Grains - what is it, really?

[tkamiya]

I am trying to understand the role of grains on film and what it really means to me in terms of image creation. I understand as much that grains on film are metal silver that developed from silver halide.

Is a grain the smallest element of image? Saying this in different way, must an entire piece of grain must turn into certain shade of gray or can a grain turn into different shade in different parts? Is the size of grain the limiting factor on resolution of the image?

When are the grains created? At the time emulsion is placed on the sub-strait or at the time developer turns latent image into a real image? I thought the grain may equal to the crystal that were created when silver halide is placed on film but then if so, the size won't be different when different developers are used. Some developers are known to create smaller or larger grain.

Can someone explain please, or point me to a material that may explain this?

Thank you.

 

[keithwms]

It's actually quite a long story. Let me suggest that you first look at the wikipedia article on the latent image.

You might also look at slide 35 in this colloquium I gave:

http://www.phys.virginia.edu/Announcements/Seminars/Slides/S1433.pdf

After that, you might be inclined to look at the broader reviews on photographic sensitivity, which explain it all in more detail. Do bear in mind that not all b&w film has the same grain structure, not all has the same sensitization mechanism, and not all of it is developed the same way.

 

[tkamiya]

Thank you, thank you, thank you. I think, page 35/48 of the pdf above illustrates what I was really asking. Page 71 almost caused me to spit out my drink from nose....

So, what I understand from all this is, that GRAIN is the smallest unit in image forming then. The photons from incoming light turns the crystal "on" and the development process turns the "on" crystal into silver which we recognize as 'grains'.

 

[keithwms]

So, what I understand from all this is, that GRAIN is the smallest unit in image forming then.

Almost but not quite. I think it would be more correct to say that the sensitivity centers are the smallest unit in the image formation process. But in the final image, yes, the grain is arguably the smallest unit. But again, there are several different development processes and for some you see dye clouds as the smallest unit of the final image.

Perhaps Ron or one of the other experts can clarify further....

 

[MattKing]

Be careful about this, because the "grain" we see, tends to actually consist of a clump of individual grains, each of which is smaller than what we are able to see.

Matt

 

[tkamiya]

Can you give me an idea of what kind of scale we are discussing here? At x1000 magnification (under microscope) if I see a particle, am I looking at individual grains or a clump?

 

[keithwms]

That's true, what we see is not the same as what is actually the smallest information-carrying unit. The grains are measured in microns; the smallest 'dots' we discern are a good bit larger. But there isn't one answer for all films, nor even just b&w films- there are many different kinds of grain, and if you develop with stains then you get a different visual effect. Some have a distribution of sizes and some are more uniform. One of the slides in my talk shows some different kinds of grains as viewed by electron microscope.

 

[tkamiya]

So, in realistic sense then, a grain AS WE SEE IT, can have more than one shade because it contains hundreds of actual crystals/grains and each can be in different shade. I would imagine, since we are talking about clumps, they are not distributed evenly. I also see, on page 55, distribution and the size of grains aren't even either.

At 10^-6, it is at the edge of resolving power of my microscopes....

 

[Philippe-Georges]

I thought that the 'grain' we see on the print is actually the hole between the grains in the film (negative). I thought that the grain in the film is somewhat 'stopping' the light to travel trough the film emulsion and to hit the photographic paper. So, if this is right, then what we see on (in?) the print is a kind of a reversed image of the film's grain in the sense that it is the supposed 'surrounding' of the film's grain.
To say it with a little boutade, the grain in film is slain by light on to the paper (where in Spain it is slain by the rain)...
Or am I wrong again?

Philippe

 

[AgX]

Be careful about this, because the "grain" we see, tends to actually consist of a clump of individual grains, each of which is smaller than what we are able to see.

Matt

Yes, we have the grain that is just the crystal, then we have the grain that is the developed crystal, an aggregate of silver in different shapes, depending on processing, and last the optical impression all the stacked aggregates of silver make on the viewer/the print when illuminated from behind.

The latter is the actual `element´ of image forming. Or their equivalent of dye-clouds.


But to make things even more complicated, on the level of silver aggregates, the way of illumination is of influence too (Callier Effect).

 

[Ray Rogers]

You might also look at slide 35 in this colloquium I gave:

http://www.phys.virginia.edu/Announcements/Seminars/Slides/S1433.pdf

Keith,

Is this the same as the Mitchell colloquium ?
In either case, I can not get either to open for me.
Can you perhaps e-mail it (them?) to me until the web gets fixed?
Thanks,

Ray

 

[Bruce Watson]

I am trying to understand the role of grains on film and what it really means to me in terms of image creation.

Try Tim Vitale's exceptional paper on film grain. Perhaps more than you want to know, but it certainly covers the topic in detail, and with lots of photomicrographs as well. He does a good job of illustrating what he's talking about.

 

[keithwms]

Keith,

Is this the same as the Mitchell colloquium ?
In either case, I can not get either to open for me.
Can you perhaps e-mail it (them?) to me until the web gets fixed?
Thanks,

Ray

Ok, will do. Yes, it is the impromptu memorial colloq for JAck Mitchell... really more like a review of the history of photography and trying to put his work in context, which was very hard to do in 50 mins!

