I think more to the point, if 0 doesn't represent 0.0, and 255 doesn't represent 1.0, congratulations you've just lost your additive and multiplicative identities and most of the math used in colors falls apart.

The argument for 0-256 feels compelling when thinking about the physical display, but it seems like a very poor fit for any digital image processing or rendering.

> Remember how the 0 and 255 bins poked slightly beyond the [0,1][0,1] range’s edges? In the standard approach, the range of representable values is actually [−0.5/255,255.5/255][−0.5/255,255.5/255], meaning the bins are spaced further apart than strictly needed for [0,1][0,1] inputs

This is of course silly: the "range of representable values" of floating point colour components is [0,1] independent of quantization and how an invalid input would be quantized is irrelevant.

Looking at the actual "big picture" there are 256 representable values and (taking into account gamma correction, arbitrary ranges other than [0,1], deliberately nonuniform quantization bins, and other plausible complications) their correspondence to 256 floating point values should be regarded as a generic lookup table, abandoning all hope of using elegant and cheap formulas and making it obvious than encoding and decoding differently is not an option.

good point - alpha is a notable exception, it is not luminance