Human lightness response though is a complex non-linear response that depends on the viewing conditions and the particular observer. This is why I'm not convin

Human lightness response though is a complex non-linear response that depends on the viewing conditions and the particular observer. This is why I'm not convinced that the right solution is simply filtering in linear intensity. Consider a black and white checker board where the individual squares are big enough that you can easily see them. If you scale this image down such that the squares disappear, the resulting gray should be the one that minimizes the perceptual error. But since sRGB is roughly perceptually uniform and the squares are mostly low frequency information, that gray would be 0x80 and not the 0xba you would get from the supposedly correct algorithm.