Method for visual optimisation of embedded block codes to exploit visual masking phenomena
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United States of America Patent
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Jul 6, 2004
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app pub date -
Mar 1, 2002
filing date -
Feb 19, 1999
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Abstract
A method for lossy compression of images reduces visual distortion for a given compressed bit-rate or, equivalently, requires a lower bit-rate for a given level of visual distortion. An image is decomposed using a space-frequency transform and frequency bands are then partitioned into small blocks. The blocks are independently quantized and coded using an embedded block coder, so that each block bit-stream contains a large number of finely spaced truncation points. A visual distortion measure is computed for each block at each truncation point, where the metric is sensitive to masking properties of the Human Visual System. The distortion values and bit-stream lengths corresponding to each block's truncation point are used to optimise overall visual distortion at one or more target bit-rates or to minimise the bit-rate corresponding to one or more target visual distortion levels. A computationally and memory efficient procedure is described for computing the visual distortion measure for each block's truncation point, within each frequency band, as required by the subject compression system.
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