KR100759902B1 - Liquid crystal display and method of adjusting brightness for the same - Google Patents

Abstract

A liquid crystal display and a method of adjusting brightness for the same are provided to enhance brightness ratio by controlling brightness for each area of a back light unit in correspondence to image signals. A liquid crystal display comprises a back light unit(300), a liquid crystal display unit(400), and a control unit(200). The back light unit includes a light emitting unit(320) divided into a plurality of partial areas such that the brightness of each partial area is controlled. The liquid crystal display unit includes an LCD panel unit(420) and an LCD drive unit(410). The control unit calculates representative value applied to control brightness of each partial area in correspondence to image signals, reduces the representative value by a predetermined ratio to reduce power consumption, and outputs the reduced representative value to the back light unit.

Description

Liquid crystal display and method of adjusting brightness for the same}

1 is a block diagram schematically showing the overall configuration of the present invention.

2 is a diagram illustrating a method for calculating a representative value of a partial region according to an embodiment of the present invention.

3 is a diagram illustrating a method of compensating a representative value of a partial region according to an exemplary embodiment of the present invention.

4 is a view showing a method for reducing a representative value for power saving according to an embodiment of the present invention.

5 illustrates a method of compensating for brightness of image pixels according to an exemplary embodiment of the present invention.

6 is a flow chart showing a brightness adjustment process according to an embodiment of the present invention.

* Description of the main parts of the drawings *

100: image processing unit 200: control unit

300: backlight 310: drive unit

320: light emitting unit 400: liquid crystal display unit

410 LCD driver 420 LCD panel

The present invention relates to a liquid crystal display device and a brightness adjustment method thereof, and more particularly, the brightness can be adjusted for each partial region of the backlight in response to an input image signal, so that the contrast ratio is improved. The present invention relates to a liquid crystal display device and a brightness adjusting method in which power can be effectively reduced by reducing a representative value to be applied at a predetermined ratio.

In general, the liquid crystal display device is used to display an image on a monitor such as a TV, a notebook computer, a desktop computer, and the like, and does not generate light by itself, and therefore, light from a separate light source should be used. Therefore, the liquid crystal display includes a backlight for forming a light source on the rear side of the liquid crystal panel, and is configured to display an image by controlling the transmittance of light emitted from the backlight according to the movement of the liquid crystal.

Conventional backlights have used a uniform backlight that supplies a uniform light source throughout the panel. The uniform backlight supplies uniform light to the entire LCD panel, but due to the loss of light incident on the panel, the dark image (when the pixel value is 0) is not completely dark, which significantly reduces the contrast ratio.

Also, both dark and bright images use the same backlight brightness. Therefore, a low brightness causes a waste of power in a partial region of the backlight corresponding to a dark image sufficient. Accordingly, a backlight capable of individually adjusting brightness for each partial region of the backlight is required to correspond to the input image.

The present invention is to solve the above problems, the brightness can be adjusted for each partial region of the backlight in response to the input image signal, the contrast ratio is improved, the representative value to be applied for the brightness adjustment for each partial region at a predetermined ratio It is an object of the present invention to provide a liquid crystal display and a brightness adjusting method capable of reducing power effectively.

In order to achieve the above object, a liquid crystal display device according to the present invention includes a backlight unit including a light emitting unit which is divided into a predetermined number of partial regions and whose brightness is adjusted for each partial region; A liquid crystal display including an LCD panel unit and an LCD driver; And a controller configured to calculate a representative value to be applied to brightness adjustment of each partial region in response to an input image signal, reduce the representative value by a predetermined ratio for power saving, and output the reduced representative value to the backlight unit. .

Preferably, the predetermined ratio is calculated by the formula:

R = A / (A + T_Thr * (255-A))

Here, R is a predetermined ratio, A is a cutoff gray level, a maximum gray level value of an image pixel corresponding to a partial region excluding white Gaussian noise, and T_Thr is a predetermined threshold value in the range of 0 to 1.

Also preferably, the cutoff graylevel A is a value that satisfies the following equation:

Here, g is a gray level, H (g) is a total number of pixels corresponding to 0 to g, and Cut_Thr is a predetermined threshold value such that the number of pixels belonging to gray levels 0 to A is large.

