JP3135280B2 - Color image processing apparatus and method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image processing apparatus and method for calculating color correction conditions.

[0002]

2. Description of the Related Art Conventionally, this type of YMCBk input, YMCB
The Bk output image processing apparatus does not perform any operation, or performs only a predetermined operation.

There is also known an automatic setting method called photomasking for setting a color correction state.

[0004]

However, in the above-mentioned prior art, there is a problem that the image signal of YMCBk produced for a certain output device is supplied to another type of output device, and the colors are different when printed out. Was. Even in the method of determining the color processing parameters, there is a problem that the parameters cannot be determined in the YMCBk input image signal. In any case, in the above-described conventional example, the YMCB is used for the output device having different color reproducibility.
There is a disadvantage that color correction cannot be performed with the k color signal. (For example, as shown in FIG. 4, the YMCBk image signal generated for printer A becomes a different color when output to printer B.) In a conventional printer, data of four colors, for example, YMCBk is stored in the same pixel. If they overlap, there arises a problem that image quality is degraded due to bleeding or flying off of toner or ink, or fixing ability is lowered.

[0005]

According to the present invention, it is an object of the present invention to make it possible to match the output of a first output device with the output of a second output device as a reference. It is another object of the present invention to calculate a color correction condition in consideration of a color mixing limit value, so that it is possible to calculate a color correction condition that does not cause image degradation due to flying of a recording material such as ink or toner. In order to achieve this object, the image processing apparatus according to the present invention uses the second output device based on the input image data to output the color of the output image output by the first output device based on the input image data. An image processing apparatus for matching colors of an output image to be output, and first colorimetric data indicating a colorimetric result of a patch output by the first output device,
Storage means for storing second colorimetric data indicating a colorimetric result of the patch output by the second output device,
Input means for inputting the color mixing limit value of the second output device, and the first colorimetric data, the second colorimetric data and the output of the second output device based on the color mixing limit value, Calculating means for calculating a color correction condition for performing color correction so as to match the output of the first output device as a reference; andthe calculated color correction condition to the color correction unit for the second output device. Setting means for setting.

Further, the first and second colorimetric data are characterized by a plurality of correspondences between density data and luminance / chromaticity data.

[0007]

FIG. 1 is a circuit block diagram of an embodiment of the present invention. An input YMCBk image signal is input from, for example, a computer, is calculated by a color calculator 1, and outputs Y'M'C '. The image signal of Bk ′ is obtained. Then, it is output to a printer or the like. The color operation unit 1 has masking, U
Processing such as CR and inking, and processing using an LUT such as direct mapping are performed. Here, an example in which only masking is performed will be described.

As an example of masking, if 4 × 4 is performed,

[0009]

[Outside 1] Is performed. In order to perform this operation in the color operation unit 1, it is necessary to obtain and set parameters from m _1,1 to m _{4,4 in} advance.

[0010] For this purpose, the characteristics of the printer that targets the input signal YMCBk and the characteristics of the printer that prints the output signal of Y'M'C'Bk 'are required. Taking FIG. 5 of the conceptual diagram of this embodiment as an example, the characteristics of the printers A and B will be examined.

Therefore, the user prepares the table shown in FIG. 2 in advance as shown in FIG. In the table of FIG.
Bk is a combination of three levels (0, 128, 255), and 3 × 3 × 3 × 3 = 81 combinations. A hard copy is made by the printer 7 of FIG. 3 so that the number of color patches becomes 81, and the chromaticity is obtained by a chromaticity meter. FIG.
L ^* a ^* b ^* is used in the example of the table. The tables in FIG. 2 are obtained by the printers A and B.

FIGS. 6 and 7 are flowcharts showing the operation of an embodiment of the present invention. This flowchart is CP
U4 executes. The program is written in the ROM in advance. This will be described with reference to FIGS. First. The YMCBk signal and chromaticity value of the printer A are read (S10). The user inputs these data from the key input device 3 or the computer 2 in FIG. These input data are saved in the RAM 5. Next, the YMCBk signal and the chromaticity value of the printer B are read (S20). These data are also input by the user from the key input device 3 or the computer 2 in FIG.
Saved to. Next, the same calculation parameters as those of the color calculator 1 are set. In this example, initial values of parameters of masking _m1,1 to _m4,4 are set (S30).

