JPH08256267A - Color image processor - Google Patents

Abstract

PURPOSE: To efficient set a coding object area with an optimum size while taking a visual characteristic of human being into when a chrominance signal of a color image signal is coded for a prescribed area such as a preset block or the like. CONSTITUTION: A color separate circuit 107 separates a color image signal to generate a luminance signal L*, and chrominance signals a*, b*, an edge detection section 108 separates the signal into a prescribed area based on the chrominance signals, an area discrimination section 120 sets plural coding object areas within a range of the prescribed area based on the characteristic of the luminance signal. An averaging circuit 111 obtains a mean value of the chrominance signal as to each of the plural coding object areas and uses an LUT 112 for encoding based on the average value.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a color image processing apparatus for efficiently compressing color image information.

[0002]

2. Description of the Related Art Conventionally, when encoding a luminance signal and a chromaticity signal of a color image, if the encoding is performed for each pixel, the amount of encoded data becomes very large, so that the image is divided into blocks. Then, the pixels in the block share the encoded data to some extent to reduce the amount of encoded data.

[0003]

However, in the above-mentioned prior art, when encoding a chromaticity signal in block units,
If encoding does not work well with the initially set block size, for example, if encoding with the initially set block size causes significant image degradation to the human eye, the initially set block is And must be changed to the coding target areas of different sizes.

The present invention has been made in view of the above conventional example. Therefore, when the chromaticity signal of the color image signal is encoded for each predetermined area such as a preset block, the code of the optimum size is encoded. An object of the present invention is to provide a color image processing device that efficiently sets a region to be converted in consideration of human visual characteristics.

[0005]

In order to achieve the above object, a color image processing apparatus of the present invention has the following constitution. That is, a generation unit that generates a luminance signal and a chromaticity signal from a color image signal, a dividing unit that divides the chromaticity signal into predetermined regions, and a plurality of units within the predetermined region based on the characteristics of the luminance signal. And a coding means for setting a coding target area and coding a chromaticity signal for each of the plurality of coding target areas.

[0006]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will be described in detail below with reference to the accompanying drawings. [Description of Image Processing Device (FIGS. 1 and 2)] FIG. 1 is a block diagram of the image processing device according to the present embodiment.

In the figure, 101 is a glass original placing table 102.
It is a color original placed face down. The color original 101 is illuminated from below by the lamp 100 and imaged on the R, G, B color separation sensors 104 by the rod lens array 103. In this way, the sensor 104 reads the color original 101 by photoelectric scanning, and the three primary colors (RG
The analog image signal of B) is converted and output. Sensor 1
Each of the R, G, and B analog image signals from 04 is held for a predetermined time by a sample hold circuit (S / H) 105, and based on the held voltage value, an A / D converter 106 outputs 8 for each color. Converted to bit digital data.

Reference numeral 107 denotes a color separation circuit that separates each input 8-bit signal into a luminance signal and a color difference signal.
It is decomposed into three-dimensional Cartesian coordinates in the uniform color space of CIE 1976, and brightness L * is used as a luminance signal and chromaticity coordinates a * and b are used as color difference signals.
You get *. The color separation circuit is not limited to the color separation into the L * a * b * color space.
Q or CIE 1976 L * u * v * or other color series may be used.

Numeral 108 inputs chromaticity coordinates a * and b * from the color separation circuit 107, detects the magnitude of chromaticity change in a preset block of a plurality of pixels, and determines the color of image data. It is an edge detection unit that detects an edge due to.

This change in chromaticity is detected, for example, by a *, b *.
The chromaticity signal is subjected to a differential process or the like in the block, and the differential value is compared with a predetermined threshold value to detect the magnitude of the change amount. Hereinafter, a block whose chromaticity change amount is larger than the threshold value will be called an edge block, and a block whose chromaticity change amount is smaller than the threshold value will be called a flat block.

Reference numeral 109 denotes a switch for inputting the detection result 118 from the edge detection unit 108 and selecting and inputting the a * and b * signals to either the averaging circuit 110 or 111. ) Is determined to be a flat block, a *, b * data 119 is input to the averaging circuit 110, and if it is determined to be an edge block, a *, b * data 11
It operates so as to input 9 into the averaging circuit 111.

