Method and device for clipping a gray scale level of pixels during the dimming of the backlight of a display device

Patent metadata

Field	Value
Publication number	US-2016133205-A1
Application number	US-201514918487-A
Country	US
Kind code	A1
Filing date	Oct 20, 2015
Priority date	Nov 7, 2014
Publication date	May 12, 2016
Grant date	—

Abstract

The present disclosure provides method and device for dimming the backlight of an LCD. A number of pixels at each grayscale level of an input image is determined. The determined number of pixels at each grayscale level is accumulated to generate an accumulated distribution of the number of pixel and the accumulated distribution is filtered. A threshold grayscale level at which the filtered accumulated distribution exceeds a threshold value is determined. A scaling factor is determined based on the threshold grayscale level. The grayscale level of pixels of the input image having a grayscale level lower than or equal to the threshold grayscale level are up-scaled based on the scaling factor, the grayscale value of pixels of the input image having a grayscale level greater than the threshold grayscale level are set to have a predetermined clipping grayscale level, and the LCD backlight is dimmed based on the scaling factor.

First claim

What is claimed is:

1 . A method for dimming the backlight of a liquid crystal display (LCD), the method comprising:
determining number of pixels at each grayscale level of an input image to the LCD; accumulating the determined number of pixels at each grayscale level to generate an accumulated distribution of the number of pixel at each grayscale level; filtering the accumulated distribution of the number of pixels at each grayscale level; determining a threshold grayscale level at which the filtered accumulated distribution of the number of pixels exceeds a threshold value; determining a scaling factor based on the determined threshold grayscale level; up-scaling the grayscale level of pixels of the input image having a grayscale level lower than or equal to the determined threshold grayscale level based on the scaling factor; setting the grayscale value of pixels of the input image having a grayscale level greater than the threshold grayscale level to have a predetermined clipping grayscale level; and dimming a backlight of the LCD based on the scaling factor.

2 . The method of claim 1 , wherein filtering the accumulated distribution of the number of pixels at each grayscale level comprises:
applying a low pass filter to the accumulated distribution of the number of pixels at each grayscale level.

3 . The method of claim 1 , wherein filtering the accumulated distribution of the number of pixels at each grayscale level comprises:
accumulating the accumulated distribution of the number of pixels at each grayscale level.

4 . The method of claim 1 , wherein the scaling factor is inversely proportional to the threshold grayscale level.

5 . The method of claim 4 , wherein the scaling factor is directly proportional to a maximum grayscale level of the LCD.

6 . The method of claim 1 , wherein setting the grayscale value of pixels having a grayscale level greater than the threshold grayscale level to have a predetermined clipping grayscale level comprises:
setting the grayscale value of pixels having a grayscale level greater that the threshold grayscale level to have a grayscale level equal to a maximum grayscale level of the LCD.

7 . The method of claim 1 , wherein the backlight is dimmed by a factor inversely proportional to the scaling factor.

8 . The method of claim 1 , wherein the accumulation of the determined number of pixels at each grayscale level starts from a maximum grayscale level of the LCD.

9 . A liquid crystal display (LCD) comprising:
a histogram generator configured to determine a number of pixels at each grayscale level of an input image of the LCD; a first accumulator configured to receive the number of pixels at each grayscale level from the histogram generator, and to generate an accumulated distribution of the number of pixels at each grayscale level by accumulating the received number of pixels at each grayscale value; a filter configured to receive the accumulated distribution of the number of pixels at each grayscale level from the first accumulator, and filter the accumulated distribution of the number of pixels at each grayscale level; a comparator configured to receive the filtered accumulated distribution of the number of pixels at each grayscale level from the filter, compared the filtered accumulated distribution to a threshold value, and determine a threshold grayscale level at which the filtered accumulated distribution of the number of pixels exceeds a threshold level; a data modulator configured to receive the threshold grayscale level from the comparator, to determine a scaling factor based on the determined threshold grayscale level, to up-scale the grayscale level of pixels of the input image having a grayscale level lower than or equal to the determined threshold grayscale level based on the scaling factor, and to set the grayscale value of pixels of the input image having a grayscale level greater than the threshold grayscale level to have a predetermined clipping grayscale level; and a backlight controller configured to receive the scaling factor from the data modulator, and dim the backlight of the LCD based on the scaling factor.

