protected function ensureResource()
	{
		if ($this->resource === null)
		{
			$path = $this->image->getPathname();
			// if valid image type, make corresponding image resource
			switch ($this->image->imageType)
			{
				case IMAGETYPE_GIF:
					$this->resource = imagecreatefromgif($path);
					break;
				case IMAGETYPE_JPEG:
					$this->resource = imagecreatefromjpeg($path);
					break;
				case IMAGETYPE_PNG:
					$this->resource = imagecreatefrompng($path);
					break;
			}
		}
	}