Hello all,
This is the folow-up to my previous message, in which I praised the
negpos plug-in to invert negatives. In this message I will outline my
negpos workflow. It is based on just a few days of experience, so it
might not be perfect yet. Even so, for those interested it might give a
good starting point to get the most out of the plug-in. This workflow is
aimed at batch scanning a whole roll of negatives. At certain points I
will refer to the Minolta scanning software, as this is what I use with
my Elite 5400. Even so, it should be applicable to other scan software
as well.
1. Set the scan software to produce linear 16-bit scans.
[In minolta scan: set 16 bit linear. Any mode, negative or positive will
do, but negative gives finer exposure control]
2. Take an empty leader or trailer image. Adjust the exposure such that
the empty negative is almost overexposed, but the total distribution
remains visible. (This is not a critical step, but it is used to
optimally use the dynamic range of the scanner – it’s only useful if the
exposure is a *hardware* control.)
[In minolta scan : in negative scanning mode, this means clustering the
histograms towards the left. Save the exposure settings under the film
roll name. Separate exposure settings are usually not needed when ICE is
enabled. The rest of the procedure should be done separately for
scanning with and without ICE.]
3. Scan the empty image as a black reference.
4. (Batch) Scan all the pictures using the same exposure settings.
5. Next, open photoshop:
6. Open the reference image in a neutral editing space (R=G=B implies
grey) and locate the median location of the film base peak using the
histogram (PS CS). Write down the RGB values.
7. Open a representative image from the same roll into photoshop and
open the negpos window.
8. For the shadow tail, enter the median values found in the reference
image and set the blackpoint setting to ‘tail’. In the ‘Gamma C’ box,
enter the gamma of the profile you have assigned to the image. If you
selected ‘don’t color manage’, use the gamma of your working space. In
the other ‘Gamma’ boxes on the bottom left, enter the appropriate
numbers for the film type you’re using – see also the list at the end of
this post.
9. For the other parameters, use whatever looks best. A good starting
point is to use equal perecentages in the RGB boxes of the shadow,
highlight and highlight tail columns. Then adjust the highlight settings
until the grey balance is correct. Note that negpos only controls the
grey balance, not the intensity of any or all colours. This should be
done afterwards, by assigning a different profile or adjusting curves
etc. It’s like selecting a different type of film and has little to do
with the processing as such.
10. Uncheck ‘ex by %’ and run negpos. This will cause subsequent images
to be adjusted with the exact same setpoints instead of percentages.
11. In the ideal case, simply apply the negpos filter to all other
images in the same roll. This uses the same settings for every image. In
practice you will often use the above settings as a starting point for
further tweaking. A save/load option in negpos is sorely missed…
In step (8), one has to enter the inverse gamma values for the film type
(for an explanation, see the documents on
and the manual). I quickly
measured some response curves from the data sheets of the Fuji film
types I’m using. The values are listed below. Note that I wasn’t
extremely precise, and even if I was, slight differences in processing
will mean that these values can fluctuate for actual films.
name ISO R G B
nph 400 1.79 1.74 1.92
npz 800 1.48 1.54 1.72
reala 100 1.48 1.48 1.48
superia 100 1.3 1.19 1.12
superia 200 1.29 1.25 1.38
superia/press 400 1.53 1.43 1.38
superia/press 800 1.33 1.22 1.21
superia 1600 1.37 1.43 1.27
I hope this information is of use to you! If you find some
inconsistencies or have improvements, please let me know.
Greetings,
Simon
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