Digital standards conversion: Comparison of colour decoding methods
Abstract
A number of PAL and NTSC decoding methods, several of which involve comb filters based on line delays, are compared, primarily for use in standards conversion. To simplify comparisons, the circuits are all converted into a general form consisting of a chrominance pass filters, used to obtain luminance and a chrominance demodulator. The theoretical performance of each circuit is summaried as a set of vertical frequency characteristics which show luminance and chrominance resolution, cross luminance and cross color and, where present, other crosstalk and aliasing effects. In addition, practical impressions of the performance of each method were obtained from a fully decoder using line-locked sampling and switched filters. The optimum PAL decoding arrangements for direct viewing, for subsequent recoding to PAL and for standards conversion are all found to be different. For direct viewing, a two line luminance circuit with nulls to reject subcarrier components, combined with a two line version of the conventional delay line chrominance circuit produces the most acceptable pictures.
- Publication:
-
NASA STI/Recon Technical Report N
- Pub Date:
- June 1982
- Bibcode:
- 1982STIN...8230428C
- Keywords:
-
- Color Coding;
- Decoding;
- Digital Techniques;
- Frequency Converters;
- Luminance;
- Delay Circuits;
- Demodulation;
- Television Systems;
- Communications and Radar