Increasing contrast when viewing radiographic images.

Illuminating a developed photographic film with parallel or nearly parallel light provides increased contrast compared with the contrast obtained with diffuse incident light. The viewer of radiographic images can obtain increased contrast simply by increasing the distance between the view box and the radiograph, since this results in more parallel incident light. The authors found a contrast increase of more than 40% when x-ray film was positioned 4 m from a view box. Tilting the film relative to the surface plane of the view box gave additional contrast increase at the cost of somewhat distorted geometry. The photographic effects involved deserve a more thorough discussion in textbooks of radiologic and radiographic physics.