procedure write_ppm(sequence filename, sequence image)
integer fn,dimx,dimy
sequence colour_triple
    fn = open(filename,"wb")
    dimx = length(image)
    dimy = length(image[1])
    printf(fn, "P6\n%d %d\n255\n", {dimx,dimy})
    for y = 1 to dimy do
        for x = 1 to dimx do
            colour_triple = sq_div(sq_and_bits(image[x][y], {#FF0000,#FF00,#FF}),
                                                            {#010000,#0100,#01})
            puts(fn, colour_triple)
        end for
    end for
    close(fn)
end procedure