ACES Rec 709 Legal vs Full Data Levels

JorgePiquer · November 19, 2021, 5:12pm

Hi first time here hope this topic will help the others and I can found a solution.

So Ive been grading in ACES for a couple of years now and Im really happy with the results.

Mainly for theatrical releases grading on projectors I go for DCI P3 D65 full levels and when working on a monitor Ive been using Rec 709 also at full data levels.

I came to a friend studio to verify a GAM graded on Rec709 @ full levels. Checked on a projection DCI P3 D65 also @ Full levels and the conversion is really good as usual.

Checked on another room with LG OLED at Full levels Rec 709 and its great too.

Then I also checked on another suite that has Video levels and the problem happened.
The room has a LG OLED on Video levels so Resolve is also set at video levels.

No matter if I set my GAM Open EXR at Full levels (to match my export setings) or at Video levels the result will look wrong, clipped blacks, wrong contrast, saturation and exposure.

My main surprise is that when working on ACES 1.1 (Resolve 17) No matter if I set Resolve to work on Full or Video levels it wont have any impact on the interpretation of my GAM. With RCM changin the data levels will work as intended.

Does it means that when working on ACES we always need to stay on Full levels?
Is it not possible or not recomended to do ACES on Video Levels?
Is it a problem of Resolve? A well know issue?

I might be getting confused but I always thought your Data levels just depend on your pipeline and monitoring but you can set them as you need if you just respect to match them on your software, Video card, and monitoring the result should be equal.

Hope someone can help me out, I could not find any info about it.
Thanks a lot.

nick · November 19, 2021, 7:28pm

EXRs are a linear float format, so full/video levels is not relevant to them. In an ACES pipeline with an EXR source, the only place data levels should be of concern is to match the SDI/HDMI output of Resolve with what the display is expecting.

If you are seeing clipping, that suggests that the output of Resolve is set to full range, and the display is expecting “legal”.

JorgePiquer · November 20, 2021, 1:19pm

Hi Nick
Thans for your answer; I totally agree and understand it but still doesnt solve the problem, maybe I try to explain it better.

The problem on Resolve ACES is that when changing the data levels, it doenst change them, as if it just works on Full, changing to Video levels doenst afect the signal, so the only way of displaying the EXRs correctly is when the hole signal Resove and monitor are set to Full. When both are set to Video the clipping occurs. Would be great if someone could check or confirm this issue, Ill try it in a diferent studio to see if the same error happens.
Thanks

nick · November 22, 2021, 2:39pm

Stupid question, but just double checking. You are setting the data levels in the Video Monitoring tab of the Project Settings, not under Clip Attributes, aren’t you? Setting Video in Clip Attributes for an ACES EXR will cause clipping. Setting it under Video Monitoring certainly has the expected result for me.