JPH056827B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of the Invention) The present invention provides a color image input/output system comprising:
The present invention relates to a method for automatically setting color correction conditions for accurately finishing a specific portion in a final output image to a desired color tone.

(Technical Background of the Invention and Prior Art) In color images such as color printed matter, it is sometimes desired to finish not only the overall tone but also the color tone of a specific part extremely accurately. For example, the color tone of the skin in a human image, the color tone of a product in a product catalog for automobiles, etc.

In a color image input/output system using a color scanner, etc., the final output image (in a color image input/output system that outputs the final image directly from an image output device, it is the image; in a color image input/output system that performs color platemaking, it is the final output image) Conventionally, color correction (color correction) and gradation processing, which are performed by inputting the input density signal of each color to an image processing circuit, have been known as methods for changing the color tone on printed matter (printed material printed using a printed plate). It is being
To explain the above color collection using a color prepress system using a normal color scanner as an example, first, the scanner input head is manually moved to a specific part of the document on the scanner drum, and each color (usually yellow, magenta,
Check the finished density (cyan, black), or in this case, the dot area ratio display, and operate the color correction condition (color correction coefficient) correction knob of the image processing circuit to obtain the desired dot area ratio for each color. I was doing it.

However, setting the color correction conditions as described above is done manually by operators relying on their intuition, which is time-consuming and requires skill. It has a number of drawbacks, such as the difficulty in predicting the taste, the tendency for individual differences in color correction condition settings, and the inability to guarantee a uniform finished color.

(Object of the Invention) The present invention has been made in view of the above-mentioned circumstances, and provides color correction conditions for accurately finishing a specific part to a desired color tone in a color image input/output system using a color scanner or the like described above. It is an object of the present invention to provide an automatic setting method for color correction conditions that can be set easily and without individual differences without requiring any skill.

(Structure of the Invention) The method for automatically setting color correction conditions in the color image input/output system of the present invention is such that color correction coefficients are automatically corrected by inputting a code of a color patch to be referred to as a color sample. In other words, like the color plate making system using the color scanner mentioned above, each color input density signal from an image input device that separates and reads a color document is input to an image processing circuit, and each of these signals is In a color image input/output system that performs color correction based on color correction conditions defined by color correction coefficients for each color, and inputs each color output signal after color correction to an image output device, the density or halftone of each color is A large number of color patches are created by changing the area ratio, and each color reference output signal corresponding to the density or halftone area ratio of each color in these color patches is stored in a storage means in correspondence with an input code unique to each color patch, References to each color input density signal of a specific part of the document to be finished in a final output image with a color tone similar to that of the specific color patch, and each color of the specific color patch read out from the storage means by specifying the input code of the specific color patch. The output signal and the data of predetermined reference color correction coefficients for each color are input to a calculation means, and the calculation means performs color correction using the reference color correction coefficients for each color with respect to each color input density signal of the specific portion. The data of the corrected color correction coefficients after correction is transferred to the image processing circuit, and the corrected color correction coefficients are used as the corrected color correction coefficients. This is set as a color correction coefficient that defines the correction conditions.

(Embodiments) Hereinafter, the present invention will be described in detail based on embodiments shown in the drawings.

FIG. 1 shows an example of a color image input/output system in which color correction conditions are automatically set using the method of the first embodiment of the present invention, and a specific portion of a final output image is accurately finished in a desired color tone. It is. A color original 2 set on the circumferential surface of a rotating input drum 1 is color-separated and scanned by an input optical head 3 equipped with a color separation filter, and image signals of yellow, magenta, and cyan are obtained through a photoelectric converter 4. Y, M, and C are converted into digital color input density signals IY, IM, and IC by a logarithmic conversion circuit 5 and an AD converter 6. Note that the signal processing after the photoelectric converter 4 is performed in a series for each color, but since the signal processing is performed in the same way in each series, in the diagrams and the following description, each series is not particularly separated, and the same information is used for each series. explain.

The input density signals IY, IM, and IC of each color are subjected to gradation processing in the image processing circuit 7, and are color corrected based on color correction conditions defined by color correction coefficients, which will be described in detail later, and each output density signal OY, Output as OM, OC. These color output density signals OY,
OM, OC are light intensity control signal converter 8, DA converter 9
analog light intensity control signals Y′, M′,
converted to C′. These light amount control signals Y′, M′,
C' is input to a modulator 11 that modulates the recording light from the exposure light source 10, and these light amount control signals Y', M',
The recording light modulated according to C' is sent to exposure head 1.
2, a color image is formed as a final output image on a film 14 on a rotating output drum 13.

