Is Callier Effect Necessarily a 'bad' thing?

Folks,

I am posing this question relative to scanners with collimated light
sources (e.g. Nikon Coolscans) and let's say black and white silver
based negative films.
I have read many threads on here saying how this is a bad combination
(silver negs and collimated LED source) since it enhances grain
due to the Callier effect. While grain is generally modeled as a sort
of noise, seems to me that the image IS the grain. After all what else
is the image composed of but the silver 'grains' on the negative.
Furthermore, it seems that the Callier effect is a sort of signal
gain if one considers the silver on the negative to be the signal.
In fact it is an optical signal gain before any CCD or further downstream
electronics have a chance to add in there own electrical noise.
Think of a low density (almost clear) part of a negative.
The Callier effect would present the strongest optical 'signal'
to the CCD, i.e. it would 'enhance' the optical contrast prior to
electronic noise corruption. In the case of a dense (dark) portion
of the negative, today's better scanners have a strong enough DMAX
to handle what may be an enhanced density due to the Callier effect.
If the Callier effect creates an image that is too contrasty, in
today's scanner workflow it is trivial to reduce contrast (vs. enlarger
workflow where paper selection and exposure might make this a trickier task).

I would like to hear others thoughts on my above assertion that the
Callier effect may in fact have benefits in todays scanner based
workflow. Unfortunately, I don't have access to enough equipment to
empirically demonstrate my assertion.

W

"WD" <winhag@yahoo.com> wrote in message
news:3ed2ed45.0409110613.533272f6@posting.google.com...
> Folks,
>
> I am posing this question relative to scanners with collimated
> light sources (e.g. Nikon Coolscans) and let's say black and
> white silver based negative films.
> I have read many threads on here saying how this is a bad
> combination (silver negs and collimated LED source) since
> it enhances grain due to the Callier effect.

Small refinement, the Callier effect describes the apparent (!)
density increase caused by scatter in the emulsion. When the light
source is diffuse, the additional scatter by grainy emulsions doesn't
make a difference, because the light was already coming in at a
variety of angles and some will be refracted/scattered in the
dorection of the sensor. Directional/collimated light can only be
scattered away from the sensor, causing the apparent higher density.
The Callier quotient is larger for silverbased film densities than for
semi-transparent chromogenic black and white or color dye based films.

The graininess we can see are 3D clusters of grains or dye clouds, and
the degree of clustering is an attribute of the film, and developer
combination.

> While grain is generally modeled as a sort of noise, seems to
> me that the image IS the grain. After all what else is the image
> composed of but the silver 'grains' on the negative.

Correct in a sense, the grains are samples of luminance exceeding a
threshold at a particular random position.

> Furthermore, it seems that the Callier effect is a sort of signal
> gain if one considers the silver on the negative to be the signal.

It's a bit more complicated, because the Callier effect is different
at different densities.

> In fact it is an optical signal gain before any CCD or further
> downstream electronics have a chance to add in there own
> electrical noise.
> Think of a low density (almost clear) part of a negative.
> The Callier effect would present the strongest optical 'signal'
> to the CCD, i.e. it would 'enhance' the optical contrast prior
> to electronic noise corruption. In the case of a dense (dark)
> portion of the negative, today's better scanners have a strong
> enough DMAX to handle what may be an enhanced density
> due to the Callier effect.

Not exactly. The effect increases the apparent density as (diffuse)
density increases to approx. 1.2-1.5, after which the effect reduces.
The reason is that at low densities there are too few grains to cause
scatter, at medium densities there is optimal scatter, and at high
densities there is already little non scattered light that reaches the
sensor (most is absorbed anyway).

> If the Callier effect creates an image that is too contrasty, in
> today's scanner workflow it is trivial to reduce contrast (vs.
> enlarger workflow where paper selection and exposure might
> make this a trickier task).

As indicated above, the Callier effect causes an increased contrast
gradient up to densities 1.2-1.5, at the expense of a reduced contrast
gradient at higher densities. So in fact it causes a more non-linear
density as the collimation increases. Formally, densities are called
'diffuse optical densities', exactly for that reason.

