Digital standards conversion: Interpolation theory and aperture synthesis
Abstract
A frequency domain approach is used to investigate digital interpolation for standards conversion. To illustrate the background theory, one-dimensional sampling and interpolation is described in general terms, including methods for synthesising interpolation apertures and the effects of aperture quantisation. With the two-dimensional vertical-temporal sampling of television scanning, interpolation can be carried out as two one-dimensional processes or, with improved performance but somewhat greater complexity, as a single two-dimensional processes or, with improved performance but somewhat greater complexity, as a single two-dimensional process. Standards conversion impairments are shown to arise from the interpolation frequency characteristic departing from the ideal low-pass form in particular regions of the television signal spectrum. Also identified are the positions in the vertical-temporal spectrum of cross-luminance, cross-color and other residual impairments left by PAL or NTSC decoding. Using an experimental converter, apertures of duration two, three and four field periods were developed. For two-field apertures the performance is a compromise between movement judder, line flicker and vertical resolution; four-field apertures give stationary pictures of good resolution, free from flicker and other aliasing effects and reduce impairments left by color decoding. Movement impairments, remain because of the overlap of spectral components which results with normal television scanning.
- Publication:
-
NASA STI/Recon Technical Report N
- Pub Date:
- December 1984
- Bibcode:
- 1984STIN...8522857C
- Keywords:
-
- Interpolation;
- Standards;
- Synthetic Apertures;
- Television Transmission;
- Color;
- Color Television;
- Conversion;
- Decoders;
- Low Pass Filters;
- Luminance;
- Television Equipment;
- Communications and Radar