Raster graphics (or bitmap graphics) is one of two kinds of computer graphics. With raster graphics, images are modeled as big collections of pixels. Usually they form an image shaped like a rectangle. Each pixel holds something, like color or transparency. Raster images are used very often. Computer screens are made of a raster of points. Vector graphic images are rasterised that way. Images that are difficult to make as a vector, like photographs, are often made in the form of a raster image.