TheAlgorithms/Python · error · ValueError

Expected int of the range 0..255

Error message

Expected int of the range 0..255

What it means

Raised by rgb_to_cmyk() in conversions/rgb_cmyk_conversion.py when any channel is outside 0..255 (checked as 0 <= x < 256 after the int-type check). It protects the 0..1 normalization step (x / 255) and the CMYK arithmetic from out-of-range values.

Source

Thrown at conversions/rgb_cmyk_conversion.py:48

    (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

View on GitHub (pinned to f5988cc097)

Solutions

1. Clamp before calling: max(0, min(255, v)).
2. Verify your scaling: 0..1 floats must be multiplied by 255 and rounded, not by 256 or left as-is.
3. Inspect upstream color math for overflow instead of silently clamping if exactness matters.

Example fix

# before
rgb_to_cmyk(300, -20, 128)  # ValueError: Expected int of the range 0..255

# after
r, g, b = (max(0, min(255, int(v))) for v in (300, -20, 128))
rgb_to_cmyk(r, g, b)

r, g, b = (int(v) for v in (r, g, b))
if not all(0 <= c <= 255 for c in (r, g, b)):
    raise ValueError('RGB channels must be in 0..255')
rgb_to_cmyk(r, g, b)

def in_rgb_range(r: int, g: int, b: int) -> bool:
    return all(isinstance(c, int) and 0 <= c <= 255 for c in (r, g, b))

try:
    rgb_to_cmyk(r, g, b)
except ValueError as e:
    if 'range 0..255' in str(e):
        rgb_to_cmyk(*(max(0, min(255, c)) for c in (r, g, b)))
    else:
        raise

When it happens

Trigger: Calling rgb_to_cmyk(256, 0, 0), rgb_to_cmyk(-1, 128, 128), or a value like 300 from an unchecked computation (e.g. summing colors without clamping).

Common situations: Arithmetic on color channels (blending, gamma correction) that can overflow past 255; passing 0..1 normalized floats scaled incorrectly; negative values from subtractive compositing.

Related errors

• hue should be between 0 and 360
• saturation should be between 0 and 1
• value should be between 0 and 1
• red should be between 0 and 255
• green should be between 0 and 255

AI-assisted analysis of TheAlgorithms/Python@f5988cc097 (2026-08-14). Data as JSON: /api/errors/39c6bbb8af230eeb. Report an issue: GitHub.