Automatic brightness control system and method for a display device using a logarithmic sensor

• US 6,762,741 B2
• Filed: 12/22/2000
• Issued: 07/13/2004
• Est. Priority Date: 12/22/2000
• Status: Active Grant

• Current Assignee: Visteon Global Technologies Incorporated (Visteon Corporation)
• Original Assignee: Visteon Global Technologies Incorporated (Visteon Corporation)
• Inventors: Weindorf, Paul Fredrick Luther
• Primary Examiner(s): AWAD, AMR A
• Application Number:
  US09/747,597
• Publication Number:
  US 20020118182A1
• Time in Patent Office: 1,299 Days
• Field of Search: 345/87, 345/88, 345/204, 345/211, 345/102, 345/207, 345/690, 315/149, 315/150, 315/307, 349/61, 349/64, 349/114
• US Class Current: 345/102
• CPC Class Codes: G09G 2320/0285 using tables for spatial correction of display data
• CPC Class Codes: G09G 2320/0606 Manual adjustment
• CPC Class Codes: G09G 2320/0626 for control of overall brightness
• CPC Class Codes: G09G 2360/144 the light being ambient light
• CPC Class Codes: G09G 3/20 for presentation of an assembly of a number of characters, e.g. a page, by composing the assembly by combination of individual elements arranged in a matrix no fixed position being assigned to or needed to be assigned to the individual characters or partial characters
• CPC Class Codes: G09G 3/3406 Control of illumination source illumination devices structurally associated with liquid crystal cells G02F1/1336

Abstract

This invention provides an automatic brightness control system for display devices, which may have a lighted display, a sensor, and control circuitry. The sensor logarithmically generates a first signal in response to the ambient light near the lighted display. The control circuit selects a display luminance from one or more luminance adjustment sequences having essentially constant ratio steps. The display luminance is a fractional power function of the ambient light near the display. The fractional power function may be adjusted by a constant luminance ratio offset.

Claims

1. A display device having an automatic brightness control system, comprising:

a lighted display;

a sensor disposed to logarithmically sense ambient light near the lighted display; and

control circuitry connected to receive a first signal from the light sensor, the control circuitry connected to provide a display luminance to the lighted display,

where the control circuitry selects the display luminance from at least one luminance adjustment sequence,

where each luminance adjustment sequence has a plurality of luminance values with constant ratio steps, and

where the display luminance is controlled by a transfer function that includes a term having a power relation to the ambient light near the lighted display and where an exponent of the term is a fraction.

2. The display device according to claim 1, where the fractional power function is adjusted by a constant ratio offset.

3. The display device according to claim 1, where the control circuitry further comprises digital-to-analog converter (DAC) circuitry, where the DAC circuitry converts the luminance value into an analog signal.

4. The display device according to claim 1, where the control circuitry comprises at least one digital to analog converter (DAC) connected to provide the display luminance to the lighted display, where the sensor provides the first signal with essentially equal DAC increments to the DAC, where the DAC increments correlate to constant ratio steps.

5. The display device according to claim 1, where the display luminance provides a brightness level according to the equation, $B=\mathrm{Bo}·$

[B

 



maxB

 



min]((SNS-So)/(T-1))·

BGLC

where B is a display emitted luminance, Bo is a constant corresponding to a brightness offset on a log-log plot of the relationship between the display emitted luminance and the display background illuminance, Bmax is a maximum display brightness, Bmin is a minimum display brightness, SNS is a selected step number, S_O is a midpoint of an SNS range, T is a total number of brightness steps, BGL is a display background luminance due to reflected ambient light, and C is an exponent describing the slope on a log-log plot of the relationship between the display emitted luminance and the display background illuminance.

6. The display device according to claim 5, where the relationship between the display emitted luminance and the display background illuminance is according the equation, B=Bo·

BGL^C.

7. The display device according to claim 5 where C is in the range of about 0 through about 1.

8. The display device according to claim 5, where C is a positive fraction.

9. The display device according to claim 1, where the lighted display further comprises:

a display panel; and

a backlight operatively disposed adjacent to the display panel.

