KR100751461B1 - Liquid crystal display device for reducing power consumption by controlling backlight brightness - Google Patents

Abstract

An LCD device for reducing power consumption by adjusting backlight brightness is provided to enhance luminance of image signals by compensating for the image signals using a luminance compensation coefficient. An LCD(Liquid Crystal Display) device includes a controller(100), an LCD panel(110), a backlight lamp(120), and a backlight lamp power supply(130). The controller includes an image information receiver(101) for receiving image signals, a luminance compensation coefficient producing unit(103) for producing a luminance compensation coefficient on the image signals, an image information compensator(105) for compensating the image signals using the luminance compensation coefficient, an image information transmitter(106) for transmitting the compensated image signals to the LCD panel, and a lamp power controller(108) for controlling the backlight lamp power supply by a lamp power compensation coefficient, which is obtained from the luminance compensation coefficient.

Description

Liquid crystal display device for reducing power consumption by adjusting backlight brightness {Liquid crystal display device for reducing power consumption by controlling backlight brightness}

1 is a block diagram schematically illustrating a configuration of a liquid crystal display according to a first exemplary embodiment of the present invention.

2 is a flowchart sequentially illustrating a process of calculating a luminance correction coefficient by the luminance correction coefficient calculator of the controller of the liquid crystal display according to the first exemplary embodiment of the present invention.

3 is a flowchart sequentially illustrating a process of calculating a luminance correction coefficient by the luminance correction coefficient calculating unit of the controller of the liquid crystal display according to the third exemplary embodiment of the present invention.

4 is a flowchart sequentially illustrating a process of calculating a luminance correction coefficient by the luminance correction coefficient calculator of the controller of the liquid crystal display according to the fourth exemplary embodiment of the present invention.

<Explanation of symbols for the main parts of the drawings>

10: liquid crystal display device

100: control unit

110: LCD panel

120: backlight lamp

130: backlight lamp power generator

101: image information receiving unit

103: luminance correction coefficient calculation unit

105: image information correction unit

106: image information transmission unit

108: lamp power control unit

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid crystal display device that minimizes power consumption. More particularly, the present invention relates to a liquid crystal display that increases the luminance value of an image signal and decreases the brightness of a backlight lamp, thereby reducing power consumption by the backlight lamp. An apparatus and a control method thereof are provided.

TFT-LCD is a display device widely used in computers, personal digital assistants (PDAs), such as laptop computers, notebook computers, desktop computers and the like. Since the LCD itself is non-luminous, unlike the CRT, PDP, etc., which are luminescent displays, it cannot be used in the absence of light. The backlight unit, which makes the LCD panel uniformly flat light, is a key component of the LCD panel, and is used as a dimming device to uniformly transmit light to the entire LCD panel. The backlight unit is used to provide an image with high brightness while maintaining a uniform brightness of light emitted from the lamp throughout the LCD panel.

However, the power consumed by the lamp of the backlight unit and the inverter circuit for driving the backlight unit occupies about 30% of the total power consumed by the end user terminal. Since the power consumption by the backlight unit occupies a significant portion of the total power consumption of the user terminal, by reducing the power consumption in the backlight unit, a substantial portion of the total power consumption of the user terminal can be reduced.

In particular, recently, various types of portable multimedia terminals have been released. Since such portable multimedia terminals play multimedia content that consumes a lot of power using a limited battery, various methods for reducing battery consumption have been proposed. It is true.

Accordingly, the present inventors propose a method of reducing power consumption of the terminal by controlling the brightness of the backlight unit of the LCD and the luminance value of the image signal.

An object of the present invention to solve the above problems is to increase the luminance value of the image signal and to reduce the brightness of the backlight lamp to reduce the power consumption by the backlight lamp while maintaining the image quality of the original image To provide.

Another object of the present invention is to obtain a luminance correction coefficient for correcting the luminance value of the image signal and to reduce the lamp correction coefficient for adjusting the brightness of the backlight lamp in order to reduce power consumption by the backlight lamp in the above-described liquid crystal display device. It is to provide a way to obtain.

A feature of the present invention for achieving the above-described technical problem relates to a liquid crystal display device comprising a control unit for controlling the overall operation, the LCD panel, a backlight lamp and the backlight lamp power generating device,

A video information receiver for receiving a video signal to be played;

A luminance correction coefficient calculator for calculating a luminance correction coefficient for the image signals received by the image information receiver;

An image information corrector configured to correct the image signals by using the luminance correction coefficients;

An image information transmitter for transmitting the image signals corrected by the image information corrector to the LCD panel;

A lamp power control unit calculating a reciprocal of the luminance correction coefficient to obtain a lamp power correction coefficient, and controlling the backlight lamp power generator using the lamp power correction coefficient.

