Film Optical Density

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# Film Optical Density - PowerPoint PPT Presentation

Film Optical Density. Film screen. Radiographic Density Overall blackening of the radiographic image as a result of the energy deposited inthe film emulsion. Film screen. Radiographic Contrast / Grayscale The difference between two adjacent radiographic densities in the image.

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### Film Optical Density

Film screen
• Overall blackening of the radiographic
• image as a result of the energy deposited
• inthe film emulsion.
Film screen

Radiographic Contrast / Grayscale

• The difference between two adjacent
• radiographic densities in the image.
• The overall number of density shades
• present in the image.
.25 TO -2.5

The straight line of the H&D curve

Density
To see changes in optical density
• In order to see changes in optical density on a radiograph you must increase you mAs by at least 20 – 30%
• To double the density on a radiograph you must double your density
Optical Density
• A numerical value indicating the degree of blackening on the film.

(average OD seen on a radiograph = 1.2 Range is 0.21 – 2.5)

# of photons coming through film = OD # # of photons hitting film

OD= 1 2 3

1 = 0 100 1 = 1 1011 = 2 1021 = 3 103

1 10 100 1000

• Density log = incident light intensity
• transmitted light intensity
• OD # % of light photons transmitted
• 0 100 %
• 1 10 %
• 2 1 %
• 3 0.1 %
• If the quantity of black metallic silver on a radiograph
• is such that it allow
• 1 % of the light to pass through – what is the OD?
• 10%
• 100%
• zero
• 0.1
• 1.0
• 2.5
If the quantity of black on the film allows 1% of light to pass through, that film has a density of
• 0.01
• 0.1
• 1.0
• 2.0
If the quantity of black on the film allows 10% of light to pass through, that film has a density of
• 0.01
• 0.1
• 1.0
• 2.0
The relationship between the intensity of light striking a film and the intensity of

light transmitted through the film is an expression of which of the following?