An image processing system (100) includes an image generation unit (101) that has at least two observation modes and generates an image in one of the observation modes; a brightness detection unit (106) that detects brightness of the image generated in one observation mode by the image generation unit (101); and a control unit (107) that controls image generation in the other observation mode of the image generation unit (101) based on the brightness of the image detected by the brightness detection unit (106).