JPH0448276B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an image conversion device that converts a color image into a color image consisting of blocks containing only two or fewer types of colors.

[Conventional technology]

Conventionally, in this type of device, as described in Reference 1, when selecting two colors from three or more colors included in a block consisting of a predetermined number of pixels, the frequency of appearance within the block is Two colors with a large number of pixels (that is, a large number of pixels having that color) were selected.

As an example, a case as shown in FIG. 5 will be explained. In the figure, the smallest rectangle represents a pixel, the middle rectangle represents a block, the alphanumeric symbol represents the type of color, and the size of the block is 4×4 pixels. Here, if the block 19 in the center is the block of interest, the block of interest 19 contains three colors: color A = 4 pixels, color B = 6 pixels, color C = 6 pixels, and the Two large colors: color B and color C
If you select , and change the pixels of color A to color B or color C, colors B and C will remain, and color A will disappear.

[Problem that the invention seeks to solve]

By the way, when looking at the vicinity of the block of interest 19 in FIG. 5, color A also exists in adjacent blocks 20 and 21, and there is a high possibility that the pixels of color A are important as figures. However, in the conventional example, only the block of interest is looked at, and two colors with high frequency are selected, so continuous important information such as color A is lost.
As a result, there was a problem in that continuous information, such as a line, was interrupted.

This invention was made to solve the above-mentioned problems, and when there is continuous information between the block of interest and blocks adjacent to it, it is easier to prevent the loss of this information than in the past. The purpose of this invention is to obtain an image conversion device that can perform the following steps.

[Means for solving problems]

The image conversion device according to the present invention includes a color number detection device that divides a color image input through an image input device into blocks each consisting of a predetermined number of pixels, and detects the number of types of colors included in each block. A frequency detecting means for detecting the appearance frequency of each color in each of the above blocks, a common color detecting means for detecting a color that is also included in an adjacent block among each color in each of the above blocks, and each of the above respective detecting means A two-color determining means for determining two or less colors to be retained for each block based on the output, and changing pixels of colors other than the two colors determined by the two-color determining means to one of the two colors mentioned above. pixel color changing means, and the two color determining means selects the sum of the frequencies of the top two colors in the frequency order of each color in the block of interest and the top two colors in the frequency order of the common color.
The sum of the color frequencies is compared, and if the difference is smaller than a predetermined threshold, the top two colors in the frequency order of common colors are determined, otherwise the top two colors in the frequency order of each color are determined. It is something.

[Effect]

In this invention, the number of color types and appearance frequencies in the block of interest and common colors with adjacent blocks are detected, and the detection results are used to determine two or less types of colors to be left in the block of interest, Pixels of colors other than these two colors are changed to one of the above two colors.

〔Example〕

An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is an overall configuration diagram showing each function of the image conversion apparatus according to the present invention, in which 1 is an image input means for inputting a color image, and 2, 3, and 4 are input means for inputting a color image through the image input means 1, respectively. A color number detection means for detecting the number of types of colors included in each block consisting of a predetermined number of pixels from a color image, a frequency detection means for detecting the appearance frequency of each of the above colors, and a frequency detection means for detecting the appearance frequency of each of the above colors; 5 is a two-color determining means for determining two or less colors to be left in each block based on the outputs of the respective detecting means; 6 is the two-color determining means; This is a pixel color changing means that changes pixels of a color other than the two determined colors to one of the two colors. As is clear from the figure, the image input from the image input means 1 is detected by the color number detection means 2, the frequency detection means 3, and the common color detection means 4 to determine the number of colors, frequency of appearance, and common colors for each block. Detected, and referring to these respective outputs, two colors are determined by the two-color determining means 5. Then, the pixel color changing means 6 changes the colors of pixels of colors other than the two determined colors in the block.

FIG. 2 shows an example of the system configuration of this image processing apparatus. Note that the same reference numerals as in FIG. 1 above correspond to the respective means described above, and 7 is a memory for temporarily storing a color image. First, the general operation of the main parts will be explained. A color image input by the image input section 1 is stored in the memory 7. The color number detecting section 2 detects and outputs the number of types of colors in one block, and if it is within two colors, the two color determining section 5 directly determines the colors that should remain in the block. In the case of three or more colors, the colors are determined by the two-color determining section 5 based on the outputs of the frequency detecting section 3 and the common color detecting section 4. The common color detection unit 4 detects the colors commonly included in the block of interest and the blocks around it. When processing is performed in the order of raster scan from the upper left, the blocks to the right and below the block of interest are Since the color has not been determined, memory 7 will be referred to. Also, for the upper and left blocks for which two colors have been determined,
The output of the two-color determining section 5 can be referred to. Each of the above processes is carried out by a central processing unit (CPU) not shown in the memory 7.
This is done by accessing working memory (not shown).

Next, the above embodiment will be explained in detail with reference to the flowchart of FIG. In this embodiment, the input image is scanned twice in block units.

First, the number of colors is detected in the first scan (step 8), and if there are three or more colors, all colors are registered in the table in the working memory (step 9→
Ten). If the color is within two colors, that color is registered as the determined color (steps 9 to 11). Repeat steps 8 to 11 for all blocks (step 12).

