An image compression bit rate control method and device

Abstract

The invention discloses a method and a device for controlling bit rate of compressed images. Data quantity in data cache is first obtained; if the number of the AC coefficient preserved presently is the maximum number of the AC coefficient and the data cache is judged to over run, the number of the AC coefficient preserved presently is set as the minimum number of the AC coefficient and a target compression ratio is set as initial valve of the target compression ratio; if the data cache is judged not to over run, the maximum valve of the data quantity during data caches is counted when the record is interrupted for N times and the present target compression ratio is reduced if the maximum valve is less than the low threshold of the data cache; the present target compression ratio is increased if the maximum valve is more than the high threshold of the data cache. The invention realizes dynamic target compression ratio adjustment and is combined with the number adjustment of the AC coefficient at the same time, and therefore the over-run is avoided to the utmost extend when image of comparatively good quality is guaranteed, thereby improving the quality of the compressed image.

Description

technical field [0001] The invention relates to the technical field of image processing, in particular to a method and device for controlling the bit rate of compressed images. Background technique [0002] In the existing camera system, due to the limitation of the transmission bandwidth, the processed image data is often sent out for display after being compressed. A commonly used image compression method is an image compression method in JPEG (Joint Photographic Experts Group, Joint Photographic Experts Group) format. As shown in Figure 1, be the functional block diagram of JPEG image compression camera system in the prior art, this system comprises image acquisition unit, image processing unit, JPEG coder unit, first-in / first-out (FIFO, First Input / FirstOutput) data cache The unit and the computer unit realize the bit rate control of the compressed picture through the Q value adjustment unit contained in the JPEG encoder unit. [0003] The compressed image data usually...

AI Technical Summary

Problems solved by technology

[0012] This method uses a fixed TCR. If the TCR is set too high, the image quality will be degraded, and if the TCR is set too low, overflow will occur from time to time.

[0013] The compressed image bit rate control method in the existing camera technology mostly adopts the above-mentioned fixed target compression rate, which is not conducive to achieving a good balance between avoiding overflow and ensuring image quality

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