Number of Silver Halide Crystals vs Film Speed.

Photo Engineer · Oct 20, 2007

Mark;

Be my guest. Also, if you can, run the sharpness comparisons. I have and they are eye opening.

PE

Mark Antony · Oct 20, 2007

Here is my Blog,
http://photo-utopia.blogspot.com/
anything you'd like to add?
Mark

CBG · Oct 20, 2007

Mark Antony said:
Thanks for your explanation PE, it was this 'article' that confused me.
http://www.luminous-landscape.com/essays/clumps.shtml
I didn't think film grain was binary
Mark

That link encourages a simplistic way or looking at film and digital.

Without rehashing the endless boring debate on what's better etc ... Here's a way of looking at the comparison that gets too little attention:

First, it's always dangerous to treat very different media as if they were the same, i.e. just two differnt ways of doing the exact same thing. They are different ways of doing different but related things. The link and it's ilk encourage the false perception of a binary argument who's only possible answers are: a is better than b, or b is better than a.. In truth, each media imposes it's own character upon the results and much like PE's thoughts, the real answer is, "it depends".

A film based image breaks the image down into random grain based clumps with varying edge softness or sharpness, varying size and distribution of sizes. Beyond a very modest enlargement, the grain becomes a very important part of the image. It is a part of the aesthetic. Silver grain imaging is so different from digital that comparison is pointless. Like comparing apples and anvils.

Digital on the other hand offers up a "Chuck Close" grid based world. Utterly different from film. Again, why try to compare? Who's Close? Look at: http://www.artsconnected.org/artsnetmn/identity/close.html and http://en.wikipedia.org/wiki/Chuck_Close

The grain itself is an integral part of the film image, and to reproduce the grain with great fidelity demands huge amounts of information. If you want a result that looks like film, choose film. If you want a digital look, go digital. If you want images at an undemandingly low enlargement then it may just be mundane practicalities that make the decision.

Digital does one thing well and film another.

Best,

C

Photo Engineer · Oct 20, 2007

Well, here are some other facts.

For every ~108 grams of silver there are 6.023 x 10^23 atoms that divided by 3 can form any level of density you wish. That is a HUGE range. It is 2 followed by 23 zeros!

Now, in addition, silver grains can be stacked while sensors are side by side, so you have the additional enhancement of stacking or the detraction in digital caused by aliasing of the image by the nature of the pixel arrangement.

These additional facts should be of some use to explain the incredible detail in film images.

Digital is convenient and very portable. Good for snapshots and proofing professional LF shots in the studio. Analog is good for perfect professional pictures and is economical. It is slower to yield up the pictures.

Analog pictures are permanent. Digital pictures are fugitive.

PE

Photo Engineer · Oct 20, 2007

For those who don't know what aliasing is, here is a description.

Lets say there is a red thread on a white dress. In analog it is recorded as-is.

In digital, the thread may cross over 3 pixels R/G/B and therefore may not be recorded as-is, but may appear and vanish many times as it crosses the various pixels.

This is not related to the jagged lines caused by digital images.

I hope that this simple explanation helps.

Until digital sensors have stacked R/G/B sensors, aliasing will remain a problem. Some such sensors are being tested. Kodak has just invented a new type of sensor that supposedly eliminates this problem.

PE

AgX · Oct 20, 2007

But PE,

there is a difference between the ability of an exposed AgX-grain to yield an incredible huge number of shades (in the form of a latent image) and a development that reduces the grain thoroughly. To my understanding the classical type of development did it this way.

I guess this is where that confusion comes from.

Photo Engineer · Oct 20, 2007

Of course, this is true, but that is why silver halide is coated with grains stacked up, so as to get the dmax up to the desired level.

In any case, the arguments hold true regardless of speed, and hold up also when compared with digital.

PE

AgX · Oct 20, 2007

Thus if one employs the classical method of development on a classical homogenic (not core/shell) grain, this method will give the grain a binary character.