The above-mentioned color correction conditions are set by taking in data of a reference color correction coefficient (which may be selected as appropriate depending on the situation) inputted from the parameter input section 15 via the calculation section 16. If the reference color correction coefficient data is set as is, it may not be possible to precisely finish a specific portion of the final output image of the film 14 that is desired to have a desired color tone. A method according to a first embodiment of the present invention for correcting and automatically setting color correction conditions so as not to cause such problems will be described in detail below.

In the method of the present invention, first, color batches 101, 102, 103 as shown in FIG.
..., 201, 202, 203... are prepared. As shown in the figure, a large number of color patches are created with different densities of Y, M, and C colors, and the operator selects the most suitable color for the specific portion from among these color patches. These color patches 10
1, 102, 103..., 201, 202, 203
... are systematized by main hue to facilitate searching, and are organized into, for example, "skin color chart" 51, "gray color" 52, etc., as shown in the figure. Then, as shown in FIG.
In the reference density table 17 in 6, each color patch 101, 102, 103..., 201, 20
2,203…numbers 0101, 0102, 0103…,
They are stored in correspondence with 0201, 0202, 0203...

Next, the third section illustrating the flow of signals in the arithmetic unit 16 will be described.
The color correction condition setting operation will be explained with reference to the drawings. After setting the color original 2 on the input drum 1, the parameter input section 15
The data P1 of the gradation conversion curve of each color and the data P2 of the reference color correction coefficient are calculated by the calculation unit 16.
is input. Next, the input optical head 3 is moved to the specified portion on the color original 2, and each color input density signal P3 of the specified portion is input to the calculation section 16. At the same time, the number of the specific color patch selected as the finishing color of the specific part is input as an input code to the parameter input section 15,
Thereby, the parameter input section 15 outputs a signal P4 carrying the number of the specific color patch.
is input to the calculation unit 16. When this color patch number signal P4 is input, each color reference density signal P5 unique to this designated specific color patch is read out from the reference density table 17.

The read reference density signal P5 of each color, the data P1 of the gradation conversion curve, the data P2 of the reference color correction coefficient, and the input density signal P3 of each color of the specific portion are input to the color correction coefficient correction calculation circuit 18, The reference color correction coefficient is calculated and corrected (in this color image input/output system, the image processing circuit 7 performs gradation processing along with color correction, and the data P1 of the gradation conversion curve is (transferred to the processing circuit 7 and set in the gradation conversion table 7a). Next, the calculation and modification of the reference color correction coefficients will be explained in detail. Various color correction methods have been known in the past, but here we will discuss, for example, the method of
As shown in Publication No. 181045, Y (yellow), M
(magenta), C (cyan), B (blue), G (green), R
Consider the case where a color correction signal is obtained by linearly combining six (red) hue signals.
For example, regarding the color correction of the Y signal,
Color correction signals include six hue signals (Y),
_{Linear combination a 1 ( Y _} )＋a ₂
(M) + a ₃ (C) + a ₄ (B) + a ₅ (G) + a ₆ (R), that is, the input density signal is IY, and the signal after this input density signal IY has undergone color correction is IY. ′, IY′=IY+a ₁ (Y)+a ₂ (M)+a ₃ (C)+a ₄ (B)+a ₅ (G)+a ₆ (R)
...(1) becomes. Here, each hue signal is (Y)={IY−max(IM, IC)} (M)={IM−max(IC, IY)} (C)={IC−max(IY, IM)} (B ) = {min (IM, IC) - IY} (G) = {min (IC, IY) - IM} (R) = {mn (IY, IM) - IC} (max (IM, IC) is the input concentration Among the signals IM and IC, the one with the larger signal value, min(IM, IC), is the one with the smaller signal value among the input concentration signals IM and IC.
The same applies to the others), and the generated hue signal changes depending on the magnitude relationship of the three input density signals IY, IM, and IC, but in any case, at most 2 of the above hue signals (Y) to (R).
Only one hue signal is generated (see Figure 4). Therefore, if the formula for the hue signals (Y) to (R) above is a negative value, the formula for that hue signal is 0 (zero).
If it is defined as a value, the above equation (1) will always be a linear combination of two hue signals and a reference color correction coefficient.
It is expressed as the sum of IY. In other words, when hue signals (Y) and (R) are generated as in the example _shown in _FIG . The output concentration signal OY is as follows: OY=g _Y {IY'} = g _Y {IY+a ₁ (Y)+a ₆ (R)} ...(2). However, _gY is the gradation conversion characteristic for the Y signal.

