Still Image Coding: Standard JPEG
This chapter introduces the Joint Photographic Experts Group (JPEG) standard. This standard allows for lossy and lossless encoding of still images, and four distinct modes of operation are supported: sequential discrete cosine transform (DCT)-based mode, progressive DCT-based mode, lossless mode, and hierarchical mode. Image coding is an important application of data compression. When an analog image or picture is digitized, each pixel is represented by a fixed number of bits, which correspond to a certain number of gray levels. In this uncompressed format, the digitized image requires a large number of bits to be stored or transmitted. As a result, compression becomes necessary due to the limited communication bandwidth or storage size. In the sequential coding an image is encoded part-by-part according to the scanning order while in the progressive coding, the image is encoded by multiscanning process and in each scan the full image is encoded to a certain quality level.