A versatile DCT coding system for HDTV with interlaced and progressive scanning

Abstract

HDTV implies various new technologies with strong implications for information and imaging technology, and telecommunications as well. Various standards, image formats and scanning modes are under discussion for various applications. Until now of HDTV signals via satellite and B-ISDN a video data rate of 125 Mbit/s was considered to be necessary for distribution. But the fast development of efficient coding methods indicates that also for HDTV the trend is moving toward lower bit-rates. That could open new areas of application in the range of 50 Mbit/s. We present a DCT coding concept that is versatile with respect to scanning mode - interlaced and progressive - and data rate. It shows very good image quality also at the low data rate of 50 Mbit/s. It contains efficient mechanisms for local adaptivity which are applied for switching between different coding modes and for the control of quality parameters. For this purpose local image analysis is largely performed. Criteria and activity measures are computed in the spatial domain in a regular ways as sums of absolute spatial differences. To some extent analysis is also performed in the DCT domain for coefficient thresholding and an adaptive assignment of Huffman coding classes. An advanced computationally efficient motion estimation method is described. It improves the coding performance and open the possibility for coding with much lower bit-rates. We have performed a comparison experiment at 125 Mbit/s between interlaced and progressive scanned scenes. The most noticeable gain with the progressive scene is the absence of aliasing defects. This positive effect influences the quality more than a slightly increased coding noise and advocates the usage of the progressive scan format for high quality studio application. In a second experiment an interlaced scene is coded at 50 Mbit/s with the usage of the advanced motion estimated prediction scheme. The result is very promising with respect to a possible application for distribution.