JPS63304384A - Picture restricting color display device - Google Patents

Abstract

PURPOSE:To select the restricted number of colors from an inputted image with the small consumption of a memory by forming a cluster specification art and a histogram forming part, and simultaneously executing histogram formation and clustering. CONSTITUTION:When an image to be displayed is inputted to an image input part 11, the cluster specification part 12 specifies the neighboring area of picture element data in a color space around the data as a cluster. The histogram forming part 13 updates the frequency of the center color of the cluster to which the picture element data belong to form a histogram. A similar color is clustered by the specification part 12 and the histogram increasing only the appearing frequency of the center colors of respective clusters is obtained from the formation part 13. Even if colors having high appearance frequency in the histogram are successively selected by a look-up table setting part 14, selection of only similar colors can be prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to an image-limited color display device that displays an image using only a limited number of colors.

A conventional display device having a limited number of colors that can be produced simultaneously has a configuration as shown in the block diagram of FIG. In FIG. 4, 41 is an image input unit, and 42 is a lookup table showing the relationship between the intensity of red, green, and blue colors, that is, R-G-B, and the number assigned to that color, that is, the color number. be. 43, 44, 45 are R respectively
-GB D/A converter, and 46 is a display. Each pixel data of the input image represents a color number. With this configuration, it is not possible to directly display an image in which each pixel data is represented by the intensity of red, green, and blue. For this reason, a display device has been developed that selects several colors that are simultaneously generated from such an image, assigns a color number to each color, and converts each pixel data into an appropriate color number for display. This display device has a configuration as shown in the block diagram of FIG. 5, for example. In FIG. 5, numeral 51 is an image input section that inputs the original image, and 52 is a histogram generation section that counts the appearance frequency of each color of each pixel data obtained from the image input section 51 and generates a histogram. 53 is a limited color selection section that selects a limited number of colors corresponding to the number of simultaneous color generation from the histogram obtained from the histogram generation section, and the resulting colors and color numbers assigned to the colors are stored in the lookup table 5.
Set to 4. 55 is a pixel data conversion section that converts each pixel data obtained from the image input section 51 into an appropriate color number. 56 is an image display section that displays an image from the color number output from the pixel data conversion section 55 and the lookup table 54; The image display section 56 is connected to R-G in FIG.
-B D/A converters 43, 44, 45 and a display 46.

Various algorithms for color selection in the limited color selection section 53 have been proposed in the past. For example, varnish
I.G.R.N.B.H Computer Graphics Volume 16 Number 3 (1982), pages 297 to 307 (SI
GGRAPR, Coi+puter Graphics
Vol, 16 (1982) No, 3 p, p, 29
7-307), which simply selects a limited number of colors from the top of the histogram, and which examines the axis on which colors are most widely distributed in the color space and creates a color space using the median value of the distribution range for that axis. The same process is repeated for each divided subspace to obtain a limited number of subspaces, and the average color of each subspace is selected. Also, IEICE Technical Report Image Engineering IE86-4 (1986) the second of
Divide the color space published on pages 5 to 30 into small subspaces, repeat clustering of the subspaces under certain conditions to obtain a limited number of subspaces, and then calculate the color that appears most frequently in each subspace. There are things to choose from.

Many also offer a limited number of 256 colors.

Problems to be Solved by the Invention However, in the above configuration, if a limited number of colors are simply selected from the top of the histogram, the pixel data converter 55 must determine which selected color each pixel data is close to. Since each pixel must be investigated, the processing takes a lot of time, and the method of obtaining a limited number of subspaces has the problem of not only increasing the processing time but also requiring a large memory area as a work area. In addition, the number of simultaneous colors is small (
As the number of colors increases, the problem arises that simply selecting a limited number of colors from the top of the histogram results in only similar colors being selected.

In view of this, it is an object of the present invention to provide an image-limited color display device that can quickly select a limited number of colors while consuming less memory, and can also be adapted to a configuration in which the number of colors produced simultaneously is small.

