JP3756224B2 - Black signal generation method - Google Patents

Description

の関係に設定すればよい。
【００２７】
また、所定値以上の最小値Ｑｍｉｎに対して墨（Ｋ）版信号Ｋ₃ を増減させるようにするためには、Ｑｍｉｎ＞ｋ（０＜ｋ＜１）となる定数ｋを用いて、パラメータＴを、

の関係に設定すればよい。
【００２８】
さらに、（１）式では、基準信号ｓｋを求めるために１次補間式を用いているが、最大値Ｑｍａｘの変化に対して非線形となる効果を得るためには、例えば、
ｓｋ＝Ｔ² ・Ｑｍｉｎ＋（１−Ｔ² ）・Ｑｍａｘ …（１１）
として基準信号ｓｋを求めるようにしてもよい。この場合、グレーから最も遠い色に至る墨（Ｋ）版信号の影響が２次関数的に減少するため、グレーに近い領域において効果的に墨（Ｋ）版信号を生成することができる。
【００２９】
次に、ＵＣＲの分だけ修正された３色信号ＣＭＹ₃ および前記墨（Ｋ）版信号Ｋ₃ は、加算回路２８において４色修正信号ΔＣＭＹＫ₃ が加算されることにより、色修正された４色信号ＣＭＹＫ₄ が生成される。この４色信号ＣＭＹＫ₄ は、網％設定回路２４において、ハイライト（ＨＬ）およびシャドウ（ＳＨ）の網％値が出力特性に応じて調整された網％信号としての４色信号ＣＭＹＫ₅ に変換される。そして、前記４色信号ＣＭＹＫ₅ に従ってＣ、Ｍ、Ｙ、Ｋの４版のフイルム原版が作成される。
【００３０】
【発明の効果】
以上のように、本発明では、濁色に対する墨（Ｋ）版信号を、トーンカーブやカラーコレクションを用いることなく調整することができるため、グレーや鮮やかな色に影響を与えることなく、所望の調整を行うことができる。
【図面の簡単な説明】
【図１】本実施形態の墨版信号生成方法が適用される画像処理回路の構成ブロック図である。
【図２】図１に示す墨（Ｋ）版信号生成回路に設定される基準信号と墨（Ｋ）版信号との変換テーブルの説明図である。
【符号の説明】
１０…濃度設定回路 １２…カラーコレクション回路
１４…階調変換回路 １６…ＵＣＲ回路
１８…最大／最小値算出回路 ２０…基準信号生成回路
２２…墨（Ｋ）版信号生成回路 ２４…網％設定回路[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a black (K) plate signal adjustment method for converting a three-color signal of C, M, and Y obtained by reading an original image into a four-color signal of C, M, Y, and K.
[0002]
[Prior art]
For example, in the field of printing and plate making, there is a wide range of image reading / recording / reproducing systems that electrically process image information recorded on scanned originals for the purpose of streamlining work processes and improving image quality, etc. to create film originals. It is used.
[0003]
In this case, the image reading / recording / reproducing system processes the three color signals C, M, Y obtained by scanning the document image to generate the four color signals C, M, Y, K, Film originals for each color corresponding to the four color signals are prepared. The black (K) plate signal is generated from, for example, three color signals of C, M, and Y in order to compensate for the density of the shadow portion, improve the tightening of the image, and obtain a printed image with a calm feeling. The
[0004]
Conventionally, this black (K) plate signal is generated by converting from the minimum values of the three color signals of C, M, and Y as input signals, and the obtained black (K) plate signal has its tone curve. It is possible to adjust using Further, the black (K) plane signal can be adjusted together with other three color signals of C, M, and Y in a color correction circuit.
[0005]
By the way, for example, when it is desired to adjust the black (K) plate signal by paying attention to the muddy color, the conventional black (K) plate signal adjustment method can obtain a desired color tone for the following reasons. could not.
[0006]
That is, in the conventional method, when the amount of black (K) plate signal added to the muddy color is increased, adjustment is performed by changing the tone curve of the black (K) plate signal or color correction. In this case, when the tone curve of the black (K) plate signal is adjusted, not only the color but also the amount of the black (K) plate signal for gray changes, so that the reproduced gradation changes. In addition, if you try to make adjustments using color correction, the normal color correction is set so that the amount of change for vivid colors is large. K) The influence of the plate signal becomes large, or a situation occurs in which the essential turbidity is hardly adjusted.
[0007]
[Problems to be solved by the invention]
The present invention has been made to solve such a problem, and is a black plate signal that can adjust the black (K) plate signal for muddy colors without affecting gray or vivid colors. An object is to provide a generation method.
[0008]
[Means for Solving the Problems]
In the present invention, the maximum value and the minimum value of the three color signals C, M, and Y that are input signals are obtained, and if the difference between the maximum value and the minimum value is equal to or greater than a predetermined value, the input signal is vivid. as a color, the a minimum reference signal, if the difference is zero, as the input signal is a gray, the maximum value as a reference signal, the difference is 0 and the predetermined value if the result is between, as the input signal is a turbid color, the maximum and the value obtained by weighting in accordance with the difference in the minimum value as a reference signal, generating a black plate signal from the reference signal set To do.
