ABSTRACT
This chapter discusses the philosophy behind the design of a digital picture quality measure known as Picture Quality Scale (PQS). It describes this objective measure of image quality degradation caused by coding errors. The chapter shows that the PQS is applicable to a wide range of digital picture formats. Subjective assessment tests are widely used to evaluate the picture quality of coded images. The contrast sensitivity function of vision suggests a spatial frequency distortion weighting. Two psychophysical effects affect the perception of errors in the vicinity of high contrast transitions: visual masking, which refers to the reduced visibility of disturbances in active areas, and enhanced visibility of misalignments, even when they are quite small. The visual or subjective evaluation of image quality has drawn the attention of a number of researchers for many years, principally in relation to the evaluation of new transmission or coding schemes, and in the development of advanced television standards.
