Liquid crystal display device with backlight

• US 8,736,543 B2
• Filed: 04/25/2011
• Issued: 05/27/2014
• Est. Priority Date: 05/28/2010
• Status: Active Grant

• Current Assignee: Maxell, Ltd.
• Original Assignee: Hitachi Consumer Electronics Company Limited (Hitachi, Ltd.)
• Inventors: Kubota, Hidenao, Tsuru, Yasutaka
• Primary Examiner(s): Snyder, Adam J
• Application Number:
  US13/093,667
• Publication Number:
  US 20110292018A1
• Time in Patent Office: 1,128 Days
• Field of Search: 345/102
• US Class Current: 345/102
• CPC Class Codes: G09G 2320/0646 Modulation of illumination source brightness and image signal correlated to each other
• CPC Class Codes: G09G 2330/021 Power management, e.g. power saving
• CPC Class Codes: G09G 2360/144 the light being ambient light
• 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

Abstract

An area control section individually sets illumination intensity (light control value) of each backlight cell corresponding to each area of the display screen. A spatial filter corrects the light control values so that spatial distribution of the light control values becomes more moderate between adjoining areas. A black area control section sets the minimum value of the light control value based on a “black area” in the screen. A power control section corrects the light control values so that power consumption of the backlight does not exceed a limit value. A shading control section corrects the light control values to relatively lower brightness in the peripheral part of the screen compared to the central part of the screen. A micro-controller switches the operations of the above light control value correcting sections according to an image display mode selected by the user.

Claims

1. A liquid crystal display device comprising a liquid crystal panel and a backlight which illuminates the liquid crystal panel with light, wherein:

the liquid crystal panel is segmented into a plurality of areas of pixels by dividing the pixels on the panel into a plurality of pixel groups, and

the backlight is formed by a plurality of backlight cells corresponding to the areas, respectively, and

the liquid crystal display device comprises;

an area control section which individually sets a light control value for controlling illumination intensity of each backlight cell, based on a brightness level of an image signal for the area corresponding to the backlight cell;

light control value correcting sections which corrects the light control values set by the area control section; and

a controller which controls operations of the area control section and the light control value correcting sections, wherein;

the light control value correcting sections include;

a black area control section which measures a black area based on the number of pixels whose brightness signal level is a black level threshold value or less, compares the calculated black area with a black area threshold value, and sets a minimum value of the light control value based on result of the comparison, and which sets maximum values of the light control values of all the areas in a case where the black area is less than the black area threshold value,

a power control section which calculates power consumption of the backlight and corrects the light control values so that the power consumption does not exceed an electric power limit value, and

a shading control section which corrects the light control values so as to relatively lower brightness in a peripheral part of a screen of the liquid crystal panel in comparison with a central part of the screen,

the controller controls the illumination by the backlight by switching the operations of the light control value correcting sections according to one of image display modes which has been selected by a user,

the image display modes include a first image display mode in which an image is able to be displayed at highest brightness, a second image display mode which is lower in power consumption than the first image display mode, and a third image display mode in which an image is able to be displayed at higher brightness and with higher contrast,

when the first image display mode has been selected, the controller controls the black area control section and the power control section so that the black area control section is ON and the power control section is OFF,

when the second image display mode has been selected, the controller controls the black area control section, the power control section, and the shading control section so that the black area control section is OFF and the power control section and the shading control section are ON, and

when the third image display mode has been selected, the controller controls the black area control section, the power control section, and the shading control section so that the black area control section is ON and the power control section and the shading control section are OFF.

2. The liquid crystal display device according to claim 1, wherein:

the light control value correcting sections further include;

a spatial filter which corrects the light control values so that spatial distribution of the light control values becomes more moderate in consideration of effect of leaking of light between adjoining areas;

wherein, when the first or second image display mode has been selected, the controller sets the spatial filter at a low level, and, when the third image display mode has been selected, the controller sets the spatial filter at a higher level than the level at which the controller sets the spatial filter when the first or second image display mode has been selected.

3. The liquid crystal display device according to claim 2,

wherein the controller sets the black area threshold value of the black area control section, the electric power limit value of the power control section or a power reduction value of the shading control section according to selection by the user.

4. The liquid crystal display device according to claim 1,

wherein the first image display mode is an in-store demonstration mode.

5. The liquid crystal display device according to claim 1, further comprising an illuminance sensor which detects illuminance around the device,

wherein the controller controls the illumination by the backlight by switching the operations of the light control value correcting sections according to the illuminance detected by the illuminance sensor.