Liquid crystal display device and image display method thereof

• US 8,421,740 B2
• Filed: 07/16/2009
• Issued: 04/16/2013
• Est. Priority Date: 09/18/2008
• Status: Active Grant

• Current Assignee: JVC Kenwood Corporation
• Original Assignee: JVC Kenwood Corporation
• Inventors: WATANUKI, Katsumi
• Primary Examiner(s): Lao, Lun-Yi
• Assistant Examiner(s): Hegarty, Kelly B
• Application Number:
  US12/504,623
• Publication Number:
  US 20100066752A1
• Time in Patent Office: 1,370 Days
• Field of Search: 345 87-102, 345/690, 345/204, 345/207, 382/169, 348671-672, 362 971- 973
• US Class Current: 345/102
• CPC Class Codes: G09G 2310/0232 Special driving of display border areas
• CPC Class Codes: G09G 2320/0233 Improving the luminance or brightness uniformity across 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 2320/0285 using tables for spatial correction of display data
• CPC Class Codes: G09G 2320/041 Temperature compensation
• CPC Class Codes: G09G 2320/043 Preventing or counteracting the effects of ageing
• 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 3/3426 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

Abstract

A liquid crystal panel displays an image from image signals. A backlight device is disposed on the back side of the liquid crystal panel, and is divided into a plurality of regions. The backlight device comprises light sources in each of the regions. The light sources are positioned to emit light onto the liquid crystal panel. A histogram detector detects an image signal gradation distribution for each region and to produce a histogram therefrom. An image gain calculator calculates a gain from the detected gradation distribution of the histogram detector, and controls light emission from each light source in each region of the backlight device. A light emission luminance calculator controls the light emission luminance of each light source based on a maximum luminance of the light sources and based on an inverse number of the gain calculated in the image gain calculator.

Claims

1. A liquid crystal display device, comprising:

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

a backlight device disposed on the back side of the liquid crystal panel, and divided into a plurality of regions, the backlight device comprising light sources in each of the regions, wherein the light sources are positioned to emit light onto the liquid crystal panel;

a histogram detector configured to detect an image signal gradation distribution for each region and to produce a histogram therefrom;

an image gain calculator configured to calculate a gain from the detected gradation distribution of the histogram detector, and to control light emission from each light source in each region of the backlight device, and

a light emission luminance calculator configured to control the light emission luminance of each light source based on a maximum luminance of the light sources and based on an inverse number of the gain calculated in the image gain calculator

further comprising a maximum gradation detector configured to detect a first maximum gradation of the image signal displayed on each of the backlight device regions within one frame period, at predetermined intervals,

wherein the histogram detector detects at least one of a plurality of pixel ratios from the histogram of the image signal gradation distribution, the plurality of pixel ratios includes a pixel ratio lower than a first predetermined gradation and a pixel ratio higher than a second predetermined gradation and wherein pixel ratio is calculated by dividing numbers of pixels that have a certain gradation in one region by total numbers of pixels in that region, and

wherein the image gain calculator determines if a value of pixel ratio lower than the first predetermined gradation is more than or equal to a first threshold value,

when the value of pixel ratio lower than the first predetermined gradation is more than or equal to the first threshold value, the gain is set to a predetermined value based on the value of pixel ratio lower than the first predetermined gradation, and

when the value of pixel ratio lower than the first predetermined gradation is less than the first threshold value, the gain is set to a value calculated by dividing a second maximum gradation of the image signal graduation distribution by the first maximum gradation, wherein the second maximum gradation is determined by the number of bits of the image signal.

2. The liquid crystal display device of claim 1, further comprising a multiplier configured to output to the liquid crystal panel the result of multiplication of the image signals of each region and the gain obtained by the image gain calculator.

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

the image gain calculator determines if the value of pixel ratio lower than the first predetermined gradation is more than or equal to the first threshold value, and if the value of pixel ratio higher than the second predetermined gradation is less than the second threshold value,

when the value of pixel ratio lower than the first predetermined gradation is more than or equal to the first threshold value and the value of pixel ratio higher than the second predetermined gradation is less than the second threshold value, the value of the gain is set to one of a predetermined value and a value based on the pixel ratio,

when the value of pixel ratio lower than the first maximum gradation is less than the first threshold value, or the value of pixel ratio higher than the second predetermined gradation is more than or equal to the second threshold value, the value of the gain is calculated by dividing a second maximum gradation of the image signal graduation distribution by the first maximum gradation, wherein the second maximum gradation is determined by the number of bits of the image signal.

