Method to automatically regulate brightness of liquid crystal displays

• US 20070222730A1
• Filed: 03/24/2006
• Published: 09/27/2007
• Est. Priority Date: 03/24/2006
• Status: Active Grant

• Current Assignee: Marketech International Corp.
• Original Assignee: Marketech International Corp.
• Inventors: Shan, Yi-Chia, Tsai, Tsan-Hung, Kao, Hsu-Chia, Kao, Hsu-Pin
• Granted Patent: US 7,564,438 B2
• Time in Patent Office: Days
• US Class Current: 345/89
• 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 2320/0626 for control of overall brightness
• 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 3/2059 using error diffusion
• CPC Class Codes: G09G 3/36 using liquid crystals

Abstract

The present invention provides a method to automatically regulate brightness of liquid crystal displays (LCDs), which resolves the overload and easy fatigue of human eyes and poor image contrast due to high brightness of the conventional LCD. The present invention includes use of four parts, including an image brightness regulating unit, an image brightness ratio computation and output controlling unit, an ambient light detection and brightness adaptation regulating unit and an image gray level expanding unit. The image signals of an LCD are processed in such a manner to enable automatic control of optical flux of LCD TV by regulating the gray level of output images. Also, optical flux of LCD TV can be automatically controlled with the change of images and ambient light, thus alleviating overburdening of human eyes and improving the contrast and comfort of images for a better visual effect.

Claims

1. A method to automatically regulate brightness of liquid crystal displays, said method comprising the steps of:

enabling a gray level of an output image to be regulated by an image brightness regulating unit, said image brightness regulating unit being comprised of a memory unit and a multiplier, based on ambient light and images, said gray level of output image being regulated in such a manner to store images in said memory unit, after completion of statistics of image brightness ratio and identification of brightness gains, said images in said memory unit being output with red, green and blue gray levels of the images multiplied by corresponding brightness gains, thereby regulating the image brightness by changing image gray level; and

applying an image brightness ratio computing and output controlling unit for statistical analysis of image brightness, said image brightness ratio computing and output controlling unit comprising;

a gray level/brightness converting unit, enabling conversion between gray level and corresponding brightness of image, such that a linearity between gray level and brightness accurately calculates brightness of images;

a pixel brightness calculating unit converting red, green and blue gray levels of pixel into brightness;

a display brightness statistical unit used to calculate total brightness Y_image and brightness ratio BR of every display, with addition of the brightness of every point in the display so as to obtain total brightness of the display, the total brightness of the display being divided by maximum total brightness Y_total of the image, obtaining a brightness ratio of an image;

a brightness gains unit being comprised of a brightness gains table, corresponding brightness gains being checked using a brightness ratio, said brightness gains table being a relational table of brightness gains and a brightness ratio established based on a relationship between expected brightness and brightness ratio;

a gains regulation determining unit used to calculate and regulate change rate of a brightness gain, the brightness gain output by the brightness gains unit varying with a sharp change of brightness ratio, the brightness gains being output, the brightness gain varying little with slow or minor change of a brightness ratio;

an ambient light detection and brightness adaptation regulating unit, detecting the change of ambient light using an optical sensor;

with a reference to LUT after low pass filtering of the change of ambient light, and determining the brightness gain of ambient light, the sensor of ambient light being available in monocolor or multicolor type, for a multicolor light sensor, the gains being properly regulated with color change of ambient light; and

a gray level expanding unit aimed to avoid false contour of images arising from lower gray level after brightness gain operation, applying spacial error diffusion or time dithering technology to improve the hierarchical images of the lower gray level.

2. The method defined in claim 1, further comprising:

a pixel brightness calculating unit of said image brightness ratio computing and output controlling unit, controlling the brightness using color space of perceptual uniformity.

3. The method defined in claim 1, further comprising:

enabling smoothing by gain regulation determining unit of the change of brightness gains, said output brightness gain being a mean value of brightness gain output by N (positive integral) images and current brightness gain, when the brightness gain of a neighboring image has a change rate lower than a threshold.

4. The method defined in claim 1, further comprising:

omitting said memory unit of said image brightness regulating unit, regulating the image brightness via brightness of prior image.

5. A method to automatically regulate brightness of liquid crystal displays, said method comprising the steps of:

enabling a gray level of an output image to be regulated by an image brightness regulating unit, said image brightness regulating unit being comprised of a memory unit and a multiplier, based on ambient light and images, said gray level of output image being regulated in such a manner to store images in said memory unit, after completion of statistics of image brightness ratio and identification of brightness gains, said images in said memory unit being output with red, green and blue gray levels of the images multiplied by corresponding brightness gains, thereby regulating the image brightness by changing image gray level;

applying an image brightness ratio computing and output controlling unit for statistical analysis of image brightness, said image brightness ratio computing and output controlling unit comprising;

a gray level/brightness converting unit, enabling conversion between gray level and corresponding brightness of image, such that a linearity between gray level and brightness accurately calculates brightness of images;

a pixel brightness calculating unit converting red, green and blue gray levels of pixel into brightness;

a display brightness statistical unit used to calculate total brightness Y_image and brightness ratio BR of every display, with addition of the brightness of every point in the display so as to obtain total brightness of the display, the total brightness of the display being divided by maximum total brightness Y_total of the image, obtaining a brightness ratio of an image;

a brightness gains unit being comprised of a brightness gains table, corresponding brightness gains being checked using a brightness ratio, said brightness gains table being a relational table of brightness gains and a brightness ratio established based on a relationship between expected brightness and brightness ratio; and

a gains regulation determining unit used to calculate and regulate change rate of a brightness gain, the brightness gain output by the brightness gains unit varying with a sharp change of brightness ratio, the brightness gains being output, the brightness gain varying little with slow or minor change of a brightness ratio;

detecting the change of ambient light by an ambient light detection and brightness adaptation regulating unit, using an optical sensor, with a reference to LUT after low pass filtering of the change of ambient light, and determining the brightness gain of ambient light, the sensor of ambient light being available in monocolor or multicolor type, for a multicolor light sensor, the gains being properly regulated with color change of ambient light;

applying spacial error diffusion or time dithering technology to improve the hierarchical images of the lower gray level by a gray level expanding unit aimed to avoid false contour of images arising from lower gray level after brightness gain operation; and

automatically changing color of the light source in case of color change of ambient light by a LED optical module is located nearby LCD TV, the module being comprised of red, green and blue LEDs, so a ambient light detection and brightness adaptation regulating unit can be used to control LED optical module.

6. The method defined in claim 5, further comprising:

a pixel brightness calculating unit of said image brightness ratio computing and output controlling unit, controlling the brightness using color space of perceptual uniformity.

7. The method defined in claim 5, further comprising:

enabling smoothing by gain regulation determining unit of the change of brightness gains, said output brightness gain being a mean value of brightness gain output by N (positive integral) images and current brightness gain, when the brightness gain of a neighboring image has a change rate lower than a threshold.

8. The method defined in claim 5, further comprising:

omitting said memory unit of said image brightness regulating unit, regulating the image brightness via brightness of prior image.

9. A method to automatically regulate brightness of liquid crystal displays, said method comprising the steps of:

enabling a gray level of an output image to be regulated by an image brightness regulating unit, said image brightness regulating unit being comprised of a memory unit and a multiplier, based on ambient light and images, said gray level of output image being regulated in such a manner to store images in said memory unit, after completion of statistics of image brightness ratio and identification of brightness gains, said images in said memory unit being output with red, green and blue gray levels of the images multiplied by corresponding brightness gains, thereby regulating the image brightness by changing image gray level.