Liquid crystal display device and image display method thereof

• US 8,139,020 B2
• Filed: 03/12/2008
• Issued: 03/20/2012
• Est. Priority Date: 05/08/2007
• Status: Active Grant

• Current Assignee: JVC Kenwood Corporation
• Original Assignee: Victor Company of Japan Limited (JVC Kenwood Corporation)
• Inventors: Ohshima, Yoshinori
• Primary Examiner(s): Hjerpe, Richard
• Assistant Examiner(s): Okebato, Sahlu
• Application Number:
  US12/046,687
• Publication Number:
  US 20080278432A1
• Time in Patent Office: 1,469 Days
• Field of Search: 345/102
• US Class Current: 345/102
• CPC Class Codes: G09G 2320/0233 Improving the luminance or brightness uniformity across the screen
• 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 2320/041 Temperature compensation
• CPC Class Codes: G09G 2320/0646 Modulation of illumination source brightness and image signal correlated to each other
• CPC Class Codes: G09G 2320/0666 for control of colour parameters, e.g. colour temperature
• CPC Class Codes: G09G 2330/021 Power management, e.g. power saving
• 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 3/342 using several illumination sources separately controlled corresponding to different display panel areas, e.g. along one dimension such as lines
• CPC Class Codes: G09G 3/3426 the different display panel areas being distributed in two dimensions, e.g. matrix
• CPC Class Codes: G09G 3/3611 Control of matrices with row and column drivers
• CPC Class Codes: G09G 3/3648 using an active matrix G09G3/367 - G09G3/3696 take precedence

Abstract

A backlight device is divided into multiple regions, and has a configuration in which light emitted from a light source of each of the regions is allowed to leak to other regions. A maximum gradation detector detects a maximum gradation of a regional image signal displayed on each of the regions of the liquid crystal panel. An image gain calculator obtains a gain to be multiplied to each regional image signal. An emission luminance calculator obtains an emission luminance of light to be emitted by each light source, by using an operation expression according to the emission luminance of light to be emitted by the backlight device. At this time, if the emission luminance takes a negative value as a result of calculation, the emission luminance calculator makes a correction so that the emission luminance can take a value equal to or greater than 0.

Claims

1. A liquid crystal display device comprising:

a liquid crystal panel configured to display an image from image signals;

a backlight divided into regions and disposed on the back side of the liquid crystal panel, the backlight comprising light sources in the respective regions, the light sources positioned to emit light into the liquid crystal panel, and the backlight having a structure in which light emitted from each of the light sources of the plurality of regions is allowed to leak to regions other than the respective light source region;

a maximum gradation detector configured to detect, at predetermined intervals, a first maximum gradation of each of regional image signals displayed on regions of the liquid crystal panel that correspond to regions of the backlight device;

an image gain calculator configured to determine a gain value based on a value determined by dividing a second maximum gradation by the first maximum gradation, the second maximum gradation being a possible maximum gradation of the regional image signal and determined based on the number of bits of the regional image signal;

a multiplier configured to multiply a regional image signal by the gain obtained by the image gain calculator, and to output image signals for display on the liquid crystal panel; and

an emission luminance calculator configured to determine the second emission luminance by multiplying a first emission luminance by a first coefficient,

wherein the first emission luminance is the luminance from each region of the backlight obtained by multiplying the maximum luminance from the light source by the inverse number of the gain obtained by the image gain calculator,

wherein the first coefficient is determined from the amount of light that leaks out of adjacent regions and the regions in the vicinity of adjacent regions into a given region, and

wherein the second emission luminance is the luminance of light that each of the light sources of the plurality of regions of the backlight independently emits to obtain the first emission luminance.

2. The liquid crystal display device of claim 1, further comprising:

a light emission calculator configured to determine emission amount of light emitted to the liquid crystal from the light source for each backlight region, according to the second emission luminance; and

a backlight driver configured to adjust light from each region of the backlight according to the output of the emission luminance calculator.

3. The liquid crystal display device of claim 1, wherein

when the calculated second emission luminance is negative, the emission luminance calculator recalculates the second emission luminance from a revised first emission luminance to make the second emission luminance value equal to or greater than 0.

4. The liquid crystal display device of claim 3, wherein

the image gain calculator determines a gain based on the first emission luminance corrected by the emission luminance calculator.

5. The liquid crystal display device of claim 1, wherein

the light sources are configured for an absolute value of the maximum value of the derivative obtained by differentiating a curve representing a luminance distribution characteristic of light emitted by all the light sources of between 0 exclusive and 2 inclusive.

6. The liquid crystal display device of claim 5, wherein

when light emitted from each light source region leaks into adjacent regions, the luminance of leaked light in the center of each said adjacent region is between 0 exclusive and 0.3 inclusive, wherein the luminance in the center of the light source region is 1.

7. The liquid crystal display device of claim 1, wherein

the image gain calculator and emission luminance calculator operate on matrices.

