New fractional derivative hybrid methods for image enhancement

Abstract

Medical images are susceptible to noise, distortions and have low resolutions. These variations may be due to non-uniform illumination, presence of artifacts, acquisition angle, poor focus etc. It is important to process the medical images to improve their visual appearance, quality and identify the region of interest thereby assisting the medical specialist for easier interpretation of diseases. Image enhancement procedures are mathematical techniques used to make the given image more precise, so that the selected features of the image can be easily identified by the human eye or to be detected by automated diagnosis systems. Application of fractional differentials to medical image processing has been gaining importance in recent years, as they preserve the low-frequency feature information of original image which is not possible by the integral differential. The primary objective of this research is to focus on the design of new fractional differential filters for various image processing applications, especially in the field of medical imaging. The images chosen for experimentation are from standard image databases namely High-Resolution Fundus Image database, DIARETDB0 and DIARETDB1databases. The performance of the proposed methods are evaluated using standard metrics namely Information entropy, mean, Peak-Signal to Noise Ratio (PSNR), Mean square error (MSE), Structure Similarity Index (SSIM) both quantitatively and qualitatively. The thesis starts with the introductory concepts of fractional calculus and image processing, with relevant literature review. Second chapter analyzes the effectiveness and use of Grunwald-Letnikov (G-L) fractional differential operator for retinal image enhancement. In the proposed method,first a G-L based fractional differential mask is defined, in vertical and horizontal directions for the given fractional order. Then, the retinal images are linearly convolved with the defined mask. In case of noisy images, the size and fractional order of the mask are changed to improve the qua