Todd,
>>>>>>>>>>>
My primary point was that with DyR defined as Dmax - Dmin, as it is by the
ISO, it is the range between the minimum discernable signal (which is what
the ISO calls Dmax) and the maximum signal before clipping (which is what
the ISO calls Dmin). Period.
<<<<<<<<<<<
But what do you mean when you say that "dynamic range is a range"?
Dynamic range is _always_ a ratio. If it's not, it's something different.
For example:
"ISO DSC dynamic range
ratio of the maximum luminance level that appears unclipped to the minimum
luminance level that can be
reproduced with an incremental signal to temporal noise ratio of at least 1,
as determined according to ISO 15739."
df
In the definition you quote above, "Dmax - Dmin", Dmax and Dmin will be log
values, and thus the expression "Dmax - Dmin" _is_ a ratio. (I suppose these
should all be "Dmin - Dmax" <g>.)
>>>>>>>>>>>>>>>
These values can be obtained from testing, and the bit-depth/resolution
within that range is immaterial to the DEFINITION of DyR. It may be material
to the values you will measure in testing, but it is immaterial to the
definition/formula.
<<<<<<<<<<<<<<<
Yes, I think, sort of, maybe. If you are looking at the analog signal prior
to the A/D converter.
But the bit-depth is material to the scanner user, since if it is
inadequate, then the quantization error will be larger than the noise, and
value of the minimum discernable signal rises. If the bit depth is
excessive, then the noise becomes the limiting factor, since the device will
return a distribution of random values for a given density on the film. If
you start throwing away excessive bits, the range of the distribution of
those random values will get smaller and smaller...
>>>>>>>>>>
As to your point that scanners report density ranges as values...
You say a 1-bit scanner may assign a value of zero to any tone from black to
mid gray... Okay,
<<<<<<<<<<<<
Yes.
>>>>>>>>>>
but do you realize that the range that Austin is using as
his Dmin for the ISO formula is the ENTIRE density range of the scanner?
<<<<<<<<<<
Austin's explained this: in any dynamic range calculation, the maximum
signal level can be seen as corresponding to the range of levels handled,
assuming the minimum level is defined. The noise (or minimum recognizable
signal level) (and the maximum signal level) defines how many meaningful
steps the maximum signal level is from the minimum signal level. That's all
dynamic range is: the number of meaningful steps from min to max. That's
normally expressed as a ratio...
>>>>>>>
If
a 1-bit scanner can assign any range a value that is 50% of its density
range, what bit depth scanner is it that will assign a signal the entire
scanners density range?
<<<<<<<<<<<<<<<<
<See above>
>>>>>>>>>>>>>>
With all due respect, I believe the type of ranges you are speaking to
(quite small for highbit scanners) is totally disproportionate to the
discussion at hand.
<<<<<<<<<<<<<<<
My point is that a value reported by a scanner corresponds to a range of
possible values in the film, and that the size of that range is given by the
worse of the noise in the electronics or the bit resolution of the scanner.
David J. Littleboy
davidjl@gol.com
Tokyo, Japan
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