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Re: Colour Reproduction of Large Format Digital Cinema Cameras - METExpo

Re: Colour Reproduction of Large Format Digital Cinema Cameras - METExpo

Justin Johnson <johnson322@...>





However, I used Rec 2020 as the output transform (using each vendor’s native software), so I didn’t notice colours going outside the space. Interesting observation, but maybe a bug in the debayering software you used, not sure. It would be interesting to know your workflow.  

Both ARRI and RED crop (clamp) any colors that go outside of the chosen output colorspace during the debayer, except for ARC's conversion to ACES which doesn't crop any values and allows them to go negative into the float EXR container.  (Hence the artifacts seen in ARRI-ACES pipelines (purple fringing)).  Both RED and ARRI are currently working on methods for reigning in out-of-gamut colors, I assume with gamut mapping algorithms. 



In theory, monochromatic locus should be invariant to colour temperature. This, clearly doesn’t seem to be the case, as you have demonstrated in your tests. That’s one of the common findings.

ARRI has published their image processing pipeline (RDD 31:2014) where they describe the white balance specific multiplication and matrices used.  (These values are also included in the metadata of the ARRIRAW file) These push the position of the supersaturated values when WB is changed.  RED is obviously doing something similar but they don't publish the specifics.   I am not sure what other camera makers do. 



I would be interested to hear more about your workflow. You are welcome to contact me directly or on CML and see if we can get to the bottom of it.

I am using Nuke to generate these images by converting each pixel of an image into a point cloud in Yxy colorspace.   


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