 errors do not continuously concept of distortion versus coding efficiency is one of propagate. Intraframe mode will also be used to spatially the most fundamental tradeoffs in the technical evalua- encode a block whenever the Interframe encoding mode tion of video encoders. cannot meet its performance threshold. The intraframe Prediction Spatial Variable Error Ek Operator Quantizer Ike Or Eke Length Coder Transmit Prediction Encoded Inverse Intraframe Intraframe Open Quantizer Sub-block Interframe - Closed I k-mand E k-n Encoded Interframe Delayed Inverse Spatial Motion Prediction Frame Operator Compensation Error and Memory Motion Vector Variable Motion Motion Vectors Length Coder Estimation Figure 7.4-1 Generalized video compression system. Video compression CHAPTER versus interframe mode selection algorithm is not in- process. Alternatively, the quantization interval size cluded in this diagram. It is responsible for controlling can be adjusted based on the performance of the the selection of the encoding functions, data flows, and human visual system (HVS). The Joint Pictures output data streams for each mode. Expert Group (JPEG) standard includes two The intraframe encoding mode does not receive any (luminance and color difference) HVS sensitivity input from the feedback loop. Ik is spatially encoded, and weighted quantization matrices in its "Examples and subsequently encoded by the VLC forming Ike, which is Guidelines" annex. transmitted to the decoder. The receiver decodes Ike Variable length coding - The lossless variable length producing the reconstructed image sub-block Ik. During coding (VLC) is used to effectively exploit the the interframe coding mode, the current frame pre- "symbolic" redundancies contained in each block of diction Pk is subtracted from the current frame input Ik quantized transform coefficients. This step is termed to form the current prediction error Ek. The prediction "entropy coding" to designate that the encoder is error is then spatially and VLC encoded to form Eke and desig