Trying to understand the ACES workflow

[jomaro]

Hi guys,

I am trying to understand the ACES workflow on Affinity Photo.

I have few questions:

- Why AP converts my EXR ACEScg to scene linear?

- Why don't I have ACES colorspace in my preferences?

- Are "Source Color Space" and "Destination Color Space" the IDT & ODT?

- Can you open an EXR ACEScg and do your work and save as is? back to EXR ACEScg without baking any lut/converting?

 

Cheers

[James Ritson]

Hey @jomaro, hopefully this should give you enough info to work with..

 

19 minutes ago, jomaro said:

- Why AP converts my EXR ACEScg to scene linear?

Looks like you have an OCIO configuration set up, and your EXR file is appended with "acescg"? So Photo will convert from ACEScg to scene linear because it's found a matching profile.

It's just the way 32-bit linear in Photo works—everything is converted to scene linear, then the colour space is defined either by traditional display profile conversion (ICC) or via OCIO. You choose which using the 32-bit preview panel (View>Studio>32-bit Preview). Bear in mind that if you plan to export from Affinity Photo as a gamma-encoded format (16-bit, 8-bit JPEG/TIFF etc), you need to preview using ICC Display Transform.

So just to clarify, the document's colour profile (e.g. sRGB, ROMM RGB etc) is arbitrary and only applied when using ICC Display Transform—then the scene linear values are converted and bounded to that profile. If you choose Unmanaged, you'll be looking at the linear values. OCIO Display Transform will convert the scene linear values according to the view and device transforms that are mandated in the combo boxes.

19 minutes ago, jomaro said:

- Why don't I have ACES colorspace in my preferences?

You would need to install a given ICC profile for that to show up. However, I suspect you probably want to be managing with OpenColorIO. Looks like you've already managed to set it up, but here's a reference video just in case:

 

Within the 32-bit preview panel, you will want to choose OCIO Display Transform (it will be enabled by default with a valid OCIO configuration). Then you set your view transform on the left and device transform on the right.

19 minutes ago, jomaro said:

- Are "Source Color Space" and "Destination Color Space" the IDT & ODT?

The OCIO adjustment layer is for moving between colour spaces within the same document—you might want to do this for compositing layers with different source colour spaces, for example. You can also bake in colour space primaries if you wish to do that as well (typically go from scene linear to whichever colour space you require).

19 minutes ago, jomaro said:

- Can you open an EXR ACEScg and do your work and save as is? back to EXR ACEScg without baking any lut/converting?

Yes, Photo can convert to profiles on import/export by appending the file name with a given colour space. For example, if you imported a file named "render aces.exr", it would convert from the ACES colour space to scene linear. Similarly, if you append "aces" to your file name when you export back to EXR, it will convert the document primaries from scene linear back to ACES.

Hopefully the above all helps? Let me know if you have any further questions!