ACEScg vs Linear sRGB/709 CG rendering

[Thomas_Mansencal]

Hi @Colin_James,

A few things:

@Colin_James

pre-converting all textures and colors in a full CG sequence into ACEScg color space vs keeping it all linear and just comping in ACEScg color space?

ACEScg is intrinsically linear, what you are referring to as linear is currently sRGB / BT.709 / Rec. 709 colourspace with a linear transfer function.

@Colin_James

I want to make sure we’re not missing anything.

As you mentioned it, some RGB colourspaces have gamuts that are better suited for CG rendering and will get results that overall will be closer to a ground truth full spectral rendering. ACEScg / BT.2020 have been shown to produce more faithful results in that regard. Whether it matters is probably context dependent, Weta Digital has elected to go down the spectral rendering road because the company felt it mattered for what they were doing. Many other facilities did not go down that road and are still producing high quality imagery.

@Colin_James

I have a feeling this is fine for full CG scenes, but what about when working with plates, we could in theory convert the aces plates to linear, do the cg in linear, and still comp in the expanded color gamut.

Yes! Reality is that you might have to go back do some keying operations in the blessed camera vendor colourspace or even so called “native camera space”.

Cheers,

Thomas