KR102510573B1 - Transparent display device and method for driving the same - Google Patents

Abstract

The present invention provides a transparent display device capable of improving image quality by adaptively correcting an image according to driving characteristics and rear background characteristics of the transparent display device and a driving method thereof. The transparent display device according to an exemplary embodiment selectively considers transmittance characteristics of a light blocking plate and corrects an image using one of a gamma correction method and a sharpness improvement method in consideration of brightness characteristics of an input image and brightness characteristics of a rear background, thereby improving image quality. can improve

Description

Transparent display device and its driving method {TRANSPARENT DISPLAY DEVICE AND METHOD FOR DRIVING THE SAME}

The present invention relates to a transparent display device capable of improving image quality by adaptively correcting an image according to driving characteristics of the transparent display device and characteristics of a rear background, and a method for driving the same.

Recently, with the development of display devices, a liquid crystal display (LCD) and a transparent display device using an organic light emitting diode (OLED) display device have been developed.

Since the transparent display device transmits light in both front and back directions, information can be displayed in both directions of the display device, and each user facing the display device can see beyond the transparent display device.

Since the transparent display device can be applied to various applications such as automobile glass, building glass, advertising signboards, cooler doors, and screen doors, user environments are diverse.

Since the transparent display device cannot implement black in a high transmittance state, a technology for adjusting the transmittance using a light blocking plate has been developed.

However, there is a problem in that it takes a considerable amount of time until the light blocking plate is closed after the light blocking plate operates due to limitations of the light blocking plate material technology.

For this reason, until the light blocking plate is closed, the quality of the transparent display device deteriorates because the perceived image quality is greatly influenced by the transmittance characteristics of the light blocking plate, the characteristics of the rear background of the transparent display device, and the characteristics of the input image.

For example, if the transmittance of the transparent display device is high before the light blocking plate is closed, it is impossible to implement black, and thus image quality deterioration such as clumping of low grayscale regions occurs. When the rear background of the transparent display device is bright, more light is transmitted and visibility of the image is deteriorated, resulting in deterioration in image quality. When the input image is dark, it is difficult to implement black in a transparent display device, resulting in image quality deterioration.

In addition, the transparent display device may not include a light blocking plate or may display an image while maintaining the light blocking plate in a transmissive mode when it is necessary to recognize a rear background along with image information according to a use environment.

In this case, since the image is recognized together with the rear background, the transparent display device has a problem in that image quality is deteriorated because sharpness of the image is deteriorated according to the brightness of the image and the brightness of the rear background.

The present invention provides a transparent display device capable of improving image quality by adaptively correcting an image according to driving characteristics and rear background characteristics of the transparent display device and a driving method thereof.

A transparent display device according to an embodiment of the present invention includes a transparent display unit, a light blocking plate, a display driver, a light blocking plate driver, a background sensor disposed on a rear surface of the transparent display device to sense a rear background, and an image processing unit.

The image processing unit analyzes the input image to determine an image characteristic indicating whether the input image is a dark image or a bright image, and analyzes a rear background signal sensed by a background sensor to determine a background characteristic indicating whether the rear background is a bright or dark background. and determine the transmittance characteristics of the light blocking plate.

The image processing unit performs gamma correction on the input image when the image characteristics and background characteristics correspond to any one of the image quality deterioration conditions other than the normal condition of a bright image and a dark background, and the transmittance exceeds the first reference value. , the gamma-corrected image data is output to the display driver.

The image processing unit outputs the input image to the display driver without gamma correction regardless of the transmittance when the image characteristics and the background characteristics are normal conditions, and when the transmittance is equal to or less than the first reference value, the input image is gamma-corrected regardless of the image characteristics and the background characteristics. It is output to the display driver without correction.

A method of driving a transparent display device according to an embodiment of the present invention includes the steps of analyzing an input image to determine an image characteristic indicating whether the input image is a dark image or a bright image, sensing a rear background of the transparent display device, The method may include analyzing the sensed rear background signal to determine a background characteristic indicating whether the rear background is a bright background or a dark background, and determining transmittance characteristics of the light blocking plate.

In addition, in the driving method of the present invention, when the image characteristics and the background characteristics correspond to any one of the image quality deterioration conditions other than the normal condition of a bright image and a dark background, and the transmittance exceeds the first reference value, the input image performing gamma correction on; The method may further include outputting the gamma-corrected image.

In addition, the driving method of the present invention includes the steps of outputting an input image without gamma correction regardless of transmittance when the image characteristics and background characteristics are normal conditions, and when the transmittance is equal to or less than a first reference value, the relationship between the image characteristics and the background characteristics and outputting the input image without gamma correction.

A transparent display device according to an embodiment of the present invention includes a transparent display unit, a background sensor, a display driver, brightness characteristics for each block calculated by dividing an input image into a plurality of pixel blocks, and a background sensor. The intensity of sharpness enhancement for each block is determined according to the brightness characteristics of the sensed rear background, the intensity of sharpness improvement for each block is applied to the input image, the sharpness of the input image is corrected for each pixel block, and the image with the sharpness corrected and an image processing unit that outputs to the display driving unit.

The image processing unit includes a low pass filter, a mask generation unit, a sharpness improvement strength adjusting unit, a sharpness improvement mask determining unit, and an image correcting unit. The low pass filter performs low pass filtering on an input image to generate and output a blurred image. The mask generator subtracts the blur image supplied from the low pass filter from the input image to generate and output an edge mask image. The sharpness improvement intensity adjusting unit adjusts the intensity of sharpness improvement for each block according to the brightness characteristics of each block of the input image and the brightness characteristics of the sensed rear background. The sharpness enhancement mask determiner generates and outputs a sharpness enhancement mask image by applying the sharpness enhancement intensity for each block supplied from the sharpness enhancement intensity adjuster to the edge mask image supplied from the mask generator. The image correction unit synthesizes the sharpness improvement mask image supplied from the sharpness improvement mask determination unit and the input image, and outputs the sharpness-corrected image to the panel driver.

