KR100840319B1 - Liquid crystal display device having stitch reduction means - Google Patents

Abstract

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid crystal display device having a stitch reduction means, which generates and stores new corrected image data of each of R, G, and B in consideration of brightness characteristics of each shot, By separately adjusting the gamma curves of R, G, and B with respect to each other, the same luminance level is realized between shots regardless of the formation position of the stitch line, the data driver, and the like, thereby providing a high-quality liquid crystal display device. When using multi-tone conversion, temporal and spatial dithering methods are used together to prevent image sticking.

Specifically, the liquid crystal display device having the stitch reduction means according to the present invention includes a control unit for generating a timing signal for controlling the operation of the scan driver and the data driver and output the timing signal to the scan driver and the data driver, respectively, the control unit is corrected image data By gamma-correcting the raw image data of each of the R, G, and B through the control to control the liquid crystal panel consisting of a plurality of shots to implement the same brightness level.

Stitch phenomenon, timing control, stitch improvement, gamma curve, spatial / temporal dithering.

Description

Liquid crystal display device having stitch reduction means {A LIQUID CRYSTAL DISPLAY FOR REDUCING STITCH}

1A is a plan view of a thin film transistor substrate according to the prior art.

1B is a graph illustrating R, G, and B gamma curves for each gray.

2 is an overall block diagram of a liquid crystal display having a stitch reduction means according to an exemplary embodiment of the present invention.

3 is a view for conceptually explaining the stitch improvement unit according to the present invention.

4 is a diagram for explaining a concept of a method of changing a G gamma curve to an arbitrary target gamma curve according to an example of the present invention.

5A to 5C are diagrams for describing a spatial / temporal dithering processing method for representing 10-bit data as 8-bit data according to the present invention.

6 is a graph illustrating a gamma curve for each shot after removing stitch defects according to the present invention.

7 is a view for explaining a stitch improvement unit according to a first embodiment of the present invention.

8 is a view for explaining a stitch improvement unit according to a second embodiment of the present invention.

9 is a view for explaining a stitch improvement unit according to a third embodiment of the present invention.

※ Explanation of code for main part of drawing ※

100: timing controller

110: stitch improvement

200: data driver

300: scan driver

400: LCD panel

112: R data correction unit

114: G data correction unit

116: B data correction unit

120: cycle control unit

The present invention relates to a liquid crystal display device.

In general, a thin film transistor liquid crystal display (TFT LCD) is formed of a thin film transistor substrate, a color filter, and a common electrode on which a thin film transistor, a three-terminal element, a gate line to which a scan signal is applied, and a data line to which an image signal is applied. It consists of a color filter substrate, a liquid crystal material injected between two substrates, and a driving substrate on which an integrated circuit is mounted. The signals generated from the driving substrate control the light transmittance in the liquid crystal layer by controlling the gate line and the data line of the thin film transistor substrate in line units.

When the thin film transistor liquid crystal display device having the above structure is configured to have a large area of 15 inches or more, an exposure apparatus capable of forming a pattern such as a gate bus line and a data bus line by exposing a large area substrate at one time is preferable. Due to various factors such as technical limitations in manufacturing the exposure apparatus, the size of the exposure surface that can be exposed at one time is inevitably limited.

Therefore, in order to expose a large-area substrate, as shown in FIG. 1A, a partial exposure is performed by first dividing a portion of the substrate into a predetermined number of shots S1 through S4 and exposing the remaining portion later.

However, such divisional exposure causes a stitch phenomenon, which is a screen unevenness, depending on the degree of alignment between shots. The stitch phenomenon is a phenomenon in which a visually discontinuous portion occurs due to a difference in luminance at a shot boundary, and means that an uneven image is caused by alignment deviation between shots generated during a photographic process.

Figure 1a is a plan view of a thin film transistor substrate according to the prior art, Figure 1b is a graph showing the R, G, B gamma curve for each shot.

As shown, it can be seen that the gamma curves for each of the shots S1 to S5 exhibit different luminance level characteristics due to the stitch lines formed between the shots.

