KR20120040467A - Liquid crystal display device and driving method thereof - Google Patents

Abstract

PURPOSE: A liquid crystal display device and a driving method thereof are provided to correct brightness based on a face from an image, thereby improving display quality of the image. CONSTITUTION: A face region is detected from an inputted image signal(S110). Image information of the face region is detected(S120). A standard value and the image information of the face region are compared(S130). An image correction value is created based on a comparison result(S160). The image correction value is reflected in the inputted image signal. An image is displayed using the image signal.

Description

Liquid crystal display and its driving method {LIQUID CRYSTAL DISPLAY DEVICE AND DRIVING METHOD THEREOF}

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid crystal display, and more particularly, to a liquid crystal display and a method of driving the same, which improve display quality by performing luminance and color correction of image data on the basis of a face.

With the development of various portable electronic devices such as mobile communication terminals and notebook computers, there is an increasing demand for a flat panel display device applicable thereto.

The flat panel display includes a liquid crystal display device, a plasma display panel, a field emission display device, and an organic light emitting diode display device. Is being studied.

Among flat panel displays, the liquid crystal display has secured a firm market with the advantages of mass production technology, ease of driving means, low power consumption, thin thickness, high definition and large screen, and its field of application is continuously expanding.

The liquid crystal display displays an image by adjusting light transmittance for each pixel according to an input image signal. To this end, the liquid crystal display includes a liquid crystal panel in which a plurality of pixels (liquid crystal cells) are arranged in a matrix, a backlight unit for supplying light to the liquid crystal panel, and a driving circuit unit for driving the liquid crystal panel and the backlight. It is done by

The pixel voltage is formed by the voltage difference between the common voltage and the data voltage supplied to each pixel, and the gray level of the image is realized by adjusting the transmittance of the light supplied from the backlight unit through the arrangement of liquid crystals according to the pixel voltage. .

The display quality of an image implemented in such a liquid crystal display may vary depending on various factors. The brightness and color of the display image are important factors.

1 is a view showing an image processing method for improving display quality of a liquid crystal display according to the prior art.

Referring to FIG. 1, the liquid crystal display according to the related art analyzes the luminance of an input image signal and performs image processing so that the luminance of the display image is changed based on the analyzed luminance.

In general, a method of correcting a gamma curve is used to increase the quality of a display image. As a result of the luminance analysis of the image, when the display image is a dark image, the brightness of the display image is controlled by increasing a low gray level by a certain portion and, in the case of a bright image, by decreasing the high gray level by a portion.

Alternatively, if the histogram distribution of the input image is skewed, it is smoothly corrected or the image processing is performed to increase the contrast of the display image.

In the prior art, it is not known whether the image is excessively corrected by correcting the image data using only the entire luminance of the input image or the distribution of the histogram, and thus it is difficult to predict a change in the image quality of the display image.

If the display image is a landscape image, the viewer can provide a natural image even if the brightness or histogram of the image is controlled as in the conventional art. However, in the case of an image in which a face of a person sensitive to image quality is displayed, there is a problem in that the display quality is deteriorated because the face area of the person is unnaturally displayed due to the control of brightness or histogram.

An object of the present invention is to provide a liquid crystal display and a driving method for improving the display quality of an image.

SUMMARY OF THE INVENTION An object of the present invention is to provide a liquid crystal display and a driving method capable of improving display quality of an image by correcting luminance (gradation) based on a face in an image.

SUMMARY OF THE INVENTION An object of the present invention is to provide a liquid crystal display and a driving method capable of improving display quality of an image by correcting luminance of image data on the basis of a face in the image.

SUMMARY OF THE INVENTION An object of the present invention is to provide a liquid crystal display and a driving method capable of improving display quality of an image by correcting color values of image data based on faces in an image.

Other features and advantages of the invention will be set forth in the description which follows, or may be obvious to those skilled in the art from the description and the claims.

A method of driving a liquid crystal display according to an exemplary embodiment of the present invention includes detecting a face region from an input image signal and detecting image information of the face region; Comparing the image information of the face area with a reference value and generating an image correction value based on a comparison result; Reflecting the image correction value in the input image signal; And displaying an image by using the image signal reflecting the image correction value.

