Monday, October 20, 2008

Clumps and Chumps (or why film isn't binary)


There has been much talk on the internet about how many pixels it takes to out resolve film, the answer is 'it depends'
Many 'experts' have put their point of view across, some are disastrously wrong, certainly on a factual level.
here is one such assertion from Michael Reichmann:
Clumps and Chumps

"A very fine-grain film has grain particles that are about 2 microns in size. A typical DSLR has individual pixels that are about 6 microns in size. Ergo, film should outresolve digital. Right?
Not so fast! Here's the catch that many testers trip over. Grain particles are binary. An individual film grain can only be either black or not-black, on or off, exposed or not exposed. Sort of a binary device. A photo site (pixel), on the other hand, has a range of thousands of brightness levels, because it's an analog device. (Curious isn't it, that at this level film is binary and digital is analog?)
What this means is that it takes a clump of between 30-40 grains of film to represent a full tonal range, (similar in concept to the dithering done by inkjet printers to produce continious tones), while on a sensor each individual pixel can reproduce from hundreds to thousands of tonal levels."


Now for some facts.
Film emulsions are generally Ag/Br/I atoms combined into crystals from about 1 - 10 microns in size which are stacked in layers and dispersed randomly throughout the emulsion. They contain millions of atoms and many sensitivity specks which consist of sulfur and gold.
When film develops, it can form anywhere from 3 silver metal atoms minimum up to the entire grain, and grains can be stacked, and therefore the dynamic range of density is analogue in nature and virtually infinite. For practical purposes, it ranges from 0.1 - 3.0 density units in a normal negative B&W film.
Still need convincing?
Here's what's wrong with Michael Reichmanns essay.
Film grains are not binary, not even close they actually are made up of millions of silver particles that when looked at closely resemble a wire wool pad, the more photons of light that strike the grain the denser the filamentary structure becomes and the amount of light passed by that structure varies, the structure also develops randomly.

How Film Works:
Before exposure the structure of each grain consists of Ag+Br (silver bromide) atoms and sensitivity specs (sulphur and gold) the Ag atoms are positively charged (missing an electron) which is how they are bonded to the bromide atom.
When a photon of light strikes the silver atom they lose their positive charge and separate from the bromide atom, they are now silver ions and move (within the grain) towards the sulphur 'sensitivity' specks to form a filamentary structure, the more silver ions the denser the structure.
During development these structures are converted into metallic silver which is black, the bromide atoms are absorbed into the developer, fixing removes the silver atoms that weren't struck by any photons, leaving that part of the grain clear.
Here is an image (45,000x magnification) clearly showing the filaments and 'wire wool' like structure of the developed grain:


The image above pretty much nails the lie that film is binary or as Michael Reichmann put it:-
'An individual film grain can only be either black or not-black, on or off, exposed or not exposed'.

The film grain in the above picture shows that grain can be both black and clear at the same time as well as each filament differing in density, filamentary in varying degrees, letting different amounts of light pass though the grains themselves, being stacked up to 10 layers deep to give different tones.
Hardly the description of something that can have only 2 states, as would be the case if they were binary.

In his book 'The Fundamentals of Photography' C.E.K Mees states:
"Any silver deposit in the negative will let through a certain proportion of the light which falls upon it. A very light deposit may let through half the light, a dense deposit one-tenth, a very dense deposit one-hundredth or even
only one- thousandth".

I think Mr Reichmannn has made the common mistake of confusing the silver atoms that move towards the sensitivity specs with the grains themselves, coupled with not realizing that those grains are not opaque that and according to all the text books even the darkest grain will pass some light.
An easy mistake to make, I just wish his post was less 'pithy' especially considering his quite considerable errors, but I'll give him the benefit of the doubt and suggest a little research.
Here is a list of the books and references I have used for this article:

The Theory of the Photographic Process– C.E.K Mees and T.H James
The Fundamentals of Photography C.E.K Mees
The Science of Photography– H. Baines
Kodak Technical Document H1
Advice and help from Kodak research Europe (many thanks guys)

Information and help with writing this article Ron Mowrey

Here's a link to a paper by Nestor Rodriguez (Senior Technical Associate at Eastman Kodak):
Color 35mm film questions
Quote:
Q: What are the main differences between the way images are recorded on film and digital, aside from resolution?

A: "Film is analog, like the human eye. It sees and records continuous tonal gradations between black and white.

Edit: I have been asked to mention by a photographic engineer that the clumps and chumps article focuses on monochome film in order to make a more 'black and white' argument. It needs to be stressed colour film works in a similar way to mono initially but has a least three colour records, with the grains in each record being removed leaving a dye cloud which varies in size and density depending on the amount of photons that hit the parent grain. So in colour film grains(or rather dye clouds) vary in density (as in mono film) and also colour depending on the record they are contained in, not something that fits the 'on/off switch mentality of the 'clumps' argument

17 comments:

Charlie Wood said...

Hello Mark

This is interesting post. I have not yet had this argument yet.
Prints from medium format negatives speak for them selves.
I am "so glad that film is dead" because I just picked up a VGC Leitz focomat IC for £23 I have been improving my darkroom today.
Printing session imminent.
Do you want to go halfs on a 50pack of 120/XPS160?

Charlie

Photo–Smith said...

Charlie this is a slightly contentious post, not just because the article I reference is such a poorly written nonsensical piece of rubbish, but because lots of people are quoting it as gospel. Film is not binary, I know it so do a few others including PE on APUG, this is a case of someone with little knowledge passing of lies as facts.
To see the original article google the title of my post.

I too long for the day that film settles into it's niche, and I'm also enjoying the cheap film/equipment that gives me such good results.