As a result, in the case of a high-brightness product not only has a detrimental adverse effect on the overall reliability and image quality, in particular, in the actual large LCD screen, the above stitch phenomenon is more highlighted, which is a decisive factor of the product quality.

The technical problem to be solved by the present invention is to solve such a conventional problem, and the corresponding R, G, B gamma curves using the corrected image data of each of R, G, and B based on values of a predetermined correction gamma curve. By independently transforming the liquid crystal display, a liquid crystal display device capable of realizing the same luminance level between shots is provided.

In order to solve the above technical problem, the liquid crystal display having the stitch reduction means according to the present invention generates and stores new corrected image data of each of R, G, and B in consideration of luminance characteristics of each shot, and stores the stored R, The gamma curves of R, G, and B are adjusted separately for each of the G, B corrected image data. In addition, in the multi-gradation conversion of the corrected image data, a temporal and spatial dithering method is used together to prevent image fixation.

Specifically, the liquid crystal display device having the stitch reducing means according to the present invention includes a plurality of gate lines for embedding a liquid crystal material having predetermined characteristics, and for transmitting a scan signal, a plurality of data lines and gate lines for transmitting an image signal, and A liquid crystal panel having a switching element connected to the data line; A scan driver for sequentially applying a gate on voltage to the plurality of gate lines to turn on the switching element; A data driver for applying a data voltage representing an image signal to the data line; And as the raw image data of each of R, G, and B is input from the outside after initial startup, the corrected image data corresponding to the raw image data is extracted from the memory storing the corrected image data corresponding to the raw image data, and transmitted to the data driver. And a control unit for generating timing signals for controlling the operation of the scan driver and the data driver and outputting the timing signals to the scan driver and the data driver, respectively, wherein the controller gamma the raw image data of each of R, G, and B through the corrected image data. By adjusting to control the liquid crystal panel consisting of a plurality of shots to implement the same brightness level.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings so that those skilled in the art may easily implement the present invention.

2 is a schematic block diagram of a liquid crystal display device having a stitch reduction means according to an embodiment of the present invention.

Referring to FIG. 2, the liquid crystal display according to the present invention includes a timing controller 100, a data driver 200, a scan driver 300, and a liquid crystal panel 400 in which the stitch improvement unit 110 is incorporated.

The timing controller 100 incorporating the stitch improvement unit 110 may include a synchronization signal (Hsync, Vsync) and a clock signal (DE) for displaying the RGB image signal together with the RGB image signal from an external graphic controller (not shown). MCLK) or the like, and outputs an RGB corrected image signal to the data driver 200, and generates a digital signal, that is, a timing signal for driving the data driver 200 and the scan driver 300, and generates a corresponding driver. Output to (200, 300).

In more detail, the timing controller 100 may convert the horizontal clock signal HCLK and data for data shift in the data driver 200 into analog in the data driver 200, and convert the converted analog value into an LCD panel. A horizontal synchronization start signal STH that commands 400 to be applied and a load signal LOAD or TP that command the loading of data signals to the data driver 200 are output to the data driver 200, respectively.

In addition, the timing controller 100 may include a gate clock signal for setting the period of the gate-on signal applied to the gate line, a vertical synchronization start signal STV for commanding the start of the gate-on signal, and the scan driver ( An output enable signal (OE; Out Enable) for enabling the output of 300 is output to the scan driver 300.

On the other hand, the stitch improving unit 110 embedded in the timing controller 100 outputs corrected image data corresponding to the raw image data as R, G, and B raw image data are input from the outside after the initial startup. do.

In more detail, the stitch improvement unit 110 extracts corrected image data corresponding to the raw image data as raw image data for each of R, G, and B is input from the outside after the initial startup of the liquid crystal display device. Multi-gradation conversion of the extracted corrected image data is output.                     

At this time, the corrected image data before multi-gradation conversion is generated based on a predetermined correction gamma curve, and may be equal to the number of bits of the original image data or may be larger than the number of bits of the original image data. Further, the corrected image data after the multi-gradation conversion is preferably equal to the number of bits of the raw image data.

