AM OCIO Log Convert

AM OCIO Log Convert is the pack's most boring node and one of its most useful. It does exactly one thing: convert between scene-linear and a log encoding, both directions, via whatever OCIO config is active. One checkbox, one job.

It's part of comfyui-am-vfx-tools ("AM VFX Tools/Color" category), Adrian Meyer's 13-node VFX toolkit. In the pack's own framing, it's "useful as the boundary node when feeding scene-linear output into log-trained samplers and back."

Why a log boundary node exists at all

Some diffusion models - and a decent chunk of video models - are trained on log-encoded or otherwise non-linear data, not raw scene-linear. When your pipeline is properly color-managed (read → linear working space → model → back to linear), you sometimes need to hand the sampler log pixels and then undo it afterward. This node is the door: reverse off goes scene-linear → compositing_log; reverse on goes back.

The exact curve isn't hardcoded. It's whatever the active OCIO config binds its scene_linear and compositing_log roles to - ACEScg in ACES configs, Linear Rec.709 in legacy ones, and the Cineon-style log from the compositing_log role. Same code, works across Studio, CG, or a custom config. That's the OCIO way and it's the right way: you never guess at a curve, you let the config be the source of truth.

The inputs

One widget, reverse (off = linear → log, on = log → linear), plus optional image and video. The video path is lazy per-frame like every node in the pack, and alpha passes through untouched. Outputs are image - same primaries as the input, different encoding curve - and video.

Honestly, that's the whole node. If the compositing_log role isn't bound in your config, the transform degrades to whatever the config can do - so its behavior is only as good as the config you loaded. That's not a bug, it's the design: config-driven, the way a real VFX pipeline wants it.

Installing it

Same as every node in the pack - one install, all 13 nodes:

cd ComfyUI/custom_nodes
git clone https://github.com/am-pipeline-prod/comfyui-am-vfx-tools.git
cd comfyui-am-vfx-tools
pip install -r requirements.txt

Restart ComfyUI, or search comfyui-am-vfx-tools in ComfyUI Manager. The opencolorio>=2.5.0 dependency comes from that pip line.

Where people get burned

The trap is expecting it to do something when there's no meaningful config. On the identity stub (the pack's last-resort config), log convert is a no-op that looks successful - you'll think you converted and nothing happened. If your log conversion seems to change nothing, check that you're actually on a real config, and check which direction you asked for. For the 90% case - a color-managed pipeline with a real config, feeding a log-trained model - this is the exact node you reach for.