[filmscanners] Re: IV ED dynamic range... DYNAMIC RANGE!

["Todd Flashner" <tflash@earthlink.net>]

on 8/9/02 10:29 AM, Austin Franklin wrote:

>> You will notice, it is exactly as I have described it, a RANGE.
>
> I do not see ANYWHERE where it says dynamic range is "a" range.  It shows
> the RESULT of a calculation WITHIN A RANGE (Dmax), divided by the noise
> (Dmin), but the result is NOT "a" range.

Austin,

First off (Dmin) I was hoping to see how you'd respond to Julian's point
that MDS is not always defined by noise. Your eq is based upon noise, but
all definitions reference min disc signal. Where are you when the min disc
signal is not defined by noise?

> A VERY simplified example that I've used time and time again while
> contradicting what you have been saying, but you seem to fail to grasp:

> A RANGE of 0-5V (which could be stated as a range of 5V) with 1V noise
> has a dynamic range of (5-0)/1 or 5.
>
> A RANGE of 0-5V with 1/2V noise has a dynamic range of (5-0)/1/2 or 10.
>
> Note, the RANGE is identical, but the DYNAMIC RANGE is not.

I don't get how you can have a range of 5-0 when noise is 1. How do you get
a range below noise? Doesn't noise limit your range on the low end, ie
define your MDS, just as saturation/clipping does on the high end?

Seems to me in your examples above you'd have two choices for each scenario:

> A RANGE of 0-5V (which could be stated as a range of 5V) with 1V noise

This could be ISO = DR = Dmax - Dmin.... = 5 - 1 = 4, which I *think* is how
Julian would approach it.

or Austin = DR = range/noise.... = (5 - 1)/1 = 4 which would appear to
account for noise twice, though when noise is assigned a value of 1 it
doesn't affect the final DR value (while conceptually it's way different).

> A RANGE of 0-5V with 1/2V noise

This could be ISO DR = Dmax - Dmin.... = 5 - .5 = 4.5

or, Austin DR =(5 - .5)/.5 = 9

Obviously, I must be mistaken about my assumption of noise and MDS...

But the greater surprise is your definition of Dmax as a range. For your
interpretation to make sense, your Dmax would need to be the entirety of
what Julian considers to be dynamic range. For instance, if you were
determining the the DR of a frame of film, isn't Dmax just the max density
of the film? By your definition Dmax would be the entire density range of
the film?

So is DR effectively = density range / noise?

If it were that it would be pretty easy to say so. Never seen it in any of
the sources cited.

The problem is that where sources are cited as definitions, those same
sources don't also show numbers applied in the formula, so we can't see
who's approach they support.

Todd

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