It is provided to reduce the power consumption by the backlight lamp by adjusting the brightness value of the video signal to be reproduced and the brightness of the backlight lamp.

The luminance correction coefficient calculator of the control unit of the liquid crystal display having the above-mentioned characteristics analyzes histograms of the image signals to obtain an average value of luminance values among the image signals, and obtains the highest gray level value and the average value of the image signal. The luminance correction coefficient may be calculated using, and the luminance correction coefficient may be calculated as (the average value of the highest gray level value ÷ luminance value of the image signal).

The luminance correction coefficient calculator of the control unit of the liquid crystal display having the above-described feature detects a maximum value among the luminance values of the image signals, and calculates the luminance correction coefficient using the highest gray level value and the maximum value of the image signals. You may.

The luminance correction coefficient calculator of the control unit of the liquid crystal display having the above-described characteristics sets a correction level n in advance, analyzes a histogram of the image signals, and applies the correction level n to the correction level n among the image signals. The luminance value of the corresponding pixel may be detected, and the luminance correction coefficient may be calculated using the detected luminance value and the highest gray level value of the image signal.

The luminance correction coefficient calculator of the control unit of the liquid crystal display having the above-described characteristics sets a correction level n in advance, analyzes a histogram with respect to the image signals, and averages the luminance values among the image signals. , Calculates a luminance correction coefficient using the average value, the detected luminance value, and the highest gray level value of an image signal by detecting a luminance value of a pixel corresponding to the correction level n,

The luminance correction coefficient σ is determined by Equation 5 below, and the pixel reflection coefficient and the histogram reflection coefficient are preferably determined according to the standard deviation in the histogram with respect to the luminance value of the corresponding video signal.

Preferably, the lamp power control unit of the control unit of the liquid crystal display having the above-described characteristics corrects the tube current duty ratio of the backlight lamp power generator using the lamp power correction coefficient.

Hereinafter, the configuration and operation of the liquid crystal display device having reduced power consumption according to the first embodiment of the present invention will be described in detail with reference to the accompanying drawings.

1 is a block diagram schematically illustrating an internal configuration of a liquid crystal display according to a first exemplary embodiment of the present invention. Referring to FIG. 1, the liquid crystal display 10 according to the present invention includes a controller 100, an LCD panel 110, a backlight lamp 120, and a backlight lamp power generator 130, and the controller 100. ) Includes an image information receiving unit 101, a luminance correction coefficient calculating unit 103, an image information correcting unit 105, an image information transmitting unit 106, and a lamp power control unit 108.

The LCD panel 110 is displayed by using an image signal and a control signal received from the controller 100, and the backlight lamp 120 is powered by the backlight lamp power generator 130. In operation, the backlight lamp power generator 130 controls the operation of the backlight lamp 120 according to a control signal received from the controller 100. The backlight lamp power generator 130 includes an inverter, and the inverter converts a DC input voltage into an AC voltage by using a pulse width modulation method (PWM) or a pulse frequency modulation method (PFM), and the like. The voltage is boosted to generate an AC tube current. The lamp of the backlight unit blinks in accordance with the AC tube current generated by the inverter. The inverter varies the lamp tube current duty ratio and the lamp tube current intensity according to the lamp power control signal transmitted from the lamp power control unit 108 of the controller, where the lamp tube current duty ratio is the lamp lighting period of the backlight unit within one frame. It means the ratio of.

The controller 100 analyzes the luminance information of the reproduced image, and increases the luminance of the image by using the analyzed result, while reducing the brightness of the backlight lamp, thereby maintaining the image quality of the entire image as it is. It is possible to reduce the power consumption by. The liquid crystal display according to the present exemplary embodiment analyzes a histogram of an image to be reproduced to obtain an average value of luminance values of each pixel of the image signal, and then uses the average value to determine the luminance value of the image signal and the brightness of the backlight lamp. Adjust it. Hereinafter, an operation of the controller 100 for performing the above function will be described in detail.

First, the image information receiver 101 receives image information to be reproduced.

As illustrated in FIG. 2, the luminance correction coefficient calculating unit 103 analyzes a histogram of luminance values among image signals to be reproduced, and calculates an average value of luminance values of each pixel. The luminance correction coefficient σ is calculated according to Equation 1 by using.

