| 摘要 |
<p>The invention provides techniques for changing the quantization used in multiple generations of data quantization such that the errors incurred in subsequent generations are substantially the same as the error incurred in the first generations even though the complexity of the data has been changed. In a preferred embodiment, quantizing factors are selected from a preselected finite non-degenerative set of quantizing factors provided in the form of arrays of a periodic series of individual quantizer values, wherein a special numerical relationship is maintained between corresponding quantizer values in successive arrays. A different quantizing factor may be selected for each generation of compression/decompression as required by changing data complexity as when performing a layering process during the generations. In another embodiment, an over-quantizing factor is chosen large enough to compress the data to a greater extent than that required in the first generation, such that sufficient compression still is provided in subsequent generations even though the same quantizing factor is used while the complexity of the data is being changed. If for some reason the complexity of the data changes faster than expected, it is necessary to change the quantizing factor to fit the data into the allotted space. To moderate the associated increase in noise, the invention technique incudes a dither rounding process wherein a psuedo random number sequence in the range of 0...1.0 is selectively added as determined by a threshold. The invention also includes estimating a quantizing factor applied in a previous generation of image recording if this information is not available explicitly, by distinguishing the peaks and/or valleys of histogram. The amplitudes of the peaks and/or valleys represent the number of counts of the respective values of frequency coefficients to be quantized. <IMAGE></p> |
