r"""
        Returns a tuples of the normalized values of the red, green, and blue
        channels of the Colour.

        Returns:
            tuple: the rgb values of the colour (with values normalized between
                   0.0 and 1.0)

        .. note::

            Uses the formula:

            \\[ r_{norm} = \\begin{cases}
            \\frac{r_{255}}{12.92}\\ \\qquad &\\text{if $r_{255}$ $\\le$ 0.03928}
            \\\\
            \\left(\\frac{r_{255} + 0.055}{1.055}\\right)^{2.4}
            \\quad &\\text{otherwise}
            \\end{cases} \\]

        `Source <http://www.w3.org/TR/2008/REC-WCAG20-20081211/#relativeluminancedef>`_

def normalized_rgb(self):
        r"""
        Returns a tuples of the normalized values of the red, green, and blue
        channels of the Colour.

        Returns:
            tuple: the rgb values of the colour (with values normalized between
                   0.0 and 1.0)

        .. note::

            Uses the formula:

            \\[ r_{norm} = \\begin{cases}
            \\frac{r_{255}}{12.92}\\ \\qquad &\\text{if $r_{255}$ $\\le$ 0.03928}
            \\\\
            \\left(\\frac{r_{255} + 0.055}{1.055}\\right)^{2.4}
            \\quad &\\text{otherwise}
            \\end{cases} \\]

        `Source <http://www.w3.org/TR/2008/REC-WCAG20-20081211/#relativeluminancedef>`_
        """

        r1 = self._r / 255
        g1 = self._g / 255
        b1 = self._b / 255

        if r1 <= 0.03928:
            r2 = r1 / 12.92
        else:
            r2 = math.pow(((r1 + 0.055) / 1.055), 2.4)
        if g1 <= 0.03928:
            g2 = g1 / 12.92
        else:
            g2 = math.pow(((g1 + 0.055) / 1.055), 2.4)
        if b1 <= 0.03928:
            b2 = b1 / 12.92
        else:
            b2 = math.pow(((b1 + 0.055) / 1.055), 2.4)

        return (r2, g2, b2)