Electronic pan tilt zoom video camera with adaptive edge sharpening filter

• US 20030193584A1
• Filed: 04/29/2003
• Published: 10/16/2003
• Est. Priority Date: 08/27/1998
• Status: Active Grant

• Current Assignee: Daniel R. Phelps, Kenneth W. Malkin, Larry K. Baxter, Steven C. Taetzsch
• Original Assignee: Daniel R. Phelps, Kenneth W. Malkin, Larry K. Baxter, Steven C. Taetzsch
• Inventors: Baxter, Larry K., Taetzsch, Steven C., Malkin, Kenneth W., Phelps, Daniel R.
• Granted Patent: US 7,471,320 B2
• Time in Patent Office: Days
• US Class Current: 348/252
• CPC Class Codes: H04N 5/208 for compensating for attenuation of high frequency components, e.g. crispening, aperture distortion correction

Abstract

An apparatus and a method is provided for enhancing a digital image comprised of pixels by adaptively sharpening the pixels and clipping the numerical values of the sharpened edge pixels so as to fall between the smallest unsharpened numerical value and the greatest unsharpened numerical value, respectively, of the pixels located within a neighborhood of the pixels. Pixels which are located on an edge are sharpened in the direction perpendicular to the edge. The threshold value used to ascertain the presence of an edge and sharpening parameter used to control the degree of sharpening can be adaptively controlled by the zoom ratio. The apparatus of the invention is particularly suited for an electronic set-top video camera.

Claims

1. A method of enhancing a digital image, the image comprised of image pixels, each image pixel associated with a numerical value and residing in a neighborhood of image pixels, the method comprising the steps of:

locating edge pixels by applying an edge detector to the image pixel;

sharpening with a sharpening filter said edge pixel; and

limiting the sharpened numerical value of each sharpened edge pixel so as to fall between the smallest unsharpened numerical value and the greatest unsharpened numerical value of the pixels located in said neighborhood of pixels.

2. The method of claim 1, wherein said edge detector is capable of detecting for each edge pixel an edge orientation.

3. The method of claim 1, wherein said sharpening filter is adapted to receive a sharpening parameter for controlling the sharpening.

4. The method of claim 3, wherein said sharpening parameter is defined by at least one of imaging parameters and of environmental conditions.

5. The method of claim 4, wherein said imaging parameters are taken from the group consisting of scaling ratio of the image, pan position and tilt position.

6. The method of claim 4, wherein the environmental conditions comprise lighting conditions of an object being imaged.

7. The method of claim 2, wherein said edge pixels are sharpened only in a direction perpendicular to the edge orientation.

8. The method of claim 7, wherein said pixels which are located within said neighborhood of pixels and determine the smallest unsharpened numerical value and the greatest unsharpened numerical value are taken from those pixels in said neighborhood of pixels which are located in a direction perpendicular to the edge orientation.

9. The method of claim 1, wherein an edge pixel is sharpened only if an output value of said edge detector for said edge pixel exceeds a predetermined threshold value.

10. The method of claim 1, wherein image pixels which represent local minima or maxima within the neighborhood of pixels, are left unsharpened when the edge pixels are sharpened.

11. The method of claim 1, further comprising the step of scaling the image before the edge pixels are sharpened, wherein the scaled image pixel values are generated by a scaler.

12. A method of enhancing a digital image, the image comprised of image pixels, each image pixel associated with a numerical value and residing in a neighborhood of image pixels, the method comprising the steps of:

selecting image pixels to be sharpened;

selecting at least two neighborhood pixels in said neighborhood of each of said image pixels to be sharpened so that each image pixel to be sharpened has a numerical value which lies between the numerical values of said neighborhood pixels;

sharpening with a sharpening filter said image pixels to be sharpened; and

limiting the numerical value of each sharpened pixel so as to fall between the smallest unsharpened numerical value and the greatest unsharpened numerical value of the image pixels located in said neighborhood of pixels.

13. The method of claim 12, wherein an image pixel in said neighborhood of pixels is sharpened only if an output value of said edge detector for said image pixel exceeds a predetermined threshold value.

14. The method of claim 12, wherein said sharpening filter is adapted to receive a sharpening parameter for controlling the sharpening.

15. A device for enhancing a digital image comprised of image pixels, each image pixel associated with a numerical value and residing in a neighborhood of image pixels, the device comprising:

a sharpening filter for sharpening image pixels; and

a clipping device for limiting the numerical value of said sharpened pixels so as to fall between the smallest unsharpened numerical value and the greatest unsharpened numerical value of the image pixels located in said neighborhood of pixels.