Photo Engineer · Oct 20, 2007

AgX said:
Thus if one employs the classical method of development on a classical homogenic (not core/shell) grain, this method will give the grain a binary character.

Sorry, but grain is not binary either.

If you saw the raw grain plot before smoothing for publication you would see how non-binary it is. What you see is RMSG (Root Mean Square Granularity) which is considerably smoother than what is actually seen.

PE

AgX · Oct 20, 2007

I guess there is quite a misunderstanding going on.

What I wanted to point out is that an AgX-grain (in the meaning of crystal)

-) has the ability to form a stable metallic-silver latent-nucleus (starting up from 4 atoms) increasing in size depending on the exposure (number of photons)
-) has the ability to form several latent-nuclei, depending on its form and chemical structure(preexisting nuclei)

which gives it a gradual (however invisible) response to exposure.

But the same AgX-grain (crystal)

will show a binary character when processed with a developer which has the ability to develop it thoroughly, depending on whether the threshhold for development (nucleus big enough and accessible) is too high (no development/reduction), or the threshhold is passed and the whole grain is reduced.
This binary character refers only to the crystal being developed or not.
It does not apply to the physical structure of the grain, which can be quite different (e.g. chem./phys. development: nucleiform/filamentlike).

When you employ a developer which is in state to develop the crystal proportionally to the size of the latent-nuclei you get a gradual response within the crystal, a more true image of the exposure the very crystal has got.

Ian Grant · Oct 20, 2007

OK, but its not as simple as that.

But as you want it to be - I guess an optimally exposed & processed piece of Lith film "appears" to be like that. That really is the closest analogy to a binary on/off situation.

That doesn't excuse a very poor article on the link you posted.

Ian

Gigabitfilm · Oct 20, 2007

Perhaps is this helpful - in german exist a good article about -bad translated "How to discuss resolution correctly", where you find some thinking about relation crystall size - speed:

BORIS LUX, EBERHARD GÖRGENS, HORST BÖTTCHER, Über den richtigen Gebrauch des Auflösungsvermögens, Bild und Ton 40 (1987) 6, S. 165-171.
Special interesting is the remark Nr. 52 - Lichtstreuung und Detailwiedergabe von Silberhalogenid-Gelatineschichten in Abhängigkeit vom Schichtaufbau I / Bode, A.; Reuther,R. - In: J. Signalaufz. Mater. - Berlin 2 (1974) 4. - S. 229-251

Remark nr 52 means translated: light-scattering and details of silverhalogenid-gelatinecoatings depending on their different layers-.

Zitation in german: "Das strukturelle Konzept des AV versagt jedoch nicht erst bei Rezeptoren von Molekülgröße. Auch beispielsweise für die Mikrokristalle (Körner) von herkömmlichen Silberhalogenidschichten gelten infolge der wellenoptischen Eigenschaften Wirkungsquerschnitte für die Wechselwirkung mit Licht, die mit der geometrischen Korngröße in einem sehr komplizierten Zusammenhang stehen(52)."

Alan Johnson · Oct 20, 2007

Grain size vs. film speed

Here the RMS granularity is listed for some B/W films having various speeds.Film with RMS 5 is twice as grainy as RMS 4.
http://www.cacreeks.com/films.htm
Considering film types include microfilm,traditional film,tabular grain film,there is some correlation between granularity and speed.

Photo Engineer · Oct 20, 2007

AgX;

A grain can develop from each sensitivity speck with threads, as a tablet of silver etc. etc. It is not a simple matter. Once the critical level is reached though, each site is developable or not. But there are still billions upon billions of possibilities in each square unit of film that has been exposed.

This possibility yields the same billions of possible densities.

Alan;

I have not looked yet, but generally RMSG goes up with grain size all else being equal, but it is possible to manipulate a faster film to have lower grain through coating parameters or development.

PE

Neanderman · Oct 20, 2007

Photo Engineer said:
A grain has many sensitivity sites and can form from 3 - billions of atoms of Silver metal, but a digital sensor is either on or off.

