Method and device for arithmetic encoding or arithmetic decoding

1. A method for arithmetic decoding of a current spectral coefficient using preceding spectral coefficients, said preceding spectral coefficients are already decoded and both, said preceding and current spectral coefficients, are comprised in one or more quantized spectra resulting from quantizing time-frequency-transform of video, audio or speech signal sample values, said method comprising using processing means for processing the preceding spectral coefficients, using the processed preceding spectral coefficients for determining a context class being one of at least two different context classes, using the determined context class and a mapping from the at least two different context classes to at least two different probability density functions for determining the probability density function, and arithmetic decoding the current spectral coefficient based on the determined probability density function wherein processing the preceding spectral coefficients comprises non-uniformly quantizing absolutes of the preceding spectral coefficients for use in determination of the context class.

2. The method of claim 1 , wherein processing the preceding spectral coefficients comprises a first quantizing step in which the absolutes of the preceding spectral coefficients are quantized according a first quantization scheme, a step of determining a variance of the absolutes of the preceding spectral coefficients quantized according the first quantization scheme, a step of using the determined variance for selecting one of at least two different nonlinear second quantization schemes, and a second quantizing step in which the absolutes of the preceding spectral coefficients quantized according the first quantization scheme are further quantized according to the selected nonlinear second quantization scheme.

3. The method of claim 2 , wherein the step of determining the variance of the absolutes of the preceding spectral coefficients quantized according the first quantization scheme comprises determining a sum of the absolutes of the preceding spectral coefficients quantized according the first quantization scheme and comparing the determined sum with at least one threshold.

4. The method of claim 1 , wherein processing either results in a first outcome or at least a different second outcome and determining the context class further comprises determining a number of preceding spectral coefficients being non-uniformly quantized to the first outcome, and using the determined number for determining the context class.

5. The method of claim 4 , wherein one of the preceding spectral coefficients is preferred over the preceding spectral coefficients remaining, said method further comprises using the non-uniformly quantization of the preferred one among the preceding spectral coefficient for determining the context class.

6. The method of claim 5 , wherein said preferred among the preceding spectral coefficients is comprised in a preceding spectrum and said current spectral coefficient is comprised in a different current spectrum, said preferred preceding and said current spectral coefficients being comprised at a same frequency in the respective spectrum.

7. The method of claim 6 , wherein said different current spectrum further comprises at least one of the remaining preceding spectral coefficients at a frequency lower than said same frequency.

8. A device for arithmetic encoding of a current spectral coefficient using preceding spectral coefficients, said preceding spectral coefficients are already encoded and both, said preceding and current spectral coefficients, are comprised in one or more quantized spectra resulting from quantizing time-frequency-transform of video, audio or speech signal sample values, said device comprising processing means for processing the preceding spectral coefficients, first means for determining a context class being one of at least two different context classes, said first means being adapted for using the processed preceding spectral coefficients for determining the context class, second means for determining the probability density function, said second means being adapted for using the determined context class and a mapping from the at least two different context classes to at least two different probability density functions for determining the probability density function, and an arithmetic encoder for arithmetic encoding the current spectral coefficient based on the determined probability density function wherein the processing means are adapted for non-uniformly quantizing absolutes of the preceding spectral coefficients for use in determination of the context class.

9. A device for arithmetic decoding of a current spectral coefficient using preceding spectral coefficients, said preceding spectral coefficients are already decoded and both, said preceding and current spectral coefficients, are comprised in one or more quantized spectra resulting from quantizing time-frequency-transform of video, audio or speech signal sample values, said device comprising processing means for processing the preceding spectral coefficients, first means for determining a context class being one of at least two different context classes, said first means being adapted for using the processed preceding spectral coefficients for determining the context class, second means for determining the probability density function, said second means being adapted for using the determined context class and a mapping from the at least two different context classes to at least two different probability density functions for determining the probability density function, and an arithmetic decoder for arithmetic decoding the current spectral coefficient based on the determined probability density function wherein the processing means are adapted for non-uniformly quantizing absolutes of the preceding spectral coefficients for use in determination of the context class.

10. A method for arithmetic encoding of a current spectral coefficient using preceding spectral coefficients, said preceding spectral coefficients are already encoded and both, said preceding and current spectral coefficients, are comprised in one or more quantized spectra resulting from quantizing time-frequency-transform of video, audio or speech signal sample values, said method comprising using processing means for processing the preceding spectral coefficients, using the processed preceding spectral coefficients for determining a context class being one of at least two different context classes, using the determined context class and a mapping from the at least two different context classes to at least two different probability density functions for determining the probability density function, and arithmetic encoding the current spectral coefficient based on the determined probability density function wherein processing the preceding spectral coefficients comprises non-uniformly quantizing absolutes of the preceding spectral coefficients for use in determination of the context class.

11. The method of claim 10 , wherein processing the preceding spectral coefficients comprises a first quantizing step in which the absolutes of the preceding spectral coefficients are quantized according a first quantization scheme, a step of determining a variance of the absolutes of the preceding spectral coefficients quantized according the first quantization scheme, a step of using the determined variance for selecting one of at least two different non-linear second quantization schemes, and a second quantizing step in which the absolutes of the preceding spectral coefficients quantized according the first quantization scheme are further quantized according to the selected non-linear second quantization scheme.

12. The method of claim 11 , wherein the step of determining the variance of the absolutes of the preceding spectral coefficients quantized according the first quantization scheme comprises determining a sum of the absolutes of the preceding spectral coefficients quantized according the first quantization scheme and comparing the determined sum with at least one threshold.

13. The method of claim 10 , wherein processing either results in a first outcome or at least a different second outcome and determining the context class further comprises determining a number of preceding spectral coefficients being non-uniformly quantized to the first outcome, and using the determined number for determining the context class.

14. The method of claim 13 wherein one of the preceding spectral coefficients is preferred over the preceding spectral coefficients remaining, said method further comprises using the non-uniformly quantization of the preferred one among the preceding spectral coefficient for determining the context class.

15. The method of claim 14 , wherein said preferred among the preceding spectral coefficients is comprised in a preceding spectrum and said current spectral coefficient is comprised in a different current spectrum, said preferred preceding and said current spectral coefficients being comprised at a same frequency in the respective spectrum.

16. The method of claim 15 , wherein said different current spectrum further comprises at least one of the remaining preceding spectral coefficients at a frequency lower than said same frequency.