Preferably, the controller multiplies the gray level of the image pixels corresponding to each partial region by 1 / R or (1 / R) ^{1 / γ} to compensate for the decrease in brightness of the backlight unit due to the reduced representative value for power saving. Adjust the brightness of the image to be displayed.

Also, preferably, the controller spatially filters the representative value to maintain the brightness of the partial area having the maximum brightness among the partial areas.

Advantageously, the controller temporally filters the representative value using the following equation:

Here, P 'is a predetermined threshold for filtering, P' = min (P + S, 1),

P = │Mean_P-Mean_C│ / 256, S = │Mean_P-Mean_C│ / 256,

는 현재 영상의 k번째 부분영역의 필터링 후의 대표값,

는 현재 영상의 k번째 부분영역의 대표값,

는 이전 영상의 k번째 부분영역의 대표값, P는 프레임에 대한 영상의 휘도변화율, S는 부분영역에 대한 영상의 휘도변화율, Mean_P는 이전 영상의 픽셀들의 평균휘도, Mean_C는 현재 영상의 픽셀들의 평균휘도이다.

Represents a representative value after filtering of the kth subregion of the current image,

Is the representative value of the kth subregion of the current image,

Is the representative value of the k-th subregion of the previous image, P is the luminance change rate of the image for the frame, S is the luminance change rate of the image for the subregion, Mean_P is the average luminance of the pixels of the previous image, and Mean_C is the Average luminance.

In addition, the brightness adjustment method of the liquid crystal display according to the present invention comprises the steps of calculating a representative value for the brightness adjustment for each partial region of the light emitting unit in response to the input image signal; Reducing the representative value at a predetermined rate for power saving; And outputting the reduced representative value to the backlight unit to apply the reduced representative value for the brightness adjustment of each partial region.

Here, the predetermined ratio is calculated by the following equation:

R = A / (A + T_Thr * (255-A))

Here, R is a predetermined ratio, A is a cutoff gray level, a maximum gray level value of an image pixel corresponding to a partial region excluding white Gaussian noise, and T_Thr is a predetermined threshold value in the range of 0 to 1.

In addition, the cutoff gray level A is preferably a value satisfying the following equation:

Here, g is a gray level, H (g) is a total number of pixels corresponding to 0-g, and Cut_Thr is a predetermined threshold value such that the number of pixels belonging to gray levels 0 to A becomes a large number.

Also, the image to be displayed is multiplied by 1 / R or (1 / R) ^{1 / γ} by the gray level of the image pixels corresponding to each partial region to compensate for the decrease in brightness of the backlight unit due to the reduced representative value for power saving. It is preferable to further include the step of adjusting the brightness of.

The method may further include spatial filtering the representative value to maintain the brightness of the partial area having the maximum brightness among the partial areas.

In addition, it is preferable to further include the step of time filtering the representative value using the following equation:

Here, P 'is a predetermined threshold for filtering, P' = min (P + S, 1),

P = │Mean_P-Mean_C│ / 256, S = │Mean_P-Mean_C│ / 256,

는 현재 영상의 k번째 부분영역의 필터링 후의 대표값,

는 현재 영상의 k번째 부분영역의 대표값,

는 이전 영상의 k번째 부분영역의 대표값, P는 프레임에 대한 영상의 휘도변화율, S는 부분영역에 대한 영상의 휘도변화율, Mean_P는 이전 영상의 픽셀들의 평균휘도, Mean_C는 현재 영상의 픽셀들의 평균휘도이다.

Represents a representative value after filtering of the kth subregion of the current image,

Is the representative value of the kth subregion of the current image,

Is the representative value of the k-th subregion of the previous image, P is the luminance change rate of the image for the frame, S is the luminance change rate of the image for the subregion, Mean_P is the average luminance of the pixels of the previous image, and Mean_C is the Average luminance.

Hereinafter, the present invention will be described in more detail with reference to the accompanying drawings.

1 is a view schematically showing the configuration of a liquid crystal display according to the present invention.

First, the image processor 100 processes the input image information and outputs the image data separated by the signals of R, G, and B to the controller 200.

The controller 200 calculates a representative value to be applied to the brightness adjustment for each partial region and outputs the representative value to the backlight unit 300. The backlight unit 300 includes a driving unit 310 and a light emitting unit 320 whose brightness is adjusted for each partial region.

