KianTern has asked for the wisdom of the Perl Monks concerning the following question:

Hi monks, I'm trying to draw with GD and can't figure out how to use Anti Aliasing.
This is the sample code. 
use strict;
use GD;

my $gd = GD::Image->new(400,400);

my $black = $gd->colorAllocate(0,0,0);
my $white = $gd->colorAllocate(255,255,255);

$gd->filledRectangle(0,0,399,399,$white);
$gd->setAntiAliased($black);
$gd->line(0,0,399,399,gdAntiAliased);


open(IMG,">","out.png");
binmode IMG;
print IMG $gd->png;

[download]
This code supposed to draw an Anti Aliased line but it doesn't Anti Alias. I'm using perl 5.10 on Ubuntu 8.10.

Replies are listed 'Best First'.
Re: GD Anti Aliasing
by BrowserUk (Patriarch) on Jan 15, 2009 at 10:35 UTC

    Two problems with what you have.

    1. You're creating a palettised image, and anti-aliasing dooesn't work too well with them.
    2. The line you've drawn is at exactly 45 degrees, and doesn't get anti-aliased.

    Try this:

    use strict;
use GD;

my $gd = GD::Image->new(400,400, 1);  ## truecolor

my $black = $gd->colorAllocate(0,0,0);
my $white = $gd->colorAllocate(255,255,255);

$gd->filledRectangle( 0,0, 399,399, $white);
$gd->setAntiAliased($black);

for my $y ( map 10*$_, 0 .. 39 ) { ## All these will be anti-aliased
    $gd->line( 0,0, 399,$y, gdAntiAliased);
}
for my $x ( map 10*$_, 0 .. 39 ) { ## And these
    $gd->line( 0,0, $x,399, gdAntiAliased);
}

$gd->line( 0,0, 399,399, gdAntiAliased); ## But not this

open(IMG,">","out.png");
binmode IMG;
print IMG $gd->png;

    [download]
    Examine what is said, not who speaks -- Silence betokens consent -- Love the truth but pardon error.
    "Science is about questioning the status quo. Questioning authority".
    In the absence of evidence, opinion is indistinguishable from prejudice.
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Re: GD Anti Aliasing
by syphilis (Archbishop) on Jan 15, 2009 at 10:35 UTC
    I think the key to getting Anti Alias to work is (from the docs): 
    When using palette-based images, be sure to allocate a broad spectrum 
+of colors in order to have sufficient colors for the antialiasing to 
+use

    [download]
    That is, if you also allocate: 
    my $grey = $gd->colorAllocate(130,130,130);
my $grey1 = $gd->colorAllocate(32,32,32);
my $grey2 = $gd->colorAllocate(64,64,64);
my $grey3 = $gd->colorAllocate(190,190,190);

    [download]
    then you'll find that you get some Anti Aliasing. I'm not sure that you'll be able to actually *see* the difference, but a Digest::MD5 of the output files should reveal that the output has in fact changed. (At least that's what I'm finding on perl-5.8 on Win32.)

    Cheers,
    Rob
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        All that will have changed is that you've added 4 entries to the palette.

        Oh ... why does the MD5 of the output png file then change ?

        Cheers,
        Rob
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Re: GD Anti Aliasing
by spx2 (Deacon) on Apr 03, 2010 at 21:28 UTC
    I get 
    perl test.pl 
Can't locate object method "png" via package "GD::Image" at test.pl li
+ne 23

    [download]
    on your code. I've installed the latest GD
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