Patent ID: 6897865

Claim:
A three-dimensional image processing apparatus for creating a shadow image on an outer surface of a 3D model using a shadow model formed by a plurality of polygons, comprising: shadow model storage means for storing at least coordinates of vertices of the shadow model; polygon sorting means for sorting the polygons forming the shadow model into front-facing polygons facing in directions toward a viewpoint of a virtual camera and back-facing polygons facing in directions opposite from the viewpoint of the virtual camera; model image creating means for creating an image by applying rendering to a polygon model except the shadow model; model image storage means for storing the image created by the model image creating means while relating frame color data, which are color data of pixels, to Z-values, which are distances to the polygons corresponding to the respective pixels, from the viewpoint of the virtual camera in a simulated three-dimensional space; and shadow creating means for creating the shadow image in pixels which are pixels corresponding to the front-facing polygons by changing the frame color data of the pixels stored in the model image storage means for shadow creating pixels which are: a first set of pixels corresponding to the front-facing polygons of the shadow model whose distances from the viewpoint of the virtual camera in the simulated three-dimensional space are smaller than the Z-values of the corresponding pixels, and excluding a second set of pixels corresponding to the back-facing polygons of the shadow model whose distances from the viewpoint of the virtual camera in the simulated three-dimensional space are smaller than the Z-values of the corresponding pixels; said shadow creating means including means for performing an operation on said frame color data of first set of pixels which is either one of addition and subtraction of a predetermined value thereby creating modified frame color data, and for performing an additional operation on said modified frame color data of said second set of pixels which is an opposite operation of said one of addition and subtraction using said predetermined value, whereby said operation alters initial frame color data values of said first set of pixels as indicative of being the shadow creating pixels, and said second set of pixels is effectively excluded as said shadow creating pixels by a cancellation of said first operation by performance of said additional operation equal and opposite in value thereto.