A method of driving a transparent display device according to an embodiment of the present invention includes generating a blur image by low-pass filtering an input image, generating an edge mask image by subtracting the blur image from the input image, and Dividing into a plurality of pixel blocks and determining the intensity of sharpness improvement for each block in each pixel block according to the brightness characteristics of each block calculated in units of pixel blocks and the brightness characteristics of the sensed rear background; The method includes generating a sharpness enhancement mask image by applying the sharpness enhancement strength, and displaying the sharpness-corrected image on a transparent display unit by synthesizing the sharpness enhancement mask image and the input image.

The step of determining the intensity of sharpness improvement for each block includes calculating an average gray level for each block of the input image, determining the maximum and minimum values of the intensity of sharpness improvement according to the sensed brightness of the rear background, and the step of determining the average gray level for each block. When (L), the maximum and minimum values (Kmax, Kmin) of the sharpness improvement intensity, and the average gray level (L) for each block are less than the preset threshold value (Lth), the sharpness improvement for each block is performed using the function of the equation below. A step of determining intensity (K), and a step of determining a preset minimum value as the sharpness improvement intensity of the corresponding block when the average gray level of each block is greater than or equal to a threshold value.

A transparent display device and a method of driving the same according to an embodiment of the present invention analyzes transmittance characteristics of a light blocking plate, luminance characteristics of an input image, and luminance characteristics of a background image, and according to the analysis result, the transmittance is greater than the reference value and the input image and the rear surface When the background corresponds to the quality deterioration condition, the image quality may be improved by correcting the image data by adjusting the gamma.

A transparent display device and a method for driving the same according to an embodiment of the present invention adjusts the intensity of sharpness enhancement according to the brightness of an image and the brightness of a rear background, thereby applying an appropriate intensity of sharpness improvement according to an image and a viewing environment to improve clarity and image quality. can make it

A transparent display device and a method of driving the same according to an embodiment of the present invention adjust the intensity of sharpness improvement according to the brightness of the image and the brightness of the rear background, so that when both the image and the rear background convey meaningful information, the boundary between the background and the image can be emphasized to improve the visibility of both the video and the rear background.

1 is a graph showing transmittance characteristics according to driving time of a light blocking plate in a transparent display device according to the prior art of the present invention.
2 is a photograph showing a comparison of image display results according to transmittance of a light shielding plate in a transparent display device according to the prior art of the present invention.
3 is a photograph showing a comparison of image display results according to image characteristics and background characteristics in a transparent display device according to the prior art of the present invention.
4 is a block diagram schematically illustrating the configuration of a transparent display device according to an exemplary embodiment of the present invention.
5 is an equivalent circuit diagram illustrating a configuration of a subpixel according to an embodiment of the present invention.
6 is a block diagram showing the configuration of an image processing unit of a transparent display device according to an embodiment of the present invention.
7 is a flowchart illustrating an image processing method of a transparent display device in stages according to an exemplary embodiment of the present invention.
8 is a graph showing a distribution rate for each gray level of an input image according to an embodiment of the present invention.
9 is a graph showing a distribution rate for each gray level of a background image according to an embodiment of the present invention.
10 is a graph showing various gamma curves according to an embodiment of the present invention.
11 is a photograph showing an image before and after gamma correction and an image without gamma correction according to an embodiment of the present invention.
12 is a block diagram schematically illustrating a configuration of a transparent display device according to an exemplary embodiment.
13 is a block diagram showing the configuration of an image processing unit according to an embodiment of the present invention.
14 is a flowchart illustrating an image processing method step by step according to an embodiment of the present invention.
15 is a graph showing a sharpness improvement intensity function according to an average block gray level according to an embodiment of the present invention.
FIG. 16 shows an image obtained by adjusting and applying sharpness enhancement according to the brightness of the image and the brightness of the rear background in the transparent display device according to an embodiment of the present invention, in comparison with a prior art image.

Prior to the description of the embodiments of the present invention, a deterioration in image quality of a transparent display device according to the prior art of the present invention will be first described as an example.

1 is a graph showing the transmittance characteristics of a light shielding plate over driving time in a transparent display device according to the prior art of the present invention, and FIG. 2 is an image display result according to the transmittance of the light shielding plate in the transparent display device according to the prior art of the present invention. 3 is a picture showing a comparison of image display results according to image characteristics and background characteristics when the transmittance of the light blocking plate is 70% in the transparent display device according to the prior art of the present invention.

Referring to FIG. 1 , it can be seen that it takes about 3 minutes for the light blocking plate of the transparent display device according to the prior art to be closed to a transmittance of 10% or less after driving is started.

As a result, as shown in FIG. 2(a), if the transmittance of the shading plate is 80%, it is impossible to implement black of the shading plate, so the rear background is visible due to the transparent characteristic and more light is transmitted from the rear side, so the visibility of the displayed image is reduced. Able to know. As shown in FIG. 2(b), visibility of a displayed image is improved only when the light blocking plate is closed with a transmittance of 10% or less by realizing black of the light blocking plate. Therefore, when the light blocking plate transmittance is greater than 10%, there is a problem of image quality deterioration.

In addition, when the transmittance of the light blocking plate is 70%, as shown in FIGS. 3 (a) and (b), the image quality is lowered in a bright background (b) than in a dark background (a) for the same dark image, and in FIG. 3 (c) ), (d), when the same bright background, both the dark image (a) and the bright image (b) show the rear background, and it can be seen that the visibility of the displayed image is reduced.

