Re: [E-devel] Problem with Imlib2 and Alpha TIFs

[Simon W. <si...@th...>]

On Thu, Dec 01, 2005 at 01:19:41AM +0900, Carsten Haitzler said:
> the problem is tif's use pre-multiplied alpha (ie rgb is multipled BY the alpha
> value when stored) instead of non-premul (as imlib2's internals, png's argb
> etc. use). that means imlib2 is missing the "de-multiply" on load code. it has
> the multiple on save. it's a bug. :)

Hurrah! (sort of)

*insert blinding flash of realisation*

Doh!

I've just realised what was going on. I was mislead by the fact that it 
was so dark and therefore though that it couldn't be the alpha_factor 
because if it multiplied on save then it must divide on load.

But if the alpha is 146 then 146/2.550 is going to be less than 1 and 
dividing by it is the same as multiplying. 


Patch attached.

Cheers for the help.

Simon