Still pixel detection using multiple windows and thresholds
A method and system for performing still pixel detection is presented. In accordance with the present invention, still pixel detection can use multiple thresholds and multiple windows of pixels. In a particular embodiment of the present invention, a still pixel detection test is performed using a first window. If the first window test determines the pixel is a still pixel then the pixel is classified as a still pixel. If the first window test determines the pixel is not a still pixel, a still pixel detection test is performed using a second window. If the second window test determines the pixel is a still pixel then the pixel is classified as a still pixel. Otherwise, the pixel is not classified as a still pixel. Some embodiment of the present invention the still pixel tests use multiple thresholds to determine if a pixel is a still pixel.
1. A method of detecting still pixels in a video stream having a plurality of fields including an early field having an early current pixel and a late field having a late current pixel, the method comprising:
defining a first window of pixels of the late field with a noise reduction unit, wherein the first window includes the late current pixel;
performing a first window still pixel test with the noise reduction unit using the pixels of the first window; by
calculating a pixel pair difference for each pixel in the first window to generate a plurality of pixel pair differences; and
comparing an absolute value of each pixel pair difference with a difference threshold, wherein the late current pixel fails the first window still pixel test when the absolute value of any pixel pair difference of the first window is greater than the difference threshold;
defining a second window of pixels of the late field with the noise reduction unit, wherein the second window includes the late current pixel; and
performing a second window still pixel test with the noise reduction unit using the pixels of the second window.
2. The method of claim 1 , wherein the late current pixel is a still pixel when the late current pixel passes the first window still pixel test or the second window still pixel test.
3. The method of claim 1 , wherein the pixels of the first window are all from a single scan line of the late field.
4. The method of claim 3 , wherein the pixels of the first window are sequential pixels on the single scan line.
5. The method of claim 4 , wherein the late current pixel comes before the other pixels of the first window.
6. The method of claim 5 , wherein the late current pixel comes after the other pixels of the first window.
7. The method of claim 1 , wherein performing a first window still pixel test using the pixels of the first window comprises:
summing the absolute value of each pixel pair difference that is greater than a summation threshold to create a correlation sum of the first window;
comparing the correlation sum of the first window with a correlation threshold, wherein the late current pixel passes the first window still pixel test when the correlation sum divided by a size of the first window is less than or equal to the correlation threshold.
8. The method of claim 7 , further comprising adaptively updating the correlation threshold.
9. The method of claim 1 , wherein calculating a pixel pair difference for each pixel in the first window to generate a plurality of pixel pair differences comprises subtracting a luminance value of a pixel in the first window from a luminance value of a corresponding pixel in the early field.
10. The method of claim 1 , wherein calculating a pixel pair difference for each pixel in the first window to generate a plurality of pixel pair differences comprises subtracting a chrominance value of a pixel in the first window from a chrominance value of a corresponding pixel in the early field.
11. The method of claim 1 , wherein performing a second window still pixel test using the pixels of the second window comprises:
calculating a pixel pair difference for each pixel in the second window to generate a plurality of pixel pair differences; and
comparing an absolute value of each pixel pair difference with a difference threshold, wherein the late current pixel fails the second window still pixel test when the absolute value of any pixel pair difference of the second window is greater than the difference threshold.
12. The method of claim 11 , wherein performing a second window still pixel test using the pixels of the second window comprises:
summing the absolute value of each pixel pair difference that is greater than a summation threshold to create a correlation sum of the second window;
comparing the correlation sum of the second window with a correlation threshold, wherein the late current pixel passes the second window still pixel test when the correlation sum divided by a size of the second window is less than or equal to the correlation threshold.
