Composite Television Coding: Subsampling and Interpolation
In a continuing study of predictive coding of composite NTSC television signals sampled at four times color subcarrier frequency (14.3 MHz), we describe results of subsampling and interpolation. Our ultimate goal is to demonstrate a coding system for a transmission rate of 45 M/bits/sec with full broadcast quality. Adaptive Differential Pulse Code Modulation (DPCM) with Variable Word-Length Coding is used to reduce the bit rate for the channel. But this requires a buffer to smooth the data output. Buffer overflow is prevented by quantizer selection and by subsampling. — We report on 4:3 and 2:1 subsampling ratios. We present a list of general considerations for the design of subsampling patterns and interpolation filters. Various subsampling patterns and corresponding interpolation algorithms and their effects on the quality of the coded picture are evaluated. Adaptive interpolation using samples from the present and the previous field is considered. Simple motion indication circuits for interpolation mode selection are described. A particular interpolation filter using chrominance information from the previous field is effective without resorting to adaptive interpolation. Picture quality judgements are based on observations of specially-selected worst-case conditions using real time processing on a mixed hardware/software experimental facility.
- Print ISSN
- 0036-1682
- Published
- 1982-08
- Content type
- Original Research
- DOI
- 10.5594/J00273