flow and underflow. There are two popular types of rate In many video compression applications, it is essential to control algorithms. In the first approach, the proper quanticontrol precisely the bit rate produced by the encoder. One zation stepsizes is selected based on the buffer status. That critical element in a bits/buffer control algorithm is the bits is, the quantization stepsize is set small when the buffer is model that predicts the number of compressed bits when a nearly empty and the stepsize is set large when the buffer certain quantization stepsize is used. In this paper, we propose is nearly full. However, this type of control schemes such as an adaptive piecewise linear bits estimation model with a tree RM8 and SM3 often result in non-uniform picture quality structure. Each node in the tree is associated with a linear because (1) it does not have a bit budget plan that distribrelationship between the compressed bits and the activity meautes bits appropriately for every image block and (2) it does sure divided by stepsize. The parameters in this relationship not take image contents into consideration in adjusting are adjusted by the least mean squares algorithm. The effectiveness of this algorithm is demonstrated by an example of digital stepsize. Without a bit budget plan we may produce too VCR application. Simulation results indicate that this bits many bits at times; then, we have to increase stepsizes model has a fast adaptation speed even during scene changes. abruptly to reduce output bits. In the second case, smaller Compared to the bits model derived from training data based stepsizes should be used in the smooth image region and on cluster analysis, the adaptive piecewise linear bits model larger stepsizes in the texture region to match the sensitivachieves about the same high performance with a much lower ity thresholding characteristics of human perception.
complexity and high self-adaptativity. A particular advantage
A modified version of the above scheme is to precomof a rate control scheme employing a bits model over the bufferpute a budget plan for each picture frame and/or every feedback rate control such as MPEG2 Test Model 5 is that it image block. Then, quantization stepsizes are ''guessed'' can control the bits of every microblock very precisely. Β© 1997 based on the buffer status to produce the desired bits. One
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example of this kind of schemes is Test Model 5 (TM5) in the development of MPEG2 standards [3]. However, the 51