File Coverage

blib/lib/Image/ThumbHash/PP.pm

Criterion	Covered	Total	%
statement	155	221	70.1
branch	37	60	61.6
condition	4	15	26.6
subroutine	17	19	89.4
pod	0	7	0.0
total	213	322	66.1

package Image::ThumbHash::PP;
use v5.10.0;  # //
use strict;
use warnings qw(all FATAL uninitialized);

use Exporter 5.57 qw(import);
use Carp qw(croak);
use List::Util qw(min max);
use MIME::Base64 ();

use constant {
    PI => 4 * atan2(1, 1),
};

our $VERSION = '0.02';

our @EXPORT_OK = qw(
    rgba_to_thumb_hash
    rgba_to_png
    rgba_to_data_url
    thumb_hash_to_rgba
    thumb_hash_to_average_rgba
    thumb_hash_to_approximate_aspect_ratio
    thumb_hash_to_data_url
);

sub _assert_w_h_rgba {
    my ($width, $height, $rgba, $sub) = @_;
    $sub //= (caller 1)[3];

    0 <= $width && $width <= 100
        or croak "$sub: width is not in range [0, 100]: $width";
    0 <= $height && $height <= 100
        or croak "$sub: height is not in range [0, 100]: $height";
    length($rgba) == $width * $height * 4
        or croak "$sub: rgba length does not match " . ($width * $height * 4) . ": " . length($rgba);
}

sub _assert_thumb_hash {
    my ($hash, $sub) = @_;
    $sub //= (caller 1)[3];

    length($hash) >= 5
        or croak "$sub: thumb hash length is less than 5: " . length($hash);
}

sub rgba_to_thumb_hash {
    my ($width, $height, $rgba) = @_;

    # Encoding an image larger than 100x100 is slow with no benefit
    _assert_w_h_rgba $width, $height, $rgba;

    # Determine the average color
    my ($avg_r, $avg_g, $avg_b, $avg_a) = (0, 0, 0, 0);
    for my $pixel (unpack '(a4)*', $rgba) {
        my ($pr, $pg, $pb, $pa) = unpack 'C*', $pixel;
        my $alpha = $pa / 255;
        my $alpha_f = $alpha / 255;
        $avg_r += $alpha_f * $pr;
        $avg_g += $alpha_f * $pg;
        $avg_b += $alpha_f * $pb;
        $avg_a += $alpha;
    }
    if ($avg_a > 0) {
        $_ /= $avg_a for $avg_r, $avg_g, $avg_b;
    }

    my $has_alpha = $avg_a < $width * $height;
    my $l_limit = $has_alpha ? 5 : 7;  # Use fewer luminance bits if there's alpha
    my $max_w_h = max $width, $height;
    my $lx = max 1, int($l_limit * $width / $max_w_h + 0.5);
    my $ly = max 1, int($l_limit * $height / $max_w_h + 0.5);
    my (
        @l,  # luminance
        @p,  # yellow - blue
        @q,  # red - green
        @a,  # alpha
    );

    # Convert the image from RGBA to LPQA (composite atop the average color)
    for my $pixel (unpack '(a4)*', $rgba) {
        my ($pr, $pg, $pb, $pa) = unpack 'C*', $pixel;
        my $alpha = $pa / 255;
        my $alpha_f = $alpha / 255;
        my $r = $avg_r * (1 - $alpha) + $alpha_f * $pr;
        my $g = $avg_g * (1 - $alpha) + $alpha_f * $pg;
        my $b = $avg_b * (1 - $alpha) + $alpha_f * $pb;
        push @l, ($r + $g + $b) / 3;
        push @p, ($r + $g) / 2 - $b;
        push @q, $r - $g;
        push @a, $alpha;
    }

