KR102022639B1 - Liquid crystal display and dimming control method of thereof - Google Patents

Abstract

A liquid crystal display device according to the present invention includes a liquid crystal display panel for displaying modulation data; A backlight unit that includes a plurality of light sources and emits light onto a rear surface of the liquid crystal display panel; A backlight driving circuit for driving the light sources based on a dimming value; And after determining an original gain value and a marginal gain value to compensate for the luminance degradation due to the dimming value, an input gray vs. gain value graph is determined in units of the reference region based on the original gain value and the threshold gain value, A dimming control circuit that curves the input gray vs output gray graph by multiplying a gain value determined in the input gray vs gain value graph by the input gray to determine the output gray level of the modulation data; The original gain value is determined in inverse proportion to the dimming value, and the limit gain value indicates a gradation value of the largest data among the data to be displayed in the reference area with a maximum gradation representation value determined according to the number of bits of the input data. Obtained by dividing by the maximum input gradation value.

Description

Liquid crystal display and dimming control method {LIQUID CRYSTAL DISPLAY AND DIMMING CONTROL METHOD OF THEREOF}

The present invention relates to a liquid crystal display device capable of improving the contrast ratio of a display image.

BACKGROUND ART Liquid crystal display devices have tended to be gradually widened due to their light weight, thinness, and low power consumption. The liquid crystal display device is used as a portable computer such as a notebook PC, office automation equipment, audio / video equipment, indoor and outdoor advertising display devices, and the like. The liquid crystal display displays an image by using a thin film transistor (TFT) as a switching element. The transmissive liquid crystal display device, which occupies most of the liquid crystal display device, displays an image by controlling an electric field applied to the liquid crystal layer to modulate the light incident from the backlight unit.

The image quality of the liquid crystal display device depends on the contrast characteristics. Only the method of modulating the light transmittance of the liquid crystal layer by controlling the data voltage applied to the liquid crystal layer has a limitation in improving this contrast characteristic. In order to improve the contrast characteristic, a backlight dimming method for adjusting the brightness of the backlight unit according to an image has been proposed. The backlight dimming method includes a global dimming method for adjusting the luminance of the entire display surface and a local dimming method for locally adjusting the luminance of the display surface. The global dimming method may improve dynamic contrast measured between the previous frame and the next frame. The local dimming method can improve the static contrast that is difficult to improve with the global dimming method by locally controlling the luminance of the display surface within one frame period.

The global dimming method and the local dimming method reduce the power consumption by lowering the brightness of the backlight unit according to the image information. In addition, the insufficient luminance due to dimming is compensated through modulation of the pixel data. To compensate for the brightness of the backlight, the dimming method obtains a gain value and then multiplies the gain value by the input gray level of the pixel data to determine the output gray level. In the prior art, a target input gray vs output gray graph is determined in advance, and conversely, the input gray vs gain value is obtained.

When multiplying the gain value by the image information without modulation, gray scale phenomenon may occur in high gradation as in graph ① of FIG. 1. In the prior art, to solve this problem, an input gray vs output gray graph such as ② is used. If you use Graph ②, you can prevent the gradation of gradation that occurs in Graph ①, but there is a problem that the gradation step becomes visible at the starting point of gradation break and the luminance decreases as a whole.

If you create graph ③, which has a curved shape between ① and ②, you can solve the problem of gray level difference and luminance deterioration at the same time. The process of finding the equation of the same quadratic curve is so complex that it is impossible to actually implement it.

Accordingly, an object of the present invention is to obtain a gain value compared to an input gray scale by a simple method, and to determine an output gray scale based on the gain value, thereby preventing the gray level difference and the luminance deterioration phenomenon, and a dimming control method thereof. To provide.