In addition, in the above-described embodiment of the present invention, an example of embedding the stitch improvement unit in the timing control unit is described as an example. Alternatively, the stitch improvement unit may be implemented outside the timing control unit. However, the stitch improvement unit may be disposed at the rear end of the timing controller.

The data driver 200 receives the R, G, and B digital data (R [0: N], G [0: N], and B [0: N]) from the timing controller 100 and stores the received digital data. When a load signal LOAD for instructing 400 to be applied is applied, the voltage corresponding to each digital data is selected, and the data voltages V1, V2, V3, ..., Vn ( (Not shown).

In addition, the data driver 200 outputs data voltages V1, V2, V3,... And Vn so that the polarities of the pixels arranged on the LCD panel 400 are inverted with each other in each frame. At this time, the polarity of the pixel should be reversed every frame in order to prevent deterioration of the liquid crystal, as is already known.

The scan driver 300 receives a gate clock signal Gate clk and a vertical line start signal STV from the timing controller 100, including a shift register, a level shifter and a buffer, and a gate driving voltage generator (not shown). Or the voltages Von, Voff, and Vcom (not shown) are provided from the timing controller 100 to turn on or off the thin film transistors on the LCD panel 400 to apply or block pixel voltages to the pixels.

The LCD panel 400 is formed in n data lines and m gate lines arranged to be orthogonal to the data lines, and is formed in a predetermined area arranged in a lattice arrangement between the data lines and the gate lines, and one end thereof is connected to the gate lines. The other end is composed of a thin film transistor and a pixel electrode connected to the data line, and the other end is connected to the pixel electrode, and gate voltages G1, G2, ..., Gn (not shown) provided from the scan driver 300 (not shown). As the time is applied to the corresponding pixel column, the thin film transistor of the corresponding pixel column is turned on, and the data voltages D1, D2,..., Dm (not shown) provided from the data driver 200 are applied to the corresponding pixel electrode.

3 is a view for conceptually explaining the stitch improvement unit according to the present invention.

Referring to FIG. 3, the stitch improvement unit 110 according to the present invention includes an R data correction unit 112, a G data correction unit 114, a B data correction unit 116, a first multi-gradation unit 122, And a second multilevel harmony unit 124 and a third multilevel harmony unit 126.

In operation, the R, G, and B data correction units 112, 114, and 116 correct 8 N-bit raw image data of each of R, G, and B input from the outside according to the gray characteristics of each shot of the liquid crystal panel. The image data is converted into image data and then output to the first to third multi-gradation units 122, 124, and 126, respectively. Subsequently, the first to third multi-gradation units 122, 124, and 126 multi-tone convert the N-bit corrected image data into 8-bit corrected image data of each of R, G, and B, and provide the multi-gradation unit to the timing controller 100. do.

Here, preferably, the first to third multi-gradation units 122, 124, and 126 perform correction image data processing using a spatial / temporal dithering method.

Then, the above-described spatial and temporal dithering method will be briefly described.

In the present invention, when the LCD is driven, stitches in which the boundary between two shot regions are discontinuously appear due to a difference in luminance between two adjacent shot regions, and a dithering method is used to remove them.

The dithering method refers to varying the gradation voltage according to a frame or position in order to display a predetermined gradation between the gradation and gradation, for example, 1.5 gradations between 1 and 2 gradations. In detail, the spatial dithering method sequentially applies unequal gradation voltages to the pixels according to the position of the vertical line or the horizontal line during one frame, and the temporal dithering method applies non-identical gradation voltages to the pixels for each frame. It is the way of authorization.

Next, the realization method embodied using the stitch improvement part mentioned above is demonstrated.

4 is a view for explaining the concept of a method for changing a G gamma curve (G gamma curve) to an arbitrary target gamma curve in accordance with an example of the present invention.

As shown in FIG. 4, in order to change the gamma curve of the green G to the target gamma curve, for example, to reduce the luminance (corresponding point) of 130 gray to the target gamma curve, the following procedure is performed.

First, as the raw image data, for example, G data having 130 gray information is input, the luminance of the target gamma curve corresponding to 130 gray is found (1).

Then, the corresponding point of the original G gamma curve corresponding to the corresponding luminance found on the target gamma curve is found (2). If there is no corresponding point (ie, luminance) on the G gamma curve, the G gray value is found through a predetermined interpolation process.

