Computer vision bugs that are type bugs, and how a type system makes them unrepresentable. https://karhunen-loeve.github.io/ 2026-09-21T12:00:00Z Thomas Stephan https://github.com/karhunen-loeve © 2026 Thomas Stephan https://karhunen-loeve.github.io/01-rgb-bgr-the-blue-face-bug.html 2026-09-11T12:00:00Z 2026-09-11T12:00:00Z

Three bytes in memory do not say which channel comes first. Read as RGB they are a warm skin tone; read as BGR they are ice-blue. A blue face on screen is a funny bug; a blue face inside a tensor is a silent one. Why RGB/BGR confusion is a type bug, and what it looks like when the compiler catches it.

https://karhunen-loeve.github.io/02-gamma-blind-interpolation.html 2026-09-11T12:00:00Z 2026-09-11T12:00:00Z

Average a black pixel and a white pixel. You wrote (0 + 255) / 2 and got 128, but 128 carries only about 22% of the light, so the answer is visibly wrong. The correct value is 188. Gamma-encoded pixels break every naive resize, blur, and blend, and the fix belongs in the type system.

https://karhunen-loeve.github.io/03-pyramids-and-scale-space.html 2026-09-21T12:00:00Z 2026-09-21T12:00:00Z

To find an object at any size you shrink the image until the object fits your detector. Beautiful theory, and in practice a staircase of traps: odd sizes that stop round-tripping, two different things both called "scale", and coordinates that drift half a pixel per level.