Photosensitive materials (x-ray films) are used to record the invisible x-ray image. It is required to reproduce all the characteristics of the invisible image in visible form .The films ability to do so depends on its sensitometric properties.
Measures films sensitivity to light; shows the range of densities on an image. Sensitometry:-
The scientific study of the response of photosensitive material to different levels of exposure.
How is it done?
Producing a sensitometric strip and plotting a characteristic curve.
sensitometer (optical step wedge) and densitometer are used to measure film's response to light
Response of exposure & How is it manifested
The response is the change that takes place, after exposure to electromagnetic radiation (light or x-rays), in the photosensitive emulsion on the film
The response of the film to exposures is manifested as a degree of blackening produced after chemical processing Witch is quantified by:- •
Optical Density (OD(
The optical density describes how much a certain area of the film is opaque to light incident upon it . In Radiography the degree of film blackening is quantitatively indicated by the term ‘Optical Density witch is expressed as a number that is actually a logarithm, using the common base 10. Photographic density is defined by
D = log 10 Io / I
D = density.
IO= light incident on a film
. I = light transmitted by the film
is the quantitative measurement of optical density in light-sensitive materials, such as photographic paper or photographic film, due to exposure to light. Optical density is a result of the darkness of a developed picture and can be expressed absolutely as the number of dark spots (i.e., silver grains in developed films) in a given area, but usually it is a relative value, expressed in a scale. According to the principle of
operation of the densitometer, one
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