Fellow monks,

I am still on my quest to automatically create an image with a semi-transparent background and some text an top (see Another Image::Magick question for original node). All of my attempts to do so using Image::Magick failed. However, GD has prooven more successful (see code below). However, when GD adds text on top of semi-transparent background, the text seems to be "aliased" with other colors (i.e white or black) all around the periphery of the letters. It's as though adding text on top of a background with some non-zero alpha color messes up the background behind the text. Has anyone seen this before? Is there a workaround? Maybe seeing this code would spring some ideas on how to do this with Image::Magick also?

Thanks.

use strict;
use GD;

my $bg_r = 255;
my $bg_g = 255;
my $bg_b = 255;
my $bg_alpha = 60;

#my $border_r = 0;
#my $border_g = 0;
#my $border_b = 0;
#my $border_alpha = 0;

my $fn_r = 255;
my $fn_g = 0;
my $fn_b = 0;
my $fn_alpha = 0;
my $font = '/usr/share/fonts/bitstream/Vera.ttf';
my $font_size = 8;

my $output = 'x.png';

my $fortune = `fortune`;
$fortune =~ s/\n/\r\n/g;
$fortune =~ s/\t/    /g;
my $radius = 10;

GD::Image->trueColor(1);

# create temp image and colors
my $im_tmp = new GD::Image (100,100);
my $black = $im_tmp->colorAllocate(0,0,0);  # must be there for the im
+age background definition
my $text_color = $im_tmp->colorAllocate($fn_r, $fn_g, $fn_b);

# get dimensions of text
my @bounds = GD::Image->stringFT($text_color, $font, $font_size, 0, 0,
+ 0, $fortune, {linespacing=>1, charmap=>'Unicode', kerning=>0});

# scale the background correctly and define colors for new image
my $width = $bounds[2]+2*$radius;
my $height = $bounds[1]-$bounds[7]+2*$radius;
my $im = new GD::Image ($width, $height);
$im->saveAlpha(1);
$im->alphaBlending(0);
$black = $im->colorAllocate(0,0,0);  # must be there for the image bac
+kground definition
$text_color = $im->colorAllocateAlpha($fn_r, $fn_g, $fn_b, $fn_alpha);
my $bg_color = $im->colorAllocateAlpha($bg_r, $bg_g, $bg_b, $bg_alpha)
+;
#my $border_color = $im->colorAllocateAlpha($border_r, $border_g, $bor
+der_b, $border_alpha);


#$im->setAntiAliasedDontBlend($text_color,0);
 
# draw the border
#$im->arc($radius, $radius, $radius*2, $radius*2, 180, 270, $border_co
+lor);              # uppder left
#$im->arc($radius, $height-$radius, $radius*2, $radius*2, 90, 180, $bo
+rder_color);       # lower left
#$im->arc($width-$radius, $radius, $radius*2, $radius*2, 270, 360, $bo
+rder_color);       # upper right
#$im->arc($width-$radius, $height-$radius, $radius*2, $radius*2, 0, 90
+, $border_color);  # lower right
#$im->line($radius, 0, $width-$radius, 0, $border_color);             
+                   # top
#$im->line($radius, $height-1, $width-$radius, $height-1, $border_colo
+r);                # bottom
#$im->line(0, $radius, 0, $height-$radius, $border_color);            
+                   # left
#$im->line($width-1, $radius, $width-1, $height-$radius, $border_color
+);                 # right
$im->fill(0,0, $bg_color);

# draw the text
$im->stringFT($text_color, $font, $font_size, 0, $radius-$bounds[6], $
+radius-$bounds[7], $fortune, {linespacing=>1, charmap=>'Unicode', ker
+ning=>0});


# save the image
open(OUTFIL,">$output") || die "Can't write to $output: $!\n";
binmode OUTFIL;
print OUTFIL $im->png;
close(OUTFIL);

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Edited by planetscape - added readmore tags

In reply to GD semi-transparent background with text by gri6507

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