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[filmscanners] Re: Density vs Dynamic range



You could help yourself by forgetting all about dynamic range, which is a
term pertinent to thos who manufacture and design CCD type devices.
If you are a photographer all that should concern you is density range,
because that is the range that carries visual information from the original
scene.

Also consider the simple fact that a CCD is not a digital device itself, all
it does is to take light at one side and generate electrical current at the
other. All the issues relating to CCD are actually analogue, the CCD is an
analogue recieving device and it's output in electrical terms is analogue.
Where many people get confused is because it is covered with tiny light
sensitive bits of matter which they translate as digital bits....forget all
that, only after the analogue signal; passes from the CCD out to AN Other
device (The so called analogue to digital converter) does the analogue image
signal become digitised and it is at that stage when the 8 bit, 10 bit, 12
bit decision becomes an issue.

What really matters, if you are after a very wide original density range, is
the actual range of light intensities that a CCD device will respond to
before it bleaches out in the highlights or noises out in the shadows.

All the advantages of high bit facilities are currently related to post
imaging manipulation using software like Photoshop, where the greater the
number of bits the more subtle and therefore photographic will be the image
edit possibilities.

----- Original Message -----
From: "Laurie Solomon" <laurie@advancenet.net>
To: <dickbo@btopenworld.com>
Sent: Monday, June 10, 2002 5:07 AM
Subject: [filmscanners] RE: Density vs Dynamic range


>Dynamic range is, in our case, (dMax - dMin) / noise.
I guess I tend to want to stay away from that definition in part because I
am not really able to visualize it very well; but I can visualize "Dynamic
range is the number of discernable values within a density range (in our
case)" much better so I tend to favor this definition over the other.  Just
a case of my limitations getting into the act. Sorry. :-)

>Well, you HAVE to increase the scanners dynamic range for more bits to
>increase the ability to represent accurately the value coming from the CCD,
>assuming, as I've said that the number of bits was matched to the dynamic
>range of the CCD in the first place.

>Doubling the number of bits also does not increase the density range of the
>scanner, and it also doesn't increase the ability to represent accurately
>the dynamic range (as I said above)

Alas, you are beginning to lose me because of my limited technical
engineering knowledge - I suspect - with your first paragraph. With respect
to the first part of the second paragraph, I understand what you are saying
and I agree, for what it is worth.  However, my understanding and agreement
with the second part of this paragraph may turn on the terminological use of
the notion of "accurrately."  If I understand what you have been saying, I
can see that the number of bits has no bearing on "accuracy of
representation" in the literal corrspondence notion of truth sense; but in a
more figurative sense where the terms "accuracy of representation" stand for
ability to define the density range in terms of finer gradiations or more
descrete segments, I would suggest that it does increase the ability to
discern and designate finer differences within the the density range.

Unfortunately, I think the confusion stems from your desire to use the key
terms in their very precise technical sense as defined in engineering
formulas and concepts whereas I am only able to really grasp the general
theoretical sense of the concepts in more metaphorical meanings.
Nevertheless, I really appreciate the time everyone is taking to nurse me
along in my attempt to decipher the discussion.

-----Original Message-----
From: filmscanners_owner@halftone.co.uk
[mailto:filmscanners_owner@halftone.co.uk]On Behalf Of Austin Franklin
Sent: Sunday, June 09, 2002 10:15 PM
To: laurie@advancenet.net
Subject: [filmscanners] RE: Density vs Dynamic range


Hi Laurie,

> The first point of confusion in your discussion with Austin appears to be
> that what you are referring to as "dynamic range" he is referring to as
> "density range" or that you are using the two terms synonomously
> while he is
> using them as naming two different concepts.

Dynamic range is, in our case, (dMax - dMin) / noise.  Density range is
simply dMax - dMin.  Dynamic range is the number of discernable values
within a density range (in our case).  Density range is simply the max
density value you can get minus the minimum density value you can get.

> For instance, if I may take
> the liberty to put words in his mouth, take the statement:
> "If we double the number of bits (possible values) that doesn't
> increase the dynamic range of the scanner, only it's
> ability to represent
> accurately the value coming from the CCD."
>
> I think apart from maybe disagreeing with "the value coming from the CCD,"
> he would say that what you are saying should read:
> If we double the number of bits (possible values) that doesn't
> increase the DENSITY RANGE of the scanner, only it's
> ability to represent
> accurately the DYNAMIC RANGE value CAPTURED AND DIGITALIZED by the
> scanner's analog to digital converter.

Well, you HAVE to increase the scanners dynamic range for more bits to
increase the ability to represent accurately the value coming from the CCD,
assuming, as I've said that the number of bits was matched to the dynamic
range of the CCD in the first place.

Doubling the number of bits also does not increase the density range of the
scanner, and it also doesn't increase the ability to represent accurately
the dynamic range (as I said above).

> (Austin, if you are reading this and I am putting the wrong spin on it or
> words in your mouth, please feel free to correct me.)

Yeah, I think things are being confused a bit (sic ;-)...  Too bad ;-(  It's
really quite simple.

Regards,

Austin

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