Alas, as we're talking about a fixed aperture lens, there is no changing of DOF Portrait can also mean a bunch of things in postprocessing - skin tones, colour saturation, sharpening, etc.
Yes. I was not clear in my last sentence - I was trying to allude that is what happens in most P+S cameras. But as you pointed out the N900 has a fixed aperture. Yes, it can also be many other post-processing as well.
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