[filmscanners] RE: Density vs Dynamic range

["Laurie Solomon" <laurie@advancenet.net>]

Peter,

It must be the nature of the discussion or the topic; but just when I think
I am beginning to get a handle on it something muddies the water. :-)

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.  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.

(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.)

I believe that he also might agree with your statements below if you changed
dynamic range to density range and CCD to A/D converter.
        I've followed this discussion with some interest and realise that many
        people are confusing number of bits (i.e. the number of discrete values
        that can be represented) with the dynamic range of the CCD which could
        with the right A to D behind it, provide as many bits as required.

Please take my comments as an exercise in clarification for my own benefits
and not as a criticism or assertion that mu understandings are truth.

-----Original Message-----
From: filmscanners_owner@halftone.co.uk
[mailto:filmscanners_owner@halftone.co.uk]On Behalf Of
peter@softwell.co.uk
Sent: Sunday, June 09, 2002 12:05 PM
To: laurie@advancenet.net
Subject: [filmscanners] Re: Density vs Dynamic range



> Plain and simple, do you agree that a dynamic range of 5000:1 REQUIRES
> 13
> bits to represent every integer value between 1 and 5000?  If so, then
> where's the problem?  If not, then plain and simple, why not?
>
> Austin
>

I think where we differ is the assumption the a 5000:1 dynamic range
yields 5000 discrete integer values. Light intensity is a linear value so
that 5000:1 range can be divided into as many steps as you'd like to use.
It is in any case only a ratio and therefore has no units or integer
values. 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.

If the CCD has an integrated A to D and thus the number of output bits is
fixed, then I'd agree with your statement.

If not, then your statement is still wrong, or at best, an
over-simplification.

I've followed this discussion with some interest and realise that many
people are confusing number of bits (i.e. the number of discrete values
that can be represented) with the dynamic range of the CCD which could
with the right A to D behind it, provide as many bits as required.

I'm sure you'll agree that it's the noise floor and the saturation level
that define the true dynamic range.

Peter

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