Method and apparatus for driving liquid crystal display

• US 20050219179A1
• Filed: 06/28/2004
• Published: 10/06/2005
• Est. Priority Date: 12/22/2003
• Status: Active Grant

• Current Assignee: LG Display Co., Ltd.
• Original Assignee: LG Philips LCD Company Limited (LG Display Co., Ltd.)
• Inventors: Kim, Ki Duk
• Granted Patent: US 7,443,377 B2
• Time in Patent Office: Days
• US Class Current: 345/89
• 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 2320/0646 Modulation of illumination source brightness and image signal correlated to each other
• CPC Class Codes: G09G 2360/16 Calculation or use of calculated indices related to luminance levels in display data
• CPC Class Codes: G09G 3/3406 Control of illumination source illumination devices structurally associated with liquid crystal cells G02F1/1336
• CPC Class Codes: G09G 3/3648 using an active matrix G09G3/367 - G09G3/3696 take precedence

Abstract

A driving method and apparatus for a liquid crystal display is disclosed in which the contrast ratio of data to be displayed is expanded and brightness of a back light is selectively changed in correspondence with the data. Whether the data is that of an initial color field is determined. The data is converted into brightness components and arranged into a histogram for each frame. Data having an expanded contrast is generated by the histogram. A control value is extracted from the histogram. The brightness of the back light is generated in correspondence with the control value if an initial color field is not displayed. However, if an initial color field is displayed, a predetermined brightness is supplied irrespective of the extracted control value.

Claims

1. A method of driving a display, comprising:

(A) determining whether data to be displayed is that of an initial color field; and

(B) controlling a back light such that a predetermined brightness is supplied when the data is that of the initial color field.

2. The method of claim 1, wherein (A) comprises for each pixel in the display:

receiving red, green and blue data;

changing a counted value when only one of the red, green and blue data has a gray level at least a preset amount while the remaining red, green and blue data has a gray level of less than the preset amount; and

determining the red, green and blue data to be the initial color field when the counted value exceeds a predetermined critical value in which the counted value has been changed.

3. The method of claim 2, wherein the preset amount is 32.

4. The method of claim 2, wherein the critical value is half of the pixels in the display.

5. The method of claim 1, wherein the predetermined brightness is more than half of a maximum brightness able to be generated by the back light.

6. The method of claim 5, wherein the predetermined brightness is the maximum brightness.

7. The method of claim 1, wherein the display is a liquid crystal display.

8. A method of driving a frame of a display, comprising:

(A) determining whether first data to be displayed is that of an initial color field;

(B) converting the first data into brightness components and arranging the brightness components into a histogram;

(C) generating second data having an expanded contrast using the histogram;

(D) extracting a control value from the histogram; and

(E) controlling brightness of a back light in correspondence with the control value if it is determined that the first data is not that of the initial color field, and controlling the back light to emit a predetermined brightness irrespective of the control value if it is determined that the first data is that of the initial color field.

9. The method of claim 8, wherein (A) comprises:

receiving first red, green and blue data for each pixel in the display;

changing a counted value of a counter when only one of the first red, green and blue data has a gray level that is at least a preset amount while the remaining red, green and blue data has a gray level of less than the preset amount; and

determining the first data to be the initial color field when the counted value exceeds a predetermined critical value in a direction in which the counted value has been changed.

10. The method of claim 8, wherein the preset amount is 32.

11. The method of claim 9, wherein the critical value is half of a number of pixels in the display.

12. The method of claim 9, wherein changing the counted value comprises:

changing a first counter when only the first red data has a gray level of at least the preset amount;

changing a second counter when only the first green data has a gray level of at least the preset amount; and

changing a third counter when only the first blue data has a gray level of at least the preset amount.

13. The method of claim 12, wherein the preset amount is 32.

14. The method of claim 12, wherein the first data is determined to be the initial color field when one of counted values from the first, second or third counters exceeds the critical value.

15. The method of claim 12, wherein, when a counted value from the first counter exceeds the critical value, the back light supplies a first predetermined brightness in correspondence with a red color field.

16. The method of claim 12, wherein, when a counted value from the second counter exceeds the critical value, the back light supplies a second predetermined brightness in correspondence with a green color field.

17. The method of claim 12, wherein, when a counted value from the third counter exceeds the critical value, the back light supplies a third predetermined brightness in correspondence with a blue color field.

18. The method of claim 15, wherein the first predetermined brightness is more than half of a maximum brightness able to be generated by the back light.

19. The method of claim 16, wherein the second predetermined brightness is more than half of a maximum brightness able to be generated by the back light.

20. The method of claim 17, wherein the third predetermined brightness is more than half of a maximum brightness able to be generated by the back light.

21. The method of claim 12, wherein the first, second and third counters are initialized when a vertical synchronizing signal is supplied to an input thereof.

22. The method of claim 8, wherein the predetermined brightness is more than half of a maximum brightness able to be generated by the back light.

