[FFmpeg-user] convert from bt601 to bt709

[Rio Kierkels]

> Except that I was already working in 709 space.  Yes the EXR is linear,
> and was interpreted as such and converted into 709 and looks correct.
>
> The DPX on the other hand was tagged as already being 709, yet I had to
> manually "undo" the gamma to get it right in 709, which is why it seems
> to me like it was applied twice.  It should have just come in correct to
> begin with and look like the EXR snapshot did, if it really was 709.
>
> Bob

This is interesting. It looks to me that your DPX doesn't have a gamma
applied at all. But I've only been able to check using ffmpeg's histogram
filter that just shows the pixel values without any transforms (right,
people with better knowledge about it than I have?). And the lightworks
scopes. I'll compare yours and mine on the nuke, flame, smoke and lustre
machines tomorrow if I can get some time with them.

Rio