1. A method of classifying, with a computer processor, at least one feature of each of a plurality of cells from a low contrast, digital image representing the plurality of cells, the method comprising: generating a contrast-enhanced image by filtering the low contrast, digital image with a high-pass filter; smoothing the contrast-enhanced image with a first low-pass filter; generating a background image from the low contrast, digital image; subtracting the background image from the smoothed, contrast-enhanced image to generate an analysis image; and identifying the at least one feature in the analysis image, the at least one feature selected from the group consisting of bacterial infection, cellular size, cellular shape, cellular boundary, and cellular edge.