Digital images created or captured (for example, by scanning a photo) as a set of samples of a given space. A raster is a grid of x-axis (horizontal) and y-axis (vertical) coordinates on a display space. (Three-dimensional images also have a z-coordinate.) A raster image identifies the monochrome or color value with which to illuminate each of these coordinates. The raster image is sometimes referred to as a bitmap because it contains information that is directly mapped to the display grid. A raster image is usually difficult to modify without loss of information. Examples of raster-image file types are BMP, TIFF, GIF, and JPEG files. See also vector graphics.