Patent ID: 7062104

Claim:
A method of quantizing image data comprising the steps of: (a) transforming an image datum to a datum transform coefficient; (b) measuring a distortion of an image; (c) as a function of said distortion of said image, varying a range of a plurality of transform coefficients included between a lower frequency limit and a higher frequency limit of a quantization step; (d) identifying a quantization step comprising a range of transform coefficients inclusive of said datum transform coefficient; (e) substituting for said datum transform coefficient a quantizer index representing said transform coefficients of said range included in the identified quantization step; (f) wherein the step of varying said range of transform coefficients as a function of a distortion of said image data comprises the step of decreasing said range included in a first quantizer step comprising lower frequency transform coefficients relative to a range included in a second quantization step comprising higher frequency transform coefficients if a peak-to-mean amplitude of said distortion at least equals a frequency detection threshold of a basis function.