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Using a wavelet transform, the wavelet compression methods are better at representing transients, 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 widespread discrete cosine transform, had been used.

Wavelet compression is not good for all kinds of data: transient signal characteristics means good wavelet compression - smooth, periodic signals are better compressed by other methods. Some projects aim at combining discrete cosine transform with a wavelet transform to produce a hybrid compression method which will be good at representing a mix of smooth signals and transients, such as exhibited by most popular music.

Method

First a wavelet transform is applied. This produces as many coefficients as there are pixels in the image. These coefficients can be compressed more easily because the information is statistically concentrated in just a few coefficients. This principle is called transform coding. After that, the coefficients are quantized and the quantized values are entropy encoded and/or run length encoded.

Examples for wavelet compression:

• JPEG 2000JPEG 2000 is a wavelet-based image compression standard. It was created by the Joint Photographic Experts Group committee with the intention of superseding their original discrete cosine transform-based JPEG standard. The usual file extension is . JPEG 20
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