equired can be classified into two groups. The first one is called intraframe or intrafield, and is based only on the reduction of spatial redundancy. The second group is called interframe or interfield, and is based on the reduction of temporal redundancy as well as spatial redundancy. 16.9.3.2 Specific Bit Rate Reduction Techniques. The following specific bit rate reduction techniques are based on Refs. 14 and 15. Intraframe Coding. Intraframe coding techniques provide compression by removing redundant information within each video frame. These techniques rely on the fact that images typically contain a great deal of similar information; for example, a one-color background wall may occupy a large part of each frame. By taking advantage of this redun- dancy, the amount of data necessary to accurately reproduce each frame may be reduced. Interframe Coding. Interframe coding is a technique that adds the dimension of time to compression by taking advantage of the similarity between adjacent frames. Only those portions of the picture that have changed since the previous picture frame are communi- cated. Interframe coding systems do not transmit detailed information if it has not changed from one frame to the next. The result is a significant increase in transmission efficiency. Intraframe and Interframe Coding Used in Combination. Intraframe and interframe coding used together provide a powerful compression technique. This is achieved by applying intraframe coding techniques to the image changes that occur from frame frame. That is, by subtracting image elements between adjacent frames, a new image remains that contains only the differences between the frames. Intraframe coding, which removes similar information within a frame, is applied to this image to provide further reduction in redundancy. Motion Compensation Coding. To improve image quality at low transmission rates, a specific type of interframe coding motion compensation is commonly used. Motion compensation applies the fact that most changes between frames