Liquid crystal display backlight with variable amplitude LED

• US 20050088402A1
• Filed: 10/28/2004
• Published: 04/28/2005
• Est. Priority Date: 11/09/2001
• Status: Active Grant

• Current Assignee: Sharp Kabushiki Kaisha (Hon Hai Precision Industry Co., Ltd.)
• Original Assignee: Sharp Kabushiki Kaisha (Hon Hai Precision Industry Co., Ltd.)
• Inventors: Daly, Scott J.
• Granted Patent: US 7,675,500 B2
• Time in Patent Office: Days
• US Class Current: 345/102
• CPC Class Codes: G09G 2320/02 Improving the quality of display appearance
• CPC Class Codes: G09G 2320/0238 Improving the black level
• CPC Class Codes: G09G 2320/0271 Adjustment of the gradation levels within the range of the gradation scale, e.g. by redistribution or clipping
• CPC Class Codes: G09G 2320/0285 using tables for spatial correction of display data
• CPC Class Codes: G09G 2320/0646 Modulation of illumination source brightness and image signal correlated to each other
• CPC Class Codes: G09G 2320/066 for control of contrast
• CPC Class Codes: G09G 2360/16 Calculation or use of calculated indices related to luminance levels in display data
• CPC Class Codes: G09G 3/3426 the different display panel areas being distributed in two dimensions, e.g. matrix

Abstract

A display is backlit by a source having spatially modulated luminance to attenuate illumination of dark areas of images and increase the dynamic range of the display.

Claims

1-22. -22. (canceled).

23. A method of illuminating a backlit display, said method comprising:

(a) spatially varying the luminance of a light source illuminating a plurality of displayed pixels;

(b) varying the transmittance of a light valve of said display in a non-binary manner;

(c) wherein said light source is a variable amplitude light emitting device.

24. The method of claim 23 wherein the step of varying a luminance of a light source illuminating a displayed pixel comprises the steps of:

(a) determining a luminance of said pixel from an intensity value of said pixel; and

(b) varying a luminance of said light source according to a relationship of said luminance of said pixel and said luminance of said light source.

25. The method of claim 24 wherein said relationship of said luminance of said pixel and said luminance of said light source is a nonlinear relationship.

26. The method of claim 24 wherein the step of determining a luminance of a pixel from an intensity value comprises the step of filtering an intensity value for a plurality of pixels.

27. The method of claim 26 wherein said relationship of said luminance of said pixel and said luminance of said light source is a nonlinear relationship.

28. The method of claim 26 further comprising the step of sampling a filtered intensity value at a spatial coordinate corresponding to said light source.

29. The method of claim 28 further comprising the step of resealing a sample of said filtered intensity value to reflect a nonlinear relationship between said luminance of said light source and said intensity of said displayed pixel.

30. The method of claim 24 wherein the step of varying a luminance of said light source according to a relationship of said luminance of said pixel and said luminance of said light source comprises the steps of:

(a) operating said light source at substantially a maximum luminance if a luminance of at least one displayed pixel exceeds a threshold luminance; and

(b) otherwise, attenuating said luminance of said light source according to a relationship of said luminance of said light source and a luminance of a plurality of pixels.

31. The method of claim 30 wherein the step of attenuating a luminance of a light source according to a relationship of said luminance of said light source and a luminance of a plurality of pixels comprises the step of attenuating said luminance of said light source according to a relationship of said luminance of said light source and a mean luminance of said plurality of pixels.

32. The method of claim 31 wherein the step of attenuating a luminance of a light source illuminating a pixel comprises the step of attenuating a luminance of a plurality of light sources illuminating a plurality of pixels comprising a frame in a sequence of video frames.

33. The method of claim 32 wherein the step of attenuating a luminance of a plurality of light sources illuminating a plurality of pixels comprising a frame in a sequence of video frames comprises the step of attenuating said luminance of said light sources for a subset of frames of said sequence, said subset including less than all said frames of said sequence.

34. The method of claim 31 wherein said plurality of pixels comprises at least two contiguous pixels.

35. The method of claim 23 wherein the step of varying a luminance of a light source illuminating a displayed pixel comprises the step of varying a luminance of a plurality of light sources illuminating a plurality of displayed pixels substantially comprising a frame in a sequence of video frames.

36. The method of claim 35 wherein the step of varying a luminance of a plurality of light sources illuminating a plurality of pixels substantially comprising a frame in a sequence of video frames comprises the step of varying said luminance of said light sources for less than all frames of said sequence.

