Motion compensated prediction interframe coding system

Abstract

A motion compensated prediction interframe coding system which first measures characteristics regarding the fineness of a pattern or texture of a picture, which is represented by an input television signal and is divided into a group of continuous blocks each quantized by using a quantization step size, and changes the quantization step size into a smaller one if quantizes a block having a picture pattern or texture finer than patterns of the other blocks. Thereby, an amount of generated codes can be limited but a motion compensated prediction frame coding operation can be performed without degrading the fineness of the texture of the original input picture.

Description

BACKGROUND OF THE INVENTION1. Field of the InventionThis invention generally relates to a television system and more particularly to a motion compensated prediction interframe system for performing motion compensated prediction interframe coding of television signals.2. Description of the Related ArtRecently, with advance in techniques of moving picture coding, a motion compensated prediction interframe coding system has been developed as an efficient coding system for effecting an efficient coding of a color moving picture for use in a visual telephone (or video telephone), a video conference system, CD ROM, a digital video tape recorder (VTR) and so on. An example of a motion compensated prediction interframe coding system is described in T. Fukinuki: Multidimensional Signal Processing of TV Picture, Nikkan Kogyo Shinbun Company, Chapter 7 "Efficient Coding", pp. 213-291 (1988. 11. 15).When a large quantity of prediction error signals is generated, the motion compensated predictio...

AI Technical Summary

Benefits of technology

It is therefore a first object of the present invention to eliminate the first drawback of the prior art system, namely, to provide a motion compensated prediction interframe coding system which can improve the picture quality by calculating a second quantization step size for each block from a reference (i.e., a first quantization step size), which is calculated from an amount of generated codes as proportional to the visual fineness of each of the continuous blocks to be quantized by using the first quantization step size, and further quantizing the prediction error signals by using the second quantization step size, namely, by employing a second quantization step size, which is smaller than the first quantization step size, for the quantization of a block having a fine pattern to limit the amount of the generated codes and maintain the fineness of the block and to thereby improve the picture quality of the block having a fine pattern, as well as the picture quality of an entire picture.

Thus, the motion compensated prediction interframe coding system according to the fourth aspect of the present invention can limit the amount of the generated codes and improve the picture of a block, which should be coded by using the intraframe coding method and has a fine pattern and of which the averaged value of gray levels of pixels is greater or equal to a predetermined value, by measuring the fineness of a pattern of each block of the luminance signal contained in the input television signal in terms of the variance .sigma..sup.2 of the gray level and quantizing the orthogonal transform coefficients by use of a second quantization step size, which is obtained by multiplying the first quantization step size a value proportional to the fineness of patterns of blocks according to a threshold value modified on the basis of the averaged value of the pixels of the blocks, the variance of the gray level and the first quantization step size in such a manner to be smaller than the first quantization step size, for the quantization of a block, which should be code by the using intraframe coding method and has a fine pattern, other than blocks to be quantized by using the first quantization step size among the continuous blocks.

Problems solved by technology

Thus, the prior art system has a first drawback that the picture quality of the block having a fine patter is degraded, namely, what is called a "block distortion", which is a phenomenon that the block loses the fineness of the pattern thereof and comes to have a flat pattern, occurs due to the quantization of a prediction error generated from the block having a fine pattern and is visually perceived as degradation in picture quality.

Thus, the prior art system has another similar drawback (hereunder referred to as a second drawback) that the picture quality of the block, which should be coded by the interframe coding method, having a fine patter is degraded, namely, the "block distortion" occurs due to the quantization of orthogonal transform coefficients generated from the block having a fine pattern and is visually perceived as degradation in picture quality.

Thus, practically, it is not possible that the quantization step size is calculated or changed every block.

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