Anti-aliasing television signals for display

• US 6,577,351 B1
• Filed: 05/18/1998
• Issued: 06/10/2003
• Est. Priority Date: 05/18/1998
• Status: Expired due to Term

• Current Assignee: Comcast Cable Communications Management LLC (Comcast Corporation), Sony Corporation (Sony Group Corp.)
• Original Assignee: Liberate Technologies
• Inventors: Helman, James, Mott, David, Yu, Chee
• Primary Examiner(s): Kostak, Victor R.
• Application Number:
  US09/081,033
• Time in Patent Office: 1,849 Days
• Field of Search: 348/630, 348/607, 348/624, 382/269, 345/611-616
• US Class Current: 348/624
• CPC Class Codes: G09G 5/026 Control of mixing and/or overlay of colours in general G09G5/022 and G09G5/024 take precedence
• CPC Class Codes: H04N 21/4312 involving specific graphical features, e.g. screen layout, special fonts or colors, blinking icons, highlights or animations
• CPC Class Codes: H04N 21/4355 involving reformatting operations of additional data, e.g. HTML pages on a television screen optimising the visualization of content for information retrieval from the Internet G06F16/9577; adaptation of message content in packet-switching networks H04L51/066; media handling at the source in data packet switching networks H04L65/764
• CPC Class Codes: H04N 21/4858 for modifying screen layout parameters, e.g. fonts, size of the windows
• CPC Class Codes: H04N 5/44504 Circuit details of the additional information generator, e.g. details of the character or graphics signal generator, overlay mixing circuits
• CPC Class Codes: H04N 9/641 Multi-purpose receivers, e.g. for auxiliary information H04N9/642 takes precedence

Abstract

The invention provides an improved method and system for presenting television signals, including anti-aliasing of text with respect to a background. The background color is determined relatively locally for each element to be anti-aliased, and text or other graphics overlaid on that background are anti-aliased with respect to each relatively local background color. Also, anti-aliasing can be applied to blur text and graphics more vertically than horizontally to reduce flicker, and to blur chrominance more than luminance to reduce cross-chrominance artifacts resulting from Y/C separation. Similar techniques may be used for filtering images in addition to anti-aliasing text characters.

Claims

1. A system for anti-aliasing the edges of images displayed against a background on a display unit, said system comprising:

a background color detector for dynamically determining background color; and

an anti-aliasing processor for anti-aliasing the edges of images based upon said dynamically determined background color;

wherein said background color detector adjusts chrominance values for foreground color displayed on said display unit globally and adjusts chrominance values for background color displayed on said display unit locally.

2. The system of claim 1, wherein said images comprise characters of text obtained from a source document and wherein the background color is determined by instructions embedded in the source document.

3. The system of claim 2, wherein said instructions embedded in the source document comprise HTML tags.

4. The system of claim 1, wherein said background color is determined by user controls set by the user.

5. The system of claim 1, wherein said background color is determined by user controls derived from user actions.

6. The system of claim 1, wherein said background color is determined by manufacturer controls, set by the manufacturer of the display unit.

7. The system of claim 1, wherein said images comprise characters of text superimposed upon a graphic image and wherein the background color is determined by the content of said graphic image.

8. The system of claim 7, wherein said content includes a color histogram for an entire document.

9. The system of claim 7, wherein said content includes a locally-weighted color histogram for a plurality of pixels.

10. The system of claim 7, wherein said content includes a locally-weighted color histogram for at least one block of pixels.

11. The system of claim 7, wherein said content includes a color histogram for edge pixels for the entire source document.

12. The system of claim 1, wherein said anti-aliasing is based upon the background color for each edge pixel.

13. The system of claim 1, wherein said anti-aliasing is based upon the local background colors for each image.

14. The system of claim 1, wherein said anti-aliasing is based upon the global background color.

15. The system of claim 1, wherein said anti-aliasing is based upon the local background color.

16. The system of claim 1, wherein said background color is recomputed at regular intervals.

17. The system of claim 7, wherein said background color is recomputed when changes occur in dynamic background images.

18. A method of anti-aliasing the edges of images displayed against a background on a display unit, said method comprising:

dynamically determining a background color;

adjusting chrominance values for foreground color displayed on said display unit globally and adjusting chrominance values for background color displayed on said display unit locally; and

anti-aliasing said edges of said images based upon said dynamically determined background color.

19. The method of claim 18, wherein said images comprise characters of text obtained from a source document and wherein the background color is determined by instructions embedded in the source document.

20. The method of claim 19, wherein said instructions embedded in the source document comprise HTML tags.

21. The method of claim 18, wherein said background color is determined by user controls set by the user.

22. The method of claim 18, wherein said background color is determined by user controls derived from user actions.

23. The method of claim 18, wherein said background color is determined by manufacturer controls, set by the manufacturer of the display unit.

24. The method of claim 18, wherein said images comprise characters of text superimposed upon a graphic image and wherein the background color is determined by the content of said graphic image.

25. The method of claim 24, wherein said content includes a color histogram an entire document.

26. The method of claim 24, wherein said content includes a locally-weighted color histogram for a plurality of pixels.

27. The method of claim 24, wherein said content includes a locally-weighted color histogram for at least one block of pixels.

28. The method of claim 24, wherein said content includes a color histogram edge pixels for the entire source document.

29. The method of claim 18, wherein said anti-aliasing is based upon the adjacent background colors for each edge pixel.

30. The method of claim 18, wherein said anti-aliasing is based upon the adjacent background colors for each image.

31. The method of claim 18, wherein said anti-aliasing is based upon the global background color.

32. The method of claim 18, wherein said anti-aliasing is based upon the local background colors.

33. The method of claim 18, wherein said background color is recomputed at regular intervals.

34. The method of claim 24, wherein said background color is recomputed when changes occur in dynamic background images.

35. The method of claim 18, wherein said anti-aliasing uses a wider color ramp in the vertical direction than in the horizontal direction.

36. The method of claim 18, wherein said anti-aliasing uses a wider color ramp for the chrominance components than for the luminance components.

37. A system for filtering the edges of images displayed against a background on a display unit, said system comprising:

a background color detector for dynamically determining background color; and

an image filter for filtering the edges of images based upon said dynamically determined background color;

wherein said background color detector adjusts chrominance values for foreground color displayed on said display unit globally and adjusts chrominance values for background color displayed on said display unit locally.

38. The system of claim 37, wherein said image filter uses a wider filter kernel in the vertical direction than in the horizontal direction.

39. The system of claim 37, wherein said image filter uses a wider filter kernel for the chrominance components than for the luminance components.

40. A method of filtering the edges of images displayed against a background on a display unit, said method comprising:

dynamically determining a background color;

adjusting chrominance values for foreground color displayed on said display unit globally and adjusting chrominance values for background color displayed on said display unit locally; and

filtering said edges of said images based upon said dynamically determined background color.

41. The method of claim 40, wherein said filtering uses a wider filter kernel in the vertical direction than in the horizontal direction.

42. The method of claim 40, wherein said filtering uses a wider filter kernel for the chrominance components than for the luminance components.