Light leakage compensation circuit and display device comprising same

Abstract

A light leakage compensation circuit and a display device comprising same are disclosed. The light leakage compensation circuit comprises: a data analysis unit for analyzing, for each dimming area, pixel data of an input image; a low grayscale image determination unit, which detects low grayscale frame data from the input image so as output an enable signal at an activation level when the low grayscale frame data continues for a predetermined number; and a dimming signal generation unit which outputs, in response to an inactivation level of the enable signal, a first dimming signal for controlling light source luminance for each dimming area and which outputs, in response to the activation level of the enable signal, a second dimming signal for controlling light source luminance of a light leakage area set in a display panel.

Description

Light leakage compensation circuit and display device including the same

[0001] The present invention relates to a light leakage compensation circuit and a display device including the same.

[0002] Various display devices are known, such as liquid crystal displays (LCDs), organic light emitting diode displays (OLEDs), electroluminescence displays (ELDs), field emission displays (FEDs), plasma display panels (PDPs), and electrophoresis displays (EPDs).

[0003] Transmissive display devices For example, liquid crystal displays can improve the contrast of images displayed on the screen of the display device by using a backlight dimming method that adjusts the brightness of the backlight based on the results of analyzing the brightness characteristics of the input image. Backlight dimming methods include a global dimming method that adjusts the brightness of the entire display surface, and a local dimming method that divides the screen of the display device into multiple blocks and locally adjusts the brightness of the display surface. The global dimming method can adjust the brightness of the entire screen of the display panel to be brighter or darker. The local dimming method can locally adjust the brightness of the screen of the display panel, so that the brightness of a local area that is difficult to improve with the global dimming method can be differentially adjusted for each frame period.

[0004] Light leakage can be observed on the screen where input images are displayed on a display device. Light leakage defects occur due to mechanical pressure applied to the display panel, regardless of the input data of the display device. In the case of curved panels, light leakage defects can be observed at the top and bottom of the screen, which are subject to the greatest pressure on the curved surface. Conventional data compensation methods or backlight dimming cannot resolve light leakage defects.

[0005] The present invention provides a light leakage compensation circuit capable of reducing light leakage defects and a display device including the same.

[0006] According to one embodiment of the present invention, a light leakage compensation circuit includes: a data analysis unit that analyzes pixel data of an input image for each dimming area; a low-grayscale image determination unit that detects low-grayscale frame data from the input image and outputs an enable signal at an activation level when the low-grayscale frame data continues for a predetermined number of times; and a dimming signal generation unit that outputs a first dimming signal that controls light source brightness for each dimming area in response to an inactivation level of the enable signal, and outputs a second dimming signal that controls light source brightness of a light leakage area set in a display panel in response to the activation level of the enable signal.

[0007] The low-grayscale image determination unit can compare the pixel data with a first reference value to determine low-grayscale data lower than the first reference value. The low-grayscale image determination unit can compare the number of low-grayscale pixel lines composed of the low-grayscale data with a second reference value to determine frame data of the input image in which the number of low-grayscale pixel lines is greater than the second reference value as low-grayscale frame data. The low-grayscale image determination unit can generate the enable signal at the activation level when the low-grayscale frame data continues for a third reference value.

[0008] The above low-grayscale image judgment unit can generate the enable signal at the deactivation level when frame data other than the low-grayscale frame data continues as long as the third reference value.

[0009] The dimming signal generating unit may include a local dimming signal generating unit that outputs the first dimming signal with a duty ratio calculated in each of the dimming areas based on the representative luminance value for each dimming area input from the data analysis unit; a light leakage compensation unit that outputs the second dimming signal with a duty ratio smaller than the duty ratio of the first dimming signal; and a first multiplexer that outputs the second dimming signal in response to the activation level of the enable signal and outputs the first dimming signal in response to the deactivation level of the enable signal.

[0010] The light leak compensation unit may receive position information of the light leak area, first duty control data, and second duty control data to set the duty ratio of the second dimming signal. The first duty control data may indicate a difference in duty ratio between the first dimming signal and the second dimming signal at a black grayscale. The second duty control data may indicate a difference in duty ratio between the first dimming signal and the second dimming signal at a preset low grayscale upper limit.

[0011] The above light leak compensation unit can calculate the difference in duty ratio between the first dimming signal and the second dimming signal at intermediate grayscale values ​​between the black grayscale and the low grayscale upper limit value using a linear interpolation method.

[0012] The above light leakage compensation circuit may further include a first data modulation unit that modulates and receives pixel data of the input image to increase a contrast ratio between dimming areas; a second data modulation unit that modulates pixel data to be written in pixels of a boundary area between adjacent light leakage areas and non-light leakage areas through smoothing processing so that a gradation difference of the pixel data in the boundary area gradually changes at a predetermined slope; and a second multiplexer that outputs pixel data input from the second data modulation unit in response to the activation level of the enable signal and outputs pixel data input from the first data modulation unit in response to the deactivation level of the enable signal.

[0013] The second data modulation unit may receive pixel data of the input image, position information of the boundary area, and tone difference data of the boundary area. The tone difference data of the boundary area may indicate the tone difference of the pixel data within the boundary area.

[0014] The size of the above boundary area can increase in proportion to the luminance difference between the non-light source area and the light source area.

[0015] A display device according to one embodiment of the present invention includes a display panel having a plurality of data lines, a plurality of gate lines, and a plurality of pixels arranged thereon; a light source driver for lighting light sources to irradiate light onto the display panel; a data driver for converting input pixel data into a data voltage and supplying the data voltage to the data lines; a gate driver for supplying a gate signal to the gate lines; and a timing controller for controlling the data driver and the gate driver. The timing controller includes the data analysis unit, the low-grayscale image determination unit, and the dimming signal generation unit.

[0016] The present invention analyzes an input image to detect a light leak area requiring light leak compensation, and when the input image is a low-grayscale image in which light leak may be recognized, generates a dimming signal for adjusting the backlight brightness of a designated light leak area, thereby preventing light leak defects.

[0017] The present invention can prevent the recognition of a difference in brightness in a boundary area by modulating pixel data to be written to pixels in a boundary area between a light-spot area and a non-light-spot area through smoothing processing.

