use strict;
use warnings;
use feature 'say';
use GD;
use Digest::MD5 'md5_hex';

say $^V; 
say $GD::VERSION;
say eval { GD::VERSION_STRING() } || '-';

GD::Image-> trueColor( 1 );

my $fn = 'CoventryCathedral.png';
my $i = GD::Image-> new( $fn );

use constant W => 100;

my $j = GD::Image-> new( W, W );

$j-> copyResampled( $i,
    0, 0,
    ( $i-> width - $i-> height ) * .5, 0,
    W, W, 
    $i-> height, $i-> height );

say eval { md5_hex( $j-> gd )} || '-';
say md5_hex( my_gd( $j ));

sub my_gd {             # same as gd() for truecolor images
    my $gd = shift;

    my ( $w, $h ) = $gd-> getBounds;
    my $s = '';
    for my $y ( 0 .. $h - 1 ) {
        for my $x ( 0 .. $w - 1 ) {
            $s .= pack 'L>', $gd-> getPixel( $x, $y );
        }
    }
    return "\xff\xfe" .
           ( pack 'S>2', $w, $h ) .
           "\1\xff\xff\xff\xff" .
           $s
}

__END__

v5.38.0
2.78
2.3.2
-
c97e63fc792ef75b5ff49c078046321e

v5.32.1
2.76
2.2.5
c97e63fc792ef75b5ff49c078046321e
c97e63fc792ef75b5ff49c078046321e

v5.24.3
2.66
2.1.1
adc191aea66fdf99fd74aaeb20b34e5e
adc191aea66fdf99fd74aaeb20b34e5e

##</code><code>##

use strict;
use warnings;
use feature 'say';
use GD;

say $^V; 
say $GD::VERSION;
say eval { GD::VERSION_STRING() } || '-';

GD::Image-> trueColor( 1 );

my $i = GD::Image-> new( 8, 8 );
$i-> filledRectangle( 0, 0, 7, 7 ,$i-> colorAllocate( 255, 0, 0 ));

for my $w ( 1 .. 7 ) {
    my $j = GD::Image-> new( $w, $w );
    $j-> copyResampled( $i, 0, 0, 0, 0, $w, $w, 8, 8 );

    print "\t\t\t$w\n";
    for my $y ( 0 .. $w - 1 ) {
        for my $x ( 0 .. $w - 1 ) {
            my ( $r ) = $j-> rgb( $j-> getPixel( $x, $y ));
            printf '%x ', $r;
        }
        print "\n";
    }
}

__END__

v5.38.0
2.78
2.3.2
                        1
ff
                        2
ff ff
ff ff
                        3
fe fe fe
fe fe fe
ff fe ff
                        4
ff ff ff ff
ff ff ff ff
ff ff ff ff
ff ff ff ff
                        5
fe ff ff fe ff
ff fe ff ff ff
fe fe ff ff ff
fe fe ff ff fe
ff ff ff fe ff
                        6
fe ff ff ff ff ff
ff ff ff ff ff fe
ff ff ff fe ff fe
ff ff ff ff ff ff
ff fe ff ff ff fe
ff fe fe ff fe ff
                        7
fe ff ff fe fe ff fe
ff ff ff ff ff ff fe
fe ff ff ff ff ff ff
ff ff ff ff ff ff ff
fe ff ff ff ff ff ff
ff ff ff ff ff ff ff
ff fe ff ff ff ff ff

v5.24.3
2.66
2.1.1
                        1
ff
                        2
ff ff
ff ff
                        3
ff ff ff
ff ff ff
ff ff ff
                        4
ff ff ff ff
ff ff ff ff
ff ff ff ff
ff ff ff ff
                        5
fe fe fe fe fe
fe fe ff fe fe
fe fe ff fe ff
ff fe fe ff fe
fe fe ff fe ff
                        6
ff ff ff ff ff ff
ff fe ff ff ff ff
ff ff ff ff ff ff
ff ff ff ff ff ff
ff fe ff ff ff ff
ff ff ff ff ff ff
                        7
fe fe ff fe ff fe fe
fe ff fe ff ff fe ff
ff fe ff ff ff fe fe
fe ff ff ff fe ff ff
ff ff ff fe fe ff fe
fe ff ff ff ff ff ff
fe ff ff ff fe ff fe


