Digital BW, The Print

--- In DigitalBlackandWhiteThePrint@y..., "Austin Franklin" <darkroom@i...> wrote:
> > Dynamic Range is a characterization how much bigger the maximum
> > intensity is
> > from the minimum intensity of the system.
> 
> > In sound that's the
> > ratio of the loudest
> > to the quietest.
> 
> So, "bigger" == ratio.  I'm good with that.
> 
> But to move on to, what I feel, is quite important:
> 
> > In an image that's the ratio of the brightest
> > to the darkest.
> 
> 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
> 

Austin, we actually have a potential for making some progress here.
The density numbers quoted are actually LOG density.
So dMax = log10 (max density)   and  dMin = log10 (min density)
Turning these around we have:
    max density = 10^dMax
    min density = 10^dMin

So the actual ratios are:
   10^4.0 / 10^2.0 = 100
   10^3.0 / 10^1.0 = 100

So they are exactly the same.  The fact that people by convention automatically
take the log is just that, convention.

> 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.

I've made an effort to use words (but of course they are just English) that
show the parallelism.  I've used the work "intensity" since it seems usable in
both sound and light.  "Density" causes some confusion because, first, it is always
quoted with the "log" builtin and, second, density and intensity are inverses.
High density gives low intensity and vice versa.  Another term that could be
used equivalently is the "Energy" ratio.   Energy is a real scientific quantity
that should be easier to nail down.  With audio the ratio is caller a Power ratio
since audio is a time function : Power = Energy / Time.  

> 
> 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's ratio is of the high contrast to the lowest contrast.

I really don't have a problem with you calculating this.  The problem is you
want to call it Dynamic Range of Imaging and ALL and I do mean ALL others
in the Imaging world use this particular term with the ratio of brightest
to darkest.  I just don't think there's any sense bucking the world.

> 
> Yes, that works for me, thanks, I think that is well put.
> 
> > It just doesn't jive.
> 
> You're right, it doesn't even boogie ;-)
> 
> Austin

Roy