Multi-Scale Morphological Image Enhancement of Chest Radiographs by a Hybrid Scheme

Chest radiography is a common diagnostic imaging test, which contains an enormous amount of information about a patient. However,its interpretation is highly challenging. The accuracy of the diagnostic process is greatly influenced by image processing algorithms;hence enhancement of the images is indispensable in order to improve visibility of the details. This paper aims at improving radiographparameters such as contrast, sharpness, noise level, and brightness to enhance chest radiographs, making use of a triangulation method.Here, contrast limited adaptive histogram equalization technique and noise suppression are simultaneously performed in waveletdomain in a new scheme, followed by morphological top‑hat and bottom‑hat filtering. A unique implementation of morphological filtersallows for adjustment of the image brightness and significant enhancement of the contrast. The proposed method is tested on chestradiographs from Japanese Society of Radiological Technology database. The results are compared with conventional enhancementtechniques such as histogram equalization, contrast limited adaptive histogram equalization, Retinex, and some recently proposedmethods to show its strengths. The experimental results reveal that the proposed method can remarkably improve the image contrastwhile keeping the sensitive chest tissue information so that radiologists might have a more precise interpretation.