Convert to LAB color space v5.1.0

LAB is the color space you reach for when you want to edit lightness without wrecking the color, or shift the color without touching the lightness. Unlike RGB, where a brightness tweak drags all three channels along, LAB separates the job: L is pure lightness, A is the green–red axis, B is the blue–yellow axis. This node converts an RGB image into those three channels and hands each one to you as its own MASK output - ready to be edited, renormalized, or used as a lighting layer.

In this pack it's the front half of a color pipeline: split with RGB_2_LAB, tweak the L channel (the pack's renormalize_array and recolor nodes love a separated lightness layer), then merge back with the pack's LAB_2_RGB. It's also a great way to feed a depth-map-style lighting layer to something that expects a single channel.

How it works

Plain OpenCV: cv2.cvtColor(..., COLOR_RGB2LAB) per frame, then the three result channels are sliced out and converted back to ComfyUI masks. The batch dimension is preserved - if you feed N frames, you get N L, A, and B masks each. The output masks are single-channel float tensors, which is why they come out as MASK rather than IMAGE.

The inputs that matter

• input_RGB_image (IMAGE) - the only input.

Outputs:

• L (MASK) - lightness. Edit this for brightness/contrast without hue shifts.
• A (MASK) - green–red axis. Push toward red or green.
• B (MASK) - blue–yellow axis.

All three share the source's resolution, so they re-stack cleanly in LAB_2_RGB.

Installing it

Same pack, one install:

cd ComfyUI/custom_nodes
git clone https://github.com/TRI3D-LC/tri3d-comfyui-nodes
cd tri3d-comfyui-nodes
pip install -r requirements.txt

or ComfyUI Manager → "tri3d-comfyui-nodes", restart, under TRI3D.

Common issues

• Forgetting the merge node - L/A/B masks are intermediate data. Without the pack's LAB_2_RGB on the other end you'll be stuck staring at grey channels. Build the split/edit/merge chain up front.
• Edits outside the valid range - LAB values have specific ranges (L up to 255, A/B roughly -127 to +127 after conversion), and clipping happens silently. Heavy edits can clip and look washed out.
• It's not HSL/HSV - a common swap. HSL's "L" is a different beast. If you wanted hue/saturation control, the pack's HSV recolor node is the one.

It's a plumbing node - you won't gush about it, but the color pipelines in this pack and beyond are built on exactly this kind of split.