I have below function to save JPEG as Progressive JPEG. It saved, but not as progressive JPEG. Is this correct ?
function save($filename, $image_type = IMAGETYPE_JPEG, $compression = 75, $permissions = null) {
    if ($image_type == IMAGETYPE_JPEG) {
        imageinterlace($this->image, true); //convert to progressive ?
        imagejpeg($this->image, $filename, $compression);
    } elseif ($image_type == IMAGETYPE_GIF) {
        imagegif($this->image, $filename);
    } elseif ($image_type == IMAGETYPE_PNG) {
        imagepng($this->image, $filename);
    }
    if ($permissions != null) {
        chmod($filename, $permissions);
    }
}
This is how i called save() function :
function img_reconstruct($saveto) {
  $image = new SimpleImage();
  $image->load($saveto);
  list($width, $height) = getimagesize($saveto);
  if ($width > 800 && $width < 1200) {
    $image->resize(800, $height);
    $image->save($saveto);
  }
 }