First of all, I do not regard myself as an expert. But I think I do
understand what is happening with your negative of person, painting
and wall and how to correct it. And I think I know what Advanced
Workflow is aiming for. So I'll have my own try at answering and no
doubt the experts will correct me if I am wrong. That could help me as
well as you.
When I follow the advanced workflow suggestions what am I aiming for?
First of all, the purpose of advanced workflow is: (1) to save time by
determining the best compromise exposure for all frames in a roll, not
necessarily the best exposure for each frame; (2) to work out the base
colour of the film from a frame that gives the best chance of doing so
and apply that to the whole roll.
The best compromise exposure might not be as good for another frame as
allowing VueScan to calculate it specifically for that frame. But the
main purpose of the advanced workflow is to save time when scanning a
whole roll without unduly sacrificing quality. So it avoids
calculating exposure from a preview on each frame.
Am I trying to make the preview of the unexposed area of film black or
neutral? Do I alter the colour settings or should they be set to
none?
I don't think there is a specific aim here. The purpose is to correct
the film base colour, so getting a neutral colour in the unexposed
area. Whether it is neutral black or neutral grey depends on the
settings for colour balance and black point. But the colour settings
are not relevant to the advanced workflow unless you are also going to
lock the image colour. The aim is just to get a good compromise
exposure and the right film base colour.
Should the following frames then be scanned with no further
alterations or should the colour balance be further tweaked?
It is likely that colour balance will need to be tweaked. Assuming
that the exposure and film base colour were good, each scan should
have the data necessary to get a good colour balance with individual
adjustment. In my view, this is best done by scanning the film to
create raw files, outputting raw with scan. Then scan from the raw
files and adjust colour balance as required. By the way, as far as I
can see, you can adjust the film base colour (and indeed lock it) when
scanning from the saved raw file so you do not need to get that right
when scanning the film. The exposure affects the raw file but film
base colour does not (and nor do any other colour balance settings).
It affects only the final image.
To amplify I have a negative of a person in front of a white wall with
a black painting on it & I can't seem to produce an acceptable scan
(although the film has been processed & printed ok by a lab). My
scans produce unacceptable posterization in the black painting and the
person although the white seems ok.
The white wall is a large expanse of dark or black on the negative.
The black painting is a smallish area of relatively unexposed or
slightly exposed film. The person is somewhere between.
Let us first assume you are not using the advanced workflow. You
preview the frame and VueScan calculates the exposure for the whole
frame. It sees the black painting (the nearly clear area of film). It
quite correctly assumes that region contains some detail that it
should not lose. So it does not want the exposure to be so high that
that detail burns out. It sets the exposure low enough to capture the
detail in it. After all, this is what you would want if you were
looking for shadow detail from a scan of a negative. And VueScan does
not know you have a picture of a plain black picture rather than some
interesting shadow!
Right, so it has worked out an exposure low enough to get all that
detail in the black picture. It is too low for you. The white wall
will be fine. That is black on the negative. So reducing the exposure
to a too low value can only see that negative area as even blacker and
make the wall even whiter than white (i.e. it makes no difference to
the white wall). But it has produced detail in the black painting
(light negative) and in the person (quite light negative) that is not
really there. Well, it is there but you don't want to see it. There is
very little difference in magnitude of brightness between the totally
black pixels and the nearly black ones, but there is some difference.
When these differences are mapped to the available display values,
there is a limited choice of such values. So posterization is the
result as the differences go in "steps".
What you need to do is increase the exposure so that the quite dark
areas get completely black and there are no differences to posterize.
So do a preview. Then crop around the person and a bit of the white
wall, not too much, and do not include the black painting. Then lock
the exposure. Then adjust the crop to the whole image and preview
again. The exposure that was locked for person and wall, much higher
than before, will be now applied to the whole image. The black
painting (light on the negative) now gets a high enough exposure to
burn all its detail away and it goes completely black without
posterization. If you have included too much white wall the exposure
might be so high that it now shows unwanted detail in the wall but
since this is so bright, you probably will not see it. And you can get
rid of it by adjusting the white point of the image so clipping it
out.
After trying the Advanced workflow suggestions the preview of the neg
was a muddy grey.....
This is because (a) the exposure (which was, after all, a compromise),
is still too low for this frame so the black has unwanted grey detail;
(b) the white point is too small for this image so that the white wall
is not really white. Alternatively, when you did advanced workflow,
you might have cropped only on a clear area of film rather than on a
whole frame that included a big clear area. If you did that, the
exposure would be much too low. However, you probably did not do that
as that would not make the white wall muddy.
As I say, I'm no expert but I hope that all makes sense.
Stephen
