There are provided an endoscope system processor device, an endoscope system, an operation method for an endoscope system processor device, and an operation method for an endoscope system for calculating objective diagnostic information, which is easier to understand than the oxygen saturation, based on the oxygen saturation. The endoscope system processor device includes: a receiving unit that receives an image signal obtained by imaging an observation target with an endoscope; an oxygen saturation calculation unit that calculates an oxygen saturation based on the image signal; a pixel specification unit that specifies an out-of-range pixel in which the oxygen saturation deviates from a specific range set in advance; and a diagnostic information calculation unit that calculates diagnostic information as a numerical value using information of the out-of-range pixel.