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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," 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) will result in an image that looks distorted on a typical computer display (PAR of 1) ( Figure 3.100 ). Fortunately, After Effects can compensate for the distortion due to PAR ( Figure 3.101 ). 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.

03fig100.jpg

Figure 3.100 This footage uses a PAR of .9, so it appears slightly vertically squashed (or horizontally stretched) when displayed using square pixels.

03fig101.jpg

Figure 3.101 You can correct the distortion in the Layer, Composition, and Footage windows.

To toggle pixel aspect correction

  1. In a Footage, Composition, or Layer window, click the Toggle Pixel Aspect Ratio Correction button correction.gif to select it ( Figure 3.102 ).
    03fig102.gif

    Figure 3.102 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 ( Figure 3.103 ).

    03fig103.gif

    Figure 3.103 The first time you use PAR correction, After Effects reminds you how the feature works and prompts you to specify whether you want to be reminded 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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