I agree it's very cool, but I have found it to be surprisingly poor in certain scenarios. A "faint" circle will often score worse than 2 high-contrast parallel

I agree it's very cool, but I have found it to be surprisingly poor in certain scenarios. A "faint" circle will often score worse than 2 high-contrast parallel lines that happen to be the right distance apart, since the lines manage to trigger pixels along 20% of a circle's arc and their contrast massively inflates their score compared to the faint circle (higher edge pixel density). It seems like there should be a simple way to weight the results by how dispersed within the circle's arc the pixels are, but I've never dug any further, after hitting this problem I had to move on.