RE: filmscanners: Re: So it's the bits?

[Rob Geraghty]

Rafe wrote:
>Not quite.  There's no point going for extra bits, 
>without a corresponding decrease in overall system 
>noise.  If the noise is equal to one LSB at 8 bits,
>then it's 2 LSBs at 9 bits, 4 LSBs at 10 bits, etc.

I take your point Rafe, *but* most of the noise in the CCD is when the voltage
is lowest.  AFAIK there is much more thermal noise and other factors when
the input is very dark than at average light intensities.  So having more
bits to play with over most of the useful range *is* actually useful because
it reduces the size of the steps and therefore increases the accuracy of
the scan.  This is true of most A/D situations - the noise is much more
of a problem when the signal is small but *not* when there's a good signal
level.

So I agree and disagree - you're right in that there will be a lot of dark
noise unless more is done to eliminate that noise before it gets to the
A/D, but I disagree that more bits are useless for most of the image - quite
the contrary.

Rob


Rob Geraghty [EMAIL PROTECTED]
http://wordweb.com