| Summary: | 博士 === 國立交通大學 === 電控工程研究所 === 100 === Rate control plays a vital role in signal processing and video compression. Two degrees of distortion and consumed counts for measurement are selected in a tradeoff consideration. The video compression system defines two distinct frame types, as follows: intra-frame and inter-frame. The start frame in encoded video sequences is assigned as an intra-frame, and the goal is to maintain a higher image quality and lower encoded bits because the intra-frame is referenced after the encoded image, and the remaining bits are used for compression. In a real-time video compression system, referred to as H.264/AVC, the determination of the quantization parameter by rate control must refer to the encoded results in the previous frame. However, sudden occurrences such as fast-moving objects or complex backgrounds in two neighboring frames are usual. Thus, because of encoded results in previous images, producing stable image quality or accurate bits consumption is a crucial topic.
This study focused on the H.264/AVC video compression system and rate-distortion theory to obtain a workable distortion prediction method for intra-frame and inter-frame rate control. Subsequently, we used this distortion prediction method to develop four rate control algorithms for various applications.
Based on the intra-frame rate control algorithm
According to the distortion prediction method and a large number of test images, we obtained a set of system parameters to develop a fast and accurate intra-frame rate control algorithm.
Based on the inter-frame rate control algorithm
We propose an analytic inter-frame rate control algorithm according to the distortion prediction method, H.264/AVC rate prediction method, and Lagrange optimization. This algorithm can solve the problem of low bit rate limitation in H.264/AVC.
In real applications, we first considered the limitation of embedded systems. The initial QP value can be obtained through the built-in technology of QP calculation. We developed the intra-frame rate control algorithm according to the initial QP value, the distortion prediction method, and the information of image histogram.
In the proposed distortion prediction method, we can predict the measurement of image content complexity efficiently to obtain a more accurate QP value than by using the current algorithm. This algorithm was developed for low bit rate video conferencing.
We derived the distortion prediction method according to the original rate-distortion theorem. We applied the method on four differing applications to verify the results. Based on the simulation results, the method improved compressed image quality efficiently. We also considered hardware limitations for industrial application.
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