Fat Mex Image Compare

When you're A/B-ing a prompt, a denoise value, or a before/after face swap, the fastest way to see the difference is two images side by side. This node takes image_a and image_b, stitches them into one image with a small dark gap between them, and hands you a single comparison you can preview and save. It's a two-minute utility, and it's the kind of node that's trivial to build and still worth having around.

The output is a comparison IMAGE. Both inputs take the first image of their batch, so you can pipe in batch outputs without ceremony.

How it works

The mechanism is honest and simple:

1. It matches the two images' heights - the shorter one gets resized up to match the taller (Lanczos), so the seam is clean.
2. It inserts a gap (default 4px) of dark gray between them.
3. It concatenates left-to-right: image_a on the left, image_b on the right.

That's the whole node. label_a / label_b exist as inputs - one honest heads-up: in the current build they're accepted but not drawn. You get the stitch, not the text overlay. Don't expect "Before"/"After" rendered on the output.

When to reach for it

It's the glue for the pack's own workflow style - compare the quick vs quality face swap, compare two denoise settings on the Reference Sampler, compare presets before committing to one. It also makes a nice checkpoint in a chain: save the comparison, keep generating, and you've got a visual history without hunting through your output folder.

It's not a zoom-capable diff tool - for pixel-peeping two crops, you'll still want something with a magnifier. This is for "which of these two is better" at a glance, and it's perfect at that.

Install

cd ComfyUI/custom_nodes
git clone https://github.com/FatMex/ComfyUI-FatMex-Nodes.git FatMex-Nodes
pip install -r FatMex-Nodes/requirements.txt

Or ComfyUI Manager → search "Fat Mex Nodes" → Install → restart. No models, no downloads.

Where people get burned

• Labels don't show up. You set label_a to "Before" and it's not on the image. As noted, that's the current build - the stitch is all you get. Works fine; just know the fields are decorative right now.
• "It's blurry." The height-matching resize upscales the smaller image, and upscaling a small image to match a tall one softens it. That's inherent to stitching images of different sizes, not a bug - wire in the Fat Mex Upscaler first if you need both at the same resolution.