| With the rapid development of maritime traffic, ocean traffic accidents are increasing. The voyage data recorder can records navigation data including image and audio data, which can provide evidence for troubleshooting and accident investigation. In the storage space of navigation data, ship-borne radar images accounted for a large part, therefore, in the process of transmission and storage, how to compress the radar image based on reducing the storage volume and achieving a good compression is an urgent matter to be solved. At present, as most of the voyage recorder radar products adopted the MPEG standard in radar image compression, however, this method doesn’t take into account the characteristics of radar image, therefore, it’s necessary to carry out new research on the ship borne radar image compression technology.In this paper, as the successful application in image compression with wavelet transform, a combined method based on scheme lifting algorithm, SPIHT and arithmetic coding is put forward for radar image compression. In the application of wavelet transform to compress the radar image, the wavelet function and the layer of decomposition must be chosen. According to lots of research materials, the dissertation summarizes the effect of the digital characteristics of wavelet function to image compression performance. And based on it, selects several representative wavelet functions, nature and radar image, and compares the compression ratio and images’ PSNR through experiment, at last, selects the ideal wavelet function and layer of decomposition, provides a reference for the practical application.In this dissertation, the classical radar image compression methods based on the wavelet transform, EZW and SPIHT methods are compared, by comparing the compression speed and reconstruction effect between the two methods, the time consumption is reduced and compression effect is better in SPIHT method which can be applied in practical application. |
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