Next, the gray value of the corresponding point is found (3).

4, the value found in the above-described order is 128.5. The above 128.5 is a value that cannot be represented by conventional 8-bit data. Therefore, the expansion of gray is essential. That is, a corresponding value of 9 bits or more bits that can represent more gray than 8 bits is required.

For example, since 10 bits (8 bits + 2 bits) can express 1024 gray levels, it becomes possible to manage by dividing the gray and gray into four equal parts (for example, 0.25 / 0.5 / 0.75). As a result, it is possible to more accurately express the gray scales that cannot be represented by 8-bit data.

Accordingly, the above-described method can find and change 10 bit information or more bit information of G data corresponding to 256 (2 ⁸ ) pieces.

In FIG. 4, the green gamma curve of the first shot is changed based on the green gamma curve of the first shot. It can also change (or converge).

In addition, a G gamma curve having 8 bits can also be found in association with the target gamma curve or the B gamma curve of the shot by using the above-described method.

Here, the spatial and temporal dithering method used in the case of multi-grading the gray scale accurately represented by the 10-bit data by the method described above to be equal to the number of bits of the raw image data will be described in detail.

5A to 5C are diagrams for describing a spatial and temporal dither processing method for representing 10-bit data as 8-bit data according to the present invention.

The stitch improvement unit according to the present invention uses gray and gray using expanded corrected image data, for example, 10-bit corrected image data, to more accurately express a luminance level that cannot be represented by 8-bit image data input from the outside. Manage it by dividing it into quarters (0.25 / 0.5 / 0.75).

FIG. 5A is a diagram for describing a spatial and temporal dithering method in the case of adjusting the gray level of a corresponding region consisting of four pixels by 0.25. FIG.

As illustrated, the stitch improvement unit adjusts the gray level of the shot to a predetermined value (0.25) by using a temporal dithering method and a spatial dithering method.

In the case of using the temporal dithering method, the stitch improvement unit controls the gray level of each pixel to be an average of 0.25 for 4 frames (N / N + 1 / N + 2 / N + 3 frames).

For example, a method of expressing 1.25 gradations between one gradation and two gradations is described. The average gradation of the pixels is defined by setting the gradation of each pixel to be one gradation for two frames for four frames and the remaining three frames as one gradation. Is controlled to be 1.25.

The method of improving the stitch using this dithering method is as follows.

For example, when the gray level of S1 represents a normal level as 100, while the stitch line occurs because the gray level of S2 represents 99.75, the voltage of the pixel for each frame is changed so that the average gray level of S1 can be adjusted by 0.25. That is, the gray scale voltage applied to S1 is adjusted to be 99.75 gray scale on average by applying 100 gray scale for 3 frames out of 4 frames and 99 gray scales for the other 1 frame.

However, in the case of using only the above-described temporal dithering method, the image sticking phenomenon often occurs because its position is fixed (for example, 1-> 2-> 3-> 4) when the polarity of each pixel is inverted. . In order to prevent this, the present invention uses a spatial dithering method together to prevent this.

In the case of using the spatial dithering method, the stitch improvement unit controls to have a gray level voltage that is not the same for each pixel according to the position of the vertical line or the horizontal line. That is, by adjusting only one pixel of the four pixels during one frame to have a different polarity, the position of the pixel is continuously changed during one frame, thereby adjusting the average gradation of the corresponding region.

FIG. 5B is a diagram illustrating a spatial and temporal dithering method in the case of adjusting the gradation of a corresponding area by 0.5. FIG. 5C is a diagram illustrating a spatial and temporal dithering method in the case of adjusting the gradation of the corresponding area by 0.75.                     

As described above, by controlling to have different gradation voltages according to the position of each frame, the vertical line or the horizontal line, the same gradation between the shots may be implemented.

6 is a graph illustrating a gamma curve for each shot after stitch reduction according to the present invention. As shown, it can be seen that the gray characteristics between the shots show a constant gray level regardless of the data driver and the stitch line generation position.