13. The method of claim 12 , further comprising adaptively updating the correlation threshold.
14. A method of detecting still pixels in a video stream having a plurality of fields including an early field having an early current pixel and a late field having a late current pixel, the method comprising:
defining a first window containing a first plurality of pixels of the late field with a noise reduction unit, wherein the first plurality of pixels includes the late current pixel;
calculating a pixel pair difference for each pixel in the first window to generate a plurality of pixel pair differences with the noise reduction unit;
summing the absolute value of each pixel pair difference that is greater than a summation threshold to create a correlation sum of the first window with the noise reduction unit;
comparing the correlation sum of the first window with a correlation threshold with the noise reduction unit, wherein the late current pixel is classified as a still pixel when the correlation sum divided by a size of the first window is less than or equal to the correlation threshold.
15. The method of claim 14 , further comprising adaptively updating the correlation threshold.
16. The method of claim 14 , further comprising comparing an absolute value of each pixel pair difference with a difference threshold, wherein the late current pixel is classified as a non-still pixel when the absolute value of any pixel pair difference of the first window is greater than the difference threshold.
17. The method of claim 14 , wherein calculating a pixel pair difference for each pixel in the first window to generate a plurality of pixel pair differences comprises subtracting a luminance value of a pixel in the first window from a luminance value of a corresponding pixel in the early field.
18. The method of claim 14 , wherein calculating a pixel pair difference for each pixel in the first window to generate a plurality of pixel pair differences comprises subtracting a chrominance value of a pixel in the first window from a chrominance value of a corresponding pixel in the early field.
19. The method of claim 14 , wherein the pixels of the first window are all from a single scan line of the late field.
20. The method of claim 19 , wherein the pixels of the first window are sequential pixels on the single scan line.
21. The method of claim 20 , wherein the late current pixel comes before the other pixels of the first window.
22. The method of claim 20 , wherein the late current pixel comes after the other pixels of the first window.
23. A method of detecting still pixels in a video stream having a plurality of fields including an early field having an early current pixel and a late field having a late current pixel, the method comprising:
defining a first window containing a first plurality of pixels of the late field with a noise reduction unit, wherein the first plurality of pixels includes the late current pixel;
calculating a pixel pair difference for each pixel in the first window to generate a plurality of pixel pair differences with the noise reduction unit;
comparing an absolute value of each pixel pair difference with a difference threshold with the noise reduction unit, wherein the late current pixel is classified as a non-still pixel when the absolute value of any pixel pair difference of the first window is greater than the difference threshold;
summing the absolute value of each pixel pair difference to create a correlation sum of the first window with the noise reduction unit;
comparing the correlation sum of the first window with a correlation threshold with the noise reduction unit, wherein the late current pixel is classified as a still pixel when the correlation sum divided by a size of the first window is less than or equal to the correlation threshold.
24. The method of claim 23 , further comprising adaptively updating the correlation threshold.
25. The method of claim 23 , wherein calculating a pixel pair difference for each pixel in the first window to generate a plurality of pixel pair differences comprises subtracting a luminance value of a pixel in the first window from a luminance value of a corresponding pixel in the early field.
26. The method of claim 23 , wherein calculating a pixel pair difference for each pixel in the first window to generate a plurality of pixel pair differences comprises subtracting a chrominance value of a pixel in the first window from a chrominance value of a corresponding pixel in the early field.
27. The method of claim 23 , wherein the pixels of the first window are all from a single scan line of the late field.
28. The method of claim 27 , wherein the pixels of the first window are sequential pixels on the single scan line.
29. The method of claim 28 , wherein the late current pixel comes before the other pixels of the first window.
30. The method of claim 28 , wherein the late current pixel comes after the other pixels of the first window.
31. A system of detecting still pixels in a video stream having a plurality of fields including an early field having an early current pixel and a late field having a late current pixel, the system comprising:
means for defining a first window of pixels of the late field, wherein the first window includes the late current pixel;
means for performing a first window still pixel test using the pixels of the first window; wherein the means for performing a first window still pixel test includes
means for calculating a pixel pair difference for each pixel in the first window to generate a plurality of pixel pair differences; and
means for comparing an absolute value of each pixel pair difference with a difference threshold, wherein the late current pixel fails the first window still pixel test when the absolute value of any pixel pair difference of the first window is greater than the difference threshold;
means for defining a second window of pixels of the late field, wherein the second window includes the late current pixel; and
means for performing a second window still pixel test using the pixels of the second window.
