How do you convert an image to black and white in PHP

Question

How does one go about converting an image to black and white in PHP?

Not just turning it into greyscale but every pixel made black or white?

Answer 1

$rgb = imagecolorat($original, $x, $y);
        $r = ($rgb >> 16) & 0xFF;
        $g = ($rgb >> 8 ) & 0xFF;
        $b = $rgb & 0xFF;

        $gray = $r + $g + $b/3;
        if ($gray >0xFF) {$grey = 0xFFFFFF;}
        else { $grey=0x000000;}