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Topic: The "Physics" of Motion Picture Projection.

Martin Brooks
Jedi Master Film Handler

Posts: 900
From: Forest Hills, NY, USA
Registered: May 2002

posted 11-13-2004 10:41 AM

quote: Daniel Alt
I have a M.S. in astrophysics from Yale. (No kidding) It has not helped me one little bit in keeping the fershluggener projectors working. Which is not to say physics isn't cool. Just that the theory isn't always relevant to the practice

That's because you're trying to get the projectors working on Earth. But your theoretical techniques would work perfectly in outer space (except for the audio, I guess.)

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David Graham Rose
Expert Film Handler

Posts: 187
From: Cambridge, UK
Registered: Sep 2002

posted 11-13-2004 12:13 PM

Greetings All

I have a chair here in Cambridge in Cinema Technology, and still don't understand how everything works! Although I must admit, my first degree is in Physics, my second in Chemistry, my third in Philosophy and my Ph.D allthose years ago in Cinema Technology. My chair was actually awarded back in 1969 when I discovered a sound proofing method for Odeon and ABC Cinemas who wished to twin/triple single auditoria using minimal materials (at the time plasterboard and woading)

With regards to all academics on this site

Good Evening

David

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Dominic Case
Expert Film Handler

Posts: 131
From: Sydney NSW Australia
Registered: Aug 2003

posted 11-15-2004 12:00 AM

quote:
Each silver halide grain in a film is either exposed or unexposed (1 or 0 state). So at the molecular level, film IS digital,

I'm going to argue with John on this one.

What you are actually saying, John, is that film is binary. Not necessarily digital.

As I understand it, digital and analogue are two diferent ways of representing a variable). In an analogue representation, the quantity is represented by another quantity: in the case of digital, the quantity is represented by a number. (in the case of a film image, it's the brightness of a part of the image, which can either be represented by something that is greater or lesser as the brightness varies (analogue) or by a number (digital) that isn't, ITSELF, greater or lesser (the actual number 9 is no bigger than the number 6, nor is 1001 greater than 0110 - they only denote something else that's bigger).

So a conventional clock is analogue, because the amount of time elapsed is represented by the amount of angle the hands have turned through: whereas a digital clock represents the time elapsed by displaying a number (on the display, it's digital but not binary!). You need to understand the code (numbers 1,2,3,etc) to know how much time has passed.

A SR soundtrack is analogue because the level of the sound is represented by the width of the waveform in the track itself. An SRD track represents the level by a decodable number (in this case it is a binary number).

In a film image, the darkness of the original subject is not represented by a number that needs to be decoded, but by the darkness of the dyes in the film (or, if you like, the size and number of grains or dye clouds). To be digital, the image has to be represented by an encoded representation of the darkness: that is by an actual number, not a quantity of something.

That's my view of it, anyway.

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Steve Kraus
Film God

Posts: 4094
From: Chicago, IL, USA
Registered: May 2000

posted 11-15-2004 12:05 AM

I don't know how you can be binary but not digital. I see the point you are making but I don't think digital requires there to be a coding system where some...well in this case molecules...are given higher weight than others (like powers of two steps in base two digits). A number can be represented simply by having that actual number of something. Thus, digital.

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Dominic Case
Expert Film Handler

Posts: 131
From: Sydney NSW Australia
Registered: Aug 2003

posted 11-15-2004 05:18 AM

quote: Steve Kraus
I don't think digital requires there to be a coding system

But that's exactly what it does require. Digital systems are representations that consist of pure numbers. Analogue systems are representations or scales that consist of quantities.

If a system uses pure numbers, you need a code to show the number. So, white is 1024, light grey is 456, dark is 37 for example. Or white is 1000000000, dark is 00000100101 etc. Both digital. if you don't know the code, you have no idea.

If it uses quantities, we can have white is ############, grey is #####, black is #. If I could do font sizes, or shades of grey, or thicker strokes, those could also be a scale representing brightness.

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John Pytlak
Film God

Posts: 9987
From: Rochester, NY 14650-1922
Registered: Jan 2000

posted 11-15-2004 05:50 AM

Simplisticly, if each silver halide grain is considered a "pixel", once a latent image is formed by sufficient photons, after development it either forms silver (dye) or it doesn't. I agree calling it "digital" may be a stretch, but there is an analogy. Of course, for some, "digital" is a bad word. [Wink]

So "binary" is fine too.

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Steve Kraus
Film God

Posts: 4094
From: Chicago, IL, USA
Registered: May 2000

posted 11-15-2004 02:30 PM

Since we're already way off topic:

CD's and DVD's are analog media. No, really.

Discuss.

