Compression, sometimes called “encoding,” is used to represent visual information using a minimum amount of bits. Images have statistical properties that can be exploited during compression, thereby making image compression techniques better than general purpose binary data compression techniques. Videos, being sequences of images, also have the same exploitable properties.
Lossy compression techniques are commonly used to compress images. Such lossy techniques sacrifice finer details of the image in order to obtain a greater rate of compression. When a lossy-compressed image is decompressed, or decoded, the resulting image lacks the fine details that were sacrificed. However, oftentimes the lost details are unnoticeable to human viewers.
Several compression standards have been developed by industry groups such as the Moving Pictures Experts Group (MPEG) in order to encode various types of content. For example, the MPEG-1 standard is used for compact disk read-only memory (CD-ROM) video applications including video CDs, the MPEG-2 standard is used for digital video disks (DVD) and standard definition (SD) high-definition (HD) televisions, and the MPEG-4 standard, including H.264/MPEG4-AVC, is used for multimedia and web applications. Similarly, standards developed by the Joint Photographic Experts Group (JPEG) are used for lossy compression of still images. These standards work well but can be improved.