Luminance correction factor (σ) = highest gray level value / average value

Here, the highest gray level value is the highest level value among the expressible gray levels, and when the image signal is expressed with 8 bits, the total gray value is composed of 256 levels of 0 (lowest gray value) to 255 (highest gray value). . In this case, the highest gray level value may be 255.

The image information correction unit 105 receives a luminance correction coefficient from the luminance correction coefficient calculating unit, receives a corresponding image signal to be reproduced from the image information receiving unit 101, and then, for each pixel of the image signals, Luminance values are corrected using the luminance correction coefficient.

The image information transmitter 106 transmits the image signal corrected by the image information corrector 105 to a panel for display.

The lamp power control unit 108 receives the brightness correction coefficient from the brightness correction coefficient calculating unit, calculates the inverse of the input brightness correction coefficient, and calculates the lamp power correction coefficient. The tube power duty ratio for the inverter of the backlight lamp power generator is corrected using the lamp power correction coefficient. The lamp power control unit 108 transmits the corrected tube current duty ratio to the backlight lamp power generator 130, and the power generator 130 generates a PWM signal according to the corrected tube current duty ratio to generate a backlight. Power is supplied to the lamp.

An operation of the controller according to the present embodiment will be described as an example. If the highest gray level value is 255 and the average value is 150, the luminance correction factor is 255/150 = 1.7. Accordingly, the image information is corrected by multiplying the luminance of each image information by the luminance correction coefficient (ie, 1.7), and then output to the panel for display. On the other hand, the lamp power supply correction factor is 1.7 ^-1 = 0.588 as the inverse of the brightness correction factor, and the tube current duty ratio set on the basis of 100% is corrected to 100% x 0.588 = 58.8%. Thus, the tube current provided to the backlight lamp is reduced to 58.8% duty ratio. According to this embodiment, the brightness of the image is increased by 1.7 times and the brightness of the backlight lamp is reduced by 58.8%, thereby reducing power consumption by the backlight lamp while maintaining the brightness of the final image.

Second embodiment

Hereinafter, the configuration and operation of the liquid crystal display according to the second embodiment of the present invention will be described. In the liquid crystal display according to the second embodiment, other technical configurations except for the luminance correction coefficient calculating unit of the control unit are the same as those of the above-described first embodiment, and thus redundant description thereof will be omitted.

The luminance correction coefficient calculator of the control unit of the liquid crystal display according to the second exemplary embodiment analyzes a histogram of luminance values of an image signal to be reproduced, and detects the maximum value which is the largest luminance value among the image signals. Similarly, the luminance correction coefficient σ is obtained.

Luminance correction factor (σ) = highest gray level value / maximum value

By simultaneously correcting the luminance value of the image signal and the tube current duty ratio for the backlight lamp using the brightness correction coefficient calculated by the brightness correction coefficient calculator, power consumption by the backlight lamp is reduced while maintaining the image quality of the image. You can do it.

An operation of the controller according to the present embodiment will be described as an example. If the highest gray level value is 255 and the maximum value among the luminance values of the video signal is 200, the luminance correction coefficient is 255/200 = 1.275. Therefore, the luminance value of each image signal is multiplied by the luminance correction coefficient (ie, 1.275) to correct the luminance value of the image signal, and then output to the panel for display. On the other hand, the inverse of the luminance correction coefficient, 1.275 ^-1 = 0.784, which is the lamp power supply correction coefficient, is calculated, and the tube current duty ratio set on the basis of 100% is corrected to 100% x 0.784 = 78.4%. Accordingly, the tube current provided to the backlight lamp is reduced to 78.4% duty ratio. According to this embodiment, the brightness of the image is increased by 1.275 times while the brightness of the backlight lamp is reduced by 78.4%, thereby reducing power consumption by the backlight lamp while maintaining the image quality of the final image.

Third embodiment

Hereinafter, the configuration and operation of the liquid crystal display according to the third embodiment of the present invention will be described. In the liquid crystal display according to the third exemplary embodiment, other technical configurations except for the luminance correction coefficient calculating unit of the controller are the same as those of the above-described first exemplary embodiment, and thus redundant descriptions thereof will be omitted. 3 is a flowchart sequentially illustrating an operation of a luminance correction coefficient calculator of a controller of a liquid crystal display according to a third exemplary embodiment of the present invention. Hereinafter, the calculation of the luminance correction coefficient according to the third embodiment will be described with reference to FIG. 3.

