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[filmscanners] Re: Density vs Dynamic range



"Resolution" can refer both to the ability to distinguish between different
intensities and the ability to distinguish between spatially separated
details.  It can be used to refer to the distinctions between different hues
or saturation levels, too.  It just means how much or how many differences
can be seen or rendered in some aspect of the image.

----- Original Message -----
From: "Laurie Solomon" <laurie@advancenet.net>
To: <anthony@atkielski.com>
Sent: Tuesday, June 11, 2002 06:34
Subject: [filmscanners] RE: Density vs Dynamic range


I am not going to get into this highly technical discussion where I do not
belong as an active participant; however, I do have a question.  When you
say, "Resolution here is the number of discrete shades of R, G or B," are we
using the same term, "resolution," or using the term in the same way as when
we speak of "resolution" in terms of ppi, dpi, line pairs, or number of
pixels?  If so, I am confused since I did not think that this really had
anything to do with the number of discrete shades of R,G, or B but with the
number of R,G, and/or B pixels that there were regardless of the shade they
portrayed.  I further understood the number of discrete shades to be
represented by "bit depth" not "resolution."

If the term, "resolution," is not designated the same thing as indicated by
ppi, dpi, line pairs, and numbers of pixels but  is being used differently
or to designate something entirely different then knowing this is the case
would reduce my confusion and clarify the comments for this layman.

-----Original Message-----
From: filmscanners_owner@halftone.co.uk
[mailto:filmscanners_owner@halftone.co.uk]On Behalf Of Jonathan King
Sent: Monday, June 10, 2002 10:45 AM
To: laurie@advancenet.net
Subject: [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
>>define
>>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
>I
>do.
>
Try this one, unless there is a better example.  It looks like a nice CCD
for a 4000dpi, 120 film scanner?

http://www.kodak.com/US/plugins/acrobat/en/digital/ccd/kli8023Long.pdf

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,

Jon








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