3-D imaging using normalized gradient shading

Two algorithms called marching cubes and dividing cubes were previously (1987) developed and used for the three-dimensional display of objects contained in CT (computed tomography) and MRI (magnetic resonance imaging) images. A key to these algorithms is that surface normals are derived from the normalized gradient of the original tomographic images. The resulting images have been subjectively judged superior to images generated with the cuberille and ray-casting algorithms. The authors show how the cuberille and ray-casting algorithms can be extended to use the normalized gradient. The image quality attainable using the four existing and the two extended algorithms is demonstrated, and the implementation tradeoffs for the algorithms are discussed.<>