PROBLEM TO BE SOLVED: To provide an image processing apparatus, an endoscope system, an image processing apparatus operation method, and an endoscope system operation method capable accurately acquiring the thickness and depth of a blood vessel even when the observation site or patient is changed.SOLUTION: A processor device 16 provided in an endoscope system 10 includes a special image processing unit 60. The special image processing unit comprises an image signal acquisition unit 70, a signal ratio calculation unit 72, a calculation program setting unit 74, and a blood vessel information calculation unit 76. The image signal acquisition unit acquires a B image signal, a G image signal, and an R image signal. The signal ratio calculation unit calculates a first signal ratio B/R and a second signal ratio G/R. The calculation program setting unit sets a calculation program for calculating the thickness and depth of a blood vessel on the basis of an image distribution in a signal ratio space represented by the first signal ratio B/R and second signal ratio G/R. The blood vessel information calculation unit calculates the thickness and depth of the blood vessel according to the set calculation program.SELECTED DRAWING: Figure 2
