JP3676177B2 - Color tone control method and apparatus for printing press - Google Patents

Description

但し、
Ｒ（λ）：混色部の分光反射率＝Ｒ（λ）／Ｒ_ｐ（λ）…（２）
Ｒ_ｉ（λ）：分光反射率＝Ｒ_ｉ（λ）／Ｒ_ｐ（λ） ………（３）
ｉ＝ｐ（白紙）、ｃ（藍ベタ）、ｍ（紅ベタ）、ｙ（黄ベタ）、
ｋ（墨ベタ）、ｃｍ（藍、紅ベタ重ね）、
ｍｙ（紅、黄ベタ重ね）、ｙｃ（黄、藍ベタ重ね）、
ｋｃ（墨、藍ベタ重ね）、ｋｍ（墨、紅ベタ重ね）、
ｋｙ（墨、黄ベタ重ね）、ｃｍｙ（藍、紅、黄ベタ重ね）、
ｋｃｍ（墨、藍、紅ベタ重ね）、
ｋｃｙ（墨、藍、黄ベタ重ね）、
ｋｍｙ（墨、藍、黄ベタ重ね）、
ｋｃｍｙ（墨、藍、紅、黄ベタ重ね）
λ＝４００〜９００ｎｍ、１０ｎｍピッチ
Ａ_ｉ：面積占有率 ΣＡ_ｉ≡１．０
藍、紅、黄、墨の単色網点面墳率をｃ、ｍ、ｙ、ｋとすれば、
Ａ_ｐ＝（１−ｃ）（１−ｍ）（１−ｙ）（１−ｋ）
Ａ_ｃ＝ｃ（１−ｍ）（１−ｙ）（１−ｋ）
Ａ_ｍ＝（１−ｃ）ｍ（１−ｙ）（１−ｋ）
Ａ_ｙ＝（１−ｃ）（１−ｍ）ｙ（１−ｋ）
Ａ_ｋ＝（１−ｃ）（１−ｍ）（１−ｙ）ｋ
Ａ_ｃｍ＝ｃｍ（１−ｙ）（１−ｋ）
Ａ_ｍｙ＝（１−ｃ）ｍｙ（１−ｋ）
Ａ_ｙｃ＝ｃ（１−ｍ）ｙ（１−ｋ）
Ａ_ｋｃ＝ｃ（１−ｍ）（１−ｙ）ｋ
Ａ_ｋｍ＝（１−ｃ）ｍ（１−ｙ）ｋ
Ａ_ｋｙ＝（１−ｃ）（１一ｍ）ｙｋ
Ａ_ｃｍｙ＝ｃｍｙ（１−ｋ）
Ａ_ｋｃｍ＝ｋｃｍ（１−ｙ）
Ａ_ｋｃｙ＝ｋｃｙ（１−ｍ）
Ａ_ｋｍｙ＝ｋｍｙ（１−ｃ）
Ａ_ｋｃｍｙ＝ｋｃｍｙ
【００２７】
この理論式は、前記したようにドットゲインやトラツピングなどの為、実際の発色状況を精度良く予測することが難しいが、基本思想としては正しいことからこれを基に近似式を考える
【００２８】
まずドットゲインの影響であるが、印刷に用いられる網点は、印刷時の圧力などによるインキの潰れ、ドットが滲んで見える現象などで、版下のドットよりも面積が増える。これを面積率の増加と考え、（１）式における面積占有率Ａを、Ａ’に修正して次の（４）式とする。
【数２】

【００２９】
次にトラッピングであるが、重ね刷り部の色は、べ夕重ね刷りの濃度の加算性を仮定すれば、その要素の色で近似的に表現できる。例えば、藍色の上への紅色の重ね刷りの場合は次式となる。
Ｒ_ｃｍ（λ）＝｛Ｒ_ｃ（λ）×Ｒ_ｍ（λ）｝ ………（５）
但し、通常の印刷においては、後刷りである紅色は、先刷りである藍色の上に１００％転写できない（トラッピング不良）ために、濃度が低くなる。これを係数Ｔで考慮すると次式になる。

【００３０】
そのため（４）、（６）式を結合し、Ａ’_ｉ、Ｔ_ｉの代わりに係数Ｋ_ｉを用いることで次の近似式が得られる。これを基本式とする。
【数３】

【００３１】
そして（７）式を用い、基準となる印刷物と実際の印刷物とにおけるカラースケール、及び絵柄特定点での色調の違いを算出するわけであるが、色調の制御では、色調を計測して得られた色調が目標と差異がある場合、インキ量修正アルゴリズムによってその差異をなくすための修正インキ供給量を演算する。このインキ量と相関がある量はベタ濃度であるが、分光反射率とベタ濃度は、図３に示したように互いに非線形の関係にある。しかし分光濃度はこのベタ濃度の変化量（微分値）と線形的な相関があり、そのためインキ修正量を計算する際、分光濃度を用いることでベタ濃度が精度良く算出できる。
【００３２】
そのため、まず、べ夕部の分光濃度を定義する。ベタ部の分光濃度Ｄ_ｓｉ（λ）は、ベタ部の分光反射率（紙基準）Ｒ_ｓｉ（λ）から（８）式で定義する。
Ｄ_ｓｉ（λ）＝ｌｏｇ｛１／Ｒ_ｓｉ（λ）｝ ………（８）
【００３３】
基準となる印刷物と実際の印刷物とにおけるカラースケール、及び絵柄特定点での色調は、それほど大きな違いはないはずなので近似式を使うことができる。今、ベタ濃度が目標値からΔＤ_ｓｉ（i＝ｋ、ｃ、ｍ、ｙ）だけ微小変化した場合、ベタ部の分光濃度Ｄ_ｓｉ（λ）が、目標値からΔＤ_ｓｉ（λ）だけ微小変化する。これを、比例定数Ｋ_ｄｉ（λ）により、両者の関係が（９）式のように記述できると仮定する。

