Method and apparatus for reducing motion artifacts and noise in video image processing

• US 6,788,823 B2
• Filed: 10/26/2001
• Issued: 09/07/2004
• Est. Priority Date: 11/12/1998
• Status: Expired due to Term

• Current Assignee: GE Medical Systems Global Technology Company LLC (GE Healthcare Technologies, Inc.)
• Original Assignee: GE Medical Systems Global Technology Company LLC (GE Healthcare Technologies, Inc.)
• Inventors: Curtis, Steven E., Hanover, Barry K., Anderton, R. Larry, Allred, Joseph
• Primary Examiner(s): Lee, Thomas D
• Assistant Examiner(s): BRINICH, STEPHEN M
• Application Number:
  US09/999,697
• Publication Number:
  US 20020076117A1
• Time in Patent Office: 1,047 Days
• Field of Search: 382/260-269, 382/236
• US Class Current: 382/260
• CPC Class Codes: H04N 5/21 Circuitry for suppressing or minimising disturbance, e.g. moiré or halo

Abstract

A method and apparatus for reducing noise and motion artifacts in pixels of a processed or displayed video image by filtering pixel values of the video image based on a first frame having currently stored (filtered) pixel values and a second frame having recently captured but not yet filtered pixel values. The apparatus includes a spatial filter for computing a motion value of a pixel of interest by averaging difference values of selected pixels surrounding the pixel of interest. Also included is a filter function means for producing an output difference value of the pixel of interest based on the motion value and an adder for adding the output difference value to the first frame filtered pixel value of the pixel of interest. Thus, each pixel of the video image is filtered according to the amount of motion in the video image.

Claims

1. An apparatus for reducing noise and motion artifacts in pixels of a displayable video image by filtering pixel values of the pixels based on a first frame of video having filtered pixel values and a second frame of video having unfiltered pixel values, the apparatus comprising:

a subtractor to produce difference values by computing a difference between the filtered pixel values of the first frame and the unfiltered pixel values of the second frame;

a spatial filter, associated with the subtractor, to compute a motion value of a pixel of interest in the first frame of video by averaging the difference values of pre-selected pixels surrounding the pixel of interest; and

a temporal filter, coupled to the spatial filter, to receive the motion value and filter the pixel value of the pixel of interest according to the motion value, wherein the temporal filter further comprises;

a difference filter to produce an output difference value of the pixel of interest based on the motion value, wherein the difference filter comprises a multiplier or memory look-up table for multiplying the motion value of the pixel of interest with a fractional number determined from the motion value, wherein the multiplier produces the output difference value such that as the image motion increases the filter function multiplier decreases; and

an adder for adding the output difference value to the first frame filtered pixel value of the pixel of interest.

2. An apparatus as in claim 1 wherein the difference filter comprises a look-up table for producing the output difference value based on the difference value of the pixel of interest and the motion value of a group of pixels around the pixel of interest.

3. An apparatus as in claim 1 wherein the pre-selected pixels surrounding the pixel of interest comprise a group of pixel difference values about a pixel of interest selected from the group consisting of a 5.times.5 array of pixel difference values, a 3.times.3 array of pixel difference values, and an array shape optimized for the image resolution and image type for measuring localized image motion.

4. An apparatus as in claim 3 wherein the spatial filter averages the pixel difference values of pixels in a kernel array.

5. An apparatus as in claim 1 wherein the pixel of interest comprises a pixel of the first frame of video that is selected based on a scanning technique.

6. An apparatus as in claim 1 further comprising a control unit and a weighted averaging unit that receives a control signal from the control unit, wherein the control signal developed by the control unit selects different weights and ratios of the difference value and the motion value, both signals having been scaled to the same relative magnitude.

7. An apparatus as in claim 6 wherein the weighted averaging unit further comprises:

a first input for receiving the difference values produced by the subtractor;

a second input for receiving the motion value produced by the spatial filter; and

circuitry for calculating inputs and ratios for the temporal filter function based on both the difference value and the motion value from the spatial filter.

8. An apparatus as in claim 6 further comprising a filter function unit having an input wherein the filter function unit input receives a control signal produced by the control unit and the difference value as processed by the weighted average unit.

