Patent ID: 6023531
Filing Date: 2000-02-08
Classification: H04N

Abstract:
A method for compressing digitized signals digitized by a digitizer, comprising the steps of:computing a discrete cosine transform of a first plurality of the signals to create a first plurality of coefficients corresponding to frequencies;specifying a cutoff frequency above which the first plurality of the computed coefficients are to be eliminated;creating a first quantization table including a first plurality of table values indicative of the cutoff frequency, each table value corresponding to one of a plurality of frequencies;quantizing the first plurality of computed coefficients using the first quantization table and outputting compressed signals;computing a discrete cosine transform of a second plurality of the signals to create a second plurality of coefficients corresponding to the frequencies;adjusting the cutoff frequency above which the second plurality of the computed coefficients are to be eliminated;creating a second quantization table including a second plurality of table values indicative of the cutoff frequency after the step of adjusting, wherein each of the second plurality of table values corresponds to one of the plurality of frequencies, and wherein at least some of the values in the first table that correspond respectively to a subset of the frequencies are different from at least some of the values in the second table that correspond respectively to the same subset of the frequencies;quantizing the second plurality of computed coefficients using the second table and outputting further compressed signals; anddecompressing the compressed signals that were compressed according to the first table and decompressing the further compressed signals that were compressed according to the second table using a same table.