LZW lossless compression.docVIP

LZW lossless compression Youming Ning 2012201286 1.Introduction Along with the development of computer technical and network technology, the data that people need to stock and propagate is more and more. These datas have occupied plenty of disk spaces and network bandwidth. however,in data, there is also a lot of redundancies, therefore we may decrease the disk space of data occupation and the bandwidth with network occupied on transmit through compress data to stock. Data compression divides into loss compression and lossless compression, data reconciles before reducing to reduce rear content the compression that does not occur any change is called as lossless compression. Through long development has arisen a lot of lossless data compressed algorithms, we have compare various relatively lossless compression algorithm, has reached the advantage and disadvantage of each kind of algorithm. According to LZW algorithms, we have accomplished the Compresses function and Decompresses function, and realize lossless compression and decompress text. 2.LZW Fundamentals The original Lempel Ziv approach to data compression was first published in 1977, followed by an alternate approach in 1978. Terry Welchs refinements to the 1978 algorithm were published in 1984. The algorithm is surprisingly simple. In a nutshell, LZW compression replaces strings of characters with single codes. It does not do any analysis of the incoming text. Instead, it just adds every new string of characters it sees to a table of strings. Compression occurs when a single code is output instead of a string of characters. The code that the LZW algorithm outputs can be of any arbitrary length, but it must have more bits in it than a single character. The first 256 codes (when using eight bit characters) are by default assigned to the standard character set. The remaining codes are assigned to strings as the algorithm proceeds. The sample program runs as shown with 12 bit codes. This means codes