Question

This code executes in 0.8seconds and takes up 22Mb of memory on my machine.

   $x=500;
   $y=500;

   $im = imagecreatetruecolor($x,$y);
   $ia=array();
   for ($i = 0; $i < $x; $i++) {
    for ($j = 0; $j < $y; $j++) {
        $r=rand(0,96);
        $g=rand(0,128);
        $b=rand(0,255);
        $ia[$i][$j]=ImageColorAllocate($im,$r,$g,$b);
    }
   }

What can be done to speed it up, but more importantly lower the memory footprint it eats at any given time.

Answer 1

Try the following code (from http://php.net/manual/en/function.imagecolorallocate.php) instead of your direct colour assignment:

function createcolor($pic,$c1,$c2,$c3) {
   $color = imagecolorexact($pic, $c1, $c2, $c3);
   if($color==-1) {
      if(imagecolorstotal($pic)>=1000) {
         $color = imagecolorclosest($pic, $c1, $c2, $c3);
      } else {
         $color = imagecolorallocate($pic, $c1, $c2, $c3);
      }
   }
   return $color;
 }

Also, try making the function call in 1 line:

$ia[$i][$j] = createcolor($im, mt_rand(0,96), mt_rand(0,128), mt_rand(0,255));

Fiddle with the hardcoded value 1000, and see how it changes memory usage.