In addition, when the light shielding plate is not provided or the light shielding plate maintains the transmissive mode because the rear background needs to be recognized, the transparent display device according to the prior art determines the degree of recognition of the rear background according to the brightness characteristics of the image and the rear background. As a result, the sharpness of the image may be deteriorated depending on the degree of recognition of the rear background.

In order to solve the problems of the prior art, the present invention selectively considers the transmittance characteristics of the light shielding plate and corrects the image by considering the brightness characteristics of the input image and the brightness characteristics of the rear background (ie, viewing environment), thereby providing image and viewing quality. A transparent display device capable of improving image quality by appropriately improving visibility according to the environment and a driving method thereof are proposed.

Hereinafter, preferred embodiments of the present invention will be described.

A transparent display device according to an embodiment of the present invention uses at least one of a gamma correction method and a sharpness improvement method as an image processing method for improving visibility according to images and viewing environments.

4 is a block diagram schematically illustrating a configuration of a transparent display device according to an exemplary embodiment, and FIG. 5 is an equivalent circuit diagram illustrating a configuration of a subpixel according to an exemplary embodiment.

Referring to FIG. 4 , a transparent display device according to an exemplary embodiment includes an image processor 100, a timing controller 150, a data driver 200 and a gate driver 300, a transparent display 400, and a gamma voltage. It includes a generating unit 500, a background sensor 600, a light blocking plate 700 and a light blocking plate driver 800, and the like. Here, the timing controller 150 , the data driver 200 , and the gate driver 300 may be expressed as a display driver that drives the transparent display unit 400 .

The transparent display unit 400 displays an image through a pixel array in which pixels are arranged in a matrix form. The basic pixel of the pixel array is at least three or more subpixels (W/R) capable of expressing white by color mixing among the white (W), red (R), green (G), and blue (B) subpixels (SP). /G, B/W/R, G/B/W, R/G/B, or W/R/G/B).

Although a liquid crystal panel, an organic light emitting diode (OLED) panel, or the like may be used as the transparent display unit 400 , an OLED panel will be described below as an example.

When the transparent display unit 400 is an OLED panel, as shown in FIG. 5 , each sub-pixel SP has a light emitting area EA where an OLED element is located and a transmission area TA that transmits light from the front and rear surfaces. ). The light emitting area EA of the OLED device may or may not overlap the pixel circuit.

Referring to FIG. 5 , the pixel circuit includes an OLED element connected between a high potential power supply (EVDD) line and a low potential power supply (EVSS) line, and first and second switching TFTs (ST1, ST1, to independently drive the OLED element). ST2), a pixel circuit including a driving TFT (DT) and a storage capacitor (Cst), and the structure of the pixel circuit is not limited to the structure of FIG. 5 because it is diverse.

The OLED element includes an anode connected to the driving TFT (DT), a cathode connected to the low potential voltage (EVSS), and a light emitting layer between the anode and the cathode, and emits light proportional to the amount of current supplied from the driving TFT (DT). Occurs.

The first switching TFT (ST1) is driven by the gate signal of one gate line (GL1) to supply the data voltage from the corresponding data line (DL) to the gate node of the driving TFT (DT), and the second switching TFT (ST2) ) is driven by a gate signal of another gate line GL2 to supply a reference voltage from the reference line REF to the source node of the driving TFT DT. The second switching TFT ST2 is further used as a path for outputting the current from the driving TFT DT to the reference line REF in the sensing mode.

The storage capacitor Cst connected between the gate node and the source node of the driving TFT DT transmits the data voltage supplied to the gate node through the first switching TFT ST1 and the source node through the second switching TFT ST2. The differential voltage of the reference voltage supplied to is charged and supplied as the driving voltage of the driving TFT (DT).

The driving TFT DT controls the current supplied from the high-potential power supply EVDD according to the driving voltage supplied from the storage capacitor Cst, thereby supplying a current proportional to the driving voltage to the OLED element so that the OLED element emits light.

Referring to FIG. 4 , the light blocking plate 700 is disposed on the rear surface of the transparent display unit 400 and can be driven in a light blocking mode or a transmissive mode by the light blocking plate driving unit 800 when the transparent display unit 400 displays an image. . The light blocking plate 700 may implement a light blocking mode by displaying black when an electric field is applied by the light blocking plate driving unit 800 and implement a transmission mode when an electric field is not applied. When the light blocking plate 700 is driven in the light blocking mode by the light blocking plate driver 800, the light blocking plate 700 implements a black color to block light transmission, thereby improving the visibility of an image displayed on the transparent display unit 400.

For example, as the light blocking plate 700, an electrochromic device known as an electrochromic filter, an electrowetting device, or the like may be used, or a light transmission switchable by using a liquid crystal may be used. may be a device.

Meanwhile, the light blocking plate 700 may be disposed on at least one side of the front and rear surfaces of the transparent display unit 400 .

The background sensor 600 is mounted on the back of the transparent display device to sense the back background of the transparent display device, and supplies the sensed back background information (brightness or image) to the image processing unit 100 . As the background sensor 600, a known illuminance sensor or a CMOS image sensor may be applied.

The image processing unit 100 determines image characteristics by analyzing an input image supplied from the outside, and determines characteristics of a rear background by analyzing background information (brightness or image) sensed by the background sensor 600 . The image processing unit 100 may determine the transmittance of the light blocking plate 700 according to the transmission mode and the light blocking mode of the light blocking plate 700 by the light blocking plate driver 800 . In the image processing unit 100, when the light blocking plate 700 is driven in the light blocking mode, the transmittance of the light blocking plate 700 according to the lapse of driving time is measured in advance and stored in the form of a look-up table (LUT). can When the light blocking plate 700 is driven in the light blocking mode by the light blocking plate driver 800, the image processing unit 100 may determine the transmittance of the light blocking plate 700 according to the driving time of the light blocking mode.

