LIQUID CRYSTAL DISPLAY DEVICE AND BACKLIGHT CONTROL METHOD

• US 20110267379A1
• Filed: 04/15/2011
• Published: 11/03/2011
• Est. Priority Date: 04/28/2010
• Status: Active Grant

• Current Assignee: Maxell, Ltd.
• Original Assignee: Hitachi Consumer Electronics Company Limited (Hitachi, Ltd.)
• Inventors: Shiraishi, Akihiro, KURABAYASHI, Hiroyuki, Ogi, Yuya, Tsuru, Yasutaka, Tanaka, Kazuhiko
• Granted Patent: US 8,896,638 B2
• Time in Patent Office: Days
• US Class Current: 345/690
• CPC Class Codes: G09G 2320/0233 Improving the luminance or brightness uniformity across the screen
• CPC Class Codes: G09G 2320/0238 Improving the black level
• CPC Class Codes: G09G 2320/0606 Manual adjustment
• CPC Class Codes: G09G 2320/0646 Modulation of illumination source brightness and image signal correlated to each other
• CPC Class Codes: G09G 2320/0653 Controlling or limiting the speed of brightness adjustment of the illumination source
• 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 initial light control value calculation section calculates the backlight'"'"'s initial light control value K0 according to brightness of an inputted image signal for each area. A black area measurement section measures a black area S by obtaining ratio of the number of pixels satisfying Y≦Y0 (Y: brightness signal level, Y0: black level threshold) in the screen. A minimum light control value output section determines a minimum light control value Kmin based on comparison between the measured black area S and a black area threshold S0 and outputs a maximum value permissible for the light control value as the value Kmin when the black area S is the threshold value S0 or less. An LED control signal calculation section outputs a control signal to LED light sources based on a light control value K1 as the higher one of K0 and Kmin.

Claims

1. A liquid crystal display device comprising:

a liquid crystal panel;

a backlight which illuminates the liquid crystal panel with light, the backlight being segmented into a plurality of areas;

a control section which controls intensity of the light emitted from the backlight, the control section executing area control for controlling the light intensity of each area based on brightness of an image signal corresponding to the area; and

a detection section which detects proportion of image signals at a prescribe brightness level or less to all image signals for one screen based on the image signals for one screen,

wherein the control section stops the area control when the proportion detected by the detection section is a predetermined value or less.

2. A liquid crystal display device comprising:

a liquid crystal panel which displays images, the liquid crystal panel being segmented into a plurality of areas;

LED light sources as a backlight which controls brightness of each of the areas independently;

an initial light control value calculation section which detects brightness of an inputted image signal in regard to each of the areas and calculates the backlight'"'"'s initial light control value K0 corresponding to each area according to the detected brightness;

a black area measurement section which compares a brightness signal level Y of each pixel in a screen with a black level threshold value Y0 and measures a black area S by obtaining ratio of the number of pixels satisfying Y≦

Y0 to the total number of pixels in the screen;

a minimum light control value output section which determines and outputs a minimum light control value Kmin based on comparison between the black area S measured by the black area measurement section and a black area threshold value S0; and

an LED control signal calculation section which outputs a control signal to the LED light sources based on a light control value K1 as a higher one selected from the initial light control value K0 and the minimum light control value Kmin,

wherein the minimum light control value output section outputs a maximum value permissible for the light control value as the minimum light control value Kmin when the black area S is the black area threshold value S0 or less.

3. The liquid crystal display device according to claim 2, wherein the minimum light control value output section outputs an intermediate light control value previously set corresponding to the black area S and higher than a minimum value permissible for the light control value as the minimum light control value Kmin when the black area S is larger than the black area threshold value S0.

4. The liquid crystal display device according to claim 3, wherein the minimum light control value output section outputs a preset light control value for all black as the minimum light control value Kmin when the black area S corresponds to the entire screen.

5. The liquid crystal display device according to claim 2, further comprising a mode switching section which makes selection between a high image quality setting and a low power setting as a control mode of the backlight,

wherein the black area threshold value S0 or the intermediate light control value is switched in conjunction with the selected control mode.

6. The liquid crystal display device according to claim 2, further comprising an LED gain correction section which calculates an LED correction gain signal G1 according to the black area S measured by the black area measurement section,

wherein the LED control signal calculation section corrects the light control value K1 using the LED correction gain signal G1 and outputs the control signal to the LED light sources based on the corrected light control value.

7. A liquid crystal display device comprising:

a liquid crystal panel;

a backlight which illuminates the liquid crystal panel with light, the backlight being segmented into a plurality of areas; and

a control section which controls intensity of the light emitted from the backlight, the control section executing area control for controlling the light intensity of each area based on brightness of an image signal corresponding to the area, wherein;

the control section controls the backlight so as to maintain the light intensity of each area above 0 even when the brightness of the image signal corresponding to the area is 0.

8. A backlight control method for controlling a backlight of a liquid crystal display device, segmenting a liquid crystal panel for displaying images into a plurality of areas and controlling brightness of each of the areas independently, comprising the steps of:

detecting brightness of an inputted image signal in regard to each of the areas and calculating the backlight'"'"'s light control value corresponding to each area according to the detected brightness;

comparing a brightness signal level Y of each pixel in a screen with a black level threshold value Y0 and measuring a black area S by obtaining ratio of the number of pixels satisfying Y≦

Y0 to the total number of pixels in the screen; and

correcting the calculated light control value according to the measured black area S,

wherein the light control values of the backlight are set at a maximum value when the measured black area S is a black area threshold value S0 or less.

9. The backlight control method according to claim wherein when the measured black area S is larger than the black area threshold value S0, a minimum light control value Kmin as a lower limit of the light control values of the backlight is set at an intermediate light control value previously set corresponding to the black area S and higher than a minimum value permissible for the light control value.