[0009]
DETAILED DESCRIPTION OF THE INVENTION
FIG. 1 is a configuration block diagram of an image processing circuit to which the black signal generation method of the present embodiment is applied. This image processing circuit includes, for example, a black (K) plate signal for creating a printing film original plate from C, M, and Y three-color signals CMY obtained by scanning a color read original. a circuit for generating a color signal CMYK _5.
[0010]
The image processing circuit includes a density setting circuit 10 that generates a three-color signal CMY ₁ by adjusting density values of highlight (HL) and shadow (SH) of the three-color signal CMY according to a specified value. The three-color signal CMY ₁ is supplied to a color correction circuit 12, a gradation conversion circuit 14, a UCR (Under Color Removal) circuit 16, and a maximum / minimum value calculation circuit 18, respectively.
[0011]
The color correction circuit 12 adjusts the three-color signal CMY ₁ according to a desired calibration value, thereby generating a four-color correction signal ΔCMYK ₃ for C, M, Y, and K. The gradation conversion circuit 14 performs gradation conversion on the three-color signal CMY ₁ using the tone curve of each color, and generates a converted three-color signal CMY ₂ . UCR circuit 16, for example, the maximum value of the three color signals CMY ₁ and three color signals CMY ₁ according to the method shown in JP-A-4-124666 Qmax, the minimum value Qmin, the three color signals CMY ₁ for gray component A three-color correction signal ΔCMY ₂ is generated. The maximum / minimum value calculation circuit 18 calculates the maximum value Qmax and the minimum value Qmin of the three-color signal CMY ₁ .
[0012]
The image processing circuit further includes a reference signal generation circuit 20, a black (K) plate signal generation circuit 22, and a halftone setting circuit 24.
[0013]
The reference signal generation circuit 20 generates a reference signal sk that adjusts the level of the black (K) plane signal K ₃ according to the maximum value Qmax and the minimum value Qmin. The black (K) plate signal generation circuit 22 generates a black (K) plate signal K ₃ according to a preset conversion table based on the reference signal sk. Halftone% setting circuit 24, the four color signals CMYK _4, generates the highlight (HL) and 4-color signal CMYK ₅ as halftone% signal adjusted in accordance with the dot percentage values in the output characteristics of the shadow (SH).
[0014]
Between the tone conversion circuit 14 and the halftone dot% setting circuit 24, an adder circuit 26 which generates a to three color signals CMY ₃ adds the three color signals CMY ₂ into three color correction signal DerutaCMY _2, 3-color An addition circuit 28 is provided for adding the four-color correction signal ΔCMYK ₃ to the signal CMY ₃ and the black (K) plate signal K ₃ to generate the three-color signal CMYK ₄ .
[0015]
The image processing circuit to which the black signal generation method of the present embodiment is applied is basically configured as described above. Next, the processing content will be specifically described.
[0016]
An input signal, which is a color separation signal obtained by scanning a document image, is converted into a three-color signal CMY of C, M, and Y by performing a masking calculation process. Next, the three-color signal CMY is converted by the density setting circuit 10 into a three-color signal CMY ₁ set so that the highlight and shadow density values become the specified density, and then the color correction circuit 12, gradation conversion The circuit 14, the UCR circuit 16, and the maximum / minimum value calculation circuit 18 are supplied.
[0017]
The gradation conversion circuit 14 generates a three-color signal CMY ₂ by performing gradation conversion using the tone curve set for each color of the three-color signal CMY ₁ , and supplies the three-color signal CMY ₂ to the addition circuit 26. To do.
[0018]