但し、Ｄ_{ｓｉ 0}：基準となる印刷物のカラースケールのベタ濃度
Ｄ_ｓｉ：実際の印刷物のカラースケールのベタ濃度
（ｉ＝ｋ、ｃ、ｍ、ｙ）
この（１０）式におけるＫ_ｄｉ（λ）は、図３に示したように、分光反射率が微小変化したときのベタ濃度との関係を表したもので、ΔＤ_ｓｉが小さければ分光反射率の微少な違いを近似式で算出することができる。
【００３４】
そのため、ベタ部の分光反射率Ｒ_ｓｉ（λ）が、ベタ濃度にしてΔＤ_ｓｉだけ微小変化した場合の分光反射率Ｒ_{ｓｉΔＤｓｉ}（λ）（ｉ＝ｋ、ｃ、ｍ、ｙ）は、（９）式のΔＤ_ｓｉ（λ）を用いて次の（１１）式で与えられる。
Ｒ_{ｓｉΔＤｓｉ}（λ）＝｛１０^{−（Ｄｓｉ（λ）＋Ｋｄｉ（λ）ΔＤｓｉ）} −１０^{−（Ｄｓｉ（λ）}｝＋Ｒ_ｓｉ（λ）…（１１）
（ｉ＝ｋ、ｃ、ｍ、ｙ）
【００３５】
そこで、Ｄ_ｓｉ（λ）として実際の印刷物の分光濃度を用い、（１１）式で求めた分光反射率を（７）式に代入し、左辺のＲ（λ）には基準となる印刷物の分光反射率の計測値Ｒ_ｔ（λ）を代入して、全ての波長領域で（７）式を解き、ベタ濃度を少しずつ変えていって、二乗誤差が最小となるようなΔＤ_ｉ求める。そして、この求められたΔＤ_ｉが、基準となる印刷物と実際の印刷物とのベタ濃度偏差であり、この値を元にインキ供給量を制御すれば、基準となる印刷物と同一の色調を得ることができる。
【００３６】
以上が本発明の色調制御方法の基本的な考え方であるが、以上の説明からもわかるとおり、ノウゲヴァウアの式におけるドットゲインやトラッピングによる計算精度の低下は、あらかじめ係数を修正しておくことで防ぐことができる。また、印刷物の分光反射スペクトルを測定して目標とのスペクトルの偏差が少なくなるようにベタ濃度偏差を算出することにより、照明条件による測定誤差を防止できる。また、分光反射率の測定を近赤外領域まで行うことにより、絵柄特定点の墨の入った部分の色調も精度良く制御できる。
【００３７】
以下、本発明の色調制御装置の概略ブロック図である図１、及びそのフロー図である図２に従いさらに詳細に説明する。図中１は、カラースケール２を持つ印刷物３を載置し、分光センサー４とレーザ変位計５をＸＹに移動させてカラースケール２や絵柄特定点の分光反射スペクトルを測定する測定装置で、分光センサー４は前記したように可視光領域から近赤外領域までの分光反射スペクトルを測定できるようになっている。６は測定装置の測定した分光反射スペクトルを基に、用紙基準の分光反射スペクトルと分光濃度とベタ濃度を算出する分光反射スペクトル、分光濃度、ベタ濃度演算部、７は分光反射スペクトル、分光濃度、ベタ濃度演算部６が算出した分光濃度とベタ濃度から比例定数を算出する比例定数演算部、８は前記分光反射スペクトル、分光濃度、ベタ濃度演算部が算出した分光反射スペクトルからノウゲヴァウアの式の誤差修正用の係数を算出して記憶する係数演算記憶部、９は微小変化後の分光反射スペクトルを演算する微小変化後の分光反射スペクトル演算部、１０は前記分光反射スペクトル、分光濃度、ベタ濃度演算部と微小変化後の分光反射スペクトル演算部とからの算出結果と係数演算記憶部に記憶された係数を元にノウゲヴァウアの式を用いてインキ濃度偏差を算出するインキ濃度偏差演算部、１１はインキ濃度偏差から印刷機のインキ制御量を演算するインキ制御量演算部、１２は印刷機のインキ供給装置である。
【００３８】
まず実際の印刷に先立ち、図２のステップ２０で示したように、校正刷り、若しくは仮校正刷りなどの基準となる印刷物３を測定装置１に載置し、分光センサー４をＸＹに移動させてカラースケール２、及び指定された絵柄特定点の下記分光反射スペクトルを測定する。なお、この測定は、前記したように可視光領域から近赤外領域まで行い、また絵柄特定点は、レーザ変位計５等を用いてあらかじめ指示しておき、基準となる印刷物と実際の印刷物とで同じ測定点を測定できるようにしておく。
絵柄特定点（Ｔ） ……… Ｒ_ｔ０（λ）
墨（Ｋ） ……… Ｒ_ｓｋ０（λ）
シアン（Ｃ） ……… Ｒ_ｓｃ０（λ）
マゼンタ（Ｍ） ……… Ｒ_ｓｍ０（λ）
イエロー（Ｙ） ……… Ｒ_ｓｙ０（λ）
紙（Ｗ） ……… Ｒ_ｐ０（λ）
【００３９】
そしてこの測定結果は、分光反射率、分光濃度、ベタ濃度演算部６に送られ、ここで図２のステップ２１で示したように、（３）式により、用紙基準での分光反射率Ｒ_ｔ０（λ）、Ｒ_ｓｋ０（λ）、Ｒ_ｓｃ０（λ）、Ｒ_ｓｍ０（λ）、Ｒ_ｓｙ０（λ）が算出され、ついで（８）式を用いてステップ２２で分光濃度Ｄ_{ｓｉ 0}（λ）が、ステップ２３でべタ濃度Ｄ_{ｓｉ 0}が算出される。
【００４０】
そして、算出された用紙基準での分光反射率は、ステップ２４で係数演算記憶部８に送られ、前記ノウゲヴァウアの式（７）に代入されて最小二乗誤差が最小となる係数Ｋ_ｐ〜Ｋ_ｋｃｍｙが算出され、記憶される。そして、以後の作業においては、前記（７）式を用いる場合、この記憶された係数Ｋ_ｐ〜Ｋ_ｋｃｍｙが使用される。
【００４１】
こうして印刷前の準備が完了すると印刷が開始され、得られた印刷物が前記と同様測定装置１に載置されて、ステップ２５で分光センサー４を用いてカラースケール２と絵柄特定点のつぎの分光反射スペクトルが測定される。
絵柄特定点（Ｔ） ……… Ｒ_ｔ（λ）
墨（Ｋ） ……… Ｒ_ｓｋ（λ）
シアン（Ｃ） ……… Ｒ_ｓｃ（λ）
マゼンタ（Ｍ） ……… Ｒ_ｓｍ（λ）
イエロー（Ｙ） ……… Ｒ_ｓｙ（λ）
紙（Ｗ） ……… Ｒ_ｐ（λ）
【００４２】
そしてステップ２６で、図１の分光反射率、分光濃度、ベタ濃度演算部６が、前記と同様（３）式を用いて用紙基準の分光反射率Ｒ_ｔ（λ）、Ｒ_ｓｋ（λ）、Ｒ_ｓｃ（λ）、Ｒ_ｓｍ（λ）、Ｒ_ｓｙ（λ）を算出し、ステップ２７で（８）式から分光濃度Ｄ_ｓｉ（λ）を、ステップ２８でベタ濃度Ｄ_ｓｉを算出する。
【００４３】
こうして分光濃度Ｄ_ｓｉ（λ）、ベタ濃度Ｄ_ｓｉが算出されると、この値が図１の比例定数演算部７に送られ、ステップ２９で（１０）式により比例定数Ｋ_ｄｉ（λ）が算出される。

