# ImgSum.pm
package ImgSum;

use strict;
use warnings;

use Image::Magick;

sub summary {
    my ($imgf, $res) = @_;
    my $img = new Image::Magick;
    $img->Read($imgf);

    my ($w, $h) = $img->Get(qw/rows columns/);

    my @sum;
    my $i = 0;
    for (my $y = 0; $y < $h; $y += $res)
    {
        for (my $x = 0; $x < $w; $x += $res)
        {
            my $px = $img->Get("pixel[$x,$y]");
            my $rgb = [split/,/, $px];
            $sum[$i++] = $rgb;
        }
    }
    return \@sum;
}

1;

##</code><code>##

#!/usr/bin/perl

# sum.pl

use strict;
use warnings;

use ImgSum;
use Data::Dumper;
use Storable;

my ($img, $res, $out) = @ARGV;
# $res is the sampling resolution

my $sum = ImgSum::summary($img, $res);

store($sum, $out);



##</code><code>##

# SumDif.pm
package SumDiff;

use strict;
use warnings;
use Data::Dumper;

sub mean {
    my $tt = 0;
    my $s = 0;
    while (defined($_ = shift))
    {
        $tt += $_;
        $s++;
    }
    return $tt/$s;
}

sub diffmap {
    my ($s1, $s2) = @_;

    my @diff;
    foreach my $i(0..$#$s1)
    {
        my $c1 = $s1->[$i];
        my $c2 = $s2->[$i];
        my @d = map { abs($c2->[$_] - $c1->[$_]) } (0..$#$c1);
        $diff[$i] = mean(@d);
    }
    return \@diff;
}

sub diffavg {
    return mean(@{diffmap(@_)});
}

1;

##</code><code>##

#!/usr/bin/perl

# watch.pl

use strict;
use warnings;

use ImgSum;
use LWP::Simple;
use SumDiff;
use Storable;

my @refs = map {retrieve($_)} ('sum-r0.dat', 'sum-r1.dat');

sub min {
    my $mni = 0;
    for my $i(0..$#_)
    {
        if ($_[$i] < $_[$mni])
        {
            $mni = $i
        }
    }
    return $mni;
}

sub getclass {
    my $test = shift;
    my @diffs;
    for my $i(0..$#refs)
    {
        my $diff = SumDiff::diffavg($refs[$i], $test);
        $diffs[$i] = $diff;
        print "Difference to $i: $diff\n";
    }
    return min(@diffs);
}

my $lc = 1;

while (sleep 2)
{
    my $stat = getstore('http://localhost:45005/webcam.jpg', 'current.jpg');
    print "HTTP status: $stat\n";
    my $sum = ImgSum::summary('current.jpg', 4);
    my $cl = getclass($sum);
    print "Likely class: $cl\n";
    if ($lc != $cl)
    {
        system('xscreensaver-command ' .
               ($cl?'-deactivate':'-activate'));
        $lc = $cl;
    }
}


##</code><code>##


( take a picture of the empty room, save it as ref0.jpg )

$ ./sum.pl ref0.jpg 4 sum-r0.dat

( take a picture of yourself, call it ref1.jpg )

$ ./sum.pl ref1.jpg 4 sum-r1.dat

$ ./watch.pl