Next, if there are blocks of 3 or more colors (step
13) In the second scan, perform the processing from step 14 onwards. Now, assume that the frequency and common color with surrounding blocks are detected (steps 14 and 15), and the result is as shown in FIG. In Fig. 4, there are four colors in the block of interest, colors A, B, C, and D in order of frequency.
This indicates that colors A and C were common colors to the surrounding blocks. In this case, in step 16, the top two
The sum of the frequencies of the colors (A+B) and the sum of the frequencies of the two common colors (A+C) are compared, and if the difference is smaller than a predetermined threshold, the two common colors (A and C) are determined (step
17), otherwise the top two colors (A and B) are determined (step 18). Then, pixels of colors other than the two determined colors are changed to one of the two determined colors by the pixel color changing means 6. For example, the color is changed to the one that appears more frequently around the pixel to be changed. In this way, only two or fewer colors will be included within the block.

By doing this, continuous image information between blocks such as lines is preserved without being lost. By the way, in the case of fine lines, the line information may be lost even in the present invention. but,
In the block of interest (block with color C mixed in) 19 in Figure 5, the top two colors in order of frequency (colors B and C)
The sum of the frequencies is 12, the top two common colors (colors A and B)
The sum of the frequencies is 10, and the difference is 2. Therefore, if the threshold value is set to 3, the two colors that should be left are the common color 2.
colors (colors A and B), and line information (color A) remains.
As described above, according to the present invention, it can be said that there is an effect that it is possible to avoid losing continuous information when determining only based on frequency as in the conventional example.

In addition to the above embodiment, there are the following modifications. In the above embodiment, when there are three or more colors, the common color is always detected along with the frequency, but there are cases where the two colors may be determined based only on the frequency. For example, when the difference between the second and third place frequencies is greater than a predetermined threshold, the top two colors may be used. By using this to reduce the number of times common colors are detected, processing can be executed faster.

By the way, if the processing in steps 8 to 11 in FIG. It is not necessary to have a memory capacity of at least 3 block lines (3 lines per block).

In addition, in the above example, the size of the block is 4×
Although the explanation has been made using four pixels, it goes without saying that the present invention can be applied to blocks of other sizes as well.

〔Effect of the invention〕

As described above, according to the present invention, a color image input through an image input means is divided into blocks each having a predetermined number of pixels, and the number of color types contained in each block is detected. The detection means includes a frequency detection means for detecting the appearance frequency of each color in each of the blocks, a common color detection means for detecting a color that is also included in an adjacent block among the colors in each of the blocks, and each of the above detections. Based on the output of the means, determine the two or less colors that should be left for each block2.
A color determining means and two colors determined by the two color determining means.
pixel color changing means for changing a pixel of a color other than the color to one of the two colors, and the two color determining means selects the sum of the frequencies of the top two colors in the frequency order of each color in the block of interest; The sum of the frequencies of the top two colors in the frequency order of common colors is compared, and if the difference is smaller than a predetermined threshold value, the top two colors in the frequency order of the common colors are determined, and if not, the top two colors in the frequency order of each color are determined. By determining two colors, there is an effect that an image conversion device that does not lose continuous pixel information such as a line can be obtained compared to the conventional method.

Reference 1 “Conversion system that enables access to other image databases from a captain terminal”,
Nikkei Electronics, No.356, pp.159-166,
1984.11.19

[Brief explanation of drawings]

FIG. 1 is an overall configuration diagram showing each function of an image conversion device according to an embodiment of the present invention, FIG. 2 is a system configuration diagram of an image conversion device according to an embodiment of this invention, and FIG. 3 is the same as shown in FIG. 2. FIG. 4 is a flowchart for explaining the operation of the apparatus, FIG. 4 is an explanatory diagram showing an example of detection results according to an embodiment of the present invention, and FIG. 5 is an explanatory diagram for explaining the conventional technique. 1... Image input means, 2... Color number detection means, 3
...Frequency detection means, 4...Common color detection means, 5...
... Two-color determining means, 6... Pixel color changing means, 7...
memory. Note that the same reference numerals are used for the same or corresponding parts in the figures.

Claims (1)

[Claims] 1. A color number detection means that divides a color image inputted through an image input means into blocks each consisting of a predetermined number of pixels, and detects the number of types of colors included in each block. a frequency detection means for detecting the appearance frequency of the color, a common color detection means for detecting a color that is also included in an adjacent block among each color in each of the above blocks, and a common color detection means for detecting a color that is also included in an adjacent block; a two-color determining means for determining two or less colors to be used; and a pixel color changing means for changing pixels of a color other than the two colors determined by the two-color determining means to one of the two colors. ,
The two color determining means compares the sum of the frequencies of the top two colors in the frequency order of each color in the block of interest with the sum of the frequencies of the top two colors in the frequency order of the common colors, and determines if the difference is smaller than a predetermined threshold value. An image conversion device characterized in that, if the common color is determined to be the top two colors in order of frequency, if not, the top two colors are determined in the order of frequency of each color.