Performance improvements PHP GD resize and trim image background keeping the correct ratio

Question

I developed an image resizing & trimming class using PHP GD library. I used skibulks image trim script from here (thank you guy!) to trim the image background in the first step and scale the image in the second step to the needed sizes (keeping it's original ratio)!

My querstion is: Is it really necessary to do the first imagecopy job after getting the new trimmed image sizes from the $this->_trimBackground() function to recreate the image firstly by imagecopy with the new trimmed sizes (and resize it afterwards again) OR is it possible to merge this job with the following resizing part imagecopyresampled? Are there any other performance improvements possible which i didn't know? Every performance suggestion is welcome!

Function 1:

/**
 * Resize image file
 * 
 * @param   string $filepath the image filepath
 * @param   integer $width the width to resize
 * @param   integer $height the height to resize
 * @return  (image blob|boolean status)
 * @throws  Asset_Model_Image_Exception
 */
private function _resizeImageByFilepathAndReturn($filepath, $width, $height) {

    list($imageWidth, $imageHeight, $imageType) = getimagesize($filepath);

   switch($imageType) {
    case IMAGETYPE_GIF:
            $gdImage = imagecreatefromgif($filepath);
            break;
      case IMAGETYPE_JPEG:
            $gdImage = imagecreatefromjpeg($filepath);
            break;
      case IMAGETYPE_PNG:
            $gdImage = imagecreatefrompng($filepath);
            break;
      default:
                return false;
   }

   if($box = $this->_trimBackground($gdImage)) {

    $gdTrimmed = imagecreatetruecolor($box['w'], $box['h']);
    imagecopy($gdTrimmed, $gdImage, 0, 0, $box['l'], $box['t'], $box['w'], $box['h']);

    $imageWidth = $box['w'];
    $imageHeight = $box['h'];
    $gdImage = $gdTrimmed;

    unset($gdTrimmed);

   }

   if($imageWidth <= $width && $imageHeight <= $height) {

    $fwidth = $imageWidth;
        $fheight = $imageHeight;

   } else {

        $wscale = $width / $imageWidth;
        $hscale = $height / $imageHeight;
        $scale = min($wscale, $hscale);
        $fwidth = $scale * $imageWidth;
        $fheight = $scale * $imageHeight;

   }

   $gdThumbnail = imagecreatetruecolor($width, $height);

   imagefill($gdThumbnail, 0, 0, 0x00FFFFFF);

   imagecopyresampled($gdThumbnail, $gdImage, ($width - $fwidth) / 2, ($height - $fheight) / 2, 0, 0, $fwidth, $fheight, $imageWidth, $imageHeight);

   ob_start();
   imagejpeg($gdThumbnail, null, 90);
   $image = ob_get_contents();
   ob_end_clean();

   imagedestroy($gdImage);
   imagedestroy($gdThumbnail);

   return $image;

}

Function 2:

/**
 * Trim image background
 * 
 * @param $gdImage image ressource
 */
private function _trimBackground($gdImage){

    $hex = imagecolorat($gdImage, 0,0);

    $width = imagesx($gdImage);
    $height = imagesy($gdImage);

    $bTop = 0;
    $bLft = 0;
    $bBtm = $height - 1;
    $bRt = $width - 1;

    for(; $bTop < $height; ++$bTop) {
        for($x = 0; $x < $width; ++$x) {
            if(imagecolorat($gdImage, $x, $bTop) != $hex) {
                break 2;
            }
        }
    }

    if($bTop == $height) {
        return false;
    }

    for(; $bBtm >= 0; --$bBtm) {
        for($x = 0; $x < $width; ++$x) {
            if(imagecolorat($gdImage, $x, $bBtm) != $hex) {
                break 2;
            }
        }
    }

    for(; $bLft < $width; ++$bLft) {
        for($y = $bTop; $y <= $bBtm; ++$y) {
            if(imagecolorat($gdImage, $bLft, $y) != $hex) {
                break 2;
            }
        }
    }

    for(; $bRt >= 0; --$bRt) {
        for($y = $bTop; $y <= $bBtm; ++$y) {
            if(imagecolorat($gdImage, $bRt, $y) != $hex) {
                break 2;
            }
        }
    }

    $bBtm++;
    $bRt++;

    return array('l' => $bLft, 't' => $bTop, 'r' => $bRt, 'b' => $bBtm, 'w' => $bRt - $bLft, 'h' => $bBtm - $bTop);

}

Thank you for your time! I also asked the question directly at stackoverflow here.