【００４４】
そしてこれら比例定数Ｋ_ｄｉ（λ）、分光濃度Ｄ_ｓｉ（λ）、ベタ濃度Ｄ_ｓｉを用い、ステップ３０で図１の微小変化後の分光反射率演算部９で、各色毎に任意のΔＤ_ｓｉを仮定し、（１１）式から微小変化後の分光反射率Ｒ_{ｓｉΔＤｓｉ}（λ）を算出する。
【００４５】
そして得られたＲ_{ｓｉΔＤｓｉ}（λ）を、図１のインキ濃度偏差演算部１０に送り、まずステップ３１でノウゲヴァウアの式に修正係数を加えた（７）式に代入してＲ_ｔ（λ）推定値を算出し、ステップ３２で基準となる印刷物の分光反射スペクトルＲ_ｔ０（λ）目標値と推定値Ｒ_ｔ（λ）の二乗誤差を算出する。そしてステップ３３で、二乗誤差が最小かどうか判断し、最小でない場合はステップ３０から３３までをΔＤ_ｓｉの値を少しずつ変えながら繰返し、二乗誤差が最小となるΔＤ_ｓｉの組合せを求める。そして、二乗誤差が最小となったΔＤ_ｓｉが、ベタ濃度偏差である。
【００４６】
こうしてベタ濃度偏差が求められると、ステップ３４でこのベタ濃度偏差がインキ制御量演算部１１に送られ、ここでベタ濃度偏差に対応したインキ制御量が演算されて、印刷機のインキ供給装置１２に送られ、インキ供給量が調整される。そして次の印刷サンプルが来ると、このステップ２５から３３、そしてステップ３４が、印刷期間中繰り返され、色調が制御される。
【００４７】
【発明の効果】
以上記載の如く本発明によれば、前記したようにノウゲヴァウアの式におけるドットゲインやトラッピングによる計算精度の低下を、あらかじめ係数を算出しておくことで防ぐことができ、また、印刷物の分光反射スペクトルを測定してそれの目標との差異を最小とすべく、ベタ濃度偏差を算出することにより、照明条件による測定誤差を防止した装置を提供することができる。
【図面の簡単な説明】
【図１】 本発明の実施の形態に係る要部構成を示すブロック図である。
【図２】 本発明のフロー図である。
【図３】 分光反射スペクトルとベタ濃度の関係を示す図である。
【符号の説明】
１ 測定装置
２ カラースケール
３ 印刷物
４ 分光センサー
５ レーザ変位計
６ 分光反射スペクトル、分光濃度、ベタ濃度演算部
７ 比例定数演算部
８ 係数演算記憶部
９ 微小変化後の分光反射率演算部
１０ インキ濃度偏差演算部
１１ インキ制御量演算部
１２ インキ供給装置[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a color tone control method and apparatus in an offset printing machine or the like.
[0002]
[Prior art]
When continuous printing is performed on an offset printing machine, etc., the ink supply directly affects the color tone of the image. Therefore, the target color and the printed color are measured, and the deviation is detected and minimized. Various control methods have been proposed in which the color tone is controlled by adjusting the ink supply amount.
[0003]
For example, in Japanese Patent Laid-Open No. 7-205212, a difference-ink density spectrum is detected from an ink density spectrum of an image portion of a document and an image portion of a printed material, and this difference-ink density spectrum is used for overprinting. It is expressed as a linear combination function of the ink density spectrum in each printing ink, and an adjustment command for the ink supply mechanism is detected from a proportional coefficient of the linear combination function to control the color tone.
[0004]
JP-A-11-99629 discloses a spectral reflectance spectrum of a color scale printed on a printed matter, obtains a deviation from a target spectral reflectance spectrum inputted in advance, and calculates the deviation as a color matching function. In this example, the amount of ink is controlled by calculating the solid density deviation of the ink that minimizes the deviation from the target spectral reflection spectrum. ing.
[0005]
Further, Japanese Patent Application Laid-Open No. 11-216847 discloses that an image portion of a printed material is scanned with light from a visible light region to a near infrared region having a rated value absorption with respect to black, and CIE between this value and a target color value. 1 shows an apparatus for calculating the color space coordinate value L ^* a ^* b ^* (chromaticity coordinates, chromaticity vector, color position) defined in (1) and controlling the ink amount so as to reduce the difference.
[0006]
[Problems to be solved by the invention]
However, in the method disclosed in Japanese Patent Laid-Open No. 7-205212, the spectral reflectance is converted logarithmically in order to obtain the ink density spectrum, and the dot area ratio increase (dot gain) due to printing or ink overlap The density reduction due to ink transfer failure (trapping failure) at the time of printing is not considered, and a correct density value is not always obtained.
[0007]
Further, the method disclosed in Japanese Patent Application Laid-Open No. 11-99629 is intended only for the three basic colors (C, M, Y) excluding black, and when trying to keep the color tone of the pattern portion constant, Since the actual image portion is printed with four colors including black (K), the correct color tone may not be reproduced.
[0008]
In addition, what is disclosed in Japanese Patent Application Laid-Open No. 11-216847 is not a coincidence of spectrum curves, but is controlled so as to minimize a difference in color space coordinate values L ^* a ^* b ^* defined by CIE. There are innumerable spectral reflection spectrum curves having the same color coordinate value, and the color difference from the target changes when the illumination condition of the printed matter changes.
[0009]
SUMMARY OF THE INVENTION In view of the above circumstances, the present invention is to provide a color tone control method and apparatus in a printing press that can accurately control the color tone by accurately capturing the color tone of an actual image portion without being influenced by the illumination conditions for observing the printed matter. And
[0010]
[Means for Solving the Problems]
In order to solve the above-mentioned problems, the present invention measures the spectral reflection spectrum at a specific point in the color scale and pattern in the reference printed material and the actual printed material, and from this measurement result, the area occupation of the halftone dot in the Nougevauer equation Calculate the coefficient for correcting the change in the spectral reflection spectrum of the overprinted area and the coefficient of the ratio, calculate the spectral density and the solid density, and calculate the proportional constant for calculating the minute change in the spectral reflection spectrum from these values. Thus, there is provided a color tone method and apparatus in a printing press in which an ink density deviation is calculated from a Nougevauer equation to control an ink supply amount.
[0011]
And claim 1 is a method invention,
In a color tone control method in a printing press that controls the color tone by measuring the spectral reflection spectrum of a printed material, the spectral reflectance spectrum at a specific point in the color scale of the printed material and the pattern is measured, and the halftone dot in the Neugevauer equation is measured. a first step of calculating the coefficients to modify the coefficients of area occupancy, and measuring the spectral reflection spectrum of the color scale and design specific points in the actual printed matter, the Noigevaua were fixed in coefficient calculated in the first step Ink supply to be corrected from the ink density deviation calculated in the second step, comprising a second step of calculating the ink density deviation from the difference in spectral reflection spectrum between the standard printed matter and the actual printed matter using the formula The color is controlled by calculating the amount.
[0012]
In this way, by measuring the spectral reflection spectrum of the reference printed material, and correcting the calculation of the area occupancy factor of the halftone dots in the Nougevauer equation in consideration of the weight (dot gain) from this measurement result, It is possible to calculate an accurate value with no color, and by measuring the spectral reflectance spectrum of the color scale and the specific point of the pattern in the actual printed material and calculating the ink density deviation from this Nogevauer equation, it depends on the lighting conditions etc. The ink supply amount can be accurately controlled without being used.
[0013]
This, like Ri same der also how the invention described in claim 2, performs both the correction of the amount thickening of halftone dots of ink transfer in (dot gain) and overprint unit failure (trapping bad), more Accurate values can be calculated, and in the color tone control method of a printing press that controls the color tone by measuring the spectral reflection spectrum of the printed matter, the spectral reflection at a specific point in the color scale of the printed matter and the design Measure the spectrum and calculate the coefficient for correcting the change of the halftone dot area occupancy factor in the Neugevauer equation and the theoretical coefficient that does not take into account trapping defects in the overprinting of the spectral reflection spectrum of the overprinting part. 1 and the spectral reflection spectrum of the color scale and the pattern specific point in the actual printed matter are measured, and the first step is measured. And a second step of calculating an ink density deviation from a difference in spectral reflection spectrum between the reference printed material and the actual printed material using the Neugevauer equation corrected based on the coefficient calculated in the second step. The color tone is controlled by calculating the ink supply amount to be corrected from the ink density deviation calculated in (1) .
[0014]
The second step of calculating the ink density deviation is as described in claim 3 .
