What is the official ACES Team suggestion to work on footage, that has color values outside of ACEScg gamut?
I know that blue neon colors in Alexa is now a “well” known issue. But lately I came across more footage with similar issues but in other devices and light spectrums. Specifically red lights in RED cameras and red and blue lights in Blackmagic 6k pocket camera.
Both RED WideGamut and BMD Film have gamuts outside of AP0, let alone AP1 and the IDTs are not enough to accommodate for these extremes.
I work in advertising vfx and the neon / laser / LED lights are quite common in our line of work.
I know about the official blue light fix, but probably there should also be one for the red channel? Or maybe there should be some kind of tone mappings for specific cameras as well as IDTs?
Thank you very much for any suggestions.
Cheers.
Martin
This is a great question, AFAIK, there is no all-in-one solution for that. It has however (and obviously) been discussed quite a few times with things along the lines of a dedicated Camera Gamut and/or Gamut Mapping.
What would be fantastic though would be to share some offending frames with the Academy: while it is easy to simulate offending cases, nothing beats having real data, and the solution model will only be as good as the input data it is fitted to.
I know that @sdyer would be pleased to get some images
So probably something like that for multiple scenarios?
Or what would be the suggestion for these kinds of shots? For example for the RED footage with the red lights? How can I work on that shot and do VFX in ACEScg?
Beside desaturating the offending hues to bring them into ACEScg gamut, there is not much you can do atm. Systematic solutions will be/are in the work but as I was mentioning it, it requires data and research
I exported the R3D image from RED CINE-X PRO as Ungraded RWG EXR, loaded it in Nuke with the Input - RED - Linear REDWideGamutRGB IDT. This is the upper-right image, bottom right is with a simple 20% red desaturation and ensuring the values are mostly positive:
That’s good to hear. I understand the real world data for research are essential. I can send more footage or rather stills with similar light situations.
I checked my initial image with the ACES ODT and re-did it + your way in Nuke and you are totally right. The initial ACES ODT is not so severe from the get go. I don’t know why my image looks like that - I’m doing it now again and I get the same result as you…weird. Maybe my Flame + Macbook Pro GPU had hickups with the 8k R3D I’m really sorry for the misleading image.
Anyway the desaturation is good for some cases, but compared to the RED IPP2 look, it is not so solid (obviously)
Check the highlight on the knuckles for example. The edges on them.
When I show this to a colorist, I know, which way he or she will choose…
But the desaturation is probably a good start for building some gamut mapping luts maybe.
Thank you also for the graph for visual reference. Is that generated by some commercial tool or your custom one?
I’m wondering with so many vfx studios around the world using ACEScg as their working colorspace, how they go about this in a large amount of data / shots being prepared / transcoded for the artists. Is it shot by shot basis? The TDs need to “catch” these cases when the data enter the house?
@KevinJW kindly answered some questions regarding the blue channel in Alexa cameras, but because I came across these other beauties I started this topic.
No worries, it is not misleading because even with a proper conversion the problem you were underlining still exist.
Yes, although here we are wandering into a highly subjective territory and each camera almost needs a custom fix. The diagram highlights quite well the issue with a large chunk of chromaticities outside the spectral locus. They need to be gracefully brought back within it. You could do that with a 3x3 matrix like that @sdyer built for the Blue Light Artefact Fix LMT , but I reckon there is a need for a long term solution.
The figure is generated with Colour, here is a How-To to produce similar images:
Good question, in VFX we integrate the CG onto the plate as if it was shot by the camera, if the yellow on the knuckles is a feature, we would need to match it. Here, it would be hard with ACEScg as a large chunk of chromaticities from the camera is outside its gamut. I don’t know if there are standard practices for that as you cannot generate matching values with ACEScg in a renderer. I think I would handle those special cases in comp with some sort of gamut expansion. Keen to hear others opinion on that topic.
hi @Troy_James_Sobotka, you can find it still in the original drive link - in the source folder - it is the first file - it is in the original R3D format. Develop it as you wish. Thanks a lot for the interest in the topic!
I saw a forum thread with a place to upload test images for WGM research, but can’t find it now…I will get back into it. I have some more real world examples to share. Just have to find the time to sort them out and upload.