[0018] The effects of the present invention are not limited to the effects mentioned above, and other effects not mentioned will be clearly understood by those skilled in the art from the description of the claims.

[0019] FIG. 1 is a drawing showing a display device according to one embodiment of the present invention.

[0020] Figure 2 is a flowchart showing the control sequence of a backlight control method according to one embodiment of the present invention step by step.

[0021] Figure 3 is a drawing showing an example of a dimming area.

[0022] Figure 4 is a drawing showing an example of a designated light source area on the screen of a display device.

[0023] Figure 5 is a drawing showing an example of location information of a light source area and a boundary area.

[0024] FIG. 6 is a drawing showing a brightness control unit according to one embodiment of the present invention.

[0025] Figure 7 is a waveform diagram showing an example of pixel data of an input image and an enable signal.

[0026] Figure 8 is a waveform diagram showing an example of a first dimming signal and a second dimming signal.

[0027] Figure 9 is a drawing showing the boundary line and boundary area between adjacent non-light leak areas and light leak areas in a low-grayscale image.

[0028] Figure 10 is a drawing showing an example in which the grayscale values ​​of pixel data in a boundary area are smoothed according to the grayscale difference between adjacent non-grayscale areas and light-grayscale areas in a low-grayscale image.

[0029] The advantages and features of the present invention, and the methods for achieving them, will become clearer with reference to the embodiments described in detail below together with the accompanying drawings. The present invention is not limited to the embodiments disclosed below, but may be implemented in various different forms. The embodiments are provided solely to ensure that the disclosure of the present invention is complete and to fully inform those skilled in the art of the scope of the invention, and the present invention is defined solely by the scope of the claims.

[0030] The shapes, sizes, ratios, angles, numbers, etc. disclosed in the drawings for explaining embodiments of the present invention are illustrative, and the present invention is not limited to the details depicted in the drawings. Throughout the specification, the same reference numerals designate substantially the same components. Furthermore, in describing the present invention, detailed descriptions of related known technologies will be omitted if they are deemed to unnecessarily obscure the gist of the present invention.

[0031] In the specification, when “comprises,” “includes,” “has,” and “consists of,” other parts may be added unless “only” is used. When a component is expressed in the singular, it may be interpreted as plural unless otherwise explicitly stated.

[0032] When interpreting a component, it is interpreted as including the error range even if there is no separate explicit description.

[0033] When the positional relationship and interconnectedness between two components are described as ‘on’, ‘above’, ‘below’, ‘next to’, ‘connect, couple’, crossing, intersecting, etc., one or more other components may be interposed between the components unless there is a mention of ‘directly’ or ‘directly’.

[0034] When the temporal relationship is explained with phrases such as ‘after’, ‘following’, ‘next to’, or ‘before’, it may not be continuous on the time axis unless ‘right away’ or ‘directly’ is used.

[0035] Although first, second, etc. may be used to distinguish components, the function or structure of these components is not limited by the ordinal number or component name attached to the front of the component.

[0036] The following embodiments can be partially or fully combined or combined with one another, enabling various technically diverse interconnections and operations. Each embodiment can be implemented independently of the other, or can be implemented together in a related manner.

[0037] Hereinafter, various embodiments of the present invention will be described in detail with reference to the attached drawings.

[0038] Referring to FIG. 1, a display device according to one embodiment of the present invention includes a display panel (100), a display panel driving circuit (110, 120) for writing pixel data to pixels (101) of the display panel (100) under the control of a timing controller (130), a backlight unit (300) for irradiating light to the display panel (100), and a light source driving unit (500) for driving light sources of the backlight unit (300) under the control of the timing controller (130).

[0039] The display panel (100) may be a rectangular panel having a length in the X-axis direction (or first direction), a length in the Y-axis direction (or second direction), and a thickness in the Z-axis direction (or third direction), but is not limited thereto. For example, the display panel (100) may be a non-rectangular panel having at least a portion that is curved or oval.

[0040] The screen of the display panel (100) includes an input image and a pixel array of a display area (AA). The pixel array of the display area (AA) includes a plurality of data lines (102), a plurality of gate lines (103) intersecting the data lines (102), and pixels (101) arranged in a matrix form. Each of the pixels (101) is connected to a corresponding data line (102) and gate line (103).

[0041] Each of the pixels (101) may be divided into a red sub-pixel, a green sub-pixel, and a blue sub-pixel for color implementation. Each of the pixels (101) may further include a white sub-pixel. Each of the sub-pixels includes a pixel circuit for driving a light-emitting element.

[0042] The display area (AA) includes a plurality of pixel lines (L1 to Ln). Each of the pixel lines (L1 to Ln) includes pixels (101) arranged along the X-axis direction in the display area (AA) of the display panel (100). Pixels (101) arranged in one pixel line share a gate line (103). Sub-pixels arranged along the Y-axis direction share the same data line (102). One horizontal period is a time obtained by dividing one frame period by the total number of pixel lines (L1 to Ln).

[0043] The display panel (100) may include a touch sensor. The touch sensors may be disposed on the display panel (100) as an on-cell type or add-on type, or may be implemented as in-cell type touch sensors built into a pixel array.

[0044] The display panel driving circuit (110, 120) writes pixel data of an input image to pixels (101) of the display panel (100) under the control of the timing controller (130). The display panel driving circuit (110, 120) includes a data driving unit (110) and a gate driving unit (120). The display panel driving circuit (110, 120) may further include a touch sensor driving unit for driving touch sensors. The touch sensor driving unit is omitted in FIG. 1. The data driving unit (110) and the touch sensor driving unit may be integrated together in a single drive IC.

[0045] The data driving unit (110) receives pixel data of an input image from a timing controller (130) and outputs a data voltage (Vdata) of the pixel data. The data driving unit (110) can receive gamma reference voltages and generate gamma compensation voltages for each grayscale through a voltage divider circuit. The gamma compensation voltages for each grayscale are supplied to a digital-to-analog converter (Digital to Analog Converter, hereinafter referred to as “DAC”) arranged in each channel of the data driving unit (110).

