Adaptive Contrast Enhancement of Digital X-Ray Images Using N-CLAHE

Abstract

Digital chest radiography offers many advantages over film- based radiography, such as immediate image display, no film processing and room storage, wider dynamic range and lower radiation dose. In general, a raw X-ray image acquired di- rectly from a digital flat detector contains poor quality of image, which may not be suitable for diagnosis and treatment planning. Therefore, a pre-processing technique is usually required to enhance image quality. This paper presents an improved image enhancement on digital chest radiography using the so-called N-CLAHE method, which is based on global and local enhancement. The proposed technique con- sists of two main steps. Firstly, intensity correction of the raw image is encountered by the log-normalization function which adjusts the intensity contrast of the image dynamically. Secondly, the Contrast Limited Adaptive Histogram Equal- ization (CLAHE) method is used for enhancing small details, textures and local contrast of the images. The proposed ap- proach was tested using a radiographic survey phantom and a radiographic chest phantom and compared with conven- tional enhancement methods, such as histogram equalization, unsharp masking, CLAHE. The results show that the pro- posed N-CLAHE method yields great improvement on the pre-processing correction for digital chest radiography.