img bitwise

    <?php
        $bits = 2; // 0b010
        $argb = ImageColorAt($im, $x, $y) & 0xfffefefe;
        $ebits = (($bits & 4) << 14) | (($bits & 2) << 7) | ($bits & 1);
        $enbytes = $argb | $encbits;
        ImageSetPixel($im, $x, $y, $encbits);