Methods and devices for data compression using a non-uniform reconstruction space

Abstract

Encoding and decoding methods are presented that use adaptive reconstruction levels. Reconstruction space parameters are developed by an encoder and inserted in the bitstream with the encoded video data. The reconstruction space parameter may include parameters from which the decoder can determine the levels for dequantization of the encoded video data. The reconstruction space parameters may include a first reconstruction level and a step size between other levels. The first reconstruction level may not equal the step size. In some cases, neither may be equal to the quantization step size used to quantize the transform domain coefficients.

What is claimed is: 
     
         1 . A method of decoding a bitstream of encoded data, the method comprising:
 extracting reconstruction space parameters from the bitstream, wherein the reconstruction space parameters identify a first reconstruction level and a reconstruction step size for further reconstruction levels, and wherein the first reconstruction level is not equal to the reconstruction step size;   decoding the encoded data to obtain a plurality of quantized transform coefficients; and   dequantizing each quantized transform coefficient to generate a reconstructed transform coefficient based on the first reconstruction level and the reconstruction step size.   
     
     
         2 . The method claimed in  claim 1 , wherein the reconstruction step size does not equal 2 m , where m is the number of bits of precision used for representing the reconstruction step size. 
     
     
         3 . The method claimed in  claim 1 , wherein dequantizing includes calculating a first level offset based upon the difference between the first reconstruction level and the reconstruction step size, and wherein the reconstructed transform coefficient is calculated from the first level offset plus the product of the quantized transform coefficient and the reconstruction step size. 
     
     
         4 . The method claimed in  claim 1 , wherein extracting includes extracting a first set of reconstruction space parameters for luma components and extracting a second set of reconstruction space parameter for chroma components, and wherein dequantizing includes generating reconstructed transform coefficients for luma values using the first set of reconstruction space parameters, and generating reconstructed transform coefficients for chroma values using the second set of reconstruction space parameters. 
     
     
         5 . The method claimed in  claim 1 , wherein extracting reconstruction space parameters from the bitstream comprises extracting reconstruction space delta indices, and reconstructing the reconstruction space parameters based on the reconstruction space delta indices and corresponding reconstruction space parameter predictions. 
     
     
         6 . The method claimed in  claim 5 , wherein the reconstructed transform coefficients are for a current slice and wherein the reconstruction space parameter predictions are not dependent upon data from another slice. 
     
     
         7 . A decoder for decoding a bitstream of encoded data, the decoder comprising:
 a processor;   a memory; and   a decoding application stored in memory and containing instructions for configuring the processor to
 extract reconstruction space parameters from the bitstream, wherein the reconstruction space parameters identify a first reconstruction level and a reconstruction step size for further reconstruction levels, and wherein the first reconstruction level is not equal to the reconstruction step size, 
 decode the encoded data to obtain a plurality of quantized transform coefficients, and 
 dequantize each quantized transform coefficient to generate a reconstructed transform coefficient based on the first reconstruction level and the reconstruction step size. 
   
     
     
         8 . The decoder claimed in  claim 7 , wherein the reconstruction step size does not equal 2 m , where m is the number of bits of precision used for representing the reconstruction step size. 
     
     
         9 . The decoder claimed in  claim 7 , wherein the processor is configured to dequantize by calculating a first level offset based upon the difference between the first reconstruction level and the reconstruction step size, and wherein the reconstructed transform coefficient is calculated from the first level offset plus the product of the quantized transform coefficient and the reconstruction step size. 
     
     
         10 . The decoder claimed in  claim 7 , wherein the processor is configured to extract by extracting a first set of reconstruction space parameters for luma components and extracting a second set of reconstruction space parameter for chroma components, and wherein the processor is configured to dequantize by generating reconstructed transform coefficients for luma values using the first set of reconstruction space parameters, and generating reconstructed transform coefficients for chroma values using the second set of reconstruction space parameters. 
     
     
         11 . The decoder claimed in  claim 7 , wherein the processor is configured to extract reconstruction space parameters from the bitstream by extracting reconstruction space delta indices, and reconstructing the reconstruction space parameters based on the reconstruction space delta indices and corresponding reconstruction space parameter predictions. 
     
