undemanding / difference

    {

        $maximum = 0;

        for ($y = 0; $y < $height; $y++) {

            for ($x = 0; $x < $width; $x++) {

                if ($bitmap[$y][$x] > $maximum) {

                    $maximum = $bitmap[$y][$x];

                }

            }

        }

        return (float) $maximum;

    }

    {

        $standardDeviation = 0;

        for ($y = 0; $y < $height; $y++) {

            for ($x = 0; $x < $width; $x++) {

                $delta = $map[$y][$x] - $average;

                $standardDeviation += ($delta * $delta);

            }

        }

        $standardDeviation /= (($width * $height) - 1);

        $standardDeviation = sqrt($standardDeviation);

    {

        $new = array_slice($bitmap, 0);

        for ($y = 0; $y < $height; $y++) {

            for ($x = 0; $x < $width; $x++) {

                if (abs($new[$y][$x]) < $deviation) {

                    $new[$y][$x] = 0;

                }

            }

        }

        return $new;

    }