Diabetic Retinopathy is the common cause of vision loss and blindness in patients with diabetes. Diabetic Retinopathy indicative lesions include dark lesions such as Microaneurysms and Hemorrhages; and bright lesions like Exudates. Automatic detection of distinct lesions in digital color fundus photographs is a critical step in development of diabetic retinopathy automatic detection systems. Dark lesions are the early signs of the disease. In addition, preprocessing phase is affectively required in any automatic dark lesion detection system for contrast enhancement around the dark lesions. Therefore, in this paper several different methods of preprocessing digital color fundus photographs, as the first critical step of dark lesions detection, are summarized.

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