Bart

Bart,

So it sounds like your saying that the bottom line is that the Callier
effect causes a non-linear transformation between film density and scanned
results, with contrast enhancement in mid-tones only. Is this correct?
If so, seems the proper curve or LUT could be applied to 'undue' this.
In the real world, images are tailored to be 'pleasing to the eye', i.e.
curve or other transformations may be applied until the user
likes the result. So it seems the bottom line is that collimated vs.
non-collimated is really a non-issue for photographic images in a
scanned workflow. Is this your view?

W

"Bart van der Wolf" <bvdwolf@no.spam> wrote in message news:<41434999$0$65124$e4fe514c@news.xs4all.nl>...
> "WD" <winhag@yahoo.com> wrote in message
> news:3ed2ed45.0409110613.533272f6@posting.google.com...
> > Folks,
> >
> > I am posing this question relative to scanners with collimated
> > light sources (e.g. Nikon Coolscans) and let's say black and
> > white silver based negative films.
> > I have read many threads on here saying how this is a bad
> > combination (silver negs and collimated LED source) since
> > it enhances grain due to the Callier effect.
>
> Small refinement, the Callier effect describes the apparent (!)
> density increase caused by scatter in the emulsion. When the light
> source is diffuse, the additional scatter by grainy emulsions doesn't
> make a difference, because the light was already coming in at a
> variety of angles and some will be refracted/scattered in the
> dorection of the sensor. Directional/collimated light can only be
> scattered away from the sensor, causing the apparent higher density.
> The Callier quotient is larger for silverbased film densities than for
> semi-transparent chromogenic black and white or color dye based films.
>
> The graininess we can see are 3D clusters of grains or dye clouds, and
> the degree of clustering is an attribute of the film, and developer
> combination.
>
> > While grain is generally modeled as a sort of noise, seems to
> > me that the image IS the grain. After all what else is the image
> > composed of but the silver 'grains' on the negative.
>
> Correct in a sense, the grains are samples of luminance exceeding a
> threshold at a particular random position.
>
> > Furthermore, it seems that the Callier effect is a sort of signal
> > gain if one considers the silver on the negative to be the signal.
>
> It's a bit more complicated, because the Callier effect is different
> at different densities.
>
> > In fact it is an optical signal gain before any CCD or further
> > downstream electronics have a chance to add in there own
> > electrical noise.
> > Think of a low density (almost clear) part of a negative.
> > The Callier effect would present the strongest optical 'signal'
> > to the CCD, i.e. it would 'enhance' the optical contrast prior
> > to electronic noise corruption. In the case of a dense (dark)
> > portion of the negative, today's better scanners have a strong
> > enough DMAX to handle what may be an enhanced density
> > due to the Callier effect.
>
> Not exactly. The effect increases the apparent density as (diffuse)
> density increases to approx. 1.2-1.5, after which the effect reduces.
> The reason is that at low densities there are too few grains to cause
> scatter, at medium densities there is optimal scatter, and at high
> densities there is already little non scattered light that reaches the
> sensor (most is absorbed anyway).
>
> > If the Callier effect creates an image that is too contrasty, in
> > today's scanner workflow it is trivial to reduce contrast (vs.
> > enlarger workflow where paper selection and exposure might
> > make this a trickier task).
>
> As indicated above, the Callier effect causes an increased contrast
> gradient up to densities 1.2-1.5, at the expense of a reduced contrast
> gradient at higher densities. So in fact it causes a more non-linear
> density as the collimation increases. Formally, densities are called
> 'diffuse optical densities', exactly for that reason.
>
> Bart

"WD" <winhag@yahoo.com> wrote in message
news:3ed2ed45.0409111500.7b5ee0c1@posting.google.com...
> Bart,
>
> So it sounds like your saying that the bottom line is that the
> Callier effect causes a non-linear transformation between film
> density and scanned results, with contrast enhancement in mid-
> tones only. Is this correct?

No, increased contrast for densities lower than 1.2-1.5 and contrast
reduction above that.