Means for Solving the Problems The present invention includes an image input unit that inputs an image, and a cluster designation unit that designates the neighborhood of pixel data obtained from the image input unit in a color space as a cluster centered on the pixel data. , a histogram generation unit that generates a histogram by updating the frequency of the center color of the cluster specified by the cluster specification unit to which the pixel data obtained from the image input unit belongs; and a histogram generated by the histogram generation unit. a lookup table setting section that selects a limited number of colors in order of frequency of appearance, assigns color numbers, and sets a lookup table that associates color numbers with colors; and cluster information obtained from the cluster specification section. and a pixel data conversion unit that converts pixel data obtained from the image input unit into a color number using a color number corresponding to the color obtained by the lookup table setting unit, and a color number obtained from the pixel data conversion unit. and an image display unit that displays an image together with the look-up table.

Operation According to the above-described configuration, when an image to be displayed is input to the image input section, the cluster designation section assigns a neighboring area to the pixel data obtained from the image input section as a cluster in a color space centered on the pixel data. specify. The histogram generation section updates the frequency of the color at the center of the cluster to which the pixel data belongs to the pixel data obtained from the image input section, and generates a histogram. Similar colors are clustered by the cluster specification section, and a histogram in which only the color at the center of each cluster has a high appearance frequency is obtained by the histogram generation section. Even if you select colors in descending order, similar colors will not be selected. Therefore, the lookup table setting section may set colors in the lookup table in the order of colors that appear more frequently in the histogram. Furthermore, compared to the method of obtaining a limited number of subspaces, this method does not require a memory area to store information about subspaces or a work area for calculations, so processing can be realized with less memory space. In the pixel data conversion section, if the color at the center of the cluster to which the pixel data belongs is selected, it will be converted to the color number of that color, and if it is not, it is only necessary to check which selected color is closest, so all pixels This is faster than comparing the distance to the selected color. The image display section displays an image using the color number of each pixel obtained by the pixel data conversion section and the lookup table. Through the above processing, a limited number of colors can be selected from the image input to the image input section at high speed and with less memory consumption, and the image can be displayed even in a configuration in which only a small number of colors are generated simultaneously.

Embodiment FIG. 1 is a block diagram showing the configuration of an image limited color display device in an embodiment of the present invention. In FIG. 1, reference numeral 11 indicates an image input section for inputting an image, and reference numeral 12 indicates a cluster specifying section for specifying the neighborhood of pixel data obtained from the image input section 11 in the color space as a cluster centered on the pixel data. 13 is a histogram generation unit that generates a histogram by updating the frequency of the color at the center of the cluster to which the pixel data obtained from the image input unit 11 belongs; 14 is a histogram generation unit that generates a histogram from which the color appears more frequently than the histogram generated by the histogram generation unit 13; This is a lookup table setting unit that sequentially selects a limited number of colors, assigns color numbers, and sets them in a lookup table 15 that associates color numbers with colors. 1
6 converts the pixel data obtained from the image input section 11 into an appropriate color number using the cluster information obtained from the cluster specifying section 12, the color obtained from the lookup table setting section 14, and the color number corresponding to the color. A pixel data converting section 17 is an image display section that displays an image from the color number obtained from the pixel data converting section 16 and the lookup table 15.

The operation of the image limited color display device of this embodiment configured as described above will be described below.

An image in which each pixel is represented by the intensity of red, green, and blue is input to the image input section 11. A cluster specifying section specifies the vicinity of pixel data obtained from the image input section 11 in the RGB color space as a cluster centered on the pixel data. When the pixel data obtained from the image input section 11 already belongs to any cluster, the cluster specifying section does not newly specify the raster. The histogram generation unit 13 updates the frequency of the color at the center of the cluster to which the pixel data obtained from the image input unit 11 belongs, and creates a histogram. FIG. 2 shows this image input section 1, cluster specifying section 12,
3 is a flowchart showing the operation of the histogram generation section 13. FIG. 21 and 28 represent the beginning and end of this flowchart. At 22, a frequency counter used for generating a histogram is initialized, and at 23, image pixel data is input. In 24, it is examined whether this pixel data belongs to any cluster, and if it does not belong to any cluster, in 25, the neighborhood of that pixel data in the color space is specified as a new raster centered on that pixel data. do. Thereafter, in step 27, the frequency of the color at the center of the cluster to which the pixel data belongs is updated. In each cluster, frequency counters for colors other than the center color of the cluster are not updated, so store a pointer to the center color of the cluster to which that color belongs in the frequency counter for colors other than the center color of the cluster. By doing so, the histogram and cluster information can be overlapped in the memory area, reducing memory consumption. At step 27, it is checked whether the entire image has been processed, and if the image has not been processed, inputting pixel data at step 23 is repeated.

