Liquid crystal display apparatus

• US 20050231457A1
• Filed: 02/09/2005
• Published: 10/20/2005
• Est. Priority Date: 02/09/2004
• Status: Active Grant

• Current Assignee: Panasonic Intellectual Property Corporation of America (Panasonic Holdings Corporation)
• Original Assignee: Hitachi Displays Limited (Japan Display Incorporated)
• Inventors: Yamamoto, Tsunenori, Konno, Akitoyo, Wakagi, Masatoshi, Inuzuka, Tatsuki, Hiyama, Ikuo, Kajita, Daisuke
• Granted Patent: US 7,595,784 B2
• Time in Patent Office: Days
• US Class Current: 345/102
• CPC Class Codes: G02F 1/133601 for spatial active dimming
• CPC Class Codes: G09G 2300/0491 Use of a bi-refringent liquid crystal, optically controlled bi-refringence [OCB] with bend and splay states, or electrically controlled bi-refringence [ECB] for controlling the color
• CPC Class Codes: G09G 2310/0235 Field-sequential colour display
• CPC Class Codes: G09G 2320/0247 Flicker reduction other than flicker reduction circuits used for single beam cathode-ray tubes
• CPC Class Codes: G09G 2320/0257 Reduction of after-image effects
• CPC Class Codes: G09G 2320/0261 in the context of movement of objects on the screen or movement of the observer relative to the screen
• CPC Class Codes: G09G 2320/0276 for the purpose of adaptation to the characteristics of a display device, i.e. gamma correction
• CPC Class Codes: G09G 2320/0626 for control of overall brightness
• CPC Class Codes: G09G 2320/064 by time modulation of the brightness of the illumination source
• CPC Class Codes: G09G 2320/0653 Controlling or limiting the speed of brightness adjustment of the illumination source
• CPC Class Codes: G09G 2320/103 Detection of image changes, e.g. determination of an index representative of the image change
• CPC Class Codes: G09G 2360/144 the light being ambient light
• CPC Class Codes: G09G 2360/145 the light originating from the display screen
• CPC Class Codes: G09G 2360/16 Calculation or use of calculated indices related to luminance levels in display data
• CPC Class Codes: G09G 3/3413 Details of control of colour illumination sources

Abstract

The liquid crystal display apparatus includes a liquid crystal display, a backlight unit for emitting rays of light of three or more colors, the ray of each color being controlled, and applying these rays of light onto the liquid crystal display. A controller is further provided for controlling a change of display data of each color of the liquid crystal display and an emitted light quantity of each color of the backlight unit at a time, based on a video signal being inputted for displaying the corresponding image and an output signal sent from an ambient light sensor for sensing ambient light.

Claims

1. A liquid crystal display apparatus comprising:

a liquid crystal display composed of a pair of substrates, a liquid crystal layer laid between said pair of substrates, a plurality of electrode groups for applying an electric field onto said liquid crystal layer, and a plurality of active elements being connected with said electrode groups and having a plurality of sub-pixel structures; and

a backlight unit having a capability of controlling light emission of each color, for applying a ray of light of each color onto said liquid crystal display; and

a controller for controlling a change of display data of each color on said liquid crystal display and a quantity of each color ray of light emitted from said backlight unit, based on an output signal sent from a backlight sensor for sensing light emission of said backlight unit and a video signal of each color being inputted for displaying the corresponding image on said liquid crystal display.

5. A liquid crystal display apparatus as claimed in claim 1, wherein said backlight unit is composed of light-emitting diodes of three primary colors and the light emission of said backlight unit is controlled through the effect of pulse width modulation.

6. A liquid crystal display apparatus as claimed in claim 1, wherein said liquid crystal display includes a plurality of electrode groups located on one of said substrates so that the major axes of liquid crystal molecules may be aligned on a plane in parallel to said substrate when no electric field is applied to said liquid crystal layer.

7. A liquid crystal display apparatus as claimed in claim 6, wherein said display data changed for being outputted to said liquid crystal display mainly uses specific portions of a gradation characteristic of said liquid crystal display.

8. A liquid crystal display apparatus as claimed in claim 7, wherein said display data changed for being outputted to said liquid crystal display mainly uses only an area of 100/255 or more of a gradation characteristic of said liquid crystal display.

9. A liquid crystal display apparatus as claimed in claim 1, wherein said liquid crystal display includes a plurality of electrode groups located on both of said substrates so that the major axes of liquid crystal molecules are aligned perpendicularly to the substrate when no electric field is applied.

