The process captures a plurality of images under a light source whose luminance varies over time, such as a fluorescent lamp, under such an imaging condition that a plurality of images that are different from one another in terms of light source conditions can be captured (S11). The process detects a temporal luminance variation from the plurality of captured images (S12), estimates a shadow area by using the temporal luminance variation (S13), and performs an image process such as a process of synthesizing a linearized image or an image segmentation based on optical characteristics (S14).