WD said:
Kennedy,
Where is the scan data you 'publlished yesterday'? I would like to
take a look.
This same thread. Data included in post made on 21 June 2004 at
13:56:59 GMT.
We are going around in circles here, so let me state what I believe
Nikonscan
is doing.
1. It determines an exposure (probably does this adequately)
2. It scans the negative and collects all the data
3. If you can imagine a full dynamic range histogram, as you
stated,
the dynamic range of the scanner is far beyond a typical
negative's
dynamic range. Nikon Scan analyzes all the data. It internally
determines that much of the 'data' at either end of the
histogram
contains no useful information and 'throws it out'
Wrong - you assume that it does this - but there is no evidence at all
that it does and, as you will see when examining the scan statistics I
published yesterday, it does not throw information out in the first
place.
4. Nikon Scan 'presents' what it has determined to be the part of
the data
(i.e. some portion of the full scanner dynamic range)
which contains the full dynamic range of the negative scanned.
5. What the user gets to operate on in terms of curves, white point
black oint targets etc. is this data
(with what NS has deemed to be the extremes of scanner dynamic
range
beyond the negative dynamic range not included).
It is my assertion that in steps '3/4' NS in fact throws out
some data
which actually does contain useful information from the
negative.
What proves this to me is the fact that both Vuescan and Silverfast
can provide
scans of the same negative on the same scanner which in fact includes
the parts
that are irretrievably thrown out by Nikonscan.
They are not "irretrievably thrown out" - they are there and perfectly
recoverable. This is simply a matter of where the autoexposure
algorithms of NikonScan, Vuescan and Silverfast set the exposure level
in the first place.
As further evidence, NS allows no way to retrieve the full dynamic
range
that the scanner sees when scanning a negative (barring tricks like
telling NS it is actually scanning a positive and inverting manually
later on
which in fact does capture the full dynamic range of negatives even
using
Nikonscan - further evidence).
Rubbish. I have just repeated a similar exercise as yesterday with
another image which was flash lit and contained a white object in the
foreground, thus exceedingly overexposed on the film relative to the
main subject. Vuescan sets an autoexposure which reproduces the white
foreground object at just below peak white on the image. However, as a
consequence the main subject matter is, as expected, much darker in the
Vuescan image than on the actual print from the frame. NikonScan
however, using its default autoexposure setting, clips the white
foreground object but exposes the main subject matter perfectly! The
clipping occurs because the white foreground object is the densest part
of the negative and the autoexposure algorithm sets an exposure that is
too low for it to be detected by the CCD/ADC. No information is "thrown
away". Furthermore, by adjusting the master analogue gain by -0.8EV I
can produce a scan which is virtually indistinguishable from the rather
inferior, based on the main subject matter, Vuescan result. The main
subject matter can, from both scans, be lifted up to the correct level
as produced in the default Nikon scan using gamma adjustment. Viewing
the resulting histogram with the Optimax Wide Histogram plug-in shows
nearly identical combing in the black levels and the same range at white
- unsurprisingly proving that the images contain near as dammit the same
level of information.
This is a very clear indication of *exactly* where the difference arises
- and I seem to recall Ed mentioning something of this ilk in the past.
NikonScan judges the *exposure* based on median level in the frame and
does not specifically correct for the orange mask variation - hence the
black data level requires user adjustment for each film and process
combination (which changes orange mask tone and hue) - an adjustment
which can be saved by the user and called up in the future for that
specific film and process type. Vuescan, however, uses a black and
white point colour balance algorithm (as well as other processes, I
would guess, which are proprietary to Ed) to clamp the orange mask level
to black and the highlight to white. The median level in the image,
then ends up where it happens to lie.
You are completely wrong in your claim that NikonScan does not capture
the full dynamic range of negatives and does not provide a mechanism to
adjust the exposure to bring either highlights or shadows that may be
significantly off the median level into the captured dynamic range. I
demonstrated exactly that yesterday, and published the scan stats to
prove it, and have just repeated the process in the exercise documented
above.