Downsizing an encoded image

1. A method of downsizing an input disjoint block level encoded image, comprising:

Calculating, by a Discrete Cosine Transform (DCT) domain processor, a DCT downsize ratio for downsizing the input image in a DCT domain according to a target downsize ratio and according to a size of a DCT transform length associated with the input image;

Adapting, by the DCT domain processor, an I-DCT according to the DCT domain downsize ratios, including configuring a DCT anti-aliasing filter (“AAF”) according to the target downsize ratio, and applying the DCT AAF to DCT coefficients corresponding to the input image;

performing, by the DCT domain processor, the adapted I-DCT;

providing, by the DCT domain processor, an intermediate image as output of a DCT domain process; and

applying, by a pixel domain processor, a pixel domain interpolation to the intermediate image according to dimensions of the intermediate image and according to dimensions of the target image.

2. The method according to claim 1 , wherein said calculating comprises computing the DCT domain downsize ratio based on a length of the DCT transform and based on the target downsize ratio, for each dimension of the input image.

3. The method according to claim 1 , wherein said adapting comprises adapting one or both of a horizontal inverse transform length and a vertical inverse transform length, according to the calculated DCT domain downsize ratio.

4. The method according to claim 1 , wherein said adapting comprises reducing one or both of a horizontal inverse transform length and a vertical inverse transform length, according to the calculated DCT domain downsize ratios.

5. The method according to claim 3 , further comprising configuring a DCT AAF according to the target downsize ratio, and wherein said adapting further comprises applying the DCT AAF to DCT coefficients corresponding to the input image prior to said performing the adapted I-DCT.

6. The method according to claim 1 , further comprising:

after said performing the adapted I-DCT, performing an additional DCT;

configuring a DCT AAF according to the target downsize ratio and according to dimensions of the image after the adapted I-DCT;

applying the DCT AAF to DCT coefficients corresponding to the image after the adapted I-DCT, giving rise to filtered DCT coefficients; and

performing I-DCT over the filtered DCT coefficients giving rise to the intermediate image.

7. The method according to claim 2 , wherein said calculating a DCT domain downsize ratio includes:

computing a ceiling expression over a ratio among the DCT transform length associated with the input image and the target downsize ratio, for each dimension of the input image, and

computing a ratio between the DCT transform length associated with the input image and the ceiling expression, for each dimension of the input image.

8. The method according to claim 1 , wherein when the target downsize ratio received as input is larger than two implementing a multi-iteration DCT downsizing process comprising:

said calculating a DCT domain downsize ratio comprises setting the DCT domain downsize ratio to two for one or both dimensions of the input image;

said adapting an I-DCT comprises reducing one or both of a horizontal I-DCT transform length and a vertical I-DCT transform length by a factor of two according to the DCT domain downsize ratio;

said performing the adapted I-DCT comprises dividing the target downsize ratio by two for one or both dimensions of the input image; and

repeating said calculating, said adapting and said performing for one or both dimensions of the input image as long as the target downsize ratio following a previous iteration of the process is larger than two for one or both dimensions of the input image, respectively.

9. The method of claim 8 , further comprising:

after said performing the adapted I-DCT of a final iteration of said multi-iteration DCT downsizing process, performing an additional DCT;

configuring a DCT AAF according to the target downsize ratio and according to dimensions of the image after the adapted I-DCT of the final iteration of said multi-iteration DCT downsizing process;

applying the DCT AAF to DCT coefficients corresponding to the image after the adapted I-DCT of the final iteration of said multi-iteration DCT downsizing process, giving rise to filtered DCT coefficients; and

performing I-DCT over the filtered DCT coefficients giving rise to the intermediate image.

10. The method according to claim 8 , wherein as part of a final iteration of said multi-iteration DCT downsizing process, said adapting further comprises configuring a DCT AAF according to the target downsize ratio, and applying the DCT AAF prior to said performing the adapted I-DCT with respect to DCT coefficients corresponding to a result of a previous iteration of said multi-iteration DCT downsizing process.

11. The method according to claim 1 , wherein said applying a pixel domain interpolation to the intermediate image comprises computing a pixel domain downsize ratio according to the dimensions of the intermediate image and the target image dimensions or according to the DCT domain downsize ratio and the target downsize ratio.

12. The method according to claim 11 , wherein the pixel domain downsize ratio corresponds to the difference between the target downsize ratio and the size of the intermediate image.

13. The method according to claim 11 , wherein said applying a pixel domain interpolation to the intermediate image comprises configuring an adaptive support pixel domain interpolator according to the pixel domain downsize ratio and applying the adaptive support pixel domain interpolator to intermediate image.

14. The method according to claim 13 , wherein the adaptive support pixel domain interpolator is applied only to the Luma component of the intermediate image.

15. A system for downsizing an input disjoint block level encoded image, comprising:

a Discrete Cosine Transform (DCT) domain processor adapted to implement a DCT domain process, the DCT domain processor comprising:

a DCT downsize configurator adapted to calculate a DCT downsize ratio for downsizing the input image in a DCT domain according to a target downsize ratio and according to a size of a DCT transform length associated with the input image;

an I-DCT engine configured to adapt an I-DCT operation according to the DCT domain downsize ratio;

a DCT anti-aliasing filter (“AAF”) configured to apply a DCT AAF to DCT coefficients corresponding to the input image according to the target downsize ratio;

said DCT domain processor is adapted to provide an intermediate image as output of the DCT domain process; and

a pixel domain processor adapted to apply a pixel domain interpolation operation to the intermediate image according to dimensions of the intermediate image and according to dimensions of the target image.

16. The system according to claim 15 , wherein DCT downsize configurator is adapted to compute the DCT domain downsize ratio based on a length of the DCT transform and based on the target downsize ratio, for each dimension of the input image.