23. The method of claim 22, wherein the predetermined brightness is the maximum brightness.

24. The method of claim 8, wherein the control value is a most-frequent value or an average value of the histogram.

25. The method of claim 8, wherein the display is a liquid crystal display.

26. A driving apparatus for a display, comprising:

an initial color determiner that determines whether first data received at an input is an initial color field;

an image signal modulator that extracts brightness components from the first data, converts the brightness components into a histogram for each frame, and generates second data having an expanded contrast in correspondence with a result extracted from the histogram;

a back light that emits light; and

a back light controller that controls brightness of the back light under control of the initial color determiner or the image signal modulator dependent on whether the first data is the initial color field.

27. The driving apparatus of claim 26, wherein the initial color determiner comprises:

a determining unit that determines whether or not first red, green and blue data received for each pixel are that of an initial color field;

a counter unit having at least one counter for changing a value of the counter under control of the determining unit when the first data are determined to be that of the initial color field; and

a control signal generator for comparing the changed value from the counter unit with a predetermined critical value to generate a control signal.

28. The driving apparatus of claim 27, wherein the critical value is half of a number of the pixels.

29. The driving apparatus of claim 27, wherein the determining unit determines the first data to be the initial color fields when only one of first red, green and blue data for each pixel has a gray level of that is at least a preset amount.

30. The driving apparatus of claim 29, wherein the preset amount is 32.

31. The driving apparatus of claim 28, wherein the counter unit comprises:

a first counter that changes a first counted value when only the first red data has a gray level of at least a preset amount;

a second counter that changes a second counted value when only the first green data has a gray level of at least the preset amount; and

a third counter that changes a third counted value when only the first blue data has a gray level of least the preset amount.

32. The driving apparatus of claim 31, wherein the preset amount is 32.

33. The driving apparatus of claim 29, wherein the control signal generator generates the control signal when only one of first, second, or third counted values exceeds the critical value.

34. The driving apparatus of claim 33, wherein the back light controller controls the back light such that a predetermined brightness is supplied when the control signal is applied and controls the back light such that light having a brightness corresponding to a control value extracted from the histogram for each frame is supplied otherwise.

35. The driving apparatus of claim 33, wherein the predetermined brightness is more than half of a maximum brightness able to be generated by the back light.

36. The driving apparatus of claim 35, wherein the predetermined brightness is the maximum brightness.

37. The driving apparatus of claim 31, wherein the first, second, and third counters are initialized when a vertical synchronizing signal is supplied to an input thereof.

38. The driving apparatus of claim 34, wherein the control value is a most-frequent value or an average value of the histogram.

39. The driving apparatus of claim 26, wherein the display is a liquid crystal display.

40. A method of driving a display, the method comprising:

determining whether an image to be displayed on the display is substantially a single color;

determining a control value from a brightness of the image;

expanding a contrast of the image using the control value;

controlling a back light to emit light of a brightness independent of the control value if the image is substantially the single color and using the control value if the image is not substantially the single color; and

displaying the image of expanded contrast using light from the back light.

41. The method of claim 40, further comprising controlling the back light to emit light of a predetermined brightness if the image is substantially the single color.

42. The method of claim 40 further comprising:

receiving red, green and blue data for each pixel in the display;

changing a counted value when only one of the first red, green and blue data is brighter than a predetermined brightness; and

determining the image is substantially the single color when the counted value exceeds a predetermined critical value in a direction in which the counted value has been changed.

43. The method of claim 42, wherein the critical value is at least half of a number of pixels in the display.

44. The method of claim 42, wherein changing the counted value comprises:

changing a first counted value when only the red data is greater than a first predetermined value;

changing a second counted value when only the green data is greater than a second predetermined value; and

changing a third counted value when only the blue data is greater than a third predetermined value.

45. The method of claim 44, wherein the first, second, and third predetermined values are equal.

46. The method of claim 44, wherein the first, second, and third predetermined values are different.

47. The method of claim 44, wherein determining the image is substantially the single color comprises:

determining the image is substantially red when the first counted value exceeds a first predetermined critical value, the second counted value does not exceed a second predetermined critical value, and the third counted value does not exceed a third predetermined critical value;

determining the image is substantially green when the second counted value exceeds the second predetermined critical value, the first counted value does not exceed the first predetermined critical value, and the third counted value does not exceed the third predetermined critical value; and

determining the image is substantially blue when the third counted value exceeds the third predetermined critical value, the first counted value does not exceed the first predetermined critical value, and the second counted value does not exceed the second predetermined critical value.

48. The method of claim 44, wherein the first, second, and third critical values are equal.

49. The method of claim 44, wherein the first, second, and third critical values are different.

50. The method of claim 44, further comprising the back light emitting light of a different brightness dependent on which of the first, second, or third counted values exceeds the first, second, or third predetermined values, respectively.

51. The method of claim 50, wherein each of the different brightnesses is at least half of a maximum brightness able to be generated by the back light.

52. The method of claim 44, further comprising initializing the first, second and third counted values each time a new image is to be displayed.

53. The method of claim 40, wherein the control value is a most-frequent brightness of pixels in the display or an average value of a brightness of the image to be displayed.