The averaging circuit 110 calculates average values of a * and b * for all pixels in the block, and the averaging circuit 1
Reference numeral 11 divides the block into two areas, and calculates the average value of a * and b * for each area. A method of dividing into two regions is, for example, a lightness signal L * and chromaticity signals a * and b *.
This can be done by paying attention to the correlation in the edge part with.

Usually, L * and a *, b * have a low correlation, and therefore, even if the spatial resolution of a *, b * is reduced, the image does not deteriorate so much, but this correlation is obtained in the edge block. As shown in Fig. 2, the distribution of L * and a *, b
It can be considered that the distributions of * are almost the same.

FIG. 2 (A) shows the distribution of L *, and FIG. 2 (B) shows the distribution of a * in shades of 4 × 4 pixel block units (the distribution of b * is almost the same). is there. 2 (A),
In (B), one cell 21 corresponds to one pixel, and
The block is composed of 4 × 4 pixels.

The operation of the averaging circuit 111 will be described by focusing on the above points. First, the average calculating unit 121 obtains the average value L * / of L * in the target block, and the area determining unit 120 determines the target pixel block. The L * value of the pixel inside and the average value L * / are compared in size, and the block of interest is L * ≧ L * /
Divide into the area of * <L * /. Based on this area information, the averaging circuit 111 calculates the average value of a * and b * in the area of L * ≧ L * / and the average value of a * and b * in the area of L * <L * /. calculate. In this way, the average value of a * and b * of the target block is output from the averaging circuit 110 or 111 and input to the look-up table (LUT) 112 which is a coding table. Hereinafter, the processing of the LUT 112 and thereafter will be specifically described.

The chromaticity signal input to the LUT 112 is the average value (a0 * /, b0 *) of a set of a * and b * in the flat block.
/), Two sets of a * corresponding to the area in the edge block,
It is the average value of b * (a1 * /, b1 * / and a2 * /, b2 * /).

Therefore, in the LUT 112, two sets of edge blocks a1 * /, b1 * /, a2 * /, b2 * /
By encoding with a half bit number of a0 * / and b0 * / of the flat block, it is possible to equalize the amount of information in block units in both the flat block and the edge block.
That is, for example, in a flat block, (a0 * /, b0 * /) is regarded as one vector and vector-quantized into an N-bit code value C0, and in an edge block (a1 * /, b1 *).
It is only necessary to regard / as a vector and vector-quantize N / 2-bit code value C1 and (a2 * /, b2 * /) to N / 2-bit code value C2.

FIG. 3 is a diagram showing a coding example of flat blocks and edge blocks when N = 8.

Reference numeral 31 indicates an 8-bit code (C0) that encodes a flat block, 32 indicates an 8-bit code that encodes an edge block, and C1 and C2 indicate 4-bit codes corresponding to respective areas. There is.

Latches 115 and 116 in FIG. 1 are latches for producing such a code, the latch 115 is a 4-bit latch circuit, and 116 is an 8-bit latch circuit.

Reference numeral 117 is a compression circuit for performing compression processing on the luminance signal L * by a known method such as orthogonal transformation and vector quantization. [Description of Vector Quantization (Encoding) of Block (FIG. 3 to FIG.
6)] FIG. 4 shows a LUT 112 and latch circuits 115 and 11.
It is a figure which shows the connection with 6.

The LUT 112 is the averaging circuit 110 or 1
Average value 114 of a * and b * from 11 and the edge detection unit 10
The 1-bit detection signal 113 from 8 is input.
The block of interest is a flat block (detection signal 113 =
0), the LUT 112 has an 8-bit code (C
0) for 2 clock cycles. Code (C0)
The lower 4 bits are latched in the latch circuit 115 in the first clock cycle, and the 8-bit code (C0) is latched in the latch circuit 116 in the second clock cycle.

When the target block is an edge block (detection signal 113 = 1), the LUT 112 outputs C for both the upper 4 bits and the lower 4 bits in the first clock cycle.
A code of 1 is output, and a code in which the upper 4 bits and the lower 4 bits are both C2 is output in the second clock cycle. As a result, the code composed of C1 (4 bits) and C2 (4 bits) shown at 32 in FIG. 3 is latched in the latch circuit 116 in the second clock cycle.