However, if color correction is performed using the reference color correction coefficients a ₁ and a ₆ defined by the reference color correction coefficient data P2 as they are, it is not possible to accurately finish a specific part with the desired color tone, as described above. Sometimes there isn't. Therefore, the reference color correction coefficients a ₁ , a ₆ are set so that the reference density signal OY' carrying the Y color density in the specific color patch is outputted from the image processing circuit 7.
are calculated and corrected as b ₁ and b ₆ , respectively, in the color correction coefficient correction calculation circuit 18. That is, OY′=g _Y {IY+b ₁ (Y)+b ₆ (R)} ...(3) The corrected color correction coefficients b ₁ and b ₆ can be calculated from the above equation (3) and the above (2) equation. But in this case
Since b ₁ and b ₆ cannot be determined uniquely, some conditions are set and the problem is solved according to these conditions.
In other words, for example, if we set the condition that the color correction coefficient of the smaller of the two hue signals is not changed and only the color correction coefficient of the larger hue signal is modified, then in the above example, (i) When (Y)≧(R) b ₁ = {g _Y ^-1 (OY′)−IY−a ₆ (R)}×1/(R) b ₆ = a ₆ (ii) (Y)＜(R ), b ₁ = a ₁ b ₆ = {g _Y ^-1 (OY′) − IY − a ₁ (Y)}×1/(R) (However, g _Y ^-1 is the inverse function characteristic of the tone conversion characteristic ) Note that the conditions for determining b ₁ and b ₆ may be set as appropriate other than the above example.

The above-described correction of the reference color correction coefficients is of course also carried out for the M signal and the C signal, and the obtained data of the corrected color correction coefficients for each color is set in the color correction table 7b of the image processing circuit 7. Therefore, when the color original 2 is scanned over the entire surface to obtain an output image, the input density signals IY, IM, and IC of each color are subjected to gradation processing based on the gradation conversion table 7a, and the above-mentioned When color correction is performed according to the color correction table 7b for each color set in this way, each color output density signal carrying each color density of the specific color patch is output for the specific portion, and these specific portions are referenced. You will be able to finish in the same color as a specific color patch.

Figures 5 and 6 show a color image input/output system to which the second embodiment method of the present invention is applied (note that in these Figures 5 and 6, the elements in Figures 1 and 3 above are Equivalent elements are given the same number and will not be described again).
In this system, each color input density signal IY, IM, and IC over the entire surface of the document obtained by rough-scanning the color document 2 before the main scan is taken into the image signal input section 20, and is input from the image signal input section 20. The calculation unit 16 receives the above color input density signals IY, IM, and IC.
is input. In the rough scan data processing section 21, the calculation section 16 receives the above-mentioned color input density signals IY,
Each color gradation conversion curve is obtained from IM and IC, and data P1 of each color gradation conversion curve is input to the color correction coefficient correction calculation circuit 18. The above-mentioned color gradation conversion curves can be obtained, for example, by calculating the cumulative density histogram of the color original 2 from the color input density signals IY, IM, and IC, as shown in Japanese Patent Application No. 145491/1983. .

Further, each color input density signal P3 of the specific portion is each color input density signal IY from the image signal input section 20,
IM and IC are processed by the specific partial signal extraction unit 2 in the calculation unit 16.
At the same time, the coordinate signal of the desired specific portion is input to the specific portion signal extraction unit 22 by the coordinate input means 23, and the coordinate signal of each color is extracted from the input density signals IY, IM, and IC based on the specific portion coordinate signal. It is now possible to obtain

Data P1 of each color gradation conversion curve obtained as described above, data P2 of reference color correction coefficients, and input density signal P3 of each color in a specific part.
In addition, each color reference density signal P5 obtained in the same manner as in the first embodiment described above is inputted to the color correction coefficient correction calculation circuit 18, and the color correction table 7b is thereafter calculated in the same manner as in the first embodiment. Automatically set.