17. The system according to claim 15 , wherein said I-DCT engine is configured to adapt one or both of a horizontal inverse transform length and a vertical inverse DCT transform length, according to the calculated DCT domain downsize ratio.

18. The system according to claim 15 , wherein said I-DCT engine is adapted to reduce one or both of a horizontal inverse transform length and a vertical inverse transform length, according to the calculated DCT domain downsize ratios.

19. The system according to claim 17 , further comprising a DCT AAF configured to apply a DCT AAF according to the target downsize ratio, and wherein said DCT AAF is configured to apply the DCT AAF to DCT coefficients corresponding to the input image prior to the operation of said I-DCT engine.

20. The system according to claim 17 , wherein said DCT domain processor comprises a DCT AAF which is configured according to the target downsize ratio and according to dimensions of the image after the I-DCT operation, and said DCT AAF is adapted to apply a DCT AAF to DCT coefficients computed after said I-DCT operation giving rise to filtered DCT coefficients, and an additional I-DCT operation is applied to the filtered DCT coefficients, giving rise to the intermediate image.

21. The system according to claim 16 , wherein said DCT downsize configurator is adapted to:

compute a ceiling expression over a ratio among the DCT transform length associated with the input image and the target downsize ratio, for each dimension of the input image, and

compute a ratio between the DCT transform length associated with the input image and the ceiling expression, for each dimension of the input image.

22. The system according to claim 15 , wherein when the target downsize ratio received as input is larger than two, the DCT domain processor is adapted to implement a multi-iteration DCT downsizing process, and wherein:

said DCT downsize configurator is adapted to set the DCT domain downsize ratio to two for one or both dimensions of the input image, and accordingly dividing the target downsize ratio by two for one or both dimensions of the input image, respectively;

said I-DCT engine is configured to adapt an I-DCT operation according to the DCT domain downsize ratio;

said DCT downsize configurator and said I-DCT engine are configured to repeat a DCT downsizing process as long as the target downsize ratio following a previous iteration of the process is larger than two for one or both dimensions of the input image.

23. The system of claim 22 , further comprising:

said DCT domain processor is adapted to perform an additional DCT after the final iteration of said multi-iteration DCT downsizing process,

said DCT AAF is configured according to the target downsize ratio and according to dimensions of the image after the adapted I-DCT of the final iteration of said multi-iteration DCT downsizing process, and said DCT AAF is configured to applying the DCT AAF to DCT coefficients corresponding to the image after the adapted I-DCT of the final iteration of said multi-iteration DCT downsizing process, giving rise to filtered DCT coefficients; and

said DCT domain processor is adapted to perform I-DCT over the filtered DCT coefficients giving rise to the intermediate image.

24. The system according to claim 22 , wherein as part of a final iteration of said multi-iteration DCT downsizing process, said DCT AAF is configured according to the target downsize ratio, and said DCT AAF is configured to apply a DCT AAF prior to said I-DCT engine performing the adapted I-DCT with respect to DCT coefficients corresponding to a result of a previous iteration of said multi-iteration DCT downsizing process.

25. The system according to claim 15 , wherein said pixel domain processor is adapted to compute a pixel domain downsize ratio according to the dimensions of the intermediate image and the target image dimensions or according to the DCT domain downsize ratio and the target downsize ratio.

26. The system according to claim 25 , wherein the pixel domain downsize ratio corresponds to the difference between the target downsize ratio and the size of the intermediate image.

27. The system according to claim 25 , wherein said pixel domain processor is adapted to configure an adaptive support pixel domain interpolation algorithm according to the pixel domain downsize ratio, and is adapted to use the adaptive support pixel domain algorithm for downsizing the intermediate image.

28. The system according to claim 25 , wherein pixel domain processor includes a Luma pixel domain downsize module that is configured to apply a pixel domain interpolation operation to the Luminance component of the intermediate image, and wherein the Luma pixel domain downsize module is adapted to use an adaptive support pixel domain interpolation algorithm and is adapted to use the adaptive support pixel domain algorithm for downsizing the Luma component of the intermediate image.

29. A program storage device readable by machine, tangibly embodying a program of instructions executable by the machine to perform a method of downsizing an input disjoint block level encoded image, comprising:

calculating a Discrete Cosine Transform (DCT) downsize ratio for downsizing the input image in a DCT domain according to a target downsize ratio and according to a size of a DCT transform length associated with the input image;

adapting an I-DCT according to the DCT domain downsize ratios, including configuring a DCT anti-aliasing filter (“AAF”) according to the target downsize ratio, and applying the DCT AAF to DCT coefficients corresponding to the input image;

performing the adapted I-DCT;

providing an intermediate image as output of a DCT domain process; and

applying a pixel domain interpolation to the intermediate image according to dimensions of the intermediate image and according to dimensions of the target image.

30. A computer program product comprising a computer useable medium having computer readable program code embodied therein of downsizing an input disjoint block level encoded image, the computer program product comprising:

computer readable program code for causing the computer to calculate a Discrete Cosine Transform (DCT) downsize ratio for downsizing the input image in a DCT domain according to a target downsize ratio and according to a size of a DCT transform length associated with the input image;

computer readable program code for causing the computer to adapt an I-DCT according to the DCT domain downsize ratios, said adapting including configuring a DCT anti-aliasing filter (“AAF”) according to the target downsize ratio, and applying the DCT AAF to DCT coefficients corresponding to the input image;

computer readable program code for causing the computer to perform the adapted I-DCT

computer readable program code for causing the computer to provide an intermediate image as output of a DCT domain process; and

computer readable program code for causing the computer to apply a pixel domain interpolation to the intermediate image according to dimensions of the intermediate image and according to dimensions of the target image.