According to an embodiment of the present disclosure, a method of driving a liquid crystal display may generate a luminance correction value when the average luminance value of the face area is less than a set luminance reference value, and reflect the luminance correction value to the entire input image signal. do.

The driving method of the liquid crystal display according to an exemplary embodiment of the present invention generates a color correction value when the absolute value of the difference between the color value of the actual skin color and the average color value of the face region exceeds the color reference value, and generates the color correction. The value is reflected on the entire input video signal.

The liquid crystal display according to an exemplary embodiment of the present invention detects image information of a face region of an input image signal, generates an image correction value according to a result of comparing the image information of the face region with a reference value, and reflects it on the input image signal. An image controller; And a display panel which displays an image by using the image signal reflecting the image correction value.

The image controller of the liquid crystal display according to an exemplary embodiment of the present invention includes an image analyzer means for detecting a face region from an input image signal and detecting image information of the face region; Image comparison means for determining whether to correct the image signal by comparing the image information of the face region with a reference value; Correction data generating means for generating an image correction value based on a comparison result of the image comparison means; And image correction means for reflecting the image correction value on the entire input image signal.

The image controller of the liquid crystal display according to an exemplary embodiment of the present invention generates a luminance correction value when the average luminance value of the face region is less than a set luminance reference value, and the difference between the color value of the actual skin color and the average color value of the face region. When the absolute value of exceeds the set color reference value, a color correction value is generated, and at least one of the luminance correction value and the color correction value is reflected to the entirety of the input image signal.

The present invention can improve the display quality of an image by correcting the luminance (gradation) of the image data on the basis of a face in the image.

The present invention can improve the display quality of an image by correcting the color of the image signal based on the face in the image.

Other features and effects of the present invention may be newly understood through the embodiments of the present invention in addition to the features and effects of the present invention mentioned above.

1 is a view showing an image processing method for improving display quality of a liquid crystal display according to the prior art.
2 is a schematic view of a liquid crystal display according to an exemplary embodiment of the present invention.
3 is a diagram illustrating an image controller of a liquid crystal display according to an exemplary embodiment of the present invention.
4 to 8 illustrate a method of driving a liquid crystal display according to an exemplary embodiment of the present invention.

The liquid crystal display according to an exemplary embodiment of the present invention and a driving method thereof may improve display quality of an image by correcting luminance (gradation) values and color values of the image data based on faces in the image.

Hereinafter, a liquid crystal display and a driving method thereof according to an exemplary embodiment of the present invention will be described with reference to the accompanying drawings.

2 is a diagram schematically illustrating a liquid crystal display according to an exemplary embodiment of the present invention, and FIG. 3 is a diagram illustrating an image control unit of a liquid crystal display according to an exemplary embodiment of the present invention.

2 and 3, a liquid crystal display device according to an exemplary embodiment of the present invention may include a liquid crystal panel 110 displaying an image according to image data; An image controller 170 for analyzing the input image and correcting image data for improving image quality; A backlight unit 140 supplying light to the liquid crystal panel 110; It includes a driving circuit for driving the light source of the liquid crystal panel 110 and the backlight unit 140.

The liquid crystal panel 110 includes an upper substrate and a lower substrate bonded to each other with a liquid crystal layer interposed therebetween, and a plurality of pixels displaying an image are arranged in a matrix form.

The upper substrate may include a black matrix defining a pixel area to correspond to each of the plurality of pixels; And a red, green, and blue color filter formed in each pixel area defined by the black matrix.

The lower substrate includes a plurality of gate lines GL1 to GLn and a plurality of data lines DL1 to DLm, and the plurality of pixels are defined by the intersection of the gate lines and the data lines.

Each of the plurality of pixels includes a thin film transistor TFT and a storage capacitor Cst formed at an intersection of a gate line and a data line. The gate terminal of the thin film transistor is connected with the gate line, the source terminal is connected with the data line, and the drain terminal is connected with the pixel electrode.

A common electrode is formed on the upper substrate or the lower substrate, and an electric field is formed through the data voltage (image data) supplied to the pixel electrode and the common voltage Vcom supplied to the common electrode according to the switching of the thin film transistor. The liquid crystal of is driven.

