JPH069372B2 - Color image processing device - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a color image processing apparatus that corrects a digital color component signal of a plurality of colors for each pixel and outputs a corrected digital color component signal including a black component signal. .

[Prior Art] In a conventional color printer output image, black is represented by three color signals of yellow (Y), magenta (M), and cyan (C). When such a conventional image processing signal is output to a printer such as a copying machine, in the printer, since three color developers are placed at one place, for example, in the electrophotographic system, toner is not well adhered to the paper or black is generated. It was often the case that it was not completely black.

On the other hand, the black component included in the Y, M, and C color components is
U removed from each color component of M and C and replaced with black signal U
A CR (undercolor removal) technique is known.

However, when reproducing high-density black such as black characters, if the black component removed by the UCR from the Y, M, and C color component signals is used as it is as the black component signal, reproduction is performed. There was a problem that the black mark became faint because of the low.

[Purpose] It is an object of the present invention to provide a color image processing apparatus which eliminates the above-mentioned conventional drawbacks and enables ideal black color reproduction.

[Embodiment] FIG. 1 is a block diagram showing an embodiment of the present invention. In the figure, 1 is a black judgment circuit, 2 and 3 are several-bit shift registers, 4,5 and 6 are 1-bit shift registers, 7
Is an encoder, 8 is a low level signal generation circuit, 9 is a high level signal generation circuit, 10 is a black data generation circuit synthesized by UCR or the like, and 11 and 12 are data selectors for three primary color signals and black signals.

As shown in FIG. 1, a pixel signal of interest having Y, M and C is input to the register 2 and further to the black judgment circuit 1, where it is black or an intermediate color as described later. Is determined and is input to the register 4 as a 1-bit signal. The black determination signal is shifted by the shift clock from the shift clock generating circuit 21 in synchronization with the Y, M and C signals. That is, the black determination signal and the Y, M and C signals are output from the shift registers 2 and 4 by the first shift clock, and are output from the shift registers 3 and 5 by the second shift clock. If the output of the register 5 is determined to be black at this point, this signal is input to the data recovery sector 12 as a selector signal, and the high-level black signal output from the high-level signal generator 9 is output to the data selector. Output from 12.
The output signal from the black data generation circuit 10 synthesized by UCR or the like is data delayed by two shift clocks in advance. When the pixel of interest is not determined to be black by the black determination circuit 1, the encoder 7 outputs this output signal. It is selected as black data and output from the data selector 12. Similarly, when the signals from the shift registers 3 and 5 are output, a certain pixel of interest and the black determination outputs before and after the pixel of interest are output from the shift registers 4, 5, and 6, so that the encoder 7 outputs a select signal. When all the outputs from the shift registers 5, 4 and 6 are judged to be black, the data selector 11 selectively outputs the low level signal from the low level signal generating circuit 8 as the density data of Y, M and C, Otherwise, the Y, M and C signals are directly output from the data selector 11.

High level signal generation circuit 9 and low level signal generation circuit 8
Generates the highest level signal and the lowest level signal when a certain pixel of interest is judged to be a binary image due to image area separation or the like. Therefore, more ideal color reproduction can be performed.

The black judgment circuit 1 can have the configuration shown in FIG. 2, for example.
The Y, M and C signals are supplied to comparators 13, 14 and 15 respectively.
Are compared with predetermined thresholds P1, P2 and P3 in, and only when Y> P1, M> P2 and C> P3, the output signals from the comparators 13, 14 and 15 are input to the encoder 16 and the black signals are output from them. A judgment output signal is issued.

