OpenCV warpPolar_0

Most of this pack is plumbing you reach for when you need to fix something - straighten, correct, clean up. warpPolar is the fun one. It remaps an image between polar and Cartesian coordinates, which is how you turn a flat image into a "little planet" (that swirling sphere-in-a-circle effect), or unwrap a circular/annular texture into a rectangular strip, or undo a fisheye's circular projection. If you've seen those videos of a street scene melting into a vortex, this is the operation doing the melting.

How it works

Polar warping re-expresses every pixel by distance and angle from a center point instead of by x/y. Pick a center, a maxRadius to bound the circle you care about, and a dsize for the output, and the node re-samples the image accordingly. Two flavors live in the flags int: WARP_POLAR_LINEAR (256) keeps radial distances linear, and WARP_POLAR_LOG (512) spaces them logarithmically - the log version is what makes a fisheye's dense center spread out into a uniform panorama-like strip. Add WARP_INVERSE_MAP (16) to run the transform backwards, going from polar back to Cartesian.

Inputs and outputs

• src - the NPARRAY image (Image2Nparray first).
• dsize - output size as a literal, e.g. (720, 360) - width × height of the result.
• center - the pole of the transform as a literal point, (w // 2, h // 2) style. // works because it's parsed as Python; (256, 256) is fine too.
• maxRadius - FLOAT; the radius (in source pixels) that maps to the edge of the output. Too small clips the image, too large wastes output space.
• flags - interpolation bits OR'd with the polar mode. A working recipe: 257 (INTER_LINEAR=1 + WARP_POLAR_LINEAR=256). For the log/unwrap version: 513.

Optional dst - skip it. Output: one nparray, the warped image.

Installing

Standard pack install. ComfyUI Manager, search "opencv-comfyui", install, restart, or:

cd ComfyUI/custom_nodes
git clone https://github.com/geroldmeisinger/opencv-comfyui

Dependencies: opencv-contrib-python, numpy, torch.

The fiddly bits

• Flags are easy to get wrong, and there's no tooltip to catch you. 256 linear vs 512 log vs the +16 inverse - test each on a copy of your image before committing.
• center and maxRadius are literal strings - (256, 256) not 256 256. Get that wrong and you'll see invalid syntax (<unknown>, line 0).
• Preview confusion: the output of the forward pass is a polar strip that can look like a mess until you understand what you asked for. That's normal; the result makes sense as a strip, not as a picture.

This is a niche-fun node, honestly. In a ComfyUI generation workflow you'll reach for it for a stylized shot or a texture job, not for daily work. But when you want the little-planet look, it's the exact right primitive, deterministic and free.