#! /bin/bash
# Last edited on 2021-01-12 21:03:10 by jstolfi

img="$1"; shift;  # Image file name.

convert ${img} PPM:- \
  | pnmtoplainpnm \
  | gawk \
      ' BEGIN { red = 0; tot = 0; bad = 0; }
        ((NF % 3) == 0) { 
           for (i = 1; i < NF;  i += 3)
             { r = $(i); g = $(i+1); b = $(i+2);
               v = (r + g + b)/3;
               h = (r - v + 0.0001)/(v + 0.0001); 
               red += h;
               tot++;
               next;
             }
        }
        // { bad++ }
        END { printf "red = %.1f tot = %d bad = %d\n", red, tot, bad  }
      '