image2prime.pl

#!/usr/bin/perl

# Author: Trizen
# Date: 29 April 2022
# https://github.com/trizen

# Generate an ASCII representation for an image, using only digits, such that the number is a prime.

# Inspired by the following Matt Parker video:
#   https://yewtu.be/watch?v=dET2l8l3upU

# See also:
#   https://github.com/TotalTechGeek/pictoprime

use 5.010;
use strict;
use autodie;
use warnings;

use GD qw();
use List::Util qw(max);
use Getopt::Long qw(GetOptions);
use Math::Prime::Util::GMP qw(is_prob_prime);

use constant {
              GENERATE_PRIME => 1,    # true to generate primes (slow)
             };

GD::Image->trueColor(1);

my $size = 80;

sub help {
    my ($code) = @_;
    print <<"HELP";
usage: $0 [options] [files]

options:
    -w  --width=i : width size of the ASCII image (default: $size)

example:
    perl $0 --width 200 image.png
HELP
    exit($code);
}

GetOptions('w|width=s' => \$size,
           'h|help'    => sub { help(0) },)
  or die "Error in command-line arguments!";

sub map_value {
    my ($value, $in_min, $in_max, $out_min, $out_max) = @_;
    ($value - $in_min) * ($out_max - $out_min) / ($in_max - $in_min) + $out_min;
}

my @digits = split(//, "7772299408");

#my @digits = 0..9;

# The ways that we allow the algorithm to substitute a character.
# Like 0 can become 8 or 9, so on and so forth.
my %substitutions = (
    '0' => ['8', '9'],
    '1' => ['7'],
    '7' => ['1'],
    '8' => ['0', '9'],
    '9' => ['4'],
    '4' => ['9'],
                    );

# These are used to swap out the last digit if necessary.
my %edge_digit_substitutions = (
                                '0' => '3',
                                '2' => '3',
                                '4' => '9',
                                '6' => '9',
                                '8' => '9',
                                '5' => '3'
                               );

sub create_prime {
    my ($pixels) = @_;

    GENERATE_PRIME || return $pixels;

    if (substr($pixels, 0, 1) == 0) {
        substr($pixels, 0, 1, $edge_digit_substitutions{0});
    }

    if (exists($edge_digit_substitutions{substr($pixels, -1)})) {
        my $digit = chop $pixels;
        $pixels .= $edge_digit_substitutions{$digit};
    }

    my $count  = 0;
    my $copy   = $pixels;
    my $length = length($pixels);

    my @substitution_indices = grep { exists $substitutions{substr($pixels, $_, 1)} } 0 .. $length - 1;

    while (1) {

        if (is_prob_prime($pixels)) {
            return $pixels;
        }

        if (++$count > 5) {
            $pixels = $copy;
            $count  = 0;
        }

        my $rand  = $substitution_indices[int rand scalar @substitution_indices];
        my $digit = substr($pixels, $rand, 1);
        my $alt   = $substitutions{$digit};

        substr($pixels, $rand, 1, $alt->[int rand scalar @$alt]);
    }
}

sub img2prime {
    my ($image) = @_;

    my $img = GD::Image->new($image) // return;
    my ($width, $height) = $img->getBounds;

    if ($size != 0) {
        my $scale_width  = $size;
        my $scale_height = int($height / ($width / ($size / 2)));

        my $resized = GD::Image->new($scale_width, $scale_height);
        $resized->copyResampled($img, 0, 0, 0, 0, $scale_width, $scale_height, $width, $height);

        ($width, $height) = ($scale_width, $scale_height);
        $img = $resized;
    }

    my $avg = 0;
    my @averages;

    foreach my $y (0 .. $height - 1) {
        foreach my $x (0 .. $width - 1) {
            my $index = $img->getPixel($x, $y);
            my ($r, $g, $b) = $img->rgb($index);
            my $value = max($r, $g, $b);
            push @averages, $digits[map_value($value, 0, 255, 0, $#digits)];
        }
    }

    my $prime = create_prime(join('', @averages));
    unpack("(A$width)*", $prime);
}

say for img2prime($ARGV[0] // help(1));

__END__
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