Digital BW, The Print

Hi Roy,

> If we try to use this diagram as an example for the print domain,
> don't you
> need to put some labels on the axes??

I actually believe axes aren't very useful for our discussion.  I believe
you can just use one axis and describe what you need only along that one
axis, as follows:


----|..........|=|.......|-----

    ^ dMin      ^ noise  ^ dMax

and the axis is marked in density values.

> Yep, but you still have to DECIDE what constitutes "signal".

All that does is effect accuracy of your results...  I think one can
reasonably "find" the signal without much "decision" ;-)

> > > You've
> > > come up with
> > > a way to put density onto the signal diagram and so have I.
> We both had to
> > > "interpret" the signal diagram as it applies to density.
> >
> > I didn't have to interpret anything, the meaning of largest and smallest
> > discernable signal are clearly defined.
>
> Like I said: You still have to DECIDE what constitutes "signal".
> I.e what property
> do we measure to plug into the equation.

Ah, you mean in a descriptive sense, not measurement...well, scratch the
above ;-)

>  You can't just say "density".

Why not?  If that's what I am measuring the dynamic range OF, then why can't
I just "say" it?

> You're "largest" is Dmax - Dmin
> Mine is just Dmax.
> You're "smallest" variation within a single gray
> Mine is just Dmin.

And...yours don't work in the dynamic range equation...

> Is that 25 years of experience in dynamic range of photographic prints??
> Remember my issue is NOT whether you understand dynamic range in general,
> I'm concerned with how it's applied to prints.

25 years of using the concept of dynamic range.  I really can't say when
with respect to specifically photographic prints.

> You gotta realize that you know lots about dynamic range in one area, but
> that applying it to a completely different area takes some
> decisions about mapping
> concepts from one to the other.

That's what I disagree with.  I believe dynamic range is a very specific
property, and has a very specific purpose, and in your use, it does not
follow that purpose, it is merely density range, which is an entirely
different property than dynamic range.

> Can't take a single slice out of
> sound, can you?

But that's a property of the medium.  You can perceive sound without light,
but you can't perceive images without light.  I believe that "property" is
not important to the dynamic range.  You CAN get a one dimensional "image"
of signal min, signal max and noise completely without time.  "signal min"
and "signal max" as used in the dynamic range equation.

> You can't have sound without time.

But it isn't sound you're measuring, you don't have to hear it to measure
it, in fact, when measuring dynamic range of audio gear, I never hear it ;-)

> Well if the diagram is a record groove, the loud music is when
> the groove swings
> back and worth from the top bound to the bottom bound i.e. the amplitude
> of the audio signal is max.

Correct.  Gets that magnet all charged up ;-)

> The soft music is where groove moves thru a
> "small amplitude".

Yes.

> (Did you really say that small amplitude
> signal has nothing
> to do soft (i.e. quiet) audio?? Did you?)

If I did, it was because I didn't understand what you meant by "soft"...I
believe I thought you were using "soft" ambiguously, and asked you to
qualify your meaning.  I certainly know what you mean by it here.

> You do know how records work, don't you?

Yes, very well, thank you.

> You've referenced the signal diagram
> lots of times
> saying it completely defines how to measure "signal".

Well, if that's what I said, it really should say it defines the terms, by
example, used in the dynamic range equation.  It doesn't tell you how to
measure anything, though it does tell you what TO measure.

> The diagram (or make a new one) somehow  has to relate to
> a print i.e. show me what a largest signal versus a smallest signal looks
> like on paper.  If you can't say what a "largest signal" looks like or
> what a "smallest signal" looks like, how are you going to recognize it in
> a print?

But I have qualified what the terms mean, with respect to the dynamic range
equation.  Largest is dMax - dMin, very simply.

>  Briefly going back to the audio world, would you agree that
> "largest signal" is the loudest sound you get from the speakers

It depends on what you mean by "largest signal".  As it pertains to dynamic
range, it's the maximum amplitude.  This requires both the loudest AND
softest.

> and
> "smallest signal" is the quietest (noise included, of course)??
> For me in the print world, my "largest signal" looks like pure black and
> my "smallest signal" looks like pure white.  Can you describe yours
> as simply?

Well, yes.  I have dozens of times.  The terms "largest" and "smallest" are
different for density range then they are for dynamic range.

For the dynamic range equation, Dynamic range (dB) = 10log10(largest
signal/smallest discernable signal), the terms are defined as follows:

"largest signal" is the (highest value measured minus the lowest value
measured).

"smallest discernable signal" can be measured/derived in different ways, and
that depends on the application.  In an audio system, you can typically see,
and measure the amplitude of the noise on a scope.  In an image, it would
have to be derived, possibly as I've described in other posts.

> Actually, I've looked at a few books that use the term "dynamic range" as
> related to prints.  None have formal definitions, but all use it as
> a  range (i.e. min and max) of useful zones, exposures, densities,
> brightness/darkness, etc.

Would you mind providing a list of these references?

> > But Higgins shows the definition of dynamic range is...so it IS
> in a book!
>
>   Certainly not for prints!

In fact, he says "Dynamic Range EXAMPLE".

> What you calculate may be valuable in some way, but I don't think its
> what others would use the term "dynamic range of a print" for.

I understand, and that is simply because of misunderstanding/misuse.  Just
like "resolution".  It is also very misused, especially when it is related
to monitors.  It drives the monitor engineers absolutely batty.  I know a
few ;-)

> Phew is right!!

phew**2!

;-)

Regards,

Austin