Objective and Subjective Measuruments for Video Compression System

In this paper the extent to which the quality of video signal is degraded by process of compression and decompression is considered. Traditional objective video signal quality measurements based on static test signals are not able to characterise the picture degradation due to compression and decompression. These measurements are indirect and resulting distortions of test signals determine video-processing characteristics. Signal compression algorithms reduce bit rates by removing redundant or irrelevant information. Redundancy is a function of picture content. Therefore objective measurements have limited effectiveness in predicting the quality of compressed images as seen by the observes. There is no general method known for this type of evaluation except subjective evaluation. Subjective measurement is geared toward properties of human visual system and permits an integrated evaluation of picture quality. But, subjective measurement takes a large amount of time and resources and results are not always repeatable. In this paper we present an overview of the methodologies for measurement of picture quality using objective and subjective evaluation procedure. The results of objective testing using a set of test signals in compressed video system are given. The paper outlines a need for new objective picture quality measurement method providing good correlation to subjective measurements.