preserve transparence on image thumbnails

Code:
/* for PNG images*/

        if ($this->image_library == 'gd2' AND $this->image_type == 3)

        {

            imagealphablending($dst_img, false);

            $transparent = imagecolorallocatealpha($dst_img, 255, 255, 255, 127);

            imagefilledrectangle($dst_img, 0, 0, $this->width, $this->height, $transparent);

            imagesavealpha($dst_img,true);

        }



/* for GIF images */

        if ($this->image_library == 'gd2' AND $this->image_type == 1)

        {

            $transparent_index = imagecolortransparent($src_img);

            if ($transparent_index >= 0)

            {

                $transparent_color = imagecolorsforindex($src_img, $transparent_index);

                $transparent_index = imagecolorallocate($dst_img, $transparent_color['red'],

                                                              $transparent_color['green'],

                                                              $transparent_color['blue']);

                imagefill($dst_img, 0, 0, $transparent_index);

                imagecolortransparent($dst_img, $transparent_index);

            }

        }