JP2001306055A - Color palette generating and referring method and its device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent image quality from deteriorating at the displaying of image data to be expressed with full colors by limited colors, while using color palettes and to realize a high-speed processing. SOLUTION: Respective two-dimensional color spaces of an R-G plane, an R-B plane and a B-G plane are extracted from a three-dimensional color space, having three axes of R, G, B and arbitrary color values positioning at the vicinity of diagonal lines of the respective two-dimensional color spaces are selected and a B value, a G value and an R value are assigned respectively to respective quarter palettes, based on the selected color values and the B value, the G value and the R value are assigned to remaining quarter palettes equally. Moreover, 23n colors to be expressed with respective (n) bits of R, G, B are thinned into 23m colors to be expressed with respective (m) (provided, n>m) bits of R, G, B based on the specification of a display device and tables to be assigned to a fixed color palette having limited colors are preliminarily prepared by an amount which is equivalent to the 23n colors and the assigning of fixed limited colors is performed by referring to the tables.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and an apparatus for generating and referencing a color palette suitable for use in a color display system for displaying image data expressed in full color in a limited color by using a color palette.

[0002]

2. Description of the Related Art In recent years, high-performance specifications such as high-resolution display and multi-color display have been required for a display device at the core of a man-machine interface. In particular, in the multi-color display, a method of transmitting each of the three primary colors of RGB to the display with an analog voltage has been developed. By changing the brightness of each color in proportion to the voltage on the display device side, a multi-color display including an intermediate color can be realized. It has become possible. In this case, video D
The analog voltage is changed stepwise using an A converter. If 8 bits are used for each pixel of RGB (voltage change is 2 ⁸ = 256 steps), 256 ³ = 1
Display of 6,777,216 colors (16,780,000 full colors) becomes possible.

By the way, apart from the above-described display device having a full-color display function, the number of colors that can be displayed at one time on the entire display screen is eight due to the limitation of the capacity of the frame buffer memory.
There is a display device having only a limited color display function of about 256 colors. In this case, a table called a palette memory is prepared in hardware, for example, which of 256 colors corresponds to 16.78 million full colors is stored, and a method of converting at the time of image display is adopted. .

[0004]

According to the above-mentioned prior art, to select a limited display representative color, a color used uniformly in each of the RGB color spaces is selected, or a median cut color quantization is performed. Using the technique, the color of the palette was selected in accordance with the input image. In the latter, the converted color value is not the average value of the color values of the pixels located in the vicinity of the target pixel, but the median value of those pixels (the n / 2th color value if there are n pixels). Things. According to these methods, the former has noticeable image deterioration, and the latter has a drawback that although the image quality is improved as compared with the former, it takes time for processing and is not realistic.

In order to assign a representative color selected as described above, a distance between all representative colors is determined for each pixel of the original image, and a representative color which minimizes the distance is assigned, or The color space is divided into local areas in advance, and a list of a plurality of representative colors included in each of the local areas is prepared. When each pixel of the original image is given, the local area to which the color of the pixel belongs There is a method in which distance calculation is performed only for the representative color and the assigned color is obtained. As described above, the three-dimensional distance calculation is performed, the load on the controller including the software increases, and the time required for the processing cannot be ignored in performance.

[0006] The present invention has been made in view of the above circumstances, and is based on a three-dimensional color space having three axes of R, G, and B.
Each of -G plane, RB plane, and BG plane
A three-dimensional color space was extracted, and the color distribution in a general natural image was analyzed. As a result, there was little white and black, and the color distribution was concentrated on the diagonal lines of R and G, R and B, and B and G. ,
An arbitrary value located near the diagonal line of each two-dimensional color space is selected, and based on the selected value, a B value, a G value, and an R value are assigned to each quarter palette, and the remaining 1
A color palette generation method that prevents degradation of image quality and realizes high-speed processing by generating a fixed color palette of limited colors by equally assigning R, G, and B values to a パ レ ッ ト palette It is intended to provide the device.

