calc_luminance.py

import colorsys

def hex_to_rgb(hex_color):
    # Remove the '#' if present
    hex_color = hex_color.lstrip('#')
    return tuple(int(hex_color[i:i+2], 16) for i in (0, 2, 4))

def calculate_luminance(hex_color):
    # Convert hex to RGB
    r, g, b = hex_to_rgb(hex_color)
    
    # Normalize RGB values to be between 0 and 1
    r, g, b = [x / 255.0 for x in (r, g, b)]
    
    # Apply the sRGB transfer function if components are below the threshold
    def srgb_transfer_function(color):
        if color <= 0.03928:
            return color / 12.92
        else:
            return ((color + 0.055) / 1.055) ** 2.4
    
    r, g, b = [srgb_transfer_function(c) for c in (r, g, b)]
    
    # Calculate luminance using the formula: L = 0.2126 * R + 0.7152 * G + 0.0722 * B
    luminance = 0.2126 * r + 0.7152 * g + 0.0722 * b
    
    return luminance

# Example usage
hex_color = "#FF0000"  # Red
luminance = calculate_luminance(hex_color)
print(f"The relative luminance of {hex_color} is {luminance:.4f}")