Methods and systems for picture up-sampling

1. A method for direct picture up-sampling from a lower resolution picture to a higher resolution picture, said method comprising:

a) for each spatial offset in a plurality of spatial offsets, storing a set of filter coefficients associated with said each spatial offset;

b) in a video processor, wherein said video processor is a processor selected from the group consisting of a video encoder and a video decoder, for a sample position in said higher resolution picture, wherein said sample position is not associated with twice the resolution of said lower resolution picture, deriving a corresponding location in said lower resolution picture;

c) in said video processor, calculating a first position interpolation center in a first direction based on said corresponding location;

d) in said video processor, calculating a first position phase, wherein said first position phase is an offset of said corresponding location from said first position interpolation center in said first direction;

e) in said video processor, calculating a second position interpolation center in a second direction based on said corresponding location;

f) in said video processor, calculating a second position phase, wherein said second position phase is an offset of said corresponding location from said second position interpolation center in said second direction;

g) in said video processor, obtaining a first set of filter coefficients from said plurality of stored sets of filter coefficients, wherein said obtaining said first set of filter coefficients comprises obtaining said stored set of filter coefficients associated with said first position phase;

h) in said video processor, obtaining a second set of filter coefficients from said plurality of stored sets of filter coefficients, wherein said obtaining said second set of filter coefficients comprises obtaining said stored set of filter coefficients associated with said second position phase;

i) in said video processor, filtering said lower resolution picture in said first direction at said first interpolation center using a first filter comprising said first set of filter coefficients, thereby producing a first filtered picture value at said first position phase relative to said first interpolation center;

j) in said video processor, filtering a first-direction filtered picture comprising said first filtered picture value at said first position phase relative to said first interpolation center in said second direction at said second interpolation center using a second filter comprising said second set of filter coefficients, thereby directly producing a pixel value at said sample position in said higher resolution picture without formation of an intermediate resolution picture; and

k) wherein the spatial resolution of said higher resolution picture is greater than twice the spatial resolution of said lower resolution picture.

2. The method of claim 1 further comprising defining an interpolation resolution.

3. The method of claim 2 wherein said interpolation resolution is 1/16 (one-sixteenth) of an image sample.

4. The method of claim 1 wherein said obtaining of said first set of filter coefficients comprises accessing a look-up-table.

5. The method of claim 4 wherein said look-up-table comprises samples of a Lanczos-windowed sinc function.

6. The method of claim 1 wherein said obtaining of said second set of filter coefficients comprises accessing a look-up-table.

7. The method of claim 6 wherein said look-up-table comprises samples of a Lanczos-windowed sinc function.

8. A system for direct picture up-sampling from a lower resolution picture to a higher resolution picture, said system comprising:

a) a first storage for storing, for each spatial offset in a plurality of spatial offsets, a set of filter coefficients associated with a first direction, thereby storing a first plurality of sets of filter coefficients;

b) a second storage for storing, for said each spatial offset in said plurality of spatial offsets, a set of filter coefficients associated with a second direction, thereby storing a second plurality of sets of filter coefficients;

c) a relative-location deriver for deriving a lower resolution picture location corresponding to a sample position in said higher resolution picture, wherein said sample position, in said higher resolution picture, is not associated with twice the resolution of said lower resolution picture;

d) a first position-interpolation-center calculator for calculating a first position-interpolation center in said first direction based on said location;

e) a first position-phase calculator for calculating a first position phase, wherein said first position phase is an offset of said lower resolution picture location from said first position-interpolation center in said first direction;

f) a second position-interpolation-center calculator for calculating a second position-interpolation center in said second direction based on said location;

g) a second position-phase calculator for calculating a second position phase, wherein said second position phase is an offset of said lower resolution picture location from said second position-interpolation center in said second direction;

h) a first filter-coefficient selector for obtaining, from said first plurality of sets of filter coefficients associated with said first direction, a first set of filter coefficients, wherein said first set of filter coefficients are said stored set of filter coefficients associated with said first position phase;

i) a second filter-coefficient selector for obtaining, from said second plurality of sets of filter coefficients associated with said second direction, a second set of filter coefficients, wherein said second set of filter coefficients are said stored set of filter coefficients associated with said second position phase;

j) a first filter comprising said first set of filter coefficients for filtering said lower resolution picture in said first direction at said first interpolation center, thereby producing a first filtered picture value at said first position phase relative to said first interpolation center;

k) a second filter comprising said second set of filter coefficients for filtering a first-direction filtered picture comprising said first filtered picture value at said first position phase relative to said first interpolation center in said second direction at said second interpolation center, thereby producing said higher resolution picture without generating an intermediate resolution picture; and

l) wherein the spatial resolution of said higher resolution picture is greater than twice the spatial resolution of said lower resolution picture.

9. The system of claim 8 further comprising an interpolation resolution.

10. The system of claim 9 wherein said interpolation resolution is 1/16 (one-sixteenth) of an image sample.

11. The system of claim 8 wherein said obtaining of said first set of filter coefficients comprises a look-up-table.

12. The system of claim 11 wherein said look-up-table comprises samples of a Lanczos-windowed sinc function.

13. The system of claim 8 wherein said obtaining of said second set of filter coefficients comprises a look-up-table.

14. The system of claim 13 wherein said look-up-table comprises samples of a Lanczos-windowed sinc function.

15. The system of claim 8 further comprising an H.264/MPEG-4 AVC video codec.