The luminance correction coefficient calculator of the controller of the liquid crystal display according to the third exemplary embodiment analyzes the histogram with respect to an image signal to be reproduced and detects luminance values of pixels corresponding to the preset correction level n. Here, the correction level (n) is a reference value that can be set by the user or initially registered and registered in the system. The correction level (n) is a value that is used as a reference level for generating the luminance correction coefficient, and indicates an arbitrary level in the histogram for the luminance value. it means. Therefore, when the correction level is set to n, in the histogram which is a distribution of the total luminance values for each pixel in the corresponding image, the luminance value for the pixel corresponding to the upper n% is detected and the luminance is corrected as shown in Equation 3 below. Find the coefficient σ.

Luminance correction factor (σ) = highest gray level value / detected luminance value

By simultaneously correcting the luminance value of the image signal and the tube current duty ratio for the backlight lamp using the brightness correction coefficient calculated by the brightness correction coefficient calculator, power consumption by the backlight lamp is reduced while maintaining the image quality of the image. You can do it.

According to the present embodiment, when the correction level is set to 1%, since the luminance value of the pixel corresponding to the upper 1% is detected, the luminance correction coefficient is calculated by detecting the largest luminance value in the corresponding image. The result is almost similar to that of the second embodiment described above. In addition, when the correction level is set to 30%, since the luminance correction coefficient is calculated by detecting the luminance values of the pixels corresponding to the top 30%, power consumption by the lamp can be significantly reduced, but the luminance values are higher. There is a possibility that the image information of the pixel included in 30% is partially distorted.

Fourth embodiment

Hereinafter, the configuration and operation of the liquid crystal display according to the fourth embodiment of the present invention will be described. In the liquid crystal display according to the fourth exemplary embodiment, other technical configurations except for the luminance correction coefficient calculating unit of the controller are the same as those of the above-described first exemplary embodiment, and thus redundant descriptions thereof will be omitted. 4 is a flowchart illustrating a process of calculating a luminance correction coefficient according to a fourth embodiment of the present invention.

Referring to FIG. 4, the luminance correction coefficient calculator of the controller of the liquid crystal display according to the fourth exemplary embodiment analyzes a histogram of an image signal to be reproduced to obtain an average value of luminance values of the image signal, and among the image information. The luminance value of the pixel corresponding to the preset correction level n is detected, and the luminance correction coefficient according to Equation 4 is calculated using the average value and the detected luminance value. Here, the average value of the luminance values of the image signal is the same as the average value of the first embodiment described above, and the detection luminance value of the pixel corresponding to the preset correction level among the image signals is the third embodiment described above. Since it is the same as the detected luminance value in, detailed description thereof will be omitted.

σ = α × (highest gradation value / detected luminance value) + β × (highest gradation value / average value)

Is the luminance correction coefficient, α is the pixel reflection coefficient, β histogram reflection coefficient, and the sum of the pixel reflection coefficient and the histogram reflection coefficient is always one.

The pixel reflection coefficient and the histogram reflection coefficient may be arbitrarily set by a user or may be set by a predetermined method of the luminance correction coefficient calculator of the controller.

Hereinafter, a method of setting the pixel reflection coefficient α and the histogram reflection coefficient β by the luminance correction coefficient calculation unit will be described. First, the luminance correction coefficient calculating unit calculates a standard deviation in the distribution of the luminance values of the image through histogram analysis of an image to be reproduced, and the pixel reflection coefficient and the histogram reflection coefficient according to the standard deviation. Set. If the standard deviation is large, the loss of the original image may be reduced even by lowering the low power implementation ratio by increasing the ratio of the pixel reflection coefficient α to the histogram reflection coefficient β. On the other hand, if the standard deviation is small, the ratio of the pixel reflection coefficient α to the histogram reflection coefficient β is decreased to increase the low power implementation ratio. Accordingly, according to the present invention, the pixel reflection coefficient α is set to be proportional to the standard deviation of luminance values of the image, and the histogram reflection coefficient β is set to be inversely proportional to the standard deviation, thereby dynamically reducing power consumption. The preservation rate of the original image is maximized. For example, when the standard deviation is 0.5, which is a reference value, the pixel reflection coefficient and the histogram reflection coefficient are set to 0.5 and 0.5, respectively, and the pixel reflection coefficient is proportionally increased in proportion to the increase of the standard deviation from the reference value. The histogram reflection coefficient β decreases proportionally.

