resize

public function resizeImage($pic_type, $sourcePath, $destPath, $maxWidth, $maxHeight)
    {

        switch ($pic_type) {
            case 'png':
                $size = getimagesize($sourcePath);
                if ($size[1] / $size[0] > $maxHeight / $maxWidth) {
                    $newHeight = $maxHeight;
                    $newWidth = ceil($size[0] / $size[1] * $newHeight);
                } else {
                    $newWidth = $maxWidth;
                    $newHeight = ceil($size[1] / $size[0] * $newWidth);
                }
                $image = imagecreatefrompng($sourcePath);
                $newImage = imagecreatetruecolor($newWidth, $newHeight);
                imagecopyresampled($newImage, $image, 0, 0, 0, 0, $newWidth, $newHeight, $size[0], $size[1]);
                imagepng($newImage, $destPath);
                imagedestroy($image);
                imagedestroy($newImage);
                break;
       }
}

// Verkleinern für die Vorschau
$this->resizeImage($ava_type, $upload_direction, $ava_tpath . 'thumb_' . $ava_fname . '.' . $ava_type, 500, 500);