JPS5947914B2 - Color image encoding processing method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a color image encoding processing method, and particularly to a color image encoding processing method that efficiently encodes a color image and utilizes the correlation between color components.

Conventional color image encoding methods include the ΔPCM method, which is mainly used for the purpose of transmitting television signals.
The DPCM method and the like are known.

Among these, the ΔPCM method samples the television signal with an appropriate clock, compares the signal level at each sampling point with the signal level immediately before it, and calculates the difference between the two.
This is a method of encoding as an M code. Furthermore, the DPCM method is a method in which the signal level at each sampling point is predicted using the signal levels of the immediately preceding pixel and neighboring pixels, and the difference between the predicted value and the actual signal level is encoded. These encoding methods are intended to be applied to real-time television signal transmission systems, and due to processing time constraints, the encoding process is limited to simple processing, and the amount of code is 3 per pixel. ~4 bits were required. Therefore, as an encoding method used for converting color images into files, etc., where processing time is relatively loose, the method has the disadvantage that the amount of code cannot be compressed sufficiently. An object of the present invention is to divide a sampled image into blocks including a plurality of sample points (pixels), encode each block as a unit, and efficiently encode the image by utilizing the correlation between color components.

Figure 1 shows the sample points of the sampled image (hereinafter referred to as
In the figure, 1 is the sampled color image, 2 is the pixel, and 3, 4, and 5 are the colors corresponding to the color components obtained when color image 1 is separated into three color components. Each represents a plain image.

6, 7, and 8 are pixels (denoted as P and j) on color planes 3, 4, and 5, respectively.

The values of pixels P, , j will now be written as [Pij].
In the present invention, as shown in FIG. 1b, the color image 1 is
The color components are separated into two color components, and the distribution of values [P,,] on each color plane is encoded.

The separation method into color components is red, green, and blue (R, G
, B), and a method that separates the color information into luminance information Y and color information 1 and Q are known. It is. FIG. 2 is an explanatory diagram of the encoding method based on the present invention, where 9 is one color plane obtained when separating into color components,
10 has (MXm) color planes 9 (m=4 in the figure)
) including pixels, block Bk when divided into blocks
It is.

Figure 2b is an enlarged view of block Bk.
PI again the pixels inside! ′, (1, J=1,2,・
・・・・・・m) A detailed explanation of the encoding method based on the present invention will be given below.

This encoding method converts the distribution of pixel values [p1(k),] in block Bk shown in FIG.
kO,akl and AkO,a}. The resolution component elements, , , (1, J = 1, 2,) showing the distribution of 1.

BkO is the value [PO
:k), ] is smaller than the threshold Tk, B
kl is a set of pixels greater than or equal to the threshold Tk.

MkO and mkl are the numbers of pixels in the sets BkO and Bkl, respectively. As the resolution component 1,, for example, the set Bk
It is possible to assign "0"" to the pixels belonging to O, and """ to the pixels belonging to the set Bkl. At this time, any pixel P, :k) in block Bk will be approximated by one of the tone components AkO, ak, obtained by equation (1). That is, if the resolution component 1, is ``O'', the pixel value [P, lk),] is approximated by Ak, and if it is ``1'', it is approximated by Ak.As is clear from the above explanation of the encoding method, ,
The code amount q per pixel on one color plane is the sum of 1 bit of the resolution component and the per pixel share of the code amount of the two tone components given to the block Bk. .

Here, l is the code amount of the tone components AkO and akl. Therefore, the code amount Q per pixel of a color image that is a combination of three color planes is as follows.

Now, if l=6 (bits) and m=4, Q=5.25 bits, and the code amount of the resolution component reaches nearly 60% of the total code amount. The main object of the present invention is to reduce the amount of code for this resolution component. Now, when considering the separation of a color image into R, G, and B components, it is well known that there is a strong correlation between the separated R, G, and B color components.

This indicates that the two-dimensional distribution of each resolution component for the three separated color planes takes a similar distribution. By utilizing this property, the encoding of the resolution component is performed for only one color plane, and the encoding of the resolution component for the other two color planes is omitted, thereby significantly reducing the amount of code. I can do it. On the other hand, Y, I,
There is a separation method into Q signals.

It is known that when YIQ separation is performed, the Y component has higher frequency components than the I and Q components. This corresponds to the fact that the Y component has a higher spatial resolution component than the I and Q components. Therefore, only the resolution component for the Y component color plane having the highest frequency component is encoded, and this is also shared as the resolution component J for the I and Q component color planes. Y
The resolution component is significant only for the component color planes,
If it is meaningless for the I and Q component color planes, I
, two gradation components Ak, respectively, determined by equation (1) for the Q component color plane. and Ak,, have the same or similar distribution. As mentioned above, when a color image is separated into multiple color planes and encoded, the resolution component is the color with the highest spatial frequency.
・Coding is performed only on the plane, and other colors are encoded only on the plane.
- In plane encoding, the amount of code is reduced by sharing the distribution of one encoded resolution component.

Regarding the gradation components, simply (1
) may be performed, or more efficient coding may be performed. FIG. 3 is a block diagram of a configuration example of an apparatus to which the color image encoding processing method of the present invention is applied, in which 11 is a color image to be encoded, 12 is an input section, 13 is a color component separation section, 14- 1,14-2,1
4-3 is A/3 for each separated color signal component.
D conversion section, 15-1, 15-2, 15-3 are buffers for storing color signal components in block units; 16 is a control section;
17-1, 17-2, and 17-3 are encoding units for each color component, and 18 is a code storage file unit. Next, the operation of the device will be explained using the YIQ separation method as an example.

