Bit masking (or not)?

[glv]

@paulstgeorge

The widely used algorithms mentioned have floats for RGB values. For example,
Luminance = 0.2126 * Red + 0.7152 * Green + 0.0722 * Blue

The R, G and B did not need to be floats and can be efficiently extracted from the color integer with bit manipulation.
The luminance will be a float.
You may need to use floating point math in such cases and can cast results as required.

I edited my previous post for clarity on context.

@solub made some approximations here to optimize performance:

@solub

# Calculate the true relative luminance using scaled weights:
        # Luminance = 0.2126 * Red + 0.7152 * Green + 0.0722 * Blue
        # Approximation: 0.2126 * 256 = 54, 0.7152 * 256 = 183, 0.0722 * 256 = 18
        lum = (54 * r + 183 * g + 18 * b) >> 8  # Bit-shift by 8 (dividing by 256)

There are also examples of extracting and setting colors without the helper functions:
Color to grayscale algorithm - #5 by solub

:)