1. Nuke – 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.

(1) – Nuke-Default color management (sRGB Viewer) : ALEXA LogC over Rec.709 (3D-LUT) – the same image that you see on set but without a 3D-LUT being baked in the image data.
(2) – Nuke ACES 1.0.1: ALEXA ACEScg over RRT-Rec.709

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 Linear over sRGB – standard look in Nuke
(4) – ALEXA ACEScg over RRT-sRGB D60 very warm colors – usually D65 is used

(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) – ALEXA Linear over sRGB – this is only 5% of light – see how much dynamic range is captured
(6) – ALEXA ACEScg over RRT-Rec.709 – this is only 5% of light –  see how much dynamic range is captured

(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) – ALEXA LogC – the same dynamic range but fitted into a format that ranges with values between 0-1
(8) – ACEScc (or the newer ACEScct) – The ACES log format(s) with values between 0-1.

(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.

The second page is about gamma curves and the ACES RRT.