The backlight unit 140 supplies light to the liquid crystal panel 110. The backlight unit 140 guides the plurality of backlights to generate light and guides the light generated from the backlight toward the liquid crystal panel 110. It may include an optical member (light guide plate, diffusion sheet, prism sheet) to improve the efficiency of the light irradiated to 110.

CCFL (Light Emitting Diode) or LED (Light Emitting Diode) may be applied to the plurality of backlights, and the on-off time and dimming are controlled according to the control of the backlight driver 150. do.

The driving circuit unit includes a gate driver 120; A data driver; A backlight driver 150 (inverter / LED driver); Timing controller 160 (T-CON);

The timing controller 160 controls the gate control signal GCS and the data driver 130 for the control of the gate driver 120 using the vertical / horizontal synchronization signals Vsync / Hsync and the clock signal CLK. The data control signal DCS is generated. The generated gate control signal is supplied to the gate driver 120, and the data control signal is supplied to the data driver 130.

The gate control signal GCS may include a gate start pulse (GSP), a gate shift clock (GSC), a gate output enable (GOE), and the like.

The data control signal DCS may include a source start pulse (SSP), a source sampling clock (SSC), a source output enable (SOE), and a polarity control signal (POL). Polarity) and the like.

The timing controller 160 generates a backlight control signal (BCS) for controlling on-off time and dimming of the plurality of backlights, and supplies the generated backlight control signal to the backlight driver 150. do.

The gate driver 120 generates a scan signal for driving thin film transistors formed in each pixel of the liquid crystal panel 110 based on the gate control signal GCS supplied from the timing controller 160, and generates the generated scan signal. Supply to a plurality of gate lines sequentially.

The data driver 130 converts the digital image data R, G, and B provided from the timing controller 160 into analog data voltages. The data voltage is converted to a plurality of data lines according to a time when the thin film transistor TFT of each pixel is turned on based on the data control signal DCS supplied from the timing controller 160.

The backlight driver 150 drives the plurality of backlights according to the backlight control signal BCS input from the timing controller 160. The luminance of the display shape may be controlled by adjusting the duty of the backlight so that the image displayed on the liquid crystal panel 110 can be clearly expressed.

In addition, the timing controller 160 aligns the image signals provided from the image controller 170 to digital image data R, G, and B in units of frames, and converts the image data aligned in units of frames to the data driver 130. To provide.

In this case, the image signal provided from the image controller 170 to the timing controller 160 is corrected for at least one of a luminance value and a color value to improve image quality.

In the image displayed on the screen, the viewer is more sensitive to the image quality of the face of the person than the background. If the brightness of the image on which the face is displayed is too low, the image quality is deteriorated. In this case, when a face of a person, which is a region of interest sensitive to image quality, is included, the face region may look unnatural when the brightness correction is performed on the background image data.

The image controller 170 of the liquid crystal display 100 according to an exemplary embodiment of the present invention detects a face region of the person from the input image signal and detects at least one of a luminance value and a color value of the face region. Thereafter, the luminance value and the color value of the image signal are corrected by using the luminance value and the color value of the detected face region. An image signal having at least one of a luminance value and a color value corrected may be provided to the timing controller 160 to improve the image quality of the display image.

To this end, the image controller 170 of the liquid crystal display 100 according to the exemplary embodiment of the present invention may include the image analyzer 172, the comparator 174, and the correction data generator 176 as illustrated in FIG. 3. ), And an image corrector 178.

Here, the correction of the image signal may be performed for both the brightness and the color of the image, or may be performed respectively. Hereinafter, the luminance correction and the color correction of the image will be described.

Hereinafter, the configuration of the image controller 170 and the driving method of the liquid crystal display according to the first exemplary embodiment will be described with reference to FIGS. 4 to 7.

The image analyzer 172 analyzes the input image data and extracts the face region of the person from the image to be displayed as shown in FIG. 5 (S110). Thereafter, an average brightness level (hereinafter referred to as "APL") of a face image is detected (S120).

The comparator 174 compares an APL (Face APL) of the face area with a preset luminance reference value. Specifically, it is compared whether the APL of the face area is less than the preset luminance reference value (S130).

