use strict;
use warnings;
use 5.032;          # chained comparison

use Term::ANSIScreen;

use if $^O eq 'MSWin32', 'Win32::Console'; 
my $OUT;
if ( $^O eq 'MSWin32' ) {
    $OUT = Win32::Console-> new( STD_OUTPUT_HANDLE );
    $OUT-> OutputCP( 65001 );
    $OUT-> Mode( $OUT-> Mode | 4 );
}

my @shades = (
    "\N{SPACE}", "\N{LIGHT SHADE}", "\N{MEDIUM SHADE}", 
    "\N{DARK SHADE}", "\N{FULL BLOCK}"
);
utf8::encode( $_ ) for @shades;

my @hues = <red yellow green cyan blue magenta>;
my @pal;
my @chars;

BLOCK1:                     # 5 neutral grays
for my $s ( 0 .. $#shades ) {
    push @pal, [( 255 / $#shades * $s ) x 3 ];
    push @chars, colored( $shades[ $s ], 'white' )
}
BLOCK2:                     # 24 = (6 hues) * (4 shades)
for my $h ( 0 .. $#hues ) {
    for my $s ( 1 ..$#shades ) {
        push @pal, [
            map { $_ / $#shades * $s * 255 } 
                ( 0 <= $h <= 1 || $h == 5 ),                # R
                ( 1 <= $h <= 3 ),                           # G
                ( 3 <= $h <= 5 )                            # B
        ];
        push @chars, colored( $shades[ $s ], $hues[ $h ])
    }
}
BLOCK3:                     # 18 = (6 "diluted" hues) * (3 shades)
for my $h ( 0 .. $#hues ) {
    for my $s ( 1 ..$#shades - 1 ) {
        push @pal, [
            map { ( 1 + $s * ( $_ - 1 ) / $#shades ) * 255 } 
                ( 0 <= $h <= 1 || $h == 5 ),                # R
                ( 1 <= $h <= 3 ),                           # G
                ( 3 <= $h <= 5 )                            # B
        ];
        push @chars, colored( $shades[ $s ], "$hues[ $h ] on_white" )
    }
}

# PDL stuff below

use PDL::Lite;
use PDL::IO::GD;
use PDL::Transform::Color;
use PDL::Graphics::ColorDistance 'delta_e_2000';

my $image = read_true_png( 'rose.png' );
my $palette = pdl \@pal;

$image = $image-> mv( -1, 0 );              # RRR...GGG...BBB => RGBRGBRGB...
$image = t_lab-> apply(( !t_srgb )-> apply( $image ));      # RGB to Lab
$palette = t_lab-> apply(( !t_srgb )-> apply( $palette ));  # palette to Lab

my $dist = delta_e_2000( $palette, $image-> dummy( 1, scalar @pal ));

# Args to sub above are 2D and 4D; it's threading ("broadcasting") 
# in action. $dist is 3D piddle. We are only interested which index in
# distances dimension holds minimum value. That's all.

print @chars[ @$_ ], "\n"
    for @{ $dist-> minimum_ind-> unpdl };