##</code><code>##

use strict;
use warnings;
use feature 'say';
use GD;

say $^V; 
say $GD::VERSION;
say eval { GD::VERSION_STRING() } || '-';

GD::Image-> trueColor( 1 );

my $i = GD::Image-> new( 8, 8 );
$i-> filledRectangle( 0, 0, 7, 7 ,$i-> colorAllocate( 255, 0, 0 ));

for my $w ( 1 .. 7 ) {
    my $j = $i-> copyScaleInterpolated( $w, $w );

    print "\t\t\t$w\n";
    for my $y ( 0 .. $w - 1 ) {
        for my $x ( 0 .. $w - 1 ) {
            my ( $r ) = $j-> rgb( $j-> getPixel( $x, $y ));
            printf '%x ', $r;
        }
        print "\n";
    }
}

__END__

v5.38.0
2.78
2.3.2
                        1
ff
                        2
ff ff
ff ff
                        3
ff ff ff
ff fd fd
ff fd fd
                        4
ff ff ff ff
ff ff ff ff
ff ff ff ff
ff ff ff ff
                        5
ff ff ff ff ff
ff fd fd fd fd
ff fd fd fd fd
ff fd fd fd fd
ff fd fd fd fd
                        6
ff ff ff ff ff ff
ff fd fd fd fd fd
ff fd fd fd fd fd
ff fd fd fd fd fd
ff fd fd fd fd fd
ff fd fd fd fd fd
                        7
ff ff ff ff ff ff ff
ff fd fd fd fd fd fd
ff fd fd fd fd fd fd
ff fd fd fd fd fd fd
ff fd fd fd ff fd fd
ff fd fd fd fd fd fd
ff fd fd fd fd fd fd

##</code><code>##

use strict;
use warnings;
use feature 'say';
use GD;

say $^V; 
say $GD::VERSION;
say eval { GD::VERSION_STRING() } || '-';

GD::Image-> trueColor( 1 );

my $i = GD::Image-> new( 8, 8 );
$i-> filledRectangle( 0, 0, 7, 7 ,$i-> colorAllocate( 255, 0, 0 ));

my @ok_methods;

for my $m ( 1 .. 30 ) {
    eval {
        for my $w ( 1 .. 7 ) {
            $i-> interpolationMethod( $m );
            my $j = $i-> copyScaleInterpolated( $w, $w );

            for my $y ( 0 .. $w - 1 ) {
                for my $x ( 0 .. $w - 1 ) {
                    my ( $r ) = $j-> rgb( $j-> getPixel( $x, $y ));
                    die unless 255 == $r;
                }
            }
        }
        1;
    } or next;
    push @ok_methods, $m;
}

say 'looks like ok methods are: ', join ' ', @ok_methods;

__END__

v5.38.0
2.78
2.3.2
looks like ok methods are: 1 2 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20

##</code><code>##

use strict;
use warnings;
use feature 'say';
use Imager;

my $i = Imager-> new( xsize => 8, ysize => 8 );
$i-> box( filled => 1, color => Imager::Color-> new( 255, 0, 0 ));

for my $w ( 1 .. 7 ) {
    my $j = $i-> scale( xpixels => $w,
#                        qtype => 'mixing',
#                        qtype => 'preview',
    );
    
    print "\t\t\t$w\n";
    for my $y ( 0 .. $w - 1 ) {
        for my $x ( 0 .. $w - 1 ) {
            my ( $r ) = $j-> getpixel( x => $x, y => $y )-> rgba;
            printf '%x ', $r;
        }
        print "\n";
    }
    
}

__END__

                        1
ff
                        2
ff ff
ff ff
                        3
ff ff ff
ff ff ff
ff ff ff
                        4
ff ff ff ff
ff ff ff ff
ff ff ff ff
ff ff ff ff
                        5
ff ff ff ff ff
ff ff ff ff ff
ff ff ff ff ff
ff ff ff ff ff
ff ff ff ff ff
                        6
ff ff ff ff ff ff
ff ff ff ff ff ff
ff ff ff ff ff ff
ff ff ff ff ff ff
ff ff ff ff ff ff
ff ff ff ff ff ff
                        7
ff ff ff ff ff ff ff
ff ff ff ff ff ff ff
ff ff ff ff ff ff ff
ff ff ff ff ff ff ff
ff ff ff ff ff ff ff
ff ff ff ff ff ff ff
ff ff ff ff ff ff ff