Contour enhancement unit and method to enhance the contours in video images

• US 20050099537A1
• Filed: 05/04/2004
• Published: 05/12/2005
• Est. Priority Date: 11/10/2003
• Status: Abandoned Application

• Current Assignee: Huaya Microelectronics, Inc.
• Original Assignee: Huaya Microelectronics, Inc.
• Inventors: Zhu, Ge
• Application Number:
  US10/839,743
• Publication Number:
  US 20050099537A1
• Time in Patent Office: Days
• US Class Current: 348/450
• CPC Class Codes: H04N 5/142 Edging; Contouring
• CPC Class Codes: H04N 5/208 for compensating for attenuation of high frequency components, e.g. crispening, aperture distortion correction

Abstract

A contour enhancement unit and method to enhance the contours of an image is presented. Specifically, a contour detection unit determines a dominant contour direction for a current pixel and a contour enhanced luminance calculation unit enhances the contour of the current pixel in the dominant contour direction. Contour directions can be approximated by slope directions, where the magnitude of the slope across a given direction approximates the magnitude of the contour in that direction.

Claims

1. A method for enhancing an image having a plurality of pixels, the method comprising:

determining a dominant contour direction for a current pixel; and

enhancing a contour of the current pixel by a contour enhancement factor along the dominant contour direction.

2. The method of claim 1, wherein the dominant contour direction is determined using a dominant slope direction of the current pixel.

3. The method of claim 1, wherein the determining a dominant contour direction for a current pixel comprises:

calculating a plurality of slopes for a plurality of slope directions for the current pixel;

selecting a dominant slope direction from the plurality of slope directions as the dominant direction of the contour of the current pixel, wherein the dominant slope direction has a largest absolute slope value from among the slop directions.

4. The method of claim 3, wherein the calculating a plurality of slopes for the current pixel uses only luminance data.

5. The method of claim 3, wherein the calculating a plurality of slopes for the current pixel comprises:

calculating a vertical slope for the current pixel;

calculating a horizontal slope for the current pixel; and

calculating a diagonal slope for the current pixel.

6. The method of claim 5, wherein the diagonal slope for the current pixel is equal to the luminance of the current pixel minus an average luminance of a first pixel above the current pixel, a second pixel below the current pixel, a third pixel to the left of the current pixel, and a fourth pixel to the right of the current pixel.

7. The method of claim 5, wherein the vertical slope is equal to a first average luminance of the current pixel, a first pixel above of the current pixel and a second pixel below the current pixel minus a second average luminance of a third pixel above and to the left of the current pixel, a fourth pixel to the left of the current pixel, a fifth pixel below and to the left of the current pixel, a sixth pixel above and to the right of the current pixel, a seventh pixel to the right of the current pixel, and an eighth pixel below and to the right of the current pixel.

8. The method of claim 5, wherein the horizontal slope is equal to a first average luminance of the current pixel, a first pixel to the left of the current pixel and a second pixel to the right of the current pixel minus a second average luminance of a third pixel above and to the left of the current pixel, a fourth pixel above the current pixel, a fifth pixel above and to the right of the current pixel, a sixth pixel below and to the left of the current pixel, a seventh pixel below the current pixel, and an eighth pixel below and to the right of the current pixel.

9. The method of claim 3, wherein the calculating a plurality of slopes for the current pixel comprises:

calculating a vertical slope for the current pixel;

calculating a horizontal slope for the current pixel;

calculating a first diagonal slope for the current pixel; and

calculating a second diagonal slope for the current pixel.

10. The method of claim 1, further comprising calculating a secondary contour direction for the current pixel.

11. The method of claim 10, wherein the enhancing a contour of the current pixel by a contour enhancement factor along the dominant contour direction is performed only when the magnitude of the dominant contour direction minus the magnitude of the secondary contour direction is greater than a contour enhancement threshold.

12. The method of claim 11, wherein the magnitude of the dominant contour direction is equal to an absolute value of a dominant slope of the current pixel.

13. The method of claim 11, wherein the magnitude of the secondary contour direction is equal to an absolute value of a secondary slope of the current pixel.

14. The method of claim 1, wherein the enhancing a contour of the current pixel by a contour enhancement factor along the dominant contour direction further comprises replacing the luminance value of the current pixel with an enhanced luminance value such that an enhanced slope of the dominant contour direction calculated using the enhanced luminance value is equal to a contour enhancement factor multiplied by a slope of the dominant contour direction.

15. The method of claim 14, wherein the enhanced slope of the dominant contour direction is calculated using the enhanced luminance value of the current pixel and the slope of the dominant contour direction is calculated using the luminance value of the current pixel.

16. A contour enhancement unit for enhancing the contours of an image having a plurality of pixels, the contour enhancement unit comprising:

a contour detection unit configured to determine the dominant contour direction of a current pixel; and

a contour enhanced luminance calculation unit coupled to the contour detection unit and configured to generate an enhanced luminance value for the current pixel, wherein the enhanced luminance value enhances the contour of the current pixel in the dominant contour direction.

17. The contour enhancement unit of claim 16, wherein the contour detection unit is configured calculate a plurality of slopes for a plurality of slope directions and to select a dominant slope direction as the dominant contour direction, wherein the dominant slope direction has a largest magnitude from among the slope directions.

18. The contour enhancement unit of claim 16, wherein an enhanced slope of the dominant contour direction calculated using the enhanced luminance value is equal to a contour enhancement factor multiplied by a slope of the dominant contour direction.

19. The contour enhancement unit of claim 18, wherein the enhanced slope of the dominant contour direction is calculated using the enhanced luminance value and the slope of the dominant contour direction is calculated using the luminance value of the current pixel.

20. The contour enhancement unit of claim 16, further comprising a contour threshold comparison unit coupled to the contour detection unit and the contour enhanced luminance calculation unit.

21. The contour enhancement unit of claim 20, wherein the contour detection unit is configured to calculate a magnitude of the dominant contour direction and a magnitude of a secondary contour direction.

22. The contour enhancement unit of claim 21, wherein the contour threshold comparison unit controls the contour enhanced luminance calculation unit based on the magnitude of the dominant contour direction and the magnitude of the secondary contour direction.

23. The contour enhancement unit of claim 22, wherein the contour threshold comparison unit causes the contour enhanced luminance calculation unit to use the luminance value of the current pixel as the contour enhanced luminance value when the magnitude of the dominant contour direction minus the magnitude of the secondary contour direction is less than or equal to a contour enhancement threshold.