    # Encode using the DCT into DC (constant) and normalized AC (varying) terms
    my $encode_channel = sub {
        my ($channel, $nx, $ny) = @_;
        my $dc = 0;
        my @ac;
        my $scale = 0;
        for my $cy (0 .. $ny - 1) {
            for (my $cx = 0; $cx * $ny < $nx * ($ny - $cy); $cx++) {
                my @fx = map cos(PI / $width * $cx * ($_ + 0.5)), 0 .. $width - 1;
                my $f = 0;
                for my $y (0 .. $height - 1) {
                    my $fy = cos(PI / $height * $cy * ($y + 0.5));
                    for my $x (0 .. $width - 1) {
                        $f += $channel->[$x + $y * $width] * $fx[$x] * $fy;
                    }
                }
                $f /= $width * $height;
                if ($cx || $cy) {
                    push @ac, $f;
                    $scale = max $scale, abs $f;
                } else {
                    $dc = $f;
                }
            }
        }
        if ($scale) {
            for my $ac (@ac) {
                $ac = 0.5 + 0.5 / $scale * $ac;
            }
        }
        ($dc, \@ac, $scale)
    };
    my ($l_dc, $l_ac, $l_scale) = $encode_channel->(\@l, max(3, $lx), max(3, $ly));
    my ($p_dc, $p_ac, $p_scale) = $encode_channel->(\@p, 3, 3);
    my ($q_dc, $q_ac, $q_scale) = $encode_channel->(\@q, 3, 3);
    my ($a_dc, $a_ac, $a_scale) = $has_alpha ? $encode_channel->(\@a, 5, 5) : (1, [], 1);

    # Write the constants
    my $is_landscape = $width > $height;
    my $header24 = int(0.5 + 63 * $l_dc)
        | int(0.5 + 31.5 + 31.5 * $p_dc) << 6
        | int(0.5 + 31.5 + 31.5 * $q_dc) << 12
        | int(0.5 + 31 * $l_scale) << 18
        | ($has_alpha ? 1 << 23 : 0);
    my $header16 = ($is_landscape ? $ly : $lx)
        | int(0.5 + 63 * $p_scale) << 3
        | int(0.5 + 63 * $q_scale) << 9
        | ($is_landscape ? 1 << 15 : 0);
    my $hash_const = pack 'C*', (
        $header24 & 0xff,
        $header24 >> 8 & 0xff,
        $header24 >> 16,
        $header16 & 0xff,
        $header16 >> 8,
        $has_alpha
            ? int(0.5 + 15 * $a_dc) | int(0.5 + 15 * $a_scale) << 4
            : (),
    );

    # Write the varying factors
    my $ac_index = 0;
    my $hash_vary = '';
    for my $ac ($l_ac, $p_ac, $q_ac, $has_alpha ? $a_ac : ()) {
        for my $f (@$ac) {
            vec($hash_vary, $ac_index++, 4) = int(0.5 + 15 * $f);
        }
    }

    $hash_const . $hash_vary
}

sub rgba_to_png {
    my ($width, $height, $rgba) = @_;
    _assert_w_h_rgba $width, $height, $rgba;

