Digital BW, The Print

I would suspect that the difference between CCD detectors used in signal 
processing is based on the fact a lens performs a Fourier transform and 
the CCD is used as the integration in this process. The more integration 
the smaller (in frequency) the resolution cell (and less noise)- hence 
the higher the dynamic range since signal to noise ration in an 
individual cell is goes up as the integration time goes up.

There doesn't seem to be anything comparable in scanning an image and we 
seem to be stuck with the native dynamic range of the sensor.

Truman


Austin Franklin wrote:

>Truman,
>
>My experience through literally thousands of hours of design and testing
>digital imaging systems is that all you do when you increase the exposure
>time is simply shift the data values, it does not increase the dynamic range
>unless the system has a limitation in the first place.  If this limit
>exists, what you CAN do is take multiple exposures with differing exposure
>times.  This WILL increase your dynamic range, if done properly...but, the
>limitation, as always, is going to be noise.
>
>In a correctly designed system, the data out of the A/D is limited by the
>noise floor of the CCD, as the A/D is matched to the output noise of the
>CCD.  This means that expanding the voltage into the A/D doesn't buy you
>anything, as you will only be converting noise in the lower bits.
>
>Point is, as a general rule, you can't say that increasing exposure time
>increases dynamic range, it is very design dependant, and as you probably
>know, dynamic range is limited by noise if the overall signal stays the
>same.
>
>Austin
>  
>