Multimedia System 030728ppt 98 Lossy Compression Lossy Compression where the

Multimedia system 030728ppt 98 lossy compression

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Multimedia System 030728.ppt 98 Lossy Compression Lossy Compression – where the information, once uncompressed, cannot be fully recovered. Lossy compression normally involves analyzing the data and determining which information has little effect on the resulting compressed data. Compression of an image might be used to reduce the resolution of the image. Lossy compression allows much lower data rates and file sizes than lossless compression, so lossy codecs are commonly used for final production of video delivered using CD-ROM or the Internet. Multimedia System 030728.ppt 99 Lossy Compression The aim of lossy compression algorithms, is normally not to reproduce an exact copy of the source information after decompression but rather a version of it which is perceived by the recipient as a true copy. In general, with such algorithms the higher the level of compression being applied to the source information the more approximate the received version becomes. Example applications of lossy compression are for the transfer of digitized images and audio and video streams. In cases, the sensitivity of the human eye or ear is such that any fine details that may be missing from the original source signal after decompression are not detectable. Multimedia System 030728.ppt 100 Figure: Block diagram of generic image-coding algorithm Short-Term Analysis JND Estimation JND Adaptive Coding Intensity Texture Motion Just-Noticeable Distortion Profile Constant Quality or Constant Bit Rate Bit Rate Control Video Signal Perceptual Coding
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Multimedia System 030728.ppt 101 Entropy Entropy Entropy Redundancy Frequency Complexity Compression factor Compression factor Latency (delay) Signal level Worse quality Worse quality Better quality Better quality Ideal lossless coder Lossy coder (a) (b) (c) Operation of a Coder Multimedia System 030728.ppt 102 Compression Methods Used by Various Image File Formats X DCT X X Huffman X X LZ X X RLE JPEG PNG GIF BMP Multimedia System 030728.ppt 103 Entropy Encoding Entropy encoding is lossless and independent of the type of information that is being compressed. It is concerned solely with how the information is represented. Run-length Encoding Run-length encoding are when the source information comprises long substrings of the same character or binary digit. Instead of transmitting the source string in the form of independent codewords or bits, it is transmitted in the form of a different set of codewords but also an indication of the number of characters/bits in the substring. Multimedia System 030728.ppt 104 Entropy Encoding In an application that involves the transmission of long strings of binary bits that comprise a limited number of substrings, each sub-string can be assigned a separate codeword. For example, if the output of the data was: 000000011111111110000011...
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