    my $row = $width * 4 + 1;
    my $idat = 6 + $height * (5 + $row);
    my @bytes = (
        137, 80, 78, 71, 13, 10, 26, 10, 0, 0, 0, 13, 73, 72, 68, 82, 0, 0,
        $width >> 8 & 0xff, $width & 0xff, 0, 0, $height >> 8 & 0xff, $height & 0xff, 8, 6, 0, 0, 0, 0, 0, 0, 0,
        $idat >> 24 & 0xff, $idat >> 16 & 0xff, $idat >> 8 & 0xff, $idat & 0xff,
        73, 68, 65, 84, 120, 1,
    );
    my $a = 1;
    my $b = 0;
    for my $y (0 .. $height - 1) {
        push @bytes, (
            $y == $height - 1 ? 1 : 0,
            $row & 0xff,
            $row >> 8 & 0xff,
            $row & 0xff ^ 0xff,
            $row >> 8 & 0xff ^ 0xff,
            0,
        );
        $b = ($b + $a) % 65521;
        my $slice = ($row - 1) * $y;
        for my $i ($slice .. $slice + $row - 2) {
            my $u = vec $rgba, $i, 8;
            push @bytes, $u;
            $a = ($a + $u) % 65521;
            $b = ($b + $a) % 65521;
        }
    }
    push @bytes, (
        $b >> 8, $b & 0xff, $a >> 8, $a & 0xff, 0, 0, 0, 0,
        0, 0, 0, 0, 73, 69, 78, 68, 174, 66, 96, 130,
    );
    my @table = (
        0, 498536548, 997073096, 651767980, 1994146192, 1802195444, 1303535960,
        1342533948, 3988292384, 4027552580, 3604390888, 3412177804, 2607071920,
        2262029012, 2685067896, 3183342108,
    );
    for my $range ([12, 28], [37, 40 + $idat]) {
        my ($start, $end) = @$range;
        my $c = 0xffff_ffff;
        for my $i ($start .. $end) {
            $c ^= $bytes[$i];
            $c = $c >> 4 ^ $table[$c & 0xf];
            $c = $c >> 4 ^ $table[$c & 0xf];
        }
        $c ^= 0xffff_ffff;
        $bytes[$end + 1] = $c >> 24 & 0xff;
        $bytes[$end + 2] = $c >> 16 & 0xff;
        $bytes[$end + 3] = $c >> 8 & 0xff;
        $bytes[$end + 4] = $c & 0xff;
    }
    pack 'C*', @bytes
}

sub rgba_to_data_url {
    my ($width, $height, $rgba) = @_;
    _assert_w_h_rgba $width, $height, $rgba;
    'data:image/png;base64,' . MIME::Base64::encode(rgba_to_png($width, $height, $rgba), '')
}

sub thumb_hash_to_rgba {
    my ($hash) = @_;
    _assert_thumb_hash $hash;
    wantarray or croak "thumb_hash_to_rgba: must be called in list context";

    # Read the constants
    my $header24 = vec($hash, 0, 8) | vec($hash, 1, 8) << 8 | vec($hash, 2, 8) << 16;
    my $header16 = vec($hash, 3, 8) | vec($hash, 4, 8) << 8;
    my $l_dc = ($header24 & 63) / 63;
    my $p_dc = ($header24 >> 6 & 63) / 31.5 - 1;
    my $q_dc = ($header24 >> 12 & 63) / 31.5 - 1;
    my $l_scale = ($header24 >> 18 & 31) / 31;
    my $has_alpha = $header24 >> 23;
    my $p_scale = ($header16 >> 3 & 63) / 63;
    my $q_scale = ($header16 >> 9 & 63) / 63;
    my $is_landscape = $header16 >> 15;
    my $l_max = $has_alpha ? 5 : 7;
    my $l_min = max(3, $header16 & 7);
    my ($lx, $ly) = $is_landscape
        ? ($l_max, $l_min)
        : ($l_min, $l_max);
    my ($a_dc, $a_scale) = $has_alpha
        ? (map vec($hash, $_, 4) / 15,
            10, 11)
        : (1, 1);

    # Read the varying factors (boost saturation by 1.25x to compensate for quantization)
    my $ac_index = $has_alpha ? 12 : 10;
    my $decode_channel = sub {
        my ($nx, $ny, $scale) = @_;
        my @ac;
        for my $cy (0 .. $ny - 1) {
            for (my $cx = !$cy; $cx * $ny < $nx * ($ny - $cy); $cx++) {
                push @ac, (vec($hash, $ac_index++, 4) / 7.5 - 1) * $scale;
            }
        }
        \@ac
    };
    my $l_ac = $decode_channel->($lx, $ly, $l_scale);
    my $p_ac = $decode_channel->(3, 3, $p_scale * 1.25);
    my $q_ac = $decode_channel->(3, 3, $q_scale * 1.25);
    my $a_ac = $has_alpha ? $decode_channel->(5, 5, $a_scale) : [];

