Beispiel 1. Example of using imagecolorallocatealpha() 
<?php $size = 300; $image=imagecreatetruecolor($size, $size);
  // something to get a white background with black border $back = imagecolorallocate($image, 255, 255, 255); $border = imagecolorallocate($image, 0, 0, 0); imagefilledrectangle($image, 0, 0, $size - 1, $size - 1, $back); imagerectangle($image, 0, 0, $size - 1, $size - 1, $border);
  $yellow_x = 100; $yellow_y = 75; $red_x    = 120; $red_y    = 165;  $blue_x   = 187; $blue_y   = 125;  $radius   = 150;
  // allocate colors with alpha values $yellow = imagecolorallocatealpha($image, 255, 255, 0, 75); $red    = imagecolorallocatealpha($image, 255, 0, 0, 75); $blue   = imagecolorallocatealpha($image, 0, 0, 255, 75);
  // drawing 3 overlapped circle imagefilledellipse($image, $yellow_x, $yellow_y, $radius, $radius, $yellow); imagefilledellipse($image, $red_x, $red_y, $radius, $radius, $red);    imagefilledellipse($image, $blue_x, $blue_y, $radius, $radius, $blue);
  // don't forget to output a correct header! header('Content-type: image/png');
  // and finally, output the result imagepng($image); imagedestroy($image); ?>
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