> Colour could be relevent if the sensor has poor sensitivity
> to a particular frequency range, or produces more noise in
> that range (eg. blue, which I often hear contains more noise
> than other channels :).
Very true, but you have to believe the manufacturer is going to use CCDs
that don't have these problems.
>> No, that's wrong (and you were doing so well ;-). Dynamic
>> range IS resolution over ANY range, and 8 bits won't give
>> you a DMax of 4. In fact, 8 bits is 48db, or a DMax of
>> log10(2^8) or 2.4. Perhaps you are confusing the meaning
>> of DMax?
> Maybe I am. I thought that the optical density range was
> a logarithmic conversion of light intensity. If it is,
> I don't see any reason why an 8 bit system can't represent
> an optical density of 4 using a value of 255. Or zero,
> and represent an OD of 0 with 255. They're arbitrary numbers
> representing something in the analogue realm. All the number
> of bits determines is the number of steps between the
> maximum and minimum values converted. I fail to see why
> the bit depth is necessarily related directly to the
> analogue realm - it depends entirely on how one is mapped
> to the other.
Yes, it appears you are confused about what DMax is. There are two
'properties' to the system we are discussing. One is the voltage range, and
as you say, that, technically, could be represented by any number of bits.
Second is the ability to discriminate within that voltage range, which is
'resolution'....and that is what DMax is. DMax is relative in and of
itself. A voltage range of +1V and -1V (2V range) with 2 bits (4 values)
has the exact same DMax as a voltage range of +20V and -20V with 2 bits, yet
their respective ranges are different, and each bit of each range represents
a completely different voltage. In one it is .5V, and in the other it is
5V.
The output data from the scanner does not care a wit about voltages. What
it cares about is the ability to 'discriminate' as many values as possible
(DMax), and they are all relative.