9. A method for reducing noise and motion artifacts in a video image by filtering pixel values of a first frame of video having filtered pixel values, and a second frame of video having unfiltered pixel values, the method comprising the steps of:

(a) selecting a pixel of interest from among pixels in the first frame of video;

(b) computing difference values of the pixel of interest and pixels surrounding the pixel of interest, wherein the difference values are the differences between the filtered pixel value of a pixel in the first frame and the unfiltered pixel value of the same pixel in the second frame;

(c) averaging the difference values of the pixels surrounding the pixel of interest to obtain a motion value; and

(d) temporally filtering the filtered pixel value of the pixel of interest according to the motion value and taking a weighted average of the difference values based on the motion value.

10. A method as in claim 9 further comprising the step of repeating steps (a), (b), (c), and (d) for each pixel of the second frame to produce a new frame of pixel data.

11. A method as in claim 9 wherein taking the weighted average includes (i) obtaining the average of the difference values surrounding the pixel of interest, (ii) calculating the difference value of the pixel of interest, and (iii) calculating a value that is some combination of (i) and (ii), based on the motion value.

12. A method as in claim 9 wherein step (d) further comprises the steps of producing an output difference value of the pixel of interest and adding the output difference value to the first frame filtered pixel value of the pixel of interest.

13. A method as in claim 12 wherein the step of producing the output difference value comprises the steps of:

creating a look-up table having tabulated data that corresponds to output difference values relating to a range of different motion values;

acquiring the motion value as input to the look-up table; and

producing the output difference value from the look-up table according to the input motion value.

14. A method as in claim 12 wherein the step of producing an output difference value comprises the step of selecting the difference value of the pixel of interest.

15. A method as in claim 12 wherein the step of producing an output difference value comprises the step of selecting the average difference value of the pixels surrounding the pixel of interest.

16. A method as in claim 12 wherein the step of producing an output difference value comprises the step of calculating a value based on a combination of the difference value of the pixel of interest and the average difference value of the pixels surrounding the pixel of interest.

17. A method for reducing noise and motion artifacts in a video image by filtering pixel values of a first frame of video having filtered pixel values, and a second frame of video having unfiltered pixel values, the method comprising the steps of:

(a) selecting a pixel of interest from among pixels in the first frame of video;

(b) computing difference values of the pixel of interest and pixels surrounding the pixel of interest, wherein each difference value is the difference between the filtered pixel value of a pixel in the first frame and the unfiltered pixel value of the corresponding pixel in the second frame;

(c) averaging the difference values for the pixels surrounding the pixel of interest to obtain a motion value; and

(d) temporally filtering the filtered pixel value of the pixel of interest according to the motion value by adding an output difference value to the pixel of interest, wherein the output difference value is based on a combination of the difference value of the pixel of interest and the average difference value of the pixels surrounding the pixel of interest and taking a weighted average of the difference values based on the motion value.

18. An apparatus for reducing noise and motion artifacts in pixels of a displayable video image by filtering pixel values of the pixels based on a first frame of video having filtered pixel values and a second frame of video having unfiltered pixel values, the apparatus comprising:

a subtractor to produce difference values by computing a difference between the filtered pixel values of the first frame and the unfiltered pixel values of the second frame;

a spatial filter, associated with the subtractor, to compute a motion value of a pixel of interest in the first frame of video by averaging the difference values of pre-selected pixels surrounding the pixel of interest;

a temporal filter, coupled to the spatial filter, to receive the motion value and filter the pixel value of the pixel of interest according to the motion value, wherein the temporal filter further comprises;

(a) a difference filter to produce an output difference value of the pixel of interest based on the motion value; and

(b) an adder for adding the output difference value to the first frame filtered pixel value of the pixel of interest; and

a control unit and a weighted averaging unit that receives a control signal from the control unit, wherein the control signal developed by the control unit selects different weights and ratios of the difference value and the motion value, both signals having been scaled to the same relative magnitude.

19. An apparatus as in claim 18 further comprising a filter function unit having an input wherein the filter function unit receives a control signal produced by the control unit and the difference value as processed by the weighted average unit, and

wherein the weighted averaging unit further comprises: a first input for receiving the difference values produced by the subtractor;

a second input for receiving the motion value produced by the spatial filter; and

circuitry for calculating inputs and ratios for the temporal filter function based on both the difference value and the motion value from the spatial filter.