In order to achieve the above object, a liquid crystal display device according to an embodiment of the present invention comprises a liquid crystal display panel for displaying the modulation data; A backlight unit that includes a plurality of light sources and emits light onto a rear surface of the liquid crystal display panel; A backlight driving circuit for driving the light sources based on a dimming value; And after determining an original gain value and a marginal gain value to compensate for the luminance degradation due to the dimming value, an input gray vs. gain value graph is determined in units of the reference region based on the original gain value and the threshold gain value, A dimming control circuit that curves the input gray vs output gray graph by multiplying a gain value determined in the input gray vs gain value graph by the input gray to determine the output gray level of the modulation data; The original gain value is determined in inverse proportion to the dimming value, and the limit gain value indicates a gradation value of the largest data among the data to be displayed in the reference area with a maximum gradation representation value determined according to the number of bits of the input data. Obtained by dividing by the maximum input gradation value.

Dimming control method of the liquid crystal display device according to an embodiment of the present invention, a liquid crystal display panel for displaying the modulation data, a backlight unit for irradiating the back of the liquid crystal display panel including a plurality of light sources, and based on the dimming value A dimming control method of a liquid crystal display device having a backlight driving circuit for driving the light sources, the method comprising: determining an original gain value and a marginal gain value to compensate for a decrease in luminance due to the dimming value; Determining an input gray level vs. gain value graph in units of the reference area based on the original gain value and the threshold gain value; And converting the input gray vs output gray graph by determining an output gray level of the modulation data by the reference area by multiplying a gain value determined in the input gray vs gain value graph; The original gain value is determined in inverse proportion to the dimming value, and the limit gain value indicates a gradation value of the largest data among the data to be displayed in the reference area with a maximum gradation representation value determined according to the number of bits of the input data. Obtained by dividing by the maximum input gradation value.

The present invention determines the input gray vs gain graph on the input gray-gain value plane based on the original gain value and the marginal gain value, and multiplies the resulting gain value by the input gray value of the input data to determine the output gray level of the modulation data. do. According to the present invention, the relationship between the input gradation vs. the output gradation becomes a curved graph through the above process, thereby simplifying the gradation step phenomenon and the luminance deterioration phenomenon that occur when the relationship between the conventional input gradation vs. the output gradation is a straight line. Can be alleviated.

1 is a view showing a graph of an output grayscale versus an input grayscale predetermined to obtain a gain value compared to a conventional grayscale.
2 illustrates a liquid crystal display according to an exemplary embodiment of the present invention.
3 shows a detailed configuration of a dimming control circuit.
4 is a diagram illustrating an example of determining an input gray level vs. gain value graph.
FIG. 5 is a diagram showing an input gray vs output gray graph obtained by FIG. 4; FIG.
6 shows another example of determining an input gray level vs. gain value graph.
FIG. 7 is a diagram showing an input gray vs output gray graph obtained by FIG. 6; FIG.
8 illustrates another example of determining an input gray level vs. gain value graph.
FIG. 9 is a diagram showing an input gray vs output gray graph obtained by FIG. 8; FIG.

Hereinafter, exemplary embodiments of the present invention will be described with reference to FIGS. 2 to 9.

2 shows a liquid crystal display according to an embodiment of the present invention.

2, a liquid crystal display according to an exemplary embodiment of the present invention includes a liquid crystal display panel 10, a timing controller 11, a data driving circuit 12, a gate driving circuit 13, and a dimming control circuit 14. , A backlight driving circuit 15, and a backlight unit 16.

The liquid crystal display panel 10 includes two glass substrates and a liquid crystal layer formed therebetween. A plurality of data lines DL and a plurality of gate lines GL cross on the lower glass substrate of the liquid crystal display panel 10. The liquid crystal cells Clc are arranged in a matrix form on the liquid crystal display panel 10 due to the cross structure of the data lines DL and the gate lines GL. Each of the liquid crystal cells Clc includes a TFT, a pixel electrode 1 connected to the TFT, a storage capacitor Cst, and the like. A black matrix, a color filter, a common electrode 2, and the like are formed on the upper glass substrate of the liquid crystal display panel 10. The common electrode 2 is formed on the upper glass substrate in a vertical electric field driving method such as twisted nematic (TN) mode and vertical alignment (VA) mode, and has an in plane switching (IPS) mode and a fringe field switching (FFS) mode. In the same horizontal electric field driving method, the pixel electrode 1 is formed on the lower glass substrate. The liquid crystal cells Clc include R liquid crystal cells for red display, G liquid crystal cells for green display, and B liquid crystal cells for blue display. The R liquid crystal cell, the G liquid crystal cell, and the B liquid crystal cell constitute one unit pixel. A polarizing plate is attached to each of the upper glass substrate and the lower glass substrate of the liquid crystal display panel 10, and an alignment layer for setting a pretilt angle of the liquid crystal is formed on an inner surface of the liquid crystal display panel 10 in contact with the liquid crystal.