PE

It is also important to remember that reduced, exposed silver halide crystals do not form silver deposits of the same shape or form as the halide crystal. Rather, they form 'filaments' of silver metal. These filaments tend to form very complex 'bundles' that will block more or less light depending on the relative 'tightness' of the bundle.

Think of a piece of thread that you've wadded up into a ball.

Ed

AgX · Oct 21, 2007

Photo Engineer said:
...But there are still billions upon billions of possibilities in each square unit of film that has been exposed.

This possibility yields the same billions of possible densities.

This is what I was hinting at!

A single simple silverhalide crsytal is, though inhereting the possibility of a gradual response, in standard common processing developed to the fullest, or not at all. Thus having, or rather being given, a binary character.
(I assume that even one single develople latent-nucleus is sufficient to get the whole crystal reduced, independent of how many other such nuclei are sited after exposure in that very crystal. Correct me if I am wrong in this point.)

However, the size-spread of crystals, and thus later grains, forms a gradual response in each sqare unit of film. And the form of the formed silver grain/filament cluster and the staggering of crystals, grains, within the emulsion, they all form a visual impression which is far from binary.

Mark Antony · Oct 21, 2007

"A single simple silverhalide crsytal is, though inhereting the possibility of a gradual response, in standard common processing developed to the fullest, or not at all. Thus having, or rather being given, a binary character."

You seem to be suggesting that a silver halide is either developed (black) or not (transparent) therefore binary, and it is the clumps of these grains that form tone, echoing the MR article I previously linked to.

I'm no expert and I'd like clarification, but my understanding is this:
Grains are developed according to the amount of photons that strike the halide crystal, in other words they are infinitely variable in tone dependant on the amount of photons that strike the crystal and the energy of the developer that acts on that latent image.

AgX · Oct 21, 2007

Mark,

All my literature (including the Mees&James) indicates this Yes/No behaviour of an exposed (or fogged) AgX-crystal to development. However, this is elder literature and it might be I missed something while reading. (That's why I'm asking to correct me if I'm wrong.)

However in a more recent german photographic dictionary it is stated that a core/shell crystal could be developed corresponding to its exposure. I don't know details though.

And there is the contemporary strategy of Gigabitfilm and SPUR of a development of crystals of monodisperse emulsion such that the reduction corresponds to the exposure of the very crystal. In order to achieve a tonal range, which otherwise could not be found in such emulsions due to the lack of size-spread between crystals.

Photo Engineer · Oct 21, 2007

A silver halide grain, when exposed, does not need to develop to completion. It depends on the grain and on the development type.

That is the problem here.

In fact, development inhibition is one of the prime ways of controlling granularity and sharpness.

PE

AgX · Oct 21, 2007

But PE, that inhibition comes from the outside (e.g from other grains as via DIR-couplers); it does not resemble the exposure the inhibited crysta got itself.

However, even with that Yes/No behaviour in mind, it could be that a multitude of latent-nuclei could produce by forming a multitude of filaments a somewhat different form of the silver-grain, different in from what a few or a single nucleus could start. Thus yielding a relation between exposure and grain form/size.
Perhaps you were referring at this with you reference to the amount of nuclei at one single crystal, PE.

Photo Engineer · Oct 21, 2007

Well, one crystal may have one nucleus, many or none and the amount determines development. If there are none, it is a 'dead grain' which will not expose or develop.

Now, once exposed a grain can develop partially or to completion. The development to completion depends on developer and condition of development (time and concentration).

Both Haist and Mees and James show all of these variants. Solvent developers behave differently than physical developers and pure HQ behaves diffferently than others. AgCl tends to develop the entire grain, but (now get this) Iodide emulsions tend to be restrained. In an example of a pure iodide emulsion, the photomicrograph clearly shows that most of the grain is intact with filaments surrounding it.

Now, as for DIR couplers, since the coupler is NOT a grain, it only affects the grain that caused it to react by chance and therefore it is like iodide in the above example. With enough, it can terminate development or retard it.

