static dictionary technique
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The document discusses static dictionary coding techniques for data compression. It begins by explaining that dictionary coding uses a list of symbols and strings, rather than statistical models like Huffman or arithmetic coding. It then describes how static dictionary coding works: a fixed dictionary is produced in advance containing frequently occurring strings; during encoding and decoding, strings in the dictionary are replaced with indexes, while unmatched strings are encoded less efficiently. As an example, it outlines how a simple diagram coding technique encodes pairs of symbols by checking the dictionary before encoding symbols individually.
static dictionary technique
- 1. GANDHINGAR INSTITUTE OF TECHNOLOGY INFORMATION TECHNOLOGY DEPARTMENT Data Compression and Data Retrieval (2161603) STATIC DICTIONARY TECHNIQUE Enrollment no: 150120116047 Name: Prince Paneliya Guided By: Prof. Alpa Oza
- 2. Dictionary Coding • Dictionary coding is different from Huffman coding and arithmetic coding. • Both Huffman and arithmetic coding techniques are based on a statistical model . • A dictionary is a list of symbols and strings of symbols. • Dictionary coding is widely used in text coding.
- 3. • The strategy of the dictionary coding is to build a dictionary that contains frequently occurring symbols and string of symbols. • When a symbol or a string is encountered and it is contained in the dictionary, it is encoded with an index to the dictionary. • Otherwise, if not in the dictionary, the symbol or the string of symbols is encoded in a less efficient manner.
- 4. Formulation of Dictionary Coding Define dictionary coding in a precise manner • We denote a source alphabet by S. • A dictionary consisting of two elements is defined as D=(P , C,) P is a finite set of phrases generated from the S, C is a coding function mapping P onto a set of codewords.
- 5. Static Dictionary Coding A fixed dictionary, • Produced before the coding process • Used at both the transmitting and receiving ends • It is possible when the knowledge about the source alphabet and the related strings of symbols, also known as phrases, is sufficient.
- 6. • An example of static algorithms occurs is diagram coding. • A simple and fast coding technique. • In encoding, two symbols are checked at once to see if they are in the dictionary. • If so, they are replaced by the index of the two symbols in the dictionary, and the next pair of symbols is encoded in the next step.
- 7. • If not, then the index of the first symbol is used to encode the first symbol. The second symbol is combined with the third symbol to form a new pair, which is encoded in the next step. • The diagram can be straightforwardly extended to n-gram. In the extension, the size of the dictionary increases and so is its coding efficiency.
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