Further, ²³ⁿ colors represented by n bits of R, G, and B are represented by m bits (where n> m) of R, G, and B based on the specifications of the display device. A controller including software that eliminates the need for three-dimensional distance calculation processing by thinning down to ^3m colors and preparing a table that matches the color palette in advance for ^23m colors and performing color assignment processing by referring to the table It is another object of the present invention to provide a method for generating and referencing a color palette, which realizes high-speed processing while reducing the burden on the user, and an apparatus therefor.

[0008]

According to an aspect of the present invention, there is provided a color display system for displaying image data expressed in full color in a limited color by using a color palette.
From the three-dimensional color space having three axes of R, G, and B, two-dimensional color spaces of RG plane, RB plane, and BG plane are extracted, and the diagonal neighborhood of the two-dimensional color space is extracted. , And based on the selected color value, a B value, a G value, and an R value
Assign values and assign R value, G value,
The fixed color palette of the limited color is generated by uniformly assigning the B value. As a result, the deterioration of the image quality is not noticeable, and the calculation for the median cut color quantization becomes unnecessary, so that the time required for creating the palette can be reduced.

According to a second aspect of the present invention, in addition to the color pallet generating method of the first aspect, a ²³ⁿ color represented by n bits of each of RGB is converted to m (where n >
m) thinning 2 ^3m color represented by bits, the table assigned to the limited color fixed color palette 2 ^3m and color separation prepared in advance, and allocates a limited color which is the fixed by referring to the table I decided that. This eliminates the need for three-dimensional distance calculation processing, thereby reducing the load on the controller including software and realizing high-speed processing.

According to a third aspect of the present invention, in a color display system for displaying image data expressed in full color in a limited color by using a pallet, an RGB plane, an RB plane and an RB plane are pre-programmed. Means for selecting an arbitrary color value located near the diagonal of each of the two-dimensional spaces of the plane and the BG plane; and, based on the selected values, B values, G values, R Means for generating a fixed color palette of the limited color by allocating values and equally allocating R, G, and B values to the remaining 1/4 pallet. According to the above configuration, the deterioration of the image quality is not noticeable, and the calculation for the median cut color quantization is not required. Therefore, it is possible to provide a pallet generation device in which the time required for pallet creation is reduced.

The invention described in claim 4 is the third invention.
In addition to the color pallet generation device described in
The ²³ⁿ colors represented by bits are thinned out to ^23m colors represented by m (where n> m) bits of RGB based on the specifications of the display device, and are assigned to the fixed color palette of the limited color. A means for setting and storing a table for ^{23 m} colors in advance and a table reference means for allocating the limited color by referring to the table are provided. According to the above configuration, a three-dimensional distance calculation process becomes unnecessary, so that a load on a controller including software is reduced, and a color pallet generation and reference device that realizes high-speed processing can be provided.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, an embodiment of a method for generating and referencing a color palette and an apparatus therefor will be described with reference to the drawings. FIG. 1 is a diagram illustrating a basic concept of a pallet generation method according to the present embodiment. FIG. 1 shows, in order to analyze the color distribution in a general natural image such as a photograph, a three-dimensional color space having three axes of R, G, and B shown in FIG.
(B) RG plane shown in the figure, (c) RB plane shown in the figure
The two-dimensional color spaces of the plane and the BG plane shown in FIG. 3D are extracted, and the color distribution in each plane at that time is plotted. As can be seen from FIG.
There are few values close to white and black, R and G, R and B, and B and G
It can be seen that the color distribution is concentrated on the diagonal line of.

Therefore, the color palette generating method according to the present embodiment selects an arbitrary value located near the diagonal of the two-dimensional color space in each plane as shown in the table of FIG. (For example, G: 1 in FIG.
5 and R: 0, G: 14 and R: 1,..., G: 0 and R:
15) Based on the selected values, B values (for example, B:
0, 4, 8, 12), G value and R value are assigned. Further, a fixed color palette of limited colors is generated by equally assigning R, G, and B values to the remaining 1/4 color palette.

