JPH0453355B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (1) Technical field to which the invention pertains The present invention relates to an image signal processing system, particularly a color recording device such as a facsimile machine or a printer, or a color reading device, in which the gradation level of characters in a photograph is divided into two levels. The present invention relates to an image signal processing method that provides means for improving the contrast of a multicolor image portion that is a value.

(2) Conventional technology Conventional color recording methods include (i) a full-color method that can reproduce gradations of the three primary colors of yellow, magenta, and cyan to reproduce photographs, etc., and (ii) a limited color method. , for example, yellow, magenta, cyan,
There are two types: a multicolor system that reproduces red, green, blue, and black colors without gradation. The multi-color method is suitable for printing out illustrations, color graphs, etc. from a computer, for example, and has the characteristics of high contrast between graphs, illustrations, text, etc., making it easy to see the graphs, illustrations, text, etc.; Reproduction of full-color images such as photographs that require tone reproduction is not always sufficient. On the other hand, the full-color method can reproduce photographs that require delicate gradation reproduction with good naturalness.
Furthermore, graphs, illustrations, text, etc. can be reproduced.
Color reproduction ability is greater than multicolor. However, in general, in the case of a full color method, multicolor parts,
For example, the contrast of text for weights and explanations in photographs, or the contrast of multi-colored parts of graphs and sentences in images containing photographs, graphs, and sentences becomes smaller. This is because when reading a color original using an image sensor, etc., in the case of a full-color method, the point where the color changes in the multicolor part of the original, for example, the place where the color changes from white to black, becomes blurred, and the color change point of the multicolor part of the original becomes blurred. This is because the shading is reproduced more faithfully than necessary.

Figure 11 shows the output signal from the reading section when reading a multicolor original, where a is the original, b
c is a full-color output signal corresponding to the interval A-A', and c is a multi-color output signal corresponding to the interval A-A'. As is clear from the figure, in the case of the full color method shown in b, the document density is insufficient, the signal level is low, and the edges are blurred. On the other hand, in the case of multicolor c,
Since it is binarized, sufficient density is obtained, and the edges are sharp and contrast is high. Naturally, the full-color method b is superior from the viewpoint of fidelity to the original, but from the viewpoint of visibility, contrast is more important than fidelity in multicolor parts.

As described above, conventional full-color color reading or recording apparatuses have the disadvantage that the contrast of multicolor parts in full-color images is reduced.

(3) Object of the Invention An object of the invention is to provide an image signal processing method that can prevent a decrease in the contrast of a multicolor portion in a full color mode in a color reading device or a color recording device.

(4) Structure of the Invention (4-1) Features of the Invention and Differences from the Prior Art The present invention is characterized in that when in full color mode, red (R), green (G), and blue (B ) or for each primary color image signal of yellow (Y), magenta (M), and cyan (C),
The most important process is to compare the gradation level of the current pixel of each color and the adjacent pixel, extract the multicolor part from the full color image, and then binarize the pixels of the extracted multicolor part for each color. The characteristics are as follows. This method differs from the conventional technology in that means for extracting a multi-color part in a full-color image and means for binarizing the pixels of the extracted multi-color part are added as image signal processing in the full-color mode.

(4-2) Embodiment Figure 1 is a basic configuration diagram of an embodiment of the present invention, in which 1 is a multicolor part extraction circuit, 2 is a binarization circuit, 3 is a selector, and each color has 16 gradations ( 4bit) is an example. The following image signal processing is performed on each of the input Y, M, and C (or R, G, and B) image signals.

First, the current pixel P _i of the input image signal and the previous and subsequent pixels
Based on the relationship between P _i-1 and P _i+1 , the multi-color part extraction circuit 1 determines whether the current pixel belongs to a full-color part or a multi-color part in a color image. When it is determined that the current pixel P _i belongs to the multicolor part, the current pixel P _i is converted into 2 by the binarization circuit.
The data is converted into a value and output via the selector 3.
Further, when it is determined that the current pixel P _i belongs to the full color portion, the image signal is not processed, and the input image signal is outputted via the selector 3 as it is.

FIG. 2 shows a simple circuit for the multicolor part extraction circuit 1, in which 4 and 5 are delay circuits, 6,
7 is an arithmetic circuit, 8 and 9 are comparators, and 10 is an arithmetic circuit.
It is an OR circuit. The arithmetic circuits 6 and 7 calculate the absolute value of the gradation level difference between the current pixel P _i and the previous pixel P _i-1 |P _i −P _i-1
|, and the absolute value of the gradation level difference between the current pixel P _i and the next pixel P _i+1 |P _i −P _i+1 |. Arithmetic circuit 6,
The output from 7 is compared with a constant value K by comparators 8 and 9, and when |P _i −P _i-1 |>K or |P _i −P _i+1 |>K, the pixel is binarized. A signal is output.

