Lock exposure and vuescan

[I. Ordejon]

Dear experts,

if I do a preview with vuescan with a certain filmtype (say e.g. Fuji NPH
;.)) having a good part of the leader inside the crop box and lock exposure
afterwards, will the resulting exposure time be valid for all scans
regarding this film type?

I think this should be so, since the clearest (darkest) part of the exposed
image is (always) the leader.

In other words: Can I enter the exposure time I have taken from the
mentioned image for all and every roll of the same filmtype?

Or am I terribly wrong?

Regards,

Ignacio

 

[Bart van der Wolf]

Dear experts,

if I do a preview with vuescan with a certain filmtype (say e.g. Fuji NPH
;.)) having a good part of the leader inside the crop box and lock exposure
afterwards, will the resulting exposure time be valid for all scans
regarding this film type?

Depending on how much "a good part" is, Yes.
It is easier to just specifically crop small, and include a large part
of the leader or between-image space, lock and re crop on an actual
image. This will avoid things like the Input|Exposure clipping% and
the Crop|Buffer% getting in the way.

I think this should be so, since the clearest (darkest) part of the exposed
image is (always) the leader.

In other words: Can I enter the exposure time I have taken from the
mentioned image for all and every roll of the same filmtype?

Every roll may be a bit different. The ones processed in a row may be
close, but that assumes the films were from the same batch and were
stored and exposed under identical climatically conditions (e.g. film
in a black bodied camera may heat up more when used in sunny
conditions, and can be fogged a bit more).

In general your exposure will be close to optimal if you use the same
setting for all films of the same type. However, since it takes so
little time, and it takes reduced efficiency of the scanner's light
source into account, I'd re-evaluate the optimal exposure for each
individual film (especially if you scan to Raw originals for
archiving).

There may be situations where individual images are significantly
over-exposed. In those cases it would help the S/N ratio to override
the exposure and apply an increase over what would be found for clear
film areas (the film base color needs to be re-established for those
exposure times).

Bart

 

[I. Ordejon]

Depending on how much "a good part" is, Yes.
It is easier to just specifically crop small, and include a large part
of the leader or between-image space, lock and re crop on an actual
image. This will avoid things like the Input|Exposure clipping% and
the Crop|Buffer% getting in the way.

Thanks, Bart, I guess I am beginning to understand how the VS variables are
working and interacting. Actually what you describe is what I do.

Every roll may be a bit different. The ones processed in a row may be
close, but that assumes the films were from the same batch and were
stored and exposed under identical climatically conditions (e.g. film
in a black bodied camera may heat up more when used in sunny
conditions, and can be fogged a bit more).

.... and I thought it could not get more complicated anymore ...

In general your exposure will be close to optimal if you use the same
setting for all films of the same type. However, since it takes so
little time, and it takes reduced efficiency of the scanner's light
source into account, I'd re-evaluate the optimal exposure for each
individual film (especially if you scan to Raw originals for
archiving).

Problem is, that every time I re-evaluate exposure time I have to renew the
settings for filmbase color and filmtype color correction.

I think I have found a setting (based on the "Generic" film type and the
advanced workflow for the film base color - including some tweaking an the
R/G/B white points) which quite accurately matches the Fuji NPH 400 (for my
purposes at least). So I would like to keep those settings every time I scan
and just change the exposure time (if I have to). I am not at all sure, but
I think I loose these settings, when I repeat the exposure measuring, even
if I saved the settings.

There may be situations where individual images are significantly
over-exposed. In those cases it would help the S/N ratio to override
the exposure and apply an increase over what would be found for clear
film areas (the film base color needs to be re-established for those
exposure times).

Sorry Bart, I could follow all the way, but now I am lost. What is the S/N
ratio?

Regards,
Ignacio

 

[Bart van der Wolf]

SNIP

I think I have found a setting (based on the "Generic" film type and the
advanced workflow for the film base color - including some tweaking an the
R/G/B white points) which quite accurately matches the Fuji NPH 400 (for my
purposes at least). So I would like to keep those settings every time I scan
and just change the exposure time (if I have to). I am not at all sure, but
I think I loose these settings, when I repeat the exposure measuring, even
if I saved the settings.

Things will change with exposure level.

Sorry Bart, I could follow all the way, but now I am lost. What is
the S/N ratio?

Signal-to-Noise ratio or Dynamic Range.

If you lock the exposure in order to almost clip the most transparent
piece of film, an overexposed image will have more density than that
*everywhere*. That will result in a signal on the CCD that's lower
than it could be. Lower exposure creates more photon noise (like
smaller quantities in a statistical sample will exhibit more variation
around its mean). So it'll increase overall noise, most visible in the
densest parts of the negative (light parts of the final image, e.g.
clouds).

Bart

 

[I. Ordejon]

Things will change with exposure level.

Thats what I feared ...

Signal-to-Noise ratio or Dynamic Range.