The image processor 100 analyzes the input image to determine whether the input image is a dark image or a bright image, and analyzes background information to determine whether the background is a bright environment or a dark environment. A detailed description of this will be described later.

As a result of determining the characteristics of the input image and the rear background characteristics, the image processing unit 100 determines that the image quality degrade condition is that the input image is dark and the background is bright, the input image is dark and the background is dark, or the input image is bright and the background is bright. , When the transmittance of the light blocking plate 700 exceeds the first reference value (eg, 10%), gamma correction is performed on the input image according to the transmittance, and a gamma-corrected image is output to compensate the image quality.

On the other hand, the image processing unit 100 corresponds to a normal condition in which the input image is bright and the background is dark and the transmittance exceeds the first reference value (for example, 10%), or the transmittance is increased regardless of the characteristics of the input image and the rear background. When it is equal to or less than the first reference value, the input image is output without gamma correction.

The image processing unit 100 converts 3-color data (R, G, B) into 4-color data (W, R, G, B) using a conventional RGB-to-WRGB conversion method before or after gamma correction. can be converted The image processing unit 100 may further perform necessary image processing such as power consumption reduction, data rendering, image quality compensation, and degradation compensation before or after the above-described gamma correction. The image processing unit 100 supplies the processed image data and timing control signals to the timing controller 150 .

The image processing unit 100 may mean hardware implemented in the timing controller 100 or an image processing module of software stored in a memory.

The timing controller 150 generates a data control signal DCS and a gate control signal GCS using the timing control signals supplied from the image processing unit 100 and outputs them to the data driver 200 and the gate driver 300, respectively. do. The timing control signals include a dot clock, a data enable signal, a vertical sync signal, and a horizontal sync signal. Since the vertical sync signal and the horizontal sync signal can be generated by counting the data enable signal, they can be omitted. The data control signals may include a source start pulse, a source sampling clock, and a source output enable signal that control driving of the data driver 200 . The gate control signals may include a gate start pulse and a gate shift clock for controlling driving of the gate driver 300 .

With respect to the image data supplied from the image processing unit 100, the timing controller 150 calculates the deviation of driving characteristics (threshold voltage of driving TFT, mobility, OLED threshold voltage, etc.) for each subpixel of the transparent display unit 400 to the data driver ( 200), the image may be output to the data driver 200 after further performing necessary image processing such as external compensation or deterioration compensation that is sensed and compensated.

The data driver 200 receives a data control signal and image data from the timing controller 150 . The data driver 200 is driven according to the data control signal to subdivide the reference gamma voltage set supplied from the gamma voltage generator 500 into grayscale voltages respectively corresponding to the grayscale values of the data, and converts the divided grayscale voltages into grayscale voltages. digital image data is converted into an analog data signal, and the analog data signal is supplied to the data lines of the transparent display unit 400, respectively.

The data driving unit 200 is composed of a plurality of data driving ICs that divide and drive the data lines of the transparent display unit 400, and each data driving IC is TCP (Tape Carrier Package), COF (Chip On Film), FPC (Flexible Print) It may be mounted on a circuit film such as a circuit film and attached to the transparent display unit 400 using a Tape Automatic Bonding (TAB) method or mounted on the transparent display unit 400 using a COG (Chip On Glass) method.

The gate driver 300 drives the plurality of gate lines of the transparent display 400 respectively using the gate control signal GCS supplied from the timing controller 150 . The gate driver 300 supplies a scan pulse of a gate-on voltage to each gate line in a corresponding scan period in response to a gate control signal, and supplies a gate-off voltage in the remaining period. The gate driver 300 receives the gate control signal GCS from the timing controller 150, receives the gate control signal GCS from the timing controller 150 via the data driver 200, or receives the gate control signal GCS from the timing controller 150. ) through a power supply circuit (not shown).

The gate driver 300 is composed of at least one gate IC, is mounted on a circuit film such as TCP, COF, FPC, etc., and is attached to the transparent display unit 400 in a TAB method or mounted on the transparent display unit 400 in a COG method. can Unlike this, the gate driver 300 is a GIP (Gate In Panel) type embedded in the non-display area of the transparent display unit 400 by being formed on a thin film transistor substrate together with the thin film transistor array constituting the pixel array of the transparent display unit 400. can be provided with

6 is a block diagram showing the internal configuration of the image processing unit 100 according to an embodiment of the present invention, and FIG. 7 is a flowchart showing an image processing method step by step according to an embodiment of the present invention. It is explained in conjunction with 7.

Referring to FIG. 6 , the image processing unit 100 includes a transmittance LUT 102 , an image characteristic analysis unit 104 , a background characteristic analysis unit 106 , a determination unit 108 , and a gamma correction unit 110 . The image processing unit 100 may further include other well-known image processing blocks.

The image characteristic analysis unit 104 receives an input image from the outside, analyzes the input image, calculates the degree of inclusion of a dark image, that is, the degree of darkness, and determines whether the input image is a dark image or a bright image according to the degree of darkness. A judgment signal is output to the judgment unit 108 . (S12)

For example, the image characteristic analysis unit 104 uses Equation 1 below to determine the distribution ratio occupied by low grayscale values in the input image of each frame, that is, the low grayscale weighted average image level representing the degree of inclusion of dark images. Level; hereinafter WAPL_Low) is calculated as a percentage (%).

<Equation 1>

n is the number of subpixels included in a unit frame of the input image, and Gray means a grayscale value of each subpixel.