The light emitter 320 includes a plurality of light emitters and is divided into a predetermined number of partial regions. For the plurality of light emitting devices, a light emitting diode may be used as the backlight light source in the liquid crystal display. However, the present invention is not limited only to a backlight having a light emitting diode. In addition, the present invention may be equally applied to a backlight using a CCFL, a field emission display (FED), a surface-conduction electron-emitter display (SED), and the like.

The partial regions may be formed in a predetermined number so as to partially control the brightness. For example, the partial regions may be formed into 64 partial regions by dividing the light emitting unit into 8 × 8 to calculate the brightness.

The driving unit 310 is connected to the light emitting unit 320 to control the brightness of each partial region of the light emitting unit 320, and the light emitting unit 320 by a PWM (pulse width modulation) method or a linear driving method. Adjust the brightness of each subarea.

The controller 200 calculates a representative value for adjusting brightness of each partial region of the light emitter 320 in response to the image signal generated by the image processor 100.

2 illustrates a method of calculating, using a histogram, a representative value to be applied to each partial region of the light emitting unit 320 in the control unit 200 of the liquid crystal display according to the present invention.

First, image pixels corresponding to each partial region are classified by the number of pixels according to each gray level. For example, a histogram as shown in FIG. 2 is created by extracting the number of pixels corresponding to each level of gray levels from 0 to 255. FIG.

At this time, in order to determine the gray level for each pixel from the input video signal, it is preferable to take one maximum value among three gray levels of R, G, and B as shown in the following equation. This is because color distortion may occur when the maximum value of the gray levels of R, G, and B is not taken.

Where Y represents gray level.

Then, the gray level (Y) is divided at predetermined intervals, and the representative value to be applied to the brightness adjustment of each partial region is calculated using the number of pixels corresponding to each zone and the average value of the gray level (Y) of each zone. do.

2 illustrates an example of calculating a representative value for brightness adjustment to be applied to a partial region by dividing it into eight regions from R0 to R7 based on gray levels. Based on FIG. 2, the representative value of each partial region is calculated by the following equation.

Here, L_Thr is a coefficient for brightness compensation of the partial region, and Mn (n = 0, 1, 2, ...) is an average value of the gray levels (Y) in the region n, Nn (n = 0, 1, 2, …) Is the number of pixels in zone n.

The above equation allows the brightness to be adjusted based on the gray level (Y) value in which a large number of pixels of the image signal are located.

The representative value calculated as described above needs to be compensated for the light loss due to the mutual relationship with the adjacent subregions. For example, in the case of a dark image such as a star or a fireworks display in the night sky, there is a light loss due to the dark background, and thus there is a need to compensate for this. Compensate the representative value by applying the following formula.

L '= L + BEN * (L-mean)

Where L 'is a representative value that compensates for the brightness loss of the partial region, L is a representative value before compensation, BEN is a coefficient for brightness compensation, and mean is the average brightness of the entire input image.

3 illustrates a method of compensating a representative value of a specific partial region by the above equation. That is, when the average brightness of the entire input image is lower than a predetermined threshold, the partial representative region whose representative value is larger than the average brightness of the entire input image is a new representative value L 'that compensates for the brightness loss by the above equation. This value is used to adjust the brightness of the subarea.

The threshold is preset by the operator to a predetermined value as a threshold for the dark image. In addition, the average value of the representative values of the partial region may be applied as a comparison reference value of the compensation condition in place of the average brightness of the entire input image.

The representative value calculated as described above is spatially filtered using a nonlinear spatial filter to correct the gray level difference. Since a low pass filter used as a general spatial filter extracts a signal having a predetermined size or less, a problem of lowering peak luminance occurs. Therefore, the filtering is performed in such a manner that the maximum representative value is maintained during the filtering.

For example, in the case of filtering using five tabs arranged in sequence such as L1, L2, L3, L4, and L5, the maximum value of L2 and L4 is determined to determine the filtered value of the current tap L3. The filtered brightness value of the current tap L3 may be determined by taking a value obtained by multiplying a predetermined filtering coefficient, a maximum value of L1 and L5, multiplying a predetermined filtering coefficient, and a maximum value of the current tap L3. The predetermined filtering coefficient here is a value in the range of 0-1.