[0046] The data driver (110) samples pixel data from a digital signal received from the timing controller (130), latches the pixel data, and then inputs the pixel data to the DAC. The DAC converts the pixel data into a gamma compensation voltage and outputs the data voltage of the pixel data. The data voltage output from the DAC is output to the data line (102) through the output buffer.

[0047] The gate driver (120) may be formed on the display panel (100) together with circuit elements and wires of the display area (AA). The gate driver (120) may be disposed on at least one non-display area (NA) on the left and right sides outside the display area (AA) of the display panel (100), or may be disposed at least partially within the display area (AA).

[0048] The gate driver (120) is disposed in the non-display areas (NA) on both sides of the display panel (100) with the display area (AA) of the display panel (100) in between, and can supply pulses of gate signals (or scan signals) from both sides of the gate lines (103) in a double feeding manner. The gate driver (120) is disposed in at least one side of the left and right non-display areas (NA) of the display panel (100), and can supply gate signals to the gate lines (103) in a single feeding manner. The gate driver (120) can sequentially supply the signals to the gate lines (103) by shifting the pulses of the gate signals using a shift register.

[0049] The timing controller (130) receives an input image signal from the host system (200) and a timing signal synchronized with the input image signal. The timing signal may include a vertical synchronization signal, a horizontal synchronization signal, a data enable signal, etc. Since the vertical period and the horizontal period can be known by counting the data enable signal, the vertical synchronization signal and the horizontal synchronization signal may be omitted. The horizontal synchronization signal and the data enable signal have a cycle of 1 horizontal period (1H).

[0050] The timing controller (130) controls the operation timing of the display panel driving circuit (110, 120) and the light source driving unit (500) based on the timing signal received from the host system (200). The gate timing control signal output from the timing controller (130) can be provided to the gate driving unit (120) by shifting the voltage level through the level shifter (140). The gate timing signal includes a start signal and a clock input to the shift register.

[0051] The timing controller (130) includes a brightness control unit. The brightness control unit of the timing controller (130) can control local dimming and light leakage compensation based on the analysis result of the input image. The brightness control unit analyzes the brightness information of the pixels (101) in each of a plurality of dimming zones equally divided within the display area (AA) during local dimming, and controls the light source driver (500) so that the backlight light source brightness of the corresponding dimming zone is controlled based on the representative brightness value of the dimming zone. The representative brightness value of the dimming zone may be an average value, but is not limited thereto. Such local dimming can improve the contrast ratio of the image reproduced in the display area (AA) by increasing the backlight brightness corresponding to the dimming zone of the high-brightness portion of the image reproduced in the pixels of the display area (AA) and lowering the backlight brightness corresponding to the dimming zone of the low-brightness portion.

[0052] In the manufacturing process of a display device, a display panel (100) and a backlight unit (300) may be assembled into a display module using various types of hardware such as cases, covers, and housings. A lighting test may be performed on the display module. The lighting test measures the luminance of pixels while test pattern data is written on the display panel (100) and the light sources of the backlight unit are turned on. Light leakage may be detected on the display panel (100) during the lighting test.

[0053] The brightness control unit of the timing controller (130) adjusts the brightness of the backlight source in a dark image below a low grayscale where light leakage is recognized. In a dark image below a low grayscale, the low grayscale can be set to a grayscale value where a user (or viewer) recognizes light leakage based on the luminance measurement result of the lighting test. The low grayscale includes a low grayscale above a black grayscale. The black grayscale is the minimum grayscale value (or brightness value) of pixel data. A pixel into which black grayscale data is written appears black to the user (or viewer) because it blocks the light from the backlight source.

[0054] The brightness control unit of the timing controller (130) can be implemented as a circuit in which a local dimming circuit and a light leak compensation circuit are integrated, as shown in FIG. 6.

[0055] The light source driving unit (500) lights up the light sources of the backlight unit (300) arranged below the display panel (100) to irradiate light onto the display panel (100). The light source driving unit (500) adjusts the brightness of the backlight light source according to a dimming signal from the timing controller (130). The dimming signal may be a digital signal generated as a PWM (Pulse Width Modulation) signal. The higher the duty ratio of the PWM signal, the longer the lighting time of the light source, thereby increasing the brightness of the light source, whereas the lower the duty ratio of the PWM signal, the lower the brightness of the light source. The backlight light source may be a plurality of point light sources, for example, LEDs (Light Emitting Diodes), arranged below the display panel (100) so as to precisely control the brightness for each dimming area and each light leakage area.

[0056] The display device further includes a power supply unit. The power supply unit receives an input voltage applied from a host system (200) and outputs a voltage required for driving pixels (101) of a display panel (100) and a display panel driving circuit. The power supply unit may include a DC-DC converter. The DC-DC converter may include a charge pump, a regulator, a buck converter, a boost converter, etc. The power supply unit may output a constant voltage required for driving pixels, such as a high voltage and a low voltage of a gate signal, a common voltage, an IC driving voltage of a pixel circuit, etc., through the DC-DC converter. In addition, the power supply unit may output gamma reference voltages and provide them to the data driving unit (110).

[0057] The host system (200) can scale a video signal from a video source to match the resolution of the display panel (100) and transmit it to the timing controller (300) along with a timing signal. The host system (200) can execute a command or an application program linked to touch data received from a touch sensor driver.

[0058] Figure 2 is a flowchart illustrating step-by-step the control sequence of a backlight control method according to one embodiment of the present invention. This backlight control method can be implemented as a backlight control circuit of a timing controller (130).

[0059] Referring to FIG. 2, the backlight control method analyzes pixel data of an input image to determine whether one frame of data of the input image is a low-gray image that satisfies a preset low-gray condition (S1 and S2). The low-gray condition may be a condition in which the number of pixel lines determined to be low-gray lines lower than a preset low-gray upper limit value as a result of analyzing one frame of pixel data is greater than a predetermined threshold value. A low-gray image that satisfies the low-gray condition is a dark image in which light leakage is visible to a user (or viewer) before light leakage compensation. Light leakage is not visible at a grayscale higher than the low-gray upper limit value. Therefore, a low-gray image from a black grayscale to the low-gray upper limit value is a low-gray image in which light leakage is visible to a user (or viewer) on the screen of a display device before compensation for a light leakage area.

