#
# This software is Copyright 2005 by Elsevier Inc.  You may use it
# under the terms of the license at http://perl.plover.com/hop/LICENSE.txt .
#



###
### RGB_to_CMYK_caching
###

## Chapter 3 section 

my %cache;        

sub RGB_to_CMYK {
  my ($r, $g, $b) = @_;
  my $key = join ',', $r, $g, $b;
  return $cache{$key} if exists $cache{$key}; 
  my ($c, $m, $y) = (255-$r, 255-$g, 255-$b);
  my $k = $c < $m ? ($c < $y ? $c : $y)
                  : ($m < $y ? $m : $y);  # Minimum
  for ($c, $m, $y) { $_ -= $k }
  return $cache{$key} = [$c, $m, $y, $k];  
}