Next, the representative value to which the spatial filtering is applied may be reduced at a predetermined rate for power saving, and the predetermined ratio R is calculated by the following equation:

R = A / (A + T_Thr * (255-A))

Here, R is a predetermined ratio, A is a cutoff gray level, the maximum gray level value of the image pixels corresponding to the partial region excluding the white Gaussian noise, and T_Thr is a predetermined threshold in the range of 0 to 1.

Where A satisfies the following equation:

Here, g is a gray level, H (g) is a total number of pixels corresponding to 0 to g, and Cut_Thr is a predetermined threshold value such that the number of pixels belonging to gray levels 0 to A is a large number.

A is a gray level value that must satisfy Equation 5, and is the maximum value of the gray level of the corresponding partial region excluding white Gaussian noise. This indicates that a suitable R value for reducing the representative value of the partial region can be determined from the relationship with the gray level of the image pixel.

FIG. 4 illustrates that a predetermined ratio R may be determined by the above equations to reduce the representative value of the spatially filtered to a predetermined ratio. Therefore, the brightness is lowered due to the reduction of the representative value, thereby achieving the effect of power saving.

In addition, the reduced representative value for power saving can be time filtered by the following equation:

Here, P 'is a predetermined threshold for filtering, P' = min (P + S, 1),

P = │Mean_P-Mean_C│ / 256, S = │Mean_P-Mean_C│ / 256,

는 현재 영상의 k번째 부분영역의 필터링 후의 최종 출력 휘도,

는 현재 영상의 k번째 부분영역의 휘도,

는 이전 영상의 k번째 부분영역의 최종 출력 휘도, P는 프레임의 휘도변화율, S는 부분영역의 휘도변화율, Mean_P는 이전 영상의 픽셀들의 평균휘도, Mean_C는 현재 영상의 픽셀들의 평균휘도이다.

Is the final output luminance after filtering the k-th subregion of the current image,

Is the luminance of the kth subregion of the current image,

Is the final output luminance of the k-th subregion of the previous image, P is the luminance variation rate of the frame, S is the luminance variation ratio of the partial region, Mean_P is the average luminance of the pixels of the previous image, and Mean_C is the average luminance of the pixels of the current image.

Unlike the conventional time filtering, the predetermined threshold P 'has a value of 1 or less, which is advantageous to apply to an image having a large difference in brightness between frames such as when the scene changes from day to night.

In addition, the controller 200 may adjust the brightness of the image pixels corresponding to each partial region of the backlight unit 300 to compensate for the brightness of the partial region reduced for power saving by a predetermined ratio R. FIG. 5 illustrates a method of compensating for brightness of image pixels corresponding to each partial region. The value of R _re used for compensation uses a predetermined ratio R calculated for power saving, 1 / R or (1 / R) ^{1 / γ} depending on the relationship between the gray level of the pixel and the brightness to be displayed. Multiply γ> 1) to adjust the brightness of the image to be displayed. When (1 / R) ^{1 / γ} is multiplied, gamma correction is performed.

6 is a flowchart illustrating a brightness adjustment process of the liquid crystal display according to the present invention. First, the representative value of each partial region of the backlight is calculated (S601), and the calculated representative value is compensated for the representative value according to the luminance reduction (S602), and after performing the space filtering (S603), the space for power saving The filtered representative value is reduced by a predetermined ratio (S604). The representative value reduced at a predetermined ratio is time filtered (S605) and output to the backlight unit 300.

In addition, in order to compensate for the brightness of each partial area of the backlight reduced by a predetermined ratio, the brightness of the image pixels corresponding to the partial area is compensated (S606). The brightness-compensated image pixel is output to the liquid crystal display 400 and displayed on the LCD panel 420. At this time, the value used for the compensation of the brightness uses a predetermined ratio (R).

According to the present invention, the brightness ratio can be adjusted for each partial region of the backlight in response to the input image signal, thereby improving the contrast ratio, and reducing the representative value to be applied for the brightness adjustment for each partial region at a predetermined ratio to effectively reduce power. A liquid crystal display device and a brightness adjustment method thereof are provided.