8. The liquid crystal display device of claim 1, wherein

the plurality of regions of the liquid crystal panel are obtained by dividing the liquid crystal panel one-dimensionally in a vertical direction.

9. The liquid crystal display device of claim 1, wherein

the plurality of regions of the liquid crystal panel are obtained by dividing the liquid crystal panel two-dimensionally in horizontal and vertical directions.

10. The liquid crystal display device of claim 8, further comprising:

a non-uniformization processor configured to make the first emission luminance non-uniform by multiplying the first emission luminance of each backlight device region by a second coefficient to gradually lower the luminance on the liquid crystal panel from a center region in the vertical direction of regions one-dimensionally arranged in the liquid crystal panel, toward regions in the upper and lower ends of the panel.

11. The liquid crystal display device of claim 9, further comprising:

a non-uniformization processor configured to make the first emission luminance non-uniform by multiplying the first emission luminance of each backlight device region by a second coefficient to gradually lower the luminance on the liquid crystal panel from a center region in the vertical direction of regions one-dimensionally arranged in the liquid crystal panel, toward regions located in the upper and lower ends of the panel, and the luminance on the liquid crystal panel is lowered gradually from a center region in the horizontal direction of the plurality of regions one-dimensionally arranged in the liquid crystal panel, toward regions located in the left and right ends thereof.

12. The liquid crystal display device of claim 10, wherein

the second coefficient is between 0.8 and 1.0.

13. The liquid crystal display device of claim 11, wherein

the second coefficient is between 0.8 and 1.0.

14. The liquid crystal display as claimed in claim 1 wherein the light source of the backlight device comprises a light emitting diode.

15. The liquid crystal display as claimed in claim 1, wherein each region is optically isolated by a partition wall generally perpendicular to the liquid crystal panel surface and wherein the structure of the backlight that allows light to leak into regions other than the respective light source regions comprises a space between the tops of the partition walls and the liquid crystal panel.

16. The liquid crystal display as claimed in claim 1, further comprising dome lenses between the light sources and the liquid crystal panel surface.

23. The liquid crystal display device as claimed in claim 1, wherein light emission luminescences in regions along a periphery of the liquid crystal panel are further adjusted below their said calculated values.

17. An image displaying method comprising:

detecting, at predetermined intervals, a first maximum gradation of each regional image signal displayed on regions of a liquid crystal panel, while treating image signals to be displayed on the liquid crystal panel as regional image signals respectively corresponding to regions of the liquid crystal panel;

obtaining, a gain factor for each regional image signal, based on a value determined by dividing a second maximum gradation by the first maximum gradation, the second maximum gradation being a possible maximum gradation of the regional image signal and determined according to the number of bits of the regional image signal;

multiplying the regional image signal by the gain factor and supplying the resultant regional image signal to the liquid crystal panel;

obtaining a second emission luminance by multiplying a first emission luminance with a first coefficient, wherein a backlight device of the liquid crystal panel is divided into regions corresponding to the regions of the liquid crystal panel, where the first emission luminance is light emitted by each region of the backlight device, and is obtained by multiplying the maximum light source luminance by the inverse of the gain obtained by the image gain calculator, where the second emission luminance is the luminance that each light source from regions of the backlight device should independently emit to obtain the first emission luminance, and wherein the first coefficient is based on the amount of light that is emitted from each region light source and allowed to leak to other regions; and

displaying an image signal on each liquid crystal panel region, the image signal obtained by multiplying the corresponding regional image signal by the gain, while causing a light source for each region of the backlight device to emit light based on the calculated second emission luminance.

18. The method of claim 17, further comprising

obtaining an emission amount of light to be emitted to the liquid crystal panel by the light source of each of the regions of the backlight device based on the second emission luminance,

wherein the displaying image signal on each liquid crystal panel region includes displaying an image signal on the liquid crystal panel region, while causing the light source for each region of backlight device to emit light based on the emission amount of light.

19. The method of claim 17, wherein

when the second emission luminance takes a minus value as a result of calculation when the second emission luminance is calculated by using the operation expression, the second emission luminance is obtained after the first emission luminance and is corrected so that the second emission luminance is equal to or greater than 0.

20. The method of claim 19, wherein

the gain is calculated by correcting the first emission luminance by the emission luminance calculator.

21. The method of claim 17, wherein

an image signal is displayed on each liquid crystal panel region and obtained by multiplying the corresponding regional image signal while causing the light source of each backlight device region to emit light at the second emission luminance, wherein the light sources follow the characteristic in which the absolute value of the maximum value of the derivative obtained by differentiating a curve representing a luminance distribution characteristic of light emitted by all the light sources is between 0 exclusive and 2 inclusive.

22. The method of claim 21, wherein

when light from each region light source leaks to adjacent regions, the backlight device has a leaked light luminance in the center of each adjacent region between 0 exclusive and 0.3 inclusive, with respect to the leaking region light source.