[0060] The backlight control method performs local dimming operation on an input image that is not a low-grayscale image (S6). The local dimming operation method generates a local dimming signal for each dimming area based on the results of the luminance analysis of pixels in each dimming area. The duty ratio of the PWM signal increases in a dimming area that contains a relatively large number of high-luminance (or high-grayscale) pixels, whereas the duty ratio of the PWM signal decreases in a dimming area that contains a relatively large number of low-luminance (or low-grayscale) pixels. Therefore, bright images appear brighter and dark images appear darker due to local dimming, thereby improving the contrast ratio of the image reproduced in the display area (AA). In addition, the local dimming operation method can further improve the contrast ratio by modulating the grayscale value of pixel data to be written to pixels in a dark dimming area to be lower, and stretching the gamma curve of the data to further improve the contrast ratio by increasing the grayscale value of pixel data to be written to pixels in a bright dimming area.

[0061] If the image is judged to be low-grayscale at step S2, a light leak compensation driving method is implemented at steps S4 to S7. The light leak compensation driving method can reduce the brightness of the light leak area by specifying a light leak area and adjusting a dimming signal (S3 and S4). The light leak area is specified based on the brightness measurement value measured in the lighting test, and the location information for the light leak area is stored in a memory (132) accessed by the timing controller (130).

[0062] A luminance difference may be recognized at the boundary between a light-leakage area and a non-light-leakage area. The light-leak compensation driving method performs smoothing processing on pixel data to be written to pixels existing in the boundary area based on the luminance measurement result between the light-leakage area and the non-light-leakage area through a lighting inspection after light-leak compensation (S5 and S7). The smoothing processing reduces the grayscale change of pixel data to be written to pixels in the boundary area including the boundary so that the luminance of the pixels does not change so abruptly that a luminance difference may be recognized at the boundary between the light-leakage area and the non-light-leakage area. The smoothing processing may use an existing smoothing filter, but is not limited thereto.

[0063] Fig. 3 is a drawing showing an example of a dimming zone. In Fig. 3, 'DZ' is a dimming zone in which the brightness of pixels is controlled during local dimming, and 'DZL' is a virtual dimming boundary line by which dimming zones (DZ) are demarcated.

[0064] Referring to FIG. 3, in local dimming, the backlight luminance is controlled in units of dimming zones (DZ) that are evenly divided within the display area (AA). The timing controller (130) determines the luminance of the input image in units of dimming zones, thereby increasing the backlight luminance in the dimming zones (DZ) where bright images are displayed, while decreasing the backlight luminance in the dimming zones (DZ) where relatively dark images are displayed, thereby differentially controlling the backlight luminance on the screen, thereby improving the contrast ratio.

[0065] The dimming zones (DZ) are evenly divided in the display area (AA), while the light leak zones (LLA1 to LLA4) illustrated in Fig. 4 are set based on the luminance measurement results. Therefore, the size, shape, number, etc. of the dimming zones (DZ) may be different from those of the light leak zones (LLA1 to LLA4).

[0066] Fig. 4 is a drawing showing an example of a designated light leakage area on the screen of a display device. Fig. 5 is a drawing showing an example of position information of a light leakage area and a boundary area. In Figs. 4 and 5, “” and “LLA1 to LLA4” are light leakage areas, and ‘NAA’ is a non-light leakage area. ‘BSA’ is a boundary area between the light leakage areas (LLA1 to LLA4) and the non-light leakage area (NAA). ‘LED’ represents an LED used as a point light source of a backlight unit (300). The brightness of the LED can be adjusted by a dimming signal generated by a PWM signal.

[0067] Referring to FIGS. 4 and 5, when pixel data of the same black gradation is written on the screen of the display device, light leakage areas (LLA1 to LLA4) that appear relatively brighter than the non-light leakage area (NAA) on the screen may be visible. The non-light leakage area (NAA) appears to have a black gradation, which is the target gradation of the pixel data, whereas the light leakage areas (LLA1 to LLA4) appear to have a higher gradation brightness than the black gradation due to light leakage. Even at a low gradation higher than the black gradation, the luminance difference between the non-light leakage area (NAA) and the light leakage areas (LLA1 to LLA4) may be smaller than the black gradation, but the light leakage areas (LLA1 to LLA4) may be visible.

[0068] The luminance of each of the light-leakage areas (LLA1 to LLA4) may be lowered to the luminance level of the non-light-leakage area (NAA) by the light-leakage compensation driving method, so that the boundary may not be visible. After the luminance of the light-leakage areas (LLA1 to LLA4) is compensated, each of the light-leakage areas (LLA1 to LLA4) may be interpreted as a light-leakage compensation area. If a luminance difference is recognized in the boundary area (BSA) after the luminance of the light-leakage areas (LLA1 to LLA4) is compensated, the light-leakage compensation driving method may additionally compensate for the luminance of the boundary area (BSA) by modulating the pixel data written in the pixels (101) of the boundary area (BSA) by smoothing processing to the extent that the luminance difference is not recognized in the boundary area (BSA).

[0069] Each of the light leak areas (LLA1 to LLA4) can be designated as a rectangle as illustrated in Fig. 5. The position and size of the light leak areas (LLA1 to LLA4) can be defined by the coordinate values ​​of position information of two corners on the diagonal among the four corners of the rectangle, for example, A(Xa, Ya) and A(Xb, Yb). The position information of each of the light leak areas (LLA1 to LLA4) can be stored in a memory (132) accessed by the timing controller (130).

[0070] The boundary area (BSA) can be defined by the coordinate values ​​of the length in the X-axis direction (Δx), the length in the Y-axis direction (Δy), and the position information of two corners on the diagonal, for example, B(Xc, Yc) and B(Xd, Yd). Depending on the shape of the boundary area (BSA), one boundary area can be stored in the memory (132) as multiple pieces of position information. For example, as illustrated in FIG. 4, if the boundary area (BSA) is in the shape of the letter 'L', it can be designated as two pieces of rectangular position information and stored in the memory (132). In the boundary area (BSA), at least one of the length in the X-axis direction (Δx) and the length in the Y-axis direction (Δy) can vary depending on the luminance difference between the light-leaking area (LLA1 to LLA4) and the non-light-leaking area (NAA). For example, at least one of the length in the X-axis direction (Δx) and the length in the Y-axis direction (Δy) can increase in proportion to the grayscale difference (or luminance difference) between the light-leaking area (LLA1 to LLA4) and the non-light-leaking area (NAA).

