I've been writing a program using imagemagick which makes animated tiled background gifs of lots of objects falling (originally to make a snow effect but it could be anything). I'd like to have them all rendered in different random opacities over the background to get a layered effect, but I can't get the opacity function to work in Image->composite.

I've reproduced the error in the following code (adapted from an earlier reply i found on a similar subject.)

#!/usr/bin/perl -w

use strict;
use Image::Magick;

# Simulate background picture... :)
my $image1 = Image::Magick->new;
$image1->Set(size=>'100x100');
$image1->ReadImage('xc:orange');

# Textbackground image
my $image2 = Image::Magick->new;
$image2->ReadImage('testopaq.png');

# Make composite image of background and a 50 % transparent image.
$image1->Composite(compose=>'over', image=>$image2, x=>0, y=>0, 
         opacity=>50
  );

$image1->Display;
[download]

testopaq.png is a black stripe and a white stripe on a transparent background.

with opacity=0 or not stated, it does the normal 'over' overlay, with transparent areas untouched, but with opacity >0, testopaq.png is overlaid with a black background and no effect on opacity. The transparent areas of testopaq.png end up black.

when i use the 'dissolve' option instead of 'over', nothing happens at all, for any value of opacity.

using ImageMagick 5.5.5 and perl 5.6.1