JPS63304769A - Data compression system for color picture - Google Patents

Abstract

PURPOSE:To obtain a high compression ratio by taking out a luminance signal and first and second chrominance signals, and splitting the chrominance signals into the blocks different in size then encoding them. CONSTITUTION:In case of a color picture signal following a color television standard system, for example, the size of the block in a Q signal is set bigger than that in an I signal by utilizing that the characteristic of a visual space frequency in the color in the direction of a Q axis is inferior to that in the direction of an I axis. Namely, the color picture having a half tone is read, and the luminance signal and the first and the second chrominance signals are taken out. As for the first and the second chrominance signals, they are splitted into the blocks different in size and encoded at every block. Thus, two chrominance signals are respectively splitted into the blocks and the blocks different in size can be selected in accordance with the visual characteristics, whereby highly efficient data compression, in which redundancy is removed, can be executed.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to a data compression method for color images, and in particular, a method that is improved to improve the efficiency of transmission of color images having halftones. It is.

(Prior art) Conventionally, a patent application (Japanese Unexamined Patent Application Publication No. 2003-2012) proposed that data obtained by color-separating a color image into three primary colors is separated into blocks each consisting of a plurality of pixels for color data other than reference color data and encoded in block units. 59-8475).

(Problems to be Solved by the Invention) However, the conventional system does not take into consideration the fact that the visual characteristics of each color are different.
Since the blocks of each color are the same size, there is a drawback that redundancy is not sufficiently removed.

SUMMARY OF THE INVENTION Therefore, the purpose of the present invention is to eliminate the drawbacks of the above-mentioned conventional methods, remove redundancy, and compress data with high efficiency.
The object of the present invention is to provide a data compression method for color images that can be encoded.

[Means for solving problems]

In order to achieve such an object, in the present invention, for example, in the case of a color image signal according to the color television standard system, the color in the QIF 111 direction has a visual space that is smaller than that in the I-axis direction. Taking advantage of the inferior frequency characteristics, the size of the block in the Q signal is made larger than the block in the ■ signal.

That is, a color image having halftones is read, a luminance signal and first and second color signals are extracted, and the first and second color signals are divided into blocks of different sizes, and the blocks are divided into blocks. It is characterized by encoding each time.

[For production]

According to the present invention, two color signals are each divided into blocks, blocks of different sizes can be selected according to their visual characteristics, and highly efficient data compression can be performed by removing redundancy. .

〔Example〕

Hereinafter, the present invention will be described in detail with reference to the drawings.

FIG. 1 is a block diagram showing the configuration of an embodiment of the present invention.

In FIG. 1, a reader 1 reads an image and outputs signals of three primary colors, such as R (red), G (green), and B (blue). 2 is a converter which converts the output R, G, and B signals from the reader 1 into Y, 1 . Convert to Q signal. 3 and 4 are line memories, 5 and 6 are averagers, and 7.8 and 9 are encoders.

FIG. 2 is a flowchart showing the operation procedure on the fruiting end side shown in FIG. 1. The operation procedure of the embodiment shown in FIG. 1 will be explained below according to the flowchart shown in FIG. 2.

First, in step S1, a color image is read by a reader l, separated into three primary color signals (for example, RGB signals), and output. Then, in step S2, converter 2
Linear conversion is performed into a Y (Ili degrees) signal and two color signals of I and Q. Next, in step S3, the data for M lines is written into the line memory 3 for M lines. Next, in step S4, the data in the line memory 3 is written into a square of MXM pixels. It is divided into areas (blocks) and pixel data is read out for each block.

In step S5, the averager 5 calculates the average value of the data read from each pixel in the divided block. Next, in step S6, the average value output from the averager 56) is encoded by the encoder 7.

The Y signal is encoded as is by the encoder 8 for each pixel in step S7.

Regarding the Q signal, data for N lines is written in the line memory 4 for M lines in step S8. Next, in step S9, the data in this line memory 4 is
It is divided into square areas (blocks) of N pixels, and data of each pixel is read out for each block. In step S10,
An averager 6 calculates the average value of data read from each pixel in the divided block. Then step Sll
Then, the average value output from the averager 6 is encoded by the encoder 9.

Here, for colors in the Q-axis direction, the spatial frequency characteristics of visual perception are inferior compared to colors in the @ direction, so I am disappointed in the fact that No. 18 is difficult to perceive deterioration even if it is considerably blurred. M<
N, and the block of the Q signal is made large.

Regarding the values of M and N, in order to keep the deterioration of image quality within an acceptable range, 2≦M≦4.3≦
It was found through simulation that it is better to set N≦12.

As an example, let us assume that the block size is M=3. The value of N=9 is transferred, and the encoding method is to perform two-dimensional DPCM (differential encoding) with 7 quantization levels, then lluffma
The simulation results when n encoding is performed are described below.

The image used in this simulation consists of three primary color signals R,
It is a natural image with 8 bits/pixel each for G and B, and they are based on the Institute of Image Electronics Engineers chart (436 x 52
4 pixels), 5IDBA (StandardIma
ge Data Ba5e: University of Tokyo Institute of Industrial Science) V
These are three images: ANDRILL Char 1- (512 x 512 pixels) and a photo of children (360 x 234 pixels).

The amount of information of each encoded image is 2.30°3
．． 52,2.68 bit/pixel, decode and CR
When observing an image displayed on a T (cathode ray tube),
All images were evaluated as having satisfactory image quality.

As for the size of the block, the values of M and N can be varied by switching in several stages. That is,
If it is desired to transmit an image faithfully, it becomes possible to avoid blocking or to select the values of M and N according to the desired image quality and amount of information. Furthermore, it would be even more efficient if the values of M' and N are adaptively selected depending on the image.

Also, consider cases where you want to further reduce the amount of information to save memory capacity, or cases where you want to reduce the resolution of the encoded image to match the low resolution of the printer or CRT at the output unit. , Y signals can also be configured to be blocked.

As for block encoding, a method may be considered in which each block is divided into pixels having a value smaller than the average value and pixels having a value larger than the average value. That is, if GO is a set of pixels with values smaller than the average value, and Gl is a set of pixels with larger values, the resolution information is encoded by assigning 0 to pixels belonging to GO and 1 to pixels belonging to Gl,
As gradation information, the average value of data of pixels belonging to GO and the average value of data of pixels belonging to Gl are encoded.

Another possible method is to perform vector quantization on a block-by-block basis.

Regarding signal conversion, it is not limited to YIQ signals, but in the form of luminance signals and color difference signals, signals with higher orthogonality can be used, such as Y, CW, and CM used in high-definition televisions called Hi-Vision. By using a double signal, etc., it is possible to increase the waste compression efficiency.

〔Effect of the invention〕

As is clear from the above, according to the present invention, when the pixels of an image are divided into blocks, the luminance signal Y, which is visually important, is
A higher compression rate can be obtained compared to the conventional method by preserving the block size for the Q signal as is and making the block size for the Q signal larger than the block size for the ■ signal. Furthermore, when comparing images with the same amount of information, deterioration in image quality can be suppressed to a lower level.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing the configuration of an embodiment of the present invention;
FIG. 2 is a flowchart showing the operation of the embodiment shown in the first diagram. 1... Reader, 2... Converter, 3.4... Line memory, 5.6... Averager, ? , 8.9... encoder. FIG. 1 is a block diagram showing the configuration of an embodiment of the present invention.

Claims (1)

[Claims] A color image having halftones is read, and a luminance signal and a first
and a second color signal, and the first and second color signals are extracted.
A data compression method for a color image, characterized in that a color signal is divided into blocks of different sizes, and each block is individually encoded.