10. The display device according to claim 9, where the display panel is an active matrix liquid crystal display.

11. The display device according to claim 9, where the backlight comprises at least one of a cold cathode fluorescent lamp, and electro-luminescent lamp, and a light emitting diode (LED).

12. The display device according to claim 1, where the lighted display is a backlit display.

13. The display device according to claim 1, where the lighted display is a frontlit display.

14. The display device according to claim 1, where the lighted display is an emissive display.

15. The display device according to claim 1, where the lighted display comprises a pixel light source.

16. The display device according to claim 15, where the pixel light source comprises a light emitting diode.

17. The display device according to claim 1, where the sensor is a logarithmic sensor.

18. The display device according to claim 17, where the logarithmic sensor comprises a logarithmic amplifier connected to a photodiode.

19. The display device according to claim 1, where essentially all the luminance values have constant ratio steps in the luminance adjustment sequence.

20. The display device according to claim 1,

where the control circuitry determines a first display luminance value from a first luminance adjustment sequence, the first display luminance corresponding to the first signal from the light sensor,

where the control circuitry determines a second display luminance value from a second luminance adjustment sequence, the second display luminance value corresponding to a user brightness selection, and

where the control circuitry selects the display luminance from one of the first and second display luminance values.

21. The display device according to claim 1, where a look-up table provides the at least one luminance adjustment sequence.

22. The display device according to claim 1, where the control circuitry calculates at least one of a look-up table and the luminance value, the look-up chart to provide the at least one luminance adjustment sequence.

23. The display device according to claim 22, where the control circuitry further comprises at least one microprocessor to calculate at least one of the look-up table and the luminance value.

24. The display device according to claim 1, further comprising a bezel having a surface adjacent to the display panel, and where the sensor is disposed on the surface.

25. The display device according to claim 1, where the display device is part of a navigation radio.

26. The display device according to claim 1, where the control circuitry comprises at least one integrated circuit (IC) chip.

27. The display device according to claim 1, where the display device is connected to a remote control device.

28. The display device according to claim 1, where the display device comprises a display of an electronic device.

29. The display device according to claim 28, where the electronic device is one of a communication device, a personal computer, and a personal organizer.

30. A display device having an automatic brightness control system, comprising:

a lighted display;

a sensor disposed to logarithmically sense ambient light near the display panel;

a user interface; and

control circuitry connected to receive a first signal from the sensor, the control circuitry connected to receive at least one user brightness selection from the user interface, the control circuitry connected to provide a display luminance to the lighted display,

where the control circuitry selects the display luminance from at least one luminance adjustment sequence,

where each luminance adjustment sequence has a plurality of luminance values with constant ratio steps,

where the display luminance is controlled by a transfer function that includes a term having a power relation to the ambient light near the lighted display and where an exponent of the term is a fraction and,

where the transfer function is adjusted by a constant ratio offset based on the at least one user brightness selection.

31. The display device according to claim 30, where the control circuitry comprises at least one digital to analog converter (DAC) connected to provide the display luminance to the lighted display, where the sensor provides the first signal with essentially equal DAC increments to the DAC, where the DAC increments correlate to constant ratio steps.

32. The display device according to claim 30, where the display luminance provides a brightness level according to the equation, $B=\mathrm{Bo}·$

[B

 



maxB

 



min]((SNS-So)/(T-1))·

BGLC

where B is a display emitted luminance, Bo is a constant corresponding to a brightness offset on a log-log plot of the relationship between the display emitted luminance and the display background illuminance, Bmax is a maximum display brightness, Bmin is a minimum display brightness, SNS is a selected step number, S_O is a midpoint of an SNS range, T is a total number of brightness steps, BGL is a display background luminance due to reflected ambient light, and C is an exponent describing the slope on a log-log plot of the relationship between the display emitted luminance and the display background illuminance.

33. The display device according to claim 32, where the relationship between the display emitted luminance and the display background illuminance is according to the equation, B=Bo·

BGL^C.