If you lock the exposure in order to almost clip the most transparent
piece of film, an overexposed image will have more density than that
*everywhere*. That will result in a signal on the CCD that's lower
than it could be. Lower exposure creates more photon noise (like
smaller quantities in a statistical sample will exhibit more variation
around its mean). So it'll increase overall noise, most visible in the
densest parts of the negative (light parts of the final image, e.g.
clouds).

Seems I am just beginning to start to learn ... So (for Dummies) in these
cases I should manually increase exposure time in order to have an
overexposed image look like an overexposed image but reducing noise, right?

Thanks Bart. Now at least I know what I don't know

Ignacio

 

[Bart van der Wolf]

SNIP

Sointhese cases I should manually increase exposure time in
order to have an overexposed image look like an overexposed
image but reducing noise, right?

Not exactly. The image should not look like an overexposed one, but it
should be exposed as long as possible without clipping the least dense
parts of the image, which requires a longer exposure on an overexposed
negative.

Bart

 

[I. Ordejon]

Thank you for your patience, Bart

Ignacio

 

[Bob Whatsima]

Bart

Is noise in the highlight areas necessarily a bad thing? Most of my images
are outdoor scenics, and the highlight detail in the vast majority of them
is in the clouds.

These highlights (clouds) are meant to have a slight grainy texture to
them - we're not talking about photos of smooth fridge doors or snooker cue
balls.

I set my exposure clipping very low, something like 0.1%, for my Nikon Super
Coolscan 5000, and there is noticable photon noise when I zoom in very close
on my final scans. This noise looks like slightly mustard dots with a much
sharper edge to them then the average grey speckle in a cloud. But when I
view the image at a screen size similar to my print size, these dots are
mixed up with with the rest of the speckles contained in the clouds, and
aren't noticable at all.

I figure that the slight amount of photon noise is worth it in this case.
Would you advise against, and if so, what would you set your exposure
clipping at for a Coolscan?

Thanks in advance. Your frequent input to this group - along with my friend
google - have been a huge help in my scanning learning curve.

 

[Bart van der Wolf]

Bart

Is noise in the highlight areas necessarily a bad thing? Most of my
images are outdoor scenics, and the highlight detail in the vast
majority of them is in the clouds.

Noise isn't necessarily a bad thing, if it isn't obtrusive. As soon as
it claims more attention than it deserves, i.e. distracts from a
realistic depiction of a scene, I generally don't like it, but YMMV.
A technical benefit of noise is that it reduces the chance of
posterization becoming visible.

These highlights (clouds) are meant to have a slight grainy texture
to them - we're not talking about photos of smooth fridge doors
or snooker cue balls.

If you intend the clouds to be somewhat grainy, fine, but real clouds
don't look grainy to me. Our eyes are too slow, and too busy scanning
the surroundings, to detect photon noise. That's why I think it is
best to avoid the accumulation of noise sources as much as is
practical, you can always add noise later if desired.

I set my exposure clipping very low, something like 0.1%, for my
Nikon Super Coolscan 5000, and there is noticable photon noise
when I zoom in very close on my final scans.

I think film graininess will be more visible than photon noise,
depending on the actual integration time per sensel. If you have the
exposure clipping set to 0.1%, there is not much more you can do
(other then multi-scanning) to reduce photon noise at scan time.

This noise looks like slightly mustard dots with a much sharper
edge to them then the average grey speckle in a cloud. But when I
view the image at a screen size similar to my print size, these dots
are mixed up with with the rest of the speckles contained in the
clouds, and aren't noticable at all.

If the output density is such that the noise/graininess is unresolved,
there is no problem.

I figure that the slight amount of photon noise is worth it in this case.
Would you advise against, and if so, what would you set your
exposure clipping at for a Coolscan?

It sounds like the necessary precautions are taken, and the result is
to your liking, so things seem fine to me. You could try and see if
multi-scanning improves the technical quality of the scan visibly, but
I doubt it will (if at all) beyond 2-4x.

Thanks in advance. Your frequent input to this group - along with
my friend google - have been a huge help in my scanning learning
curve.

Glad to be of assistance, and yes, Google (or similar search engines)
is my friend as well.

Bart

 

[Bob Whatsima]

Thank you Bart, once again. Do you use a Nikon Super Coolscan, and if so,
what do you set your exposure clipping it for most of your scans?

TIA

 

[Bart van der Wolf]

Thank you Bart, once again. Do you use a Nikon Super Coolscan, and if so,
what do you set your exposure clipping it for most of your scans?

My Coolscan is an old LS2000, but I use a Minolta DiMAGE Scan Elite
5400 nowadays for my 35mm films. My Exposure clipping % is left at
default (0.01). My exposure times are usually manual (see Advanced
workflow suggestions), so I can determine the amount of clipping as I
wish.

Bart

 

[Bob Whatsima]

Merci once again Bart. I appreciate the fact that you've taken the time to
answer my questions, and the NG archive is full of great tips from you.