[opendtv] Re: Definition of Anamorphic
- From: Craig Birkmaier <craig@xxxxxxxxx>
- To: opendtv@xxxxxxxxxxxxx
- Date: Wed, 7 Oct 2009 11:06:32 -0400
At 3:58 PM -0500 10/6/09, Manfredi, Albert E wrote:
Poor choice of words. I meant to say, that would translate to an
aspect ratio of 1.5:1 were the pixels meant to be square.
The point of my thesis remains the same. Which is, pixels in the DVD
format are never square, whether for 4:3 or for 16:9 content. So
that the term "anamorphic," when related to DVD content, cannot mean
distorted with respect to a square pixel frame.
It must indicate, instead, "distorted with respect to a 4:3 frame,
requiring the compensating distortion in playback."
NO. Both ATSC and DVD use non-square samples for BOTH 4:3 and 16:9
aspect ratio sources.
In the case of 4:3 the pixels are narrower than they are tall (i.e.
720 x 480 versus 640 x 480 for square sample 4:3). Note that ATSC
does allow the square sample 640 x 480 format for the 4:3 aspect
ratio. To present in pillarbox on a square sample 16:9 display the
samples must be filtered to square at the resolution of the display
(e.g. 960 x 720 on a 720 line display).
In the case of 16:9 the samples are also narrower than they are tall
( i.e. 720 x 480 versus 854 x 480 for square sample 16:9). ATSC does
not permit the square sample version of 16:9 at 480 lines (854 x
480). SD-DVD does not support 854 x 480 either, as this exceeds the
sample rate for MPEG-2 MP@ML (10.4 Msamples per second). To present
widescreen on a square sample 16:9 display the samples must be
filtered to square at the resolution of the display (e.g. 1280 x 720
on a 720 line display).
Also true for "anamorphic" DVDs. The horizontal dimension in
playback is created from fewer pixels per unit length than the
vertical. I'm talking about source data pixels here, not diplay
system pixels.
True and false. For 4:3 source there are more samples than needed for
the square sample format at 480 lines, thus for a 480P display
samples would be reduced to 640. For a 16:9 source there are less
samples than needed for the square sample format at 480 lines, thus
for a 480P widescreen display the number of samples would increase to
854. For HD displays an SD-DVD must be upsampled to square at 720 or
1080 lines.
Regards
Craig
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