In the second step of calculating the ink density deviation, the spectral density and the solid density are calculated from the spectral reflection spectrum, and from the result, a proportional constant between the spectral density and the solid density for calculating a minute change in the solid density is calculated and Neugevauer is calculated. The ink density deviation is calculated by the following formula.
[0015]
In this way, the ink density deviation can be calculated more accurately.
[0016]
And the invention described in claim 4 , which is an apparatus invention for carrying out the method invention of claims 1 to 3,
In a color tone control device in a printing press that controls the color tone by measuring the spectral reflection spectrum of a printed material, a measuring device that measures the spectral reflectance spectrum at a specific point in the color scale and picture of the reference printed material and the actual printed material; A spectral reflection spectrum for calculating a spectral density and a solid density based on the spectral reflection spectrum calculated by the measuring apparatus, a spectral density, a solid density calculation unit, and an error correction of the Neugevauer equation from the spectral reflection spectrum in the reference print A coefficient calculation storage unit that calculates and stores a coefficient, and the spectral reflection spectrum, spectral density, spectral density calculated by the solid density calculation unit, and spectral density for calculating a minute change in solid density in the spectral reflection spectrum from the solid density, a proportional constant calculating unit for calculating the proportionality constant between the solid density, proportional constant the proportional constant calculating unit has calculated And ink density deviation calculation unit for calculating the ink density deviations from the spectral reflection spectrum using the equation of the Noigevaua applying the error correction coefficient equations Noigevaua stored in the coefficient operation storage unit, the ink density deviation calculation unit The ink control arithmetic unit that calculates the ink supply amount to be corrected from the calculated ink density deviation, and the ink density deviation is calculated using the Neugewauer formula from the difference in the spectral reflection spectrum between the standard printed matter and the actual printed matter. The ink supply amount to be calculated and calculated from the ink density deviation is calculated by the ink control calculation unit to control the ink supply amount.
[0017]
By configuring the color tone control device in this way, as described above, by using the coincidence of spectral reflection spectra, it is not affected by illumination conditions, etc., and an approximation formula using an error correction coefficient in the Nougevauer formula is used. By using it, it is possible to provide a color tone control device capable of accurately controlling the ink supply amount.
[0018]
And, as described in claims 5 and 6 , the error correction coefficient of the Neugevauer equation stored in the coefficient calculation storage unit is as follows.
Error correction coefficient equations Noigevaua said coefficient calculating storage unit is stored, characterized in that it is a coefficient data for correcting the variation area occupancy of halftone dots on the printed material of the plate of the relative dot occupancy .
Or (or in addition to the coefficient data of claim 5 wherein), error correction coefficient equations Noigevaua said coefficient calculating storage unit is stored, the trapping failure in overprinting of the spectral reflection spectrum of overprinting unit It is characterized by being coefficient data for correcting a change with respect to a theoretical coefficient that is not considered .
[0019]
In this way, more accurate ink supply is possible by storing and using the correction factor for the dot thickening (dot gain) in the Nougevauer equation and the ink transfer defect (trapping defect) in the overprinting section. It is possible to provide a color tone control device capable of quantity control.
[0020]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be exemplarily described in detail with reference to the drawings. However, the dimensions, materials, shapes, relative arrangements, and the like of the components described in this embodiment are not intended to limit the scope of the present invention only to specific examples unless otherwise specified. Only.
[0021]
FIG. 1 is a schematic block diagram of a color tone control apparatus according to the present invention, FIG. 2 is a flowchart thereof, and FIG. 3 is a graph showing the relationship between a spectral reflection spectrum and a solid density. Prior to the description, the outline and basic concept of the present invention will be described.
[0022]
First, an outline of a color tone control method in the printing press of the present invention will be described. In the present invention, first, the color scale and the pattern of the reference printed material such as proof printing or provisional proof printing and the actual printed material are changed. Measure the spectral reflection spectrum at a specific point. In this measurement, black ink (K) is also used for the design specific point as described above, and therefore, the range from the visible light region to the near infrared region where the rated value is absorbed with respect to black is included. Measure in the region of ~ 900 nm. Then, using Nougevauer's equation, the solid density deviation is detected from the target spectral reflection spectrum (spectral reflection spectrum of the reference print) and the spectral reflection spectrum of the actual print, and the ink supply to be corrected is calculated from the deviation. To control the color tone.
[0023]
However, although Nougevauer's equation is theoretically correct, it cannot be used to predict the effects of situations that occur on actual prints, such as optical dot gain (halftone dots) and trapping (overprinting of ink). Cannot calculate. Therefore, first measure the spectral reflection spectrum of the solid patch on the color scale of the printed material that becomes the reference for proof printing or provisional proof printing and the pattern specific point, and using this value, the dot gain to the coefficient in the Nougevauer equation, Correct and calculate the effect of density reduction in overprinting.
[0024]
Then, the spectral reflection spectrum of the actual printed matter is measured, and the spectral density and solid density (substitution characteristic value of the ink film thickness supplied to the paper surface) in the solid patch of the color scale are calculated from the measured value. Then, the estimated spectral reflection spectrum when this value changes slightly is calculated by the Neugevauer equation with the coefficient modified, and the spectral reflectance spectrum of the printed material that is the first measurement, and the estimated spectral reflectance spectrum The small change amount of the solid density that minimizes the square error is defined as the solid density deviation, and the ink supply amount is calculated from this value and controlled.
[0025]
The above is the outline of the color tone control method of the present invention. As can be seen from the above description, it is possible to prevent a decrease in calculation accuracy due to dot gain or trapping in the Nougevauer equation by calculating the coefficient in advance. . Also, by measuring the spectral reflection spectrum of the printed material and calculating the solid density deviation so that the difference from the target value is reduced, the spectral reflection spectrum matches the target better, and the measurement error due to illumination conditions is reduced. Can be prevented. Further, by measuring the spectral reflection spectrum up to the near infrared region, the color tone of the black portion of the design specific point can be controlled with high accuracy.
[0026]
Next, the basic concept of the color tone control method of the present invention will be described. As is well known, Nougevauer's formula is a formula that leads to what spectral reflectance can be obtained when C (indigo), M (red), Y (yellow), and K (black) are combined at a free area ratio. Yes, when the measured spectral reflectances R (λ) and R _i (λ) are normalized by the spectral reflectance R _p (λ) of the paper, the following equation is obtained.
[Expression 1]

