David Kilpatrick wrote:Is what you desribe also what Nikon have been doing all along - something so simple that no-one bothered to think of it at Sony?
It doesn't seem like Nikon/Canon do anything like that. Those two rather play with 'optimizing' the colour matrix to minimize the noise at expense of colour fidelity. Nikon also uses rather heavy threshold filtering on raw in their D90 and especially in D5000 as obvious from the fact that 1px and 2px components of raw noise are far weaker than the lower freq noise components would suggest. The sensor itself in those two is actually nothing better than that in D300 which raw surely can be developed to even better S/N result than D5000/D90 since you can control the strength of that threshold filtering.
On the other hand, Panasonic and Olympus use exactly that kind of developing - separate for luma and chroma, and exactly into the Lab colour internally. But they adjust the 'bin' size for chroma depending on ISO, the higher ISO - the larger the bin. At lowest ISOs they seem to use an almost 'normal' demosaicing.
(E.g. an Lx3 obviously switches to chroma binning at ISO400, while at ISO80-100 it works more like demosaicing; yet the luma is still developed separately from chroma, and the Lab is the only colour space used internally.)