JPH04362869A - Color image processor and its method - Google Patents

Abstract

PURPOSE:To enable a color image processor to unify color data items output from even different output units into nearly the same by setting a color correcting condition based on a combined value of four different color data items and each corresponding color chromaticity. CONSTITUTION:When a color image signal of a combination of yellow Y, magenta M, cyian C, and black BK for use in a printer or the like is input, a color arithmetic unit 1 reads color chromaticities corresponding to color data items saved in a RAM via a CPU 4. Further, based on input color image signals and chromaticities, the color arithmetic unit 1 sets up a color correcting condition, and calculates four color data combinations of Y', M', C', and BK'. Correcting calculation of data Y', M', C', and BK' into data Y, M, C, and BK is also executed in the same manner, thereby enabling the color image processor to unify color data items printed out from printers of even different types of output units into nearly the same color.

Description

[Detailed description of the invention]

0001

[Field of Industrial Application] The present invention relates to a color image processing device, and more particularly to a color image processing device capable of inputting image data of four colors: Y (yellow), M (magenta), C (cyan), and Bk (black). and methods.

0002

[Prior Art] Conventionally, this type of YMCBk input, YMC
Bk output image processing devices either do not perform any calculations or perform only predetermined calculations.

An automatic setting method called photomasking is also known for setting the color correction state.

0004

[Problems to be Solved by the Invention] However, in the conventional example described above, there is a problem that when a YMCBk image signal created for one output device is supplied to another type of output device and printed out, the colors will be different. Ta. Even when using a method for determining color processing parameters, there is a problem in that the parameters cannot be determined using YMCBk input image signals. In any case, in the conventional example described above, YMCB is used for output devices with different color reproducibility.
The drawback is that color correction cannot be performed using the k color signal. (For example, as shown in Figure 4, when a YMCBk image signal created for printer A is output to printer B, it will be a different color.) Also, in conventional printers, for example, four color data of YMCBk are stored in the same pixel. If they overlap, a problem arises in that the image quality deteriorates or the fixing ability decreases due to bleeding or scattering of toner or ink.

[0005]

[Means for Solving the Problems] According to the first invention of the present application, there is provided a means for inputting a combination value of YMCBk signals and a chromaticity value corresponding to the combination, and a color correction means according to the input value. has means for setting the color correction state of the color correction state.

According to another invention of the present application, when automatically setting the conversion state of the conversion means for converting given color image data into reproduced color image data, the degree of color mixing of the color image data is equal to or less than a predetermined value. It is characterized in that the conversion state is set so that.

[0007]

[Embodiment] FIG. 1 is a circuit block diagram of an embodiment of the present invention. Input YMCBk image signals are input from, for example, a computer, are calculated by a color calculator 1, and are output as YMCBk image signals.
'M'C'Bk' image signals are determined. Then, it is output to a printer or the like. Color calculator 1 performs masking, UC
Processing such as R, inking, and processing using an LUT such as direct mapping is performed. Here, an example in which only masking is performed will be explained.

As an example of masking, if we perform 4×4,

[0009]

The following calculation will be performed. In order to perform this calculation with the color calculator 1, it is necessary to determine and set the parameters from m1,1 to m4,4 in advance.

[0010] For this purpose, the characteristics of the printer for which the input signal YMCBk is intended and the characteristics of the printer that prints the Y'M'C'Bk' output signals are required. Using FIG. 5, which is a conceptual diagram of this embodiment, as an example, the characteristics of printer A and printer B will be investigated.

Therefore, the user creates the table shown in FIG. 2 in advance, as shown in FIG. In the table of Figure 2, YMC
Each Bk is a combination of three levels (0, 128, 255), resulting in 3×3×3×3=81 combinations. A hard copy is made using the printer 7 in FIG. 3 so that there are 81 color patches, and the chromaticity is determined using a chromaticity meter. Figure 2
In the example table below, L*a*b* is used. Printer A
and B, find the table in Figure 2.

FIGS. 6 and 7 show flowcharts of the operation of one embodiment of the present invention. This flowchart is CP
U4 executes. Write the program to ROM in advance. This will be explained with reference to FIGS. 6 and 7. first. The YMCBk signals and chromaticity values of printer A are read (S10). The user inputs these data using the key input device 3 or the computer 2 shown in FIG. These input data are saved in RAM5. Next, read the YMCBk signals and chromaticity values of printer B (
S20). These data are also input by the user through the key input device 3 or the computer 2 shown in FIG. 1, and are saved in the RAM 5. Next, the same calculation parameters as those of the color calculation unit 1 are set. In this example, initial values of parameters for masking m1,1 to m4,4 are set (S30).

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

Next, the color mixing limit value of the printer on the output side is set (S50). For 4-color printers, YMCB
If the signal value of k is output in full (255 for 8 bits), problems such as ink bleeding and toner scattering may occur, which may impair image quality. Therefore, a color mixture limit value is required to prevent the overlapping of a certain number of mixed colors. For example, if the color mixing limit value is L, then L≧(Y+M+C
+Bk)/255, and the value of L changes depending on the type of printer, but for example, L=
It is a value such as 3. The parameters of the color calculator 1 are determined so that the value is equal to or less than this L.

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

Next, the initial value N of the patch number is set to 1 (S70).

Next, the value of YMCBk for patch number N is retrieved from the RAM, and the CPU performs masking calculation according to (2) to obtain Y'M'C'Bk' (S80).

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

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

[0020] Let N=N+1 (S110).

