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Dentomaxillofacial Radiology, Vol 31, Issue 2 131-136, Copyright © 2002 by British Institute of Radiology

ARTICLES

Visual linearization of the display of digital radiographs

G. Li, K. Yoshiura, U. Welander, P. Sallstrom and W. D. McDavid
Department of Oral Radiology, Karolinska Institutet, Stockholm, Sweden. Gang.Li@ofa.ki.se

OBJECTIVES: To derive and test a method to linearize the visual response of the display of digital radiographs so that equal steps in gray levels will be perceived as equal steps in brightness. METHOD: A mathematical analysis was performed and expressions for visual linearization were derived. Twenty-four test images were computer generated to confirm that visual linearization may be achieved. Each image had three groups of square areas of different size placed in three rows. The left and right squares in each row were given different gray levels to simulate various contrast levels. The middle squares were initially given the same gray level value as one of the outer squares. The images were examined by ten observers who could change the gray levels of the middle squares so that the step in brightness between the middle square and the outer squares become subjectively equal. The test was performed three times employing two different monitors. RESULTS: The experimental test confirmed that visual linearization could be achieved. Linear regression analyses gave determination coefficients of 0.9926 amd 0.9942 for monitors with gamma-values of 1.93 and 2.50. respectively. The mean data from the ten observers perfectly fitted those theoretically calculated. CONCLUSION: Visual linearization of gray levels can be achieved but further clinical research is needed to determine if this improves diagnosis.


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