Module-IV 093.pdf
- 3. • Definition: Compression means storing data in a format that requires less space than usual. • Data compression is particularly useful in communications because it enables devices to transmit the same amount of data in fewer bits. 3
- 4. • The bandwidth of a digital communication link can be effectively increased by compressing data at the sending end and decompressing data at the receiving end. • There are a variety of data compression techniques, but only a few have been standardized. 4
- 5. Types of Data Compression • There are two main types of data compression : Lossy and Lossless. • In Lossy data compression the message can never be recovered exactly as it was before it was compressed. 5
- 6. • In a Lossless data compression file the original message can be exactly decoded. • Lossless compression is ideal for text. • Huffman coding is type of lossless data compression. 6
- 7. Compression Algorithms • Huffman Coding • Run Length Encoding • Shift Codes • Arithmetic Codes • Block Truncation Codes • Transform codes • Vector Quantization 7
- 8. Huffman Coding • Huffman coding is a popular compression technique that assigns variable length codes (VLC) to symbols, so that the most frequently occurring symbols have the shortest codes. • On decompression the symbols are reassigned their original fixed length codes. 8
- 9. • The idea is to use short bit strings to represent the most frequently used characters • and to use longer bit strings to represent less frequently used characters. 9
- 10. • That is, the most common characters, usually space, e, and t are assigned the shortest codes. • In this way the total number of bits required to transmit the data can be considerably less than the number required if the fixed length ASCII representation is used. • A Huffman code is a binary tree with branches assigned the value 0 or 1. 10
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