The timing controller 11 supplies digital video data RGB input from a system board on which an external video source is mounted, to the dimming control circuit 14, and modulated data R′G modulated by the dimming control circuit 14. 'B' is supplied to the data driving circuit 12. The timing controller 11 includes timing control signals for controlling the operation timing of the data driving circuit 12 and the gate driving circuit 13 based on the timing signals Vsync, Hsync, DE, and DCLK from the system board. DDC, GDC). The timing controller 11 inserts an interpolation frame between frames of an input video signal input at a frame frequency of 60 Hz, multiplies the data timing control signal DDC and the gate timing control signal GDC, and 60 × N The operation of the data driving circuit 12 and the gate driving circuit 13 can be controlled at a frame frequency of two or more positive integers Hz.

The data driver circuit 12 includes a plurality of data drive integrated circuits. The data drive integrated circuit stores a shift line for sampling a clock signal, a register for temporarily storing digital image data (RGB), a line of data in response to a clock signal from the shift register, and stores one line of data. A latch for outputting at the same time, a digital / analog converter for selecting a positive / negative gamma voltage under reference to a gamma reference voltage corresponding to a digital data value from the latch, and an analog converted by a positive / negative gamma voltage And a multiplexer for selecting a data line DL to which data is supplied, and an output buffer connected between the multiplexer and the data line DL. The data driving circuit 12 latches the modulation data R'G'B 'under the control of the timing controller 11, and the latched modulation data R'G'B' is subjected to positive / negative gamma compensation. The voltage is converted into the positive / negative analog data voltage and then supplied to the data lines DL.

The gate driving circuit 13 includes a plurality of gate drive integrated circuits. The gate drive integrated circuit includes a shift register, a level shifter for converting an output signal of the shift register into a swing width suitable for driving a TFT of a liquid crystal cell, an output buffer, and the like. The gate driving circuit 13 sequentially outputs scan pulses (or gate pulses) and supplies them to the gate lines GL under the control of the timing controller 11, thereby selecting a horizontal pixel line to which a data voltage is applied.

The dimming control circuit 14 analyzes the input data RGB to derive an image representative value of the reference region, and dimming values in units of the reference region to control the brightness of the light sources of the backlight unit 16 according to the image representative value. Determine the (DIM). The dimming control circuit 14 sets the original gain value according to the image representative value in units of the reference region to compensate for the luminance degradation due to the dimming value DIM, and also sets the threshold gain value for the normal gray scale expression as the reference region. Calculate in units. Then, the dimming control circuit 14 determines the input gray vs gain value graph on the input gray scale-gain value plane based on the original gain value and the marginal gain value in units of reference area so that the input gray vs output gray graph is curved. . The dimming control circuit 14 determines the output gradation in units of a reference area by multiplying the input gradation by the gain value determined in the input gradation vs. gain value graph. That is, the dimming control circuit 14 generates and outputs modulation data R'G'B 'for luminance compensation in units of reference areas by multiplying the gain value determined from the input gray vs gain value graph by the input data RGB. do.