FIG. 2 is a block diagram showing an embodiment of a color palette generation and reference device according to the present invention. FIG.
In the figure, reference numeral 1 denotes a CPU serving as a control center, which performs display control according to a program recorded in the program memory 2 and generates and refers to a pallet according to the present embodiment. 3 is a search table memory. In this embodiment, it is assumed that a total of 12-bit data is obtained by thinning out each of the R, G, and B bits from 8 bits to 4 bits, and 4096 tables matching the color palette are prepared in advance. The palette memory 6 is selected by referring to the table memory, and a desired color display is performed. FIG. 3 shows an example of the data structure of the search table memory 3.

Reference numeral 4 denotes an LCD controller. LCD
The controller 4 controls the display of the LCD display monitor 7 capable of displaying 256 colors, for example, based on the contents programmed by the CPU 1. 5 is a video RAM (hereinafter referred to as a video RAM) in which image data is written in a bitmap format.
(Hereinafter simply referred to as VRAM) and has a function of storing an index into the palette memory 6. Reference numeral 6 denotes a color pallet memory of 256 colors fixed according to the method shown in FIG. Reference numeral 8 denotes a bus to which the CPU 1, the program memory 2, the search table memory 3, the LCD controller 4, and the VRAM 5 are commonly connected.

Hereinafter, the operation of the color pallet generation and reference device according to the present embodiment will be described in detail with reference to FIGS. Prior to the operation, the CPU 1 needs to prepare fixed palette data in the color palette memory 6 and the matching table shown in FIG. 3 in the search table memory 3 in advance. As shown in FIG. 1, the fixed palette data is generated by displaying image data that can be displayed in full color in a limited color by using a color palette, as shown in FIG.
From a three-dimensional color space having three axes of B, R-G plane, R
-Extract each two-dimensional color space of the B plane and BG plane, select an arbitrary color value located near a diagonal line of each two-dimensional color space, and, based on the selected color value, each 1 /
This is achieved by assigning B, G, and R values to the four pallets, and equally assigning the R, G, and B values to the remaining パ レ ッ ト pallet. In this way 2
The fixed color palette data of 56 limited colors is generated, and this value is written in the color palette memory 6.

Further, the CPU 1 converts R, G, B into, for example, 4096 colors represented by 4 bits based on the specifications of the LCD display device, based on the specifications of the LCD display device. The search table that matches the fixed color palette created as described above is
Prepare 96 colors in advance. The search table thus created is written in the search table memory 3. The contents of the search table created here are shown in FIG. When an image display command arrives from the host, the CPU 1 performs color assignment by referring to the search table memory 3 and performs display processing via the LCD controller 4.

After the above processing, the CPU 1 stores the data in the 24-bit full-color image data storage memory 9
By referring to the search table memory 3 shown in FIG. 3 for the 4-bit full-color image, an optimal palette index value (0 to 255) of each pixel is selected. Subsequently, the CPU 1 writes the index values of the selected palette to the VRAM 5 in the order of the pixels of the bitmap. Then, the LCD controller 4 displays an image on the LCD display monitor 7 capable of displaying 256 colors based on the data in the VRAM 5 and the palette memory 6.

As described above, the color pallet generation and reference device according to the present embodiment converts an RG plane, an RB plane, and a B-plane from a three-dimensional color space having three axes of R, G, and B. When the two-dimensional color space of the G plane is extracted and the color distribution in a general natural image is analyzed, there are few white and black, and the color distribution is concentrated on the diagonal lines of R and G, R and B, and B and G. Therefore, an arbitrary value located near the diagonal of each two-dimensional color space is selected, and based on the selected value, a B value and a G value are respectively stored in each quarter palette.
Value, R value and assign R value,
By generating a fixed color palette of limited colors by equally assigning the G value and the B value, deterioration of image quality is prevented and high-speed processing is realized.

The ²³ⁿ color represented by n bits of each of R, G, and B is converted to m, each of R, G, and B based on the specifications of the display device.
(However, thinning out to ^23m color represented by (n> m) bits)
A table matching the color palette is prepared in advance for ^23m colors, and color allocation processing is performed by referring to the table, thereby eliminating the need for three-dimensional distance calculation processing and reducing the load on the controller including software. In addition, high-speed processing is realized.

