a bitmap memory and a bitmap display can be used instead of DP3.
[0097]
【The invention's effect】
As described above, according to the present invention, the threshold matrix is corrected according to the type of printing paper and / or printing ink used for the color printed matter, or the data after being developed into bitmap data is used. By correcting in accordance with the printing paper, a color printing proof having a state equivalent to the finished feeling at the time of printing can be faithfully and easily obtained with a relatively inexpensive low-resolution image output apparatus.
[Brief description of the drawings]
FIG. 1 includes a process flow according to an embodiment of the present invention, and is a flowchart used to explain a process of creating a color print proof corresponding to a color print as a whole.
FIG. 2 is a diagram used for explanation when creating general bitmap data when creating a color print in the processing flow of FIG. 1;
FIG. 3 is a diagram for explaining color misregistration correction data created by image structure simulation;
FIGS. 4A and 4B are provided for explaining the creation of average colorimetric value data from relatively high resolution bitmap data when creating a color print proof during the processing flow of FIG. FIG.
FIG. 5 is a diagram showing a configuration of an anti-aliasing filter.
FIG. 6 is a diagram showing the frequency response of an anti-aliasing filter.
FIG. 7A and FIG. 7B are diagrams used for explanation when an anti-aliasing filter is applied to colorimetric value data.
FIG. 8 is a diagram used for explaining creation of color misregistration correction data associated with the use of a color printer.
FIG. 9 is an explanatory diagram of a standard deviation LUT corresponding to a recording medium set for correcting a threshold matrix.
FIG. 10 is a flowchart for explaining a conventional technique.
[Explanation of symbols]
2 ... Image original 3 ... Color printer
11 ... Color printing system 12 ... Color printed matter
21, 22 ... Color misregistration correction LUT 26 ... Printing paper correction LUT
28 ... Standard deviation LUT 30 ... Random number generator
aj: Halftone dot area ratio data bj: Bitmap data
ci ... Area ratio CPb ... Color printing proof

Claims (4)

Printing proof creation method for developing halftone dot area ratio data into bitmap data by comparing with predetermined threshold data, and creating a print proof of a color printed matter created based on the bitmap data via an image output device Because
A first step of setting standard deviation data according to a feeling of finishing of an image by a recording medium comprising printing paper and / or printing ink constituting the color printed matter;
A second step of adjusting the threshold data by applying a random number having a standard deviation according to the standard deviation data to predetermined threshold data;
A third step of developing the dot area ratio data into bitmap data using the adjusted threshold data;
A fourth step of creating a print proof based on the bitmap data;
A method for producing a print proof, comprising: Printing proof creation method for developing halftone dot area ratio data into bitmap data by comparing with predetermined threshold data, and creating a print proof of a color printed matter created based on the bitmap data via an image output device Because
A ratio between the density value of each pixel of the color printed matter formed in a certain area of the printing paper constituting the color printed matter and the average value of the density values of the pixels is set as correction data for the printing paper. Steps,
A second step of developing the dot area ratio data into bitmap data using threshold data;
A third step of correcting the bitmap data using the correction data;
A fourth step of creating a print proof based on the bitmap data corrected in the third step;
A method for producing a print proof, comprising: A printing proof creation device for developing halftone dot area ratio data into bitmap data by comparing with predetermined threshold data, and creating a print proof of a color printed matter created based on the bitmap data via an image output device Because
Standard deviation data holding means for holding standard deviation data corresponding to the finished feeling of an image by a recording medium comprising printing paper and / or printing ink constituting the color printed matter;
Random number generating means for generating a random number having a standard deviation according to the standard deviation data;
Threshold data holding means for holding threshold data;
Threshold data correction means for selecting the standard deviation data according to the printing paper and / or the printing ink, controlling the standard deviation of the random number according to the standard deviation data, and correcting the threshold data by the random number;
And a halftone dot area ratio data developed into bitmap data using the corrected threshold data to create a print proof. A printing proof creation device for developing halftone dot area ratio data into bitmap data by comparing with predetermined threshold data, and creating a print proof of a color printed matter created based on the bitmap data via an image output device Because
Correction data for holding, as correction data for the printing paper, the ratio between the density value of each pixel of the color printing material formed in a fixed area of the printing paper constituting the color printing material and the average value of the density values of the pixels. Holding means;
Threshold data holding means for holding threshold data;
Bitmap data correction means for selecting the correction data according to the printing paper and correcting the bitmap data with the correction data;
A halftone dot area ratio data which is developed into the bitmap data using the threshold data, and the bitmap data is corrected by the correction data to create a print proof creating apparatus. .

Images