And, the image characteristic analysis unit 104 determines the input image as a dark image when the WAPL_Low calculated from Equation 1 is less than the second reference value α%, and conversely, when the WAPL_Low is greater than or equal to the second reference value α%, the input image is It is determined as a bright image, and a first determination signal indicating whether the input image is a dark image or a bright image is output to the determination unit 108 according to the determination result. (S12) Here, the second reference value α% is set in advance by the designer and varies depending on the characteristics of the transparent display device and the light blocking plate 700, but a value of 30≤α≤50 is appropriate as a reference value for determining whether or not a dark image is present.

When the WAPL_Low calculated from Equation 1 is smaller than the second reference value α% (30≤α≤50), the distribution rate of the low grayscale region is relatively large, as shown in the graph showing the distribution ratio by grayscale of the input image shown in FIG. 8. means case.

The background characteristic analyzer 106 receives the background image sensed by the background sensor 600, analyzes the background image, calculates the brightness level, and generates a second determination signal indicating whether the background is bright or dark according to the brightness level. It is output to the gamma correction unit 108. (S14)

For example, when the sensed rear background information is image information, the background characteristic analysis unit 106 uses Equation 2 below to determine the number of pixels with high grayscale values in the background image of each frame, that is, the brightness of the background image. A high grayscale weighted average image level (hereinafter referred to as WAPL_High) representing the degree is calculated as a percentage (%).

<Equation 2>

n is the number of subpixels included in a unit frame of the background image, and Gray means a grayscale value of each subpixel.

Further, the background characteristic analysis unit 106 determines that the background image is bright when WAPL_High calculated from Equation 2 is greater than the third reference value β%, and conversely, when WAPL_High is less than the second reference value β%, the background image is dark. and outputs a second determination signal indicating whether the background image is bright or dark according to the determination result to the determination unit 108 . (S14) Here, the second reference value β% is set in advance by the designer and varies depending on the characteristics of the transparent display device and the light blocking plate 700, but about 50≤β≤70 is appropriate as a reference value for determining a bright background.

When WAPL_High calculated from Equation 2 is greater than the third reference value β% (50≤β≤70), the distribution rate of the high grayscale region is relatively large, as shown in the graph showing the distribution ratio for each grayscale of the background image shown in FIG. means case.

In the transmittance LUT 102 , the transmittance of the light blocking plate 700 according to the lapse of driving time is previously measured and stored. The transmittance LUT 102 receives the driving time of the light blocking plate 700 from an external system (not shown), selects the transmittance according to the driving time of the light blocking plate 700, and supplies it to the determination unit 108 (S16). The transmittance LUT 102 may classify and store a plurality of transmittance sections according to driving time. For example, the transmittance (t) section may be classified and stored as t>70, 60<t≤70, ..., 20<t≤30, 10<t≤20, t≤10. The transmittance LUT 102 may output information about the transmittance (t) section corresponding to the driving time to the determination unit 108 . (S18)

The determination unit 108 includes a first determination signal indicating whether the input image supplied from the image characteristic analysis unit 104 is dark or bright, and a second determination signal indicating whether the background supplied from the background characteristic analysis unit 106 is bright or dark. The logical combination of the signals determines whether or not to perform gamma correction. The determination unit 108 outputs the signal for determining whether to perform gamma correction and transmittance information supplied from the transmittance LUT 102 to the gamma correction unit 110 . The determination unit 108 may output maximum transmittance information to the gamma correction unit 110 when the light blocking plate 700 is in a transmission mode by the light blocking plate driver 800 .

The determination unit 108 determines whether the first determination signal from the image characteristic analysis unit 104 and the second determination signal from the background characteristic analysis unit 106 predict the degradation of image quality among the four conditions shown in Table 1 below. Corresponds to one of the first to third conditions (dark image and bright background, dark image and dark background, bright image and bright background), which is any one of the image quality degradation conditions (S18, YES), transmittance information supplied from the LUT 102 When γ exceeds the first reference value (for example, 10%) (S20, YES), a gamma correction required signal is output to the gamma corrector 110. The determination unit 108 outputs the transmittance information together with the gamma correction required signal to the gamma correction unit 110 .

<Table 1>

On the other hand, the determination unit 108 uses the first determination signal from the image characteristic analysis unit 104 and the second determination signal from the background characteristic analysis unit 106 under the fourth condition (bright image and dark background), a gamma correction unnecessary signal is output to the gamma correction unit 110 regardless of transmittance information (S18, NO)

Meanwhile, when the transmittance information supplied from the transmittance LUT 102 is less than or equal to the first reference value (eg, 10%), the determination unit 108 converts the gamma correction unnecessary signal to the gamma correction unit regardless of the above-described image characteristics and background characteristics. output to (110). (S20, NO)

When the gamma correction required signal is supplied from the determination unit 108, the gamma correction unit 110 supplies the input image via the image characteristic analysis unit 104 according to the transmittance information supplied through the determination unit 108. Gamma correction is performed on (S22), and a gamma-corrected image is output (S24).

On the other hand, when the gamma correction unnecessary signal is supplied from the determination unit 108, the gamma correction unit 110 outputs the supplied input image without gamma correction via the image characteristic analysis unit 104 (S24).

In the gamma correction unit 110, a plurality of gamma correction LUTs having different gamma values (a value defining a gamma curve representing an output grayscale value with respect to an input grayscale value) are preset and stored according to transmittance information as shown in FIG. there is.

For example, the gamma correction unit 110 selects different gamma values (GMA) according to transmittance (t) information as shown in Table 2 below, and uses a LUT corresponding to the selected gamma value to select each data (input grayscale) of the input image. value), differential gamma correction is performed on the input image according to the transmittance, and the gamma-corrected image is output.

<Table 2>

In Table 2, the gamma value of 2.2 corresponding to the case where the transmittance (t) information is less than 10% means that the input image is output without gamma correction as a default setting value of the transparent display device.

As shown in Table 2, the gamma value increases as the transmittance increases, and as shown in FIG. 9, the output grayscale value relative to the input grayscale value decreases as the gamma value increases.

