crappy :)

COLORS = dict()
def get_color(ctup):
    try:
        return COLORS[ctup]
    except KeyError:
        r,g,b = ctup
        r = r / 8
        g = g / 4
        b = b / 8
        COLORS[ctup] = "%s%s" % (chr((r<<3) + (g>>3)), chr(((g&7)<<5) + b))
        return COLORS[ctup]

arr = numpy.fromstring(content, dtype=numpy.uint8)
content = "".join(map(get_color, map(tuple, numpy.reshape(arr, (len(arr)/3, 3)))))