The Research On Radar Image Compression Based On Wavelet Transform

A whole piece of radar image usually is required to be sampled every fifteen seconds, which is different from video image that generally has twenty-five frames per second, so it means radar images can be treated as static images. Radar image plays an very important role in voyage data recorder(VDR), and the quality of this kind of image needs to be relatively high which cannot be valuated arbitrarily by people's eyes but should be estimated through some objective standard. So first and foremost, the desired compression algorithm should achieve an ideal compression ratio and keep a high quality of radar image.With the consideration that radar image with high resolution generally has huge amount of information, a large compression ratio, low distortion and especially high reliability are expected to be derived through the compression technique adopted. After an overall comparison of various compression algorithms and coding standards, a sort of wavelet coding algorithm based on block bit-length which can be used to compress radar image effectively was presented in this dissertation, which also aims at solving the problems such as occupancy of comparatively large amount of memory in coding process and difficulty in hardware realization which might exist in some kinds of wavelet algorithms used presently.According to visual characteristics of human eyes, of present static colorful image was analyzed. Along with the principle of the tricolor and the knowledge about the scalar component combination format of static colorful image, the scalar component transform for regular images was analyzed, also an innovative format transform without conversion from RGB to YCbCr was derived for radar image particularly and there is no voltage shift as well.Some research work focused on the fundamental of Wavelet Transform, and systematic introduction and analysis about wavelet theory linking with principles of signal processing technology was introduced additionally. In the dissertation, the concept of wavelet followed the introduction of Fourier Transform, Wavelet Transform and Multi-resolution Analysis were put forward subsequently. Then, Mallat algorithm on the base of Multi-resolution Analysis structure was acquired with some reference to digital signal processing theory. After that, basic principle for the improvement of the algorithm was discussed briefly accompanied with the realization of improvement method for traditional Wavelet Transform. Moreover, wavelet LS(9,7) was employed and some improvement was also implemented for the purpose about hardware realization.Following the above, a few of typical image coding arithmetics, EZW, SPIHT and SPECK, which based on Wavelet Transform were studied. The fundamental principle of image coding algorithm founded on the base Wavelet Transform was explored through the deep sights on the principles and coding processes of those three kinds of arithmetics, and some shortcomings in SPECK was overcome with the characteristics of SPIHT. The improved algorithm provided the concrete realization method and split method corresponding to the sets of S-block and I-block, which acted as a foundation for coding realization. The performance of this algorithm is identical with that of SPECK without increasing entropy codes and its coding process was simplified after getting rid of complex nest function. When the resolution was increased, the coding speed could be boosted with the elimination of the procedure where LIS link tables were resorted orderly.Tow sorts of wavelet coding algorithms connected with the concept of block bit-length were presented to overcome the drawbacks exists in some current wavelet coding methods. One is Zero Block Wavelet Coding algorithm without nested link based on block bit-length, and the other is called Wavelet Block Coding algorithm without link table based on block bit-length, both of them can provide comparatively high SNR, respectively. Under the consideration that both memory and time consumption in the coding process cannot be ignored when the corresponding arithmetics were implemented in practical hardware equipment, Wavelet Block Coding algorithm without link table based on block bit-length will have much more superiority, so this algorithm was employed in radar image compression system.In the last section of this dissertation, the hardware realization platform for radar image compression system was given in details, including its working principle, the introduction for main chips and the explanation for the implement of wavelet coding algorithm through the platform. Subsequently, the testing program loaded into PC and corresponding concrete program diagram, the main window for the testing program and parameter configuration window were presented as well. Finally, particular tests for radar image compression system were conducted according to some international testing standards set for radar image compression techniques in " Test Guidance for Shipborne Voyage Data Recorder" issued by CCS, the test result showed that the performance and its characteristics of this radar image compression system can reach the international standards entirely and it has a long time period working stability and reliability.