[0071] FIG. 6 is a diagram illustrating a brightness control unit according to one embodiment of the present invention. The timing controller (130) may include the brightness control unit illustrated in FIG. 6, but is not limited thereto. For example, the brightness control unit may be manufactured as a separate IC electrically connected to the timing controller (130) and mounted on a PCB.

[0072] Referring to FIG. 6, the brightness control unit (600) includes a data analysis unit (510), a dimming signal generation unit (520), a dimming signal transmission unit (540), a low-grayscale image determination unit (550), and a data modulation unit (560).

[0073] The data analysis unit (510) can receive pixel data (R, G, B) of the input image and a timing signal from the host system (200). The timing signal can include a vertical synchronization signal, a horizontal synchronization signal, a data enable signal, etc. that are synchronized with the pixel data. For local dimming, the screen can be virtually divided into multiple dimming areas. The data analysis unit (510) analyzes the pixel data (R, G, B) of the input image for each dimming area and calculates a representative luminance value of the dimming area.

[0074] The low-grayscale image determination unit (550) can detect a low-grayscale image or a black-grayscale image in which a light leak area can be recognized. The low-grayscale image determination unit (550) can read the grayscale values ​​of pixel data (R, G, B) of the input image and determine that the frame data is black (or low-grayscale) frame data if the pixel data of the black-grayscale value in one frame data is higher than a predetermined ratio. The low-grayscale image determination unit (550) can be expressed as a black screen determination unit.

[0075] The low-grayscale image determination unit (550) can analyze the pixel data of the input image from various viewpoints by considering other image quality enhancement algorithms and the low-grayscale range in which light leakage is recognized, and determine the low-grayscale image in which the light leakage area is recognized on a frame-by-frame basis. For example, the low-grayscale image determination unit (550) receives pixel data (R, G, B) of the input image, a timing signal, a first reference value (LGM), a second reference value (BRM), and a third reference value (BFN). The low-grayscale condition in which light leakage compensation is performed is set according to the first reference value (LGM), the second reference value (BRM), and the third reference value (BFN).

[0076] The first reference value (LGM) is the low-gray upper limit at which light leakage can be recognized. For example, when the maximum grayscale value of pixel data is 255, the low-gray upper limit can be set to grayscale 20, but is not limited thereto. The low-gray upper limit can be selected from a grayscale value that is 50% or less of the maximum grayscale value.

[0077] The second reference value (BRM) is a threshold value of the number of pixel lines composed of low-gray pixels below the low-gray upper limit value. For example, as illustrated in FIG. 1, when the number of pixel lines (L1 to Ln) of the display panel (100) is n (n is a natural number greater than or equal to 100), the threshold value may be set between n / 2 and n, but is not limited thereto. The second reference value (BRM) is set as a standard for determining whether 1 frame data is low-gray frame data in which low-gray data in which light leakage may be recognized is mostly occupied. For example, when the second reference value (BRM) is n / 2, when data of n / 2 or more pixel lines in the currently input 1 frame data is low-gray data below the first reference value (LGM), this 1 frame data may be determined as low-gray frame data in which light leakage may be recognized.

[0078] The third reference value (BFN) represents the number of consecutive low-grayscale frame data. The third reference value (BFN) may be set to M (M is a natural number greater than 2 and less than n). For example, when low-grayscale frame data is consecutive more than M set as the third reference value (BFN), light leakage compensation may be executed. Meanwhile, the timing controller (130) may execute a black data insertion (hereinafter, referred to as 'BDI') algorithm to improve the picture quality of the display device. BDI may improve motion blur, afterimage, and sharpness of the image reproduced on the display panel (100) by inserting black frame data between frames of the input image. If the third reference value (BFN) is not set, light leakage compensation may be executed in the BDI, which may reduce the BDI effect.

[0079] The low-gray image determination unit (550) analyzes the pixel data (R, G, B) of the input image, compares the grayscale values ​​of the pixel data with the first reference value (LGM), and determines low-gray image data lower than the first reference value (LGM). The low-gray image determination unit (550) increases the count value by 1 each time a low-gray pixel line composed of low-gray data in which light leakage may be recognized is detected, compares the accumulated count value with the second reference value (BRM), and determines frame data having a count value greater than the second reference value (BRM) as low-gray frame data. In other words, one frame data having a number of low-gray pixel lines greater than the second reference value can be determined as low-gray frame data.

[0080] The low-grayscale image judgment unit (550) generates a light leakage compensation enable signal (hereinafter referred to as “enable signal”) (LLC_EN) at an activation level to start light leakage compensation operation when low-grayscale frame data continues as long as the third reference value (BFN). The activation level of the enable signal (LLC_EN) may be a high level (High Level, H) of a digital signal as illustrated in FIG. 7, but is not limited thereto. The low-grayscale image judgment unit (550) generates the enable signal (LLC_EN) at a deactivation level so that local dimming can be performed when frame data other than low-grayscale frame data continues as long as the third reference value (BFN). The deactivation level of the enable signal (LLC_EN) may be a low level (High Level, L) of a digital signal as illustrated in FIG. 7, but is not limited thereto.

[0081] The dimming signal generation unit (520) includes a local dimming signal generation unit (522), a light leakage compensation unit (530), and a first multiplexer (MUX) (532).

[0082] The local dimming signal generation unit (522) calculates the duty ratio of each dimming area based on the representative luminance value of each dimming area input from the data analysis unit (510) and outputs the first dimming signal (DSG_PWM) as a PWM signal having the duty ratio. Some of the dimming areas may overlap with the light leakage area (LAA).

[0083] The first dimming signal (DSG_PWM) is a dimming signal for local dimming operation. The first dimming signal (DSG_PWM) is selected by the first multiplexer (532) and transmitted to the light source driver (500) when the enable signal (LLC_EN) is at a deactivated level (L). The enable signal (LLC_EN) is at a deactivated level (L) under the condition that the low-grayscale frame data is not continuous by the third reference value (BFN).

