ACEScg, the basic must-know when rendering

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This is taken from the ACEScg Discord server community - from the #acescg-guide channel.

This is a good summary of ACEScg in practical:

• ACES (default, as non-CG) → ACES 2065-­1 → the largest gamut and is referred to as AP0 (ACES Primaries 0). DO NOT USE AP0 FOR RENDERING! Use ACEScg = AP1. used for archival copies and transfer material between departments.
For more information, check this post from the ACES central forum: What am I rendering AP1 or AP0?

• ACEScg: Intended to be a working space for compositing and cg. The ACEScg specification, S-2014-004, defines a 16-bit or 32-bit floating point color encoding corresponding to linear exposure values encoded relative to the ACES AP1 primaries. The AP1 primaries lie near the spectral locus and encompass the Rec-2020 gamut and the DCI-P3 gamut for a range of white points. The AP1 primaries are within the ultra-wide AP0 primaries, used for the ACES2065-1 color encoding,and are well-suited for lighting, rendering, and compositing applications. Source: http://duikerresearch.com/wordpress/wp-content/uploads/2015/09/ACEScg-Digipro-2015.pdf | In some software ACEScg is also referred to as AP1, which stands for “ACES Primaries 1”.

IDT - The must know
If you don’t pre-convert your images to get the correct primaries then they will look off and incorrect.

• Utility – sRGB – Texture: for your LDR (low dynamic range) aka 8bit textures: Color (Albedo/Diffuse), Specular etc…
• Utility – Linear – sRGB: for HDR (high dynamic range) images like HDRIs IBL and all files with a linear transfer function within the sRGB gamut. Also valid for 16 bit EXR or TIFF files for instance.
• Utility – Raw: for scalar maps that need to be linearized when rendering such as: roughness, displacement, normal maps etc…
• Render in ACEScg and use OUTPUT - ACES sRGB, assuming that your monitor is in sRGB. If not, find out what your monitor is set to and use the appropriate ODT.

• Highly recommending the full guide from @ChrisBrejon https://chrisbrejon.com/cg-cinematography/chapter-1-5-academy-color-encoding-system-aces
• Also: https://acescolorspace.com

Additionally, this comment from: ACEScc vs ACEScct

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Hi @kn9,

sRGB does not technically define an OETF, so it is really (EOTF and Inverse EOTF). I would not qualify sRGB as legacy though, I can see it staying with us for the foreseeable future, especially when Output/Display-Referred workflow is the normative workflow in a lot of industries, VFX is a small fish in the tank and many games are still produced using sRGB as the working space.

This is not quite true, sRGB has infinite dynamic range, it is only bounded in Output/Display-Referred workflow. The part about photo-realism is not true either, there have been many shows and many artworks produced with sRGB that looks photorealistic and probably many will still be produced like so.

That being said, ACEScg offers a wider gamut that behaves better with CG in general while enabling artists to access more colourful palettes which is important when one needs to match plates that feature narrowband light sources such as LED and lasers.
However, and, important to keep in mind: ACEScg does not encompass the full visible spectrum and even less so what cameras capture, likewise for ACES2065-1 for the latter.

Cheers,

Thomas

Hello Thomas, you are correct, I was not clear enough and will edit. Some parts here are not from me but a copy/paste and I don’t have the source but I could find it back. My mistake.

I’ve removed that part as there are many articles on the advantages of ACEScg and kept it to the essential. That said, I would never go back to a classic sRGB workflow.

Thank you for your comment.

All good, not saying you should work with sRGB either! Only disambiguating and correcting what is misleading or incorrect :slight_smile: It would be worth amending/fixing whatever is on the Discord guide for obvious reasons!

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Hey thanks so much for this Post! Does that mean that I should conform my .R3D clips to ACEScg and not AP0 for comping? I could also conform to AP0 and use and an IDT to ACEScg…

Hello Robin, just to clarify: this post is specifically for a full CGI workflow without plates/footages involved. I believe you can have a look at this post: VFX work in ACEScg with out of gamut devices. Feel free to post a dedicated new post on the forum if your answer hasn’t been covered already.

Best

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