System and method for reducing blocking artifacts and providing improved coding efficiency
A system and method of reducing blocking artifacts and providing enhanced coding efficiency based, as least in part, upon evaluation of relative smoothness of signals at a coding boundary. In some embodiments, a boundary threshold difference can be established beyond which it is determined that the difference is representative of a natural or intended boundary and filtering can be applied to those boundaries having differences below the boundary threshold difference. In some further embodiments, the ramps of the signal across the boundary can be evaluated to determine whether weak or strong filtering might be appropriate. In some further embodiments, weak filtering can be performed that reduces blocking artifacts, improves coding efficiency, but does not distort ramp signals across the boundary.
1. A method comprising:
acquiring first pixel information regarding pixels on a first side of a coding boundary; acquiring second pixel information regarding pixels on a second side of said coding boundary;
determining a strength of said boundary based at least in part on said first pixel information and said second pixel information;
determining a desired deblocking filter based, at least in part, on said boundary strength; and
using the determined deblocking filter to determine new first pixel information and new second pixel information based at least in part on said boundary strength.
2. The method of claim 1 wherein said step of using the determined deblocking filter to determine said new first pixel information and said new second pixel information is based is based upon a weak filter based, at least in part, on the difference of six times a difference between pixel values immediately adjacent to said boundary and two times a difference between pixel that are one pixel away from said boundary plus a fixed value.
3. The method of claim 2 wherein the difference of six times a difference between pixel values immediately adjacent to, said boundary and two times a difference between pixel that are one pixel away from said boundary plus a fixed value is right shifted by 4.
4. The method of claim 3 wherein said fixed value is 8.
5. The method of claim 2 wherein said step of using the determined deblocking filter to determine said new first pixel information and said new second pixel information is based, at least in part, on a filter having the form (1, 5, 3, −1)/8.
6. The method of claim 5 wherein said step of using the determined deblocking filter to determine said new first pixel information and said new second pixel information is based, at least in part, on a filter having the form (4, 9, 1, 3, −1)/16.
7. The method of claim 6 encoding at least one of said new first pixel information and said new second pixel information.
8. The method of claim 3 wherein said step of using the determined deblocking filter to determine said new first pixel information and said new second pixel information is based, at least in part, on a filter having the form (1, 5, 3, −1)/8.
9. The method of claim 8 wherein said step of using the determined deblocking filter to determine said new first pixel information and said new second pixel information is based, at least in part, on a filter having the form (4, 9, 1, 3, −1)/16.
10. The method of claim 9 encoding at least one of said new first pixel information and said new second pixel information.
11. The method of claim 4 wherein said step of using the determined deblocking filter to determine said new first pixel information and said new second pixel information is based, at least in part, on a filter having the form (1, 5, 3, −1)/8.
12. The method of claim 11 wherein said step of using the determined deblocking filter to determine said new first pixel information and said new second pixel information is based, at least in part, on a filter having the form (4, 9, 1, 3, −1)/16.
13. The method of claim 12 encoding at least one of said new first pixel information and said new second pixel information.
14. The method of claim 1 further comprising:
determining a first value of a first smoothness of said first pixels on said first side of said coding boundary;
determining a second value of a second smoothness of said second pixels on said second side of said coding boundary; and
defining a smoothness threshold;
wherein said step of using the determined deblocking filter to determine said new first pixel information and said new second pixel information is based, at least in part, on whether a difference between said first value and said second value is below a first predefined threshold.
15. The method of claim 14 wherein said step of using the determined deblocking filter to determine said new first pixel information and said new second pixel information is based, at least in part, on whether a difference between said first value and said second value is below a second predefined threshold.
16. The method of claim 15 encoding at least one of said new first pixel information and said new second pixel information.
17. The method of claim 1 where the desired deblocking filter is a ramp preserving and low pass filter.
18. The method of claim 1 where the desired deblocking filter operates to equalize a DC level in a narrow region across the coding boundary.