ppmchange - change all pixels of one color to another in a PPM image

ppmchange

[-closeness=closeness_percent] [-remainder=remainder_color] [-closeok] [oldcolor newcolor] ... [ppmfile]

ppmchange red blue redimage.ppm >blueimage.ppm

ppmchange red red -remainder=black myimage.ppm >redblack.ppm

ppmchange -closeness=90 white white black black