import math


def get_color_table_size(num_colors):
    """Total values in the color table is 2**(1 + int(result, base=2)).

    The result is a three-bit value (represented as a string with
    ones or zeros) that will become part of a packed byte encoding
    various details about the color table, used in the Logical
    Screen Descriptor block.
    """
    nbits = max(math.ceil(math.log(num_colors, 2)), 2)
    return '{:03b}'.format(int(nbits - 1))