However,
R (λ): Spectral reflectance of color mixture portion = R (λ) / R _p (λ) (2)
R _i (λ): Spectral reflectance = R _i (λ) / R _p (λ) (3)
i = p (white paper), c (blue solid), m (red solid), y (yellow solid),
k (solid black), cm (indigo, red solid),
my (red, yellow solid overlay), yc (yellow, indigo solid overlay),
kc (ink, indigo solid), km (ink, red, solid),
ky (black, yellow solid overlay), cmy (indigo, red, yellow solid overlay),
kcm (ink, indigo, red solid)
kcy (ink, indigo, yellow solid),
kmy (ink, indigo, yellow solid),
kcmy (black, indigo, red, yellow solid)
λ = 400 to 900 nm, 10 nm pitch A _i : area occupation ratio ΣA _i ≡1.0
If the monochrome halftone dot area ratio of indigo, red, yellow, and black is c, m, y, k,
A _p = (1-c) (1-m) (1-y) (1-k)
A _c = c (1-m) (1-y) (1-k)
A _m = (1-c) m (1-y) (1-k)
A _y = (1-c) (1-m) y (1-k)
A _k = (1-c) (1-m) (1-y) k
A _cm = cm (1-y) (1-k)
A _my = (1-c) my (1-k)
A _yc = c (1-m) y (1-k)
A _kc = c (1-m) (1-y) k
A _km = (1-c) m (1-y) k
A _ky = (1-c) (11 m) yk
A _cmy = cmy (1-k)
A _kcm = kcm (1-y)
A _kcy = kcy (1-m)
A _kmy = kmy (1-c)
A _kcmy = kcmy
[0027]
This theoretical formula is difficult to accurately predict the actual color development state because of dot gain and trapping as described above, but since the basic idea is correct, an approximate formula is considered based on this. [0028]
First, regarding dot gain, halftone dots used for printing have a larger area than dots on the plate due to ink crushing due to pressure during printing and the phenomenon that dots appear blurred. Considering this as an increase in the area ratio, the area occupancy A in the equation (1) is corrected to A ′ to obtain the following equation (4).
[Expression 2]

