Rob,
I agree with what you wrote, except that having read some of Tony's old
posts I think this last point quoted below is not true - rather, there is a
definite limit to dynamic range prescribed by the number of bits. An 8 bit
scanner can never do better than a "Dmax" or ~dynamic range of log10 2^8 =
2.4. This is because the lowest usable level "step" has to be around one
LSB to be meaningful. Even introducing offsets to set the LSB decision
point to the top of the noise level doesn't help you because the next
usable level is still one bit away, and it is this step height which
effectively sets the minimum usable level, not the threshold you set the
LSB decison point to.
This is a change of view for me, I started out the other way round!
Julian
At 10:53 12/01/01, you wrote:
>In fact, referring back to my argument above, there's no reason why an 8
>bit per channel scanner couldn't have a dynamic range of (say) 4 if the
>analog circuitry is capable of measuring that range of light intensities.
Julian Robinson
in usually sunny, smog free Canberra, Australia
