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[filmscanners] RE: Density vs Dynamic range - was: RE: opinions? Reviews? of Primefilm 1800 ?



Austin,

> That is correct....providing the system can actually take
> advantage of those
> bits.  If you have a 24 bit converter, and 12 bits of it is
> useless (noise),
> then what good are the 24 bits?

Yes, that is a given (I understand that and accept that as a limiting
condition).
As for the general points, I think that my understanding parallels what you
are saying for the most part, aside from my terminological mistatement where
I used "density range instead of "dynamic range" which you caught and
objected to.

In so far as my use of the two terms in the mistatement, "dynamic range" and
"density range" tend to be used in the literature and manufacturer's specs
synonymously as denoting the same thing (ie. the contrast range), I,
following their lead, slipped into using the two as identical terms in my
comments; but in doing so, I did no mean to suggest that bit depth was
connected to the contrast range as both "dynamic range" and "density range"
appear to make reference to in common marketing parlance of some
manufaqcturers and magazines.

Having said that,let me see if I got it by putting it into my own words.

 "Density range" refers to the "contrast range" from white point to black
point covered by the scanner and is measured in terms of 3.0 to 4.2 Dmax or
D ( it appears that in the current ads only Canon and Nikon are among the
few who refer to the guage as a measure of "dynamic range."  Whereas "bit
depth" refers the degree of quality information or detail that can be
obtained within the given "density range" and is measured in terms of 8, 12,
16, 24, 36, 48 bits or the like.  Thus, in your terms since most of the
literature does not use any term to describe what is being measured except
to refer to it as bit depth or x number of bits, bit depth measures the
"dynamic range" that a device can capture within its given "density range,"
as meeasured by the Dmax specification.

Is my understanding close enough for government work or do I need to go back
to the contemplation place and rethink it?


> -----Original Message-----
> From: filmscanners_owner@halftone.co.uk
> [mailto:filmscanners_owner@halftone.co.uk]On Behalf Of Austin Franklin
> Sent: Friday, June 07, 2002 10:37 AM
> To: laurie@advancenet.net
> Subject: [filmscanners] Density vs Dynamic range - was: RE: opinions?
> Reviews? of Primefilm 1800 ?
>
>
>
....Snip...
>
> Hi Laurie,
>
> First off, any density range can be represented by any number
> of bits (2 or
> more).  Because you have 100 bits, doesn't mean you automatically can
> represent a density range of X...and because you have two
> bits, doesn't
> limit the density range these bits can represent.
>
> What number of bits give you is DYNAMIC range, NOT DENSITY
> range.  They are
> NOT the same, no matter how hard people try to claim they
> are, they are not.
> They are two entirely different things.  Density range is
> merely the dMax
> and dMin, it has nothing to do with how finely you can
> discriminate (resolve
> tones) within that range.  Kind of like the difference
> between a 3 foot
> ruler with one foot markings...and a 3 foot ruler with 1/4"
> markings.  They
> both measure the same RANGE, but not to the same accuracy.
> Dynamic range is
> the ability to discern within the overall range, really the
> resolution.
>
> If you want to discern 256 things, you NEED 8 bits...but that
> has nothing to
> do with what those 8 bits represent...as they are simply relative unto
> themselves.
>
> > It has always been my understanding, rightly or
> > wrongly, that the
> > higher the number of bits the more detailed or refined the
> informational
> > date captured from the original that is transmitted as data
> in the digital
> > file with respect to highlight and/or shadow detail
>
> That is correct....providing the system can actually take
> advantage of those
> bits.  If you have a 24 bit converter, and 12 bits of it is
> useless (noise),
> then what good are the 24 bits?
>
> > with the density range
> > figure represetning the range of contrast that can be captured.
>
> And...that is correct too.
>
> > In other
> > words, "dynamic range" representing the contrast range of
> the capture's
> > capabilities,
>
> No, DENSITY range represents the contrast range...as you said
> just above...
>
> > while the bit depth represented the quality of the data
> > captured within that range particularly the extremes.
>
> Which is DYNAMIC range.
>
> Where apparently the confusion has arisen from, is the fact
> that density
> range values are stated in relation ":1" as in "to 1", so a
> density of 1.0
> is 10**1 or 10, and means "10:1", so people simply assume that the
> resolution of the system is relative to some "1", which it is not
> necessarily.  The values out of the A/D are not calibrated in
> any way, shape
> or form to density ratio values...they are simply a relative
> measurement in
> and of themselves.  You could, of course, design a film scanner and
> calibrate it so it reads "accurately" like a
> densitometer...but none do.
>
> As an example, your B&W 256 value (8 bit) file, can
> "represent" a density
> range captured from B&W film of say, .1 to 2, which is a
> density range of
> 1.8 or 10**1.8 or 63:1...yet, you get different values for 256
> tones...therefore, there, obviously, is no relationship between 8 bit
> values, and the actual density range of the original film.
>
> Regards,
>
> Austin
>
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