Semi-automated analysis of chlorophyll fluorescence images of leaf discs taken with a 'Walz' 'IMAGING-PAM' fluorometer. Provides an R interface to the 'fvfmPy' 'Python' package, which detects leaf discs, assigns them to a grid of rows and columns, and computes the maximum quantum efficiency of photosystem II, Fv/Fm = (Fm - Fo) / Fm, for each disc. The interactive 'fvfmPy' window is launched from R and the results are returned to R as a data frame.