What's the difference between Rec. 709 Gamma 2.4 and HDTV (Rec. 709) in AE? Which one should I use for advanced VFX when working in linear color space?

You can use any of those or even sRGB in a linearized workspace, as the gamma in the profile is not used, only the color coordinates of the primaries and white point.

When you are working in LINEARIZED space, your gamma is 1.0

 sRGB and Rec709 use the same primary coordinates, so there is no difference between them when linearizing your workspace. The only difference between sRGB and Rec709 are the gamma curves.

None of those profiles should be used for output in most cases. When you are converting from linearized space to render out to a Rec709 video, you want to use the correct gamma for video files, and the gamma of such a profile is closer to 1.9-2.0, and not 2.4.

The "HDTV (Rec709).icc" ICC Profile uses a 2.2 gamma curve (and appears no different than sRGB) with no offset as is specified in the actual ITU-R. We do not recommend using this profile.

The profile I am now recommending is: Rec709-elle-V4-rec709.icc

Downloadable here:

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

It is the only one I've found that appears to have the correct linear "knee" in the near black area. It seems many other profiles, including those that Adobe distributes, are using an incorrect gamma curve.

Rec709-elle-V4-rec709.icc matches the scene-referred profile as specified in ITU-R, and as such we recommend using it in workflows involving Rec709 sources, particularly for unwinding a Rec709 source into a linearized workspace.

For outputs, due to the proliferation of the other profiles, tests should be run to ensure it is suitable for all workflows where different Rec709 profiles may be in use, in order to match correctly.

 

This article was originally written circa 2012, but updated July of 2018

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