     
         12 . The decoder claimed in  claim 11 , wherein the reconstructed transform coefficients are for a current slice and wherein the reconstruction space parameter predictions are not dependent upon data from another slice. 
     
     
         13 . A non-transitory processor-readable medium storing processor-executable instructions which, when executed, configures one or more processors to perform the method claimed in  claim 1 . 
     
     
         14 . A method for encoding data, the data including quantized transform domain coefficients, the method comprising:
 generating reconstruction space parameters based upon the quantized transform domain coefficients, wherein the reconstruction space parameters identify a first reconstruction level and a reconstruction step size for further reconstruction levels, and wherein the first reconstruction level is not equal to the reconstruction step size;   entropy encoding the quantized transform domain coefficients; and   generating a bitstream containing the encoded quantized transform domain coefficients and the reconstruction space parameters.   
     
     
         15 . The method claimed in  claim 14 , wherein the reconstruction step size does not match a quantization step size associated with a quantization parameter specified in the bitstream. 
     
     
         16 . The method claimed in  claim 14 , wherein generating includes determining the first reconstruction level using an average of the transform domain coefficients quantized to the first level. 
     
     
         17 . The method claimed in  claim 14 , wherein generating includes determining the reconstruction steps size using an average step size between the transform domain coefficients quantized to levels other than the first level. 
     
     
         18 . The method claimed in  claim 14 , wherein generating includes generating a first set of reconstruction space parameters for luma components and generating a second set of reconstruction space parameter for chroma components. 
     
     
         19 . The method claimed in  claim 14 , wherein generating includes predicting the reconstruction space parameters, determining an error in the prediction, quantizing the error, and encoding the quantized error, and wherein generating the bitstream includes inserting the encoded quantized error in a slice header. 
     
     
         20 . The method claimed in  claim 19 , wherein the quantized transform domain coefficients are for a current slice, and wherein predicting the reconstruction space parameters is not dependent upon data from another slice. 
     
     
         21 . An encoder for encoding transform domain coefficients for a group of coding units, the encoder comprising:
 a processor;   a memory storing the data points; and   an encoding application stored in memory and containing instructions for configuring the processor to
 generate reconstruction space parameters based upon the quantized transform domain coefficients, wherein the reconstruction space parameters identify a first reconstruction level and a reconstruction step size for further reconstruction levels, and wherein the first reconstruction level is not equal to the reconstruction step size, 
 entropy encode the quantized transform domain coefficients, and 
 generate a bitstream containing the encoded quantized transform domain coefficients and the reconstruction space parameters. 
   
     
     
         22 . The encoder claimed in  claim 21 , wherein the reconstruction step size does not match a quantization step size associated with a quantization parameter specified in the bitstream. 
     
     
         23 . The encoder claimed in  claim 21 , wherein the processor is configured to generate by determining the first reconstruction level using an average of the transform domain coefficients quantized to the first level. 
     
     
         24 . The encoder claimed in  claim 21 , wherein the processor is configured to generate by determining the reconstruction steps size using an average step size between the transform domain coefficients quantized to levels other than the first level. 
     
     
         25 . The encoder claimed in  claim 21 , wherein the processor is configured to generate by generating a first set of reconstruction space parameters for luma components and generating a second set of reconstruction space parameter for chroma components. 
     
     
         26 . The encoder claimed in  claim 21 , wherein the processor is configured to generate by predicting the reconstruction space parameters, determining an error in the prediction, quantizing the error, and encoding the quantized error, and wherein generating the bitstream includes inserting the encoded quantized error in a slice header. 
     
     
         27 . The encoder claimed in  claim 26 , wherein the quantized transform domain coefficients are for a current slice, and wherein the processor is configured to predict the reconstruction space parameters without using data from another slice. 
     
     
         28 . A non-transitory processor-readable medium storing processor-executable instructions which, when executed, configures one or more processors to perform the method claimed in  claim 14 .