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

[0022] Using the obtained color difference of each patch as an evaluation function,
Sixteen masking parameters are determined using an optimization algorithm so that each color difference is minimized. Repeat this a predetermined number of times. Of course, a target color difference may be set in advance, and if the color difference becomes smaller than the target color difference and is within the color mixing limit of the output printer, the process may end (S130).

Known optimization methods include the steepest descent method, the least squares method, the damped least squares method, and the orthogonalization method. Any method may be used, but the following example uses the least squares method. It will be explained as follows. Evaluation function fi (corresponds to color difference in this case), variable x (corresponds to masking parameter), and those with 0 are set as initial values (starting points), and only the vicinity of fi = fi0 + Σaij (xj - xj0) is handled. . aij=∂fi/∂xj=Δfij/Δxj where Δfi
j=fi(x10, ---, xj-10, xj0+Δx
j, xj+10, ---xn0)-fi0xj=xj-
Let xj0 and n is 16 masking pieces in this case.

[0024]

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

[0025]

[3], and if there is a solution near the starting point, then AX=-(
f0-ft) ft is set as the target value. φ=Σwi2(fi-fit)2 where φ is a single evaluation scale and wi is a weight

[0026]

[4] φ=(f-ft)T(f-ft) =‖f-ft‖2 Here, if we find the solution X where gradφ=0, we get AT(f-ft)
ft)=AT(AX+f0-ft)=0 to X=-(A
TA)-1AT(f0-ft) Update the initial value from this X and repeat. There are various optimization methods, and the appropriate one should be 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 a Y'M'C'Bk' image signal is output.

(Other Embodiments) In the above-described embodiments of the present invention, the input/output signals are YMCBk, but some printers are capable of inputting three colors of YMC. YMC as shown in Figure 8
It is also possible to make the input YMCBk output. In this case, the printer characteristics on the input side use a combination of YMC signals and their chromaticity values.

It is also possible to use YMCBk input and YMC output. It is also possible to use YMC input and YMC output.

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

In FIG. 2, there are three levels of YMCBk combinations, making a total of 81 types, but other combinations may be used. For example, there may be 4 levels (256 types in total), 5 levels (625 types in total), or even more.

In addition, in FIG. 2, the signal values include 0 and 255, but interpolation (extrapolation, etc.) is performed without including 0 and 255.
You can also find it by

Further, in FIG. 2, each color of YMCBk has 8 bits, but it may be other than 8 bits.

Furthermore, although L*a*b* is used as the chromaticity in FIG. 2, any chromaticity may be used (for example, xyY
, L*u*v*, uvY), and may be the concentration value of a densitometer.

Further, the color calculator 1 shown in FIG. 1 may perform any color processing as long as the parameters can be changed and the output color signal value can be changed by changing the parameters. Therefore, UCR including parameters, skeleton black, high-order masking, a combination thereof, or combination with direct mapping may be used.

Furthermore, as shown in FIG. 9, a reading device 100,
The color image processing apparatus 101 shown in FIG. 1 may be incorporated into a color copying machine consisting of a color printer 103, or the structure of the above-described embodiment may be provided. Also,
It is also possible to incorporate the color image processing device 101 into the color printer 105 as shown in FIG. In this case, since the printer for output has been determined, it may be possible to store in advance the YMC or YMCBk signal values and chromaticity values of the printer characteristics on the output side in the ROM 6 of FIG. It is also conceivable to input the printer's characteristics from outside only when the printer's characteristics change.

In addition, the initial value parameters of the color calculator 1 shown in FIG. Parameters may be loaded from the ROM 6 into the color calculator 1 by selecting the type of printer.

Furthermore, the RAM 5 in FIG. 1 may be backed up to back up the parameters calculated by the CPU 4.

As explained above, according to this embodiment, 2
By providing a means for inputting the color characteristics of different types of printers and a means for determining parameters based on that data, YMCBk image signals created for one printer can be transferred to other printers without deteriorating color reproducibility. There is an effect that can be converted into

Furthermore, according to this 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, thereby preventing image quality deterioration due to ink and toner scattering, etc. You can.

[0042]

As explained above, according to the present invention, color correction can be performed satisfactorily and deterioration of image quality can be prevented.

[Brief explanation of drawings]

FIG. 1: Circuit block diagram of one embodiment of the present invention

[Figure 2] Examples of signal values and chromaticity values used in one embodiment of the present invention

[Figure 3] Example of how to obtain chromaticity values used in one embodiment of the present invention

[Figure 4] Conventional example

[Fig. 5] Conceptual diagram of an 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 diagram showing another embodiment of the present invention.

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

[Explanation of symbols]

1 Color calculator 4 CPU

Claims (4)

[Claims] 1. A color image processing device that reproduces an image in response to an image input of four-color data after undercolor processing, comprising:
A color device comprising means for inputting a combination value of the four color data and a chromaticity value corresponding to the combination, and means for setting a color correction state of the color correction means in accordance with the input from the input means. Image processing device. 2. The setting means adjusts the colors so that the combination of four-color data output from the color correction means does not exceed a preset color mixing limit of the printer, regardless of the combination of input four-color data. 2. The color image processing apparatus according to claim 1, further comprising means for setting a color correction state of the correction means. 3. A color image processing apparatus according to claim 1, wherein said color correction means is adapted to handle input images as YMC signals. 4. When automatically setting the conversion state of a conversion means for converting given color image data into reproduced color image data, the conversion state is set so that the degree of color mixing of the color image data is equal to or less than a predetermined value. A color image processing method characterized by: