Operating Manual

111
13.1 Factors influencing image quality
With regard to image quality, the term frequently used is “sensitivity”.
Sensitivity determines the extent to which a radiograph is able to clearly show (anoma-
ly) details of a certain size. Sensitivity in this sense must not be confused with the
sensitivity or “speed” of the film. (see section 7.5).
Discernibility of defects on a radiograph depends in general on:
• the quality of the radiation
• the properties of the film
• the film viewing conditions
Image quality is governed by contrast, sharpness and film graininess.
Image contrast is affected by :
• differences in thickness of the specimen
• the radio-opacity (radiation transparency) of the specimen and its defects
• the shape and (depth)location of the defects
• the quality (hardness) of the radiation
• the amount and effects of scattered radiation
• the effect of filters used
Film contrast depends on:
• the type of film
• the density level
Sharpness of an image is governed by:
• the (effective) size of the focal spot or radiation source
• the source-to-object distance
• the object-to-film distance
• the contact between film and intensifying screens
• the type of intensifying screens used
• the radiation energy used
110
13
Image quality
Digitised and enhanced image of a radiograph of the (American) Liberty Bell.
The image was used to monitor possible lengthening of the crack.