Nikon LS2000, NikonScan3: Exposure question

[stuart]

Hi,

I'm scanning negatives with NikonScan3.1.2 on an LS2000
and I'm rather puzzled with the exposure. It seems to make
very little difference whether I use the default exposure
(i.e. neither press the autoexposure button nor set
autoexposure in the preferences) or set autoexposure
before scanning. The scans look good, but whereas the black
point in the histogram is always set correctly (the curve
goes smoothly to zero) the white point seems to cut the
curve off sharply. I have found no way to set the white point
higher or, to put it differently, shrink the histogram, other
than choosing the Prescan Mode "LoContrast" instead of
"Automatic" (which makes a small improvement) or by sliding
the Contrast setting in Color Balance (which just shrinks
the histogram curve and moves the white cutoff to the left
as well as the black point to the right but still doesn't
make the curve go smoothly to zero). Setting the Analog Gain
down just moves the whole curve to the right, thus spoiling
the black point.

I know from experience with my Nikon E995 digicam that if the
available tonal range is not contained completely in the
histogram curve then, for instance, the highlights are burnt
out. So in this case I nearly always choose a low contrast
setting and correct later with Photoshop. I would like to do
the same with the scanner.

The few tutorials I have read and the Documentation to
NikonScan4 seem to assume that after a prescan the histogram
curve sits nicely in the middle of the range and all I have
to do is slice off the unwanted bits left and right.

Of course the problem could lie with my negatives on Kodak
Gold 200 taken with a point and shoot camera (Nikon TW2).
Maybe this consistently overexposed.

Is there any way to control the exposure on the LS2000 using
NikonScan3?

Stuart

 

[Don]

I'm scanning negatives with NikonScan3.1.2 on an LS2000
and I'm rather puzzled with the exposure. It seems to make
very little difference whether I use the default exposure
(i.e. neither press the autoexposure button nor set
autoexposure in the preferences) or set autoexposure
before scanning.

That's because when AutoExposure is selected in preferences it's used
automatically whether you press the AutoExposure button or not.

Furthermore, if you deselect AutoExposure in Preferences you need to
exit NikonScan *and* turn off the scanner for the change to take! At
least in my experience.

Finally, are you sure you're turning off the correct AutoExposure?
There are at least 3 different ones: Preview, Single Scan and Batch
Scan. Of course you also have to choose Negative, not Positive.

The scans look good, but whereas the black
point in the histogram is always set correctly (the curve
goes smoothly to zero) the white point seems to cut the
curve off sharply.

Have a look at Preferences/Advanced color tab. In there you can
specify how much clipping you want. Set this to 0 if you don't want
any clipping. Do note however, this has nothing to do with exposure
but only affects the software adjustments *after* the scan.

However, it has been reported by some that this image editing has a
tendency to clip slightly. If you believe that to be the case, the
best thing to do is turn AutoExposure off (as explained above) and set
the exposure manually, followed by editing your image in Photoshop
afterwards (see "raw scan" below).

I have found no way to set the white point
higher or, to put it differently, shrink the histogram, other
than choosing the Prescan Mode "LoContrast" instead of
"Automatic" (which makes a small improvement) or by sliding
the Contrast setting in Color Balance (which just shrinks
the histogram curve and moves the white cutoff to the left
as well as the black point to the right but still doesn't
make the curve go smoothly to zero). Setting the Analog Gain
down just moves the whole curve to the right, thus spoiling
the black point.

A bit of background first (please ignore if you know this already).
Scanner software is composed of two distinct components: the actual
scanning part and an image editing part. People often confuse - and,
indeed, think - that the image editing part is *the* software. It's
not.

So, the curves, the color balance and the rest of it all happen
*after* the scan. You could just as well - indeed, it's much better to
- do it in dedicated image editing software afterwards. For one, you
won't be squinting through the microscopic Preview window!

Since you already do some editing in Photoshop later, may I introduce
you to "raw scanning"? ;o)

The idea is to use the scanner to... well... scan! And do the rest
later in a dedicated program with a full toolbox. In other words, when
scanning, only modify the settings which affect the hardware (e.g.
analog gain and ICE) which you can *not* do later. Some people also
use "linear" gamma (set it to 1.0) but I don't think that really
achieves anything. Unlike curves, contrast, etc which are based on
"feelings", gamma is fixed at 2.2 (or 1.8 of you're a Macite) and
there is little point in doing it later.

