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Author
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Topic: Film Grain Question
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Peter Berrett
Jedi Master Film Handler
Posts: 602
From: Victoria, Australia
Registered: Nov 2000
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posted 07-29-2006 03:49 AM
Hi all
Can someone help me out please regarding my film education.
Whilst looking around at these and other forums I frequently see mention of "film grain" and how it can be seen in super 8 and other forms of film.
I looked at Wikipedia and found the following definition
http://en.wikipedia.org/wiki/Film_grain
quote:
Film grain or granularity is the random optical texture of processed photographic film that derives from the fact that film derives tone from a collection of small grains of metallic silver developed from grains of silver halide that have received enough photons.
Granularity is a numerical quantification of film grain, equal to the root-mean-square (rms) fluctuations in optical density, measured with a microdensitometer with a 0.048 mm (48-micrometre) diameter circular aperture, on a film area that has been exposed and normally developed to a mean density of 1.0 (that is, it transmits 10% of light incident on it). Granularity is often quoted "times 1000", so that a film with granularity 10 means an rms density fluctuation of 0.010 in the standard aperture area.
When the grains are small, the standard aperture area measures an average of many grains, so the granularity is small. When the grains are large, fewer are averaged in the standard area, so there is a larger random fluctuation, and a higher granularity number.
The standard 0.048 mm aperture size derives from a drill bit that some guy at Kodak had lying around.
After reading this, I am still totally confused by what film grain actually looks like. And surprised at how the standard 0.048 mm aperture size was derived!
Could someone please provide a laymans explanation for what film grain is and perhaps some photos to illustrate when film grain is noticeable and when it isn't?
Thanking you
Regards Peter
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Charles Greenlee
Jedi Master Film Handler
Posts: 801
From: Savannah, Ga, U.S.
Registered: Jun 2006
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posted 07-30-2006 03:24 AM
Or take some oiled paper and look at it through the light. Film isn't perfectly smooth. Under high magnification, you can see it's surface texture. This means on a microscopic level, film is thicker and thinner, much like the raised grain on paper. The thicker spots would disrupt the light slightly more, and thinner spots slightly less. This is so minute that you can't perceive it unless under extreme magnification. If you want to see real filmg grain, just look at some old world war 1 and 2 films, or earlier cinema films. You will see how grainy they can be. Or, watch Fantasia. In the pastoral peice, where the centaurs are rolling out the red carpet for Baccus (the fat drunk guy), the picture was edited to remove a character that was an "embarrasing racial stereotype" by zooming the image in, and making the offensive character out of frame. On a normal TV, you can see the grain. Maybe watch it on a larger TV, for better effect.
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John Pytlak
Film God
Posts: 9987
From: Rochester, NY 14650-1922
Registered: Jan 2000
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posted 07-31-2006 12:15 PM
Kodak has a good tutorial about Graininess on its website:
http://www.kodak.com/US/en/motion/support/h1/exposureP.shtml#graininess
quote:
Understanding Graininess and Granularity
The terms graininess and granularity are often confused or even used as synonyms in discussions of silver or dye-deposit distributions in photographic emulsions. The two terms refer to two distinctly different ways of evaluating the image structure. When a photographic image is viewed with sufficient magnification, the viewer experiences the visual sensation of graininess, a subjective impression of a random dot-like pattern in an image. This dot-like pattern in the image structure can also be measured objectively with a microdensitometer. This objective evaluation measures film granularity.
Motion picture films consist of silverhalide crystals dispersed in gelatin (the emulsion) which is coated in thin layers on a support (the film base). The exposure and development of these crystals form the photographic image, which is, at some stage, made up of discrete particles of silver. In color processes, where the silver is removed after development, the dyes form dye clouds centered on the sites of the developed silver crystals. The crystals vary in size, shape, and sensitivity, and generally are randomly distributed within the emulsion. Within an area of uniform exposure, some of the crystals will be made developable by exposure; others will not.
The location of these crystals is also random. Development usually does not change the position of a grain, so the image of a uniformly exposed area is the result of a random distribution either of opaque silver particles (black-and-white film) or dye clouds (color film), separated by transparent gelatin...
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