feat: RGB to CMYK color converter

conversions/rgb_cmyk_conversion.py

@@ -0,0 +1,71 @@
+def rgb_to_cmyk(r_input, g_input, 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()