public function get_luminance( $num_samples = 10 ) 
	{
		$x_step = (int) $this->width / $num_samples;
		$y_step = (int) $this->height / $num_samples;

		$total_lum = 0;
		$sample_no = 1;

		for ( $x=0; $x<$this->width; $x+=$x_step ) 
		{
			for ( $y=0; $y<$this->height; $y+=$y_step ) 
			{
				$rgb = imagecolorat($this->image_context, $x, $y);
				$r = ($rgb >> 16) & 0xFF;
				$g = ($rgb >> 8) & 0xFF;
				$b = $rgb & 0xFF;

				$lum = ($r+$r+$b+$g+$g+$g)/6;

				$total_lum += $lum;
				$sample_no++;
			}
		}

		return (int) ( $total_lum / $sample_no );
	}