Re: 704 x 480 NTSC, where from?

peter wrote:

I always thought NTSC DV is 720x480, but I have seen references to
704 x 480 NTSC from various places (e.g. tmpgenc's default input is
set to 704 x 480).
Where do this resolution come from?

704×480 is an edge-truncated variation of 720×480. That is, the 720×480 area contains the 704×576 area in the middle. If you're going to convert from 720×480 to 704×480, you crop 8 pixels off from both edges. If you're going to convert into the other direction, you add 8 (black) pixel columns to both sides. No interpolation or scaling is involved in these conversions - the shape of the pixels (PAR) stays the same but the width of the image changes.

Where does 704×480 come from? That's a good question. For one thing, it is a double-sized version of the so-called "CIF" resolution (352×240) - in both directions. That might explain its existence: it can be thought of as being the full-resolution equivalent of the CIF resolution. The CIF resolution is used, among other things, in MPEG-1 applications - such as in the Video CD format. Video CD 2.0 format (the "White Book" specification) specifically allows "high resolution" still images in the 704×480 format.

TMPGEnc may display "704×480" in various places, but as far as I can tell, it considers the 720×480 as its equivalent. (Just as it should, too - they're basically just minor variations of the same format. The user never sees the edges on a normal tv set, anyway.) Even if you use templates that nominally say "704×480", you can offer TMPGEnc 720×480 video and it will happily accept and process it the correct way, without scaling or cropping.

--
znark

.

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