34. The display device according to claim 32 where C is in the range of about 0 through about 1.

35. The display device according to claim 32, where C is a positive fraction.

36. The display device according to claim 30,

where the control circuitry determines a first luminance value from a first luminance adjustment sequence, the first luminance value corresponding to at least one of the first signal and a first user brightness selection,

where the control circuitry determines a second luminance value from a second luminance adjustment sequence, the second luminance value corresponding to at least one of the first signal and a second user brightness selection,

where the control circuitry selects the display luminance from one of the first and second luminance values, and

where the constant luminance ratio offset is based on one of the first and second user brightness selections.

37. The display device according to claim 30, where the control circuitry calculates at least one of a look-up chart and the luminance value, the look-up chart to provide the at least one luminance adjustment sequence.

38. The backlight display device according to claim 30, further comprising a bezel having a surface adjacent to the display panel, where the sensor is disposed on the surface, and where the user interface is disposed on the bezel.

39. The display device according to claim 30, where the control circuitry selects the luminance value from a manual luminance adjustment sequence when at least one user brightness selection includes a manual mode.

40. The display device according to claim 30, where the control circuitry selects the luminance value corresponding to a step number from a manual luminance adjustment sequence when at least one user brightness selection includes a manual mode and the step number selection.

41. The display device according to claim 30,

where at least one user brightness selection includes one of a manual mode and an automatic mode and provides a determination of one of daytime and nighttime,

where the control circuitry selects a manual night luminance value as the luminance value when at least one user brightness selection is a nighttime manual mode, the manual night luminance value provided by a manual night luminance adjustment sequence,

where the control circuitry selects a manual day luminance value as the luminance value when at least one user brightness selection is a daytime manual mode, the manual day luminance value provided by a manual day luminance adjustment sequence,

where the control circuitry selects an automatic night luminance value as the luminance value when the at least one user brightness selection is a nighttime automatic mode, the automatic night luminance value provided by an automatic night luminance adjustment sequence, and

where the control circuitry selects an automatic day luminance value as the luminance value when the at least one user brightness selection is a daytime automatic mode, the automatic day luminance value provided by an automatic day luminance adjustment sequence.

42. A method for controlling the brightness of a display device, comprising:

(a) logarithmically generating a first signal in response to the ambient light associated with a lighted display;

(b) selecting a display luminance from at least one luminance adjustment sequence, each luminance adjustment sequence having a plurality of luminance values with constant ratio steps; and

(c) providing the display luminance to a lighted display, where the display luminance is controlled by a transfer function that includes a term having a power relation to the ambient light associated with the lighted display where an exponent of the term is a fraction.

43. The method according to claim 42, where (a) further comprises:

sensing the ambient light on the display panel;

providing an analog signal in response to the ambient light; and

logarithmically amplifying the analog signal to generate the first signal.

44. The method according to claim 42, further comprising providing the display luminance with a brightness level according to the equation, $B=\mathrm{B0}·$

[B

 



maxB

 



min]((SNS-So)/(T-1))·

BGLC

where B is a display emitted luminance, Bo is a constant corresponding to a brightness offset on a log-log plot of the relationship between the display emitted luminance and the display background illuminance, Bmax is a maximum display brightness, Bmin is a minimum display brightness, SNS is a selected step number, SO is a midpoint of an SNS range, T is a total number of brightness steps, BGL is a display background luminance due to reflected ambient light, and C is an exponent describing the slope on a log-log plot of the relationship between the display emitted luminance and the display background illuminance.

45. The method according to claim 44, where the relationship between the display emitted luminance and the display background illuminance is according to the equation, B=Bo·

BGL^C.

46. The method according to claim 42, where (b) further comprises:

determining a first luminance value from a first luminance adjustment sequence, the first luminance value corresponding to the first signal;

determining a second luminance value from a second luminance adjustment sequence, the second luminance value corresponding to at least one user brightness selection; and

selecting the display luminance from one of the first and second luminance values.

47. The method according to claim 42, further comprising:

providing a determination of one of daytime and nighttime;

where if the determination is nighttime, selecting a night luminance value as the luminance value, the night luminance value provided by a night luminance adjustment sequence, the night luminance value corresponding to the step level commanded by the instrument dimming control or other nighttime control; and

where if the determination is daytime, selecting a day luminance value as the luminance value, the day luminance value provided by a day luminance adjustment sequence, the day luminance value corresponding to the first signal.

