engleski

Subjective Assessment of Picture Quality

A general discussion of picture quality must take into consideration a variety of factors including spatial and temporal resolution and color reproducibility. In this paper the extent to which the quality of video signal is degraded by process of compression and decompression is considered. The aim of image and video data compression is to minimize bandwidth for transmission and memory for storage. Significant compression is achievable only by lossy compression algorithms which do not permit the exact recovery of the original image. The difference between the original and decompressed image is given as reconstruction error which is the standard objective measure of picture quality. Objective measurements quantify the influence of spatial resolution and there is not possible to infer the effect of variations in temporal domain (temporal resolution). 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 testing, by including variations in temporal domain, permits an integrated evaluation of picture quality. Subjective assessment is geared directly toward properties of the human visual system. It is based on a subjective judgment and a mental comparison of an external image with the image impressions stored and remembered more or less distinctly by the observer, who allows the loss of detail in areas too small to be resolved by the eye. In this paper we describe the methodologies for measurement of picture quality using subjective evaluation procedure. MPEG-1 coding algorithm for video compression was applied to four difference type of video sequences with different levels of movement at several bit rates to produce the test material for subjective assessment of picture quality. The results are evaluated using the mean opinion score as the measure of picture quality.

picture quality evaluation; subjective assessment; mean opinion score; test sequences

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