ACES and tx conversion

[paul.clements]

Working in aces, I have noticed that if I bulk convert a folder of .pngs into tx (set to auto color space) the created normal maps don't seem to work.

However, if I link the pngs up into a standard surface shader and start the IPR, the automatically created TX normal maps work fine.

Does anyone know why this is? Is it simply that when batch converting a folder Arnold can't tell what type of map it is and just applies the aces color conversion to everything regardless?

Many thanks,

[peter.horvath6V6K3]

'auto' defines the color space based on the bit-depth of the image. 8-bit textures, like pngs, are expected to be in sRGB space, so when you generate Tx files, they will be transformed from sRGB to ACEScg. I suppose, since they are normal maps, you don't want any color transform (raw), so you have to disable color transform instead of 'auto'.

When you connect an image shader to standard_surface.normal, the plugin tries to be clever and automatically sets the color space on the image shader to raw. That would explain why auto tx works as expected.

[paul.clements]

Ah that explains it thanks Peter.

Peak whites in textures seem to be brought down with aces conversion. Presuming this is the case, would you set roughness, metallic, and AO maps to raw also?

[peter.horvath6V6K3]

Yes, everything which is not a color should be raw. I would also recommend using 32-bit images for raw maps (e.g. EXR), because normally a png or jpeg has an sRGB curve baked in, so it's not obvious whether a color transform is needed to extract the raw data or not. It really depends on how the file was saved.