Method for transforming a digital signal from the time domain into the frequency domain and vice versa

1. A method carried out by an audio, image or video processing device for transforming a digital signal from the time domain into the frequency domain and vice versa using a transformation function comprising a transformation matrix, the digital signal being an audio signal, an image signal or a video signal, the digital signal comprising data symbols which are grouped into a plurality of blocks, each block comprising a predefined number of the data symbols, the method comprising:

transforming two blocks of the digital signal by one transforming element, wherein the transforming element corresponds to a block-diagonal matrix comprising two sub-matrices, wherein each sub-matrix comprises the transformation matrix and the transforming element comprises a plurality of lifting stages and wherein each lifting stage comprises the processing of blocks of the digital signal by an auxiliary transformation and by a rounding unit, wherein one or more of the lifting stages comprises the transformation matrix.

2. The method of claim 1 , wherein the transformation function is a DCT-I transformation function, DCT-IV transformation function, DFT-I transformation function, DFT-IV transformation function, DST-I transformation function, DST-IV transformation function, DWT-I transformation function or DWT-IV transformation function.

3. The method of claim 2 , wherein each lifting stage corresponds to a lifting matrix, wherein the lifting matrix is a block-triangular matrix comprising four sub-matrices with two invertible integer matrices as two of the sub-matrices in one diagonal, and with the transformation matrix and a zero as the other two of the sub-matrices in the other diagonal.

4. The method of claim 3 , wherein the invertible integer matrices in each lifting matrix are identity matrices or negative identity matrices.

5. The method of claim 1 , wherein each lifting stage corresponds to a lifting matrix, wherein the lifting matrix is a block-triangular matrix comprising four sub-matrices with two invertible integer matrices as two of the sub-matrices in one diagonal, and with the transformation matrix and a zero as the other two of the sub-matrices in the other diagonal.

6. The method of claim 5 , wherein the invertible integer matrices in each lifting matrix are identity matrices or negative identity matrices.

7. The method of claim 1 , wherein the transforming element comprises three lifting stages.

8. A device for transforming a digital signal from the time domain into the frequency domain and vice versa using a transformation function comprising a transformation matrix, the digital signal comprising data symbols and being divided into a plurality of blocks, each block comprising a predefined number of the data symbols, the device comprising:

a transformation unit for transforming two blocks of the digital signal by one transforming element, wherein the transforming element corresponds to a block-diagonal matrix comprising two sub-matrices, wherein each sub-block comprises the transformation matrix and the transforming element comprises a plurality of lifting stages, wherein one or more of the lifting stages comprises the transformation matrix.

9. The device of claim 8 , wherein the transformation unit comprises auxiliary transformation units for each lifting stage for processing the blocks of the digital signal.

10. The device of one of the claims 9 , wherein the transformation unit comprises rounding units for each lifting stage for processing the blocks of the digital signal.

11. The device of one of the claims 8 , wherein the transformation unit comprises rounding units for each lifting stage for processing the blocks of the digital signal.

12. The device of claim 8 , wherein the transformation unit comprises:

a modified discrete cosine transform device coupled to receive the a plurality of data blocks and configured to domain transform each data block into MDCT coefficients;

a quantizer coupled to receive each of the MDCT coefficients, the quantizer operable to produce, in response, quantized MDCT coefficients;

a bit stream encoder coupled to receive the quantized MDCT coefficients, the bit stream producing, in response, a perceptually coded bit stream;

an inverse quantizer coupled to receive the quantized MDCT coefficients, the inverse quantizer operable to restore the MDCT coefficients to an non-quantized state; and

a rounding unit coupled to receive the restored MDCT coefficients and operable to produce integer value MDCT coefficients.

13. The device of claim 12 , wherein the transformation unit further comprises:

an integer modified discrete cosine transform device coupled to receive the data blocks and operable to produce, in response, IntMDCT coefficients;

means for computing the difference between respective IntMDCT coefficients and integer value MDCT coefficients to produce respective residual MDCT coefficients; and

an entropy coder coupled to receive the residual MDCT coefficients and operable to generate, in response, a lossless enhancement bitstream.

14. The device of claim 13 , wherein the transformation unit further comprises:

a bitstream decoder coupled to receive the perceptually coded bitstream and operable to output, in response, a decoded bitstream;

an inverse quantizer coupled to receive the decoded bitstream and to produce, in response, restored MDCT coefficients;

a rounding unit coupled to receive the restored MDCT coefficients and operable to round each MDCT coefficient to an integer value; and

an inverse MDCT device coupled to receive the restored MDCT stream, and to produce in generate in response, a reconstructed copy of the perceptually coded signal.

15. The device of claim 14 , wherein the transformation unit comprises:

an entropy decoder coupled to receive the lossless bit stream and operable to generate, in response, residual IntMDCT coefficients;

means for adding the residual IntMDCT coefficients to the integer value MDCT coefficients to produce IntMDCT coefficients; and

an inverse IntMDCT device coupled to receive the summation of the integer value MDCT coefficients and the IntMDCT coefficients to produce a reconstructed copy of the losslessly coded audio signal.

16. A computer readable medium having a program recorded thereon, wherein the program is adapted to make a computer perform a method for transforming a digital signal from the time domain into the frequency domain and vice versa using a transformation function comprising a transformation matrix, the digital signal being an audio signal, an image signal or a video signal, the digital signal comprising data symbols and being divided into a plurality of blocks, each block comprising a predefined number of the data symbols, the computer readable medium comprising:

code for transforming two blocks of the digital signal by one transforming element, wherein the transforming element corresponds to a block-diagonal matrix comprising two sub-matrices, wherein each sub-block comprises the transformation matrix and the transforming element comprises a plurality of lifting stages and wherein each lifting stage comprises the processing of sub-blocks of the digital signal by an auxiliary transformation and by a rounding unit, wherein one or more of the lifting stages comprises the transformation matrix.