Noise estimation and reduction apparatus for video signal processing
First Claim
Patent Images
1. Apparatus for compressing an image representative video signal containing pixel data comprising:
- means for estimating noise in said video signal and providing an output;
means for generating residues having lower and higher amplitude components, said residues representing differences of pixel values between predicted pixel values and real pixel values of a current frame of said video signal being compressed;
nonlinear processing means, coupled to said generating means, for attenuating lower amplitude residues greater than higher amplitude residues and providing processed residues at an output, wherein a transfer function of said nonlinear processing means is responsive to said noise estimate; and
transform means for transforming said processed residues and providing a compressed video data output.
2 Assignments
0 Petitions
Accused Products
Abstract
Video signal compression apparatus generates residues representing pixel value differences between predicted and real pixel values of a current frame of a video signal. Noise reduction circuitry, in the form of nonlinear processing functions, attenuates lower amplitude residues greater than higher amplitude residues and is responsive to a noise estimate. The processed residues are transformed to provide a compressed video data output. The nonlinear processing functions attenuate noise and reduce image distortion.
55 Citations
21 Claims
-
1. Apparatus for compressing an image representative video signal containing pixel data comprising:
-
means for estimating noise in said video signal and providing an output;
means for generating residues having lower and higher amplitude components, said residues representing differences of pixel values between predicted pixel values and real pixel values of a current frame of said video signal being compressed;
nonlinear processing means, coupled to said generating means, for attenuating lower amplitude residues greater than higher amplitude residues and providing processed residues at an output, wherein a transfer function of said nonlinear processing means is responsive to said noise estimate; and
transform means for transforming said processed residues and providing a compressed video data output. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15)
said noise estimate is produced as a function of pixel prediction error. -
3. The apparatus set forth in claim 2 wherein
said noise estimate is produced when motion in an image area is substantially zero. -
4. The apparatus set forth in claim 1 wherein
said transfer function responds to said noise estimate at variable time intervals. -
5. The apparatus set forth in claim 1 further including
a filter with a variable time constant for temporally filtering said noise estimate and wherein said transfer function of said nonlinear processing means is responsive to said temporally filtered noise estimate. -
6. The apparatus set forth in claim 5 wherein
said variable time constant filter provides a longer (slower) filter time constant for increasing noise estimate values and a shorter (faster) filter time constant for reducing noise estimate values. -
7. The apparatus set forth in claim 1 further including
a filter for spatially filtering said noise estimate; - and wherein said transfer function of said nonlinear processing means is responsive to said spatially filtered noise estimate.
-
8. The apparatus set forth in claim 1 wherein
said transfer function is a coring function with a coring window, said window having a width w for attenuating said lower amplitude residues, and w is responsive to said noise estimate. -
9. The apparatus set forth in claim 1 wherein
said apparatus processes said pixel data on a block by block basis and the degree of coring within a coring function is responsive to motion in a pixel block. -
10. The apparatus set forth in claim 1 wherein
said apparatus processes said pixel data on a block by block basis and said a coring function is applied only to residues corresponding to pixel blocks exhibiting image motion below a predetermined threshold. -
11. The apparatus set forth in claim 1 wherein
said noise estimate is inversely related to the degree of motion in an area of an image. -
12. The apparatus set forth in claim 1 wherein
said nonlinear processing means provides a plurality of selectable transfer functions including a linear transfer function. -
13. The apparatus set forth in claim 1 wherein
said transfer function is a coring function with a coring window and said coring function is a function of a change in image content of said current frame. -
14. The apparatus set forth in claim 1 wherein
said transfer function is a coring function with a coring window and said coring function substantially comprises an identity function outside said coring window. -
15. The apparatus set forth in claim 1 wherein
said transfer function is a coring function with a coring window and said coring function substantially comprises a convex-downward and continuously increasing function inside said window.
-
-
16. Apparatus for filtering noise in a signal comprising:
-
an input processor for receiving and processing said signal to provide an output suitable for filtering; and
a nonlinear processing means, coupled to said input processor, for attenuating lower amplitude components of said processed output more than higher amplitude components and for providing a filtered output, wherein the transfer function of said nonlinear processing means is in the class of coring functions, having a coring window, that substantially provide;
(a) an identity function, in which the output is equal to the input, outside said coring window; and
(b) a convex-downward and continuously increasing function inside said coring window. - View Dependent Claims (17, 18, 19, 20)
said transfer function is adaptively selected from a plurality of coring functions that include a transfer function in said class. -
18. The apparatus set forth in claim 17 wherein
said transfer function is selected based on an estimate of noise in said video signal. -
19. The apparatus set forth in claim 16 wherein
said transfer function is a piece-wise linear transfer function. -
20. The apparatus set forth in claim 16 wherein
said transfer function is represented by (f(x)) and inside said coring window is of the form -
( x ) = W ( x W ) n where n is an integer and W is a coring window width for attenuating said lower amplitude components and the magnitude of x is less than or equal to W.
-
-
-
21. Video signal compression apparatus comprising:
-
means for estimating noise in a video signal and providing an output;
nonlinear processing means for adaptively filtering said video signal with a coring function and providing a filtered video output signal, said coring function substantially providing a convex-downward and continuously increasing function inside a coring window of said coring function, wherein said coring function is responsive to said noise estimate; and
transform means for compressing said filtered video output signal to provide a compressed video data output.
-
Specification