def color_worker(srcs, window, ij, args):
    """A user function."""
    src = srcs[0]
    arr = src.read(window=window)
    arr = to_math_type(arr)

    for func in parse_operations(args["ops_string"]):
        arr = func(arr)

    # scaled 0 to 1, now scale to outtype
    return scale_dtype(arr, args["out_dtype"])
A user function.