[0029]
Next, with regard to trapping, the color of the overprinting portion can be approximately expressed by the color of the element, assuming that the density of the evening overprinting density is added. For example, in the case of red overprinting on indigo, the following equation is obtained.
R _cm (λ) = {R _c (λ) × R _m (λ)} (5)
However, in normal printing, the red color, which is the post-print, cannot be transferred 100% onto the indigo color, which is the pre-print (the poor trapping), so the density is low. When this is taken into consideration with the coefficient T,

[0030]
Therefore, the following approximate expression is obtained by combining the expressions (4) and (6) and using the coefficient K _i instead of A ′ _i and T _i . This is the basic formula.
[Equation 3]

[0031]
Then, using equation (7), the difference in color scale between the reference printed material and the actual printed material and the color tone at the specific point of the pattern is calculated. In color tone control, the color tone is obtained by measuring the color tone. If there is a difference between the target color tone and the target, a correction ink supply amount for eliminating the difference is calculated by an ink amount correction algorithm. The amount correlated with the ink amount is the solid density, but the spectral reflectance and the solid density are in a non-linear relationship with each other as shown in FIG. However, the spectral density has a linear correlation with the change amount (differential value) of the solid density. Therefore, when calculating the ink correction amount, the solid density can be accurately calculated by using the spectral density.
[0032]
Therefore, first, the spectral density of the evening part is defined. The spectral density D _si (λ) of the solid part is defined by the equation (8) from the spectral reflectance (paper standard) R _si (λ) of the solid part.
D _si (λ) = log {1 / R _si (λ)} (8)
[0033]
Since the color scale between the reference printed material and the actual printed material and the color tone at the design specific point should not be so large, an approximate expression can be used. If the solid density is slightly changed from the target value by ΔD _si (i = k, c, m, y), the solid density spectral density D _si (λ) is slightly changed from the target value by ΔD _si (λ). To do. It is assumed that the relationship between the two can be described as in equation (9) by the proportionality constant K _di (λ).

