An image model stacks windows like the blur in “Same rule everywhere”. Layer 1 slides a window widths[0] pixels wide along a row of pixels, moving steps[0] pixels each time. Layer 2 slides a window widths[1] wide over layer 1’s outputs, moving steps[1] of them each time, and so on. Write sees(widths, steps): how many input pixels can one output of the last layer see, counting every pixel that can change it?