Well done on the Focomat, they are v good enlargers what paper do you use?

As for the 160 Agfa I truly loved that film, processed thousands of rolls (it smells like pear drops when you take off the backing) how much is it?
I don't use much colour neg, but may give you some cash for a small part 10-20 films.

Anyhow thanks for you comment-have fun!!

Charlie Wood said...

What paper do you use.

Well you are going to love this. My local pro-lab stopped wet printing B&W about 2 months before I walked in the door. In short I bid them £5 a box for all there B&W papers and 50p a roll for all there fridged outdated B&W film.
I got mainly Agfa MCP and fibre paper Ilford multigrade RC and fibre. Kodak Polymax IIRC. The smallest sizes are 7x5 the largest is 10x12 (agfa)
I had to make two trips to the car due to the weight of paper He He.
Most of it is in my freezer
I have not had a great deal of experience of printing mainly due to the very poor enlarger I did have.
This thing used to drive me mad it was not a precision instrument.
There is money to be made taking portraits and printing onto proper photo paper.

The XPS 160 is dated 10/07 and is fridge stored and came direct from agfa. It is £60 for a box of 50 rolls plus 17 euro postage. I have some 35mm XPS 160 to.

If you want 20 rolls I can bring them down to you. I am going to visit Norwich in a few weeks.
I am going to get some as the price is good and this film will keep well if I freeze it down. Once the agfa colour films have gone that's it gone!
Is your Pentax 6x7 getting any use??

Charlie

Photo–Smith said...

Charlie,
What a great find, I wish I could do as much B&W as I used to, but alas I have no enlarger at home, but can get to use a Devere if I need to.

I'd love to meet and chat about film and Yes I'll give you some cash for 20 Rolls 160 Agfa.

I'm on Holiday next week and plan to take the Pentax and my little Rollei 35.
I think I'm going to shoot some 400X and possibly some Adox 25

Mark

Charlie Wood said...

I am a member of flicker. There are some myths on there regarding films.
I have heard some corkers.


The XPS is in the post from Germany to me.
The guy I am getting it from told me that at the end of this year all AGFA colour roll films will be out of date.
I got some Optima to.
I have a found a lab that will process C41 roll films for a very Good price my local pro lab charges £12/roll which is a bit expensive. I am going to shoot more colour roll films.
Enjoy your holidays.
Charlie

black and white photography said...

wow, this is an useful resource! very interesting articles.

Dave M said...

An interesting post. One thing to keep in mind, regarding articles about film-versus-digital resolution: They inevitably compare digital images to scanned film. Apples and oranges, really. Scanning of film is a great convenience, but it brings an entire extra technology into the loop.

The only conclusion such articles should reach is the comparison of their digital images to their scanned images. Unfortunately, most are written as if the answer provided is the entire (no pun intended) picture.

Noons said...

Mr Reichman also claimed in writing to me, that "more than a million people had downloaded" his 5dm2 "review".

Obviously, he is unable to discern the difference between a million downloads and a million people downloading.

Particularly when he stops anyone from saving the downloaded video: anyhone wanting to watch it twice counts as two "people", in his distorted logic.

I'm not at all surprised he doesn't have a clue what he's talking about when it comes to film...

Photo–Smith said...

Noons
I don't want to knock MR, just he sets himself up as an educator and he is very wrong in his assertion that film is binary.
This blog piece has taken me 18 months to research and write asking many imaging engineers for info and cross referencing each source with at least two others.
Why bother?
Well I have seem the MR article quoted as 'imaging science' by some people, it's dangerous that people like MR have such influence and trust that the urban myth of 'binary film' is born.
If the few people who do understand how film works keep quiet then the average Joe will have the 'clumps and chumps' as his only reference point, obviously 'The Theory of the Photographic Process' by Mees and James is not good bedtime reading (except for me in research)
Also the MR article is bullish and condescending, if it was just bad science with goodwill I could excuse it. But unfortunately he is putting down peoples valid arguments with his ignorance.
If you ever see anyone claim film is binary link them to this blog.
Mark

Peter Smythe said...

Thank you for the research and the blog post. I'm happy that I haven't left film.

Photo–Smith said...

you're welcome Peter.
I just had to put the record straight, so many were parroting the 'grain is binary' thing that i felt I needed to write an article debunking the LL pseudo science.
Glad you are enjoying film, and at the end of the day that's what is most important....
Mark

Gary said...

Thanks for the research. Nice to have theory to explain actual results. Good work

Photo–Smith said...

Thank you Gary
I may do more how and why articles on film in the future.
Mark

Dan said...

Film also has a scattering of light effect, more scattering with thicker films, hence t-grains of the same surface area size can potentially be a bit sharper due to potentially being able to make a thinner film.

Dean Taylor said...

a random observation from an ardent devotee--but newcomer to theory--of film...

Regarding the retina in the eye as an 'extension' of the brain--all part of the visual process chain: is it not the case that the neurons of our central nervous system are either firing or not, i.e., are binary?

Someone had referred to the human brain as "a waterlogged computer," i.e., a computer being binary-based, indeed. Please respond. I am a film lover playing devil's advocate, i.e., anticipating future arguments.

Dean Taylor

Photo–Smith said...

First of all I don't think of the eye as an 'extension of the brain' but rather a a peripheral device that converts light to chemical signals that the brain interprets.
Rather like digital camera sensors are analogue and then have to convert those to a digital signal that a CPU can process to construct an image.

A better way to think of things is digital printing which is defined as having variable sized ink blots on a defined grid or same sized ink blots on a variable frequency–anything else in analogue

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