Warren writes:
<<
The 42 bit might be just advert hype or it might represent something real.
Few programs can handle a 42 bit file internally (PS can handle 36 bit I
think). Most scanners that advertise 42 bit are really 24 bit because they
take the 42 bit data and output it at 8X3 = 24. If it is a good scanner, the
42 bit figure will represent a true dynamic range of the CCD.
>>
I can expand on this comment a little:
There are really two parts 1) the CCD dynamic range and
2) the Analog to digital convertor range (that turns the CCD signal to
Digital numbers)
Specmanship often comes into both parts so effective range may be less than
the number of bits.
Where the user program limits the maximum number of bits it inputs,
if the TWAIN driver supports it,you can often adjust contrast gamma etc in
the TWAIN driver interface.
This is quite a big advantage for tricky scans.
You can use this to expand a small portion of the measured scale with very
much better
results when outputing the common 24 bit output.
For example I scanned some 130year old photographs for a neighbour. My 24 bit
home
scanner did not have sufficient resolution to expand the limited dynamic
range of the photographs.
A scanner at work did a significantly better job with careful adjustment in
the TWAIN capture
settings even though both were set to 24bits output.
Regards,
Tim Hughes
>>Hi100@xxxxxxx<<
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