DigitalVideoAndHDTVAlgorithmsAndInterfaces.pdf

sampling, and it is difficult to imagine any future studio
standard being established with nonsquare sampling.
Resampling
Analog video can be digitized with square sampling
simply by using an appropriate sample frequency.
However, SDTV already digitized at a standard digital
video sampling rate such as 13.5 MHz must be resampled
– or interpolated, or in PC parlance, scaled – when
entering the square-sampled desktop video domain. If
video samples at 13.5 MHz are passed to a computer
graphics system and then treated as if the samples are
equally spaced vertically and horizontally, then picture
geometry will be distorted. Rec. 601 480i video will
appear horizontally stretched; Rec. 601 576i video will
appear squished. In desktop video, often resampling in
both axes is needed.
The ratio 10 ⁄11 relates 480i Rec. 601 to square
sampling: Crude resampling could be accomplished by
simply dropping every eleventh sample across each scan
line! Crude resampling from 576i Rec. 601 to square
sampling could be accomplished by replicating
5 samples in every 54 (perhaps in the pattern
11-R-11-R-11-R-11-R-10-R, where R denotes
a repeated sample). However, such sample dropping
and stuffing techniques will introduce aliasing.
I recommend that you use a more sophisticated interpolator,
of the type explained in Filtering and sampling,
on page 141. Resampling could potentially be
performed along either the vertical axis or the horizontal
(transverse) axis; horizontal resampling is the
easier of the two, as it processes pixels in raster order
and therefore does not require any linestores.
102 DIGITAL VIDEO AND HDTV ALGORITHMS AND INTERFACES