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Alpha channel interpretation in video and image sequences (Photoshop Extended)
Video
and image sequences with alpha channels can be straight or premultiplied.
If you’re working with video or image sequences containing alpha channels,
it’s important to specify how Photoshop Extended interprets the
alpha channel to get the results you expect. When premultiplied
video or images are in a document with certain background colors,
it’s possible to get undesirable ghosting or halos. You can specify
a matte color so the semi-transparent pixels blend (multiply) with
the background without producing halos.
- Ignore
- Ignores the alpha channel in the video.
- Straight-Unmatted
- Interprets the alpha channel as straight alpha transparency.
If the application you used to create the video doesn’t premultiply
the color channels, select this option.
- Premultiplied-Matte
- Uses the alpha channel to determine how much of the matte
color to mix with the color channels. If necessary, click the color
swatch in the Interpret Footage dialog box to specify the matte
color.
 Item with premultiplied channels (top) appears with a black
halo when interpreted as Straight-Unmatted (lower-left). When interpreted
as Premultiplied-Matte with black specified as background color,
halo does not appear (lower-right).
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