Kennedy wrote:
> Actually, Peter, CCD's are ANALOGUE devices - the output needs to be fed
> to an ADC before it can be read by computer.
snip...
> So the limit for a typical high performance CCD detector is
> around 10 bits.
As far I know, the number of bits of an CCD device produce has nothing
to do with the dynamical range of this device.
They are just an indication how fine, exact, it measure the differences
in brightness, reflection of an object (dynamical range, D), like meter,
centimeter and milimeter on an ruler.
For example, flatbed scaners are produced with 8, 10 and 12 bits, but
there dynamical range is 1.8, slidescaner are also produced with 8, 10,
and 12 bits, but with an dynamical range between 3.0 (Nikon) and 3.4
(Polaroid Sprintscan Plus). Nikon has anounced an new slidescaner with
an D of 3.6, the reason for this lies in the dynamical range of the
slides, up to 3.8. If your scaner has an lower D as your orginal, you
have to sacrifie either the highlights or the shadows.
> So, until someone invents a higher dielectric optically sensitive
> material than silicon for CCD's to be manufactured from, the practical
> resolution limit for digital designs is less than 10 bits, and since
> silicon technology has been dominant for the past 50 years - don't hold
> your breath waiting for that alternative!
We don´t have to wait, there is already an superior solution. Of course
with outdated technology, tubes. Photomultiplier tubes, like the one
used in drum scaner have an higher dynamical range than the "modern"
silicon solutions (actualy the reason to use CCD instead of PMTs in
scaner is money)
Richard
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