LUTs and ACEScc in OCIO

Is it necessary for the working space to be in ACEScc or ACEStt when applying a grade LUT file?
Or should the question be: Is the LUT only applied on log images in the 0-1 range using OCIO in Nuke? Is this method software-specific or is it the standard and preferred way, applying LUTs on log images? And if it is the preferred method, why is it? I have limited knowledge of LUTs and shapers so if someone thinks this is not the right place for this question, can someone point me to the right place or papers written about this subject. Thank you.

The reason I ask this is that I want to apply a grade, created in Nuke, in linear ACEScg working space, and generate LUT from it, so I can use it let’s say as a “look” accompanied by a view transform in ocio.config file. But when I process the image(in my case an ACEScg image) with the LUT in Nuke using the OCIO File Transform Node, all the values above 1.0 get clipped and the information in the image above that value is lost, no matter what working space I specify this LUT is applied in, except when I choose ACEScc or ACEStt of course. In that case, after processing the image with the LUT, the values above 1.0 are preserved (let’s say is not an extreme LUT). Maybe behind the scenes, OCIO File Transform does several color space transformations like in my case ACEScg to ACES 2065-1 to ACEScc, (LUT is applied) to ACEScg? I expected a similar process to happen when specifying a linear working space for some LUT generated for use in this working space. I’m not sure.

Not that this is a big deal. With some color space conversion, one can always create a grade LUT in ACEScc/tt in Nuke or simply export one from Davinci Resolve while in ACEScc/tt working space, but I want to make sure that this is the case.

The opposite thing happens in the Vectorfield node in Nuke, where Nuke generated LUTs from CMSPattern, when applied with Vectorfield node on an image in Nuke, the information above 1.0 is preserved (if it’s not an extreme LUT of course). But, if I use an externally generated LUT file, for example, a .csp LUT from the repository of OCIO Aces 1.2 baked LUTs (sRGB for ACEScg Maya.csp) file, which I assume is generated in OCIO), after processing the image with the LUT, the information above 1.0 is not preserved. BUT, in this case, although information above 1.0 is lost, the ACES tone mapping and the look are applied to the whole dynamic range of the processed image, as intended by the name of the LUT.

I should mention again, that I have limited knowledge of shapers and LUTs. At the time of writing this, I’ve read that most LUTs are combined with a 1D shaper LUT + 3D LUT. So in the case of (sRGB for ACEScg Maya. csp) LUT, the 1D shaper LUT normalizes the image in 0-1 range by applying tone mapping (the ACES S-curve shape). And is there another conversion of this tonally mapped image to log so that the 3D LUT gets applied correctly (as my first question in this post)? I assume these LUTs are only used as view transforms for some software that does not support ACES natively.

I am not a specialist but follow it closely as a 3D artist and film and photography, it can feel like you are going around in circles. If you think of Luts like this, the are actions, a repeat of what has been done before and saved out to this format. If you are familiar with photoshop, 1D luts are like adjusting curves, 3D luts are like colour correction applied to specific colours or tones (more targeted and transformative). Let’s say you add several adjustment over an image, you can save that combination out as a LUT file, and hand that LUT to other designers to replicate what you achieved. So if the file you created the LUT in was sRGB, you wouldn’t get the same result if a designer used it in their CMYK image. LUTs should be used in the same colour space they were created in. It’s all they are, a replication of what someone has developed. That’s why all the IDT and ODT files, to get your image into the right colour space, to work on it and save it out to the final colour space, that’s ACES.

Hey there, in my experience depends on the config of OCIO you are working. It always work for my to apply in ACEScct and for the problem of 0-1 range the node OCIOColorTransform would not let you pass de 1 because thats the limit.
I will try to go from ACEScct apply Lut then another node to ACEScg and then export a .cc so it’s easy to import in the future in Nuke. Color managment it will be ok but you don’t solve the problem of range.

Another option is doing this in Davinci and export the LUT with tone mapping. Then import to Nuke. Doing this maybe you can preserve the information above 1.0.

I hope this help you and don’t create noice in your workflow.
Tell me if you solve this.