11 is a photograph showing an image before and after gamma correction and an image without gamma correction according to an embodiment of the present invention.

When the transmittance of the light blocking plate is 70%, the input image is dark, and the background is bright, displaying the image using the 2.2 gamma before the present invention is applied as shown in FIG. 11(a) reduces the visibility of the displayed image. , As shown in FIG. 11(b), it can be seen that when the present invention is applied and an image is displayed using a 3.4 gamma, visibility is improved and image quality is improved.

Meanwhile, when the background is dark and the input image is bright, as shown in FIG. 11(c), it can be seen that gamma correction is not required.

As described above, the transparent display device and its driving method according to an embodiment of the present invention analyzes the transmittance characteristics of the light blocking plate, the luminance characteristics of the input image and the luminance characteristics of the background image, so that the transmittance is greater than the reference value and the input image When the image quality and the background background correspond to the image quality deterioration condition, image quality may be improved by correcting image data by adjusting gamma.

12 is a block diagram schematically illustrating a configuration of a transparent display device according to an exemplary embodiment.

In contrast to the embodiment shown in FIG. 4 , the transparent display device shown in FIG. 12 allows the image processing unit 1000 to reduce the sharpness of the image affected by the brightness of the image and the brightness of the rear background (viewing environment). There is a difference in that image processing is performed to improve the image quality by adaptively improving the sharpness of the image according to the degree of recognition). In FIG. 12 , components other than the image processor 1000 are the same as those in FIG. 4 , so descriptions of the same components as those in FIG. 4 will be omitted.

The transparent display device shown in FIG. 12 requires recognition of the rear background along with image display. In the transparent display device shown in FIG. 12, the light blocking plate 700 and the light blocking plate driver 800 shown in FIG. 4 are omitted. can Meanwhile, in the case of including the light blocking plate 700 and the light blocking plate driver 800 shown in FIG. 4 , the light blocking plate 700 may be maintained in a transmission mode by the light blocking plate driver 800 .

In order to improve the sharpness of the image, the image processing unit 1000 may use a sharpness improvement method of improving the sharpness in proportion to the edge strength of the image by applying unsharp masking. In addition, the image processing unit 1000 prevents the brightness of the image and the brightness of the rear background from deteriorating at least one of the sharpness and image quality of the image due to the degree of recognition of the rear background being changed according to the brightness of the image and the brightness of the rear background. Adaptively adjusts the intensity of sharpness improvement according to . As a result, the image processing unit 1000 can improve the sharpness appropriately for the image and the viewing environment by adjusting the sharpness improvement strength considering both the edge strength characteristics of the image, the brightness characteristics of the image, and the brightness characteristics of the rear background, thereby improving the image quality. can improve

Specifically, in the transparent display device, the rear background of the bright area of the image is not well recognized due to the bright image, whereas the rear background of the dark area is recognized together with the image, reducing the expressiveness of the edge of the image, so the brightness of the image is reduced. The sharpness of the image may decrease as the number of pixels decreases. In order to prevent the sharpness of the image from deteriorating according to the brightness of the image, the image processing unit 1000 increases the intensity of sharpness improvement because the degree of sharpness degradation of the image is high in the dark area of the image because the degree of recognition of the rear background is high, In the bright area of , the degree of perception of the rear background is low, and the degree of deterioration in sharpness is low, so the intensity of sharpness improvement is reduced. To this end, the image processing unit 100 divides the image frame into a plurality of pixel blocks, calculates an average gray level for each pixel block, and adjusts the intensity of sharpness improvement for each block according to the average gray level for each block (average brightness for each block).

In addition, in order to prevent the sharpness of the image from being reduced because the background visibility increases as the brightness of the rear background increases, the image processing unit 100 adjusts the intensity of sharpness improvement according to the brightness of the rear background. In the case of a dark rear background, the degree of sharpness deterioration is low, so the image processing unit 100 reduces the intensity of sharpness improvement, and in the case of a bright rear background, the degree of sharpness deterioration is high because the degree of sharpness deterioration is high. increase strength; To this end, the image processing unit 100 senses the brightness of the rear background and changes the function for determining the intensity of sharpness improvement according to the average gray level of each block of the image by applying a background weight according to the brightness of the rear background, thereby adjusting the brightness of the rear background. Adjust the sharpness improvement strength accordingly. A detailed description of this will be given later.

13 is a block diagram showing the configuration of an image processing unit 1000 of a transparent display device according to an embodiment of the present invention, and FIG. 14 is a step-by-step diagram showing an image processing method of a transparent display device according to an embodiment of the present invention. 15 is a flow chart, and FIG. 15 shows a graph of a function for determining the intensity of sharpness improvement according to the average gray level of each block of an image according to an embodiment of the present invention. Hereinafter, description will be made with reference to FIGS. 13 to 15 .

The image processing unit 1000 shown in FIG. 13 includes a sharpness improvement strength adjusting unit 1200 that adjusts the sharpness improvement strength K according to the brightness of the image and the brightness of the rear background, and the input image FD through unsharp masking. An unsharp mask filter 1100 is provided to improve the sharpness of an image in proportion to the edge strength and the sharpness improvement strength K of and outputs an image FD' with improved sharpness.

The unsharp mask filter 1100 includes a low pass filter 1110, a mask generator 1120, a sharpness improvement mask determiner 1130, and an image corrector 1140.

The low pass filter 1110 performs low pass filtering on the input image FD in units of frames to generate a blurred image in which a luminance difference between pixels is reduced and outputs the blurred image.