Don.

 

[stuart]

Furthermore, if you deselect AutoExposure in Preferences you need to
exit NikonScan *and* turn off the scanner for the change to take! At
least in my experience.

Never thought of that, I'll give it a try.

Have a look at Preferences/Advanced color tab. In there you can
specify how much clipping you want. Set this to 0 if you don't want
any clipping. Do note however, this has nothing to do with exposure
but only affects the software adjustments *after* the scan.

Ah, there's my mistake. I'm a complete novice here and had thought that
by changing the settings to the preview *before* the scan that I could
influence the exposure and somehow make the best of the dynamic range.

A bit of background first (please ignore if you know this already).
Scanner software is composed of two distinct components: the actual
scanning part and an image editing part. People often confuse - and,
indeed, think - that the image editing part is *the* software. It's
not.

So, the curves, the color balance and the rest of it all happen
*after* the scan. You could just as well - indeed, it's much better to
- do it in dedicated image editing software afterwards. For one, you
won't be squinting through the microscopic Preview window!

Well I am a bit confused, because as I understood the documentation these
adjustments can be made *before* the scan and therefore to my way of
thinking should have an influence on the scan.

Since you already do some editing in Photoshop later, may I introduce
you to "raw scanning"? ;o)

The idea is to use the scanner to... well... scan! And do the rest
later in a dedicated program with a full toolbox. In other words, when
scanning, only modify the settings which affect the hardware (e.g.
analog gain and ICE) which you can *not* do later. Some people also
use "linear" gamma (set it to 1.0) but I don't think that really
achieves anything. Unlike curves, contrast, etc which are based on
"feelings", gamma is fixed at 2.2 (or 1.8 of you're a Macite) and
there is little point in doing it later.

Now that is exactly what I want to do, scan the negatives as well as
possible, store and archive them, and then play about with them later
using Photoshop. But my main worry was to extract the information from
the negatives with as little loss as possible, therefore the desire
to set the exposure correctly.

Don.

Thanks for your help.

But now I have two questions:
1. I'm still not quite clear as to what Autoexposure does. Is it an
automatic correction to the hardware before the scan (useful) or
is it just an afterscan processing option (not so useful)?

2. Are you telling me that analog gain is the only way I can influence
the exposure myself?

Stuart

 

[Bart van der Wolf]

SNIP

But now I have two questions:
1. I'm still not quite clear as to what Autoexposure does. Is
it an automatic correction to the hardware before the scan
(useful) or is it just an afterscan processing option (not so
useful)?

It adjusts the exposure time to the average density of the film image.

2. Are you telling me that analog gain is the only way I can
influence the exposure myself?

Analog gain is a minomer, it is actually the exposure time that is
changed, and indeed the only way you can change it.

Bart

 

[stuart]

SNIP

It adjusts the exposure time to the average density of the film image.


Analog gain is a minomer, it is actually the exposure time that is
changed, and indeed the only way you can change it.

Bart

Thanks, now things are beginning to make sense. So if autoexposure
is enabled for the preview, the scanner will make a rough adjustment
which I could tweak with analog gain and use for the main scan
if autoexposure is disabled here. Is that right?

Stuart

 

[Don]

Well I am a bit confused, because as I understood the documentation these
adjustments can be made *before* the scan and therefore to my way of
thinking should have an influence on the scan.

The confusion is due to what they mean by "scan". As explained above
they consider the "scanning and editing" as one single indivisible
unit. Therefore, to them the "scan" is the whole process of presenting
you with an image.

However, what really happens is that the image first gets digitized
(that's what I call a scan) and then edited. The curves, the color
balance, and friends, are all applied *after* the image has been
digitized but *before* you get the file.

I hope that's not even more confusing... ;o)

Now that is exactly what I want to do, scan the negatives as well as
possible, store and archive them, and then play about with them later
using Photoshop. But my main worry was to extract the information from
the negatives with as little loss as possible, therefore the desire
to set the exposure correctly.