[0084] The light leak compensation unit (530) outputs a second dimming signal (LLA_PWM) based on the position information (LAP) of the light leak area (LLA), the first duty control data (DDB), and the second duty control data (DDG). The light leak area position information (LAP) includes position information of each of the light leak areas illustrated in FIGS. 4 and 5. The position information (LAP) of the light leak area (LLA), the first duty control data (DDB), and the second duty control data (DDG) may be stored in the memory (132). The light leak compensation unit (530) outputs the second dimming signal (LLA_PWM) with a duty ratio smaller than the duty ratio of the first dimming signal (DSG_PWM).

[0085] The first duty control data (DDB) indicates the duty ratio difference between the first dimming signal (DSG_PWM) and the second dimming signal (LLA_PWM) in the black grayscale as illustrated in FIG. 8. The first duty control data (DDB) defines the difference between the duty ratio of the light leakage area (LAA) in the low grayscale frame of the black grayscale and the duty value of the dimming area overlapping the light leakage area (LAA). The first duty control data (DDB) may be set to a value greater than the second duty control data (DDG) as illustrated in FIG. 8.

[0086] The second duty control data (DDG) indicates the duty ratio difference between the first dimming signal (DSG_PWM) and the second dimming signal (LLA_PWM) at the low grayscale upper limit value. The second duty control data (DDG) defines the difference between the duty ratio of the light leak area (LAA) in the low grayscale frame at the low grayscale upper limit value and the duty value of the dimming area overlapping the light leak area (LAA).

[0087] In the low-gray range where light leakage can be recognized, the duty ratio difference can be calculated in real time by the linear interpolation method at intermediate grayscale values ​​between the black grayscale and the low-grayscale upper limit value. For example, in the low-grayscale close to the black grayscale, the duty ratio difference compared to the first dimming signal (DSG_PWM) can be set to a value similar to the first duty control data (DDB). And in the low-grayscale close to the low-grayscale upper limit value, the duty ratio difference compared to the first dimming signal (DSG_PWM) can be set to a value similar to the second duty control data (DDG).

[0088] The duty ratio of the second dimming signal (LLA_PWM) output from the light leak compensation unit (530) is smaller than the duty ratio of the first dimming signal (DSG_PWM) for local dimming, as illustrated in Fig. 8. In addition, the closer the average grayscale of pixel data in a low grayscale frame is to a black grayscale, the smaller the duty ratio of the second dimming signal (LLA_PWM) may be.

[0089] The second dimming signal (LLA_PWM) is selected by the first multiplexer (532) and transmitted to the light source driver (500) when the enable signal (LLC_EN) is at the activation level (H).

[0090] The first multiplexer (532) selects one of the first and second dimming signals (DSG_PWM, LLA_PWM) under the control of the low-grayscale image determination unit (550). The first multiplexer (532) selects the second dimming signal (LLA_PWM) in response to the activation level (H) of the enable signal (LLC_EN) in a low-grayscale condition in which light leakage can be recognized in a light leakage area and provides the second dimming signal (LLA_PWM) to the dimming signal transmission unit (540). The first multiplexer (532) selects the first dimming signal (DSG_PWM) in response to the deactivation level (L) of the enable signal (LLC_EN) when the low-grayscale condition is not present and provides the first dimming signal (DSG_PWM) to the dimming signal transmission unit (540).

[0091] The dimming signal transmission unit (540) transmits the dimming signal (OPWM) output from the first multiplexer (532) to the light source driving unit (500) along with the data (SPIDATA) and the clock (SPICLK) of the dimming signal (OPWM) via a standard interface, for example, SPI (Serial Peripheral Interface Bus). The light source driving unit (500) responds to the dimming signal (OPWM) received from the brightness control unit (600) by driving the light sources of the backlight unit (300) to adjust the brightness of the light sources for each dimming area to improve the contrast ratio, or to lower the brightness of the light sources in the light leakage area under low grayscale conditions.

[0092] The data modulation unit (560) includes a first data modulation unit (562), a second data modulation unit (570), and a second multiplexer (572).

[0093] The first data modulation unit (562) receives pixel data (R, G, B) of an input image and modulates the pixel data to increase the contrast ratio. The first data modulation unit (562) modulates the grayscale value of the pixel data using look-up table data in which a gamma stretching curve is set, thereby increasing the contrast ratio between dimming areas during local dimming. The pixel data (CER, CEG, CEB) output from the first data modulation unit (562) is provided to the second multiplexer (572).

[0094] The second data modulation unit (570) receives pixel data (R, G, B) of an input image, position information (BSP) of a boundary area (BSA), and tone difference data (BGD) of the boundary area (BSA) and modulates pixel data to be written to pixels of the boundary area (BSA) through smoothing processing. The position information (BSP) and tone difference data (BGD) of the boundary area (BSA) may be stored in a memory (132).

[0095] The position information (BSP) of the boundary area (BSA) indicates the boundary area (BSA) as shown in FIGS. 4 and 5. The grayscale difference data (BGD) of the boundary area is set to the grayscale difference between the adjacent non-light-leakage area (NAA) and the light-leakage area (LAA), as shown in FIGS. 9 and 10. The second data modulation unit (570) modulates pixel data to be written to pixels of the boundary area (BSA) by smoothing processing within the grayscale difference of pixel data defined by the grayscale difference data (BGD) of the boundary area, so that the grayscale value gradually changes with a low slope at which the grayscale difference of neighboring pixels is not recognized. The second data modulation unit (570) can significantly adjust the boundary area (BSA) when the grayscale difference of the boundary area (BSA) increases, as shown in FIG. 9. The pixel data modulated by the second data modulation unit (570) is provided to the second multiplexer (572).