The present invention may employ a global dimming method or a local dimming method. In the case of employing the global dimming method, the reference area indicates the entire screen as long as an image of one frame is displayed. On the other hand, when the local dimming method of dividing and driving one screen into a plurality of blocks, the reference area indicates each block. The present invention does not predetermine a target input gray vs output gray graph in advance and inversely obtains an input gray vs gain value as in the prior art, but directly gains from an input gray vs gain graph based on the original gain value and the marginal gain value. Obtaining the value simplifies the process of deriving the gain.

The backlight driving circuit 15 is a pulse width modulation (PWM) in which the duty ratio is changed according to the dimming value DIM input from the dimming control circuit 14. Drive. The dot time of the light sources is controlled by the PWM duty ratio.

The backlight unit 16 includes a plurality of light sources to irradiate light to the liquid crystal display panel 10. The backlight unit 16 may be implemented as one of a direct type and an edge type. The direct type backlight unit 16 has a structure in which a plurality of optical sheets and a diffusion plate are stacked below the liquid crystal display panel 10 and a plurality of light sources are disposed below the diffusion plate. The edge type backlight unit 16 has a structure in which a plurality of optical sheets and a light guide plate are stacked below the liquid crystal display panel 10 and a plurality of light sources are disposed on the side of the light guide plate. The light sources may be implemented as point light sources such as light emitting diodes (LEDs).

3 shows a detailed configuration of the dimming control circuit 14. 4

Referring to FIG. 3, the dimming control circuit 14 may include an image analyzer 141, a dimming value determiner 142, a gain value determiner 143, a gain value graph determiner 144, and a data modulator ( 145).

The image analyzer 141 analyzes the input data RGB to derive an image representative value in units of reference areas. The picture representative value may be selected as an average picture level (APL). The average image level is obtained by selecting the maximum gradation value among the RGB values of pixels in each reference region and dividing the sum of these maximum values by the number of pixels included in the reference region.

The dimming value determiner 142 maps the image representative value from the image analyzer 141 to a preset dimming curve to determine the dimming value DIM in units of reference areas. The dimming curve may be implemented as a lookup table. The dimming value DIM may be determined high in the reference region where the image representative value of the data is high and low in the reference region where the image representative value is low.

The gain value determiner 143 determines the original gain value and the marginal gain value in units of a reference area. The original gain value is determined in accordance with the image representative value and in inverse proportion to the dimming value DIM. One original gain value is determined for each reference area, but may be determined to be low in a reference area having a high image representative value of data and high in a reference area having a low image representative value. The marginal gain value is obtained from the maximum gray scale expression value / maximum input gray scale value. The maximum gray scale expression value is a value determined according to the number of bits of the input data RGB. For example, when the input data RGB is each implemented with 8 bits, the maximum gray scale expression value is determined as '255', and when the input data RGB is implemented with 10 bits, the maximum gray scale expression value is determined as '1023'. The maximum input gray scale value indicates a gray scale value of the largest data among the data to be displayed in the reference area. The reason for setting the marginal gain value in the present invention is to enable gradation expression in the entire gradation region and to prevent gradation inversion.

The gain value graph determining unit 144 determines the input gray level vs. gain value graph in the reference area unit on the input gray level-gain value plane based on the original gain value and the threshold gain value input from the gain value determining unit 143. As a result, the relationship between the input gray level vs. the output gray level becomes a graph in a curved form.

The gain value graph determiner 144 determines the input gray vs. gain value graph differently when the limit gain value is smaller than the original gain value and when the limit gain value is larger than or equal to the original gain value.

When the marginal gain value is smaller than the original gain value, the gain value graph determination unit 144 stores the gain value in the input gray scale interval between the minimum gray scale expression value '0' and the gray scale starting point as shown in FIGS. 4 and 6. The gain value is maintained, and the gain value is converged to the marginal gain value in the input gradation interval between the gradation starting point and the maximum input gradation value. That is, the gain value graph determiner 144 sets the gain value in the input gray scale interval between the start point of gray scale and the maximum input gray scale value such that the gain value is lowered from the maximum input gray scale value to the threshold gain value as shown in FIG. 4. Can be lowered linearly to the marginal gain. Here, the gradation starting point indicates an input gradation value corresponding to the inflection point of the gain value when modulating the gain value in order to prevent the high gradation aggregation phenomenon, and is preset by the user. To obtain a gain value from the input gray vs. gain value graph as shown in FIG.