Through the above processing, a histogram in which clustering is considered for the frequency counter is obtained.

After the clustered histogram is obtained, the lookup table setting unit 14 in FIG. . Next, the pixel data converter 16 uses the lookup table setting unit 1
4, and the cluster information obtained from the cluster specifying section 12, the pixel data obtained from the image input section 11 is converted into an appropriate color number.

FIG. 3 is a flowchart showing the operation of the pixel data converter 16. 31 and 37 represent the beginning and end of this flowchart. At 32, pixel data is input. At step 33, it is examined whether the color at the center of the cluster of this pixel data is the color selected by the lookup table setting section 14, and if so, at step 34, the selected color is set as the color at the center of the cluster, and only if it is not. Step 35 searches for the selected color that is closest to the pixel data in color space. At step 36, check whether the entire image has been processed, and if not, input pixel data at step 32.
repeat.

After the above processing, an image is displayed on the image display section 17 in FIG. 1 based on the color number obtained from the pixel data conversion section 16 and the lookup table 15.

If the number of simultaneous colors produced by the image display section 17 is large, the range specified as a cluster for pixel data is made small in the cluster specifying part 12, and if the number of simultaneous colors produced is small, the cluster specifying part 12
You can increase the range specified as a cluster using .

As described above, according to this embodiment, the cluster specifying section 12 that specifies clusters and the histogram generating section 13 that generates a histogram are provided, and by simultaneously performing histogram generation and clustering, the data input to the image input section 11 is A limited number of colors can be selected from an image at high speed without using much memory, and the image can be displayed even on an image display section 17 that can simultaneously develop only a small number of colors.

DETAILED DESCRIPTION OF THE INVENTION According to the present invention, a limited number of colors can be selected from an input image at high speed and with low memory consumption;
Even if the configuration is such that only a small number of colors are generated at the same time, the image can be displayed, so the practical effect is great.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of an image limited color display device according to an embodiment of the present invention, FIG. 2 is a flowchart showing the operations of an image input section, a cluster specifying section, and a histogram generation section according to an embodiment of the present invention. FIG. 4 is a flow chart showing the operation of the pixel data converter according to an embodiment of the present invention, FIG.
FIG. 5 is a block diagram of a conventional image-limited color display device. 11... Image input section, 12... Cluster specification section, 1
3... Histogram generation unit, 14... Lookup table setting unit, 15... Lookup table, 1
6... Pixel data conversion section, 17... Image display section. Name of agent: Patent attorney Toshio Nakao and one other person Figure 1 Figure 3 Figure 4

Claims (1)

[Claims] an image input section for inputting an image; a cluster specifying section for specifying a neighborhood of pixel data obtained from the image input section in a color space as a cluster centered on the pixel data; a histogram generation unit that generates a histogram by updating the frequency of the center color of the cluster specified by the cluster specification unit to which it belongs, and a limited number of colors in descending order of frequency of appearance according to the histogram generated by the histogram generation unit; a lookup table setting section that selects a color, assigns a color number, and sets it in a lookup table that associates the color number with the color; cluster information obtained from the cluster specification section and the color obtained from the lookup table setting section; a pixel data converting section that converts pixel data obtained from the image input section into a color number using a color number corresponding to the pixel data converting section; and displaying an image from the color number obtained from the pixel data converting section and the lookup table. An image-limited color display device comprising: an image display section.