> If so, seems the proper curve or LUT could be applied to
> 'undue' this.

It would seem so, however the film itself also has a non-linear
density response to exposure. It compresses shadows and highlights
with a lower contrast. So if the goal is an accurate linear density
response it should be achieved through calibration, but for a pleasing
tonescaling I would not worry about it. Tonescaling is better done on
image content, because the eye/brain is easily fooled and it is not
very accurate in absolute luminance (see e.g.
http://web.mit.edu/persci/people/ad...w_illusion.html).

> In the real world, images are tailored to be 'pleasing to the
> eye', i.e. curve or other transformations may be applied until
> the user likes the result. So it seems the bottom line is that
> collimated vs. non-collimated is really a non-issue for
> photographic images in a scanned workflow. Is this your view?

Fact is that the grain clusters do look more grainy in collimated
light, and scratches/dust are also more prominent. I really like the
result of a diffuse lightsource, partly because ICE doesn't function
on a silver based black and white film and partly because it reduces
graininess. Tonality can be adjusted quite easily once the image is
digtized. Since the Callier effect is marginal in dye densities there
is less of a tonality effect on those, but it still reduces the
graininess (at the cost of longer exposure times when scanning).

Bart

Bart,

Thanks for spending the time to share your insights and knowledge. Two
more related questions:

1. Where can I find more reference material on the Callier effect?
2. Any ideas how I might try to diffuse the light in my Nikon scanner
(e.g. laying a piece of translucent plastic of the frame in an FH-3
film strip holder)?

I think it would be interesting to experiment to get a feel for how
strong
this effect is in practice. I do scan a fair amount of BW (mostly
TMAX-100) and am generally quite please with the results but there is
always
room for improvement.

W

"Bart van der Wolf" <bvdwolf@no.spam> wrote in message news:<4143984f$0$78279$e4fe514c@news.xs4all.nl>...
> "WD" <winhag@yahoo.com> wrote in message
> news:3ed2ed45.0409111500.7b5ee0c1@posting.google.com...
> > Bart,
> >
> > So it sounds like your saying that the bottom line is that the
> > Callier effect causes a non-linear transformation between film
> > density and scanned results, with contrast enhancement in mid-
> > tones only. Is this correct?
>
> No, increased contrast for densities lower than 1.2-1.5 and contrast
> reduction above that.
>
> > If so, seems the proper curve or LUT could be applied to
> > 'undue' this.
>
> It would seem so, however the film itself also has a non-linear
> density response to exposure. It compresses shadows and highlights
> with a lower contrast. So if the goal is an accurate linear density
> response it should be achieved through calibration, but for a pleasing
> tonescaling I would not worry about it. Tonescaling is better done on
> image content, because the eye/brain is easily fooled and it is not
> very accurate in absolute luminance (see e.g.
> http://web.mit.edu/persci/people/ad...w_illusion.html).
>
> > In the real world, images are tailored to be 'pleasing to the
> > eye', i.e. curve or other transformations may be applied until
> > the user likes the result. So it seems the bottom line is that
> > collimated vs. non-collimated is really a non-issue for
> > photographic images in a scanned workflow. Is this your view?
>
> Fact is that the grain clusters do look more grainy in collimated
> light, and scratches/dust are also more prominent. I really like the
> result of a diffuse lightsource, partly because ICE doesn't function
> on a silver based black and white film and partly because it reduces
> graininess. Tonality can be adjusted quite easily once the image is
> digtized. Since the Callier effect is marginal in dye densities there
> is less of a tonality effect on those, but it still reduces the
> graininess (at the cost of longer exposure times when scanning).
>
> Bart

"WD" <winhag@yahoo.com> wrote in message
news:3ed2ed45.0409120659.7e807f47@posting.google.com...
> Bart,
>
> Thanks for spending the time to share your insights and knowledge.
> Two more related questions:
>
> 1. Where can I find more reference material on the Callier effect?

I'm not sure. Google just turns up bits of info related to enlargers
and contactprinting. An encyclopedia on photography might have
something.

