Method and apparatus for shift DCT-based sharpening of a video image

1. A method of processing a decoded digital image of an encoded digital image, wherein the decoded digital image is divided into a plurality of blocks, comprising:

shifting a block of the decoded digital image by x vertical pixels and y horizontal pixels to produce a shifted digital image block;

applying a discrete cosine transform (DCT) to the shifted digital image block to produce a DCT coefficient;

applying a non-linear transform to the DCT coefficient to produce a modified DCT coefficient without quantization information for the encoded digital image, the non-linear transform being configured to amplify the DCT coefficient by approximately a unity gain which varies as a function of a value of a parameter of non-DC DCT coefficients having frequencies near a low end and near a high end of a range of frequencies and a non-unity gain for non-DC DCT coefficients therebetween;

applying an inverse DCT to the modified DCT coefficient to produce a modified shifted digital image block;

shifting the modified shifted digital image block by −x vertical pixels and −y horizontal pixels to produce a realigned digital image block;

repeating the acts of shifting by x and y pixels, applying the DCT, applying the non-linear transform, applying the inverse DCT, and shifting by −x and −y pixels for a plurality of different values of x and y to produce additional realigned digital image blocks; and

combining the plurality of realigned digital image blocks to produce a processed digital image.

2. The method of claim 1 , further comprising storing predetermined gain values for the function in a lookup table (LUT).

3. The method of claim 2 , wherein applying the non-linear transform includes multiplying a non-DC DCT coefficient by a gain selected from the LUT based on a value of that non-DC DCT coefficient.

4. The method of claim 1 , wherein the function is configured to produce approximately the unity gain for the non-DC DCT coefficients corresponding to at least one of a noise signal and an overshoot signal.

5. The method of claim 4 , wherein a non-DC DCT coefficient represents an amplitude, and wherein the function is further configured to produce an increasing gain as the amplitude increases below a predetermined value, and to produce a decreasing gain as the amplitude increases above the predetermined value.

6. The method of claim 1 , further comprising performing the acts of shifting by x and y pixels, applying the DCT, applying the non-linear transform, applying the inverse DCT, and shifting by −x and −y pixels for the plurality of different values of x and y to a plurality of blocks substantially simultaneously.

7. The method of claim 1 , wherein combining the plurality of realigned digital image blocks comprises averaging the plurality of realigned digital image blocks.

8. A non-transitory computer readable medium comprising computer-executable instructions stored thereon that when executed on at least one processor perform the method according to claim 1 .

9. An image processing device, comprising:

at least one processor configured to:

receive a decoded digital image of an encoded digital image, wherein the decoded digital image is divided into a plurality of blocks;

shift a block of the decoded digital image by x vertical pixels and y horizontal pixels to produce a shifted digital image block;

apply a discrete cosine transform (DCT) to the shifted digital image block to produce a DCT coefficient;

apply a non-linear transform to the DCT coefficient to produce a modified DCT coefficient without quantization information for the encoded digital image, the non-linear transform being configured to amplify the DCT coefficient by approximately a unity gain which varies as a function of a value of a parameter of non-DC DCT coefficients having frequencies near a low end and near a high end of a range of frequencies and a non-unity gain for non-DC DCT coefficients therebetween;

apply an inverse DCT to the modified DCT coefficient to produce a modified shifted digital image block;

shift the modified shifted digital image block by −x vertical pixels and −y horizontal pixels to produce one of a plurality of realigned digital images;

repeat the acts of shifting by x and y pixels, applying the DCT, applying the non-linear transform, applying the inverse DCT, and shifting by −x and −y pixels for a plurality of different values of x and y to produce additional realigned digital image blocks;

combine the plurality of realigned digital image blocks to produce a processed digital image; and

output the processed digital image to a display device.

10. The image processing device of claim 9 , further comprising a lookup table (LUT) which stores pre-determined gain values for the function.

11. The image processing device of claim 10 , wherein applying the non-linear transform includes multiplying a non-DC DCT coefficient by a gain selected from the LUT based on a value of that non-DC DCT coefficient.

12. The image processing device of claim 9 , wherein the function is configured to produce approximately the unity gain for the non-DC DCT coefficients corresponding to at least one of a noise signal and an overshoot signal.

13. The image processing device of claim 12 , wherein a non-DC DCT coefficient represents an amplitude, and wherein the function is further configured to produce an increasing gain as the amplitude increases below a predetermined value, and to produce a decreasing gain as the amplitude increases above the predetermined value.

14. The image processing device of claim 9 , wherein the processor is further configured to perform the acts of shifting by x and y pixels, applying the DCT, applying the non-linear transform, applying the inverse DCT, and shifting by −x and −y pixels for the plurality of different values of x and y to a plurality of blocks substantially simultaneously.

15. The image processing device of claim 9 , wherein the processor is configured to average the plurality of realigned digital image blocks.

16. The image processing device of claim 9 , wherein the image processing device is configured to be integrated into a digital television.

17. The image processing device of claim 9 , wherein the image processing device is configured to be integrated into a mobile telephone.

18. The image processing device of claim 9 , wherein the image processing device is configured to be integrated into a set top box.

19. The image processing device of claim 9 , wherein the image processing device is configured to be integrated into an integrated circuit.