Here, the luminance reference value is a criterion for determining a dark image. If the APL of the face area is less than the luminance reference value, it is determined as a dark image, and the image signal is corrected based on this.

As a result of the comparison of S130, when the APL of the face area is equal to or greater than the preset luminance reference value, even if the image is implemented as an input video signal, the face area is not darkly expressed, that is, the image quality is not degraded by the brightness of the face area. This does not correct the luminance value of the video signal.

Meanwhile, as a result of the comparison of S130, when the APL of the face region is less than the preset luminance reference value, when the image is implemented as the input image signal, the face region may be darkly expressed, resulting in deterioration of image quality. To correct.

The correction data generator 176 generates correction data for correcting the luminance value of the image signal. As an example, as shown in FIG. 6, reference points for generating a spline curve are generated (S140).

Here, the reference points may be composed of first reference points to third reference points P1 to P3.

The first reference point P1 and the third reference point P3 define a start point and an end point of the spline curve, and there is no change in output luminance compared to input luminance.

The second reference point P2 represents the luminance value of the face region to be actually output, that is, the luminance correction value of the image signal, compared to the face region APL of the input image signal. Here, the first reference point P1, the third reference point P3, and the second reference point P2, that is, the luminance correction value, may be generated through Equation 1 below.

In Equation 1, the brightness intensity may have a real value between 0 and 1.

As an example, when the face area APL is 80, the luminance reference value is 128, and the brightness intensity is 0.5, the second reference point P2, which is the luminance correction value, is 104.

Subsequently, as illustrated in FIG. 7, the correction data generator 176 generates a spline curve having the first reference point P1 to the third reference point P3 as a node (S150).

Subsequently, the image corrector 178 corrects the luminance values of the entire image signals by using the generated spline curve as a lookup table (LUT). That is, the input image signal having an APL of 80 in the face region is corrected to an output signal having a luminance value of 104 based on the face region. Thereafter, an image signal having a corrected luminance value is provided to the timing controller 160.

At this time, the dark image is determined through the APL of the face region among the entire image signals, but the luminance value is corrected for the entire image signal. When luminance correction is performed only on the face area, a contour phenomenon may occur in which the boundary between the background and the face is unnaturally expressed. Therefore, in the present invention, the luminance value is corrected for the entire video signal.

In the above description, the configuration and method for correcting the luminance of the image signal when the APL of the face area is less than the luminance reference value have been described. However, this is an example of the present invention. As another example, when the luminance of the face region is expressed too brightly, the luminance of the image signal may be reduced by using Equation 2 below.

In Equation 2, the brightness intensity may have a real value between 0 and 1.

As an example, when the face area APL is 250, the luminance reference value is 200, and the brightness intensity is 0.5, the second reference point P2 which is the luminance correction value is 225.

The correction data generator 176 generates a spline curve having the generated first reference point P1 to the third reference point P3 as a node, and the image correction unit 178 displays the generated spline curve as a lookup table (LUT). It can be used to correct the luminance value of the entire video signal. That is, the input image signal having the APL of 250 in the face region may be corrected to the output signal having the luminance value of 225 based on the face region.

Hereinafter, the driving method of the liquid crystal display according to the second exemplary embodiment of the present invention will be described with reference to FIG. 8.

The image signal may be generated in various formats according to an application method. When the color information of the image is displayed as R, G, and B data, the amount of data increases. Therefore, in order to reduce the amount of the video signal, the video signal is configured by separating the luminance component and the color component.

The driving method of the liquid crystal display according to the second exemplary embodiment of the present invention performs color correction of the image signal using the YCbCr format representing the digital image signal. In this case, color correction of the image signal may be performed using the CbCr, which is a color component, except for Y, which is a brightness component, of the YCbCr.

Among the color values (CbCr) of the input video signal, the color value of the background screen does not significantly affect the image quality, but the difference between the color value of the actual skin color (target CbCr) and the average color value (Face CbCr) of the face area is large. The picture quality may deteriorate.

The driving method of the liquid crystal display according to the second exemplary embodiment of the present invention is a color in which the difference between the average color value (Face CbCr) of the face region and the color value (target CbCr) of the actual skin color is greater than the reference value in the input image signal. The display quality of the display image can be improved by correcting the.