    # Decode using the DCT into RGB
    my $ratio = $is_landscape
        ? $l_max / ($header16 & 7)
        : ($header16 & 7) / $l_max;
    my ($width, $height) = $ratio > 1
        ? (32, int(0.5 + 32 / $ratio))
        : (int(0.5 + 32 * $ratio), 32);
    my $rgba = '';
    my (@fx, @fy);
    for my $y (0 .. $height - 1) {
        for my $x (0 .. $width - 1) {
            my $l = $l_dc;
            my $p = $p_dc;
            my $q = $q_dc;
            my $a = $a_dc;

            # Precompute the coefficients
            my @fx = map cos(PI / $width * ($x + 0.5) * $_), 0 .. max($lx, $has_alpha ? 5 : 3) - 1;
            my @fy = map cos(PI / $height * ($y + 0.5) * $_), 0 .. max($ly, $has_alpha ? 5 : 3) - 1;

            # Decode L
            {
                my $j = 0;
                for my $cy (0 .. $ly - 1) {
                    my $fy2 = $fy[$cy] * 2;
                    for (my $cx = !$cy; $cx * $ly < $lx * ($ly - $cy); $cx++) {
                        $l += $l_ac->[$j++] * $fx[$cx] * $fy2;
                    }
                }
            }

            # Decode P and Q
            {
                my $j = 0;
                for my $cy (0 .. 2) {
                    my $fy2 = $fy[$cy] * 2;
                    for my $cx (!$cy .. 2 - $cy) {
                        my $f = $fx[$cx] * $fy2;
                        $p += $p_ac->[$j] * $f;
                        $q += $q_ac->[$j] * $f;
                        $j++;
                    }
                }
            }

            # Decode A
            if ($has_alpha) {
                my $j = 0;
                for my $cy (0 .. 4) {
                    my $fy2 = $fy[$cy] * 2;
                    for my $cx (!$cy .. 4 - $cy) {
                        $a += $a_ac->[$j++] * $fx[$cx] * $fy2;
                    }
                }
            }

            # Convert to RGB
            my $b = $l - 2 / 3 * $p;
            my $r = (3 * $l - $b + $q) / 2;
            my $g = $r - $q;
            $rgba .= pack 'C*', map max(0, 255 * min(1, $_)), $r, $g, $b, $a;
        }
    }

    $width, $height, $rgba
}

sub thumb_hash_to_average_rgba {
    my ($hash) = @_;
    _assert_thumb_hash $hash;
    wantarray or croak "thumb_hash_to_average_rgba: must be called in list context";
    my $header = vec($hash, 0, 8) | vec($hash, 1, 8) << 8 | vec($hash, 2, 8) << 16;
    my $l = ($header & 63) / 63;
    my $p = ($header >> 6 & 63) / 31.5 - 1;
    my $q = ($header >> 12 & 63) / 31.5 - 1;
    my $has_alpha = $header >> 23;
    my $a = $has_alpha ? (vec($hash, 5, 8) & 15) / 15 : 1;
    my $b = $l - 2 / 3 * $p;
    my $r = (3 * $l - $b + $q) / 2;
    my $g = $r - $q;

    max(0, min(1, $r)),
    max(0, min(1, $g)),
    max(0, min(1, $b)),
    $a
}

sub thumb_hash_to_approximate_aspect_ratio {
    my ($hash) = @_;
    _assert_thumb_hash $hash;
    my $has_alpha = vec($hash, 2, 8) & 0x80;
    my $is_landscape = vec($hash, 4, 8) & 0x80;
    my $l_max = $has_alpha ? 5 : 7;
    my $l_min = vec($hash, 3, 8) & 0x7;
    $is_landscape
        ? $l_max / $l_min
        : $l_min / $l_max
}

sub thumb_hash_to_data_url {
    my ($hash) = @_;
    _assert_thumb_hash $hash;
    rgba_to_data_url thumb_hash_to_rgba $hash
}

1
__END__