The mask generation unit 1120 generates an edge mask image MD representing an edge component of the input image FD by subtracting the blurred image supplied from the low pass filter 1110 from the input image FD, and generates an edge mask image MD. outputs (MD). (S42)

The sharpness enhancement mask determining unit 1130 outputs the edge mask image MD supplied from the mask generating unit 1120 to the sharpness enhancement intensity adjusting unit 1200 according to the brightness of the image and the brightness of the rear background (K ) is applied to determine the sharpness improvement mask image MD' and output the sharpness improvement mask image MD'. (S54) The sharpness enhancement mask determiner 1130 multiplies the edge mask image MD and the sharpness improvement intensity K, so that the intensity of the edge component in the edge mask image MD is increased by the sharpness improvement intensity K. A sharpness enhancement mask image (MD') is generated. The sharpness improvement intensity adjusting unit 1200 outputs the sharpness improvement intensity (K) for each block adjusted according to the average gray level of each pixel block and the back background brightness. Accordingly, the sharpness enhancement mask determiner 1130 generates the sharpness enhancement mask image MD′ by applying the sharpness enhancement intensity K for each block of the edge mask image MD in units of pixel blocks.

The image correction unit 1140 synthesizes the input image FD and the sharpness improvement mask image MD' supplied from the sharpness improvement mask determination unit 1300 to generate an output image FD' with improved sharpness, An output image FD' is output. (S56)

The sharpness improvement intensity control unit 1200 uses the average gray level (L) for each block of a plurality of pixel blocks obtained by dividing the input image (FD) and the weights (Kmax, Kmin) adjusted according to the brightness of the rear background, A sharpness improvement intensity (K) is determined for each block, and the sharpness improvement intensity (K) for each block is output. (S44, S46, S48, S50, S52) To this end, the sharpness improvement strength adjusting unit 1200 includes an average gray level calculator 1210, a background weight determining unit 1220, and a sharpness strength determining unit 1230.

The average grayscale calculator 120 divides the input image FD into a plurality of pixel blocks, calculates an average grayscale L for each block, and outputs an average grayscale L for each block. (S44) The size of each pixel block (n*n, where n is the number of pixels) for calculating the average gray level (L) can be set in various ways. About n≤10 is appropriate.

The background weight determination unit 1220 determines weights (Wmax, Wmin) according to the brightness information (E) of the rear background sensed by the background sensor 600 (FIG. 12), and calculates the weights (Wmax, Wmin) according to the equation below. The maximum and minimum sharpness improvement strengths (Kmax, Kmin) according to the brightness of the rear background are determined by applying to the maximum and minimum sharpness improvement strengths (K0max, K0min) of the preset darkroom environment, such as 3, and the maximum and minimum sharpness enhancement strengths Output (Kmax, Kmin) as the background weight. (S50)

<Equation 3>

Kmax = K0max * Wmax

Kmin = K0min * Wmin

In other words, the background weight determiner 1220 varies the maximum and minimum sharpness enhancement intensities (Kmax, Kmin) according to the brightness (E) of the rear background. For example, based on an office lighting environment, the maximum value (Kmax) of the intensity of sharpness improvement is appropriately about 1.5≤Kmax≤3.0, and the minimum value (Kmin) is appropriate about 0.01≤Kmin≤0.5.

The sharpness intensity determiner 1230 determines the maximum and maximum values that are varied according to the average grayscale (L) for each block supplied from the average grayscale calculator 120 and the background weight supplied from the background weight determiner 1220, that is, the back background brightness. The minimum sharpness improvement strength (Kmax, Kmin) is used to determine and output the sharpness improvement strength (K) for each block as shown in Equation 4 below. (S52)

<Equation 4>

In Equation 4, Lth means a threshold value of an average gray level for each block. The determination of the sharpness improvement intensity (K) using Equation 4 is applied only when the average gray level (L) of each block is smaller than the threshold value (Lth). (S52) If the average gray level (L) for each block is above a certain level, the background background is not well recognized, so the sharpness strength determiner 1230 sets the threshold value (Lth), and the average gray level (L) for each block is When the value is greater than or equal to the threshold value Lth, the sharpness improvement intensity K of the block is determined as a minimum value, which is a set value. (S48) For example, the threshold value (Lth) of the average gray level is about 128 ≤ Lth ≤ 255.

Referring to FIG. 15 , when the average gray level (L) of each block is greater than the threshold value (Lth), the sharpness intensity determiner 1230 uses the quadratic function of Equation 2 above to determine the average gray level (L) of each block. It can be seen that the sharpness improvement intensity (K) decreases as it increases. When the maximum and minimum sharpness improvement intensities (Kmax, Kmin) are varied according to the brightness of the rear background, the curve graph of the quadratic function shown in FIG. (K) also becomes variable. In FIG. 15 , when the average gray level (L) of each block is greater than or equal to the threshold value (Lth), the sharpness improvement intensity (K) of each block is determined as the minimum value (Kmin).

As described above, the transparent display device and method of driving the same according to an embodiment of the present invention adjusts the intensity of sharpness improvement according to the brightness of the image and the brightness of the rear background, thereby applying an appropriate intensity of sharpness improvement according to the image and the viewing environment to improve sharpness and brightness. picture quality can be improved. Therefore, when both the video and the rear background convey meaningful information, visibility of both the video and the rear background can be improved by emphasizing the boundary between the background and the video.

FIG. 16 shows an image obtained by adjusting and applying the intensity of sharpness improvement according to the brightness of the image and the brightness of the rear background in the transparent display device according to an embodiment of the present invention, in comparison with an image of the prior art.

Referring to FIG. 16(a), the transparent display device of the prior art has a problem in that the sharpness of the dark area of the image is affected by the bright rear background, and the sharpness is lowered. It can be seen that the edge strength is improved by increasing the sharpness improvement strength according to the rear background, and thus the sharpness is improved.

