The code below should do the trick.
However, I'm looking for a way to make the image over transparent to 50%. It doesn't seem to work with the 'Over' compose method. The only way to do it would be to create a PNG with an alpha transparency set to 50%, but I can't find a way to make one with Image::Magick or GD. Has anyone have an idea?

     $image_over->Read("over.gif");
     $image_under->Read("under.jpg");

     $image_over->Transparent("white"); # Set the transp. color
     $image_under->Composite(
      compose => 'Over',
      opacity => 50, # Doesn't seem to work with 'Over'
      x => 20,
      y => 25,
      image => $image_over,
        ) ;
     $image_under->Write("Composite.jpg");
[download]

The ImageMagick documentation is quite... unimpressive.

Having said that, I stared at http://www.simplesystems.org/ImageMagick/www/combine.html for a few minutes and decided that I would suggest using "atop" rather than "over", for no apparent reason other than that's the way I always am forced to work with ImageMagick... trial and error. {grin}

It's so sad that such a great tool has such lousy documentation. I've used it for only a half dozen tasks or so, and three times have had to go to the source code to get my answer for simple things.

-- Randal L. Schwartz, Perl hacker

I cannot believe that--after weeks of sweat--I came to nearly the same conclusion as a Perl icon.

("Nearly", because without Mr. Schwartz's deep-and-wide experience, I could not recognize that the documentation was "unimpressive." I thought it "sucked.")

I had come to the same conclusion that the PerlMagick module (a depressingly confusing synonym for Image::Magick) is best designed for "trial and error."

Here's the thing: what I have always loved-loved-loved about Perl is that when I know what I want to do, there's Perl, right there with more than one way to do it. I know what I want to do with Image::Magick--and that isn't helping much at all.

I'll ask it in a new ticket, but what I'd like to do is interrogate the Image::Magick module, and whatever is associated with it (however that's done) and ask it to spit out Just What Methods I can use, and Just What Parameters they take.

Thank you Mr. Schwartz. Your comment here gives me new hope that I maybe ain't crazy. (And thanks for the PP book--which I paid retail for, probably back when it cost about-seven-fifty. Sorry I'm late with the thanks, but I had no idea how to get ahold of you.)

Update: Actually, I've found the way to achieve the effect I wanted, so if anyone's interrested, here's the code you have to add just before the call to Transparent:

     $CD_map->MatteFloodfill(
          x => $x_inside, 
          y => $y_inside,
          matte => 90);
[download]

Where $x_inside and $y_inside are the coordinates of a point inside the polygone you want to make translucid. the value of matte is set to 90 here, but it seems to be more or less the same than 50% transparency...

Anyway, it's a real good way to dynamically paint area in a graphic file, once the hassle of compiling Image::Magick for Win32 is finished!

I have a Cº logo set as a background image on their site. What I'm trying to do is load a transparent *.gif file, write (annotate: user input) a message to the *.gif file, and eventually display the annotated *.gif over the logo image in order for it to be clickable (put within DIV and HREF it). If I get this sussed, I'll also be looking into morphing it or animating it - so something... (probably just leave it as is!).

I too have visited ImageMagick.org and have found it confusing - http://shawn.apocabilly.org/PGP/ (O'Reilley) slightly less confusing as there are examples (which I've been pulling apart with only moderate success!!) and there's little else I've managed to find out.

Hopefully someone out there has the know-how...

Eagerly awaiting,
Richard.