Color in ACES - VFX in LOG

Hi Everyone,

What workflow would you suggest upon the following scenario?

Footage is being shot using a R3D - RedWideGamutRGB - BT1886 - Client wants to work in ACES.

We figured out it would be best for us to work our VFX in EXRs RWG-LOG3G10, We would however need to revew shots as per final output ACES - how can this be possible in Nuke/AE? We need to understand what method to use to convert LOG3G10 to ACES, . Is this possible and how would you suggest converting the LOG3G10 to ACES?

You do not want to write Log3G10 to EXR files. EXR should be linear.

OCIO in Nuke, using the ACES 1.0.3 config, can convert between different colour spaces including ACES and RED Wide Gamut (linear or Log3G10).

OCIO is also available as a plugin for After Effects, which can emulate the Nuke colour pipeline.

I believe the Log3G10 is just a gamma curve. But that Red Wide Gamut has different color primaries than ACES. Is that right?

If so do I simply need to multiply the log values by the REDWideGamutRGB to ACES AP0 matrix before doing the Log3G10 to linear conversion?

REDWideGamutRGB to ACES AP0 matrix :
0.785043, 0.083844, 0.131118,
0.023172, 1.087892, -0.111055,
-0.073769, -0.314639, 1.388537

Thank you,

For every color space there’s the “color primarires” and the “linear/non-linear encoding”. For example, REDWideGamutRGB (primaries) Log3G10 (non-linear encoding) or ARRI WideGamut (primaries) LogC (non-linear encoding). So yes if your files are linear REDWideGamutRGB, then you just need to apply a matrix to go from REDWideGamutRGB to AP0. (Note as @nick points out - encoding log data in an EXR is a bad idea)

Again as @nick points out, you can use OCIO with the ACES 1.0.3 config and set the color space and linear/non-linear encoding separately. You could “brew your own” color science and apply a matrix node manually but that’s only advised for people who know very well what they’re doing. Even then, an excellent tool (OCIO) already exists and is in wide use for applying these sorts of simple transformations.

Thanks. What is the order of operation to go from REDWideGamutRGB Log3G10?

Do I apply the color matrix transform 1st and then the Log3G10 to linear or vice versa?

Linearise first, and then multiply by the matrix.