- Wavelet compression
Wavelet compression is a form of
data compression well suited forimage compression (sometimes alsovideo compression andaudio compression ). The goal is to store image data in as little space as possible in a file. Wavelet compression can be either lossless or lossy. [JPEG 2000 , for example, may use a 5/3 wavelet for lossless (reversible) transform and a 9/7 wavelet for lossy (irreversible) transform.]Using a
wavelet transform , the wavelet compression methods are adequate for representingtransient s, such as percussion sounds in audio, or high-frequency components in two-dimensional images, for example an image of stars on a night sky. This means that the transient elements of a data signal can be represented by a smaller amount of information than would be the case if some other transform, such as the more widespreaddiscrete cosine transform , had been used.Wavelet compression is not good for all kinds of data: transient signal characteristics mean good wavelet compression - smooth, periodic signals are better compressed by other methods. Data statistically indistinguishable from random noise is not compressible by any means.
Method
First a
wavelet transform is applied.This produces as manycoefficient s as there arepixel s in the image (i.e.: there is no compression yet since it is only a transform).Thesecoefficient s can then be compressed more easily because the information is statistically concentrated in just a few coefficients.This principle is calledtransform coding . After that, thecoefficient s are quantized and the quantized values are entropy encoded and/or run length encoded.Examples for wavelet compression:
* Still images
** ECW
** Embedded Zerotrees of Wavelet transforms / EZW
**ICER
**JPEG 2000
**MrSID
**Progressive Graphics File
**SPIHT
* Video
** Dirac
**Pixlet
** Snow
** Tarkin
**Rududu [http://rududu.ifrance.com/rududu/]
**Bink Video
** Redcode [http://www.red.com/techspecs.shtml]
**Motion Compensated Temporal Filtering (MCTF) can use wavelets both in time and in spaceNotes
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