In the above description, an example of changing the 8-bit raw image data into 10-bit corrected image data has been described as an example. However, it can be changed to 9-bit corrected image data.

The overall driving concept for implementing such an embodiment is described as follows.

In particular, only the case where the final output of the timing controller is 8 bits will be described. This is because the 6-bit output uses a dithering method corresponding to the 6-bit output.

FIG. 7 is a diagram for explaining a stitch improvement unit according to the first embodiment of the present invention. In particular, FIG. 7 is a conceptual diagram of a circuit configuration for storing extension data in an internal ROM.

Referring to FIG. 7, the stitch improvement unit 110 according to the first embodiment of the present invention may include a first ROM 142, a second ROM 144, a third ROM 146, and a first multi-gradation unit 122. ), A second multi-gradation unit 124 and a third multi-gradation unit 126.

The first ROM 142 to the third ROM 146 store the corrected image data corresponding to the raw image data provided from the outside in the form of a predetermined look up table, and correct from the timing controller 100. According to the image data output request, the corrected image data corresponding to the raw image data is extracted and provided. In this case, the corrected image data stored in the form of a predetermined lookup table is corrected image data for each of R, G, and B. The corrected image data is measured by measuring a gamma curve for each shot of the liquid crystal panel, and then correcting them by digitization.

In operation, the stitch improvement unit 110 reads the extended data (10 bits) using digital image data input from the outside as an address of the internal ROMs 142, 144, and 146, and then performs temporal / spatial dithering. The data is sent to the multilevel adjustment unit 122, 124, and 126 and finally output to the data driver 200 via the timing control unit 100.

In the drawing, the 8-bit data received from the outside is expanded to 10-bit data, and the 8-bit data is output through dithering. For example, the expanded data is not necessarily 10-bit data. It may be.

The circuit configuration of the stitch improvement unit according to the first embodiment of the present invention can reduce the unit cost of the LCD due to the advantage of not using an additional ROM separately.

FIG. 8 is a diagram for explaining a stitch improvement unit according to a second embodiment of the present invention. In particular, FIG. 8 is a conceptual diagram of a circuit configuration for storing extension data in an external memory.

Referring to FIG. 8, the stitch improvement unit 110 according to the second embodiment of the present invention includes a first multi-level harmony unit 122, a second multi-level harmony unit 124, and a third multi-level harmony unit 126. do.

The external ROM 146 stores the corrected image data corresponding to the raw image data provided from the outside in the form of a predetermined lookup table (LUT) and, upon request for outputting the corrected image data from the timing controller 100, the original image. The corrected image data corresponding to the data is extracted and provided.

In operation, the stitch improvement unit 110 reads the extended data (10 bits) using digital image data input from the outside as an address of the external ROM 146 and then performs dither processing. 126, and finally output to the data driver 200 via the timing controller 100.

Since the circuit configuration of the stitch improvement unit 110 according to the second embodiment of the present invention stores extended data in the external ROM 146, the gray level of the changed liquid crystal panel, in particular, a stitch line, is generated even when the liquid crystal panel is changed. Since only the ROM value storing the extended data that can be adjusted to the gray level of a specific shot can be changed, the same gray level can be realized regardless of the position of the stitch line and the data driver.

On the other hand, unlike the above, when the operation of the liquid crystal display after the process is often caused by a slight shift (shift) at a predetermined position due to various factors occur. For example, a stitch line does not occur in the 180 th pixel, but a stitch line occurs in the 178 th to 182 th pixels. To this end, the present invention solves the above problem by forming a hardware option outside the timing controller.

9 is a view for explaining a stitch improvement unit according to a third embodiment of the present invention.

Referring to FIG. 9, the stitch improving unit 110 in the timing controller 100 corresponds to the raw image data as raw image data for each of R, G, and B is input from the outside after the initial startup of the liquid crystal display device. The corrected image data is extracted, and the extracted corrected image data is multi-graded converted and output.

The period controller 120 applies a corrected image data application period of the timing controller 100 so that the image data for correcting the stitch line may be accurately applied to the corresponding pixel when the position of the stitch line is shifted even after the start of the liquid crystal display. To adjust it. To this end, the first to fourth resistors in the period controller 120 are used.