FIG. 3 shows a specific example of the operation of the circuit shown in FIG. In the figure, the gradation levels "0" to "15" of the 4-bit image signal are shown as bar graphs, and
This is an example where TH=7 and K=5. As is clear from the figure, pixels where the gradation level difference between adjacent pixels is "5" or more are binarized and are converted to "0" or "15".
It will be one of the values. For each color of Y, M, C, the binarized pixels are Y, M, C, R,
Since it is one of seven colors (G, B, and black) and has a high density, a high-contrast multicolor image without color unevenness can be obtained in a full-color image.

Note that full-color areas and multi-color areas are distinguished based on the gradation level difference between adjacent pixels, and this takes advantage of the fact that the variation in shading in multi-color areas is considerably larger than in full-color areas. Therefore, if the value of K is appropriately selected, it is possible to distinguish between a full-color part and a multi-color part with a considerable probability.

FIG. 4 shows a first embodiment of the multicolor part extraction circuit 1 according to the present invention, in which 11 is an arithmetic circuit;
2 and 13 are comparators, and 14 is a flip-flop. The arithmetic circuit 11 calculates the current pixel P _i and the previous pixel P _i-1
The difference P _i −P _i-1 is calculated, and the comparator 12,1
3 detects P _i −P _i-1 >K and P _i-1 −P _i >K. Furthermore, the flip-flop 14 is set when P _i -P _i-1 >K, and reset when P _{i-1 -P i >K, and the flip-flop 14 is set when P i -P i-1} >K, and is reset when P i-1 -P _i >K, and the pixel whose gray level level is K or higher is higher than the pixel whose gray level level is K or higher. The pixels up to the reduced number are binarized. FIG. 5 shows a specific example of the operation of the circuit shown in FIG. While the tone level remains at the original "14", it is now "15" in FIG. 5, and density unevenness within the multicolor area is reduced.

FIG. 6 shows a second embodiment of the multicolor part extraction circuit according to the present invention, in which 15 is a comparator;
16 is an AND circuit. A specific example of operation is shown in FIG. In this embodiment, a comparator 15 and an AND circuit 16 are added to the example shown in FIG. 4, and the binarization process is effective only for pixels where P _i >TH by the comparator 15. Therefore, like the pixels with i = "6" to "10" in Fig. 7, the output of the flip-flop 14 becomes "1" and the pixels below TH (for example, low-density text) are not subjected to the binarization process. It can be prevented from disappearing due to twisting. In FIG. 7, the slice level TH' of the comparator 15 and the slice level TH of the binarization circuit 2 (FIG. 2) are set to the same value, but it is also possible to set TH'≠TH.

8 to 10 show examples in which the multicolor processing circuit 18 of the present invention shown in FIG. 1 is applied to a specific device. 8 and 9 show examples in which the multicolor processing circuit 18 is applied to an input/output device such as a color facsimile or a computer, and the multicolor processing circuit 18 is connected to the transmitter 1.
7. It is built into one of the receivers 19. FIG. 10 shows an example in which a reading section 21 and a recording section 22 are integrated into a facsimile or copying machine 20 for both sending and receiving purposes.

(5) Effects of the Invention As explained above, according to the present invention, the outlines of multicolor parts such as characters, graphs, and illustrations in a full-color image are emphasized, resulting in a sharp image without color unevenness. Furthermore, the naturalness of full-color image parts such as photographs is not degraded. Furthermore, since full-color images and multi-color images are automatically distinguished, the operator does not have to be careful about specifying the document mode.

[Brief explanation of the drawing]

Fig. 1 is a basic configuration diagram of an embodiment of the present invention, Fig. 2 is a simple circuit for a multicolor part extraction circuit,
Figures 4 and 6 show the multicolor part extraction circuit 1, respectively.
Embodiment configuration diagrams, Fig. 3, Fig. 5, Fig. 7, Fig. 8
10 to 10 are explanatory diagrams showing an example of an apparatus to which the present invention is applied, and FIG. 11 shows full color and multicolor signal waveform diagrams. 1...Multicolor part extraction circuit, 2...Binarization circuit, 3...Selector, 4, 5...Delay circuit, 6,
7, 11... Arithmetic circuit, 8, 9, 12, 13, 15
...Comparator, 10...OR circuit, 14...Flip-flop, 16...AND circuit, 17...Transmitter,
18...Multicolor processing circuit, 19...Receiver, 2
0... Copy machine, 21... Reading section, 22... Recording section.

Claims (1)

[Claims] 1. In an apparatus for obtaining a color recorded image based on an image signal containing color information, yellow, magenta, cyan, or red of the image signal containing gradation information;
For each color of green and blue, a means is provided to compare the gradation level of each adjacent pixel, and the gradation level is determined from the pixel where the gradation level changes from low density to high density and the difference in gradation level is more than a certain value. The range of pixels up to which the density changes from high density to low density and the difference in gradation level is a certain value or more is set as the target range of binarization processing, and other pixels are not binarized. An image signal processing method characterized by outputting.