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Old 25th November 2011, 11:48   #10  |  Link
hello_hello
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Join Date: Mar 2011
Posts: 4,821
Quote:
Originally Posted by vampiredom View Post
Fortunately, only certain dimensions tend to have non-square pixels and most sources of these sizes tend to follow one of the standards.
The problem is, they generally don't. At least not in my opinion. How were you able to come to a definitive conclusion they do?
(Edit) Sorry, I noticed in a later post you modified "tend to" with "should".
I don't think you can really generalise and say something like "crop to a width of 704 then use this pixel aspect ratio" etc. and know it'll be correct much of the time, because there's no way to know it will be. Admittedly if it's wrong it won't be out by much, but it can still be wrong. If only DVDs did all stick rigidly to some sort of standard.....

Personally I think DVDs (at least) are less likely to follow one of the standards than they are to follow them. My usual way of resizing DVDs is to use a straight 16:9 or 4:3 resize (I can't remember the exact PARs off the top of my head) then crop off only the necessary crud (or crop to mod16), encode what's left and at least 9 times out of 10 that'll be correct. I think DVDs which use the "official" PARs are the exception, not the norm, and I've come to this conclusion after comparing many old DVD encodes with their Bluray equivalent.

Anyway, being a GUI kind of guy I tend not to think about PAR all that much (I just choose non-ITU resizing, crop and encode) but for those times I do have to think about it, this resize calculator comes in quite handy as it'll let you choose between resize methods and it'll calculate the aspect ratio distortion for you as you crop. Yoda's Resize Calculator
At least with the calculator handy it's not necessary to remember a table of PARs.

Last edited by hello_hello; 25th November 2011 at 12:01.
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