Raster images in computing

This chapter places video into the context of computing. Images in computing are represented in three forms: symbolic image description, raster image, and compressed image. A symbolic image description does not directly contain an image, but contains a high-level 2-D or 3-D geometric description of an image—such as its objects and their properties. A two-dimensional image in this form is sometimes called a vector graphic. Raster image enumerates the grayscale or color content of each pixel directly in scan-line order. There are four fundamental types of raster images: bilevel, pseudocolor, grayscale, and truecolor. A fifth type, hicolor, is best considered as a variant of truecolor. A compressed image originates with raster image data, but the data has been processed to reduce storage or transmission requirements. The chapter recommends that a file format must accommodate at least 24 bits per pixel to convey photographic-quality color images, and nonlinear coding should be used to make maximum perceptual use of a limited number of bits per component.