OCIO Transform

This is the node that decides whether Radiance is a toy or a tool. The KB's read on the whole colour-management corner is that it's real, thinly discussed, and specialist - "OCIO" shows up in barely a handful of threads in the corpus, and "OpenImageIO" in fewer, because the people who need it talk in VFX channels, not r/StableDiffusion. The reason to care is concrete: hand an sRGB PNG to a Nuke comp and gamma-encoded values get treated as linear light, which blows out every merge. You need to decode to scene-linear, speak the same transforms as the rest of the shot, and carry float.

OCIO Transform does exactly that, using an actual OpenColorIO config rather than a hardcoded matrix. It's the general-purpose partner to HDR Color Convert: that node does fast primaries math, this one runs whatever your config can express, including camera logs and looks.

How it works

You name a source_colorspace and a target_colorspace, and OCIO resolves both against the active config, then runs the processor. The pack does the setup for you at startup: if you already have $OCIO set, it uses yours (validated, never overwritten - the same contract as Nuke and Resolve). Otherwise it activates OpenColorIO's built-in ACES 2.0 studio config, serialising it once to ACES/studio-config.ocio inside the package so that other tools and custom nodes that only accept a path can use the same file. On OpenColorIO older than 2.2 there are no built-in configs, so it falls back to the bundled ACES 2.0 CG config. Nothing downloads.

Aliases and roles resolve, which is the quality-of-life feature: ACEScg, ACES - ACEScg and lin_ap1 all land on the same space.

Inputs and outputs

Required: image, source_colorspace (default ACEScg), target_colorspace (default ACEScct). Both are free-text strings, and the tooltip tells you to connect ACES Config Manager → List Colorspaces to see valid names in your config - do that once and save yourself a lot of typos.

Optional: ocio_config_path (blank uses the environment or the locally installed config), look (e.g. ACES 1.3 Reference Gamut Compress, which is a genuinely good look to have available), exposure_stops, direction (Forward or Inverse), and clamp_output.

Two design details worth understanding. exposure_stops multiplies the raw source values by 2^stops before the transform, so it's true exposure only when the source is linear - on a log source it's just a pre-scale. And direction: Inverse runs target→source, which is how you write a roundtrip test: forward then inverse, then check the reconstruction error is near zero.

Outputs: image and metadata. Alpha passes through untouched; only RGB goes through OCIO.

Install

Manager → search Radiance → Install → restart ComfyUI → refresh your browser. Manual:

cd ComfyUI/custom_nodes
git clone https://github.com/fxtd-studios/radiance.git
cd radiance
python -m pip install -r requirements.txt

Windows portable users: python_embeded\python.exe for the pip step. OpenColorIO is a hard requirement of the pack, and install.py will also try to make sure OpenEXR, diffusers and accelerate are present - because the colour pipeline is built on the first two.

Where people get burned

CG config versus studio config. The two bundled configs aren't equivalent: camera log targets like ACES - ARRI LogC4 (EI800) or ACES - Sony S-Log3 SGamut3.Cine need the ACES Studio config. If you set your own $OCIO to a CG config, those names won't exist, OCIO will refuse the transform, and it'll look like the node is broken rather than the config being smaller than you assumed.

clamp_output off is correct for HDR. Leave it on and you'll clip legitimate values above 1.0 in log or HDR outputs - the tooltip warns about this, and it's easy to flip "for safety."

The config is process-wide. Radiance makes its chosen config OCIO's current config so every OCIO consumer in ComfyUI resolves the same names. Useful for consistency, but it also means another pack that wanted a different config is now sharing yours.