10. A liquid crystal display apparatus as claimed in claim 9, wherein said display data changed for being outputted to said liquid crystal display mainly uses only a specific portion of a gradation data characteristic of said liquid crystal display.

11. A liquid crystal display apparatus as claimed in claim 10, wherein said display data changed for being outputted to said liquid crystal display mainly uses an area except 20/255 to 80/255 of a gradation characteristic of said liquid crystal display.

12. A liquid crystal display apparatus as claimed in claim 9, wherein a gradation data distribution among colors of said display data changed for being outputted to said liquid crystal display is smaller (shaped more similarly) than a gradation data distribution of said display data before being changed.

13. A liquid crystal display apparatus as claimed in claim 1, wherein said backlight unit includes light-emitting diode elements located under said liquid crystal display in a planar manner.

14. A liquid crystal display apparatus as claimed in claim 1, wherein said backlight unit is composed of a light waveguide under said liquid crystal display and light-emitting diodes located on the edges of said light waveguide.

15. A liquid crystal display apparatus as claimed in claim 14, wherein said backlight unit is composed so that its plane is divided into several areas and these areas are selectively controlled to be light-emitted.

16. A liquid crystal display apparatus as claimed in claim 1, wherein a normalized output characteristic of inputted data to a maximum luminance in the control for a backlight emission quantity is the same input and output characteristic as a normalized output characteristic of an inputted video signal to a maximum luminance of said liquid crystal display apparatus, and including the control of:

determining a conversion maximum gray scale point MAX on an analyzed result of a video signal of each color to be inputted for displaying the corresponding image onto said liquid crystal display;

changing said display data so as to convert said inputted video signal at the MAX gray scale into a signal at a gray scale in which a liquid crystal transmittance becomes maximum; and

lowering a backlight luminance output into a luminance level indicated by the MAX in said input and output characteristic.

20. A liquid crystal display apparatus as claimed in claim 16, wherein a normalized output characteristic of inputted data to a maximum luminance in said backlight quantity control circuit and a normalized output characteristic of an inputted video signal to a maximum luminance in said liquid crystal display apparatus are represented by a γ

power of an inputted signal value (γ

is a gamma characteristic value).

21. A liquid crystal display apparatus as claimed in claim 16, further comprising a subtitle detecting circuit for detecting if a subtitle is present and a location on the screen if any, and wherein if any subtitle is detected, said conversion maximum gray scale point MAX is determined on an analyzed result of a video signal excepting a signal portion corresponding with said detected subtitle.

22. A liquid crystal display apparatus as claimed in claim 16, wherein about a 0 gray scale signal of each color in said inputted video signal, no conversion of said 0 gray scale signal is executed with respect to the color with the highest MAX of the three colors and about the other colors the conversion of said 0 gray scale signal is executed so as to make the 0 gray scale of each color equal to a 0 gray scale luminance level at which said MAX becomes the highest.

23. A liquid crystal display apparatus as claimed in claim 16, further comprising a subtitle detecting circuit for detecting if a subtitle is present and a location on the screen if any, and about a data signal representing a subtitle included in an inputted video signal, about the color with the lowest MAX of the three colors, said data signal representing a subtitle is not converted, and about the other colors, said data signal is converted so as to make the maximum gray scale of each color equal to the maximum luminance level of the color with the lowest MAX.

24. A liquid crystal display apparatus as claimed in claim 16, further comprising a scene change detecting circuit for detecting a change of a scene displayed by said inputted video signal, and wherein said conversion maximum gray scale point MAX determined only on the display data on the screen is reset on the basis of a signal sent from said scene change detecting circuit.

25. A liquid crystal display apparatus as claimed in claim 24, wherein said conversion maximum gray scale point MAX has a restricted inter-frame variation and a convertible quantity if no scene change takes place is smaller than a convertible quantity if any scene change is present.

2. A liquid crystal display apparatus comprising:

a liquid crystal display composed of a pair of substrates, a liquid crystal layer laid between said pair of substrates, a plurality of electrode groups for applying an electric field onto said liquid crystal layer, and a plurality of active elements being connected with said electrode groups and having a plurality of sub-pixel structures;

a backlight unit having a capability of controlling light emission of each color, for applying a ray of light of each color onto said liquid crystal display;

a display contents analyzing circuit for analyzing a video signal to be inputted for displaying the corresponding image on said liquid crystal display;

a light sensor for sensing light emission of said backlight unit;

an image quality controller for controlling a changing quantity of each color of display data and a quantity of each color ray of light emitted from said backlight unit based on signals sent from said display contents analyzing circuit and said light sensor;

a display data changing circuit for changing data of each color to be displayed on said liquid crystal display based on a signal sent from said image quality controller; and

a backlight quantity control circuit for controlling an emitted light quantity of each color of said backlight unit based on a signal sent from said image quality controller.

