Re: Image Format / Pre-Multiplied Alpha Related Feature Request

Lawrence D'Oliveiro <[email protected]> Thu, 28 Jan 2016 18:15:52 +1300

Newsgroups	gmane.comp.lib.cairo
Organization	Geek Central
Message-ID	<[email protected]>

On Wed, 27 Jan 2016 22:25:42 -0500, William Kappler wrote:

>    - Most libraries, shaders, and users/programmers expect textures
> in 3D contexts to be non-pre-multiplied.

Premultiplied alpha is the usual convention for rendering and
compositing in both 2D and 3D
<http://wiki.blender.org/index.php/Dev:Ref/Release_Notes/2.66/Image_Transparency>.

Why premultiplied alpha? <http://keithp.com/~keithp/porterduff/>

So if you want to reuse a rendered image in a context which does not
understand premultiplied alpha, you will have to convert it.

If you care about image quality, you will maintain your assets in a
floating-point format like OpenEXR, which normally uses premultiplied
alpha anyway.
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