[0096] The second multiplexer (572) selects one of the pixel data (CER, CEG, CEB) input from the first data modulation unit (562) and the pixel data (BSR, BSG, BSB) input from the second data modulation unit (570) under the control of the low-grayscale image judgment unit (550). The second multiplexer (572) selects the pixel data (BSR, BSG, BSB) input from the second data modulation unit (570) in response to the activation level (H) of the enable signal (LLC_EN) under low-grayscale conditions in which light leakage can be recognized in the light leakage area and transmits the selected pixel data to the data driving unit (110). The second multiplexer (572) selects pixel data (CER, CEG, CEB) input from the first data modulation unit (562) in response to the deactivation level (L) of the enable signal (LLC_EN) when the above low-grayscale condition is not met and transmits the data to the data driving unit (110).

[0097] Meanwhile, the second data modulation unit (570) and the second multiplexer (5782) may be omitted. If the low-gray luminance of the light-leakage area (LLA) is adjusted to the same level as the low-gray luminance of the adjacent non-light-leakage area (NAA) by the light-leakage compensation unit (530), in most cases, no luminance difference is recognized at the boundary between the light-leakage area (LLA) and the non-light-leakage area (NAA). Therefore, in cases where additional luminance compensation is not required in the boundary area (BSA), the second data modulation unit (570) and the second multiplexer (572) may be omitted.

[0098] Fig. 7 is a waveform diagram showing an example of pixel data of an input image and an enable signal. In Fig. 7, 'DATA' is pixel data of the input image. 'BDATA' is low-gray data below the low-gray upper limit at which light leakage can be recognized in the light leakage area before light leakage compensation, and 'NDATA' is pixel data having a gray value higher than the low-gray upper limit. 'Vsync' is a vertical synchronization signal. The vertical synchronization signal (Vsync) defines one frame period of the input image by including pulses that occur at one frame period cycle of the input image.

[0099] Referring to FIG. 7, the low-gray image determination unit (550) can compare each pixel data of the input image with the first reference value (LGM) to determine whether it is low-gray data below the low-gray upper limit value, and compare the number of low-gray pixel lines composed of low-gray data with the second reference value (BRM) to determine whether the frame data input in the current frame period is low-gray frame data. The low-gray image determination unit (550) can activate the light-leak compensation unit (530) and the second data modulation unit (570) by generating an enable signal (LLC_EN) at an activation level (H) to start light-leak compensation operation when the low-gray frame data continues as long as the third reference value (BFN), thereby performing light-leak compensation. When non-low grayscale frame data is detected after low grayscale frame data, the low grayscale image judgment unit (550) counts the non-low grayscale frame data and, when the non-low grayscale frame data continues as long as the third reference value (BFN), inverts the enable signal (LLC_EN) to a deactivation level to switch to local dimming operation.

[0100] Figure 8 is a waveform diagram showing an example of a first dimming signal and a second dimming signal.

[0101] Referring to FIG. 8, the dimming signal generating unit (520) outputs a first dimming signal (DSG_PWM) when local dimming is driven in response to the deactivation level of the enable signal (LLC_EN) to control the backlight luminance (or light source luminance) of each dimming area set in local dimming to increase the contrast ratio of the image reproduced on the screen of the display device. The dimming signal generating unit (520) outputs a second dimming signal (LLA_PWM) in response to the activation level of the enable signal (LLC_EN) to control the backlight luminance (or light source luminance) of each light leakage area (LLA) in a low-grayscale image in which light leakage may be recognized, thereby reducing the luminance of the light leakage area (LLA) so that light leakage is not recognized in the low-grayscale image reproduced on the screen of the display device.

[0102] The dimming signal generator (520) can control the duty ratio of the second dimming signal (LLA_PWM) to a value smaller than the duty ratio of the first dimming signal (DSG_PWM) based on the first duty control data (DDB) and the second duty control data (DDG). The first duty control data (DDB) sets the duty ratio difference between the first dimming signal (DSG_PWM) and the second dimming signal (LLA_PWM) in the low grayscale frame of the black grayscale. The second duty control data (DDG) sets the duty ratio difference for the first dimming signal (DSG_PWM) and the second dimming signal (LLA_PWM) in the low grayscale frame of the low grayscale upper limit value. The first duty control data (DDB) may have a value larger than the second duty control data (DDG). In order to reduce the memory capacity in which the duty control data (DDB, DDG) is stored, intermediate values ​​between the black gray level and the low gray level upper limit are calculated in real time by a linear interpolation method, so that the duty ratio difference between the first dimming signal (DSG_PWM) and the second dimming signal (LLA_PWM) can be automatically calculated between the first duty control data (DDB) and the second duty control data (DDG).

[0103] Fig. 9 is a diagram showing a boundary line and boundary area between adjacent non-light leak areas and light leak areas in a low-grayscale image. Fig. 10 is a diagram showing an example in which the grayscale values ​​of pixel data in a boundary area are smoothed according to the grayscale difference between adjacent non-light leak areas and light leak areas in a low-grayscale image.

[0104] Referring to FIGS. 9 and 10, a pixel area including a plurality of pixels centered on a boundary line (BDL) between adjacent non-light-leaking areas (NAA) and light-leaking areas (LAA) can be set as a boundary area (BSA). The boundary area (BSA) can be set as a pixel area of ​​a predetermined size or can be varied according to a luminance difference (or grayscale difference) between the adjacent non-light-leaking areas (NAA) and light-leaking areas (LAA). For example, the size of the boundary area (BSA) can increase in proportion to the luminance difference (or grayscale difference) between the non-light-leaking areas (NAA) and light-leaking areas (LAA). When pixel data is smoothed in the boundary area (BSA), the grayscale change of the pixel data from one side of the boundary area (BSA) to the other side can gradually change with a slope at which a luminance difference is not recognized.

[0105] The size of the boundary area (BSA) may vary depending on the luminance difference (or grayscale difference) of the pixels located at both ends of the boundary area (BSA) set as the default. For example, as illustrated in FIG. 10, when the grayscale difference of the pixels located at both ends of the boundary area (BSA) between the adjacent non-light leakage area (NAA) and light leakage area (LAA) is 10G, the boundary area (BSA) may become larger than when it is 4G. Here, 4G represents a grayscale value of 4, and 10G represents a grayscale value of 10. If the boundary area (BSA) is small when the grayscale difference increases, a change in luminance may be recognized even if the pixel data is smoothed. As described above, smoothing of the boundary area (BSA) may be omitted.