16. The device of claim 15, further comprising an edge detector for locating edge pixels within said neighborhood of image pixels.

17. The device of claim 16, wherein said edge detector is capable of detecting an edge orientation of the edge pixels.

18. The device of claim 15, wherein said sharpening filter is adapted to receive a sharpening parameter for controlling the sharpening.

19. The device of claim 18, wherein said sharpening parameter is defined by at least one of imaging parameters and of environmental conditions.

20. The device of claim 19, wherein said imaging parameters are taken from the group consisting of a scaling ratio of the image, a pan position and a tilt position.

21. The device of claim 19, wherein said environmental conditions comprise lighting conditions of an object being imaged.

22. The device of claim 17, wherein said edge pixels are sharpened only in a direction perpendicular to the edge orientation.

23. The device of claim 22, wherein said image pixels located within said neighborhood of pixels and determining the smallest unsharpened numerical value and the greatest unsharpened numerical value are taken from those image pixels in said neighborhood of pixels which are located in a direction perpendicular to the edge orientation.

24. The device of claim 16, wherein a pixel is sharpened only if an output value of said edge detector for said pixel exceeds a predetermined threshold value.

25. The device of claim 16, wherein said edge detector comprises a precalculation block and an edge angle detection block.

26. A video camera system comprising:

a video camera controllable by a user and capable of acquiring a digital image of an object, said image comprised of pixels;

an image sharpening device connected to said camera and comprising;

a sharpening filter for sharpening pixels located within a neighborhood of pixels; and

a clipping device for limiting the sharpened numerical value of said sharpened pixels so as to fall between the smallest unsharpened numerical value and the greatest unsharpened numerical value of the pixels located within said neighborhood of pixels.

27. The camera system of claim 26, the image sharpening device further comprising an edge detector for locating edge pixels.

28. The camera system of claim 26, wherein the user can adjust at least one of a tilt and pan movement of the camera.

29. The camera system of claim 28, wherein said adjustment is accomplished by electro-mechanical actuators.

30. The camera system of claim 28, wherein said adjustment is accomplished electronically by selecting from said pixels a subset of pixels.

31. The camera system of claim 26, wherein said camera system is capable of providing a zoom function by selecting from said pixels a subset of pixels forming the image and wherein said sharpening filter is adapted to receive a sharpening parameter for controlling the sharpening, with the sharpening parameter depending on the subset of pixels.

32. The camera system of claim 31, wherein said sharpening parameter is large if said subset of pixels contains a small number of pixels and said sharpening parameter is small if said subset of pixels contains a large number of pixels.

33. The camera system of claim 28, wherein each of the tilt and pan movements comprises a coarse adjustment and a fine adjustment, and wherein the coarse adjustment is provided by pivoting the camera about mutually perpendicular axes and zooming a lens of the camera, and wherein the fine adjustment is provided by selecting from said pixels a subset of pixels.

34. A video camera system for a set-top box comprising:

a video camera operatively integrated in said set-top box and adapted to acquire a digital image of an object, said image comprised of pixels;

said camera capable of electronically providing a tilt, pan and zoom function of the image, wherein said tilt, pan and zoom function is accomplished by selecting from said pixels a subset of pixels;

a sharpening filter for sharpening pixels within a neighborhood of pixels in said subset of pixels; and

a clipping device for limiting the sharpened numerical value of said sharpened pixels so as to fall between the smallest unsharpened numerical value and the greatest unsharpened numerical value of the pixels located within said neighborhood of pixels.

35. The video camera system of claim 34, further comprising:

an edge detector for locating edge pixels in said subset of pixels.

36. The video camera system of claim 34, further comprising:

a scaler adapted to generate new pixel addresses and new pixel values associated with the new pixel addresses for scaling the subset of pixels so as to correspond to a predetermined video output format.

37. A device for enhancing a digital image, the image comprised of pixels, each pixel associated with a numerical value and residing in a neighborhood of pixels, the device comprising:

a sharpener for sharpening pixels in said neighborhood of pixels, and

a clipping device for limiting the numerical value of said sharpened pixels so as to fall between the smallest unsharpened numerical value and the greatest unsharpened numerical value of the pixels from said neighborhood of pixels.

38. A device for enhancing a digital image, the image comprised of pixels, each pixel associated with a numerical value and residing in a neighborhood of pixels, the device comprising:

means for sharpening the pixels in said neighborhood of pixels; and

means for limiting the numerical value of said sharpened pixels in said neighborhood of pixels so as to fall between the smallest unsharpened numerical value and the greatest unsharpened numerical value of the pixels located in said neighborhood of pixels.