ARRI Wide Gamut 4

What it is

A one-purpose primaries converter for ARRI Wide Gamut 4 - the colour space ARRI introduced with the Alexa 35. Four directions, one image in, one image out, no widgets beyond the direction dropdown. If you're round-tripping Alexa 35 footage through a ComfyUI pipeline, this is the node that keeps the primaries honest.

If you've never touched an Alexa, this node has no use for you. That's not a limitation, it's the point - this pack is built for people who finish shots.

The four directions

AWG4 to ACEScg is the one most people want: camera-native primaries into the ACES working space, which is where everything else in the ACES half of this pack expects to be. ACEScg to AWG4 is the return leg. AWG4 to Linear sRGB and Linear sRGB to AWG4 cover the workflows that never touch ACES at all.

Two things are happening under the hood that are worth knowing about.

First, the ACEScg directions include a Bradford chromatic adaptation from D65 to D60. AWG4 is a D65 space; ACEScg is D60. Converting primaries without adapting the white point is a common and subtle error - your whites come out slightly off and nothing else looks obviously wrong, which is exactly the kind of mistake that survives to delivery. The tooltip calls this out.

Second, the AWG4→XYZ matrix in the source has a fixed third row of [0, 0, 1.0890578] rather than ARRI's originally published values. That's not an arbitrary edit: ARRI's AWG4 primaries are defined so that this row is exactly that, and the older row gave a white point about 22% short on blue. Someone checked M @ [1,1,1] == D65 XYZ, which is the right test, and corrected it.

Inputs and outputs

image and direction. That's it. Output is image.

The input rule that matters

The tooltip is explicit: the image must be linear, and any LogC4 encoding must be removed first, because this node converts primaries only. It does not decode a log curve.

That's the trap. Alexa 35 footage is LogC4 by default, and LogC4 is a transfer curve and a set of primaries held apart on purpose. If you feed LogC4-encoded footage into this node you get a grey, washed, low-contrast mess - which people usually diagnose as "the node is broken" when it's actually working exactly as specified on the wrong input. Decode LogC4 first. Radiance's own colour-space convert node lists LogC4 (ARRI Alexa 35) as a source space for precisely this, and LogC3 (ARRI EI800) for the older Alexas.

Where it sits in a chain

Typical path: read your LogC4 frame, decode the log curve, run AWG4 to ACEScg, grade or generate in ACEScg, then hand off to an output transform. The Bradford adaptation is the reason this is safe at either end - you can go AWG4 → ACEScg → back to AWG4 and land where you started.

If you're also working with Resolve, the sibling DaVinci Wide Gamut node covers the same job for Resolve's working space, including the DaVinci Intermediate log curve where relevant. Mixing the two conversions is possible and occasionally correct, but you should know why you're doing it.

Install

ComfyUI Manager → search Radiance → install → restart → refresh the browser. Manually:

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 should run pip with ComfyUI's bundled python_embeded\python.exe. This node is numpy/torch matrix maths, so it needs nothing exotic - but the pack's install pulls in OpenEXR, OpenImageIO and OpenColorIO, and if you're feeding it actual Alexa footage from an EXR sequence, you do need those working. The requirements file skips the OpenEXR wheel on Python 3.14 (none exists) and falls back to OpenImageIO and OpenCV for EXR I/O, so EXR reads still work there.

Gotchas

• LogC4 in, grey out. Decode the transfer curve first. Read the tooltip before assuming anything else.
• Using it as your only conversion. It's primaries-only in both directions; it doesn't know anything about encoding.
• Assuming it's an ACES node. Two of the four directions never go near ACES.
• Feeding display-encoded Rec.709. The Linear sRGB paths mean linear Rec.709/sRGB primaries, not sRGB with its curve applied.
• Expecting a menu full of camera formats. This pack handles AWG4 and DaVinci's spaces explicitly, and other camera gamuts through the general colour-space convert node.