My point being this: You are right in saying that unchecked, an exposed silver halide grain under ideal conditions develops totally! However, developmet is checked by the photographer, modified for desired effect and grains are never ideal. This process results in a fully analog process with nuances to be supplied in an artistic manner.

And, to highlight this, digital is always on or off, under control of the computer and does not allow this control. Therefore we see the differences being discussed.

For those interested, I refer them to Haist, Volume I, and Mees and James for some excellent electron micrographs showing developent at all stages and on all types of crystals (or at least as many as possible in a limited volume).

PE

AgX · Oct 21, 2007

Well, I re-read those corresponding chapters in the Mees&James (3rd ed.) and got quite a headache know. (Who has got this book, will understand.)

My theory of the silver-halide crystal being developed to completion or not at all was confirmed. Not any reference to a development resembling the exposure of the very crystal has recieved.
However a lot of discussion on threshholds: energies to form develople nuclei. The aibility of the developer to reach those nuclei. And about effective densities which refers to the form of the grain itself and the grains cluster and the ability to block light.

Gigabitfilm · Oct 21, 2007

Mr. AgX: You write "And there is the contemporary strategy of Gigabitfilm and SPUR of a development of crystals of monodisperse emulsion such that the reduction corresponds to the exposure of the very crystal."

This is only correct for Gigabitfilm and Spur-Ludwig, no other company. Typically for this procedure is its enormous overexposue-latitude with full resolution, showing no diffusion-phenomena in highlights.

The emulsions of today without exception reach high speeds thanks to special inner structures of the individual silver halide crystals. Mostly so-called "internal fogging" is used for this purpose. Ultra-high-resolution emulsions are monodisperse and too small for increasing film speed by means of known emulsion making procedures. To exploit the full sensitivity potential of such films it is necessary to employ a developer which is highly restrained in its action on unexposed areas, tends to fog areas of low exposure and develops strongly exposed areas proportionally to their exposure. This is Gigabitfilm's internal-fogging-developer.

Photo Engineer · Oct 21, 2007

AgX said:
Well, I re-read those corresponding chapters in the Mees&James (3rd ed.) and got quite a headache know. (Who has got this book, will understand.)

My theory of the silver-halide crystal being developed to completion or not at all was confirmed. Not any reference to a development resembling the exposure of the very crystal has recieved.
However a lot of discussion on threshholds: energies to form develople nuclei. The aibility of the developer to reach those nuclei. And about effective densities which refers to the form of the grain itself and the grains cluster and the ability to block light.

Mees and James state clearly that the degree of development depends on development condition and show partial grain development.

They also go on to caution that the examples were done ex-situ on microscope slides and do not represent the mediating effects of partial development or of gelatin even. They go on then, to qualify all of the results and the bottom line is 'we don't really have proof due to the qualifiers, but this is the way it seems' (this is in my words).

You must understand that if you leave an emulsion in a developer long enough you get 100% development of all of the grains, and that normal development represents a rather short time which thereby allows for partial grain development. This is why analog has so much control and what allows for push and pull processing. It is rather obvious that if a grain is developing and is only partly done doing so, quenching development with a stop bath gives us only partial grain development. Otherwise we would have a lith type effect all the time, and then fog.

Haist says much the same.

PE

AgX · Oct 21, 2007

As I stated I found no reference in the M&J nor at any other literature I got at hand tonight that a developed crystal reveals gradually its exposure.

However a university script intended for scientific users of photography (the best of its kind I found so far) referring to the Mees book states that “The process of development goes through until all AgBr of a grain is reduced, as long as we do not stop the process before.”
Well, such only to a part developed crystal and thus the metallic grain does not resemble the exposure that crystal has received…

It’s late at night; I’ll stop the discussion for my part here. (I still got the impression that we are talking about different aspects.) But I shall do my inquiries on this issue and report as soon as I found out more.

Number of Silver Halide Crystals vs Film Speed.

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