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



Thanks for the response.  I will need some time to chew on it a bit before I
either ask more questions based on what you have said or conclude that I
understand and accept your points.

> -----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 ?
>
>
>
> > >Another misconception...though equally as common...the
> number of bits the
> > converter
> > >has, have nothing to do with the scanners ability to capture any
> > particular
> > >density range.
> >
> > Just out of curiousity and in simple layman's terms, what
> do the number of
> > bits that the converter has  have to do with if not the
> density range? How
> > does it impact on what is captured?
>
> 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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