[Cin] Color erase like GIMP

[Stefan de Konink]

On Sunday, September 26, 2021 11:58:42 AM CEST, Igor BEGHETTO via Cin 
wrote:
> I don't know how animejs works and I think it is a pity you can 
> not make a render with it (and using alpha channel).
> In Cinelerra-GG there are "Chroma key" and "Chroma key (HSV)" 
> plugins for that but may be it doesn't work very well for your 
> goal. "Chroma key (HSV)" plugin is very powerful but you need to 
> work on it to achieve a good output.

The problem with Chroma key HSV is that it will clamp a light green color 
to 'white' and not 'white+transparant'. At least that is my experience last 
night. I am still interested (and motivated) to see the Color Erase happen 
by the algorithm GIMP uses. I have found that ffmpeg has a blend filter, 
but subtract is not equal to color erase.

What I have done during the early hours. I have implemented a QML Webkit 
based browser. I am able capture the onscreen RGBA surface (yes, really...) 
but because this is a single threaded effort I cannot do that at the 
'native' speed to PNG. So I multiplied all the timing by 10, and captured 
at 2.5fps, this gives me:

<http://stefan.konink.de/proRes444_output.mov>

-- 
Stefan