Retinal vessel enhancement based on directional field

Motivated by the goal of improving detection of micro-vessels with low contrast, a new technique based on directional field is presented for enhancing vessels in retinal images. This technique consists of two steps: the estimation of directional field and the enhancement. We will make enhancement along the vascular direction and normalize the brightness of image in a single step. After estimating the directional field, the mean and variance values in a local neighborhood were calculated pixel-by-pixel, accordingly normalize and enhance the local neighborhood. In order to eliminate the artificial boundary between two adjacent areas, an anisotropic Gaussian kernel was introduced to weight the enhancement. The proposed method can obviously increase the contrast of retinal vessels. 20 retinal images were tested in our experiments, and the results demonstrate an effective vessel enhancement algorithm.