Brightness Preserving Enhancement for Dental Digital X-ray Images Based on Entropy and Histogram Analysis

Enhancing dental x-ray images could be of great importance in helping the dentist for proper diagnosis. Image enhancement by histogram equalization, log transform, gamma correction for multiple gamma values, and contrast limited adaptive histogram equalization (CLAHE) were considered. Matlab 2015 was used to perform all the enhancement tasks. Dental x-rays images (periapical images) were obtained from a dataset published on the internet. It is preferred to preserve the x-ray images brightness so that the dentist can still use it for diagnosis with gray levels as close as possible to the originals. The CLAHE image enhancement, with eight rows and eight columns with clip limit of 0.01, proves to be the best. Two metrics were used for deciding the best enhancement, the entropy, looking for the highest obtained entropy, and the flatness of the resulted histogram. Eye inspection agrees with the metrics used.