A probability based model for subjective quality evaluation of MPEG-2 coded sequences

Many different quality metrics have been proposed in order to evaluate the reconstructed quality of compressed sequences. The most used measures are quantitative metrics based on a simple difference between frames. They are easily analytically tractable, reliable and can be reproduced at any time. Their main drawback is that they do not correlate well with subjective quality evaluations. Up to now, the only standardized method used to estimate the perceived quality of a coding system has been subjective assessment: a series of test scenes is shown to a number of selected observers in a controlled environment. This method of quality evaluation shows limits in term of time consumption and interpretation of results; this is mainly due to a multiplicity of elements: viewing conditions, choice of the test materials, timing of the presentation, scale of rating, etc., whose effects on the subjective quality scores are difficult to estimate. The purpose of many recent studies has been to develop objective measures having good correlation with the subjective quality scores in relation to the same video system and test scenes. A number of parameters influence the viewers´ judgment of the sequence quality; in this paper, we analyze the sequence motion effects on the viewers´ video quality perception. The paper proposes preliminary results in terms of the correlation between a linear model, that takes into account the “criticality” of the scene motion, and the results of formal subjective assessments