2009.04.27 20:32 "Re: [Tiff] Question regarding unassociated alpha", by Amir Ebrahimi

On Apr 27, 2009, at 1:26 PM, Edward Lam wrote:

  > Probably a bug.

This code only gets used in the high-level libtiff TIFFReadRGBAImage() interfaces. Given that it's supposed to do all sorts of conversions for you, I think it's semantically supposed to always return pre-multiplied alpha images. Reading the code, it leaves the RGB components alone when reading an associated alpha tiff, and multiplies in the alpha for unassociated alpha tiff files.

Given that this code was originally developed on SGIs, the norm back then was probably to use premultiplied alpha. ie. influenced by Duff's Compositing Digital Images paper.

http://keithp.com/~keithp/porterduff/p253-porter.pdf

Okay, so maybe a conditional define or read option is due?

:: Amir Ebrahimi::
Developer @ Unity Technologies
www.unity3d.com