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Definition: bilinear interpolation

A texture mapping technique that produces a reasonably realistic image, also known as "bilinear filtering" and "bilinear texture mapping." An algorithm is used to map a screen pixel location to a corresponding point on the texture map. A weighted average of the attributes (color, alpha, etc.) of the four surrounding texels is computed and applied to the screen pixel. This process is repeated for each pixel forming the object being textured.

The term bilinear refers to the performing of interpolations in two dimensions (horizontal and vertical). The top and bottom pairs of each texel quadrant are averaged (horizontal) and then their results are averaged (vertical). This method is often used in conjunction with MIP mapping. See texture map, MIP mapping, point sampling and trilinear interpolation.

Bilinear Mapping
Each screen pixel of the object is mapped onto the corresponding texel in the texture map. The red dots are an example of one pixel. The attributes of the weighted average of the four nearest texels is applied to the screen pixel. Two horizontal interpolations are made (texels 1-2 and 3-4), and then the results are averaged together for the vertical interpolation. (Redrawn from illustration courtesy of Intergraph Computer Systems.)