Blender Input Load Mask

Inpainting and regional workflows need a mask, and a mask is really just an image whose alpha channel says "touch here, leave that alone." BlenderInputLoadMask is the ComfyUI-Blender version of LoadImageMask with one opinion baked in: it reads the alpha channel and gives you a MASK - and nothing else. You pick a file on the Blender panel, the node loads its alpha as the mask, and your inpainting node gets exactly the shape it expects.

The source shows the opinion clearly. It subclasses ComfyUI's LoadImageMask, strips the channel widget entirely, and hard-codes the call to use the alpha channel in execute. Then it slices the image output off the tuple so you get a pure MASK output - no IMAGE sitting there tempting you into wiring the wrong thing. For a workflow whose mask comes from an image's transparency (very common when you're rendering mattes or exporting PNGs with alpha from Blender), this is the node you want, and it's simpler than the general-purpose loader.

Inputs and outputs

• image - the file to read the mask from, from the server's input folder. A dropdown in Blender.
• order - panel position, lower first.

Output is a single MASK. Wire it into inpainting, conditioning, or anywhere a mask tensor is expected. That's the whole node - one input that matters, one output.

Installing it

Standard for the pack. ComfyUI side, ComfyUI Manager → search "ComfyUI-Blender", or:

cd ComfyUI/custom_nodes
git clone https://github.com/alexisrolland/ComfyUI-Blender

Restart ComfyUI. No extra Python dependencies, but you need a current ComfyUI - schema v3 nodes won't load on older builds. The Blender add-on is the other half, a ZIP from the latest release installed via Edit > Preferences > Add-ons > Install from Disk.

Where people get burned

The big one: the mask comes from the alpha channel, so a file with no alpha (a plain JPEG, a flattened render) produces a mask that's empty or all-or-nothing, and inpainting silently does the wrong thing. Export your matte with transparency - in Blender, that means the PNG with alpha or a rendered mask pass - or you'll debug a "why is it painting everything" mystery for an hour. Second, the file has to live on the server's input folder; a remote ComfyUI means the file must be uploaded there, not on your Blender machine. And the panel only builds after an API-format export and import, title-as-label and all ("Mask" beats "mask_2"). It's a one-trick node, but it's the right trick for alpha-derived masks - pick it deliberately, not by default, and only when your mask genuinely lives in an image's alpha.