Tham khảo tài liệu 'anatomy of a robot part 15', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | 266 CHAPTER NINE are compressed again using run-length compression described later . Compression ratios of 50 1 can be achieved. It is not simple to write from scratch a program to perform this type of compression. Here are some web sites and a PDF discussing image compression http jongejan 461 http grosenkrans http LAB_PUBLICATIONS Books dip_material chapter_4 Run-Length Compression One of the oldest and most intuitive techniques of compression is simple run-length compression. Instead of sending for example a series of 2 415 zero byes we can simply send a block of data that is about 4 bytes long explaining it represents 2 415 zero bytes. The protocol is simple and can be written from scratch if need be. The following URLs explain a few different types of run-length encoding research compress algorithms fund rl http Huffman Compression Huffman compression can be used if the data can be broken up into symbols like text bytes . Then all the symbols are reassigned a different code before transmission. The most often transmitted symbols are assigned short codes. Symbols that are rarely transmitted are assigned longer codes. Run-length coding is also applied. The following web pages are interesting lectures on data compression in general WoolleySI All7 kingd WoolleySI All7 Encryption and Security Instances occur when data must be encrypted before it is transmitted. The physical links of most communication channels move through areas that are in public. Certainly all radio frequency RF communications that move through free space can be intercepted and phone communications move through common wiring and facilities. We ve all COMMUNICATIONS 267 heard of the infamous hackers who eavesdrop and create other problems on the Internet. We ll use
