[FFmpeg-devel] avfilter/vf_premultiply : use full range for RGB input

[Paul B Mahol]

On 3/18/18, Hendrik Leppkes <h.leppkes at gmail.com> wrote:
> On Sun, Mar 18, 2018 at 9:26 AM, wm4 <nfxjfg at googlemail.com> wrote:
>> On Sat, 17 Mar 2018 20:46:50 +0100
>> Martin Vignali <martin.vignali at gmail.com> wrote:
>>
>>> Hello,
>>>
>>> Patch in attach change premultiply/unpremultiply filter for RGB input
>>> to process it at full range
>>>
>>> Avoid very strange result in unpremultiply mode
>>>
>>> To test :
>>> ./ffmpeg -i ./fate-suite/mov/mov_alpha_premult.mov -vf
>>> unpremultiply=inplace=1 resStraight.png -y
>>>
>>> ./ffmpeg -i ./fate-suite/mov/mov_alpha_premult.mov -vf
>>> format=gbrap16,unpremultiply=inplace=1 resStraight16.png -y
>>
>> I thought all alpha in ffmpeg is "straight" (not premultiplied). Was I
>> lied to?
>
> If you pre-multiplty the alpha and then save it as a file, how it is
> supposed to know that you did that? :)

There must be flag, which is ignored.