[FFmpeg-user] convert from bt601 to bt709

[Rio Kierkels]

Here's also a capture of my scope from the DPX sequence and of the EXR.

>  You can see the arc in the ramp on the DPX, the elevated chroma levels,
> etc.
>
> DPX Imported: http://clients.idolum.com/get/6714cf583c5b
> EXR Imported: http://clients.idolum.com/get/08f993a4c57c
>

Both of these seem to me to be correct. The EXR is rendered linearly so
without a power curve and using linear-light RGB tristimulus values.
The DPX is rendered from those values to BT.709 primaries and a BT.1886
powerfunction creating that curve along the greyscale ramp so we get R'G'B'
in BT.709.
Which is what we are going for right? Or are we aiming for linear RGB with
no powerfunction?


> It seems like maybe the DPX is either tagged wrong, or some operation
> happened twice.  If I apply a 'Remove Rec709 Transform' LUT to the DPX,
> it winds up correct.
>

This makes sense as it will do an inverse powerfunction on the image
leading to a linear waveform readout but an incorrect image as your monitor
will do that inverse powerfunction again.
However you should also see your primaries leave the squares and shift back
to the center in your vectorscope if the LUT is a true inverse of BT.709.

I've just did an export on one of our flames from the EXR like you did with
the standard DPX 10bit presets and it also doesn't apply a gamma curve,
which puzzles me.

It just could be me not understanding the BT.709/BT.1886 HD spec.

-- 
C018 4C82 3701 9CAC B723  4C29 2C04 E81A 7418 D158