alpha blending

In computer graphics, the combining of the alpha channel with other layers in an image in order to show translucency. The alpha channel is an additional eight bits used with each pixel in a 32-bit graphics system that can represent 256 levels of translucency. Black and white represent opaque and fully transparent, while various gray levels represent levels of translucency.

More than one layer in a multilayered image may contain a translucent component, thus multiple levels of blending may be required. If the graphics accelerator performs the blending in its own hardware, the results are displayed considerably faster. See alpha channel and translucency.