Although the above has been illustrated and described with respect to preferred embodiments of the present invention, the present invention is not limited to the above-described specific embodiments, and those skilled in the art without departing from the gist of the present invention. Anyone can make various modifications, as well as such modifications or variations are within the scope of the appended claims.

Claims (12)

A backlight unit including a light emitting unit which is divided into a predetermined number of partial regions and whose brightness is adjusted for each partial region; A liquid crystal display including an LCD panel unit and an LCD driver; And A liquid crystal including a control unit configured to calculate a representative value to be applied to brightness adjustment of each partial region in response to an input image signal, reduce the representative value by a predetermined ratio for power saving, and output the reduced representative value to the backlight unit; Display. The liquid crystal display of claim 1, wherein the predetermined ratio is calculated by the following equation: R = A / (A + T_Thr * (255-A)) Here, R is a predetermined ratio, A is a cutoff gray level, a maximum gray level value of an image pixel corresponding to a partial region excluding white Gaussian noise, and T_Thr is a predetermined threshold in a range of 0 to 1. The liquid crystal display device of claim 2, wherein the cutoff gray level A is a value satisfying the following equation:

Here, g is a gray level, H (g) is a total number of pixels corresponding to 0 to g, and Cut_Thr is a predetermined threshold value such that the number of pixels belonging to gray levels 0 to A is a plurality. The method according to claim 3, wherein the control unit 1 / R or (1 / R) ^{1 / γ} to the gray level of the image pixels corresponding to each partial region to compensate for the decrease in brightness of the backlight unit due to the reduced representative value for the power saving LCD to adjust the brightness of the image to be displayed by multiplying. The liquid crystal display of claim 1, wherein the controller spatially filters the representative value to maintain the brightness of the partial region having the highest brightness among the partial regions. The liquid crystal display of claim 1 or 5, wherein the controller performs time filtering on the representative value by using the following equation.

Here, P 'is a predetermined threshold for filtering, P' = min (P + S, 1), P = │Mean_P-Mean_C│ / 256, S = │Mean_P-Mean_C│ / 256,

Represents a representative value after filtering of the kth subregion of the current image,

Is the representative value of the kth subregion of the current image,

Is the representative value of the k-th subregion of the previous image, P is the luminance change rate of the image for the frame, S is the luminance change rate of the image for the subregion, Mean_P is the average luminance of the pixels of the previous image, and Mean_C is the Average luminance. Calculating a representative value for brightness adjustment of each partial region of the light emitting unit in response to an input image signal; Reducing the representative value at a predetermined rate for power saving; And And outputting the reduced representative value to a backlight unit to apply the reduced representative value for the brightness adjustment of each of the partial regions. The method of claim 7, wherein the predetermined ratio is calculated by the following equation: R = A / (A + T_Thr * (255-A)) Here, R is a predetermined ratio, A is a cutoff gray level, a maximum gray level value of an image pixel corresponding to a partial region excluding white Gaussian noise, and T_Thr is a predetermined threshold in a range of 0 to 1. The method of claim 8, wherein the cutoff gray level A is a value satisfying the following equation:

Here, g is a gray level, H (g) is a total number of pixels corresponding to 0-g, and Cut_Thr is a predetermined threshold value such that the number of pixels belonging to gray levels 0 to A is a plurality. The method according to claim 9, wherein the gray level of the image pixels corresponding to each partial region is multiplied by 1 / R or (1 / R) ^{1 / γ} to compensate for the decrease in brightness of the backlight unit due to the reduced representative value for power saving. Adjusting the brightness of the image to be displayed further comprising the brightness adjustment method of the liquid crystal display device. The brightness adjusting method of claim 7, further comprising: spatially filtering the representative value such that brightness of a partial region having a maximum brightness among the partial regions is maintained. 12. The method of claim 7 or 11, further comprising time filtering the representative value by using the following equation.

Here, P 'is a predetermined threshold for filtering, P' = min (P + S, 1), P = │Mean_P-Mean_C│ / 256, S = │Mean_P-Mean_C│ / 256,

Represents a representative value after filtering of the kth subregion of the current image,

Is the representative value of the kth subregion of the current image,

Is the representative value of the k-th subregion of the previous image, P is the luminance change rate of the image for the frame, S is the luminance change rate of the image for the subregion, Mean_P is the average luminance of the pixels of the previous image, and Mean_C is the Average luminance.

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