37. A method of illuminating a backlit display, said method comprising:

(a) spatially varying the luminance of a light source illuminating a plurality of displayed pixels;

(b) varying the transmittance of a light valve of said display in a non-binary manner;

(c) wherein said spatially varying luminance of said light source is based upon reducing point contrast by rescaling image data to be displayed on said display.

38. The method of claim 37 wherein the step of varying a luminance of a light source illuminating a displayed pixel comprises the steps of:

(a) determining a luminance of said pixel from an intensity value of said pixel; and

(b) varying a luminance of said light source according to a relationship of said luminance of said pixel and said luminance of said light source.

39. The method of claim 38 wherein the step of varying a luminance of said light source according to a relationship of said luminance of said pixel and said luminance of said light source comprises the steps of:

(a) operating said light source at substantially a maximum luminance if a luminance of at least one displayed pixel exceeds a threshold luminance; and

(b) otherwise, attenuating said luminance of said light source according to a relationship of said luminance of said light source and a luminance of a plurality of pixels.

40. The method of claim 39 wherein the step of attenuating a luminance of a light source according to a relationship of said luminance of said light source and a luminance of a plurality of pixels comprises the step of attenuating said luminance of said light source according to a relationship of said luminance of said light source and a mean luminance of said plurality of pixels.

41. The method of claim 40 wherein the step of attenuating a luminance of a light source illuminating a pixel comprises the step of attenuating a luminance of a plurality of light sources illuminating a plurality of pixels comprising a frame in a sequence of video frames.

42. The method of claim 41 wherein the step of attenuating a luminance of a plurality of light sources illuminating a plurality of pixels comprising a frame in a sequence of video frames comprises the step of attenuating said luminance of said light sources for a subset of frames of said sequence, said subset including less than all said frames of said sequence.

43. The method of claim 40 wherein said plurality of pixels comprises at least two contiguous pixels.

44. A method of illuminating a backlit display, said method comprising:

(a) spatially varying the luminance of a light source illuminating a plurality of displayed pixels;

(b) varying the transmittance of a light valve of said display in a non-binary manner;

(c) wherein spatially varying luminance of said light source is based upon simulating performance of a non-backlit display by rescaling image data to be displayed on said display.

45. The method of claim 44 wherein said non-backlit display is a CRT, the output of said CRT expressed by the equation:

${\mathrm{LS}}_{\mathrm{attenuation}}<br><br>\left(\mathrm{CV}\right)=\frac{L_{\mathrm{CRT}}}{L_{\mathrm{LCD}}}=\frac{{\mathrm{gain}\left(\mathrm{CV}+V_d\right)}^{\mathrm{\gamma <br><br>}}+{\mathrm{leakage}}_{\mathrm{CRT}}}{{\mathrm{gain}<br><br>\left(\mathrm{CV}+V_d\right)}^{\mathrm{\gamma <br><br>}}+{\mathrm{leakage}}_{\mathrm{LCD}}}$

where;

LS_attenuation(CV)=the attenuation of the light source as a function of the digital value of the image pixel

L_CRT=the luminance of the CRT display

L_LCD=the luminance of the LCD display

V_d=an electronic offset

γ

=the cathode gamma

46. The method of claim 44 wherein the step of varying a luminance of a light source illuminating a displayed pixel comprises the steps of:

(a) determining a luminance of said pixel from an intensity value of said pixel; and

(b) varying a luminance of said light source according to a relationship of said luminance of said pixel and said luminance of said light source.

47. The method of claim 46 wherein the step of varying a luminance of said light source according to a relationship of said luminance of said pixel and said luminance of said light source comprises the steps of:

(a) operating said light source at substantially a maximum luminance if a luminance of at least one displayed pixel exceeds a threshold luminance; and

(b) otherwise, attenuating said luminance of said light source according to a relationship of said luminance of said light source and a luminance of a plurality of pixels.

48. The method of claim 47 wherein the step of attenuating a luminance of a light source according to a relationship of said luminance of said light source and a luminance of a plurality of pixels comprises the step of attenuating said luminance of said light source according to a relationship of said luminance of said light source and a mean luminance of said plurality of pixels.

49. The method of claim 48 wherein the step of attenuating a luminance of a light source illuminating a pixel comprises the step of attenuating a luminance of a plurality of light sources illuminating a plurality of pixels comprising a frame in a sequence of video frames.

50. The method of claim 49 wherein the step of attenuating a luminance of a plurality of light sources illuminating a plurality of pixels comprising a frame in a sequence of video frames comprises the step of attenuating said luminance of said light sources for a subset of frames of said sequence, said subset including less than all said frames of said sequence.

51. The method of claim 48 wherein said plurality of pixels comprises at least two contiguous pixels.