Referring to FIG. 16(b), since the transparent display device of the prior art has low sharpness degradation in the bright area of the image because the effect of the rear background is small, an embodiment of the present invention reduces the intensity of sharpness improvement in the bright area of the image. It can be seen that the deterioration of image quality is low, and deterioration of image quality such as over-sharpening due to the increase in intensity of sharpness improvement in a bright image can be prevented.

Referring to FIG. 16(c), since the transparent display device of the prior art has a low sharpness degradation in the dark area of the image when the brightness of the rear background is dark, an embodiment of the present invention is suitable for the image brightness of the dark area and the dark rear background. Accordingly, it can be seen that the image quality degradation is low even when the intensity of the sharpness improvement is reduced.

As described above, the transparent display device and its driving method according to an embodiment of the present invention perform image processing of a gamma correction method and a sharpness improvement method in consideration of the brightness characteristics of an input image and the brightness characteristics of a rear background. By correcting the image, visibility and image quality of the image may be appropriately improved according to the image and the viewing environment.

Through the above description, those skilled in the art will understand that various changes and modifications are possible without departing from the 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 determined by the claims.

100, 1000: image processing unit 102: transmittance LUT
104: image characteristic analysis unit 106: background characteristic analysis unit
108: determination unit 110: gamma correction unit
150: timing controller 200: data driving unit
300: gate driving unit 400: transparent display unit
500: gamma voltage generator 600: background sensor
700: light blocking plate 800: light blocking plate driver
1100: unsharp mask filter 1110: low pass filter
1120: Mask generation unit 1130: Sharpness improvement mask determination unit
1140: image correction unit 1200: sharpness improvement intensity control unit
1210: average gradation calculation unit 1220: background weight determination unit
1230: sharpness strength determining unit

Claims (7)

In the transparent display device,
a transparent display including a transmission area and a light emitting area;
a background sensor disposed on a rear surface of the transparent display device to sense a rear background;
a display driver supplying an output image to the transparent display;
The input image is divided into a plurality of pixel blocks, and the intensity of sharpness improvement for each block is determined according to the brightness characteristics of each block calculated in units of pixel blocks and the brightness characteristics of the sensed rear background, and in the input image An edge mask image is generated by extracting an edge component, a sharpness enhancement mask image is generated by applying the sharpness enhancement intensity for each block to the edge mask image, and then the sharpness enhancement mask and the input image are synthesized to generate the pixel block unit A transparent display device comprising an image processing unit that corrects the sharpness of the input image and outputs the corrected sharpness image to the display driver. The method of claim 1,
The image processing unit
a low pass filter for low pass filtering the input image to generate and output a blurred image;
a mask generating unit generating and outputting an edge mask image by subtracting the blurred image supplied from the low pass filter from the input image;
a sharpness improvement intensity adjusting unit for adjusting the sharpness improvement intensity for each block according to the brightness characteristics of each block of the input image and the brightness characteristics of the sensed rear background;
a sharpness improvement mask determination unit for generating and outputting a sharpness enhancement mask image by applying the sharpness improvement intensity for each block supplied from the sharpness enhancement intensity adjusting unit to the edge mask image supplied from the mask generator;
and an image correction unit configured to synthesize the sharpness improvement mask image supplied from the sharpness improvement mask determination unit and the input image and output the sharpness-corrected image to the display driver. in claim 2
The sharpness improvement intensity control unit
an average grayscale calculation unit for calculating and outputting an average grayscale for each block of the plurality of pixel blocks with respect to the input image;
a background weight determination unit that determines maximum and minimum values of sharpness improvement intensity according to the sensed brightness of the rear background and outputs them as background weights;
The average gray level (L) for each block supplied from the average gray scale calculation unit, the maximum and minimum values (Kmax, Kmin) of sharpness improvement strength supplied from the background weight determination unit, and the function of the following equation are used to determine the block A sharpness improvement strength determining unit for determining a star sharpness improvement strength (K);

The sharpness improvement strength determining unit
When the average gray level (L) of each block is less than a preset threshold value (Lth), determining the sharpness improvement intensity (K) of the corresponding block by the above equation;
and determining a preset minimum value as the sharpness improvement intensity of the corresponding block when the average gray level of each block is equal to or greater than the threshold value. The method of claim 1,
The image processing unit,
The transparent display device that increases the intensity of the sharpness improvement as the brightness of each block decreases and decreases the intensity of the sharpness improvement as the brightness of each block increases. The method of claim 1,
The image processing unit,
The transparent display device for reducing the intensity of the sharpness improvement as the brightness of the rear background decreases and increasing the intensity of the sharpness improvement as the brightness of the rear background increases. Generating a blurred image by low-pass filtering an input image;
generating an edge mask image by subtracting the blur image from the input image;
Dividing the input image into a plurality of pixel blocks and determining a sharpness improvement intensity for each block according to the brightness characteristics of each block calculated in units of pixel blocks and the brightness characteristics of the sensed rear background;
generating a sharpness-enhanced mask image by applying the sharpness-enhanced intensity for each block to the edge mask image;
A method of driving a transparent display device comprising synthesizing the sharpness improvement mask image and the input image and displaying the sharpness-corrected image on a transparent display unit. The method of claim 6,
The step of determining the sharpness improvement strength for each block
calculating an average gray level of each of the plurality of pixel blocks in the input image;
determining maximum and minimum values of sharpness improvement intensity according to the sensed brightness of the rear background;
When the average gray level (L) for each block is less than the preset threshold value (Lth), the function of the average gray level (L) for each block, the maximum and minimum values (Kmax, Kmin) of the sharpness improvement intensity, and the following equation Determining a sharpness improvement strength (K) for each block using

and determining a preset minimum value as a sharpness improvement intensity of a corresponding block when the average gray level of each block is greater than or equal to the threshold value.

Images