A STUDY ON OBJECTIVE PICTURE QUALITY SCALES FOR PICTURES DIGITALLY ENCODED FOR BROADCAST

Considering the trend towards adopting high efficiency picture coding schemes into digital broadcasting services, we investigate objective p icture quality scales for evaluating digitally encoded still and movin g pictures. First, the study on the objective picture quality scale fo r high definition still pictures coded by the JPEG scheme is summarize d. This scale is derived from consideration of the following distortio n factors; 1) weighted noise by the spatial frequency characteristics and masking effects of human vision, 2) block distortion, and 3) mosqu ito noise. Next, an objective picture quality scale for motion picture s of standard television coded by the hybrid DCT scheme is studied. In addition to the above distortion factors, the temporal frequency char acteristics of vision are also considered. Furthermore, considering th at all of these distortions vary over time in motion pictures, methods for determining a single objective picture quality value for this tim e varying distortion are examined. As a result, generally applicable o bjective picture quality scale is obtained that correlates extremely w ell with subjective picture quality scale for both still and motion pi ctures, irrespective of the contents of the pictures. Having an object ive scale facilitates automated picture quality evaluation and control .