octave> g=readpgm('ganymede.pgm');
magic number = P2
rows = 128 cols = 128
grey levels = 255
octave> gdisplay(g);



octave> gh=histogram(g,256); # Ganymede's histogram.
octave> plot(0:255,gh);



octave> gc=cdf(g); # Ganymede's cdf.
octave> plot(0:255,gc);



octave> c=readpgm('callisto.pgm');
magic number = P2
rows = 128 cols = 128
grey levels = 255
octave> gdisplay(c);



octave> ch=histogram(c,256); # Callisto's histogram.
octave> plot(0:255,ch);



octave> ci=icdf(c); # Callisto's icdf.
octave> plot(0:255,ci);



octave> m=match(g,c); # Make a Ganymede with a histogram like Callisto's.
octave> gdisplay(m);



octave> mh=histogram(m,256);
octave> mplot(0:255,mh,0:255,gh); # Callisto's histogram (green). Matched histogram (red).