PHP implementation of stackblur algorithm available?

Question

I am trying to blur an image and need a faster solution.

This is my current attempt which is much too slow for large images and I do not want to use imagick.

public function blur($filename, $extension, $factor = 20){
    if (strtolower($extension) === "jpg" || strtolower($extension) === "jpeg") $image = imagecreatefromjpeg($filename);
    if (strtolower($extension) === "png") $image = imagecreatefrompng($filename);

    for ($x=1; $x<=$factor; $x++)
       imagefilter($image, IMG_FILTER_GAUSSIAN_BLUR);
    imagejpeg($image, "$filename.blur.$extension");
    imagedestroy($image);

}

Is there a PHP implementation of stackblur or another fast algorithm available?

Answer 1

The simple solution is to scale the image down before you apply the blur filter. Here are some examples:

Original image:

20× Gaussian Blur (2.160 seconds):

{
  $start = microtime(true);
  for ($x=0; $x<20; $x++) {
    imagefilter($image, IMG_FILTER_GAUSSIAN_BLUR);
  }
  $end =  microtime(true);
  $howlong = $end - $start;
}

Combination of scaling and Gaussian blur (0.237 seconds):

{
  $start = microtime(true);

  /* Scale by 25% and apply Gaussian blur */
  $s_img1 = imagecreatetruecolor(160,120);
  imagecopyresampled($s_img1, $image, 0, 0, 0, 0, 160, 120, 640, 480);
  imagefilter($s_img1, IMG_FILTER_GAUSSIAN_BLUR);

  /* Scale result by 200% and blur again */
  $s_img2 = imagecreatetruecolor(320,240);
  imagecopyresampled($s_img2, $s_img1, 0, 0, 0, 0, 320, 240, 160, 120);
  imagedestroy($s_img1);
  imagefilter($s_img2, IMG_FILTER_GAUSSIAN_BLUR);

  /* Scale result back to original size and blur one more time */
  imagecopyresampled($image, $s_img2, 0, 0, 0, 0, 640, 480, 320, 240);
  imagedestroy($s_img2);
  imagefilter($image, IMG_FILTER_GAUSSIAN_BLUR);
  $end =  microtime(true);
  $howlong = $end - $start;
}