Adaptively coding method and apparatus utilizing variation in quantization step size

摘要

An adaptive coder includes a circuit for calculating the number of intraframe and interframe blocks in one frame to be coded. When the calculated picture data is supplied to the coder, a quantization controller selects one of a number of curves for the determination of quantization step sizes, to thereby take optimal advantage of the number of blocks of each mode applied to the mode determine. In particular, a frame having a relatively large number of intraframe blocks results in selection of a curve having a large quantization step size. In contrast, a frame having a relatively large number of interframe blocks results in selection of a curve having a small quantization step size. The quantization controller determines and outputs the quantization step size, thereby taking advantage of a present buffer occupancy rate and the determined curve. Accordingly, the adaptive coder can prevent sudden changes in quantization step sizes due to the buffer occupancy rate, thereby permitting maintenance of a high picture quality during scene changes. A corresponding method is also described.