;;; Runs an edge-detector (derivative filter) ;;; on a stream. Adjusts the scale of the ;;; image to since derivative filters tend to ;;; result in intensities between -1 and 1, not ;;; 0 and 1. (define (stream-edges s1) (stream-scale (stream-add ones (stream-scale (stream-delay s1 -1) 1) (stream-scale (stream-delay s1 1) -1)) 0.5))