 

[Marco B]

Try Tim Vitale's exceptional paper on film grain.

Yes, I second Tim Vitale's document on film grain. But in addition, you may want to have a look at this historic, but still very informative, video at my website:

* The Alchemist in Hollywood

Just don't mind the boring voice over... it's 1940's you know

And read this document about silvergrains in photopaper, including some electron microscope images. It is a chapter from a book by James M Reilly. If found the cross sections of paper very intriguing and interesting, and also the difference between printing out paper and modern filamentous silver developing out paper... I have never before seen such detailed and clear images:

* JamesMReilly - Care and Identification of 19th Century Photographic Prints - pages 14-26

Marco

 

[keithwms]

Keith,

Is this the same as the Mitchell colloquium ?
In either case, I can not get either to open for me.
Can you perhaps e-mail it (them?) to me until the web gets fixed?
Thanks,

Ray

Ray, I just tried to PM you to ask for your email address but the PM bounced, it says your mailbox is full

 

[Ray Rogers]

Ray, I just tried to PM you to ask for your email address but the PM bounced, it says your mailbox is full

Sorry, I emptied the PM box...
I also made it possible to get my e-mail address by clicking on my name
in the left hand corner of each post.

Sorry!

Ray

 

[Maris]

The grain in the positive is a map of the spaces between the grains of the negative.

Where the negative is dense there are few and widely spaced gaps between the grains. That's why the light tones in the positive tend to be grainy and show less gradation. Large format film has more grains, therefore more spaces between grains, therefore smoother highlight detail.

 

[Philippe-Georges]

The grain in the positive is a map of the spaces between the grains of the negative.

This is very close to what I was trying to say but now it is put in better English...

Philippe

 

[Ray Rogers]

The grain in the positive is a map of the spaces between the grains of the negative.

I probably should not open my mouth here.
(The taste of foot has never made me very happy!)
But I love this postulate!

What is curious, is that on casual observation, it would appear that this would imply that a LARGER grain in the negative would, by blocking up those "holes" or "spaces between the grains", result in FINER grained photographic prints.

Likewise, by use of ultra-fine grain negative material, the resulting increased space between the grains in the negatives... should make for right grainy photographs!

Of course, we are totally ignoring one important parameter: grain number.
As grain size changes, very often... so does grain count.

But lets play with our fantasy a bit longer, at least until Dr. Sheldon Cooper (from The Big Bang Theory sitcom) enters the thread and tells us how the Universe really works...

Lets carry this analogy one step further: imagine if you will a totally grainless negative material... would the print from such a negative be a total, single grain? Yet, since there would be no change in density attributable to "graininess", the "single" grain picture should be essentially the same as a grainless print... sort of like nothingness & infinity, matter and energy, space and time... being 2 sides of the same thing!

OK, Now I KNOW I really should have kept my mouth shut!

 

[tkamiya]

The grain in the positive is a map of the spaces between the grains of the negative.

I've never thought of it this way but it's very true! Thank you for pointing this out. I was stuck in "pixel" type thinking.

 

[Philippe-Georges]

Larger grains have large 'intergrainspace' [a bit like the intermoleculairianspace?] (*).
But the thinking path about "… a totally grainless negative material..." is interesting because it takes us to the graphic application — lithography — film...
And, Ray Rogers, I beg you : please do go on 'eating'...

Philippe

(*) the expressions might be wrong, but after all I am a non English speaker who is very confident that, on this forum, there are intelligent people who will understand what I am trying to say. Perhaps, "...I really should have kept my mouth shut..." don't I? But, sometimes, I like to go in to the woods.

 

[Ray Rogers]

Larger grains have large 'intergrainspace' [a bit like the intermoleculairianspace?] (*).

If by intermoleculairianspace you mean the space within molecules, that quantity may increase with molecular growth perhaps. But the space between growing molecules, should not be increasing unless the space within the growing molecules is getting "pushed out" by crowding.

Ah, you must have been thinking about increasng grain size by optical magnification... in that case, yes the spaces grow as well. But what about negs from different emulsions, say ISO 0.1, 1.0, 100 and 1000? In those cases, the intergrain space should not grow as a result of dfferences in grain size... however this brings up another topic I have not considered... Do the developed grain sizes... relate directly to the intial grain size, or is there some compensating mechanism at play? I suspect they relate directly... but perhaps I should start looking for the salt and pepper!

Oh, I am getting a headache on all these the slippery slopes.

Sheldon! knock knock knock.
Sheldon! knock knock knock.
Sheldon! knock knock knock.

And, Ray Rogers, I beg you : please do go on 'eating'...

Perhaps you might care to join me for dinner?

But, sometimes, I like to go in to the woods.

Me too I guess, let's just hope this is not the story of Little Red Riding Hood!

 

[Philippe-Georges]

Me too I guess, let's just hope this is not the story of Little Red Riding Hood!

Who is afraid of the (grey-grained) wolf?

Philippe