#!/usr/bin/perl

# call as ./png2ascii.pl /path/to/image.png

use strict;
use warnings;
use GD;

my @master_ascii = (qw(W M 0 @ N & ), ',', qw(' - . `), ' ');
my $matrix = [];

my $gdimg = GD::Image->newFromPng(shift @ARGV);
my ($w, $h) = $gdimg->getBounds();

my $x = 0;

while ($x < $w) {
	my $y = 0;
	while ($y < $h) {
		my $index = $gdimg->getPixel($x, $y);
		my ($r,$g,$b) = $gdimg->rgb($index);
		$matrix->[$y]->[$x] = ($r + $g + $b) / 3;
		$y++;
	}
	$x++;
}

my ($num, $den) = (2,3);
	
my $blocksize = $den - $num + 1;
my $skipblock = $den - $blocksize;
	
my $matrix2 = [];

my $m2line = 0;

my $spacer = 0;

foreach my $l (0..$#$matrix) {
	if ($spacer > $skipblock){
		$spacer = ($spacer + 1) % $den;
		next;
	}
	
	$spacer = ($spacer + 1) % $den;
	
	my $m2pix = 0;
	
	my $line = $matrix->[$l];
	
	foreach my $p (0..$#$line) {
		my $total = 0;
		foreach my $multiplier (0..$blocksize - 1) {
			$total += $matrix->[$l + $multiplier]->[$p]
			     if defined $matrix->[$l + $multiplier]->[$p];
		}
		my $m2value = int($total / $blocksize);
		$matrix2->[$m2line]->[$m2pix++] = $m2value;
	};

	$m2line++;
};

$matrix = $matrix2;


foreach my $m (@$matrix) { 
	foreach my $g (@$m) {
		my $idx = undef;
	
		#find out the ascii value we'll use. 0 is always our black, 
		#255 is always our white
		if ($g == 0){
			$idx = 0;
		}
		elsif ($g == 255){
			$idx =  $#master_ascii;
		}
		else {
			$idx = @master_ascii * $g / 256;
		};

		print $master_ascii[$idx];
	}
	print "\n";
}