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Bad pixel aspect correction – is this a workaround ?
Hello again 🙂
Someone told me that I might use a 1920×1080 square pixel composition for HDV work. As the pixel aspect correction for the preview does a very poor job in interpolation, this seems a good way do get a good preview in AE without jaggies.
But is there a disadvantage to that technique ?
I thought of maybe when I output to 1440*1080 the primary 1.33 interpreted footage gets upscaled to full width and then the whole comp get downscaled back to 1440.
One could change the comp setting to 1440*1080 with 1.33 at rendering time. That might be ok. Is it ?
Anyhow I wonder, why AE does such a bad job with the pixel aspect preview.
I mean, it’s adobe … to they have a problem scaling images ?Seems like. As Premiere does it equaly bad, but there when rendering out. But that will be fixed in Premiere CS3 as I learned in this forum 🙂
So any comments are welcome.
Peter
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8 Replies
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yeah you can work in a square px hd comp as you described, then drop that com into a non-square (1.33) px hd comp for final render. a big advantage of working this way (aside from the preview issue) is that not all effects work in non-square pixels (they work, but the see pixels as square, so the effect may be dispropotioned), this workflow would fix those issues.
the only disadvantage i can think of is more pixels = more render time… so your renders will take a little longer.
Kevin Camp
Designer – KCPQ, KMYQ & KRCW -
Another option is creating a final render composition with the proper resolution & pixel aspect ratio, drag your wokring comp in there and use the fit to comp command (cmd-opt-f/ctrl-alt-f).
Darby Edelen
DVD Menu Artist
Left Coast Digital
Aptos, CA -
watch out for the fit command and make sure that your x and y scale values are equal. I always use the fir horizontal command instead.
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[sam.mltn] “watch out for the fit command and make sure that your x and y scale values are equal. I always use the fir horizontal command instead.”
If you’re putting a square pixel composition into a non-square output you don’t want the X and Y scales to be the same. If they’re the same then you still have square pixels!
Darby Edelen
DVD Menu Artist
Left Coast Digital
Aptos, CA -
oh yes you do. You never want them different unless you’re distorting intentionally. AE handles the PAR correction perfectly every time as long as the footage is interpreted correctly and the comp is set up correctly. If you want undistorted video the x and y scale values should NEVER the be different. drop a 648 X 720 square pixel image or solid in a 720 X 480 D1 comp at .9 par and it will fit perfectly every time and X and Y will be 100%
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[sam.mltn] “oh yes you do. You never want them different unless you’re distorting intentionally. AE handles the PAR correction perfectly every time as long as the footage is interpreted correctly and the comp is set up correctly. If you want undistorted video the x and y scale values should NEVER the be different.”
The original post was about working with a Square Pixel composition and outputting to a non-square pixel format. This process does not follow the same arbitrary AE rules as you cite above.
If you place a square pixel composition into a non-square pixel composition After Effects will automatically attempt to maintain the correct ‘look’ of your square pixel composition even though it’s in a non-square pixel composition (which I believe is what you’re referring to).
However, the square pixel composition is at a larger resolution than your non-square pixel composition (a square pixel NTSC comp is 720 x 540, a non-square is 720×480). In the case of NTSC DV your square pixel composition will have the top and bottom cut off of it if you DON’T scale one dimension more than the other!
https://livedocs.adobe.com/en_US/AfterEffects/8.0/WS3878526689cb91655866c1103906c6dea-7f10.html
In the case of the HDV footage the original post was about using a 1920 x 1080 square pixel composition. This is the effective resolution that a 1440 x 1080 composition at 1.33 PAR will appear, however if you just put a 1920 x 1080 square pixel composition into a 1440 x 1080 non-square composition it will have the left and right sides each clipped by 240 pixels! The 1920 x 1080 square pixel composition needs to be scaled down by 1/1.33 (75%) in the X dimension in order to be properly displayed at 1.33 PAR.
[sam.mltn] “drop a 648 X 720 square pixel image or solid in a 720 X 480 D1 comp at .9 par and it will fit perfectly every time and X and Y will be 100%”
I’m not sure what you mean by ‘it will fit perfectly’ but your vertical resolution of the image seems large, especially for your horizontal resolution. The aspect ratio of 648 x 720 is 4:4.4 while the aspect ratio for standard NTSC DV should be 4:3 (648 x 486 or 720 x 540). The benefit of using 720 x 540 instead of 648 x 486 would be that you have extra pixel information for the conversion to 0.9 PAR.
Darby Edelen
DVD Menu Artist
Left Coast Digital
Aptos, CA -
648 X 720 was a typ0 should have been 648 X 480….
I know all about the adobe doc. There’s no place, no where, no time, that you should monkey with different X and Y scale values in standard square or non square comps. AE is PAR aware and if the footage is distorted on final render then the interpretation is wrong.
Check out this tutorial
or better yet, drop a HDV sized comp 1440 X 1080 @1:33 in a HD comp 1920 X 1080 @ square pixel, or a D1 square pixel solid (720 X 540 @ square pixel) scaled exactly to 90% X and Y into a D1 (720 X 486 @ .9) comp, or a NTSC Sq pixel Widescreen (864 X 486 @ square) comp in a D1 widescreen (720 X 486 @ 1.2) comp and you’ll see that not only do they fit exactly and that the renders are not distorted. You should never scale X and Y differently. If you follow the referred to Adobe doc exactly you’ll see that the X and Y scale values are exactly equal unless you use 720 X 534 square pixel example and the Fit command because there is no exact 720 wide square pixel equivalent for a 720 X 480 DV comp because DV isn’t 4:3 because 6 scan lines, 4 from the top and 2 from the bottom, are not encoded in DV and 720 X 534 is the closest whole pixel equivalent that’s .9 PAR
I don’t expect that this post will change your mind, but creating any square square pixel solid and then turning it into a perfect circle using a double click in the oval mask tool, then putting that solid in any par comp and rotating it will show you no wobble if you don’t mess with the X and Y scale values. If you try scale the circle to match the PAR of the comp your circle will wobble when rotated, which proves my point.
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Welp, I have two words for you:
You’re right.
I know now why I was confused, and apologize if my confusion led anyone astray =)
Darby Edelen
DVD Menu Artist
Left Coast Digital
Aptos, CA
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