OCIO display transform might be bugged while exporting

[stger]

Hello,

I have a Blender render which I exported as an 32bit EXR for postprocessing in Affinity Photo.

I'm using OCIO Display transform noen in combianation with an OCIO Adjustment layer, which gives me accactly the Filmic look from Blender

 

 

 

 

This is how the image looks in Affinity after my post edit:

 

 

But as soon I want to export it, it's becomming much too bright:

 

I already figured out what is causing this. It behaves like the Display transform would be set to ICC Display transform:

I get the same look in Affinity if I change the value to this.

But if I import the aphoto file to Publisher an export it via Publisher the export looks correctly.

 

 

Is there something which I'm doing wrong? Or is this a bug?

[Lee D]

It's the way it's designed, exporting will always use a gamma encoding based on the document profile.

[James Ritson]

Hi @stger, to expand on this: OCIO display transform is primarily meant to be used for a VFX pipeline where Photo is used to ingest an EXR document, perform some edits in linear space, then export back to EXR using colour space conversion if applicable.

Using File>Export for any gamma-encoded format (JPEG, 8-bit or 16-bit TIFF etc) will use the ICC Display Transform result, since this mimics the gamma encoded view you would see in those formats.

OCIO display transform employs a non-destructive device and view transform on top of the linear data you're working with, effectively allowing you to preview it in various colour space and device configurations. You can of course move between colour spaces using the OCIO adjustment layer—this is primarily for compositing material together with different source colour spaces. For example, you might bring in a composite layer that's actually in Rec.709 whereas you might be working in ACES. So you would use an OCIO adjustment layer to go from ACES to Rec.709, place that layer above this, then use another OCIO adjustment to go back from Rec.709 to ACES.

Finally, the export process would involve going back to EXR so that all the colour values remain linear.

To add another layer of complexity, you can control the input and output colour space for EXR by appending the colour space to the file name. For example, if you have an EXR document whose primaries are in linear ACES, you could name it "filename aces.exr", and Photo would convert from ACES to scene linear when importing it.

When exporting, you can also convert to an output colour space—so if your export filename was "filename acescg.exr", it would convert the primaries to ACES CG.

Of course, none of this is helpful when you simply want to export a colour managed bitmap from Photo 😅

As you've discovered, this approach needs to use ICC Display Transform: the issue here is that you're also battling a non-linear gamma transform that gets applied at presentation stage (and then encoded into the document profile upon export).

I do have some free macros here which might be helpful: https://jamesritson.co.uk/resources.html#hdr

The Blender Filmic macros allow you to apply the filmic transforms to linear EXR/HDR data without any OCIO dependencies, so you can open your EXR files, apply whichever contrast look you want, then go about your editing and finally use File>Export safe in the knowledge that everything will look consistent.

The one thing you may have to be mindful of is that if you have OCIO configured, any EXR you open will switch to OCIO display transform by default, so you'll have to manually switch it to ICC Display Transform.

Hope that helps!

 

[stger]

Hello,

Thank you for the answer. Most if it I already figured out myself.

Originally I just wanted to do Blender EXR post edit in Affinity, and yes I already found

https://jamesritson.gumroad.com/l/jr_blender_filmic_macros?layout=profile

Which is an excellent solution. ❤️

However, it would be awesome if we could get the Blender Filmatic transformation built-in as a filter, to make the life of the Blender users easier

It was really a long journey for me until I found that macro.