def compare_bits(olds, news):
    """Subtract 2D list to determine changes to bit state."""
    rows = len(olds)
    cols = len(olds[0])
    delta = [[0] * cols for i in range(rows)]
    for i in range(0, rows):
        for j in range(0, cols):
            delta[i][j] = news[i][j] - olds[i][j]
    return delta