Estimating sample-domain distortion in the transform domain with rounding compensation
First Claim
1. An encoder comprising:
- a frequency transformer for applying a frequency transform to convert samples in a sample domain into transform coefficients in a transform domain;
a quantizer for quantizing the transform coefficients;
an entropy encoder for entropy encoding the quantized transform coefficients;
an inverse quantizer for de-quantizing the quantized transform coefficients;
a rounding compensation module for adding a rounding offset to the de-quantized transform coefficients; and
a controller for making encoding decisions after considering post-inverse frequency transform rounding effects on de-quantized transform coefficient values, wherein the controller includes a module for estimating pixel-domain distortion between original transform coefficients of a block and corresponding de-quantized transform coefficients of the block in the transform domain after the rounding compensation module adds the rounding offset by compensating for rounding in at least one of the corresponding de-quantized transform coefficients of the block and computing the estimated pixel-domain distortion using the original transform coefficients of the block, the at least one rounding-compensated coefficient and other coefficients of the de-quantized transform coefficients of the block.
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Abstract
Techniques and tools are described for compensating for rounding when estimating sample-domain distortion in the transform domain. For example, a video encoder estimates pixel-domain distortion in the transform domain for a block of transform coefficients after compensating for rounding in the DC coefficient of the block. In this way, the video encoder improves the accuracy of pixel-domain distortion estimation but retains the computational advantages of performing the estimation in the transform domain. Rounding compensation includes, for example, looking up an index (from a de-quantized transform coefficient) in a rounding offset table to determine a rounding offset, then adjusting the coefficient by the offset. Other techniques and tools described herein are directed to creating rounding offset tables and encoders that make encoding decisions after considering rounding effects that occur after an inverse frequency transform on de-quantized transform coefficient values.
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Citations
13 Claims
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1. An encoder comprising:
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a frequency transformer for applying a frequency transform to convert samples in a sample domain into transform coefficients in a transform domain; a quantizer for quantizing the transform coefficients; an entropy encoder for entropy encoding the quantized transform coefficients; an inverse quantizer for de-quantizing the quantized transform coefficients; a rounding compensation module for adding a rounding offset to the de-quantized transform coefficients; and a controller for making encoding decisions after considering post-inverse frequency transform rounding effects on de-quantized transform coefficient values, wherein the controller includes a module for estimating pixel-domain distortion between original transform coefficients of a block and corresponding de-quantized transform coefficients of the block in the transform domain after the rounding compensation module adds the rounding offset by compensating for rounding in at least one of the corresponding de-quantized transform coefficients of the block and computing the estimated pixel-domain distortion using the original transform coefficients of the block, the at least one rounding-compensated coefficient and other coefficients of the de-quantized transform coefficients of the block. - View Dependent Claims (2, 3, 4, 5)
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6. A method comprising:
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identifying a range of values for a de-quantized transform coefficient; computing a rounding offset for each of plural values in the range; identifying a periodic pattern in the computed rounding offsets; mapping representative values to corresponding rounding offsets in an offset table, wherein the corresponding rounding offsets show at least one period of the pattern without the offset table including all values in the range; and storing the offset table. - View Dependent Claims (7, 8, 9)
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10. A method comprising:
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identifying a range of values for a de-quantized transform coefficient; computing a rounding offset for plural values in the range; identifying a periodic pattern in the computed rounding offsets; and mapping representative values to corresponding rounding offsets in an offset table, wherein the corresponding rounding offsets show at least one period of the periodic pattern without the offset table including all values in the range. - View Dependent Claims (11, 12, 13)
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Specification