Computer Vision simulators
What can be measured in a picture, and what has to be guessed.
Image Representation
A photograph in memory is a grid of whole numbers and nothing else. Move the magnifier and the same patch is a picture and its numbers at once, then take the numbers apart: one channel at a time, and fewer and fewer values each.
Image Filters
A filter is a small square of numbers. Slide it over a photograph and the same handful of weights will blur it, sharpen it or leave nothing but its edges. Pick one, resize it, or drag the weights until it is yours.
Finding an Object
A detector is a picture of the thing you want and a window that walks the scene asking how much this looks like that. Drag the window about, or set it sweeping, and watch a score appear at every position and every size before any box exists.
Boxes and Overlap
A detector returns a heap of overlapping guesses, not one box per object. Two rules turn the heap into an answer: a number for how much two boxes are the same box, and a procedure that keeps the best and deletes its neighbours.
Shape from Shading
A photograph is flat, yet you see a surface in it. Brightness is decided by how each patch leans towards the light, and turning that around recovers the shape, provided you guess the light right.