To provide a game system and an information storage medium capable of forming a realistic image reflecting each light reflecting characteristic in the case of a given material being mixed with other material with a different light reflecting characteristic.

This game system forms images. A by-material light source processing part 132 and a by-material image plotting part 142 perform processing for generating plotting information in the pixel units of first to n-th images with first to n-th light source processing applied to a given primitive. A translucent plotting part 144 performs translucent plotting processing on the basis of the plotting information of the corresponding pixels of the first to n-th images. It is preferable that the first to n-th light source processing is light source processing corresponding to the light reflecting characteristics of the first to n-th materials. At least one image out of the first to n-th images may be an image formed by mapping a texture image corresponding to at least one material out of the first to n-th materials, on the given primitive with reflecting the luminance value of the corresponding light source processing.