[0106] Since the content of the specification described in the problem to be solved, the means for solving the problem, and the effect described above does not specify the essential features of the claim, the scope of the claim is not limited by the matters described in the content of the specification.

[0107] While the embodiments of the present invention have been described in more detail with reference to the attached drawings, the present invention is not necessarily limited to these embodiments, and various modifications may be implemented without departing from the scope of the technical spirit of the present invention. Accordingly, the embodiments disclosed in the present invention are intended to illustrate, rather than limit, the technical spirit of the present invention, and the scope of the technical spirit of the present invention is not limited by these embodiments. Therefore, it should be understood that the embodiments described above are illustrative in all respects and not restrictive.

Claims

1. Data analysis unit that analyzes pixel data of input image by dimming area; A low-grayscale image judgment unit that detects low-grayscale frame data from the input image and outputs an enable signal at an activation level when the low-grayscale frame data continues for a predetermined number of times; and A light leakage compensation circuit including a dimming signal generating unit that outputs a first dimming signal for controlling the light source brightness for each dimming area in response to the deactivation level of the enable signal, and outputs a second dimming signal for controlling the light source brightness of a light leakage area set in a display panel in response to the activation level of the enable signal.

2. In paragraph 1, The above low-grayscale image judgment unit, Compare the above pixel data with the first reference value to determine low-gray data below the first reference value, The number of low-gray pixel lines composed of the above low-gray data is compared with a second reference value, and the frame data of the input image in which the number of low-gray pixel lines is greater than the second reference value is determined as low-gray frame data, A light leakage compensation circuit that generates the enable signal at the activation level when the low-grayscale frame data continues as long as the third reference value.

3. In paragraph 2, The above low-grayscale image judgment unit is a light leakage compensation circuit that generates the enable signal at the deactivation level when frame data other than the low-grayscale frame data continues as long as the third reference value.

4. In paragraph 1, The above dimming signal generating unit, A local dimming signal generation unit that outputs the first dimming signal with a duty ratio calculated in each dimming area based on the representative brightness value for each dimming area input from the data analysis unit; A light source compensation unit that outputs the second dimming signal with a duty ratio smaller than the duty ratio of the first dimming signal; and A light leakage compensation circuit comprising a first multiplexer that outputs the second dimming signal in response to the activation level of the enable signal and outputs the first dimming signal in response to the deactivation level of the enable signal.

5. In paragraph 4, The above light source compensation unit is, By receiving the location information of the light source area, the first duty control data, and the second duty control data, the duty ratio of the second dimming signal is set, The above first duty control data indicates the difference in duty ratio between the first dimming signal and the second dimming signal at black gradation, A light leakage compensation circuit in which the second duty control data indicates a difference in duty ratio between the first dimming signal and the second dimming signal at a preset low-gray upper limit value.

6. In paragraph 5, The above light source compensation unit is, A light leakage compensation circuit that calculates the difference in duty ratio between the first dimming signal and the second dimming signal by a linear interpolation method at intermediate grayscale values ​​between the black grayscale and the low grayscale upper limit value.

7. In paragraph 4, A first data modulation unit that modulates pixel data of the input image and receives it to increase the contrast ratio between dimming areas; A second data modulation unit that modulates pixel data to be written in pixels of a boundary area between adjacent light-spot areas and non-light-spot areas by smoothing processing so that the gradation difference of the pixel data in the boundary area gradually changes at a predetermined slope; and A light leakage compensation circuit further comprising a second multiplexer that outputs pixel data input from the second data modulation unit in response to the activation level of the enable signal and outputs pixel data input from the first data modulation unit in response to the deactivation level of the enable signal.

8. In paragraph 7, The second data modulation unit, Receive pixel data of the input image, location information of the boundary area, and grayscale data of the boundary area, A light leakage compensation circuit in which the grayscale data of the above boundary area indicates the grayscale data of the pixel data within the above boundary area.

9. In paragraph 7, A light leak compensation circuit in which the size of the above boundary area increases in proportion to the luminance difference between the non-light leak area and the light leak area.

10. A display panel having a plurality of data lines, a plurality of gate lines, and a plurality of pixels arranged thereon; A light source driving unit that illuminates the light sources to irradiate light onto the display panel; A data driver that converts input pixel data into a data voltage and supplies it to the data lines; A gate driver for supplying gate signals to the above gate lines; and It includes a timing controller that controls the data driving unit and the gate driving unit, The above timing controller, A data analysis unit that analyzes pixel data of an input image by dimming area; A low-grayscale image judgment unit that detects low-grayscale frame data from the input image and outputs an enable signal at an activation level when the low-grayscale frame data continues for a predetermined number of times; and A display device comprising a dimming signal generating unit that outputs a first dimming signal for controlling the brightness of a light source for each dimming area in response to the deactivation level of the enable signal, and outputs a second dimming signal for controlling the brightness of a light source in a light leak area set in a display panel in response to the activation level of the enable signal.

11. In paragraph 10, The above dimming signal generating unit, A local dimming signal generation unit that outputs the first dimming signal with a duty ratio calculated in each dimming area based on the representative brightness value for each dimming area input from the data analysis unit; A light source compensation unit that outputs the second dimming signal with a duty ratio smaller than the duty ratio of the first dimming signal; A first multiplexer that outputs the second dimming signal in response to the activation level of the enable signal and outputs the first dimming signal in response to the deactivation level of the enable signal; and Transmitting the first dimming signal and the second dimming signal output from the first multiplexer to the light source driving unit, A display device, wherein the light source driving unit drives the light source in response to the first dimming signal and the second dimming signal.

12. In paragraph 11, The above timing controller, A first data modulation unit that modulates pixel data of the input image and receives it to increase the contrast ratio between dimming areas; A second data modulation unit that modulates pixel data to be written in pixels of a boundary area between adjacent light-spot areas and non-light-spot areas by smoothing processing so that the gradation difference of the pixel data in the boundary area gradually changes at a predetermined slope; and A display device further comprising a second multiplexer that outputs pixel data input from the second data modulation unit in response to the activation level of the enable signal and outputs pixel data input from the first data modulation unit in response to the deactivation level of the enable signal.

Images