Midterm | RADIOGRAPHIC PHOTOGRAPHY: Sensitometry & Characteristic Curve Flashcards
Sensitometry as a photographic science has been credited to two Americans
Ferdinand Hurter and
Vero Charles Driffield
Ferdinand Hurter and Vero Charles Driffield first proposed a form of evaluation of the performance of photographic material in the year
1876
The main interest in radiography is how the film
will react to (apparently) _____________, although
usually the real interest is how the film will react
to the light produced by the ___________________.
x-radiation; intensifying screen
The study of the relationship between intensity of exposure of the film and the blackness after processing.
SENSITOMETRY
The measurement of the sensitivity of the film towards radiation.
SENSITOMETRY
is normally the blackness of the film.
Photographic density
is the graph which shows the relationship between the log of exposure and the density produced in the film.
Characteristic curve
It increases with exposure.
Photographic density
Density of an image is approximately proportional to the amount of _________ present in emulsion.
silver
conveniently express large differences in numbers on a small scale.
Logarithms
If the films are _______________, the resulting density is equal to the sum of densities.
superimposed
The human eye seems to respond to different tones in a way which is approximately logarithmic. A density of two looks twice as dark as a _________________.
density of one
enable a much wider range of values to be appreciated with understanding
Logarithmic scales
equal increments have the __________ ratio.
same
Two pieces of apparatus are needed to construct a characteristic curve:
Optical step wedge
Densitometer
Optical step wedge is AKA
sensitometer
measures OD (optical density)
Densitometer
as the film or the film-screen is subjected to greater and greater exposure, a point is reached when further increase in exposure can’t result any increase in density. thus, the film achieves a maximum level of density known as
Dmax (maximum density/over-exposed region)
in this region, subject contrast do not produce image contrast and no subject detail can be visualized
over-exposed region (dmax)
it has small density (around 0.5), even at the starting point although there has been no exposure or only a very small exposure
Dmin (minimum density/under-exposed region)
this is the result of base density plus fog
Dmin
the useful range of optical density
0.25 to 2.5
most radiographs have an optical density of
0.5 to 1.25
base plus fog optical density is
0.1 to 0.3