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Mark Gulbrandsen
Resident Trollmaster

Posts: 16657
From: Music City
Registered: Jun 99

posted 11-15-2004 02:41 PM

Yes, because the signal you get back off the disk is an FM signal from which the data must be extracted. All digital formats work thihs way and this s the step at which much digital jitter is introduced. I think you'll be seeing less of this sort of system in the future though. The Blue Ray(no relation to Ray Charles) is straight digital read back like a hard drive. Some Blue Ray recorders are already available overseas and they all are using hard drives so far as the exact specs for the CD part are nailed down. Sony has also sucessfully used paper CD's in the laboratory.......

Mark

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Ron Yost
Master Film Handler

Posts: 344
From: Paso Robles, CA
Registered: Aug 2003

posted 11-15-2004 05:00 PM

Speaking of optical disk developments, I read this this morning:

"Pioneer develops a 500GB optical disc

   Japanese consumer electronics company Pioneer has, according to Nikkei Business Daily, managed to develop an optical disc that holds 500GB of data each side, making it 20 times bigger than the basic single-layer versions of "next generation" optical discs that are based on blue laser (including Blu-Ray and HD-DVD).

   The new technology is apparently based on ultraviolet laser, which has shorter wavelength than the blue laser does, thus making it possible to store data much more efficiently on the disc."

Neat, huh? [Big Grin]

Ron Yost

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Dominic Case
Expert Film Handler

Posts: 131
From: Sydney NSW Australia
Registered: Aug 2003

posted 11-15-2004 08:39 PM

quote:
after development it either forms silver (dye) or it doesn't. I agree calling it "digital" may be a stretch,

John - if you've just convinced anyone that film is digital, you've also convinced them that it has a bit depth of ONE. Which, to people who are turned on by anything digital, is a big turn-off (since arguments usually rage over 8-bit, 10-bit or up to 16-bit!)

I think you should quit while you aren't too far behind on this one;-)

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John Pytlak
Film God

Posts: 9987
From: Rochester, NY 14650-1922
Registered: Jan 2000

posted 11-16-2004 07:41 AM

Fortunately, the tremendous tonal range of film exceeds that of any of the current digital camera or projection systems. Pretty good for a century-old "binary" imaging system based on chemistry. [Cool]

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John Hawkinson
Film God

Posts: 2273
From: Cambridge, MA, USA
Registered: Feb 2002

posted 11-16-2004 09:34 AM

Isn't it true that film does have a bit depth of one? It's like
a very fine halftone screen, no?

--jhawk

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Daniel Alt
Expert Film Handler

Posts: 111
From: Lakewood, OH, USA
Registered: Mar 2004

posted 11-16-2004 09:38 AM

My brain hurts.

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Steve Kraus
Film God

Posts: 4094
From: Chicago, IL, USA
Registered: May 2000

posted 11-16-2004 10:51 AM

Not exactly because the grains (or dye clouds) are not only randomly laid out (which you could do with a randomized halftone screen) but also may be in front of or behind one another which I presume would mean there are density differences going across the image whereas a halftone as you go across it it's either (assuming B&W) white or black with no in betweens.

Mark: Wouldn't it be cool to use that FM carrier to carry high quality wideband analog audio signals for a truly analog CD?

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John Pytlak
Film God

Posts: 9987
From: Rochester, NY 14650-1922
Registered: Jan 2000

posted 11-16-2004 11:27 AM

quote: Steve Kraus
Not exactly because the grains (or dye clouds) are not only randomly laid out (which you could do with a randomized halftone screen) but also may be in front of or behind one another which I presume would mean there are density differences going across the image whereas a halftone as you go across it it's either (assuming B&W) white or black with no in betweens.

Right on!

http://www.kodak.com/US/en/motion/support/h1/exposureP.shtml#graininess

quote:
Figure 15
(a) A 2.5X enlargement of a negative shows no apparent graininess. (b) At 20X, some graininess shows. (c) When a segment of the negative is inspected at 60X, the individual silver grains start to become distinguishable. (d) With 400X magnification, the discrete grains are easily seen. Note that surface grains are in focus while grains deeper in the emulsion are out of focus. The apparent "clumping" of silver grains is actually caused by the overlap of grains at different depths when viewed in two-dimensional projection. (e) The makeup of individual grains takes different forms. This filamentary silver enlarged by an electron microscope, appears as a single opaque grain at low magnification.

quote:
Figure 19
The above illustrations are 1200X photomicrographs of a special cyan color film layer with incorporated coupler made very thin to permit showing the structure. The upper left picture is the film after color development and shows the metallic silver grains surrounded by dye clouds. The upper right picture shows another area of the same film after bleaching and fixing with the grain removed. The lower two pictures show the same type of film developed with a color developer containing a completing coupler which reduces the size of the dye clouds; hence, reducing the graininess.

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