for ($x = 0; $x < $x_i; $x++) {
			for ($y=0; $y < $y_i; $y++) {

				$rgb = ImageColorAt($im, $x, $y);
				$a = ($rgb >> 24) & 0xFF;
				$r = ($rgb >> 16) & 0xFF;
				$g = ($rgb >> 8) & 0xFF;
				$b = $rgb & 0xFF;

				$a = (127-$a) / 127;
				$a=1;
				
				$gris = round($a*($r+$g+$b) / 3);
				$r = round($a*$r);
				$g = round($a*$g);
				$b = round($a*$b);
				
				$val_gris[$gris] ++;
				$val_r[$r] ++;
				$val_g[$g] ++;
				$val_b[$b] ++;
			} 
		}
		$max = max( max($val_gris), max($val_r), max($val_g), max($val_b));
		$rapport = (127/$max);