def METHOD_NAME(self, iseq):
    """Return: oheaders (one per output) and islices (one per input)
    """
    ihdr = iseq.header
    dtype = ihdr['_tensor']['dtype']
    shape = ihdr['_tensor']['shape']
    maxval = 255
    filename = os.path.join(self.outpath, self.filename_callback(ihdr))
    self.outfile = open(filename, 'wb')
    self.outfile.write(b"P5\n")
    # HACK This sets the height to gulp_nframe because we don't know the
    #        sequence length apriori.
    self.outfile.write(b"%i %i\n%i\n" % (shape[-1], ihdr['gulp_nframe'], maxval))