Digital BW, The Print

----- Original Message -----
From: "Austin Franklin" <darkroom@...>
To: <DigitalBlackandWhiteThePrint@yahoogroups.com>
Sent: Wednesday, April 03, 2002 9:03 PM
Subject: RE: [Digital BW] Thoughts about Imaging


(snip)

> Hum.  Do you mean the darkest to the brightest when talking about density
> values?  I'll fly with that ;-)  Let's use two examples, both with DENSITY
> range = 2.0:
>
> dMax = 4.0
> dMin = 2.0
>
> This gives 4.0 / 2.0 or a ratio is 2.0
>
> dMax = 3.0
> dMin = 1.0
>
> This gives 3.0 / 1.0 or a ratio of 3.0
>
> Note the density range is the same for both (and we agree that density
range
> is dMax - dMin)....but using your "brightest" and "darkest"
qualifications,
> the dynamic ranges are entirely different...but the difference in
intensity
> is exactly the same - 100:1 (a density value of 2 is 10**2, or 100, no
> matter what the dMax or dMin is).  That's why using "brightest" and
> "darkest" doesn't work for dynamic range.
>
> So, the RATIO of the brightest to the darkest, for two examples of the
same
> density range, do not yield the same dynamic range...how can that be?
Their
> RATIOS are the same!
>
> BUT...if we used the equation I have been using, ((dMax - dMin) / noise),
> the dynamic ranges WOULD be the exact same, given the same amount of noise
> for each.  Hum.

Austin,

Once again the confusion over logs and Density as a derived log value from
Reflectance. To determine the "darkest" to "brightest" ratio you have to
subtract Dmin from Dmax to get a representation of the ratio of Rmax divided
by Rmin.

dMax = 4.0 gives you a reflectance of 1/(10^4) = 0.01%
dMin = 2.0 gives 1%
A ratio of 100:1

dMax = 3.0 gives 0.1%
dMin = 1.0 gives 10%
A ratio of 100:1

For both cases the ratio of the Reflectance is 100 so the ratio of
Reflectance would fit your dynamic range criteria of being the same for both
cases.

Does that boogie?

Martin