1. A computing system for automated detection of active pixels in retinal images, the computing system comprising: one or more hardware computer processors; and one or more storage devices configured to store software instructions configured for execution by the one or more hardware computer processors in order to cause the computing system to: access a retinal image; generate a first median normalized image using the retinal image with a median computed over a first geometric shape of a first size; generate a second median normalized image using the retinal image with a median computed over the first geometric shape of a second size, the second size different from the first size; automatically generate a difference image by computing a difference between the first median normalized image and the second median normalized image; generate a binary image by computing a hysteresis threshold of the difference image using at least two thresholds to detect dark and bright structures in the difference image; and store the binary image in a memory of the computing system.