In the color correction circuit 12, for example, the three-color signal CMY ₁ is classified into six hues C, M, Y, R, G, and B, and then adjusted according to a correction coefficient for the hue to perform color adjustment. , C, M, Y, and K, a four-color correction signal ΔCMYK ₃ is generated. The four-color correction signal ΔCMYK ₃ is supplied to the adding circuit 28.
[0019]
In the maximum / minimum value calculating circuit 18, by comparing the magnitude relation of the three color signals CMY _1, the maximum value Qmax and the minimum value Qmin of the three color signal components, UCR circuit 16 and the reference signal generating circuit 20 To supply.
[0020]
In the UCR circuit 16, based on the maximum value Qmax and the minimum value Qmin supplied from the maximum value / minimum value calculation circuit 18 and a desired UCR intensity setting value, a correction value by the UCR of the three-color signal CMY ₁ is obtained. The three-color correction signal ΔCMY ₂ is supplied to the adding circuit 26.
[0021]
The adder circuit 26, by adding the gradation conversion circuit 14 3-color correction signal DerutaCMY ₂ against three color signals CMY ₂ supplied from, and generates a 3-color signals CMY ₃ that fixes by the amount of UCR This is supplied to the adder circuit 28.
[0022]
On the other hand, the maximum value Qmax and the minimum value Qmin output from the maximum value / minimum value calculation circuit 18 are supplied to the reference signal generation circuit 20 to generate the reference signal sk for generating the black (K) plate signal K _3. Is done.
[0023]
Here, the reference signal sk is generated as follows. That is, the reference signal sk uses a maximum value Qmax, a minimum value Qmin, and a predetermined control coefficient Gidx (0 ≦ Gidx ≦ 1) for controlling a muddy color range ,
sk = T · Qmin + (1−T) · Qmax (1)
As required. The parameter T is
T = 1 (when Qmax ≧ (Gidx + 1) · Qmin or Qmin = 0)
... (2)
T = 0 (when Qmax = Qmin) (3)
T = (Qmax−Qmin) / (Gidx · Qmin)
(When Qmin <Qmax <(Gidx + 1) · Qmin)
(4)
It shall be in the relationship.
[0024]
In this case, the condition of the equation (2) indicates that the difference between the maximum value Qmax and the minimum value Qmin is large, and the color of the three-color signal CMY ₁ is in a vivid color region. Further, the condition of the expression (3) indicates that the maximum value Qmax and the minimum value Qmin are equal, and the color of the three-color signal CMY ₁ is gray. Further, the condition of the expression (4) is that the difference between the maximum value Qmax and the minimum value Qmin is within a certain range of gray, that is, the color of the three-color signal CMY ₁ is in a muddy region. Show. Therefore, the reference signal sk obtained based on equation (1), when the color of the three color signals CMY ₁ is in the region of vivid colors is equal to the minimum value Qmin as T = 1, 3-color signal CMY ₁ If the color of the three-color signal CMY ₁ is gray, T = 0 and the three-color signal CMY ₁ itself (Qmax = Qmin), and if the color of the three-color signal CMY ₁ is in the turbid color region, 0 <T <1. There is a weighted value of the maximum value Qmax and the minimum value Qmin.
[0025]
The reference signal sk obtained as described above is supplied to the black (K) plate signal generation circuit 22 as a signal for adjusting the level of the black (K) plate signal K ₃ . The black (K) plate signal generation circuit 22 generates a black (K) plate signal K ₃ based on the reference signal sk, for example, according to a conversion table set as shown in FIG. In this case, when the color of the three-color signal CMY ₁ is in a muddy color region, the black (K) plate signal K ₃ can be increased or decreased according to the degree of muddy color according to the maximum value Qmax and the minimum value Qmin. The muddy color range can be adjusted by the control coefficient Gidx. That is, when Gidx = 0, it is equivalent to the conventional method, and when the value of Gidx increases, the range obtained by weighting Qmax and Qmin as the reference signal sk increases.
[0026]
Here, in order to generate the black (K) plate signal K ₃ more effectively for a bright color, the parameter T is set to

