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Correcting for Pixel Aspect Ratios

In Chapter 2, you learned the importance of correctly interpreting an image's pixel aspect ratio (PAR) to prevent the image from appearing distorted (if you missed the discussion, turn to the sidebar "PAR Excellence: Pixel Aspect Ratios" in Chapter 2). But even properly interpreted footage and comps that use a nonsquare PAR (such as DV or D1, with a PAR of .9) result in an image that looks distorted on a typical computer display (PAR of 1) ( Figure 3.83 ). Fortunately, After Effects can compensate for the distortion due to PAR ( Figure 3.84 ). As After Effects warns you when you use the Toggle Pixel Aspect Ratio Correction button, correcting the image this way is for viewing purposes only; it doesn't affect the image's actual scale. And because correcting an image requires some processing, it will take slightly longer to render frames.

03_83_parcorrectoff.jpg

Figure 3.83 This footage uses a PAR of .9, so it appears slightly vertically squashed (or horizontally stretched) when displayed using square pixels.

03_84_parcorrecton.jpg

Figure 3.84 You can correct the distortion in the Layer, Composition, and Footage panels.

To toggle pixel aspect correction:

  1. In a Footage, Composition, or Layer panel, click the Toggle Pixel Aspect Ratio Correction button vwr_par.jpg to select it ( Figure 3.85 ).
    03_85_parcorrectbutton.jpg

    Figure 3.85 Click the Toggle Pixel Aspect Ratio Correction button.

    If this is the first time you've used the button during this session, After Effects reminds you how PAR correction works and prompts you to specify whether you want to see the warning once per session or never again.
  2. Select an option in the dialog box, and click OK. If the image's PAR doesn't match your computer monitor's PAR, After Effects scales the image so that it no longer appears distorted.
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