In addition, the gain graph determining unit 144 sets the gain value in the input gradation section between the gradation starting point and the maximum input gradation value such that the gain value is lowered from the maximum input gradation value to the limit gain value as shown in FIG. 6. It can also be lowered in the form of a quadratic curve from to the limit gain. Obtaining a gain value from the input gray vs gain value graph shown in FIG. 6 is expressed by Equation 2 below.

On the other hand, if the marginal gain value is greater than or equal to the original gain value, the gain value graph determining unit 144 may convert the gain value in the entire input gray scale interval between the minimum gray scale expression value and the maximum input gray scale value as shown in FIG. 8. Keep it. In this case, the relationship between the input gradation vs. the output gradation is not a curve graph but a linear graph as shown in FIG. 9. However, in this case, since the low gradation image is displayed, the high gradation aggregation phenomenon shown in the graph ① of the prior art is not a problem.

The data modulator 145 multiplies the gain value determined in the input gray vs gain value graph by the input gray of the input data RGB to output the gray level of the modulation data R'G'B 'for luminance compensation in units of a reference area. Determine. When the gain value determined from the input gray vs gain value graph is multiplied by the input gray of the input data RGB, the input gray vs output gray graph as in ④ of FIG. 5 or the input gray vs output gray graph as in ⑤ of FIG. Is obtained.

As described above, the present invention can simplify the process of deriving the gain value since the gain value is directly obtained from the input gray level vs. gain value graph based on the original gain value and the limit gain value. The present invention determines the input gray vs gain graph on the input gray-gain value plane based on the original gain value and the marginal gain value, and multiplies the resulting gain value by the input gray value of the input data to determine the output gray level of the modulation data. do. According to the present invention, the relationship between the input gradation vs. the output gradation becomes a curved graph through the above process, thereby simplifying the gradation step phenomenon and the luminance deterioration phenomenon that occur when the relationship between the conventional input gradation vs. the output gradation is a straight line. Can be alleviated.

Those skilled in the art will appreciate that various changes and modifications can be made without departing from the technical spirit of the present invention. Therefore, the technical scope of the present invention should not be limited to the contents described in the detailed description of the specification but should be defined by the claims.

10 liquid crystal display panel 11 timing controller
12: data driving circuit 13: gate driving circuit
14 dimming control circuit 15 light source driving circuit
16: backlight unit 141: image analysis unit
142: dimming value determining unit 143: gain value determining unit
144: gain value graph determiner 145: data modulator

Claims (16)

