Content area
Abstract
In order to solve problems presented in the multimedia data coding in the Nation "9th Five Year’s "Project, researches on fractal image coding、fractal speech coding and video coding are made in this dissertation. There are seven chapters in this dissertation. The chapter 1 is the introduction of the development of image coding、speech coding and video coding. The main research work in this dissertation is also presented in this chapter.In chapter 2, we proposed a fractal image coding method based on genetic algorithms. The searching scheme problem of domain block in fractal image coding is well solved by applying a robust genetic algorithm with well-selected populations and revised genetic operators. Experimental result has show that it can increase fractal image coding speed by this method.In chapter 3, a mathematical model based on short distance self-similarity is suggested and it can be used to predict the searching space of domain block in fractal image coding. Experimental result indicates that it can decrease coding time without degrading image quality and compression rate by applying this model in fractal image coding. The relationship between the prediction model and its parameter is also studied in this chapter.In chapter 4, we proposed a speech coding method based on iterated function system. In order to cut down the computation complexity, a dynamic noise filter is used to erase the non-speech signal. According to the character of speed signal, we realized a two layers fractal speech codec with fractad interpolation method. This codec can work at 8kbits/s (with good speech quality. Since the compressed speech data can be divided into two layers (resample signal layer and error signal layer), therefore, it is suitable to be transmitted on computer networks.In chapter 5, we submit an image distortion criterion based on visual threshold and visual masking effect. In order to increase coding speed, this distortion criterion is applied into H.263 codec. Experimental result indicates that it can cut down H.263 coding time without decreasing compression rate and subjective dquality of reconstructed image by this way. In chapter 6, a H.263 algorithm based on face detection is proposed. H.263 is a video coding standard for low bitrate video conference. The searching range of the motion vector is one of the most important parameters that can influence the coding speed of H.263. considering the character of image sequence in the video conferencing, we design a method to quickly detect the displacement of the face in the sequence and adjust the searching range of the motion vector dynamically. The experiment results indicate that it can greatly increase the coding speed by applying this method in H.263. In chapter 7, the summary is made and the main results are given.