fogging
Unlike alpha blending, fogging, which is intended to create a fog effect, includes depth information in the calculation, increasing the depth effect. A fogging graphic takes into account how far an object is in space.
The fogging effect is stronger the further back an object is placed in the view. The effect gives an increased impression of depth. Pixels that have no spatial depth are therefore unclouded, whereas pixels that are deep in space have a strong clouding.
In fogging, represented by a gray fog color, alpha blending increases continuously. Pixels farther from the viewer are grayer, pixels closer to the viewer are less gray.
Depth cueing is a technique similar to fogging, except that in depth cueing the fade is to black, not white as in fogging.