We've are compositing in rec709 as opposed to the default no-color space in AE, and when we switched to 709, it seems to be quite a bit brighter in gamma and offset.

Something we discovered is that not all Rec709 profiles are created the same - some have a technically wrong gamma. This includes Rec709 profiles that ship with Adobe products.

For instance the profile named "HDTV (Rec709).icc" does not have the correct gamma curve - in fact HDTV (Rec709).icc seems indistinguishable from the sRGB profile!!!

Unfortunately there are many Rec709 profiles out there with different gamma curves. 

The profile named Rec709-elle-V4-Rec709.icc is one of the few correct ones, and it is the one we recommend at this time. It can be downloaded here:

https://github.com/ellelstone/elles_icc_profiles/blob/master/profiles/Rec709-elle-V4-rec709.icc

This profile has both the correct linearization at levels lower than 0.018, and the correct gamma offset that results in a perceptual gamma that varies about 1.9 to 2.0 depending on level. It is definitely the profile we recommend for unwinding camera sourced Rec709 footage into linear space.

Should you use it for output? Perhaps - but as always this should be tested in a workflow pipeline test to ensure uniformity. For instance, if a look LUT is being baked in, and the other footage with the baked in LUT is using a different profile, then that profile might be a better choice for outputs.

This article was originally written June 2018, updated July of 2018

 
 
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