48. The method according to claim 47, further comprising:

comparing the first signal to a threshold, where signals below the threshold indicate nighttime, where signals above the threshold indicate daytime;

where if the first signal is below the threshold, providing a nighttime determination; and

where if the first signal is above the threshold, providing a daytime determination.

49. The method according to claim 47, where the display device is provided in a vehicle having at least one headlight, where the at least one headlight is turned-on.

50. The method according to claim 47, where the display device is provided in a vehicle having dashboard lights, and further comprising adjusting the night luminance value in response to a dimming level of the dashboard lights.

51. The method according to claim 47, further comprising filtering the day luminance to control fluttering from changes in the ambient light.

52. The method according to claim 42, where (b) further comprises selecting the luminance value from at least one luminance adjustment sequence provided on a look-up table.

53. The method according to claim 42, where (b) further comprises calculating at least one of a look-up table and the luminance value, the look-up table to provide the at least one luminance adjustment sequence.

54. A method for controlling the brightness of a display device, comprising:

(a) determining at least one user brightness selection;

(b) logarithmically generating a first signal in response to the ambient light near a lighted display;

(c) selecting a display luminance value from at least one luminance adjustment sequence, each luminance adjustment sequence having a plurality of luminance values with constant ratio steps;

(d) providing the display luminance to the lighted display, where the display luminance is controlled by a transfer function that includes a term having a power relation to the ambient light near the lighted display where an exponent of the term is a fraction; and

(e) adjusting the transfer function by a constant luminance ratio offset based on the at least one user brightness selection.

55. The display device according to claim 54, further comprising providing the display luminance with a brightness level according to the equation, $B=\mathrm{B0}·$

[B

 



maxB

 



min]((SNS-So)/(T-1))·

BGLC

where B is a display emitted luminance, Bo is a constant corresponding to a brightness offset on a log-log plot of the relationship between the display emitted luminance and the display background illuminance, Bmax is a maximum display brightness, Bmin is a minimum display brightness, SNS is a selected step number, S_O is a midpoint of an SNS range, T is a total number of brightness steps, BGL is a display background luminance due to reflected ambient light, and C is an exponent describing the slope on a log-log plot of the relationship between the display emitted luminance and the display background illuminance.

56. The display device according to claim 55, where the relationship between the display emitted luminance and the display background illuminance is according to the equation, B=Bo·

BGL^C.

57. The method according to claim 54, where (a) further comprises receiving the at least one user brightness selection from a user interface.

58. The method according to claim 54, where (c), when at least one user brightness selection includes a manual mode, further comprises selecting the display luminance from a manual luminance adjustment sequence.

59. The method according to claim 54, where (c), when the at least one user brightness selection includes a manual mode and a step number selection, further comprises selecting the display luminance corresponding to the step number selection on a manual luminance adjustment sequence.

60. The method according to claim 54, where step (c), when the at least one user brightness selection includes a manual mode, further comprises:

providing a determination of one of daytime and nighttime;

where if the determination is nighttime, selecting a manual night luminance value as the luminance value, the manual night luminance value provided by a manual night luminance adjustment sequence; and

where if the determination is daytime, selecting a manual day luminance value as the luminance value, the manual day luminance value provided by a manual day luminance adjustment sequence.

61. The method according to claim 60, where the at least one user brightness selection provides the determination of one of daytime and nighttime.

62. The method according to claim 60, where step (c), when the at least one user brightness selection includes an automatic mode, further comprises:

providing a determination of one of daytime and nighttime;

where if the determination is nighttime, selecting an automatic night luminance value as the luminance value, the automatic night luminance value provided by an automatic night luminance adjustment sequence; and

where if the determination is daytime, selecting a automatic day luminance value as the luminance value, the automatic day luminance value provided by an automatic day luminance adjustment sequence.

63. The method according to claim 54, where essentially all the luminance values have constant ratio steps in each luminance adjustment sequence.