The image analyzer 172 analyzes the input image data and extracts the face region of the person from the image to be displayed as shown in FIG. 5 (S210). Then, the average color value (Face Cb, Face Cr) of the face area is detected (S220).

The comparator 174 compares an absolute value obtained by subtracting an average color value (Face Cb, Face Cr) of a face region from a target CbCr value (Target CbCr) indicating an ideal skin color, and comparing the preset color reference value (reference CbCr) with the absolute value. Determine whether to correct the color of the image signal. At this time, the determination of whether to correct the color of the image signal is made for each of the Cb and Cr color components. In the present invention, Cb is defined as the first color component and Cr as the second color component among the CbCr components.

Specifically, it is compared whether the absolute value obtained by subtracting the first average color value Face Cb of the face area from the target Cb value Target Cb representing the ideal skin color exceeds the first color reference value (reference Cb) (S230). ).

Here, the first color reference value (reference Cb value) is a reference for determining whether to correct the first color component (Cb), and the first color value (target Cb) of the actual skin color and the average first color of the face area. The value (Face Cb) means the allowable difference.

As a result of the comparison in S230, when the absolute value of the first color value (target Cb) of the actual skin color minus the average first color value (Face Cb) of the face area exceeds the first color reference value (reference Cb value). It is determined that deterioration in image quality occurs due to the first color component Cb of the input image signal.

In this case, the correction data generator 176 generates a first color correction value (Cb correction value) using Equation 3 below (S240).

In Equation 3, the Cb color intensity may have a real value between 0 and 1.

As an example, when the first color value (target Cb) of the actual skin color is 150, the average first color value of the face area is 100, and the Cb color intensity is 0.5, the first color correction value (Cb correction value) is 25 Becomes

On the other hand, as a result of the comparison of S230, the absolute value obtained by subtracting the average first color value (Face Cb) of the face area from the first color value (target Cb) of the actual skin color exceeds the first color reference value (reference Cb value). Otherwise, it is determined that no deterioration in image quality occurs due to the first color component Cb. In this case, by setting the first color correction value (Cb correction value) to 0, the first color component Cb is not corrected in the input image signal (S245).

Subsequently, a second color correction value (Cr correction value) is generated in the same manner as the generation process of the first color correction value (Cb correction value) described above.

Specifically, it is compared whether the absolute value obtained by subtracting the second average color value (Face Cr) of the face area from the target Cr value (Target Cr) indicating the ideal skin color exceeds the second color reference value (reference Cr) (S250). ).

Here, the second color reference value (reference Cr value) is a criterion for determining whether the second color component Cr is corrected, and the second color value (target Cr) of the actual skin color and the average second color of the face area are determined. Value (Face Cr) It means the allowance of difference.

Here, the second color reference value (reference Cr value) is a criterion for determining whether the second color component Cr is corrected, and the second color value (target Cr) of the actual skin color and the average second color of the face area are determined. Value (Face Cr) It means the allowance of difference.

As a result of the comparison of S250, when the absolute value obtained by subtracting the average second color value (Face Cr) of the face area from the second color value (target Cr) of the actual skin color exceeds the second color reference value (reference Cr value). It is determined that deterioration in image quality occurs due to the first color component Cb of the input image signal.

In this case, the correction data generator 176 generates a second color correction value (Cr correction value) by using Equation 4 below (S260).

In the above Equation 4, the Cr color intensity may have a real value between 0 and 1.

As an example, when the second color value (target Cr) of the actual skin color is 150, the average second color value of the face area is 100, and the Cr color intensity is 0.5, the second color correction value (Cr correction value) is 25 Becomes

On the other hand, as a result of the comparison of S250, the absolute value obtained by subtracting the average second color value (Face Cr) of the face area from the second color value (target Cr) of the actual skin color exceeds the second color reference value (reference Cr value). Otherwise, it is determined that no deterioration in image quality occurs due to the second color component Cr. In this case, by setting the second color correction value (Cr correction value) to 0, the second color component Cr is not corrected in the input image signal (S265).

