Simple RGB to CMYK conversion. Returns percentages of CMYK paint. https:www.programmingalgorithms.comalgorithmrgbtocmyk Note: this is a very popular algorithm that converts colors linearly and gives only approximate results. Actual preparation for printing requires advanced color conversion considering the color profiles and parameters of the target device.  rgbtocmyk255, 200, a Traceback most recent call last: ... ValueError: Expected int, found class 'int', class 'int', class 'str'  rgbtocmyk255, 255, 999 Traceback most recent call last: ... ValueError: Expected int of the range 0..255  rgbtocmyk255, 255, 255   white 0, 0, 0, 0  rgbtocmyk128, 128, 128   gray 0, 0, 0, 50  rgbtocmyk0, 0, 0     black 0, 0, 0, 100  rgbtocmyk255, 0, 0   red 0, 100, 100, 0  rgbtocmyk0, 255, 0   green 100, 0, 100, 0  rgbtocmyk0, 0, 255     blue 100, 100, 0, 0 changing range from 0..255 to 0..1
def rgb_to_cmyk(r_input: int, g_input: int, b_input: int) -> tuple[int, int, int, int]:
    """
    Simple RGB to CMYK conversion. Returns percentages of CMYK paint.
    https://www.programmingalgorithms.com/algorithm/rgb-to-cmyk/

    Note: this is a very popular algorithm that converts colors linearly and gives
    only approximate results. Actual preparation for printing requires advanced color
    conversion considering the color profiles and parameters of the target device.

    >>> rgb_to_cmyk(255, 200, "a")
    Traceback (most recent call last):
        ...
    ValueError: Expected int, found (<class 'int'>, <class 'int'>, <class 'str'>)

    >>> rgb_to_cmyk(255, 255, 999)
    Traceback (most recent call last):
        ...
    ValueError: Expected int of the range 0..255

    >>> rgb_to_cmyk(255, 255, 255)  # white
    (0, 0, 0, 0)

    >>> rgb_to_cmyk(128, 128, 128)  # gray
    (0, 0, 0, 50)

    >>> rgb_to_cmyk(0, 0, 0)    # black
    (0, 0, 0, 100)

    >>> rgb_to_cmyk(255, 0, 0)  # red
    (0, 100, 100, 0)

    >>> rgb_to_cmyk(0, 255, 0)  # green
    (100, 0, 100, 0)

    >>> rgb_to_cmyk(0, 0, 255)    # blue
    (100, 100, 0, 0)
    """

    if (
        not isinstance(r_input, int)
        or not isinstance(g_input, int)
        or not isinstance(b_input, int)
    ):
        msg = f"Expected int, found {type(r_input), type(g_input), type(b_input)}"
        raise ValueError(msg)

    if not 0 <= r_input < 256 or not 0 <= g_input < 256 or not 0 <= b_input < 256:
        raise ValueError("Expected int of the range 0..255")

    # changing range from 0..255 to 0..1
    r = r_input / 255
    g = g_input / 255
    b = b_input / 255

    k = 1 - max(r, g, b)

    if k == 1:  # pure black
        return 0, 0, 0, 100

    c = round(100 * (1 - r - k) / (1 - k))
    m = round(100 * (1 - g - k) / (1 - k))
    y = round(100 * (1 - b - k) / (1 - k))
    k = round(100 * k)

    return c, m, y, k


if __name__ == "__main__":
    from doctest import testmod

    testmod()
