1. A photon counting detecting system operating method comprising: (a) electronically storing for each of a plurality of pixels of a photon counting detector a plot of pulse counts output by the pixel over a range of corresponding photon flux densities; (b) electronically storing a plot, determined from the plots of step (a), of an intermediate number of pulse counts output by all of the pixels over the range of photon flux densities; (c) electronically acquiring for one pixel of the photon counting detector a number of pulse counts output by the pixel in response to photons striking the pixel during a sample interval; (d) electronically determining a photon flux density corresponding to the pulse counts output by the pixel in step (c) from the corresponding plot of step (a); (e) electronically correcting the value of the photon flux density determined in step (d) as a function of parameters of a curve fitting function that approximates the plot of step (b) and as a function of other parameters of the curve fitting function that separately approximates the plot of step (a) for the pixel of step (c); and (f) electronically determining from the corrected photon flux density value a corrected number of pulse counts for the pixel.