Representative images from the (A) Acceptable Quality (AQ), (B) Possibly Acceptable Quality (PAQ), and (C) Not Acceptable Quality (NAQ) classes. Note that as image quality degrades, visualization of retinal vasculature becomes more complex, if not impossible. Because NAQ images were not highly represented in our data set (5.6%), they were grouped with the PAQ images into a single category. The final representation of AQ and PAQ images in our data set was 50.8% and 49.2%, respectively.