Rasterization is done to transform the data represented by the object database into a pixel-based image. Texture mapping, color computation, shading and anti-aliasing are done at this stage.
For a polygon based object, a scanline algorithm is commonly used to render the final image. The pixels are scanned a line at a time and their color is determined from the polygons that contribute to that part of the screen.
The colors of the polygons are specified either at the vertices, in which case interpolation is used to find the pixel color, or by a texture map, which can be transformed into the appropriate pixels.
A Z-buffering algorithm is used to ensure that objects closer to the image (along the z direction) are rendered last, so that partially obscured polygons are overwritten (as they should be).
