use strict;
use warnings;
use PDL;
use PDL::IO::Image;

# data
my $x = sequence( 100, 100 );

# ranges
my $range1 = $x < 3000;
my $range2 = ( $x >= 3000 ) * ( $x <= 7000 );
my $range3 = $x > 7000;

my $bytes = (     $range1 
            + 2 * $range2
            + 3 * $range3 )-> byte;

my $palette = byte [ 
    [  0,   0,    0 ],
    [ 255,  50,  50 ],
    [ 128, 255,   0 ],
    [ 255, 215,   0 ]
];

$bytes-> wimage( 'test.png', { palette => $palette });