The relationship may be set.
[0027]
Further, in order to increase / decrease the black (K) plate signal K ₃ with respect to the minimum value Qmin equal to or greater than a predetermined value, the parameter T is set using a constant k such that Qmin> k (0 <k <1). The

The relationship may be set.
[0028]
Further, in the equation (1), a linear interpolation equation is used to obtain the reference signal sk. In order to obtain an effect that is nonlinear with respect to the change in the maximum value Qmax, for example,
sk = T ² · Qmin + (1−T ² ) · Qmax (11)
The reference signal sk may be obtained as follows. In this case, since the influence of the black (K) plate signal reaching the color farthest from gray is reduced by a quadratic function, the black (K) plate signal can be effectively generated in a region close to gray.
[0029]
Next, the three-color signal CMY ₃ corrected by the UCR and the black (K) version signal K ₃ are added to the four-color correction signal ΔCMYK ₃ in the adder circuit 28, so that the four-color corrected color Signal CMYK ₄ is generated. The four-color signal CMYK ₄ is converted into a four-color signal CMYK ₅ as a half-tone signal in which half-tone values of highlight (HL) and shadow (SH) are adjusted according to output characteristics in the half-tone setting circuit 24. Is done. Then, in accordance with the four-color signal CMYK ₅ , four plate originals of C, M, Y, and K are created.
[0030]
【The invention's effect】
As described above, in the present invention, the black (K) plate signal for the muddy color can be adjusted without using a tone curve or a color correction, so that a desired color can be obtained without affecting the gray or vivid color. Adjustments can be made.
[Brief description of the drawings]
FIG. 1 is a configuration block diagram of an image processing circuit to which a black signal generation method according to an embodiment is applied.
FIG. 2 is an explanatory diagram of a conversion table between a reference signal and a black (K) plane signal set in the black (K) plane signal generation circuit shown in FIG. 1;
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 10 ... Density setting circuit 12 ... Color correction circuit 14 ... Gradation conversion circuit 16 ... UCR circuit 18 ... Maximum / minimum value calculation circuit 20 ... Reference signal generation circuit 22 ... Black (K) plate signal generation circuit 24 ... Halftone setting circuit

Claims (6)

Obtaining a maximum value and a minimum value of three color signals of C, M, and Y as input signals;
If the difference between the maximum value and the minimum value is greater than or equal to a predetermined value, the input signal is determined to be a signal relating to a vivid color, the minimum value is used as a reference signal, and if the difference is 0, the input The signal is determined to be a signal related to gray and the maximum value is used as a reference signal. If the difference is between 0 and the predetermined value, the input signal is determined to be a signal related to muddy color and the maximum value and Using a value obtained by weighting the minimum value according to the difference as a reference signal;
Generating a black plate signal from the set reference signal;
A method for generating a black plate signal, comprising: The method of claim 1, wherein
The reference signal sk uses a maximum value Qmax, a minimum value Qmin, and a weighting parameter T (0 ≦ T ≦ 1) according to a difference between the maximum value Qmax and the minimum value Qmin.
sk = T · Qmin + (1−T) · Qmax
(However, when the input signal is determined to be a signal related to a bright color, T = 1, and when the input signal is determined to be a signal related to gray, T = 0, and the input signal is a signal related to muddy color. Is determined, 0 <T <1)
A black signal generation method characterized in that: The method of claim 1, wherein
The reference signal sk uses a maximum value Qmax, a minimum value Qmin, and a weighting parameter T (0 ≦ T ≦ 1) according to a difference between the maximum value Qmax and the minimum value Qmin.
sk = T ² · Qmin + (1−T ² ) · Qmax
(However, when the input signal is determined to be a signal related to a bright color, T = 1, and when the input signal is determined to be a signal related to gray, T = 0, and the input signal is a signal related to muddy color. Is determined, 0 <T <1)
A black signal generation method characterized in that: The method according to claim 2 or 3,
The parameter T is a control coefficient Gidx (0 ≦ Gidx ≦ 1) that adjusts the muddy color range .
T = 1 (when Qmax ≧ (Gidx + 1) · Qmin or Qmin = 0)
T = 0 (when Qmax = Qmin)
T = (Qmax−Qmin) / (Gidx · Qmin)
(When Qmin <Qmax <(Gidx + 1) · Qmin)
A black signal generation method characterized in that: The method according to claim 2 or 3,
The parameter T is a control coefficient Gidx (0 ≦ Gidx ≦ 1) that adjusts the muddy color range .
T = 1 (when Qmax ≧ Qmin + Gidx / 2 or Gidx = 0)
T = 0 (when Qmax = Qmin)
T = 2 · (Qmax−Qmin) / Gidx
(When Qmax <Qmin + Gidx / 2)
A black signal generation method characterized in that: The method according to claim 2 or 3,
The parameter T is a control coefficient Gidx (0 ≦ Gidx ≦ 1) for adjusting the muddy color range, and a constant k such that Qmin> k (0 <k <1).
T = 1 (when Qmax ≧ (Gidx + 1) · Qmin or Qmin <k)
T = 0 (when Qmax = Qmin)
T = (Qmax−Qmin) / (Gidx · (Qmin−k)
(When Qmax <(Gidx + 1) · Qmin−Gidx · k)
A black signal generation method characterized in that:

Images