Role of Image Contrast Enhancement Technique for Ophthalmologist as Diagnostic Tool for Diabetic Retinopathy

Analysing the retinal colour fundus is a critical step before any proposed computerised automatic detection of eye disease, especially Diabetic Retinopathy (DR). The retinal colour fundus image contains noise and varying low contrast of the blood vessel against its surrounding background. It makes it difficult to analyse the proper order of the vessel's network for detecting DR disease progress. The invasive method Fluorescein Angiogram Fundus (FFA) resolves these problems, but is not recommended due to an agent injection that leads to other side effects on the patient's health, in the worst cases death. In this research work, we propose a new image enhancement method based on a morphological operation along with proposed threshold based stationary wavelet transform for retinal fundus images and Contrast Limited Adaptive Histogram Equalisation (CLAHE) for the vessel enhancement. The experimental results show much better results than the FFA images. Experimental results are based on three databases of retinal colour fundus images and FFA images. The performance is evaluated by measuring the contrast enhancement factor of retinal colour fundus images and FFA images. The results show that the proposed image enhancement method is superior to other non-invasive image enhancement methods as well as invasive methods, thus it will play an important role in imaging retinal blood vessels. An average contrast improvement factor of 5.63 on colour fundus images is achieved as well as 5.57 on FFA images. This significant contribution to the enhancement of the contrast of retinal colour fundus will be one primary tool to reduce the use of an invasive method.