Next, the last number NMAX of the patch of the printer A is set (S40). In this embodiment, when 81 types of patches are used, NMAX = 81.

Next, the color mixing limit value of the printer on the output side is set (S50). YMCB for 4-color printer
If the signal value of k is output in full (255 for 8 bits), problems such as ink bleeding and toner scattering may occur, and image quality may be impaired. Therefore, it is necessary to set a color mixing limit value so as not to exceed a certain color mixture.
For example, if the color mixing limit is L, then L ≧ (Y + M + C
+ Bk) / 255, and the value of L is changed depending on the type of printer.
A value such as three. The parameters of the color calculator 1 are determined so that the value is equal to or less than L.

Next, the number of optimizations MMAX is set (S60).

Next, an initial value N = 1 for the patch number is set (S70).

Next, the value of YMCBk at the time of the patch number N is fetched from the RAM, and the CPU performs masking calculation to obtain Y'M'C'Bk '(S80).

Next, the CPU obtains the chromaticity corresponding to Y'M'C'Bk 'by interpolation using the signal value and the chromaticity value of YMCBk of the printer B (S90). This can be easily obtained by, for example, linear interpolation.

Next, a color difference between the obtained chromaticity value and the chromaticity value of the patch number N of the printer A is obtained (S100).

It is assumed that N = N + 1 (S110).

This routine is repeated until N = 81 (S120).

Using the obtained color difference of each patch as an evaluation function,
An optimization algorithm finds 16 masking parameters so that each color difference is minimized. This is repeated a predetermined number of times. Of course, a target color difference may be set in advance, and the process may be terminated when the color difference becomes smaller than the target color difference and is within the color mixing limit of the output side printer (S130).

As this optimization method, a steepest descent method, a least square method, an attenuated least square method, and an orthogonalization method are known, and any of these methods may be used. It will be described as. An evaluation function f _i (corresponding to a color difference in this case), a variable x (corresponding to a masking parameter), and a _value with ₀ are set as initial values (starting points), and f _i = f _i0 + Σa _ij (x _j − Only the neighborhood of x _j0 ) is handled. a _ij = ∂f _i / ∂x _j = Δf _ij / Δx _j where Δf _ij = f _i (x ₁₀ , −−−, x _j−10 , x _j0 + Δ
_{x j, x j + 10,} --- x n0) -f i0 x j = x j -x j0 Distant, n represents the case masking 16
Pieces

[0024]

[Outside 2] In this case, m is the color difference, which is a number obtained by adding 81 × 3 (from three values of 81 types of patches and chromaticity) and the color mixing limit value of the printer on the output side.

[0025]

[Outside 3] Then, assuming that there is a solution near the starting point, AX = − (f ₀ −f _t ) f _t can be obtained as the target value. A single rating scale and φ, and the weight of the ^{_{w i φ = Σw i 2 (}} f i -f it) 2

[0026]

[Outside 4] φ = (f−f _t ) ^T (f−f _t ) = {f−f _t } ² Here, when a solution X satisfying grad φ = 0 is obtained, ^AT (f−f _t ) = A ^T (AX + f ₀ − From f _t ) = 0 to X = − (A ^T A) ⁻¹ A ^T (f ₀ −f _t ) The initial value is updated from this X and repeated. There are various optimization methods, and an appropriate method is used.

The 16 parameters thus obtained are set in the color calculator 1 (S160).

Next, when the YMCBk image signal enters the color calculator 1, color processing is performed according to the set parameters, and the Y'M'C'Bk 'image signal is output.

(Other Embodiments) In the above-described embodiment of the present invention, the input / output signal is YMCBk. However, some printers have a YMC three-color input. As shown in FIG.
It is also possible to make C input YMCBk output. In this case, the printer characteristics on the input side use a combination of YMC signals and their chromaticity values.

Further, it is possible to make YMCBk input and YMC output. It is also possible to make YMC input and YMC output.

Further, YMC or YMCBk input YM
It is also possible to use a combination of C or YMCBk outputs.

In FIG. 2, there are a total of 81 combinations of YMCBk in three levels, but other combinations may be used. For example, there may be four levels (total of 256 types), five levels (total of 625 types), and even more.

In FIG. 2, the signal values include 0 and 255, but the signal values do not include 0 and 255, and interpolation (extrapolation or the like) is performed.
You can also ask for

In FIG. 2, each color of YMCBk is 8 bits, but may be other than 8 bits.

