Color retinal image enhancement by Rayleigh contrast-limited adaptive histogram equalization

Retinal fundus image is important for ophthalmologist to identify and detect many vision-related diseases, such as diabetes and hypertension. From an acquisition process, retinal images often have low gray level contrast and low dynamic range. This paper proposes a method using improved nonlinear hue-saturation-intensity color model(iNHSI) to preserve color information of the retinal images. The intensity component is enhanced by Rayleigh transformation in contrast-limited adaptive histogram equalization (Rayleigh CLAHE) algorithm. This algorithm help to increase the contrast and improve the overall appearance. The proposed algorithm was tested by using standard public database for benchmarking diabetic retinopathy detection from digital image. The proposed method can preserve the original hue component unchanged; because, the hue information of the input images is important to ophthalmologist in diagnosis process.