In image display devices provided with backlights such as liquid crystal display devices, by controlling the luminances of the backlights on the basis of input images, the power consumption of the backlights can be suppressed and the image quality of a displayed image can be improved. In particular, by dividing a screen into a plurality of areas and controlling the luminances of backlight sources corresponding to the areas on the basis of portions of an input image within the areas, it is rendered possible to achieve lower power consumption and higher image quality. Hereinafter, such a method for driving a display panel while controlling the luminances of backlight sources on the basis of an input image in each area will be referred to as “area-active drive”.
Liquid crystal display devices that perform area-active drive use, for example, LEDs (light emitting diodes) of three RGB colors or white LEDs, as backlight sources. Luminances (Luminances upon emission) of LEDs corresponding to areas are obtained on the basis of, for example, maximum or mean values of pixel luminances within the areas, and are provided to a backlight driver circuit as LED data. In addition, display data (in the case of liquid crystal display devices, data for controlling the light transmittance of the liquid crystal) is generated on the basis of the LED data and an input image, and the display data is provided to a driver circuit for a display panel. In the case of liquid crystal display devices, the luminance of each pixel on the screen is the product of the luminance of light from the backlight and the light transmittance based on the display data.
By the way, light emitted from LEDs in an area illuminates not only that area but also its surrounding areas. In other words, an area is illuminated not only by light emitted from LEDs in that area but also light emitted from LEDs in its surrounding areas. Accordingly, luminances achieved for display in areas by all LEDs emitting light have to be calculated considering diffusion (spread) of light emitted from each LED. Therefore, when generating the aforementioned display data, for example, a luminance spread filter 104 as shown in FIG. 5 is conventionally used. The luminance spread filter 104 has stored therein numerical data, which indicates how light emitted from LEDs in areas is diffused. In addition, the luminance spread filter is used to calculate luminances (hereinafter, referred to as “display luminances”) that can be achieved upon display (or estimated to be achieved upon display) in areas by all LEDs emitting light, and display data is generated on the basis of the display luminances and an input image.
By driving a driver circuit for a display panel on the basis of the display data thus generated and a driver circuit for a backlight on the basis of the aforementioned LED data, image display based on an input image can be performed.
Note that the following conventional technology documents are known in the art relevant to the present invention. Japanese Laid-Open Patent Publication Nos. 2004-184937, 2005-258403, and 2007-34251 disclose inventions of display devices in which the screen is divided into a plurality of areas and the emission luminance of a backlight provided for each area is controlled to reduce power consumption. In particular, the liquid crystal display device disclosed in Japanese Laid-Open Patent Publication No. 2004-184937 achieves reduced power consumption by automatically turning off backlight sources for a non-display region.