Digital BW, The Print

----- Original Message -----
From: "Todd Flashner" <tflash@...>
To: <DigitalBlackandWhiteThePrint@yahoogroups.com>
Sent: Friday, March 29, 2002 10:55 PM
Subject: Re: [Digital BW] Is dynamic range more important than densityrange?


> on 3/29/02 11:12 PM, Martin Wesley wrote:
>
(snip)
> >
> > Then shouldn't were be looking at the limit of our eyes and not the
prints?
> > And if the prints all exceed the discernable limit of our eyes wouldn't
the
> > factor of interest then be the density range?
>
> Martin, isn't the point about noise this: you have to measure it (even if
> that measure is a casual visual assessment) to know if it's relevant or
not?

I absolutely agree with you that you have to measure it. But I think it
needs to be more than an assessment. My immediate reaction to the noise in
the base white of a piece of quality inkjet or silver paper is that it is so
small I can't see it and I am not sure it is there at all. The same for a
patch of Dmax. There may be some variation there that could be measure with
good instruments that could give a value to be used as noise in Austin's
equation but we need to check.
>
> I hear and respect the logic of what you are saying IF the condition of
> noise is so low as to be negligible, but in some instances that wont be
the
> case, and if you want to describe the state of negligible noise to a
techie
> you're going to need a measured value to present. Therefore, once you have
> the measured value you might as well stick it into the DyR equation and
see
> what you get?

You are correct and you could determine the threshold where you do or don't
need to be concerned about the DyR.  Like CD players. Most of them have more
than enough DyR so that it is no longer a good measure to look at when
comparing them.
>
> I mean I hear what you are saying, that sometimes it will be near enough
to
> zero that your DyR will be ABOUT the same as your DnR, but that doesn't
make
> that measure irrelevant, it simply allows one to decide whether it is
> relevant or not.

No as the noise gets smaller in the equation DyR=10log(Dmax-Dmin/Noise) DyR
gets bigger and bigger. The closer DyR gets to zero the closer DyR would get
to infinity. Ultimately you can't divide something by zero since trying to
calculate how many time nothing goes into something doesn't make any sense.
It would be mathematically relevant up to the point the noise truly was
zero.

So it would be helpful to measure the noise and then see what level of noise
visually degrades the image.

My intuition is that it is so small that it can safely be ignored but to
resolve this issue some tests could be done with densitometers to see if
there is anything measurable within the resolution of the instrument. Since
these are more sensitive then out eyes, if they show no noise then I think
we can ignore it. If they do show noise then we need to compare the
magnitude of the noise to our vision to see if it is large enough to be
concerned about.

Martin