FIG. 5 shows a * when the input original is a reflection original,
It is a figure showing distribution of ab * chromaticity signal.

The hexagonal vertices 401 to 406 are the six primary colors of subtractive colors, and are the colors of yellow (Y), green (G), cyan (C), blue (B), magenta (M) and red (R). Corresponds to the degree coordinate. Therefore, in order to quantize a * and b * of a flat block, the inside of the hexagon of FIG.
The look-up table is divided into (8-bit) areas and an 8-bit code is assigned to each area.
It is provided in 2.

On the other hand, in the edge block, the hexagonal area of FIG. 5 is divided into 16 (4 bit) areas, and a look-up table L is assigned so that a 4-bit code is assigned to each area.
The UT 112 must be configured. Therefore, focusing on the following points, the area division is performed. At the edge portion of the image, color reproducibility with respect to the input document is not so important. ⇒ Y, M, C, R, G, B 6 is mainly used in the edge part of the image.
It is often composed of primary colors and either white or black. ⇔ In the low-saturation edge part, if the area division is made rough, the change in color is noticeable.

An example of area division focusing on the above points is shown in FIG.
Shown in

In the figure, the area is divided into 16 areas 501 to 516, but the area is divided finely in the vicinity of the achromatic color (513
It can be seen that the division in the direction connecting the origin and the hexagonal vertex is finely divided.

By storing the look-up table having the above characteristics in the LUT 112, the unique 8-bit code C0 is obtained in the flat block, and the two 4-bit codes C1 and C2 are obtained in the edge block. Become.

As described above, the color image data is obtained by compressing a 1-bit code indicating whether a predetermined pixel block of the color image data is a flat block or an edge block, for example, an 8-bit code obtained by encoding the pixel block and L *. The compressed image data is represented by a multi-bit code.

The pixel configuration of the block and the chromaticity signal selection method in this embodiment are completely arbitrary. Also, the input signal does not have to be the R, G, B signals, and for example, NT
A signal obtained by A / D converting the SC YIQ composite signal as it is may be used, or I and Q may be treated as chromaticity signals.

As described above, according to this embodiment,
Efficient compression coding with a fixed data length can be performed regardless of the flat portion and edge portion of the image. Especially, since the chromaticity signal can be encoded with a sufficient number of bits in the flat portion, pseudo contour portions do not occur. In addition, there is an effect that it is possible to prevent the color from becoming dirty at the edge portion.

[0033]

As described above, according to the present invention, when a chromaticity signal of a color image signal is coded for each predetermined area such as a preset block, a color that is difficult to be recognized by the human eye. Optimum size to be encoded by setting more than one encoding target area for the chromaticity signal according to the characteristics of the luminance signal The encoding target area can be efficiently set in consideration of the visual characteristics of human eyes, and the color image can be encoded with little deterioration in image quality.

[0034]

[Brief description of drawings]

FIG. 1 is a block diagram of an image processing apparatus according to the present embodiment.

2A and 2B are diagrams for explaining the correlation between a luminance signal and a chromaticity signal at an edge portion. FIG. 2A shows an L * distribution and FIG. 2B shows an a * distribution of 4 × 4. The pixel blocks are shown in shades.

FIG. 3 is a diagram showing an example of bit configurations of an edge block and a flat block after encoding.

FIG. 4 is a diagram showing an example of a data format conversion circuit.

FIG. 5 is a diagram showing a distribution of chromaticity signals of a reflective original.

FIG. 6 is a diagram showing an example of region division.

[Explanation of symbols]

 31 coded code of flat block 32 coded code of edge block 101 color original 104 color separation sensor 105 sampling hold circuit (S / H) 106 A / D converter 107 color separation circuit 108 edge detection unit 109 selector 110, 111 average A digitization circuit 112 LUT 115, 116 Latch circuit 117 Compression circuit 120 Area determination unit 121 Average calculation unit.

Claims (1)

[Claims] 1. A generation unit that generates a luminance signal and a chromaticity signal from a color image signal, a dividing unit that divides the chromaticity signal into predetermined regions, and a predetermined region of the predetermined region based on a characteristic of the luminance signal. A color image processing device, comprising: a plurality of coding target areas set within a range; and coding means for coding a chromaticity signal for each of the plurality of coding target areas.