#!/usr/local/bin/perl -w
###########################################
# cardfind - Find reference cards in pic
# Mike Schilli, 2008 (m@perlmeister.com)
###########################################
use strict;
use Imager;
use YAML qw(Dump);

my($file) = @ARGV;
die "No file given" unless defined $file;

my $img = Imager->new();
$img->read(file => $file) or 
    die "Can't read $file";

  # Blur
$img->filter(
    type   => "gaussian", 
    stddev => 10 ) or die $img->errstr;

my $y     = int( $img->getheight() / 2 );
my $width = $img->getwidth();

my @intens_ring = ();
my @diff_ring   = ();
my $found       = 0;
my @ctl_points  = ();

for my $x (0..$width-1) {
  my $color = $img->getpixel( x => $x,
                              y => $y );
  my @components = $color->rgba();

    # Save current intensity in ring buffer
  my $intens = @components[0,1,2];
  push @intens_ring, $intens;
  shift @intens_ring if @intens_ring > 50;

    # Store slope between x and x-50
  push @diff_ring, 
       abs($intens - $intens_ring[0]);
  shift @diff_ring if @diff_ring > 50;

  if($found) {
      # Inside flat region
    if(avg(\@diff_ring) > 10) {
      $found = 0;
    }
  } else {
      # Outside flat region
    if($x > $width/3 and 
       $x < 2/3*$width and
       avg(\@diff_ring) < 3) {
      $found = 1;
      push @ctl_points, 
           [@components[0,1,2]];
    }
  }
}

my $out = {};
my @labels = qw(low medium high);

  # Sort by intensity
for my $ctl_point (sort { 
        $a->[0] + $a->[1] + $a->[2] <=> 
        $b->[0] + $b->[1] + $b->[2] } 
        @ctl_points) {
  my $label = shift @labels;
  $out->{$label}->{red}  = $ctl_point->[0];
  $out->{$label}->{green}= $ctl_point->[1];
  $out->{$label}->{blue} = $ctl_point->[2];
  last unless @labels;
}

print Dump($out);

###########################################
sub avg {
###########################################
    my($arr) = @_;

    my $sum = 0;
    $sum += $_ for @$arr;
    return $sum/@$arr;
}