I've been wrestling with that for over two years, first using an LS-30
and now an LS-50. I also started with the same notion of getting
maximum quality and expected it all to be done in a matter of weeks.
The problem is that, if you do care for quality, scanning is quite
complex and there are many "gotchas". Every time I thought I figured
it out something else would pop up and I had to start all over again.
In my case it's gone so far that I'm now writing my own scanning
software.

But don't be discouraged by all this. I'm only mentioning it to alert
you that answers often may only address the question narrowly but
leave other things out.

Thanks for your help.

My pleasure.

But now I have two questions:
1. I'm still not quite clear as to what Autoexposure does. Is it an
automatic correction to the hardware before the scan (useful) or
is it just an afterscan processing option (not so useful)?

It's the former. What happens is that the scanner performs a very low
resolution scan to "see" what the image looks like. After that it does
the analysis of that image and adjusts (calculates) the exposure so
that the highlights are touching the right edge of the histogram but
are not going over.

But, here's the catch! This value is stored internally and you never
see it. After this "optimal" exposure has been determined NikonScan
presents it to you as a *baseline* on top of which you may want to
make *additional* fine adjustments with Analog Gain (to adjust any
minor inaccuracies due to the fact that calculated exposure was based
on a low resolution scan).

In other words, take two diametrically different shots, one bright and
one dark. After you perform the AutoExposure on them NikonScan will
show you the same AnalogGain at 0. However *internally* they start
with a totally different exposure before this AnalogGain is applied.

Finally, do note that once the AutoExposure (AE) has been performed,
that internal value stays the same until the next AE. This is very
important! It means that if you subsequently turn AE off, you will be
still starting from the same internal value! That's why you need to
exit NikonScan after turning off AE because the only way to reset this
internal value is to run the program again. Just to be on the safe
side, I also turn the scanner off to make sure this value has not been
saved in the internal scanner memory.

2. Are you telling me that analog gain is the only way I can influence
the exposure myself?

Yes. Bearing in mind what I wrote above, once you turn AE off, then
Analog Gain is the only way to influence exposure.

One quick tip, even though AG has a limited range of +/- 2 ev, you can
also use individual RGB AG to boost this to a total of +/- 4 ev! For
example, setting Master AG at +2 and then *all three* RGB AGs at +1,
the resulting exposure will be +3.

Don.

 

[Bart van der Wolf]

SNIP

Thanks, now things are beginning to make sense. So if
autoexposure is enabled for the preview, the scanner will
make a rough adjustment which I could tweak with analog
gain and use for the main scan if autoexposure is disabled
here. Is that right?

Yes, that's how it should work. In practice there can/will be small
differences due to cropping and differences in scan resolution between
preview and final scan, but they should be minor.

Bart

 

[Kennedy McEwen]

SNIP

It adjusts the exposure time to the average density of the film image.

Actually, it adjusts the exposure to the minimum density of the film
image - and that is the entire image, not just the crop. The reason for
this is that CCDs bloom when they are sufficiently overexposed, so even
if the minimum density is outside of your area of interest, the crop,
overexposure can cause the device to bloom into the area of interest.
The autoexposure algorithm prevents this. The reason why the algorithm
adjusts to the minimum density is that this is the area that fills the
CCD wells most, and the best performance of the system occurs when the
wells are as full as possible.

 

[Kennedy McEwen]

Thanks, now things are beginning to make sense. So if autoexposure
is enabled for the preview, the scanner will make a rough adjustment
which I could tweak with analog gain and use for the main scan
if autoexposure is disabled here. Is that right?

Yes, except for the "rough adjustment". Whether prior to preview or the
main scan the autoexposure is the same quality, its just an
autoexposure.

 

[Don]

Actually, it adjusts the exposure to the minimum density of the film
image - and that is the entire image, not just the crop. The reason for
this is that CCDs bloom when they are sufficiently overexposed, so even
if the minimum density is outside of your area of interest, the crop,
overexposure can cause the device to bloom into the area of interest.
The autoexposure algorithm prevents this. The reason why the algorithm
adjusts to the minimum density is that this is the area that fills the
CCD wells most, and the best performance of the system occurs when the
wells are as full as possible.

But not overflowing... ;o)

Seriously though, that explains what I often wondered about; why
NikonScan bases exposure on the whole image rather than the crop.

Don.

 

[stuart]

thanks for all the advice

stuart