“…Variations of pixel intensities were detected via a background subtraction technique (Zivkovic, 2004; Zivkovic & van der Heijden, 2006), making use of a predefined set of initial (reference) images of the membrane surface to arrive at a background probability density function (PDF) of the intensities for each pixel. During the RO pilot operation, membrane images from the RO membrane monitor were analyzed, and pixel intensities were compared with the background PDF pixel intensities (Boufares, Aloui, & Cherif, 2016). Corrections due to possible variability in illumination were made, relative to the reference image, via the image channel histogram matching technique (Bevilacqua & Azzari, 2007; Shapira, Avidan, & Hel‐Or, 2013), also using a lookup (indexing) algorithm (Bevilacqua & Azzari, 2007; Shapira et al, 2013).…”