def COL_DISTINF(col1, col2):
    """
    Computes inf-distance between two RGB vectors, i.e.
        = max(abs(r), abs(g), abs(b))
    """
    r, g, b = (col1[i] - col2[i] for i in range(0, 3))
    return max(abs(r), abs(g), abs(b))