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Contrast enhancement of portal images by selective histogram equalization
Author(s) -
Crooks I.,
Fallone B. G.
Publication year - 1993
Publication title -
medical physics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.473
H-Index - 180
eISSN - 2473-4209
pISSN - 0094-2405
DOI - 10.1118/1.597085
Subject(s) - adaptive histogram equalization , histogram equalization , histogram matching , histogram , sobel operator , computer science , artificial intelligence , computer vision , equalization (audio) , contrast (vision) , image processing , edge detection , image (mathematics) , algorithm , decoding methods
Because of the high energy of the treatment beam, contrast of portal verification films is very poor. A simple contrast enhancement technique is described which we have labeled selective histogram equalization (SHE), to improve visualization of double‐exposure portal images and this facilitate the beam verification process. The technique performs separate histogram equalization on the treatment‐ and open‐field sections of double‐exposure portal images. Delineation of the treatment field edge and separation into two regions is performed automatically for off‐line portal radiographs by a strategic combination of Sobel filtration and morphological processes. Analyses of images processed by SHE and other adaptive histogram equalization techniques indicate that SHE produces improved contrast enhancement with minimal addition of noise or artifacts, thus simplifying the beam verification procedure. The simple implementation of an automatic SHE process with on‐line portal systems is also discussed.