10 . The LCD of claim 9 , wherein filtering the accumulated distribution of the number of pixels at each grayscale level comprises:
applying a low pass filter to the accumulated distribution of the number of pixels at each grayscale level.

11 . The LCD of claim 9 , wherein filtering the accumulated distribution of the number of pixels at each grayscale level comprises:
accumulating the accumulated distribution of the number of pixels at each grayscale level.

12 . The LCD of claim 9 , wherein the scaling factor is inversely proportional to the threshold grayscale level.

13 . The LCD of claim 12 , wherein the scaling factor is directly proportional to a maximum grayscale level of the LCD.

14 . The LCD of claim 9 , setting the grayscale value of pixels having a grayscale level greater than the threshold grayscale level to have a predetermined clipping grayscale level comprises:
setting the grayscale value of pixels having a grayscale level greater that the threshold grayscale level to have a grayscale level equal to a maximum grayscale level of the LCD.

15 . The LCD of claim 9 , wherein the backlight is dimmed by a factor inversely proportional to the scaling factor.

16 . The LCD of claim 9 , wherein the accumulation of the determined number of pixels at each grayscale level starts from a maximum grayscale level of the LCD.

17 . A display driver circuit for driving a display panel of a liquid crystal display (LCD) and a backlight of the LCD, the display driver comprising:
a histogram generator configured to determine a number of pixels at each grayscale level of an input image of the LCD; a first accumulator configured to receive the number of pixels at each grayscale level from the histogram generator, and to generate an accumulated distribution of the number of pixels at each grayscale level by accumulating the received number of pixels at each grayscale value; a second accumulator configured to receive the accumulated distribution of the number of pixels at each grayscale level from the first accumulator, and filter the accumulated distribution of the number of pixels at each grayscale level; a comparator configured to receive the filtered accumulated distribution of the number of pixels at each grayscale level from the second accumulator, compared the filtered accumulated distribution to a threshold value, and determine a threshold grayscale level at which the filtered accumulated distribution of the number of pixels exceeds a threshold level; a data modulator configured to receive the threshold grayscale level from the comparator, to determine a scaling factor based on the determined threshold grayscale level, and to up-scale the grayscale level of pixels of the input image having a grayscale level lower than or equal to the determined threshold grayscale level based on the scaling factor, and set the grayscale value of pixels of the input image having a grayscale level greater than the threshold grayscale level to have a predetermined clipping grayscale level; and a backlight controller configured to receive the scaling factor from the data modulator, and dim the backlight of the LCD based on the scaling factor.

18 . The display driver circuit of claim 17 , wherein filtering the accumulated distribution of the number of pixels at each grayscale level comprises:
accumulating the accumulated distribution of the number of pixe

Assignees

• Lg Display Co Ltd

Inventors

• Kwon Kyungjoon
• Heo Cheon

Classifications

• G09G3/3607 Primary

  for displaying colours or for displaying grey scales with a specific pixel layout, e.g. using sub-pixels (display of colours in flat matrix panels other than liquid crystal displays G09G3/2003; grey scales specific for television H04N3/127) · CPC title

• G09G2320/0626

  for control of overall brightness · CPC title

• G09G2320/0233

  Improving the luminance or brightness uniformity across the screen · CPC title

• G09G3/3406

  Control of illumination source (illumination devices structurally associated with liquid crystal cells G02F1/1336) · CPC title

• G09G2320/029

  by monitoring one or more pixels in the display panel, e.g. by monitoring a fixed reference pixel · CPC title