Automatic processing of digital images of falling raindrops is complicated by a less than ideal grayscale image histogram. These histograms do not display a bimodal shape and lack an easily defined minimum, making it difficult to choose a threshold for creating a binary image. To help identify peaks in these histograms, and simplify threshold selection, a histogram modification technique originally developed by Peleg is used. This method was modified slightly and then applied to raindrop image processing. Its performance is quantified.
John R. Saylor,
"Application of a histogram modification algorithm to the processing of raindrop images," Optical Engineering 47(3), 037011 (1 March 2008). https://doi.org/10.1117/1.2899101