ACES: apply LUTs as is (no extra transformations)

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waltervolpatto

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ACES: apply LUTs as is (no extra transformations)

PostTue Sep 28, 2021 7:02 pm

in the color management there is a choice of process node LUTs as "AP1 or AP0" and an inherent transform is applied to it.

I would like an option where the LUT is applied AS IS (in the ACEScct color space of he node that is, with no further manipolation.....)
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Re: ACES: apply LUTs AS IS (no extra transformations)

PostTue Sep 28, 2021 11:12 pm

There might be a reason it's in ACEScc instead of cct that has to do with the toe part but I could be totally wrong.
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Re: ACES: apply LUTs as is (no extra transformations)

PostWed Sep 29, 2021 7:45 am

You could try tricking it by applying inverse transform before the lut node and removing it afterwards. This way when Resolve applies its transform, data gets back to ACEScct colorspace istead.
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Re: ACES: apply LUTs as is (no extra transformations)

PostWed Sep 29, 2021 8:01 am

But AP1 is the color space used for ACEScc(t) though.
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Re: ACES: apply LUTs as is (no extra transformations)

PostWed Sep 29, 2021 8:29 am

RikshaDriver wrote:But AP1 is the color space used for ACEScc(t) though.

It is kind of ambiguous imho, lets say with AP1 it stays either in ACEScc or ACEScct depending on what is set for project working space. With AP0 does it transform to ACES2065-1? It has way bigger dynamic range than normalized 0.0-1.0, so for most LUTs would need a shaper. Where is that shaper defined? Or is AP0 just changing the gamut and transfer function is kept the same ACEScc/ACEScct, producing some out-of-aces-specs mixed colorspace? I don't use this myself and can't currently check the manual...
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Re: ACES: apply LUTs as is (no extra transformations)

PostThu Sep 30, 2021 5:16 pm

If a LUT is expecting a certain color space input and then output, are you asking this because you plan on doing a CST before and after?
And does that defeat the Aces color space math? Shouldn’t a LUT used in aces be “wide” enough to not clip any data/math if it’s going to be used? (Forgive my rudimentary understanding of the math:workflow – asking to learn/update my knowledge).
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Re: ACES: apply LUTs as is (no extra transformations)

PostThu Sep 30, 2021 6:20 pm

dariobigi wrote:And does that defeat the Aces color space math? Shouldn’t a LUT used in aces be “wide” enough to not clip any data/math if it’s going to be used?

Value wise colorspaces are all the same ”width”, only value range, whether values outside normalized 0.0-1.0 range make sense or not, differ. For linearized values they do (regardless of gamut, be it rec709, AWG or AP1/0), for gamma and log encoding usually not. So if LUT is prepped for ACEScct for example, it numerically operates on the same input value range as any rec709 LUT does.
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Re: ACES: apply LUTs as is (no extra transformations)

PostFri Oct 01, 2021 1:03 am

dariobigi wrote:If a LUT is expecting a certain color space input and then output, are you asking this because you plan on doing a CST before and after?
And does that defeat the Aces color space math? Shouldn’t a LUT used in aces be “wide” enough to not clip any data/math if it’s going to be used? (Forgive my rudimentary understanding of the math:workflow – asking to learn/update my knowledge).
Respectfully asked.


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Yes, the idea is to get temporarily out of ACES cc(t) in a known color space, apply a LUT an get back to ACEScc(t)
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Re: ACES: apply LUTs as is (no extra transformations)

PostTue Oct 05, 2021 10:08 pm

I’m guessing right clicking on a node and changing its color space does not yield the results you’re looking for. I haven’t tested it, just a thought as I’m away from my system at the moment


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Re: ACES: apply LUTs as is (no extra transformations)

PostWed Oct 06, 2021 10:38 am

waltervolpatto wrote:Yes, the idea is to get temporarily out of ACES cc(t) in a known color space, apply a LUT an get back to ACEScc(t)

Not sure what you're going after with the original question of applying a LUT 'as is' but I think any LUT that is designed to work for any colorspace can just be applied in an ACES workflow by going to that colorspace before and back out to your timeline space after with the exception that display spaces can't be fully inverted perfectly but the differences can be minor.
In ACES the ODT+RRT is always present (if you picked one) so if the intent is to actually use the lut to go to display instead you would have to bypass the color management for that clip instead.

I presume the distinction between process node LUTs in AP1 or AP0 has to do with LUT look modifications that might need to be in linear AP0 like the ACES 0.1.1 Emulation. I think that project setting is virtually the same as if you'd change the node itself to ACES-2065-1 but haven't tested that.
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