7 Replies Latest reply on Sep 29, 2008 7:09 AM by (Steve_Patterson)

    Square Pixels Question

    londoncalling1979 Level 1
      I have made an animation that is 640 X 480 with Square Pixels.

      I was told that I have to give the animation to a video guy, but that it has to be 720 X 480.

      Do I simply have to change it to the .9 setting and change the settings to 720 X 480? Because when I tried that, it looked stretched on my computer screen. It looks correct at 640 X 480 with square pixels.

      Thanks.
        • 1. Re: Square Pixels Question
          Mylenium Most Valuable Participant
          The behavior is normal and the whole point of doing stuff for video. On a computer, which is a square pixel device, video resolutions will look squeezed, because the computer has no knowledge of them actually being rectangular. however, in AE you can use pixel aspect ratio correction in the comp viewer to compensate. In any case - do not simply change your comp resolution. The proper way to treat your existing composition is to nest it into a new composition and have AE do the pixel conversion. If you only change the comp, positions may get out of whack or some effects will look different, which is not what you'd want.

          Mylenium
          • 2. Re: Square Pixels Question
            londoncalling1979 Level 1
            If I next the 640 X 480 Square Pixels Comp into a 720 X 480 Comp, which setting should I use? Square Pixels or the D1/DV (0.9) setting?
            • 3. Re: Square Pixels Question
              Mylenium Most Valuable Participant
              The 640x480 remains square, the otehr comp uses the correct 0.9 PAR. The rest is AE magic. ;-)

              Mylenium
              • 4. Re: Square Pixels Question
                Another option (if you're in a real hurry) is to stretch the output of your original comp to 720x480 by adjusting the stretch parameters in the Output Module settings.

                The correct way to do this kind of work though is to create your animation in the first place at the square-pixel equivalent size of the NTSC frame. Note that that size is actually 720x540 rather than 640x480 (the larger size means no upscaling is involved in the conversion).

                If you want to know more about this kind of thing, here's a great article: http://library.creativecow.net/articles/gerard_rick/pixel_madness.php

                Best of luck with it.
                • 5. Re: Square Pixels Question
                  Level 1
                  After Effects automatically and properly combines footage of any pixel aspect ratio with footage of any other pixel aspect ratio. The only time things get fouled up is when you mis-interpret the footage.

                  If your footage is square pixels it must be interpreted as square pixels. If it is DV widescreen then it must be interpreted as DV wide screen. After Effects will try and guess what the pixel aspect ratio is supposed to be for any footage that isn't tagged with a PAR identifier. It makes this guess based on the size of the frame.

                  For example, if you create a square pixel image in photoshop that's 720 X 480 the After Effects will assume that it's D1 Pixel aspect ratio because 720 X 480 is the standard size of a D1 frame. In this case, After Effects guesses wrong so you have to manually correct the problem and set interpretation to square pixels.

                  In your case all you have to do is drop your square pixel comp in a D1 comp for render and you're good to go. There will be a bit of black on the left and right side of the rendered video but you will never see these black edges in a TV when the video is played. In face, most DV cameras don't even fill the frame and leave 4 to 9 pixels of black on the right and left edge of the frame anyway.

                  I hope this helps. Just remember that your footage should always be interpreted as what it is, that AE will guess properly unless you create square pixel footage that is a standard rectangular pixel size or your widescreen footage does not have a PAR tag in the header.

                  As far as rendering goes, unless you can find a place to designate the pixel aspect ratio in the video settings the codec does not support such a tag and the footage may have to be interpreted properly in your NLE or other app to prevent distortion.
                  • 6. Re: Square Pixels Question
                    A. Cobb Level 3
                    The correct way to do this kind of work though is to create your animation in the first place at the square-pixel equivalent size of the NTSC frame. Note that that size is actually 720x540 rather than 640x480 (the larger size means no upscaling is involved in the conversion).

                    Not really. The correct way to do this is to create your animation at 720x486 with D1 (.9) pixels. Working at 720x540 is only the second best option, since it requires that the image be resampled vertically.

                    Of course, AE doesn't exactly make doing things the correct way as easy as it could, given its horrible algorithm for doing pixel aspect ratio correction.
                    • 7. Re: Square Pixels Question
                      (Steve_Patterson) Level 1
                      Since it's often easier to design in a square pixel environment, keep in mind the following:

                      648x486 is the square pixel equivalent of a 720x486 (.9) D1 frame.