Subsequently, the image corrector 178 corrects the image data by adding the generated first and second color correction values add Cb and add Cr to the first and second color values CbCr of the image signal.

In this case, the color of the video signal is corrected by adding the color correction value to the color values of the entire video signal. That is, the input image signal having the first and second color values of the face area of 100 is corrected to the output signal having the first and second color values of 125 of the face area. Thereafter, an image signal having a color value corrected is provided to the timing controller 160.

As described above, when the difference between the average color value (Face CbCr) of the face region and the color value (target CbCr) of the actual skin color is larger than the reference value, the color of the entire image signal may be corrected to increase the display quality of the display image. have.

In the above description, the color correction is performed based on the YCbCr format, but this is an example of the present invention. As another example of the present invention, color correction may be performed using an image signal format of HSI, HSL, LCH, Lab, YIQ, YUV, and CMYK.

In the above description, the luminance correction and the color correction of the image signal are separately performed, but the luminance correction and the color correction of the image signal may be performed together.

In the above, the image controller 170 is illustrated and described as being implemented in a separate configuration in the liquid crystal display 100, but this is an example of the present invention. In another embodiment of the present disclosure, the image controller 170 may be implemented as an internal configuration of the timing controller 160.

In the above description, the image signal correction is performed using the liquid crystal display as an example of the flat panel display device. However, the luminance correction and color correction method of the video signal of the present invention is not limited to the liquid crystal display device, but can be similarly applied to other flat panel display devices.

It will be understood by those skilled in the art that the present invention can be embodied in other specific forms without departing from the spirit or essential characteristics thereof. Therefore, it is to be understood that the embodiments described above are exemplary in all respects and not restrictive.

The scope of the present invention is shown by the following claims rather than the detailed description, and all changes or modifications derived from the meaning and scope of the claims and their equivalent concepts should be construed as being included in the scope of the present invention. do.

100: liquid crystal display 110: liquid crystal panel
120: gate driver 130: data driver
140: backlight unit 150: backlight driver
160: timing controller 170: image control unit

Claims (10)

Detecting a face region from an input image signal and detecting image information of the face region;
Comparing the image information of the face area with a reference value and generating an image correction value based on a comparison result;
Reflecting the image correction value in the input image signal; And
And displaying an image by using the image signal reflecting the image correction value. The method of claim 1, wherein the image information
And at least one of an average luminance value and an average color value of the face area. The method of claim 2, wherein the reference value is
And at least one of a luminance reference value for luminance correction of the input image signal and a color reference value for color correction. The method of claim 3, wherein the image correction value is
And at least one of a luminance correction value that is reflected in the input image signal to correct luminance and a color correction value that corrects color. The method of claim 4, wherein
When the average luminance value of the face area is less than the set luminance reference value, a luminance correction value is generated.
And applying the luminance correction value to the entire input image signal. The method of claim 4, wherein
When the absolute value of the difference between the color value of the actual skin color and the average color value of the face area exceeds the color reference value, a color correction value is generated.
And driving the color correction value to the entirety of the input image signal. The method of claim 1, wherein the input video signal
A method of driving a liquid crystal display device, characterized in that it is generated by any one of YCbCr, HSI, HSL, LCH, Lab, YIQ, YUV, CMYK. An image controller for detecting image information of a face region among input image signals, and generating an image correction value based on a result of comparing the image information of the face region with a reference value and reflecting the reflected image to the input image signal; And
And a display panel configured to display an image by using the image signal reflecting the image correction value. The method of claim 8, wherein the image control unit
Image analyzer means for detecting a face region from an input image signal and detecting image information of the face region;
Image comparison means for determining whether to correct the image signal by comparing the image information of the face region with a reference value;
Correction data generating means for generating an image correction value based on a comparison result of the image comparison means; And
And image correction means for reflecting the image correction value on the entire input image signal. The method of claim 9, wherein the image control unit
When the average luminance value of the face area is less than the set luminance reference value, a luminance correction value is generated.
When the absolute value of the difference between the color value of the actual skin color and the average color value of the face area exceeds the set color reference value, a color correction value is generated.
And at least one of the luminance correction value and the color correction value is reflected on the entirety of the input image signal.

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