32. The system of claim 31 , wherein the means for late current pixel is a still pixel when the late current pixel passes the first window still pixel test or the second window still pixel test.
33. The system of claim 31 , wherein the means for performing a first window still pixel test using the pixels of the first window comprises:
means for summing the absolute value of each pixel pair difference that is greater than a summation threshold to create a correlation sum of the first window;
means for comparing the correlation sum of the first window with a correlation threshold, wherein the late current pixel passes the first window still pixel test when the correlation sum divided by a size of the first window is less than or equal to the correlation threshold.
34. The system of claim 31 , further comprising means for adaptively updating the correlation threshold.
35. The system of claim 31 , wherein means for calculating a pixel pair difference for each pixel in the first window to generate a plurality of pixel pair differences comprises means for subtracting a luminance value of a pixel in the first window from a luminance value of a corresponding pixel in the early field.
36. The system of claim 31 , wherein the means for calculating a pixel pair difference for each pixel in the first window to generate a plurality of pixel pair differences comprises means for subtracting a chrominance value of a pixel in the first window from a chrominance value of a corresponding pixel in the early field.
37. A system of detecting still pixels in a video stream having a plurality of fields including an early field having an early current pixel and a late field having a late current pixel, the system comprising:
means for defining a first window containing a first plurality of pixels of the late field, wherein the first plurality of pixels includes the late current pixel;
means for calculating a pixel pair difference for each pixel in the first window to generate a plurality of pixel pair differences;
means for summing the absolute value of each pixel pair difference that is greater than a summation threshold to create a correlation sum of the first window;
means for comparing the correlation sum of the first window with a correlation threshold, wherein the late current pixel is classified as a still pixel when the correlation sum divided by a size of the first window is less than or equal to the correlation threshold.
38. The system of claim 37 , further comprising means for adaptively updating the correlation threshold.
39. The system of claim 37 , further comprising means for comparing an absolute value of each pixel pair difference with a difference threshold, wherein the late current pixel is classified as a non-still pixel when the absolute value of any pixel pair difference of the first window is greater than the difference threshold.
40. The system of claim 37 , wherein the means for calculating a pixel pair difference for each pixel in the first window to generate a plurality of pixel pair differences comprises means for subtracting a luminance value of a pixel in the first window from a luminance value of a corresponding pixel in the early field.
41. The system of claim 37 , wherein the means for calculating a pixel pair difference for each pixel in the first window to generate a plurality of pixel pair differences comprises means for subtracting a chrominance value of a pixel in the first window from a chrominance value of a corresponding pixel in the early field.
42. A system of detecting still pixels in a video stream having a plurality of fields including an early field having an early current pixel and a late field having a late current pixel, the system comprising:
means for defining a first window containing a first plurality of pixels of the late field, wherein the first plurality of pixels includes the late current pixel;
means for calculating a pixel pair difference for each pixel in the first window to generate a plurality of pixel pair differences;
means for comparing an absolute value of each pixel pair difference with a difference threshold, wherein the current pixel is classified as a non-still pixel when the absolute value of any pixel pair difference of the first window is greater than the difference threshold;
means for summing the absolute value of each pixel pair difference to create a correlation sum of the first window;
means for comparing the correlation sum of the first window with a correlation threshold, wherein the late current pixel is classified as a still pixel when the correlation sum divided by a size of the first window is less than or equal to the correlation threshold.
43. The system of claim 42 , further comprising means for adaptively updating the correlation threshold.
44. The system of claim 42 , wherein the means for calculating a pixel pair difference for each pixel in the first window to generate a plurality of pixel pair differences comprises means for subtracting a luminance value of a pixel in the first window from a luminance value of a corresponding pixel in the early field.
45. The system of claim 42 , wherein the means for calculating a pixel pair difference for each pixel in the first window to generate a plurality of pixel pair differences comprises means for subtracting a chrominance value of a pixel in the first window from a chrominance value of a corresponding pixel in the early field.