TABLE OF CONTENTS In video and audio signal processing, it is often necessary to take a set of sample values and produce another set that approximates the samples that would have resulted had the original sampling occurred at different instants at a different rate, or at a different phase. This is called resampling. (In PC parlance, resampling for the purpose of picture resizing is called scaling.) Resampling is an essential part of video processes such as these:
Chroma subsampling (e.g., 4:4:4 to 4:2:2)
Downconversion (e.g., HDTV to SDTV) and upconversion (e.g., SDTV to HDTV)
Aspect ratio conversion (e.g., 4:3 to 16:9)
Conversion among different sample rates of digital video standards (e.g., 4 f SC to 4:2:2, 13.5 MHz)
Picture resizing in digital video effects (DVE)
One-dimensional resampling applies directly to digital audio, in applications such as changing sample rate from 48 kHz to 44.1 kHz. In video, 1-D resampling can be applied horizontally or vertically. Resampling can be extended to a two-dimensional array of samples. Two approaches are possible. A horizontal filter, then a vertical filter, can be applied in cascade (tandem) this is the separable approach. Alternatively, a direct form of 2-D spatial interpolation can be implemented.
| Note | I write resampling ratios in the form input samples:output samples. With my convention, a ratio less than unity is upsampling. |
Upsampling produces more result samples than input samples. In audio, new samples can be estimated at a higher rate than the input, for example when digital...
