Filmscanners mailing list archive (firstname.lastname@example.org)
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RE: filmscanners: Nikon MF LED light source...
I think I almost agree with you here Austin (heaven forbid!) but the
problem is that the only logical reference when Dmax is quoted on its own
is against full transparency, as you state - i.e. no film, nothing in the
way of the path betw the light source and the detector. Trouble is there
is no guarantee that the scanner is not in saturation at this level, in
which case Dmin is not 0. But this would not be stated by the manufacturer.
So I don't agree that if a manufacturer states a Dmax figure on its own, it
necessarily means that this is the scanner's dynamic range - it is very
easy to steal some dB in the figure by not owning up to a Dmin of a few dB
which is perhaps more likely than not.**
A different example is the Nikon scanners with their analogue gain which
are capable of turning up the wick on their LEDs or the gain on their amps
so that you can see into really dark images. Hence they could quote a much
better Dmax (relative to 0) than their competitors (those who don't have
analogue gain control). But when you do turn the gain up like this, all
your highlights blow out impossibly, in other words it is not able to
handle the RANGE from Dmax to 0, that is, Dmin is not = 0. But the Dmax
figure is still valid as a density figure which the scanner can "see
through" accurately, although it has nothing to do with the dynamic range.
I think the example about the Nikons shows that there *IS* some value in
DMax without quoting DMin associated with it, but it doesn't tell you
anything necessarily about dynamic range, which is the point I think Tony
And there is the additional point that *dynamic* range is not necessarily
the same as *static* (my word because I can't think of a better one) or
absolute density range. Dynamic range is the Dmax-Dmin that can be
recorded at one time i.e. more or less, in a single scan. But the total
density range is the maximum density which can be handled under one set of
circumstances minus the minimum density that can be handled (and doesn't
cause saturation) under another set of circumstances.
Once again the Nikons are the example - you can measure a Dmax with the
gain turned right up which will be 2 stops or so better than with the gain
at 'normal'. (6db difference I think). But near-clear highlights will not
be usable at that setting. So assuming that with the gain at 'normal' the
Nikon can record near-clear highlights, then we have two settings...
1. With gain = 'normal', Dmax(1) = x, Dmin(1) = ~0;
Dynamic range = x - 0 = x dB
2. With gain = 'max', Dmax(2) = x+6. Dmin(2) = ~6;
Dynamic range = x+6 - 6 = x dB (the same figure)
But the STATIC or ABSOLUTE range of densities that can be accurately
measured by the scanner is ...
Absolute range = greatest density that can be measured in any circumstances
minus minimum density that can be measured in any (other) circumstances
which (in our example)
= Dmax(2) - Dmin(1)
= x+6 - 0
= x+6 dB.
So the absolute range is validly 6dB better than the dynamic range. And as
I think everyone agrees, both figures need a relevant Dmax and a relevant
Dmin to be meaningful.
**In any case as we know and has already been discussed many times on this
list, the **quoted** dynamic range is usually based on the num of A/D bits
and so is not related to either Dmax OR Dmin in any case!
>DMax is of no value what so ever unless there is a DMin associated with it
>(and vice versa). Typically, DMin is assumed to be 0 when DMax is used by
>it self. DMax is equal to the dynamic range if DMax is referenced to a DMin
>of 0. Plain and simple. Having a DMax of 4 and a DMin of 1 is exactly the
>same dynamic range as a DMax of 3 and a DMin of 0. The dynamic range is
>still 3. All density values are ratio values, and are therefore relative,
>and all you need to know is what the number is relative to. Without a
>relation, density values are useless. Dynamic range does not need a
>relation, as it is a "range".
in usually sunny, smog free Canberra, Australia