use Image::Magick;

opendir(sat, "sat") or die "can't open dir: $!" ;
@files = readdir(sat) ;
shift(@files) ;
shift(@files) ;

for $g (@files) {
substr($g, -4, 4) = "" ;

$sat = Image::Magick->new;
$streets = Image::Magick->new;

$sat->Read("sat\\$g\.jpg");
$streets->Read("streets\\$g\.png");

print "Processing file $g\n" ;
$sat->Set(depth=> 4);
$sat->Composite(image=>$streets,compose=>'over');
$sat->Write("png:gtiles\\$g\.png");
}
closedir(sat);