However, D _{si 0} : solid density of the color scale of the reference printed material D _si : solid density of the color scale of the actual printed material (i = k, c, m, y)
As shown in FIG. 3, K _di (λ) in the equation (10) represents the relationship with the solid density when the spectral reflectance _slightly changes. If ΔD _si is small, the spectral reflectance is A slight difference can be calculated by an approximate expression.
[0034]
Therefore, the spectral reflectance R _siΔDsi (λ) (i = k, c, m, y) when the spectral reflectance R _si (λ) of the solid _{portion slightly} changes by ΔD _si as the solid density is (9 ) Is given by the following equation (11) using ΔD _si (λ).
R _siΔDsi (λ) = {10− ^{(Dsi (λ) + Kdi (λ) ΔDsi)} −10 ^{− (Dsi (λ)} } + R _si (λ) (11)
(I = k, c, m, y)
[0035]
Therefore, the spectral density of the actual printed material is used as D _si (λ), the spectral reflectance obtained by the equation (11) is substituted into the equation (7), and the R (λ) on the left side is the spectrum of the reference printed material. reflectance measurements R _t a _(lambda) is substituted, solving all the wavelength region (7), go to change the solid density portions and obtaining [Delta] D _i as square error is minimized. And it thus determined was [Delta] D _i is a solid density deviation of the actual printed matter and the printed matter serving as a reference, by controlling the ink supplying amount based on this value, to obtain the same colors and printed matter serving as a reference Can do.
[0036]
The above is the basic idea of the color tone control method of the present invention. As can be seen from the above description, the calculation accuracy can be prevented from being lowered due to dot gain and trapping in the Neugevauer equation by correcting the coefficients in advance. be able to. Further, by measuring the spectral reflection spectrum of the printed matter and calculating the solid density deviation so that the deviation of the spectrum from the target is reduced, measurement errors due to illumination conditions can be prevented. In addition, by measuring the spectral reflectance up to the near infrared region, the color tone of the black portion of the design specific point can be accurately controlled.
[0037]
Hereinafter, it will be described in more detail with reference to FIG. 1 which is a schematic block diagram of the color tone control apparatus of the present invention and FIG. 2 which is a flowchart thereof. In the figure, reference numeral 1 denotes a measuring device that mounts a printed matter 3 having a color scale 2 and moves the spectroscopic sensor 4 and the laser displacement meter 5 to XY to measure the spectroscopic reflection spectrum of the color scale 2 and a specific pattern point. As described above, the sensor 4 can measure the spectral reflection spectrum from the visible light region to the near infrared region. 6 is a spectral reflection spectrum, spectral density, solid density calculation unit for calculating a paper-based spectral reflection spectrum, spectral density, and solid density based on the spectral reflectance spectrum measured by the measuring apparatus, and 7 is a spectral reflection spectrum, spectral density, A proportionality constant calculation unit that calculates a proportionality constant from the spectral density and the solid density calculated by the solid density calculation unit 6, and 8 is an error in the equation of Nougevauer from the spectral reflection spectrum, the spectral density, and the spectral reflection spectrum calculated by the solid density calculation unit. A coefficient calculation storage unit for calculating and storing correction coefficients, 9 is a spectral reflection spectrum calculation unit after a minute change for calculating a spectral reflection spectrum after a minute change, and 10 is a calculation for the spectral reflection spectrum, spectral density, and solid density. Based on the results of the calculation and the coefficients stored in the coefficient calculation storage unit from the spectral reflection spectrum calculation unit after the slight change. Ink density deviation calculation unit for calculating the ink density deviation by using a 11 ink control amount calculation unit for calculating the ink control of a printing press from the ink density deviation, 12 is an ink supply apparatus for a printing press.
[0038]
First, prior to actual printing, as shown in Step 20 of FIG. 2, a printed material 3 serving as a reference such as a proof or temporary proof is placed on the measuring apparatus 1 and the spectroscopic sensor 4 is moved to XY. The following spectral reflection spectrum of the color scale 2 and the specified pattern specific point is measured. This measurement is performed from the visible light region to the near infrared region as described above, and the pattern specific point is instructed in advance using the laser displacement meter 5 or the like, and the reference printed material and the actual printed material The same measurement point can be measured with.
Design specific point (T) ……… R _t0 (λ)
Black (K) ……… R _sk0 (λ)
Cyan (C) ……… R _sc0 (λ)
Magenta (M) ……… R _sm0 (λ)
Yellow (Y) ……… R _sy0 (λ)
Paper (W) ……… R _p0 (λ)
[0039]
The result of this measurement, spectral reflectance, spectral density, is sent to the solid density calculator 6, wherein as shown in step 21 of FIG. 2, the equation (3), the spectral reflectance in the sheet reference R _t0 (Λ), R _sk0 (λ), R _sc0 (λ), R _sm0 (λ), R _sy0 (λ) are calculated, and then the spectral density D _{si 0} (λ) is calculated in step 22 using equation (8). However, the solid density D _{si 0} is calculated in step 23.
[0040]
Then, the spectral reflectance in the calculated sheet reference is sent to the coefficient calculation storage unit 8 in step 24, the minimum square error is substituted into Equation (7) of the Nougevaua is minimum coefficient K _p ~K _kcmy Is calculated and stored. In the subsequent work, when the equation (7) is used, the stored coefficients K _{p to} K _kmmy are used.
[0041]
When preparation before printing is completed in this way, printing is started, and the obtained printed matter is placed on the measuring apparatus 1 in the same manner as described above. In step 25, the spectral sensor 4 is used to perform the spectral measurement next to the color scale 2 and the pattern specific point. The reflection spectrum is measured.
Pattern specific point (T) ……… R _t (λ)
Black (K) ……… R _sk (λ)
Cyan (C) ……… R _sc (λ)
Magenta (M) ……… R _sm (λ)
Yellow (Y) ……… R _sy (λ)
Paper (W) ……… R _p (λ)
[0042]
In step 26, the spectral reflectance, spectral density, and solid density calculation unit 6 in FIG. 1 uses the equation (3) as described above to use the paper-based spectral reflectances R _t (λ), R _sk (λ), R _sc (λ), R _sm (λ), and R _sy (λ) are calculated. In step 27, the spectral density D _si (λ) is calculated from the equation (8), and in step 28, the solid density D _si is calculated.
[0043]
When the spectral density D _si (λ) and the solid density D _si are calculated in this way, these values are sent to the proportionality constant calculation unit 7 of FIG. 1, and in step 29, the proportionality constant K _di (λ) is obtained from the equation (10). Calculated.

