| 摘要 |
The invention relates to a method and a device for image coding, primarily intended to be applied in the transmission of video signals. The video signal is converted to a bit stream by coding and quantising. The bit stream is stored in a buffer store before it is sent at a constant bit rate on a transmission line. Problems experienced with the known technology have been the prevention of overflow in the buffer store and the buffer store being emptied prematurely. Both of these problems give rise to a deterioration in image quality. At the same time, the buffer store content should be as small as possible. According to the invention, the content in the buffer store is regulated by varying the step height in the quantiser. With the frame rate at the input being known and the frame rate and bit rate at the output being known, the ideal buffer store content can be determined. The actual buffer store content is sensed and compared with the ideal buffer store content and the difference between these two values is determined. The step height in the quantiser is adjusted as a function of the difference. The device according to the invention in preferably constructed as an integrated circuit, for example, a VLSI circuit. <IMAGE> |