Although L ^* a ^* b ^* is used as the chromaticity in FIG. 2, any chromaticity may be used (for example, xyY, xyY,
L ^* u ^* v ^* , uvY) or the density value of a densitometer.

The color calculator 1 shown in FIG. 1 can change any parameter, and any color processing may be used as long as the color signal value of the output can be changed by changing the parameter. Therefore, the UCR containing the parameters
However, skeleton black, higher-order masking, a combination thereof, or combination with direct mapping may be used.

Further, as shown in FIG.
The color image processing apparatus 101 shown in FIG. 1 may be incorporated in a color copier including the color printer 103, or the configuration of the above-described embodiment may be provided. Also,
It is also conceivable that the color image processing apparatus 101 is built in the color printer 105 as shown in FIG. In this case, since the printer to output is determined, YMC or YMCBk
It is also conceivable that the signal value and the chromaticity value are stored in the ROM 6 of FIG. Only when the characteristics of the printer have changed, the characteristics of the printer may be externally entered.

The initial value parameters of the color calculator 1 shown in FIG. 1 are stored in advance in the ROM 6 with values of assumed printer combinations. By selecting the type of the printer, the parameters may be loaded from the ROM 6 into the color calculator 1.

Also, the RAM 5 in FIG. 1 may be backed up, and the parameters calculated by the CPU 4 may be backed up.

As described above, according to the present embodiment, 2
By providing a means for inputting the color characteristics of one type of printer and a means for obtaining parameters based on the data, the image signal of YMCBk made for one printer can be used for another printer without lowering the color reproducibility. There is an effect that can be converted.

According to the present embodiment, the color mixing limit value of the printer is set in advance, and the color correction coefficient is automatically set so as not to exceed the limit value. You can do it.

[0042]

According to the present invention, the output of the first output device can be matched with the output of the second output device as a reference. In addition, by calculating the color correction condition in consideration of the color mixing limit value, it is possible to calculate a color correction condition that does not cause image degradation due to flying of a recording material such as ink or toner.

[Brief description of the drawings]

FIG. 1 is a circuit block diagram of one embodiment of the present invention.

FIG. 2 shows examples of signal values and chromaticity values used in an embodiment of the present invention.

FIG. 3 is an example of a method of calculating a chromaticity value used in one embodiment of the present invention.

FIG. 4 Conventional example

FIG. 5 is a conceptual diagram of one embodiment of the present invention.

FIG. 6 is a flowchart of an embodiment of the present invention.

FIG. 7 is a flowchart of an embodiment of the present invention.

FIG. 8 is a circuit block diagram of another embodiment of the present invention.

FIG. 9 is a view showing another embodiment of the present invention.

FIG. 10 is a view showing still another embodiment of the present invention.

[Explanation of symbols]

 1 color calculator 4 CPU

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int. Cl. ⁷ , DB name) H04N 1/60 B41J 2/525 G06T 1/00 510 H04N 1/46

Claims (3)

(57) [Claims] A first reference based on input image data;
An image processing apparatus for matching the color of an output image output by a second output device based on the input image data with the color of an output image output by an output device, the image processing device outputting the color output by the first output device Storage means for storing first colorimetric data indicating a colorimetric result of the patch, and second colorimetric data indicating a colorimetric result of the patch output by the second output device; and An input unit for inputting a color mixing limit value of an output device, and a first colorimetric data, a second colorimetric data based on the color mixing limit value, based on the output of the second output device as the reference Calculating means for calculating color correction conditions for performing color correction so as to match the output of the first output device; and setting means for setting the calculated color correction conditions in the color correction unit for the second output device. The image processing apparatus characterized by having and. 2. The image processing apparatus according to claim 1, wherein the first and second colorimetric data are configured by a plurality of correspondences between density data and luminance / chromaticity data. 3. Inputting first data indicating characteristics of a first output device and second data indicating characteristics of a second output device as a reference, and inputting a color mixing limit value of the second output device. Based on the first and second data and the color mixing limit value,
Calculate color correction conditions for performing color correction so as to match the output of the first output device with reference to the output of the second output device, and use the calculated color correction conditions for the second output device. An image processing method, wherein the image processing method is set in a color correction unit.