4. The liquid crystal display device of claim 1 wherein

the backlight device is configured to allow light emitted from the light source of each of the plurality of regions to leak to nearby regions,

wherein the light emission luminance calculator calculates a second light emission luminance by multiplying a first light emission luminance by a coefficient that is based on light leaked from nearby regions,

wherein the first light emission luminance is light emission luminance emitted from each region in the backlight device is calculated by multiplying the maximum luminance that the light source can deliver by the inverse of the gain calculated by the image gain calculator, and

the second light emission luminance is light emission luminance emitted by each light source of the regions in the backlight device to obtain the first light emission luminance.

5. An image display method comprising:

obtaining, as image signals for display on a liquid crystal panel, an image signal per each region of a first set on the liquid crystal panel detecting a first maximum gradation of the gradation distribution of image signals per each of the first plurality of regions, at predetermined intervals;

wherein the calculating the gain, comprising;

determining if the value of pixel ratio lower than the first gradation is more than or equal to a first threshold value;

setting the gain to a predetermined value based on the value of pixel ratio lower than the first predetermined gradation, when the value of pixel ratio lower than the first predetermined gradation is more than or equal to a first threshold value, and

setting the gain to a value by dividing a second maximum gradation of the image signal by the first maximum gradation, when the value of pixel ratio lower than the first predetermined gradation is less than the first threshold value, wherein the second maximum gradation is determined by the number of bits of the image signal;

detecting a histogram of the gradation distribution of image signals per each region of the first set including detecting at least one of a plurality pixel ratios from the histogram gradation distribution, the plurality of pixel ratio includes a pixel ratio lower than or equal to a first predetermined gradation and a pixel ratio higher than or equal to a second predetermined gradation;

calculating a gain based on the detected histogram, in order to control light emission luminance of a backlight device, the backlight device being divided into second set of regions corresponding to the first set of regions of the liquid crystal panel wherein calculating the gain comprises setting the gain to a predetermined value based on the value of pixel ratio lower than the first predetermined gradation, when the value of pixel ratio lower than the first predetermined gradation is more than or equal to a first threshold value, and setting the gain to a value by dividing a second maximum gradation of the image signal by the first maximum gradation, when the value of pixel ratio lower than the first predetermined gradation is less than the first threshold value, wherein the second maximum gradation is determined by the number of bits of the image signal; and

displaying an image according to the image signal per region of the liquid crystal panel while causing each light source in respective regions of the backlight device to emit light emission luminance based on a maximum luminance of the light sources and an inverse of the gain.

6. The method of claim 5, wherein respective regions of the backlight device emit light emission luminance based on a value obtained by multiplying the maximum luminance of the light sources by the inverse of the gain.

7. The method of claim 5, wherein calculating the gain comprises:

determining if the value of pixel ratio lower than the first predetermined gradation is more than or equal to the first threshold value, and if the value of pixel ratio higher than the second predetermined gradation is less than the second threshold value,

setting the value of the gain to a predetermined value based on the pixel ratio, when the value of pixel ratio lower than the first predetermined gradation is more than or equal to the first threshold value and the value of pixel ratio higher than the second predetermined gradation is less than the second threshold value,

setting the value of the gain to a value that is calculated by dividing a second maximum gradation of the image signal by the first maximum gradation, when the value of pixel ratio lower than the first predetermined gradation is less than the first threshold value, or the value of pixel ratio higher than the second predetermined gradation is more than or equal to the second threshold value, wherein the second maximum gradation is determined by the number of bits of the image signal.

8. The method of claim 5, wherein the backlight device is configured to allow light emitted from the light source of each of the plurality of regions to leak to nearby regions, wherein

the image displaying comprises:

calculating a second light emission luminance by multiplying a first light emission luminance by a coefficient that is based on light leaked from nearby regions,

wherein the first light emission luminance that is emitted from each of the multiple regions in the backlight device is calculated by multiplying the maximum luminance that the light source can deliver by the inverse of the gain calculated by the image gain calculator, and

wherein the second light emission luminance is light emitted by each light source of the regions in the backlight device to obtain the first light emission luminance; and

displaying an image according to the image signal per region of the liquid crystal panel while causing each light source in respective regions of the backlight device to emit light at the second light emission luminance.