One useful tool for color modification is the look-up table. Generally speaking, a look-up table takes a value, maps it to a location in a table, and replaces the incoming value with the contents of the table entry. OpenGL provides three mechanisms which are basically look-up tables. Two, pixel maps and color tables, look up components independently in one-dimensional tables. These mechanisms provide efficient mapping for applications requiring no between the channels of the image. A third mechanism, pixel texturing, uses the OpenGL texturing capability to perform multi-dimensional look-ups.