Issue No. 06 - June (1986 vol. 6)
David Salesin , California Insitute of Technology
Ronen Barzel , California Insitute of Technology
Ordinary bitmaps allow pixels to be black or white. We introduce a second bitmap, the "alpha" bitmap, which allows pixels to be transparent as well. The alpha bitmap makes it possible to have black-and-white images that are nonrectangular or that have holes in them. It also provides a richer set of operations for working with bitmaps. We present the mathematics for a two-bit compositing algebra, and suggest extensions for two-bit compositing, painting, and region filling. Each of these operations can be implemented with ordinary bitblts and presented on ordinary bitmap displays. We analyze the cost of each two-bit operation in terms of the number of bitblts it requires.
D. Salesin and R. Barzel, "Two-Bit Graphics," in IEEE Computer Graphics and Applications, vol. 6, no. , pp. 36-42, 1986.