I’m new to ACES, and I want to apply it to SDR images, but I’ve noticed that when using ACES, the mapping goes from (1.0) to (0.8). I understand that the 0.8-1.0 range is reserved for the ‘over bright’ parts of HDR images, which doesn’t seem necessary for SDR images.
I found a step in the ODT called ODT_48nits, and removing it or changing it to ODT_1000nits allows the brightness to reach the maximum. Is this the step that causes it? But I couldn’t find ODT_100nits.
Currently, we are simply stretching the result from 0.8 to 1.0 after mapping, which doesn’t feel quite right. Which step should I modify?
Hello @lysis013 and welcome to ACES Central !
I don´t think you should apply ACES to SDR images. I think it is meant to be used on High-Dynamic Range “data” only.
Regards,
Chris
When I want to work with photographic SDR imagery (such as Rec. 709 video) in an ACES environment, I use what I call the “inverse ODT” method, setting the Rec. 709 ODT as the input transform.
This process is not currently 100% lossless for some very saturated colors, but it essentially promotes the SDR source to HDR by un-doing a plausible assumption of what might have been its HDR-to-SDR encoding curve.
Not all SDR sources respond well to this extreme processing. Don’t expect the highlight detail to be pretty or hold up well to downstream processing.
However, basic corrections do respond well.
If Chris or others want to strongly discourage this I’m all ears. I wrote a whole lot more about it here: Linear Light, Gamma, and ACES — Prolost
Nice read! If you feel like it, you may want to update it at some point since After Effects and Magic Bullet have had OCIO and ACES support implemented natively a while back.
1 Like
Thanks! I did add addendums to that effect, but it’s probably time for a whole new post. Maybe after 2.0 is released.
1 Like
Pleased to hear that Stu, refer to this doc frequently - was back n fwd with maxon asking why (in AE aces 1.3) if I used Looks and pushed the blue shadows extreme Vs colorista log mode sandwiched CCT pushed blue extreme the result is quite different - not really wrong but as I thought it was it was, I tinkering in and out of transforms in AE for days to try and work out what was going on. Still wondering if there is a way to stay aces and overlay the motion graphics and logos etc. Thinking no, there are some odd inverts you can do but the colours have ugly aliased edges as its a hack. Presently I composite and grade in aces (sandwiched cct for most footage) - output to rec 709 and add the motion grfx etc there. One comp to rule them all tho would be nice.