[Oiio-dev] Pre-multiplication

Jeremy Selan jeremy.selan at gmail.com
Fri Jul 13 09:37:14 PDT 2012


Yup.

screen =  A+B-AB, where AB term represents the if intersection of the
subpixel geometry.

But in the case where you have two mattes where you know the
correlation == -1, (which denotes no overlap in the subpixel
geometry), adding mattes reduces to a simple A+B.  An example of no
overlap in the subpixel geometry would be the alpha rasterization of
two adjacent triangles in a mesh.

So to summarize, if the subpixel geometry has a correlation of 0, the
math for combining alphas is A+B-AB.  If the correlation is -1, the
math is A+B.  And for perfectly correlated subpixel geometry?  Sounds
like a good white-board project for this weekend... Surely there's
some paper from 1985 that has worked this all out? :)

-- Jeremy

On Thu, Jul 12, 2012 at 9:05 PM, Troy Sobotka <troy.sobotka at gmail.com> wrote:
> And the inevitable question: What is the canonical compositing formula
> for correlated then? Simple add?
>


More information about the Oiio-dev mailing list