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Alpha type: Staight or Pre-mulitplied?

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Alpha type: Staight or Pre-mulitplied? - 4/14/2012 5:35:37 AM

bluebird

Posts: 5
Joined: 4/14/2012
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Hi, I'm a newbie. Just wondering when using Juicer to render something with alpha channel, how to decide when to use straight and when to use pre-mulitplied? Is that any cues on it? Thanks for reply in advance

RE: Alpha type: Staight or Pre-mulitplied? - 4/14/2012 12:22:58 PM

DuaneConatser

Posts: 46
Joined: 12/2/2009
Status: offline

This link gives all you ever wanted to know about this subject!!

http://en.m.wikipedia.org/wiki/Alpha_channel

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Duane L. Conatser

(in reply to bluebird)

RE: Alpha type: Staight or Pre-mulitplied? - 4/14/2012 7:48:10 PM

bluebird

Posts: 5
Joined: 4/14/2012
Status: offline

Thanks for your information

quote:

Premultiplied alpha has some practical advantages over normal alpha blending because premultiplied alpha blending is associative and linear interpolation gives better results, although premultiplication can cause a loss of precision and, in extreme cases, a noticeable loss of quality.

It seems that straight alpha can have a more precise result but premulitplied is more natural in output? (though has a chance to mix things up). So deciding to use which is not always, it depends on the color combination of the background and the foreground object. I don't know if my understanding is right or not