Support different alpha modes

[castano]

Support different alpha modes

[GoogleCodeExporter]

Charles Nicholson points out this article from Tom Forsyth about pre-multiplied 
alpha:

http://home.comcast.net/~tom_forsyth/blog.wiki.html#%5B%5BPremultiplied%20alpha%
5D%5D

Original comment by [email protected] on 4 Mar 2008 at 10:59

[GoogleCodeExporter]

Ignacio-

Here's a patch against 2.0.1 with the following features:

InputOptions has "void setPremultiplyAlpha(bool b)", backed by 
InputOptions::Private
"bool premultiplyAlpha".

Compressor has the private method "premultiplyAlphaMipmap(Mipmap&, const
InputOptions::Private&)", that converts the mipmap to a FloatImage, multiplies 
the
RGB channels by A into a new FloatImage, and overwrites the old one with the 
new one.
 This happens after mipmap initialization, but before quantization/compression.

nvcompress.exe has the command-line flag "-premula" to invoke this 
functionality.


The code in Compressor is a little sloppy in that it doesn't confirm the correct
number of channels, or error if conflicting options exist.  I'm pretty sure you 
can
do it to a normal map, which you probably don't want.  I adhered to the coding
standard in as much as i could glean without a doc.

Best,
charles

Original comment by [email protected] on 5 Mar 2008 at 9:49

Attachments:

• premultiplied-alpha.patch

[GoogleCodeExporter]

Thanks, I checked that in with some changes. I think alpha premultiplication 
should
be applied in the destination gamma space. If you apply it in linear space, 
then when
you transform the color to gamma space you will also transform the 
premultiplied alpha.

Original comment by [email protected] on 7 Mar 2008 at 1:49

• Changed state: Started

[GoogleCodeExporter]

The cuda compressors now have support for alpha modes.

Original comment by [email protected] on 6 May 2008 at 8:04

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Original comment by [email protected] on 11 Oct 2008 at 7:30

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Original comment by [email protected] on 24 Nov 2008 at 10:36

• Changed state: Fixed