Note that the sample may be a pixel line audio sample

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Unformatted text preview: c compression techniques are described below. An actual compression technique for multimedia object is often a combination of one or more of these basic compression techniques. Lossless Techniques The following two are the commonly used lossless compression techniques: 1. Run-length coding. In this method, repeated symbols in a string are replaced with the symbol and the number of instances it is repeated. For example, "aaaabbcccccaaaaaababbbb" is expressed as "a4b2c5a6blalb4". 2. Variable-length coding. In general, coding schemes for a given character set use a fixed number of bits per character. For example, BCD, EBCDIC and ASCII coding schemes use a fixed number of bits per character. If it is known (through statistical studies) that the frequency of occurrence of different characters in a character set is different (for example we all agree that the character Z is not so frequently used as the character A in the character set of English alphabets), then a coding scheme that employs a variable number of bits per character may be used to obtain tighter packaging of data. A variable-length coding scheme is based on this concept. In such a coding scheme, fewer bits are used to represent the more frequently occurring characters than the less frequently occurring ones. Obviously, the most frequently occurring character would be represented with only one bit. Huffman coding is an example of this method. It is briefly described below with an example. To make the example simple and easy to understand, let us assume that our character set consists of only six characters: A, B, C, D, E, and F. A conventional coding scheme that uses a fixed number of bits per character would require three bits per character (because 22 < 6 < 23). Now suppose the relative frequency of occurrence of the characters in this character set is as shown in Figure 19.9. The figure also displays a Huffman coding of these six characters, which minimizes the total number of bits for ch...
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