What is the colorspace conversion / transformation matrix of ACEScg to V3 LogC EI800 Wide Gamut ?
I need to use t he matrix directly instead of using the ociocolorspace node to do the transformation

Also, Is there a way in colour science or python in general to figure out a colorspace’s coordinates and conversion matrices?

Thanks Shebbe for your reply !
I indeed looked there, but I couldn’t find the Arri logC Wide gamut colorspace. Do you know what is it listed as if it’s in there?

As @Shebbe pointed out, you can find a table of the ALEXA Wide Gamut RGB chromaticities and conversion matrixes on pg 10 of “Alexa_LogC_Curve_in_VFX.pdf”

@Thomas_Mansencal : the conversion matrix generated from ACEScg - > Alexa wide Gamut doesn’t match the ocio transformation from ACEScg → input Arri V3 LogC (EI800) - Wide Gamut , which is my intention . I’m trying to avoid ocio usage and instead use the matrix directly

as I understand, AWG and Arri logC colorspaces are not quiet the same colorspace?

LogC v3 is, as the name implies, logarithimic. So as well as applying an AP1 to ARRI Wide Gamut v3 matrix, you then need to apply the LogC v3 transfer function.

It looks like you’re applying the LogC curve to the matrix values themselves. Instead, you want to apply the logC curve to the resulting RGB after applying the matrix to AP!. It should be two separate steps.

e.g.

// Apply matrix to AP1 RGB to get ARRI WG RGB (linear)
RGB_linear_ARRI_WG = RGB_linear_AP1 * m3
// Apply LogC curve to linear ARRI WG RGB to get get LogC ARRI WG RGB
RGB_logC_ARRI_WG = logC( RGB_linear_ARRI_WG )