Meanwhile, a method of arbitrarily setting the pixel reflection coefficient and the histogram reflection coefficient by the user will be described. First, when the user selects the low power mode through the user input unit, the luminance correction coefficient calculator increases the histogram reflection coefficient with respect to the pixel reflection coefficient to the maximum possible ratio, thereby maximizing the low power implementation ratio. The device will operate in a low power mode. In this case, the liquid crystal display may have some distortion in an image, but may operate for a long time.

By simultaneously correcting the image information and the tube current duty ratio for the backlight lamp by using the brightness correction coefficient calculated by the brightness correction coefficient calculator by the above-described method, power consumption by the backlight lamp while maintaining the image quality of the image as it is. Can be reduced.

Although the present invention has been described above with reference to preferred embodiments thereof, this is merely an example and is not intended to limit the present invention, and those skilled in the art do not depart from the essential characteristics of the present invention. It will be appreciated that various modifications and applications which are not illustrated above in the scope are possible. And differences relating to such modifications and applications should be construed as being included in the scope of the invention defined in the appended claims.

According to the present invention, by reducing the power consumption by the backlight lamp while maintaining the image quality of the image displayed on the liquid crystal display device, it is possible to minimize the total power consumption of the liquid crystal display device.

In addition, when the user operates in the low power mode, the liquid crystal display according to the present invention may reproduce the desired image for a desired time at a sacrifice to some extent.

In addition, the liquid crystal display according to the present invention can be operated in an optimized state with respect to two factors such as the original image preservation rate and the power consumption minimization by adjusting the coefficient using the standard deviation in the distribution of the luminance values of the image. Therefore, the power consumption is reduced while maintaining the image quality of the image.

Claims (9)

A liquid crystal display comprising a control unit for controlling an overall operation, an LCD panel, a backlight lamp, and the backlight lamp power generator, wherein the control unit An image information receiver configured to receive an image signal to be reproduced; A luminance correction coefficient calculator for calculating luminance correction coefficients for the image signals received by the image information receiver; An image information corrector configured to correct the image signals using the luminance correction coefficients; An image information transmitter for transmitting the image signals corrected by the image information corrector to the LCD panel; A lamp power control unit calculating a reciprocal of the luminance correction coefficient to obtain a lamp power correction coefficient, and controlling the backlight lamp power generator using the lamp power correction coefficient. And reducing power consumption by the backlight lamp by adjusting brightness of the image signal and the backlight lamp to be reproduced. The image display apparatus of claim 1, wherein the luminance correction coefficient calculator is further configured to analyze a histogram of the image signals to obtain an average value of luminance values of the image signals, and to correct the luminance using the highest gray level value and the average value of the image signals. The liquid crystal display device which calculates a coefficient. The liquid crystal display device according to claim 2, wherein the luminance correction coefficient is calculated as (average value of highest gradation value ÷ luminance values of an image signal). The method of claim 1, wherein the luminance correction coefficient calculating unit detects a maximum value among luminance values of the image signals, and calculates a luminance correction coefficient using the highest gray level value and the maximum value of the image signals. Liquid crystal display. The luminance correction coefficient calculator of claim 1, wherein the luminance correction coefficient calculator is configured to set a correction level n in advance, and analyze a histogram of the image signals to determine the luminance of a pixel corresponding to the correction level n of the image signals. Detecting a value, and calculating a luminance correction coefficient using the detected luminance value and the highest gray level value of the image signal. The display apparatus of claim 1, wherein the luminance correction coefficient calculating unit sets a correction level n in advance, analyzes a histogram of the image signals, obtains an average value of luminance values of the image signals, and corrects the correction. And detecting a luminance value of the pixel corresponding to the level (n) and calculating a luminance correction coefficient using the average value, the detected luminance value, and the highest gray level value of the image signal. 7. The liquid crystal display device according to claim 6, wherein the luminance correction factor (σ) is determined by equation (5).  σ = α × (highest gradation value / detected luminance value) + β × (highest gradation value / average value) Is a luminance correction coefficient, α is a pixel reflection coefficient, β is a histogram reflection coefficient, and the sum of the pixel reflection coefficient and the histogram reflection coefficient is always one. The liquid crystal display of claim 7, wherein the pixel reflection coefficient and the histogram reflection coefficient are determined according to a standard deviation in the histogram with respect to the luminance value of the corresponding video signal. The liquid crystal display of claim 1, wherein the lamp power control unit corrects the tube current duty ratio of the backlight lamp power generator using the lamp power correction coefficient.

Images