In detail, after grasping how far the pixel position where the stitch line has occurred since the start of the liquid crystal display is located from the expected pixel position, the data is applied so that the correction image data to be applied to the expected pixel can be applied to the pixel where the stitch line has occurred. Control the authorization cycle. For example, when a stitch line occurs in the 180th pixel instead of the 178th pixel, the timing controller 100 connects (+2) all of the first to fourth resistors outside the stitch improvement unit 110 with the power terminal. The application period of the image data from is delayed by about two pixels.

That is, the stitch improvement unit 100 adjusts the correction image data application timing for a predetermined time through the data input from the period control unit 120.

As described above, depending on whether the first to fourth terms are connected to the ground or the power terminal, the timing controller 100 shifts the data output timing to the corresponding pixel by two pixels or delays the stitch line by two pixels. Control gradation adjustment caused by occurrence.                     

Although the above has been described with reference to a preferred embodiment of the present invention, those skilled in the art will be able to variously modify and change the present invention without departing from the spirit and scope of the invention as set forth in the claims below. It will be appreciated.

As described above, according to the present invention, as raw image data of each of R, G, and B is input from the outside, new R, G, and B correction image data are generated and stored in consideration of luminance characteristics of each shot, and stored R By adjusting the gamma curves of R, G, and B separately for the corrected image data of each of the G and B, the same luminance level is realized between shots regardless of the position of the stitch line and the data driver. There is an effect that can be provided.

Claims (7)

A liquid crystal panel having a liquid crystal material therein and having a plurality of gate lines transmitting scan signals and a plurality of data lines transferring image signals and switching elements connected to the gate lines and the data lines; A scan driver for sequentially applying a gate-on voltage for turning on the switching element to the plurality of gate lines; A data driver for applying a data voltage representing an image signal to the data line; And As raw image data of each of R, G, and B is input from the outside after initial startup, the data driver is extracted by extracting the corrected image data corresponding to the raw image data from a memory storing the corrected image data corresponding to the raw image data. And a control unit for generating a timing signal for controlling the operation of the scan driver and the data driver and outputting the timing signal to the scan driver and the data driver, respectively. Including; The control unit gamma-corrects raw image data of each of R, G, and B through the corrected image data to control the liquid crystal panel having a plurality of shots to achieve the same luminance level. Display device. According to claim 1, The control unit, A stitch improving unit configured to extract corrected image data corresponding to the raw image data from the memory, multi-gradation conversion, and output the raw image data from outside after initial startup; And A timing controller configured to output the multi-graded corrected image data to the data driver, generate a timing signal for controlling the operation of the scan driver and the data driver, and output the timing signal to the scan driver and the data driver, respectively Liquid crystal display having a stitch reduction means comprising a. The method of claim 2, The stitch improvement unit, And a stitch reduction means characterized in that the extracted corrected image data are subjected to temporal and spatial dithering to perform multi-gradation conversion. The method of claim 3, wherein The stitch improvement unit, Nonvolatile memory; After the initial startup, corrected image data corresponding to the raw image data of each of R, G, and B inputted from the outside is extracted from the memory and stored in the nonvolatile memory. A data controller for outputting corrected image data corresponding to the raw image data from the nonvolatile memory as image data is input; And A gradation unit for multi-gradation converting the corrected image data and outputting the multi-graded corrected image data to the data driver Liquid crystal display having a stitch reduction means comprising a. The method of claim 3, wherein The stitch improvement unit, A data controller for outputting corrected image data corresponding to the raw image data from an external volatile memory as raw image data of each of R, G, and B is input after the initial startup; And A gradation unit for converting the corrected image data and outputting the converted corrected image data to the data driver Including; And the volatile memory changes and stores the gray scale adjustment value according to the change of the liquid crystal panel, and provides the volatile memory to the stitch improvement unit. According to claim 1, And a period control section for adjusting the transmission period of the correction image data to the data driver so that the correction image data is applied to the correct position where the stitch line is generated. According to claim 1, And said corrected image data is obtained through bit expansion of said raw image data on the basis of a correction gamma curve.

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