I am only posting two replies to what has been posted during my
overnight. This one is a short response to the nitty gritty of Austin's
argument. The other includes replies in a single post to other points by
everybody.
There are two points I am addressing in this post:
1. Dynamic range is a range, not a resolution
2. Dynamic range is the range that the scanner can capture AT ONE TIME i.e.
dynamically i.e in one scan
I address them purely by providing the resource that Austin requests. For
logical discussion, see other posts.
1. Dynamic range is a range, not a resolution
*************************************************
Julian:
> > It is a simple enough concept. Most explicitly, dynamic RANGE is
> > ***not***
> > the RESOLUTION,
Austin:
>Yes it absolutely is.
Julian:
> > and there is no book or standard that has ever said
> > this.
Austin:
>Well, the ISO spec shows clearly it is exactly what I've said it is, as well
>as every other resource I've posted on this subject before. I simply don't
>understand where you get the resources for your misguided understanding of
>it. YOU HAVE NO RESOURCES THAT SUPPORT YOUR BELIEF.
Julian now replies:
Hmmm. Here is the draft ISO spec, from
. It is entitled
"Photography — Electronic scanners for photographic images — Dynamic range
measurements." Perhaps there is another ISO spec from which you are
deriving your beliefs? Perhaps you could post it?
-------direct quote from Proposed ISO standard-------------------
7.2 Scanner dynamic range
The dynamic range is calculated from the Scanner OECF by:
DR = Dmax - Dmin (7.2)
DR = Scanner Dynamic Range
Dmax = Density where the Signal to noise ratio is 1
Dmin = Minimum density where the output signal of the luminance OECF
appears to be unclipped
-------end quote from Proposed ISO standard-------------------
(and OECF is opto-electronic conversion function)
You will notice, it is exactly as I have described it, a RANGE. It is the
range between Dmax and Dmin. It is not a resolution, there is no mention of
resolution. Can you tell me then how this says that Dynamic Range is a
resolution?
2. Dynamic range is the range that the scanner can capture AT ONE TIME
********************************************************************************
Julian:
> > 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.
Austin:
>Absolutely not correct. Where on earth did you get that? Please please
>provide any credible source that says anything to the such. The ISO spec
>doesn't define dynamic range that way...nor do any of the resources I have
>seen.
On the contrary, the ISO standard states a fairly precise process in which
the Dynamic Range is measured by scanning a single slide in a single
pass. (They do repeat the same single-scan measurement several times to
improve accuracy).
Here is the relevant text, remembering that the dynamic range is calculated
from the OECF:
----quote from proposed standard------------
6 Measuring the Scanner OECF
The scanner OECF shall be calculated from values determined from a test
chart 4 that consists of a density range higher than the range the scanner
is expected to be able to reproduce. For reflective targets the density
range shall be higher than the range of typical reflective media scanned on
this scanner. Many scanners will automatically adapt to the dynamic range
of the scene as reproduced on the film or reflective media and the
luminance distribution of the film. The results may also differ if the scan
mode is grey scale or RGB
A minimum of 10 trials shall be conducted for each scanner OECF
determination. A trial shall consist of one scan of the test chart. For
each trial, the digital output level shall be determined from a 64 by 64 1
pixel area located at the same relative position in each patch. Identical,
non-aligned patches may be averaged, or the patch with the least scanning
artifacts, such as dust or scan lines, may be used. The scanner OECF so
determined shall be used to calculate the resolution measurements for this
trial. If the scanner OECF is reported, the final digital output level data
presented for each step density shall be the mean of the digital output
levels for all the trials
6.1 Scanner settings
The scans for the determination of the scanner OECF shall be made in RGB or
grey scale mode with a resolution set to the maximum sample frequency
(given in Dpi or Ppi) divided by an integer to avoid interpolation
R = Rmax / i
R = scanning resolution
Rmax = maximum scanning resolution of the scanner
i = integer value (6.1)
The scanner shall be set to automatic adaptation to the dynamic range and
the digital values representing the dark grey patches shall be increased by
applying a suitable gamma correction so that the maximum number of patches
can be distinguished
...
-------end quote--------------------------------------------------
Austin, I have looked long and hard through archives to find where you have
quoted supporting information for your views, without success. There is
not a single quote I can find anywhere which contradicts what I am saying.
Perhaps you are assuming what I am saying, not actually reading it?
Julian
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