Standard sRGB/3D-LUT vs. ACES 1.0.1
In the last years we got used to work in Nuke in a gamma- but not color managed way with the help of standard 3D-LUTs (ARRI or CINEON for RED material) or primary grade look LUTs from Resolve. Nuke handled the gamma, the 3D-LUTs handled the gamut.
This works fine in Compositing until you have to work with material form different cameras in the same shot.
I am using an ARRIRAW ALEXA 65 file (A003C025_150830_R0D0.0078471.ari) from the ARRI ALEXA SAMPLE FOOTAGE website. The 6k-file was cropped and scaled down to HD.
What you see on set & in editorial and what you want to see in Comp.
The two images are looking quite similar. The tone mapping of the RRT is a little brighter and shows more contrast. Both images are handled internally in scene linear light values. The tone mapping and gamut is happening in the viewer and only baked in the image date once it is written out for viewing the images.
Still these are two very different ways of working and handling the image data.
(1) is not color managed whereas (2) is color managed by ACES.
What you shouldn’t have to see in Nuke.
(3) ALEXA footage seen through the standard sRGB viewer. The image data is correct, the viewer can only show a small “window” of all the image data. The linear light values range from 0-55 (in practice more around 35-40), but the sRGB Viewer can only handles values between 0-1. The colors are washed out, they are recorded in Alexa Wide Gamut (AWG) and are not properly mapped to be viewed on a sRGB/REC.709 display.
(4) An ACES limitation until version 1.0.2. The sRGB ODT is D60, but all the sRGB monitors that we usually use are D65.
The image looks too “warm”. OCIO 1.0.3 has a RRT-sRGB in D65.
Linear light – no gamma curve applied.
(5) and (6) show that in both cases the underlying image data is preserved. A simple multiplication of 0.05 was used.
Log formats – an efficient way to store more data in standard file formats.
(7) and (8) show log encoding of linear light image data.
The first eight images show how similar an ARRI Alexa LogC/3D-LUT Rec.709 workflow is in comparison to ACES.