17. A liquid crystal display apparatus as claimed in claim 2, wherein a normalized output characteristic of inputted data to a maximum luminance in the control for a backlight emission quantity is the same input and output characteristic as a normalized output characteristic of an inputted video signal to a maximum luminance of said liquid crystal display apparatus, and including the control of:

determining a conversion maximum gray scale point MAX on an analyzed result of a video signal of each color to be inputted for displaying the corresponding image onto said liquid crystal display;

changing said display data so as to convert said inputted video signal at the MAX gray scale into a signal at a gray scale in which a liquid crystal transmittance becomes maximum; and

lowering a backlight luminance output into a luminance level indicated by the MAX in said input and output characteristic.

3. A liquid crystal display apparatus comprising:

a liquid crystal display composed of a pair of substrates, a liquid crystal layer laid between said pair of substrates, a plurality of electrode groups for applying an electric field onto said liquid crystal layer, and a plurality of active elements being connected with said electrode groups and having a plurality of sub-pixel structures; and

a backlight unit having a capability of controlling light emission of each color, for applying a ray of light of each color onto said liquid crystal display; and

a controller for controlling a change of display data of each color on said liquid crystal display and a quantity of each color ray of light emitted from said backlight unit, based on an output signal sent from a backlight sensor for sensing light emission of said backlight unit, a video signal of each color being inputted for displaying the corresponding image on said liquid crystal display, and an output signal sent from an ambient light sensor for sensing ambient light.

18. A liquid crystal display apparatus as claimed in claim 3, wherein a normalized output characteristic of inputted data to a maximum luminance in the control for a backlight emission quantity is the same input and output characteristic as a normalized output characteristic of an inputted video signal to a maximum luminance of said liquid crystal display apparatus, and including the control of:

determining a conversion maximum gray scale point MAX on an analyzed result of a video signal of each color to be inputted for displaying the corresponding image onto said liquid crystal display and an output signal sent from said ambient light sensor;

changing said display data so as to convert said inputted video signal at the MAX gray scale into a signal at a gray scale in which a liquid crystal transmittance becomes maximum; and

lowering a backlight luminance output into a luminance level indicated by the MAX in said input and output characteristic.

4. A liquid crystal display apparatus comprising:

a liquid crystal display composed of a pair of substrates, a liquid crystal layer laid between said pair of substrates, a plurality of electrode groups for applying an electric field onto said liquid crystal layer, and a plurality of active elements being connected with said electrode groups and having a plurality of sub-pixel structures;

a backlight unit having a capability of controlling light emission of each color, for applying a ray of light of each color onto said liquid crystal display;

a display contents analyzing circuit for analyzing a video signal to be inputted for displaying the corresponding image on said liquid crystal display;

a backlight sensor for sensing light emission of said backlight unit;

an ambient light sensor for sensing ambient light;

an image quality controller for controlling a changing quantity of each color of display data and a quantity of each color ray of light emitted from said backlight unit based on signals sent from said display contents analyzing circuit, said backlight sensor, and said ambient light sensor;

a display data changing circuit for changing data of each color to be displayed on said liquid crystal display based on a signal sent from said image quality controller; and

a backlight quantity control circuit for controlling an emitted light quantity of each color of said backlight unit based on a signal sent from said image quality controller.

19. A liquid crystal display apparatus as claimed in claim 4, wherein a normalized output characteristic of inputted data to a maximum luminance in the control for a backlight emission quantity is the same input and output characteristic as a normalized output characteristic of an inputted video signal to a maximum luminance of said liquid crystal display apparatus,

said image quality controller determines a conversion maximum gray scale point MAX based on an analyzed result of a video signal of each color being inputted for displaying the corresponding image on said liquid crystal display,

said display data changing circuit changes said display data so as to convert an inputted video signal at said MAX gray scale into a signal at a gray scale where a liquid crystal transmittance becomes maximum, and

said backlight quantity control circuit controls a backlight luminance output to be lowered to the gray scale level indicated by the MAX in said input and output characteristic.