Method of and apparatus for controlling contrast of liquid crystal displays while receiving large dynamic range video

• US 6,414,664 B1
• Filed: 11/13/1997
• Issued: 07/02/2002
• Est. Priority Date: 11/13/1997
• Status: Expired due to Fees

• Current Assignee: Honeywell Incorporated (Honeywell International Inc.)
• Original Assignee: Honeywell Incorporated (Honeywell International Inc.)
• Inventors: Conover, Kurt M., Wood, Teddy J.
• Primary Examiner(s): Saras, Steven
• Assistant Examiner(s): Awad, Amr
• Application Number:
  US08/970,118
• Time in Patent Office: 1,692 Days
• Field of Search: 345/87-101, 345/150, 358/457, 358/456, 358/455, 358/426, 358/448, 378/58, 378/22, 378/62, 348/30, 348/671-686, 395/500, 395/84
• US Class Current: 345/89
• CPC Class Codes: G09G 2320/041 Temperature compensation
• CPC Class Codes: G09G 2320/0606 Manual adjustment
• CPC Class Codes: G09G 2320/066 for control of contrast
• CPC Class Codes: G09G 2320/0673 for control of gamma adjustment, e.g. selecting another gamma curve
• CPC Class Codes: G09G 2320/068 for control of viewing angle adjustment
• CPC Class Codes: G09G 3/2007 Display of intermediate tones
• CPC Class Codes: G09G 3/36 using liquid crystals
• CPC Class Codes: G09G 3/3648 using an active matrix G09G3/367 - G09G3/3696 take precedence

Abstract

An apparatus and method for controlling contrast for a liquid crystal display (“LCD”), especially active-matrix LCDs, while receiving large dynamic range video data to be displayed to the user by the LCD. Contrast settings of the LCD correspond to a single look-up table from a set of different and multiple look-up tables rather than using the contrast setting of the LCD to select different voltage values from a single look-up table. The values of the reference voltages of the LCD are varied so that all shades of gray are available with each contrast selection resulting in a high image quality and a high contrast.

Claims

1. A method for controlling contrast in a liquid crystal display (“

LCD”

) device in which a full gray scale comprising minimum light out to maximum light out is used with variable video signal input ranges, with each video signal input range comprising a fraction of a total range of zero to full amplitude to be displayed by the LCD device, the full gray scale having a finite number of shades of gray, the LCD device having a contrast control for input by a user, the LCD device communicating with a drive voltage generator that supplies drive voltages V to the LCD device corresponding to the video signal input and a user contrast control setting, the method comprising the steps of;

providing a plurality of look-up tables, the plurality of look-up tables representing a plurality of contrast settings of the LCD device; and

selecting a single look-up table from the plurality of look-up tables in response to the contrast control setting selected by the user from the plurality of contrast settings through the contrast control device to affect a transfer function of the LCD device, the single look-up table containing all shade of gray available on the gray scale with each contrast setting.

2. The method of claim 1, wherein the LCD device is an active-matrix LCD.

3. The method of claim 1, wherein the LCD device is a passive-matrix LCD.

4. The method of claim 1, further comprising the step of varying the drive voltages so that all shades of gray are available with a selected contrast setting.

5. The method of claim 1, wherein the step of translating contrast control into a pre-defined transfer function comprises providing a contrast control input into the drive voltage generator.

6. The method of claim 5, wherein the contrast control comprises digital signals.

7. The method of claim 5, wherein the contrast control comprises analog signals.

8. The method of claim 7, wherein the analog signals are a function of the drive voltages.

9. The method of claim 5, wherein the contrast control comprises modulated signals.

10. The method of claim 9, wherein the modulated signals are pulse-width modulated signals.

11. The method of claim 9, wherein the modulated signals are amplitude modulated signals.

12. The method of claim 1, wherein the contrast control is represented by drive voltages as a function of the shades of gray of the gray scale.

13. The method of claim 1 further comprising a plurality of viewing angle controls with respect to the LCD device.

14. The method of claim 1, wherein the plurality of look-up tables are pre-determined.

15. The method of claim 1, wherein the transfer function is non-linear.

16. The method of claim 15, wherein the transfer function is defined by transmission T as a function of drive voltages V, and wherein the transfer function comprises a plurality of dynamic sets of drive voltages V and is not fixed to a single distribution of gray scale.

17. An apparatus for controlling contrast in a liquid crystal display (LCD) device in which a gray scale comprising minimum light out to maximum light out is used with variable video signal input ranges, with each video signal input range comprising a fraction of a total range of zero to full amplitude to be displayed by the LCD device, the gray scale having a finite number of shades of gray, the LCD device having a contrast control for input by a user, the LCD device communicating with a drive voltage generator that supplies drive voltages V to the LCD device corresponding to the video signal input and a user defined contrast control setting, the LCD device comprising:

a memory device containing a plurality of look-up tables, the plurality of look-up tables representing a plurality of contrast settings of the LCD device; and

means for accessing the memory device to search through the plurality of look-up tables and for selecting a single look-up table from the plurality of look-up tables in response to the contrast setting selected by the user through the contrast control device to affect a transfer function of the LCD device, the single look-up table containing all shades of gray available on the gray scale with each contrast setting.

18. The apparatus of claim 17, wherein the LCD device is an active-matrix LCD.

19. The apparatus of claim 18, wherein the contrast control input comprises digital signals.

20. The apparatus of claim 17, wherein the LCD device is a passive-matrix LCD.

21. The apparatus of claim 17, wherein the drive voltages vary so that all shades of gray are available with a selected contrast setting.

22. The apparatus of claim 17, wherein said apparatus for translating a contrast setting into a pre-defined transfer function comprises a contrast control input into the drive voltage generator.

23. The apparatus of claim 22, wherein the contrast control input comprises analog signals.

24. The apparatus of claim 23, wherein the analog signals are a function of the drive voltages.

25. The apparatus of claim 22, wherein the contrast control input comprises modulated signals.

26. The apparatus of claim 25, wherein the modulated signals are pulse-width modulated signals.

27. The apparatus of claim 25, wherein the modulated signals are amplitude modulated signals.

28. The apparatus of claim 17, wherein the contrast settings are represented by drive voltages as a function of the shades of gray of the gray scale.

29. The apparatus of claim 17 further comprising a plurality of viewing angle controls with respect to the LCD device.

30. The apparatus of claim 17, wherein the plurality of look-up tables has contents that are pre-determined.

31. The apparatus of claim 17, wherein the transfer function is non-linear.

32. The apparatus of claim 31, wherein the transfer function is defined by transmission T as a function of drive voltages V, and wherein the transfer function comprises a plurality of dynamic sets of drive voltages V and is not fixed to a single distribution of gray scale.

33. A method for controlling contrast in a liquid crystal display (“

LCD”

) device in which a gray scale comprising minimum light out to maximum light out is used with variable video signal input ranges, with each video signal input range comprising a fraction of a total range of zero to full amplitude to be displayed by the LCD device, the gray scale having a finite number of shades of gray, the LCD device having a contrast control for input by a user, the LCD device communicating with a drive voltage generator that supplies drive voltages V to the LCD device corresponding to the video signal input and user defined contrast control setting, the method comprising the steps of;

providing a plurality of look-up tables, the plurality of look-up tables representing a plurality of contrast settings of the LCD device; and

selecting a single look-up table from the plurality of look-up tables in response to the contrast setting selected by the user from the plurality of contrast settings through the contrast control device to affect a transfer function of the LCD device, the single look-up table containing all shades of gray available on the gray scale with each contrast setting, wherein the transfer function is non-linear and is defined by transmission T as a function of drive voltages V.