Introduction: state of the play and challenges of visual quality assessment

Quality of visual signals perceived by human observers has always been a critical issue, so has been the measurement of the signal quality throughout a process chain of acquisition/reproduction, encoding, transmission or storage, decoding, and visualization/display associated with a designated application or service in either analogue or digital form. Digital visual signals compressed using various coding techniques exhibit coding distortions which differ from those known to be associated with analogue visual signals and, therefore, require provision of both subjective and objective distortion or quality measures which quantitatively assess and evaluate the visual picture quality for the purposes of system or service evaluation and optimization. A number of fundamental issues are examined to put the current discussions and activities into perspective and context, including relationship between picture quality assessment and coding designs, how to measure effectiveness of visual signal compression performance, different scales used for visual quality assessment and their intended applications, picture distortion or quality ratings for rate-perceptual-distortion (RpD) optimization.