By Guy W. Beakley, Ph.D., StellaCom, Inc.
Conventional analog video test measurements are not adequate for compressed video signals. This is because digital video distortion and artifacts often are nonlinear, discontinuous and depend on picture content.
Most analog measurements assume that errors are of a continuous, linear nature. The only alternative to date has been subjective testing.
Formal subjective tests (e.g., CCIR 500) can provide reliable, relative measures of video quality. However, such testing is time consuming and expensive. Objective testing methods are needed to provide efficient, repeatable measures of video quality.
Presently, no standardized objective measures exist for digital video. We have implemented measures from a number of sources and others of our own design on a low-cost workstation.
These measures utilize complex digital image processing techniques to analyze differences between source and processed video sequences.
This paper presents some of these measurements and describes our implementation of an automated system to capture and test digital video quality.