A liquid crystal display panel displaying modulation data;
A backlight unit that includes a plurality of light sources and emits light onto a rear surface of the liquid crystal display panel;
A backlight driving circuit for driving the light sources based on a dimming value; And
After determining an original gain value and a marginal gain value to compensate for the luminance degradation due to the dimming value, an input gray level vs. gain value graph is determined in units of a reference area based on the original gain value and the threshold gain value, and the input is performed. The input gradation vs. output gradation graph is curved by multiplying the input gradation by a gain value determined in the gradation vs. gain value graph to determine the output gradation of the modulation data in units of the reference area, wherein the threshold gain value is larger than the original gain value. A dimming control circuit for differently determining the input gray level vs. gain value graph when it is small and when the threshold gain value is greater than or equal to the original gain value;
The original gain value is determined in inverse proportion to the dimming value, and the limit gain value indicates a gradation value of the largest data among the data to be displayed in the reference area with a maximum gradation representation value determined according to the number of bits of the input data. A liquid crystal display device obtained by dividing by the maximum input gradation value.
delete The method of claim 1,
The dimming control circuit,
When the threshold gain value is smaller than the original gain value, the gain value is maintained as the original gain value in the input gray scale interval between the minimum gray scale expression value existing on the input gray scale-gain value plane and the gray scale starting point, and the gray scale Converge a gain value to the threshold gain value in an input grayscale interval between the starting point of bending and the maximum input grayscale value;
The gray level start point indicates an input gray level value corresponding to an inflection point of the gain value when modulating the gain value to prevent high gray level aggregation. The method of claim 3, wherein
The dimming control circuit,
And a gain value is linearly lowered from the original gain value to the limit gain value in an input gray scale interval between the gray scale starting point and the maximum input gray scale value. The method of claim 3, wherein
The dimming control circuit,
And a gain value is lowered in the form of a quadratic curve from the original gain value to the limit gain value in an input gray scale interval between the gray scale starting point and the maximum input gray scale value. The method of claim 3, wherein
And the gain value corresponding to the maximum input gray value is the limit gain value on the input gray vs. gain value graph. The method of claim 1,
The dimming control circuit,
When the threshold gain value is greater than or equal to the original gain value, the gain value is converted into the original gain value in the entire input gray scale interval between the minimum gray scale expression value existing on the input gray scale-gain value plane and the maximum input gray scale value. And a liquid crystal display device characterized in that it is held. The method of claim 1,
And the reference area indicates an entire screen on which an image of one frame is displayed, or indicates a plurality of blocks for dividing and driving the one screen, respectively. A liquid crystal display device comprising a liquid crystal display panel displaying modulation data, a backlight unit including a plurality of light sources and irradiating light onto a rear surface of the liquid crystal display panel, and a backlight driving circuit driving the light sources based on a dimming value. In the dimming control method,
Determining an original gain value and a marginal gain value to compensate for the luminance degradation due to the dimming value;
Determining an input gray level vs. gain value graph in units of a reference area based on the original gain value and the threshold gain value; And
The input gray level vs. output gray level graph is curved by determining the output gray level of the modulation data by multiplying the input gray level by the gain value determined in the input gray level vs. gain value graph, wherein the threshold gain is the original gain. Determining the input gray level vs. gain value graph differently if less than a value and if the marginal gain value is greater than or equal to the original gain value;
The original gain value is determined in inverse proportion to the dimming value, and the limit gain value indicates a gradation value of the largest data among the data to be displayed in the reference area with a maximum gradation representation value determined according to the number of bits of the input data. A dimming control method for a liquid crystal display device, characterized by being obtained by dividing by the maximum input gradation value.
delete The method of claim 9,
The determining of the input gray level vs. gain value graph may include:
When the threshold gain value is smaller than the original gain value, the gain value is maintained as the original gain value in the input gray scale interval between the minimum gray scale expression value existing on the input gray scale-gain value plane and the gray scale starting point, and the gray scale Converge a gain value to the threshold gain value in an input grayscale interval between the starting point of bending and the maximum input grayscale value;
And the gray level starting point indicates an input gray level value corresponding to an inflection point of the gain value when modulating the gain value to prevent high gray level aggregation. The method of claim 11,
The determining of the input gray level vs. gain value graph may include:
And diminishing a gain value linearly from the original gain value to the threshold gain value in an input gray scale interval between the gray scale start point and the maximum input gray scale value. The method of claim 11,
The determining of the input gray level vs. gain value graph may include:
And diminishing a gain value in the form of a quadratic curve from the original gain value to the limit gain value in an input gray scale interval between the gray scale start point and the maximum input gray scale value. The method of claim 11,
And the gain value corresponding to the maximum input gray value is the limit gain value on the input gray vs. gain value graph. The method of claim 9,
The determining of the input gray level vs. gain value graph may include:
When the threshold gain value is greater than or equal to the original gain value, the gain value is converted into the original gain value in the entire input gray scale interval between the minimum gray scale expression value existing on the input gray scale-gain value plane and the maximum input gray scale value. And dimming control method for the liquid crystal display device. The method of claim 9,
And the reference area indicates an entire screen in which an image of one frame is displayed, or indicates a plurality of blocks for dividing and driving the one screen, respectively.

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