Video display apparatus including brightness control based on ambient illuminance

• US 8,963,826 B2
• Filed: 05/10/2012
• Issued: 02/24/2015
• Est. Priority Date: 08/03/2011
• Status: Expired due to Fees

• Current Assignee: Sharp Kabushiki Kaisha (Hon Hai Precision Industry Co., Ltd.)
• Original Assignee: Sharp Kabushiki Kaisha (Hon Hai Precision Industry Co., Ltd.)
• Inventors: Oda, Eishi, Takeda, Michiaki, Kure, Hiroyoshi
• Primary Examiner(s): Snyder, Adam J
• Application Number:
  US14/232,853
• Publication Number:
  US 20140160180A1
• Time in Patent Office: 1,020 Days
• Field of Search: 345/102
• US Class Current: 345/102
• CPC Class Codes: G09G 2320/0238 Improving the black level
• 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 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 3/32 semiconductive, e.g. using light-emitting diodes [LED]
• CPC Class Codes: G09G 3/3426 the different display panel areas being distributed in two dimensions, e.g. matrix

Abstract

Light leakage and black float are reduced in dark ambient while a perception of high contrast is achieved when a backlight is divided into a plurality of areas and backlight brightness is controlled depending on a video signal corresponding to each area. An area active control portion (2) divides a video signal into a plurality of areas and outputs a first feature value for each area. An LED control portion (3) acquires a first brightness for each divided area of an LED backlight (5) depending on the first feature value of each area, and acquires a second brightness for each area that is acquired by uniformly multiplying a specific multiplying factor acquired depending on the lighting ratio of the LED backlight (5) with respect to the first brightness within a range where a total value of the LED driving current does not exceed a predetermined permissible current value. When the lighting ratio of the LED backlight (5) is at or below a predetermined value, the second brightness is reduced in accordance with ambient lighting detected by a photosensor (8) to acquire a third brightness.

Claims

1. A video display apparatus comprising:

a display panel that displays a video signal;

a backlight that uses LEDs as a light source illuminating the display panel;

a control portion that controls a light emission brightness of the backlight; and

an ambient illuminance detecting portion that detects ambient illuminance, the control portion dividing the backlight into a plurality of areas and controlling light emission of the LEDs for each of the divided areas, wherein

the control portion acquires a first brightness of the LEDs for each area depending on a first feature value of the video signal of a display area corresponding to the divided area,

acquires a second brightness for each area by uniformly multiplying the first brightness by a specific multiplying factor acquired depending on a lighting rate of the backlight or a second feature value of the video signal, within a range where a total value of driving currents of the LEDs is equal to or lower than a predetermined permissible current value, and

acquires a third brightness by reducing the second brightness, when an ambient illuminance detected by the ambient illuminance detecting portion is equal to or lower than a specific value, based on the lighting rate of the backlight or the second feature value of the video signal that is equal to or lower than a predetermined value.

2. The video display apparatus as defined in claim 1, wherein

the video display apparatus has therein a brightness curve that determines a relation between the lighting rate of the backlight or the second feature value of the video signal, and maximal display brightness capable of being taken on a screen of the display panel correlated in advance with the lighting rate of the backlight or the second feature value of the video signal, and wherein

the predetermined value is set to be equal to or higher than the lighting rate of the backlight or the second feature value of the video signal for the maximal display brightness for a duty of 100% taken on the brightness curve.

3. The video display apparatus as defined in claim 1, wherein

the control portion controls light emission of the LEDs for each area based on the second brightness when the ambient illuminance is higher than a specific value, and controls the light emission of the LEDs for each area based on the third brightness when the ambient illuminance is equal to or lower than a specific value.

4. The video display apparatus as defined in claim 1, wherein

the first feature value is a maximal gray scale value of a video signal in the divided area.

5. The video display apparatus as defined in claim 1, wherein

the second feature value is an APL of the video signal.