XBM files differ markedly from most image files in that they take the form of C source files. This means that they can be compiled directly into an application without any preprocessing steps, but it also makes them far larger than their raw pixel data. The image data is encoded as a comma-separated list of byte values, each written in the C hexadecimal notation, '0x13' for example, so that multiple ASCII characters are used to express a single byte of image information.