Improved image coding system having functions for controlling generated amount of coded bit stream

The present invention calculates the complexity of the image to be coded based on the coding bit amount information is generated for each frame, and by controlling the weight for the high-frequency component at the time of quantization on the basis of the calculation result, the output bits of the coding relates to an image coding system having a bit amount adjustment to adjust the amount adaptively, the present invention is added to each frame of the encoded bitstream generated by the encoding means having the quantization, DCT and entropy coding to them bit amount calculation means for calculating a respective bit amount as a unit; And calculating an activity value of a bit amount of each of the output frame, and of these the calculated activity value with the encoding means, it referred to as the complexity of the frame to be currently encoded, and each generated using a discrete cosine transform DCT conversion coefficient block low pass further comprising: a weight generation means, probe expensive means of providing the encoding means to determine the weight corresponding to the activity value calculation of a plurality of weights section Existing to limit the bandwidth adaptively during filtering, each by limiting the pass band of each of the DCT conversion coefficient block based on the weight determined before quantization to the DCT conversion coefficient block, since each DCT transform coefficient blocks so as to selectively filter a high-frequency component, of the over-the step size of the quantization step to be able to effectively control the amount of bits generated after coding without increasing to be.