public function thumbizeByLimit( $width, $height )
	{
		if( !count( $this->size ) )
			throw new RuntimeException( 'No Source Image set.' );

		$ratio_s	= $this->size[0] / $this->size[1];
		$ratio_t	= $width / $height;
		if( ( $ratio_s / $ratio_t ) > 1 )
			$height	= ceil( $width / $ratio_s );
		else
			$width	= ceil( $height * $ratio_s );
		return $this->thumbize( $width, $height );
	}