Color image 11 is scanned by input section 12 and sent to a YIQ color separation section.

The input section 12 corresponds to a normal color TV camera, and during scanning, the signal value of each pixel is extracted for each block. If the scanning is raster scanning, the signal is converted into a signal in units of blocks by memory elements for several scanning lines. It is clear that such scan conversion can be easily implemented using known imaging techniques. Next, the color component separation section 13 converts the color signal taken in by the human power section 12 into R.
, G, B or Y, I, Q, etc., and can be easily realized using known techniques. The image signals separated into color components by the color component separation section 13 are sent to A/D conversion sections 14-1, 14-2, 1, respectively.
After being sampled by 4-3 and made into a digital signal, the buffer memo is sent in block units.
2, 15-3. Next, the control unit 16 controls the buffer memory that stores the color component with the highest spatial frequency (for example, the Y component in the case of the YIQ separation method).
is 1 or 2 or 3 or less) and the corresponding encoding unit 17-
Access * and start encoding unit 17-* (l)
Find the gradation component and resolution component defined in the equation.

The resolution component determined by the encoder 17-* is sent to the controller 16.
under the control of the other two encoders 17-**, 17-*
Sent to ** (**, *** are different from * among 1, 2, and 3). Then, the encoders 17-** and 17-** send the sent resolution component elements. , using (l
) set Bk, in the equation. and Bk, , and find the gradation component of the corresponding color component. The selection of the color component with the highest spatial frequency in the control unit 16 may be specified externally depending on the separation method into color components, or
This may be performed on a block-by-block basis using Fourier transform processing or the like based on the signal value distribution within each block.

Furthermore, it is clear that the encoding processing section which calculates the gradation component and the resolution component according to equation (l) can be easily realized using ordinary microprocessor technology. The information encoded in this manner is stored in the code storage file section 18. FIG. 4 is a block diagram showing an example of the configuration of a decoding device that decodes codes encoded by the above-described encoding method and stored in the code storage file 18 to obtain a display image signal. In the figure, 19-1, 19-2, 19-3 are decoding processing units, 20-
1, 20- 2, 20- 3 is a buffer memory section having a pixel code capacity for one screen; 21 is a color component synthesis section;
22 is a display device. Next, we will discuss the operation.

The decoding processing units 19-1, '19-2, and 19-3 receive tone components, center '. , mind:,aι'. , Ak("}, a, a, and resolution component elements, , are read out in units of blocks, gradation component codes are arranged in units of blocks according to the distribution of resolution components, , and are sequentially stored in the buffer memory 20. -1,2
Store in 0-2, 20-3. The color component synthesis unit 21 selects a color plane image reproduced as a two-dimensional array of tone component codes in the buffer memories 20-1, 20-2, and 20-3, which corresponds to the displayed scanning line. The gradation component codes of pixels are read out, D/A converted, and each color component signal is created. Thereafter, the respective color component signals are combined and output to the display device 22. It is clear that the D/A conversion technology and color component signal synthesis processing used in these decoding devices can be easily realized using conventional technology. In the above description, it has been shown that the encoded signal is filed, but it goes without saying that the present invention can be applied to a transmission system that directly transmits the encoded signal via a transmission path.

As explained above, when a color image is decomposed into color components and encoded, the correlation between the color components is used to share the resolution component among multiple color components to reduce the amount of code. This method has the advantage that color images can be encoded, stored, or transmitted with a small amount of code.

[Brief explanation of drawings]

Fig. 1 is an explanatory diagram explaining the principle of the encoding method according to the present invention, Fig. 2 is an explanatory diagram explaining the encoding method of one color plane in which an image is separated into color components, and Fig. 3 is an explanatory diagram explaining the encoding method of a single color plane in which an image is separated into color components. FIG. 4 is a block diagram showing the configuration of an embodiment of an encoding device to which the encoding method according to the invention is applied. FIG. 4 is a block diagram showing the configuration of an embodiment of the decoding device compatible with the encoding method according to the invention. 1...Color image, 2...Pixel, 3,
4, 5... Color plane image, 6, 7, 8
...Pixel, 9...Color plane,
10...Proc, 11...Color image, 12...Input section, 13...Color component separation section, 14...A/ D conversion section, 15...
...Batsufu Otsu 16... Control section, 17...
... Encoding section, 18 ... Code storage file section, 19 ... Decoding processing section, 20 ... Buffer memory section, 21 ... Color component synthesis Part, 2
2.t...display device.

Claims (1)

[Claims] 1 For three color component images obtained by separating a color image into three color components and digitizing each color component image, each color component image is divided into small rectangular blocks of the same size, and each block is divided into Divide the included pixels into two groups, find the tone component corresponding to the average value of the pixel values of the pixels in each group for each group, and identify the group to which each pixel belongs based on the pixel value of the pixels in the block. In an encoding method that approximates the resolution component corresponding to the binary code to which the pixel belongs and the gradation component of the group to which the pixel belongs, the color component image that corresponds to the color component image with the highest spatial frequency among the three color component images For the first color component image, the pixel values of the pixels in each block are compared with a predetermined threshold, and a group of pixels with a pixel value smaller than the threshold is divided into a group of pixels with a pixel value equal to or larger than the threshold. By dividing into groups, the gradation component and resolution component for the first color component image are obtained, and for the second and third color component images corresponding to the remaining two color component images, By grouping pixels so that the two-dimensional array of resolution components is the same as that of the corresponding block of the first color component image, and determining and encoding the tone components of the block according to the grouping, A color image encoding processing method characterized in that a two-dimensional array of resolution components of a second color component image and a third color component image is made in the same manner as a two-dimensional array of resolution components of a first color component image.