There is known an image generation system which can generate an image as viewed from a given viewpoint within a virtual three-dimensional or object space. Such a system is very popular since one can experience a so-called virtual reality through it. Now considering an image generation system for playing a racing game, a player can enjoy a three-dimensional game by controlling a motorcar (or object) for causing it to run in an object space and for causing the player's motorcar to compete against other motorcar(s) which are controlled by other players and/or computer.
In order to improve the virtual reality for a player in such an image generation system, it was an important technical problem to produce more realistic images. It is thus desired that even the image of an object in the background can more realistically be represented.
One of various known techniques for more realistically representing the image of an object in the background is a technique known as “depth cueing”. This depth cueing is configured to blur an object in the background by bringing the color of the object close to a target color (e.g., gray or white) depending on the distance between the object and a viewpoint.
However, when the target color used in the depth cueing is a gray color and the most distant background (background) is blue sky, the target color (gray) of the depth cueing will be different from the color (blue) of the most distant background. Therefore, the object appearing or disappearing near a clipping position will be seen even though the depth cueing brings the color of the distant object close to the target color. This will raise a problem in that the screen flickers due to the appearance and disappearance of the distant object at the clipping position.
To overcome such a problem, the following technique may be considered. Namely, a most distant background picture having the same or substantially the same color as the target color in the depth cueing may be provided. Such a most distant background picture will always be used irrespectively of the situation of game.
However, the fixed picture will monotonize the game scene. This will raise another problem in that the feel of the player for the virtual reality cannot be improved.