supervision 0.31.0 shipped on October 16, and its release notes open with "supervision now sees depth." A depth map is a single-channel image. So is a thermal frame, and so is an MRI slice like the ones in my TumorLytix project. The next two patch releases, 0.31.1 on October 20 and 0.31.2 on October 24, taught the mask, halo, crop and icon annotators to draw on grayscale scenes.

On October 25 I opened a pull request for one annotator that still crashed on those frames. It was merged on October 26. This post is the short version of that side quest, from the first ValueError to a test pattern I plan to reuse.

The short version

A colour is three numbers. A pixel in a grayscale image holds one number. ComparisonAnnotator tried to put the three numbers into every pixel under a mask, and NumPy refused. The rest of the library already had a rule for this case, keep the blue value, and a helper that applies it.…