OnSET ACES create CDL /Exposure adjustments

Discussions - Using ACES
1

I am usually working in post but I am trying to figure how the CDLs and stuff I get from set are even made. (because mostly… they suck) Pomfort Livegrade supports ACES.

The problem I am running into is , I have no idea how I can Do exposure adjustments In AcesCCT-> in linear I can just multiply all the values by 2 and go one stop up but Livegrade of course does not le me do this, I can only change between acesCCT and acesCC. (which makes sense considering where the CDL will be living in the final ocio, and thats how ive always gotten my aces stuff from Netflix and so on. (lin->cct->CDL->ODT)

I guess the issue exists for all Log formats and only having simple CDL controls… How is this done usually? I would need to have a exposure slider that then translates into CDL values should be possible as the acesCC(t) curves are known…

Resolve has solved this well with their HDR geading controlls, flame also has a very good Grading tool (masterGrade matchbox)… So how can we do this stuff on set?

Also wouldnt it be beneficial to do it like this for onset grades:

camera->idt to linear-> cdl(just slope for exposure)-> acesCCt-> CDL for look-> ODT

easy enough to do in OCIO, should be able to package this into a 3D LUT for a boxIO or sinilar

also considering we need 2 different HDR paths for reference and onset monitor (Onset monitor needs to be adjusted for surround luminance).

2

It is not possible to exactly replicate gain in linear using only ASC CDL operations in ACEScct. CDL Offset in ACEScct is equivalent to linear gain (with an offset of 0.057 being about a stop) across most of the image range. But it will alter near black pixels. Anything more than about 4.5 stops below mid grey is below the cut point in the ACEScct curve, so will behave differently.

In ACEScc, CDL Offset will be an exposure change. But if the working space will be ACEScct elsewhere in the pipeline, you cannot “mix and match” ACEScc and ACEScct.

3

ah ok thats interesting! So I can just switch to acesCC across the pipeline and use CDL offset for exposure and its done? Nice!

I fixed it right now by making compensation luts in nuke, it works well but its nicer to have it paramteric, Ill try that with acesCC next :slight_smile:

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