Blurred-mask density compression for improved reproduction of radiographs

A film-based, blurred-mask subtraction technique can be used to reduce the apparent density range of medical radiographs so that a wider range of actual densities can be captured with video digitizers or reproduced on photographic paper for publication. The density compression and the edge enhancement resulting from this process is examined. A good balance between compression and enhancement for small structures was obtained with a 6-mm gap between the subtraction film and the original when producing the mask. As an example, a photographic print of a compressed chest film showed significant condensation of image information within the restricted reflection density scale of the print paper; detail was well demonstrated in the mediastinal, retrocardiac, and subdiaphragmatic regions that was not shown in the noncompressed print.