Research Of Underwater Acoustic Image Compression Coding Based On Fractal Method

Recent years,the underwater acoustic technology has become a rapidly developed subject and has attract more and more attention.In consequence,with the explosive growth of images that generated by different kinds of underwater detection equipment directly or indirectly,it is vital for us to find solutions to meet the high-speed transmission need of underwater communication system.Because of the limited bandwidth of the underwater channel,it will cause low data transmission rate which makes the compression of images particularly important.Traditional image compression algorithms are based on the Shannon information theory,by removing the redundant information to realize compression,but due to the limit of entropy,the compression ratio is relatively low.However,the emergence of fractal theory provides a new solution.The theory is based on the self-similarity in images by removing the structural redundancy to realize compression.It can achieve high compression efficiency because of little compression affine parameters will realize the expression of the original images.In addition,fractal decoding can be implemented by several iteration operations.Nowadays,fractal image compression has received much appreciation because of its characteristic of fast decoding,high compression ratio and resolution-independent.It has become one of the most active and promising image compression methods.Since the fractal coding algorithm presented by Jacquin in 1990,there appears various improved algorithms.Unfortunately,there is still no ideal algorithm that can be generally accepted by scholars at present.Many obstacles are there in the practical pace of fractal coding algorithm.Based on the basic fractal coding algorithm and the characteristics of underwater acoustic image,the works focus on how to further accelerate the fractal encoding speed and the application of fractal coding algorithm in underwater acoustic field.The main works are as follows:(1)The significance of underwater acoustic image compression and the development,the characteristics of traditional image compression and fractal image compression are introduced.(2)The realization of basic fractal coding algorithm is presented and the effect ofdifferent factors on the coding performance is studied and analyzed by experiments.Improved strategies of fractal coding are analyzed from different aspects such as: classification matching,reducing the codebook,optimizing the search range and changing the division method of range block.Finally,the improved algorithm based on variance and correlation coefficient is presented.(3)According to the image characteristics of underwater acoustic field,a fractal coding algorithm based on region of interest is presented.The image is divided into separate sub-blocks by their importance and they will be coded respectively.Therefore,the compression ratio is increased while the detail information of the target region is preserved.(4)An improved fractal coding algorithm based on the dictionary is presented to simplify the process of encoding and decoding and accelerate the encoding and decoding speed.By analyzing the generation,extension and classification of dictionary in detail,the improved algorithm is presented which can increase the richness and applicability of the dictionary and improve the performance of dictionary coding algorithm.(5)To make full advantage of the two algorithms proposed in(3)and(4),a synthesis algorithm is presented by joining them together.Finally,the effectiveness and applicability of the synthesis algorithm are verified in experiment.