[0021]

As described above, according to the first aspect of the present invention, the R-value is calculated according to the color distribution obtained by analyzing a natural image.
A diagonal value is selected from each of the two-dimensional spaces of G, RB, and BG, and based on the selected value, the B value is obtained for RG, and the G value is obtained for RB. The value is R for BG
By creating a fixed palette according to the rule of equally allocating the values and filling the empty space of the pallet with the value of the RGB equal allocation, a full-color image can be expressed without deterioration. According to the second aspect of the present invention, each of the RGB is thinned to, for example, 4 bits and processed as 12-bit data, thereby preparing 2 ¹² (4096) tables matching the fixed color palette in advance. In color matching, by referring to this table, approximation calculation by three-dimensional distance calculation becomes unnecessary, and high-speed processing can be realized.

According to the third aspect, the deterioration of the image quality is not noticeable, and the calculation for the median cut color quantization is not required. It is possible to provide a pallet generation device that can be realized by a small-capacity VRAM without using a pallet. According to the fourth aspect of the present invention, a three-dimensional distance calculation process is not required.
It is possible to provide a color pallet generation and reference device that reduces the load on a controller including software and realizes high-speed processing.

[Brief description of the drawings]

FIG. 1 is a diagram showing a basic concept of a palette generation method according to the present embodiment, where (a) is a three-dimensional color space having three axes of R, G, and B, and (b) is an R-color space; (C) is a two-dimensional color space of an RB plane, (d) is a two-dimensional color space of a BG plane, and (e) is a color space of each color palette. It is a table to configure.

FIG. 2 is a block diagram showing a color palette generation and reference device according to the present embodiment.

FIG. 3 is a diagram showing a data structure of a search table memory shown in FIG.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... CPU 2 ... Program memory 3 ... Search table memory 4 ... LCD controller 5 ... Video RAM (VRAM) 6 ... Palette memory 7 ... 256 color LCD display monitor

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 5B057 CA12 CA16 CB12 CB16 CE17 CE18 CH18 DB06 5C060 BA09 BB01 BC01 DB00 HB27 JA18 5C066 AA13 CA00 CA08 CA23 EB02 EF04 GA02 KD06 KE09 KE17 KM13 LA03 5C079 HB01 LA02 MA28 LA28 NA11 PA05 5C082 AA01 BA34 BB15 BB51 BB53 CA12 CA54 DA53 DA71 DA73 MM10

Claims (4)

[Claims] 1. A color display system for displaying image data expressed in full color in a limited color by using a color palette, comprising: a three-dimensional color space having three axes of R, G, and B; Each two-dimensional color space of the B plane and BG plane is extracted, and an arbitrary color value located near a diagonal line of each of the two-dimensional color spaces is selected. Generating a fixed color palette of the limited color by assigning a B value, a G value, and an R value to each of the palettes, and equally assigning an R value, a G value, and a B value to the remaining 1/4 of the palette. A color palette generation method characterized by the following. 2. The method according to claim 1, further comprising the step of: generating ²³ⁿ colors represented by n bits of R, G, and B based on the specifications of the display device. m (where n> m)
Thinning out to ^23m colors represented by bits, preparing a table assigned to the fixed color palette of the limited colors for the ^23m colors in advance, and allocating the fixed limited colors by referring to the table; And a method for generating and referencing a color palette. 3. A color display system for displaying limited color by using a palette with respect to image data expressed in full color, wherein a color plane of an RG plane, an RB plane, and a BG plane based on contents programmed in advance. Means for selecting an arbitrary color value located near the diagonal of each two-dimensional color space; and assigning a B value, a G value, and an R value to each quarter palette based on the selected value, and Means for generating a fixed color palette of the limited color by equally assigning R, G, and B values to a パ レ ッ ト palette. 4. In addition to the color pallet generation device according to claim 3, ^23.sup.n colors represented by n bits of each of R, G, and B are set based on the specifications of the display device. m (where n> m)
Thinning 2 ^3m color represented by bit, performed means for 2 ^3m color separation preset stores a table assigned to a fixed color palette of the limited color, the allocation of the limited color by referring to the table the table A reference device, comprising: a color palette generation and reference device.