Liquid crystal display device and image display method thereof

• US 8,139,022 B2
• Filed: 09/08/2008
• 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:
  US12/206,010
• Publication Number:
  US 20090009456A1
• Time in Patent Office: 1,289 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 2320/064 by time modulation of the brightness of the illumination source
• 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 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 3/2092 Details of a display terminals using a flat panel, the details relating to the control arrangement of the display terminal and to the interfaces thereto suitable for both CRT and flat panel G09G5/003; specific for a CRT G09G1/165
• 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

Abstract

High quality images on liquid crystal panel can be obtained alleviating variations of the brightness and color among regions, in which backlight is divided when emission luminance of the backlight is controlled in each region based on image signal. 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 by using luminance bitmap held by luminance bitmap memory. An emission luminance calculator obtains an emission luminance of light to be emitted by each light source.

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 regions, the backlight device comprising light sources in the respective regions, the light sources positioned to emit light into the liquid crystal panel, and the backlight device configured so that light emitted from each light source of each region leaks into adjacent regions;

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

an emission luminance calculator configured to obtain, from the maximum gradation, a light luminance for each light source;

a luminance bitmap memory configured to hold a luminance bitmap that indicates luminance distribution characteristics of the liquid crystal panel, which shows the distribution of luminance of light emitted from the light source in the region of this light source, and in regions other than the region of this light source, the luminance bitmap including data that correspond to each pixel in the image signal;

an image gain calculator configured to determine a gain to multiply an image signal for display on an arbitrary point in each region of the liquid crystal panel, the gain is an inverse of a value obtained by gamma correction on an integral value of light, each value obtained by multiplying the luminance of light that each light source emits, calculated by the emission luminance calculator, from data corresponding to the arbitrary point in the luminance bitmap, the gain has a value that differs depending on the position of each region of the liquid crystal panel, the gain calculated on the basis of the luminance bitmap and the luminance of light that each light source emits, the luminance obtained by the emission luminance calculator, the image gain calculator obtains the gain in correspondence with each pixel of the image signal; and

a multiplier configured to multiply an image signal for display on each region by the gain obtained by the image gain calculator, and to output the image signal for display on the liquid crystal panel.

2. An image display method comprising:

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

obtaining, from the maximum gradation, luminance of light from each light source from each region of a backlight device, the backlight device disposed on the back side of the liquid crystal panel, divided into the plurality of regions, corresponding to the plurality of regions of the liquid crystal panel, comprising light sources in the respective regions, the light sources positioned to emit light into the liquid crystal panel, and configured so that light emitted from each light source from each region is allowed to leak to regions other than the region of the concerned light source;

obtaining a gain by which to multiply an image signal to be displayed on an arbitrary point in each region of the liquid crystal panel, the gain being an inverse of a value obtained by gamma correction on a total of (integral) value, each value obtained by multiplying the luminance of light that each light source from each region independently emits, and data corresponding to the arbitrary point in a luminance bitmap, the gain having a value that differs depending on the position in the liquid crystal panel, the gain calculated on the basis of a luminance of light that each of the light sources of the plurality of regions independently emits, the gain obtained in correspondence with each pixel of the image signal, the luminance bitmap that indicates luminance distribution characteristics of the liquid crystal panel, which shows the distribution of luminance of light emitted from the light source in the region of this light source, and in regions other than the region of this light source, the gain being obtained in correspondence with each pixel of the image signal; and

multiplying an image signal to be displayed on each of the plurality of regions by the gain, and displaying the signal on the liquid crystal panel.