> 2. Any ideas how I might try to diffuse the light in my Nikon
> scanner (e.g. laying a piece of translucent plastic of the
> frame in an FH-3 film strip holder)?

You need a thin material that has perfect Lambertian diffusion, e.g.
opaline glass, closer to the lightsource. It will reduce the amount of
light reaching the sensor, so maybe the LEDs will prove to be too weak
for this. You could experiment with some materials from Lee Filters
Lighting products (http://www.leefiltersusa.com), but try to avoid any
structure in the diffusor.

> I think it would be interesting to experiment to get a feel for
> how strong this effect is in practice.

You may find some historical info in the Minolta Multi Pro scanner
forum on Yahoo, it explains some of the considerations behind the
"ScanHancer" (http://www.allari-photo.com/scanhancer.html).

Bart

Bart,

Again, thanks. Interestingly enough, I pulled out the adapter from my
Nikon Scanner to take a look inside. I turned on the power and saw that
the light source in fact has some kind of cover on it. It started
flashing red, green, and blue. I was staring at the source at an
angle at least 45 deg. off perpendicular. Doesn't the fact that I could
see the LEDs flashing at this off angle imply that the light is not
perfectly collimated? Do we really know in fact how
collimated this light source is in the first place?

W

"Bart van der Wolf" <bvdwolf@no.spam> wrote in message news:<4144cc1d$0$568$e4fe514c@news.xs4all.nl>...
> "WD" <winhag@yahoo.com> wrote in message
> news:3ed2ed45.0409120659.7e807f47@posting.google.com...
> > Bart,
> >
> > Thanks for spending the time to share your insights and knowledge.
> > Two more related questions:
> >
> > 1. Where can I find more reference material on the Callier effect?
>
> I'm not sure. Google just turns up bits of info related to enlargers
> and contactprinting. An encyclopedia on photography might have
> something.
>
> > 2. Any ideas how I might try to diffuse the light in my Nikon
> > scanner (e.g. laying a piece of translucent plastic of the
> > frame in an FH-3 film strip holder)?
>
> You need a thin material that has perfect Lambertian diffusion, e.g.
> opaline glass, closer to the lightsource. It will reduce the amount of
> light reaching the sensor, so maybe the LEDs will prove to be too weak
> for this. You could experiment with some materials from Lee Filters
> Lighting products (http://www.leefiltersusa.com), but try to avoid any
> structure in the diffusor.
>
> > I think it would be interesting to experiment to get a feel for
> > how strong this effect is in practice.
>
> You may find some historical info in the Minolta Multi Pro scanner
> forum on Yahoo, it explains some of the considerations behind the
> "ScanHancer" (http://www.allari-photo.com/scanhancer.html).
>
> Bart

Bart,

Is this the same effect we wet darkroom workers get with a condensor (or
more radically point source) enlarger as compared to a diffuser enlarger? If
that is the case then it seems that at least in the "old days" the
enhancement of grain was considered a plus, as diffused-light-source
enlargers were mostly used for color printing; the softer look was not
considered desirable in B&W printing at all.

