Effect of the threshold correction factor (TCF) on plaque detection in GHOST(3)- CCR5/CXCR4 cells for (a) HIV-1-infected and (b) uninfected cases. The TCF is located in the IdentifyPrimaryObjects module in the APR image analysis pipeline and affects the stringency or leniency of foreground/background thresholding. Column 1: Fluorescence microscopy images with HIV-1-infected cells expressing GFP (green) and nuclei stained with DAPI (blue). Columns 2 – 4: GFP-expressing syncytia detected for various values of the TCF, as noted in the column title. The colors labeling the syncytia are used for illustrative purposes and chosen arbitrarily.