There are two such mechanisms built into the camera already. One is the focus indicator in the viewfinder. This really is there, and it really is an auxiliary means of manual focusing, even if you seem to think it isn't. Secondly, LiveView is also an auxiliary means of manual focusing, and it is considerably more accurate than "old cameras" and it works particularly well in low light.
As far as an algorithm to prevent "zero pixels" I have no idea what you mean. As far as I know, there is no way to produce a zero-pixel file.
_____ Brian... a bicoastal Nikonian and Team Member
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