The scanner has a single row of pixels, so you can use the space next to the pixel for processing elements. A camera has to put another row of pixels there (and another row beyond that, etc., etc.) for a 2D array of sensor elements.
The 'blad is probably using larger 'pixels' in its sensor. That is partly to get the signal-to-noise ratio down to the level where having 16 bits makes sense (you want signal in those extra bits, not just more bits of noise) - larger pixels have a much better signal-to-noise ratio - and partly because you need a larger area of silicon for the other circuitry (A-to-D, logic processing, etc.). All the current 35mm DSLRs seem to use 12-bit sensors; I'm sure there are 14-bit DSLRs in development, but I'd be really surprised if Nikon went directly to 16-bit. At a risk of boring you with numbers: the current technology seems to support little more than 8MP from an APS-sized sensor & 12-bit pixels. Signal-to-noise ratio goes roughly linearly with area, so to get those extra 4 bits of signal we need 16x the per-pixel area. A sensor twice the size of a 35mm frame would only really require a 14-bit sensor for any resolution greater than that same 8MP. Perhaps Hasselblad (and/or Imaco) have some technological edge that really requires those extra two bits, or have come up with some clever multi-pass exposure tricks (I doubt if they've managed to get a sensor larger than 2 35mm frames). Or perhaps it's just marketing ... Shel Belinkoff mused: > > Hi John ... > > Couldn't forget that linear stuff since I never knew it <vbg> > > Don't really understand the 2D thing. Are there two rows of pixels, one > below the other? Nah, that can't be it? So how come the 'blad can have a > 16-bit sensor, and some DSLR cameras 14-bit? Is it a matter of space > (which is what I'm inferring from your remarks)? I heard talk of a Nikon > D3 with a 16-bit sensor, BTW ... > > Shel > > > > [Original Message] > > From: John Francis <[EMAIL PROTECTED]> > > To: <[EMAIL PROTECTED]> > > Date: 10/23/2004 12:42:22 PM > > Subject: Re: istD bit depth > > > > Shel Belinkoff mused: > > > > > > The istD has a bit depth of 12. I seem to recall some DSLR with a bit > > > depth of 14 ... maybe. The specs on the new Hasselblad claim a bit > depth > > > of 16. Why is it that so many DSLR cameras are using a bit depth of > 12? > > > Is there a physical or design reason? Cost? My little Nikon scanner > has a > > > bit depth of 16 ... why not a DSLR? > > > > > > Shel > > > > Don't forget that your scanner only has a single row of sensors, not a > > two-dimensional array, and that it only has to work at a single speed. > > > > Of the two, the fact that it's only a linear sensor is more important. > > You can put the extra processing elements, etc., alongside the sensor > > without having to worry too much how much room they take up. In a 2D > > sensor you're trying to put another row of pixels there. > >
