def METHOD_NAME(self, ispan):
    """Process data from from ispans to ospans and return the number of
    frames to commit for each output (or None to commit complete spans)."""
    data = ispan.data
    print("PgmWriterBlock.on_data()")
    # HACK TESTING
    if data.dtype != np.uint8:
        data = (data - data.min()) / (data.max() - data.min()) * 255
        #data = np.clip(data, 0, 255)
        data = data.astype(np.uint8)
        #data = data.astype(np.uint16)
    if self.outfile is None:
        return
    data.tofile(self.outfile)
    # HACK TESTING only write the first gulp
    self.outfile.close()
    self.outfile = None