Parabolize

Every image editor gives you a curves tool, and most people give up on curves because they're fiddly. Parabolize is a curves tool with one equation instead of a freehand line: it remaps every pixel through a parabola - coeff * (pixel - vertex_x)² + vertex_y - and you steer the parabola by placing its vertex and bending its width. It's not the node you'll use every day, but it's a genuinely weird and useful one: it's a tone curve that can raise shadows, crush highlights, or add a strange glow, depending on where you park the vertex.

How it works

The image values (0–1) get pushed through a quadratic curve per channel, then clamped. Because it's applied to all three channels the same way, it acts on brightness/contrast rather than hue. The parabola's shape is what does the work:

• vertex_x (0–1, default 0.5) - where the curve's bottom sits on the input range. Place it low (say 0.2) and the dark end of your image gets pulled down - shadows deepen and crush. Place it high and the highlights get pulled toward the vertex, compressing the bright end.
• vertex_y (0–1, default 0.5) - how bright the bottom of the curve is. This is your black point: raise it and nothing can go fully dark (a lifted, faded-film look); lower it and blacks get crushed toward pure black.
• coeff (−10 to 10, default 1) - the steepness of the parabola. Positive coefficients open the curve upward (shadows sink, highlights rise - contrast); negative flips it so the image inverts around the vertex, which is how you get a partial-inversion "something went wrong, but it looks cool" effect.

Output is a single IMAGE.

Install

Parabolize is one of ~22 nodes in ComfyUI-post-processing-nodes.

• ComfyUI Manager: search "post processing nodes", install, restart.
• Manual:

cd ComfyUI/custom_nodes
git clone https://github.com/EllangoK/ComfyUI-post-processing-nodes

Restart after. No requirements.txt, no downloads - it's one tensor formula. It's under postprocessing → Color Adjustments in the node menu.

Getting somewhere with it

The predictable, useful setting is the contrast lift: vertex_x 0.5, vertex_y 0.5, coeff 1–2. That deepens shadows and pushes highlights without the muddy midtone shift a naive "increase contrast" gives you. The fun setting is a small negative coeff (−1 to −3) with the vertex parked in the midtones - you get a subtle solarization-adjacent glow that no slider in ColorCorrect will give you. It's a toy, but it's a surgical toy: two of the three dials place the effect, one sets its strength. If the result looks flat, check vertex_y first - that's the black point and it's the one people forget.