[0044]
Then, using these proportionality constants K _di (λ), spectral density D _si (λ), and solid density D _si , the spectral reflectance calculation unit 9 after slight change in FIG. 1 in step 30 performs any ΔD _{si for} each color. And the spectral reflectance R _siΔDsi (λ) after a minute change is calculated from the equation (11).
[0045]
Then, the obtained R _siΔDsi (λ) is sent to the ink density deviation calculation unit 10 in FIG. 1, and is first substituted into the equation (7) obtained by adding a correction coefficient to the Nougevauer equation in step 31 to estimate R _t (λ). In step 32, a square error between the target spectral reflectance spectrum R _t0 (λ) and the estimated value R _t (λ) is calculated. In step 33, the square error is determined whether the minimum, if not the smallest Steps 30 to 33 repeatedly while changing the value of [Delta] D _si gradually obtains a combination of [Delta] D _si of square error is minimized. Further, ΔD _si where the square error is minimized is a solid density deviation.
[0046]
When the solid density deviation is obtained in this way, this solid density deviation is sent to the ink control amount calculation unit 11 in step 34, where the ink control amount corresponding to the solid density deviation is calculated, and the ink supply device 12 of the printing press. And the ink supply amount is adjusted. When the next print sample comes, steps 25 to 33 and step 34 are repeated during the printing period to control the color tone.
[0047]
【The invention's effect】
As described above, according to the present invention, it is possible to prevent a decrease in calculation accuracy due to dot gain or trapping in the Nougevauer equation as described above by calculating the coefficient in advance, and the spectral reflection spectrum of the printed matter. By measuring the solid density deviation so as to minimize the difference from the target, it is possible to provide a device that prevents measurement errors due to illumination conditions.
[Brief description of the drawings]
FIG. 1 is a block diagram showing a configuration of a main part according to an embodiment of the present invention.
FIG. 2 is a flowchart of the present invention.
FIG. 3 is a diagram showing a relationship between a spectral reflection spectrum and a solid density.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Measuring apparatus 2 Color scale 3 Printed material 4 Spectral sensor 5 Laser displacement meter 6 Spectral reflection spectrum, spectral density, solid density calculation part 7 Proportional constant calculation part 8 Coefficient calculation storage part 9 Spectral reflectance calculation part 10 after a minute change Ink density Deviation calculation unit 11 Ink control amount calculation unit 12 Ink supply device

Claims (6)

In a color tone control method in a printing press that controls the color tone by measuring the spectral reflection spectrum of a printed material, the spectral reflectance spectrum at a specific point in the color scale of the printed material and the pattern is measured, and the halftone dot in the Neugevauer equation is measured. a first step of calculating the coefficients to modify the coefficients of area occupancy, and measuring the spectral reflection spectrum of the color scale and design specific points in the actual printed matter, the Noigevaua were fixed in coefficient calculated in the first step Ink supply to be corrected from the ink density deviation calculated in the second step, comprising a second step of calculating the ink density deviation from the difference in spectral reflection spectrum between the standard printed matter and the actual printed matter using the formula A color tone control method in a printing press, characterized in that the color tone is controlled by calculating an amount. In a color tone control method in a printing press that controls the color tone by measuring the spectral reflection spectrum of a printed material, the spectral reflectance spectrum at a specific point in the color scale of the printed material and the pattern is measured, and the halftone dot in the Neugevauer equation is measured. a coefficient of area occupancy, a first step of calculating the coefficients for correcting the variation with respect to the theoretical coefficients without considering trapping failure in overprinting of the spectral reflection spectrum of overprinting unit, and color scale of an actual printed matter Ink density deviation is determined from the difference in spectral reflection spectrum between the standard printed material and the actual printed material using the Neugewauer equation measured based on the coefficient calculated in the first step. And a second step for calculating the ink density deviation calculated in the second step. Color tone controlling method for a printing press, characterized in that to control the color tone by calculating the ink supply amount to be corrected from. In the second step of calculating the ink density deviation, the spectral density and the solid density are calculated from the spectral reflection spectrum, and from the result, a proportional constant between the spectral density and the solid density for calculating a minute change in the solid density is calculated and Neugevauer is calculated. 3. The color tone control method for a printing press according to claim 1, wherein the ink density deviation is calculated by the following formula. In a color tone control device in a printing press that controls the color tone by measuring the spectral reflection spectrum of a printed material, a measuring device that measures the spectral reflectance spectrum at a specific point in the color scale and picture of the reference printed material and the actual printed material; A spectral reflection spectrum for calculating a spectral density and a solid density based on the spectral reflection spectrum calculated by the measuring apparatus, a spectral density, a solid density calculation unit, and an error correction of the Neugevauer equation from the spectral reflection spectrum in the reference print A coefficient calculation storage unit that calculates and stores a coefficient, and the spectral reflection spectrum, spectral density, spectral density calculated by the solid density calculation unit, and spectral density for calculating a minute change in solid density in the spectral reflection spectrum from the solid density, a proportional constant calculating unit for calculating the proportionality constant between the solid density, proportional constant the proportional constant calculating unit has calculated And ink density deviation calculation unit for calculating the ink density deviations from the spectral reflection spectrum using the equation of the Noigevaua applying the error correction coefficient equations Noigevaua stored in the coefficient operation storage unit, the ink density deviation calculation unit The ink control arithmetic unit that calculates the ink supply amount to be corrected from the calculated ink density deviation, and the ink density deviation is calculated using the Neugewauer formula from the difference in the spectral reflection spectrum between the standard printed matter and the actual printed matter. A color tone control apparatus for a printing press characterized in that an ink supply amount to be calculated and calculated from the ink density deviation is calculated by the ink control calculation unit to control the ink supply amount. Error correction coefficient equations Noigevaua said coefficient calculating storage unit is stored, characterized in that it is a coefficient data for correcting the variation area occupancy of halftone dots on the printed material of the plate of the relative dot occupancy A color tone control apparatus for a printing press according to claim 4 . Error correction coefficient equations Noigevaua said coefficient calculating storage unit is storing is the coefficient data for correcting the variation with respect to the theoretical coefficients without considering trapping failure in overprinting of the spectral reflection spectrum of overprinting unit The color tone control apparatus for a printing press according to claim 4 or 5 , wherein

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