[dmurray]

Why would it have to be a single pixel instead of an array of sensors like any digital camera?

Sure, we probably can't make Geiger counters in a form factor that allows an array of a million of them in a handheld device, but maybe 20x16 or something?

[voidUpdate]

I mean you could make that work, but you'd have to shield between all of the detectors so that you don't get the radiation equivalent of bloom on your pictures. If you have only one, it'll be easier to shield, in my head anyway