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[filmscanners] Re: Density vs Dynamic range

Ok, I bitten my tongue long enough.  It hurts!

On Mon, 10 Jun 2002 10:32:30 -0400, Austin Franklin wrote:
>>However my point is that if you can reduce the noise level then you can
>>increase the number of steps (by halving the step size) with real
>>benefit, but without altering the range.
>Hi Peter,
>Correct, but that INCREASES the dynamic range.

No it doesn't.  You are confusing dynamic range and resolution.  Doubling
the number of steps & halving the step size will keep the same dynamic
range, but it will double the resolution.  Resolution here is the number
of discrete shades of R, G or B.  Peter's point is that if the noise of
the system is greater than the step size, decreasing the step size will
just digitize noise - Not Good, unless you play with digital processing
techniques, as alluded to.

>>My principle argument was that a 5000:1 ratio does not specifically
>>that 5000 steps are requires
>Well, yes it does...that's what it means, with respect to what we are
>talking about.  Go download a few linear CCD specs (or if you want, I can
>mail you some), and you'll see they talk about it in exactly the same way
Try this one, unless there is a better example.  It looks like a nice CCD
for a 4000dpi, 120 film scanner?


FYI Kodak defines dynamic range pretty much the way engineering schools
I've attended in the U.S., and apparently Ireland, do:  Max. Output level
divided by the dark noise level.

>>Just a quick question - do CCDs really use a +/- voltage swing? I'd have
>>thought that would have introduce noise problems around 0.

It looks like the Kodak chip uses only positive voltages, but the output
has a DC offset that the buffer amplifier and A/D have to deal with.

If you want to split technical hairs, please at least be willing to state
and consistently use terms.  First Nyquist, and now this.  It has the
appearance of trying to baffle the non-technical( Wow, photographers don't
need engineering degrees? ;), but doesn't provide any clarity.

Best Regards,


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