[opendtv] Re: Definition of Anamorphic
- From: "Manfredi, Albert E" <albert.e.manfredi@xxxxxxxxxx>
- To: "opendtv@xxxxxxxxxxxxx" <opendtv@xxxxxxxxxxxxx>
- Date: Wed, 7 Oct 2009 11:22:04 -0500
Craig Birkmaier wrote:
>> 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.
Whaaaat??
ATSC uses 1280 X 720 for HD. 1280/720 = 1.78:1 = 16:9
Therefore, each pixel must be square.
ATSC uses 1920 X 1080 for HD. 1920/1080 = 1.78:1 = 16:9
Therefore, each pixel must be square.
ATSC uses 640 X 480 for SD. 640/480 = 1.33:1 = 4:3
Since this SD mode can only be used for 4:3 material in ATSC, each pixel must
be square.
The only non-square pixels used in ATSC are when the 704 X 480 mode is used for
SD. That mode can be used for either 4:3 or 16:9, so that in both cases, the
pixels are non-square. (The ratio 704/480 = 1.46:1.)
On the other hand, DVDs *only* use non-square pixels, whether for 16:9 or for
4:3, as I said previously.
(A "square pixel" is a picture element which REPRESENTS a square shape, in the
mosaic that creates the whole frame.)
>> 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.
Since I was talking about anamorphic DVDs, i.e. the 16:9 DVDs, the statement is
true. (And this also mimicks the situation with 35mm anamorphic film, where the
horizontal dimension provides less resolution than the vertical.)
Had I included the 4:3 DVDs, then I would have said that in 4:3 DVDs, you get
more resolution in the horizontal than you do in the vertical.
Bert
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