> (define rad (read-image "radiation.pgm")) > rad #<image: rows = 243 cols = 320> >

> (load "histogram.scm") > (plot-histogram rad) >

> (plot-histograms rad (+ rad 64)) >

> (plot-histograms rad (/ rad 2)) >

> (- 255 rad) #<image: rows = 243 cols = 320> >

> (plot-histograms rad (- 255 rad)) >

> (image-map (lambda (x) (if (> x 128) x 0)) rad) #<image: rows = 243 cols = 320> >

> (plot-histograms rad (image-map (lambda (x) (if (> x 128) x 0)) rad)) >

> (define cactus (read-color-image "cactus.ppm")) > cactus #<color-image: rows = 200 cols = 300> >

> (plot-color-histogram cactus) >