As an example of color patch, "Skin color chart"
Although the description has been made of the "gray chart" etc., as shown in FIG.
Color process chart 6 consisting of 1,402...
0, 61... may be used. However, charts that group color patches by main hue, such as the above-mentioned "skin tone chart" and "gray chart",
It is easy to use and can be used selectively depending on the purpose, so it is economical to create or purchase only what you need.

Both of the two embodiments described above are applied to a color image input/output system that directly outputs a final output image, but the method of the present invention is applicable to a color plate making system that creates a three-color or four-color halftone plate. is also applicable. In this case, the density of each color of the color patch may be defined by the dot area ratio, and each color reference density signal may carry the dot area ratio of each color.

In a four-color color plate making system, color correction conditions can be automatically set for black plate color correction in exactly the same manner as described above. In other words, the following equations (1)′ and (2)′, which correspond to the above equations (1) and (2), IK′=IK+c ₁ (Y)+c ₂ (M)+c ₃ (C)+c ₄ (B)′ ＋c ₅ (G)＋c ₆ (
R)...(1)′ OK=g _K {IK+d ₁ (Y)+d ₆ (R)} ...(2)′ For example, as mentioned above, the signal of the hue signal (Y) and (R) All you have to do is decide to correct only the larger one and find the above d ₁ and d ₆ .

(Effects of the Invention) As explained in detail above, according to the method for automatically setting color correction conditions of the present invention, color correction conditions can be automatically set to obtain the hue of the referenced color patch without any troublesome operations. Therefore, even an unskilled person can easily and quickly finish a desired part of the final output image in a desired color tone without any individual differences.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing a color image input/output system to which the first embodiment method of the present invention is applied;
FIG. 2 is a schematic diagram showing an example of a color patch used in the present invention, FIG. 3 is a schematic diagram illustrating the signal flow in the calculation section of the color image input/output system of FIG. 1, and FIG. 4 is an input density signal. 5 is a block diagram showing a color image input/output system to which the second embodiment method of the present invention is applied, and FIG. 6 is a color image input/output system of FIG. 5. FIG. 7 is a schematic diagram illustrating the flow of signals in the arithmetic unit. FIG. 7 is a schematic diagram showing another example of the color patch used in the present invention. 2...Color original, 3...Input optical head, 4
...Photoelectric converter, 7...Image processing circuit, 7b...
Color correction table, 10... Exposure light source, 11... Modulator, 12... Exposure head, 14
... Film, 15 ... Parameter input section, 16
...Calculation unit, 17...Reference concentration table, 18...
...Color correction coefficient correction calculation circuit, 20...
...Image signal input section, 21...Rough scan data processing section, 22...Specific partial signal extraction section, 23...
Coordinate input means, 101, 102, 103, 20
1,202,203,301,302,401,
402...color patch, IY, IM, IC...each color input density signal, OY, OM, OC...each color output density signal, P2...each color reference color correction coefficient data, P3...each color input density signal of a specific part , P4...Color patch number signal, P5
...Reference density signal for each color.

Claims (1)

[Claims] 1. Input density signals of each color from an image input device that separates and reads a color original into an image processing circuit, and performs color correction on each of these signals based on color correction conditions defined by color correction coefficients for each color. In a color image input/output system that performs color correction and inputs each color output signal after color correction to an image output device, a plurality of color patches are created by changing the density or halftone area ratio of each color, and each color in these color patches is I want to store each color reference output signal corresponding to the density or halftone area ratio in a storage means in correspondence with the input code unique to each color patch, so that the final output image has a color tone similar to that of a specific color patch. each color input density signal of a specific portion of the original, each color reference output signal of the specific color patch read from the storage means according to the input code designation of the specific color patch;
data on predetermined reference color correction coefficients for each color is input to a calculation means, and the calculation means uses the reference color correction coefficients for each color when color correction is performed on each color input density signal of the specific portion. The calculation is corrected so as to obtain a corrected output near the reference output signal of each color, and the data of the corrected color correction coefficient after the correction is transferred to the image processing circuit, and the corrected color correction coefficient is used to define the color correction condition. A method for automatically setting color correction conditions, characterized in that the color correction conditions are set as color correction coefficients.