The operation according to the present invention will be described with reference to FIG. 4 showing an example of a mode of selecting a black signal and selecting Y, M and C signals in a black portion of an image. N pixels surrounding the area determined to be black by the black determination signal from the black determination circuit 1 (fourth
(1 pixel in the figure) is judged by the encoder 7 based on the signals from the registers 4, 5 and 6, and the data of Y, M and C is output from the data selector 11 as it is, and black also has a high level from the data selector 12. The printer output image is a black color composed of four colors (three primary colors and black). Further, the inside of the area determined to be black is the printer by the high level output of black from the data selector 12 based on the select signal from the register 5 and the low level output of Y, M and C based on the select signal from the encoder 7. Is output. Therefore, on the print,
A more realistic black image is reproduced, and an image with good toner adhesion is obtained.

According to the present invention, since the interstices of the intermediate color and black regions are composed of black and the developer of the three primary colors, the peripheral portion of the black region is emphasized, and even when misregistration occurs in the printer, the intermediate color If the (3 colors) and the black registration shift are within N pixels, the intermediate color and the black will not become white. This is shown in a printed sectional view in FIG. 5 (the output level of the low level signal generation circuit 8 is the lowest and the output level of the high level signal generation circuit 9 is the highest). As described above, in the present invention, by providing the portion D (corresponding to the portion a in FIG. 4), white or low-level YMC signal remarkably causes an image even if the registration shift occurs at the point where the intermediate color changes to black. It can prevent deterioration.

In the present invention, the Y, M, and C densities are set to low levels when one pixel before and after a certain target pixel and the target pixel are determined to be black. However, N pixels (N: It can be easily inferred that it is effective when the width of one pixel is small by using (natural number) as a criterion.

Further, the present invention can be processed by a microcomputer or the like, and a simple flowchart in that case is shown in FIG. As shown in FIG. 3, in S1, the Y, M, C and black data of the pixel of interest are read out, and in S2, it is judged from the Y, M, and C among them that the pixel signal is black, and it is black. If so, proceed to S3. If not, proceed to S4. In S3, the black data is set to a high level signal and the process proceeds to S5. In S5, it is determined whether all N pixels before and after the target pixel are black.
If s, proceed to S6. If No, proceed to S7. In S6, the three primary color signals (Y, M, C) are set to low levels and proceed to S8. In S7, the three primary color signals remain unchanged and proceed to S8. In S4, the black signal remains unchanged and proceed to S8. At S8, Y, M, C and black signals are output or written in an appropriate memory.

Further, it goes without saying that the present invention can be applied not only in the main scanning direction of an image but also in the sub scanning direction.

[Effect] As described above, according to the present invention, a black image is reproduced clearly according to the determination result of whether or not the pixel of interest represented by the digital color component signals of a plurality of colors is a predetermined black pixel. Therefore, by selectively outputting the first black component signal corresponding to UCR or the second black component signal having a higher level than the first black component signal as the black component signal of the pixel of interest, for example, black It is possible to ideally reproduce high-density black such as characters and intermediate-level black such as photographs, and it is possible to ideally reproduce black in an image.

[Brief description of drawings]

FIG. 1 is a circuit block diagram showing an embodiment of an image processing apparatus according to the present invention, FIG. 2 is a block diagram showing an example of a black judgment circuit, and FIG. 3 is a flowchart showing an example of image processing according to the present invention. FIG. 4 is a diagram showing an example of a signal output according to the present invention, and FIG. 5 is a diagram showing an example of a printed section. 1 ... Black judgment circuit, 2, 3, 4, 5, 6 ... Register, 7 ... Encoder, 11, 12 ... Data selector.

Claims (1)

[Claims] 1. A color image processing device for color-correcting digital color component signals of a plurality of colors for each pixel and outputting a corrected digital color component signal including a black component signal. A signal generating means for each of them, a determining means for determining whether or not the pixel of interest represented by the digital color component signals of the plurality of colors is a predetermined black pixel, and a black color depending on the determination result by the determining means. In order to reproduce the image clearly, UC is used as the black component signal of the pixel of interest.
A color image processing device comprising: a signal processing unit that selectively outputs a first black component signal corresponding to R or a second black component signal having a higher level than the first black component signal.