Yeah, but the description of what dynamic range, well, is simply wrong.
Austin
> BRAVO!!!!
>
> That's what I call a very usefull clear and understandable explanation. We
> need some more of these instead of the sometimes boring discussions going
> around here on the forum....:-)
>
> Thanks!
>
>
> Jean-Pierre Verbeke
>
>
>
>
>
> ----- Original Message -----
> From: "Julian Robinson" <jrobinso@pcug.org.au>
> To: <jpvb@pandora.be>
> Sent: Thursday, August 08, 2002 11:49 AM
> Subject: [filmscanners] Re: IV ED dynamic range... DYNAMIC RANGE!
>
>
> At 11:57 08/08/02, Austin wrote:
> >Density range is merely the extents that it
> >can capture density...but dynamic range is the resolution within that
> >density range.
>
> aaaaaaaaaaaaaaaaagh!!!!
>
> NO!
>
> (If you get confused by my first few paragraphs here, please go
> directly to
> the practical example at the bottom - see "PRACTICAL EXAMPLE" below).
>
> DENSITY RANGE is the maximum range of densities that the scanner can deal
> with / capture - using any available settings. You will in
> general have to
> modify gain and maybe other settings and do two different scans to capture
> the minimum density and the maximum density that the scanner can record,
> but the range between them is the Density Range.
>
> DYNAMIC RANGE on the other hand, is the smaller range within the Density
> Range that the scanner can capture AT ONE TIME i.e. dynamically i.e in one
> scan. It is the instantaneous range the scanner can handle.
>
> The reason that Nikon claim better Density Range and not dynamic
> range (see
> Bob's report in the quote at the bottom) is simply because the former is
> larger than the latter! It looks better as a spec. No mystery
> there. Someone go and ask Nikon if you don't believe me. (The
> hard part of
> this exercise is to make sure you access someone knowledgeable in Nikon).
>
> It is a simple enough concept. Most explicitly, dynamic RANGE is
> ***not***
> the RESOLUTION, and there is no book or standard that has ever said
> this. This is a confusing statement, and should not be unleashed
> on people
> who are not of engineering background.
>
> I don't want to start the war again, but simply, this statement "dynamic
> range is the resolution within that density range" is not true. To say so
> is a bit like saying that a cup handle is a saucer because if you count
> them you "always" get the same number - so they must be the same
> thing. Yes, it is true that almost always anyone who counts the number of
> cup handles in a tea set will get the same answer as the person who counts
> the saucers, but this does not mean that a cup handle is the same thing as
> a saucer. Furthermore, you will only get the same number IF the cups have
> one handle each, and IF these cups use saucers. These are assumptions and
> they are usually true, but are not true in all cases. You have to be
> careful in stating that just because two numbers are usually the
> same, they
> must be measuring the same thing. It is not true.
>
> Dynamic Range is not a resolution, although the number that you
> measure for
> Dynamic Range will OFTEN and WITH SOME ASSUMPTIONS be the same as the
> number you measure for resolution.
>
> Let me rephrase my first definitions, hoping for clarity -
>
> The ***dynamic range*** is the range of densities that the
> scanner can scan
> or discern at one time, which means in practice in a single pass.
>
> The ***Density Range*** is a larger range than the dynamic range and is
> defined by the range between -
>
> a) the greatest density the scanner can scan when you set
> exposure, gain or
> other settings to maximise detail in shadow areas, and
>
> b) the smallest density the scanner can scan when you tweak its
> settings to
> maximise highlight detail.
>
> PRACTICAL EXAMPLE
> *************************
> Here is an illustration as you might measure it in simple, practical terms
> on a Nikon scanner.
>
> In the following example, I will use decibels (dB) units. If you are not
> technically backgrounded do not fear, a dB is simply a convenient means of
> expressing the levels of things that work logarithmically, like sounds and
> light levels. If a measurement is 1dB higher than a first measurement,
> that means it is 1.26 times larger than the first measurement. So 3dB
> means a ratio of 1.26 x 1.26 x 1.26 = 2.0. And thus a density
> which is 3dB
> greater than a first density is twice as dense as the first density. That
> is, it will let half as much light through as the first density.
>
> Let's suppose you have a slide with a nice step wedge covering
> the range of
> densities from near black to near white (clear) on it, in 1dB intervals.
> The slide covers 35dB, so there are 35 steps visible. Step 1 is the
> darkest or densest and step 35 is the brightest.
>
> MEASUREMENT 1
> First, set the Nikon scanner analog gain control to a low gain, and scan
> the slide. You will get an output scan on which you can clearly
> see (let's
> say) steps 7 to 34 (that is, a 27dB density range). Because you set the
> gain low, you will be able to see most of the bright wedge steps,
> but below
> a certain point everything will appear black - equivalent to losing your
> shadow detail on a normal image. In this case your scanner can not see
> step 35, but it does see steps 34 to 7, and then there are 6 steps missing
> in the blackness at the bottom.
>
> Your dynamic range is (34 - 7) or 27dB. (This is equivalent to
> saying that
> the dynamic range is 500 to 1 if you work the maths out).
>
> MEASUREMENT 2
> Now set the scanner gain control to a high gain, and do a second scan. On
> your output scan this time you will be able to see, say, steps 2 to
> 29. This time you will miss out on the bright-end steps because you set
> the gain high and so the scanner saturated or "blew out" on the
> bright part
> of the test slide. But the range it collected was still 27dB - the same
> dynamic range. (Dynamic Range this time = 29 - 2 = 27)
>
> So you have measured your dynamic range twice, and it was 27dB.
>
> Now, what is the Density Range? It is the range from the
> brightest step it
> could record to the darkest. The brightest was in the first scan, and was
> step 34. The darkest was in the second scan, and was step 2. So the
> Density Range is 34-2 = 32 steps - that is, 32 dB.
>
> Voila. Your example Nikon scanner has a Density range of 32 dB and a
> Dynamic Range of 27dB.
>
> This illustrates the correct distinction between density range and dynamic
> range. Do not be confused by anything else!
>
> Because the Density Range is higher, this is what Nikon like to
> quote. Wouldn't you, given that 99% of us are too confused to know the
> difference? It is also a performance measure that is arguably as
> useful as
> the dynamic range in determining how good the scanner is. They measure
> different things but both are useful.
>
> Julian
>
> PS the NIkon scanners are the perfect example for this illustration,
> because they have actual, accessible, analog gain controls. Most other
> scanners hide the analog gain variation inside some kind of auto-exposure.
>
>
> >Charlie,
> >Nikon claims better 'Density Range' for the LS4000 not 'Dynamic
> Range'. I'm
> >sure Austin would tell us which is correct!!! I've forgotten already.
> >Bob Frost.
>
>
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