[Bf-codereview] Alpha premul pipeline cleanup (issue 7018048)

[Xavier Thomas]

I am patching now, but I cannot promess I will have time to debug :(


2012/12/29 <sergey.vfx at gmail.com>

> On 2012/12/29 22:41:44, xavier.thomas.1980_gmail.com wrote:
>
>> > However, byte buffers behaves quite fuzzy. When i do a stroke with
>>
> white
>
>> > brush on complete transparent image, i should see the whole stroke
>>
> being
>
>> > white in RGB display mode, but it fades up to darkish colors to the
>> > sides of brush. Converting pixels from straight-byte to premul-float
>>
> in
>
>> > IMB_rectblend and using IMB_blend_color_float doesn't give correct
>> > result here.
>>
>
>
>  Darkish colors in the semitransparent areas is often a sign of having
>> premultiplied colors by alpha twice or more.
>>
>
> I know this and it doesn't seem to be this case. If you'll try the patch
> you'll notice that blending is much more "steppy" than just multiplying
> alpha twice. It could be extra premul, but there seems to be some other
> issue involved here.
>
> https://codereview.appspot.**com/7018048/<https://codereview.appspot.com/7018048/>
>
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