Data transmission at a constant bit rate using adaptive quantisation

摘要

The image encoding apparatus includes a discrete cosine transformer 12 for discrete-cosine transforming the difference 11 between an image signal of a current frame and an image signal of a restored previous frame in units of a block and outputting the transformation coefficients. A quantization activity calculator portion 14 calculates quantization activity by counting the number of the quantization coefficients which are not zero among the quantization coefficients produced by application of various quantization step sizes. A quantization controller 16 predicts a required bit generation quantity according to fullness of a buffer memory 18 and the transmission rate R, and determines, based on the output of the quantization activity calculator 14, the quantization step size to generate the closest bit generation quantity to the predicted bit generation quantity. The transformation coefficients are then quantised 15 according to the selected quantisation level Q n-1 and variable length encoded 17. This determination is done using a linear proportional relationship between the calculated quantization activity and the variable length-encoded data generation quantity. The encoded data is then stored in a buffer 18 for transmission at a constant bit rate.