Toby

"Bart van der Wolf" <bvdwolf@no.spam> wrote in message
news:41434999$0$65124$e4fe514c@news.xs4all.nl...
>
> "WD" <winhag@yahoo.com> wrote in message
> news:3ed2ed45.0409110613.533272f6@posting.google.com...
> > Folks,
> >
> > I am posing this question relative to scanners with collimated
> > light sources (e.g. Nikon Coolscans) and let's say black and
> > white silver based negative films.
> > I have read many threads on here saying how this is a bad
> > combination (silver negs and collimated LED source) since
> > it enhances grain due to the Callier effect.
>
> Small refinement, the Callier effect describes the apparent (!)
> density increase caused by scatter in the emulsion. When the light
> source is diffuse, the additional scatter by grainy emulsions doesn't
> make a difference, because the light was already coming in at a
> variety of angles and some will be refracted/scattered in the
> dorection of the sensor. Directional/collimated light can only be
> scattered away from the sensor, causing the apparent higher density.
> The Callier quotient is larger for silverbased film densities than for
> semi-transparent chromogenic black and white or color dye based films.
>
> The graininess we can see are 3D clusters of grains or dye clouds, and
> the degree of clustering is an attribute of the film, and developer
> combination.
>
> > While grain is generally modeled as a sort of noise, seems to
> > me that the image IS the grain. After all what else is the image
> > composed of but the silver 'grains' on the negative.
>
> Correct in a sense, the grains are samples of luminance exceeding a
> threshold at a particular random position.
>
> > Furthermore, it seems that the Callier effect is a sort of signal
> > gain if one considers the silver on the negative to be the signal.
>
> It's a bit more complicated, because the Callier effect is different
> at different densities.
>
> > In fact it is an optical signal gain before any CCD or further
> > downstream electronics have a chance to add in there own
> > electrical noise.
> > Think of a low density (almost clear) part of a negative.
> > The Callier effect would present the strongest optical 'signal'
> > to the CCD, i.e. it would 'enhance' the optical contrast prior
> > to electronic noise corruption. In the case of a dense (dark)
> > portion of the negative, today's better scanners have a strong
> > enough DMAX to handle what may be an enhanced density
> > due to the Callier effect.
>
> Not exactly. The effect increases the apparent density as (diffuse)
> density increases to approx. 1.2-1.5, after which the effect reduces.
> The reason is that at low densities there are too few grains to cause
> scatter, at medium densities there is optimal scatter, and at high
> densities there is already little non scattered light that reaches the
> sensor (most is absorbed anyway).
>
> > If the Callier effect creates an image that is too contrasty, in
> > today's scanner workflow it is trivial to reduce contrast (vs.
> > enlarger workflow where paper selection and exposure might
> > make this a trickier task).
>
> As indicated above, the Callier effect causes an increased contrast
> gradient up to densities 1.2-1.5, at the expense of a reduced contrast
> gradient at higher densities. So in fact it causes a more non-linear
> density as the collimation increases. Formally, densities are called
> 'diffuse optical densities', exactly for that reason.
>
> Bart
>

"Bart van der Wolf" <bvdwolf@no.spam> wrote in message
news:4144cc1d$0$568$e4fe514c@news.xs4all.nl...
>
> "WD" <winhag@yahoo.com> wrote in message
> news:3ed2ed45.0409120659.7e807f47@posting.google.com...
SNIP
> > 1. Where can I find more reference material on the Callier effect?
>
> I'm not sure. Google just turns up bits of info related to enlargers
> and contactprinting. An encyclopedia on photography might have
> something.

One of those tidbits of info:
<http://www.photonics.com/dictionary...lookup/entrynum
..635/letter.c/pu./QX/lookup.htm>

Bart

"Toby" <zdftokyo@ggol.com> wrote in message
news:41454010$0$46683$45beb828@newscene.com...
> Bart,
>
> Is this the same effect we wet darkroom workers get with a
> condensor (or more radically point source) enlarger as
> compared to a diffuser enlarger?

Yes, the condenser concentrates the lightbulb's output on the film
area, thus increasing output which allows reduced exposure times.
There are variations with clear bulbs, frosted bulbs and on the other
side of the lighting methods is a softbox which provides diffuse
light.

> If that is the case then it seems that at least in the "old days"
> the enhancement of grain was considered a plus, as diffused-
> light-source enlargers were mostly used for color printing;
> the softer look was not considered desirable in B&W
> printing at all.

That is partly correct, although also a matter of taste, because paper
contrast is also a factor. The ultimate quality was/is considered to
be produced by contact printing, where the Callier effect is
practically non-existent.

However, in a situation where you sample the trans-illumination in
regular distances (discrete sampling), the "grain-cluster shadows"
cast by a point light source or a very collimated one, will increase
grain-aliasing (sharp edges have higher spatial frequencies than the
sampling density can resolve). So in a sampling system like a scanner,
the more diffuse lighting will reduce apparent graininess. From
thereon we are dealing with a digital image, and tonality is highly
adjustable.

Bart