DECODING OF PAL SIGNALS

Abstract

The continued interest in T.V. singal decoding and the search for better techniques of achieving the same stem from the following : (i) the tremendous growth in international T.V. programme exchange necessitating standards conversion, (ii) the ever growing use of digital studio equipment and (iii) the growing demands for better quality T.V. broadcast and reception. In this dissertation, an attempt has been made to review the techniques of PAL decoding. The 3-D PAL spectrum forms the basis of understanding the filter action, performance comparison and classification of various filter types into 1-D, 2-D, 3-D, multi-D and adaptive filters. Although the simple conventional decoder provides satisfactory performance for normal T.V. viewing, for newer applications, some of the higher order filters are essential. The 4-field decoder has been found to be the best amongst higher order non-adaptive filters on the basis of performance and lesser complexities involved. This filter requires more storage facilities which are becoming progressively cheaper. Motion adaptive filters improve performance substantially. Adaptation strategies based on corrleation judgement yield highly satisfactory performance. Sum comb and difference comb based adaptive filter gives the overall best performance. Two simpler strategies for adaption, using correlation judgement, already implemented for NTSC have been extended to PAL decoding in the present work. Laboratory realisation of two line-delay filter structures has also been carried out to observe the complexiies involved in the design and improvement in performance over conventional filter. The test results indicate better performance.