Lz Data Compression Algorithm And Its Seal System

With the development of multi-media and network technology, people has put forward the higher requirement at quality dimension and application in digital image. However, the volume of image data is very large. Therefore, how to use the limited space and bandwidth resources to store and transmit a big image becomes an urgent problem. Image compression is being regarded as one new research hotpot by more and more researchers.This thesis discusses the image compression technology. Firstly, the basic concepts of image compression and many classic compression technologies in compression areas are introduced, just like DCT coding, RLC, Huffman coding, predictive coding, etc. Next, mainly discuss a classic image compression algorithm of the specific area-LZ77 compression algorithm in detail, including the basic principles of compression, the steps of compression and decompression, and described how to code for the triple-output. Compared with other algorithms, LZ77 algorithm is easy to implement, and has higher compression and decompression speed, it is suitable for practical applications.However, though the analysis of LZ77 encoding algorithm, we find that there are some shortages in the searching string and matching the output of individual characters in the algorithm. Therefore, we made two kinds of improvement in the algorithm.1)The original algorithm found the matching-string in order. However, the improved algorithm re-organizes the text window, and save the phrase that enter the buffer zone by using binary search tree. So, to some extent, it reduces the execution time of the algorithm.2) The original algorithm in the output of a single character may lead to the length of 3-tuple higher than the length of its own. Based on this situation, the improved algorithm makes some changes in data output. That is, each output adding a postfix to represent the output is a single or multi-character encoding. Thus, the improved algorithm has a good effect on compression.This thesis also gives several examples of improved algorithm. The results show that the improved algorithm has a good effect on data compression, and increase the scales of compression, especially for the less-color image, this improved algorithm can be achieve better results on compression.Finally, this thesis shows the result of the actual project - seal management system by using LZ77 algorithm. We compress the image and save the string in the database, and though transmission and communication, the client decompresses and shows the original image. LZ77 algorithm effectively solves the contradictions between the large image data and the limited storage capacity, and achieves good results.