KR20150030864A - Organic light emitting display device and method for controlling picture quality thereof - Google Patents

Abstract

The present invention provides an organic light-emitting display device and a method of the same for controlling image quality, wherein the organic light-emitting display device can remove display spots and improve the uniformity of image quality by displaying an image of a low gray-level region. According to the present invention, the organic light-emitting display device comprises a display panel, a data conversion part, and a panel driving part. The display panel includes a plurality of unit pixels composed of white, red, green, and blue subpixels. The data conversion part performs the following procedures: converting three-color input data of red, green, and blue into four-color input data of white, red, green, and blue; generating four-color correction data of white, red, green, and blue by applying an error diffusion value delivered from a neighboring pixel to the four-color input data; comparing the four-color correction data with threshold values individually set for each dithering mask of white, red, green, and blue, and generating four-color display data of white, red, green, and blue; and calculating an error diffusion value based on an error between the four-color correction data and the four-color display data. The panel driving part displays the four-color display data of white, red, green, and blue supplied from the data conversion part on the display panel.

Description

TECHNICAL FIELD [0001] The present invention relates to an organic light emitting diode (OLED) display device and an image quality control method thereof.

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an organic light emitting diode (OLED) display, and more particularly, to an organic light emitting diode (OLED) display capable of improving image quality uniformity and a method of controlling the image quality.

2. Description of the Related Art In recent years, the importance of flat panel display devices has been increasing with the development of multimedia. In response to this, flat panel display devices such as liquid crystal display devices, plasma display devices, and organic light emitting display devices have been commercialized. Among such flat panel display devices, organic light emitting display devices are attracting attention as a next generation flat panel display device because they have a high response speed, low power consumption, and self-luminescence, so that there is no problem in viewing angle.

A conventional organic light emitting display includes a plurality of unit pixels each having a plurality of sub-pixels for displaying an image. Each sub-pixel includes an organic light emitting element including an organic light emitting layer between an anode electrode and a cathode electrode, And a pixel circuit for emitting light. The pixel circuit includes a switching transistor, a driving transistor, and a capacitor. The switching transistor is switched according to a gate signal to supply a data voltage to the driving transistor. The driving transistor is switched according to a data voltage supplied from the switching transistor to control the current flowing to the organic light emitting element, do. The capacitor stores the voltage between the gate electrode and the source electrode of the driving transistor and switches the driving transistor to the stored voltage. The organic light emitting element emits light by the current supplied from the driving transistor.

However, in the conventional organic light emitting diode display, due to a process variation or the like, there is a characteristic difference between the driving transistors such as the threshold voltage (Vth) and the mobility of the driving transistor for each sub-pixel, In the conventional organic light emitting display device, a luminance deviation occurs between sub-pixels, thereby causing a problem that a screen is spotted. In order to solve such a problem, a conventional organic light emitting display device has a compensation circuit. The compensation circuit senses a current flowing in the driving transistor and controls a voltage applied to a gate of the driving transistor. Such a compensation method can improve the problem of screen unevenness in a relay or a high gradation having a large amount of current, but the problem of a screen unevenness is still recognized at a low gradation with a small amount of current.

On the other hand, in recent years, in order to increase the luminance of each unit pixel, a four-color organic light emitting display device in which white sub-pixels are added to unit pixels has been commercialized. In such a four-color organic light emitting display, RGB input data is converted into WRGB data and displayed on the corresponding pixel. However, also in the conventional four-color organic light emitting display device, there is a problem that the unevenness is recognized on the screen of the specific low gradation region due to the difference in characteristics of the driving transistor, as described above.

SUMMARY OF THE INVENTION It is an object of the present invention to provide an organic light emitting display and its image quality control method capable of improving uniformity of image quality while eliminating screen unevenness by implementing images in a low gradation region. do.

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

According to an aspect of the present invention, there is provided an organic light emitting display including: a display panel including a plurality of unit pixels including white, red, green, and blue sub-pixels; The three-color input data of red, green, and blue is converted into four-color input data of white, red, green, and blue, and the error diffusion value propagated from the surrounding pixels is reflected in the corresponding four- Green, and blue, and compares the four-color correction data corresponding to the color-by-color threshold individually set for each of the white, red, green, and blue dithering masks to obtain white, red, A data conversion unit which generates blue four-color display data and calculates the error diffusion value based on an error between the four-color correction data and the four-color display data; And a panel driver for displaying white, red, green, and blue four-color display data supplied from the data converter on the display panel.

According to an aspect of the present invention, there is provided an image quality control method for an organic light emitting diode display having a display panel including a plurality of unit pixels including white, red, green and blue sub-pixels, A control method comprising: (A) performing inverse gamma correction on three-color input data of red, green, and blue; (B) generating four-color input data of white, red, green, and blue based on the inverse gamma corrected three-color input data of red, green, and blue; The four-color correction data is generated by reflecting the error diffusion value propagated from the peripheral pixels to the corresponding four-color input data, and the four-color correction data is generated by using the threshold value for each color individually set for each of the white, red, green, and blue dithering masks, And generating the four-color display data of white, red, green, and blue, and calculating the error diffusion value based on the error between the four-color correction data and the four-color display data C); (D) performing gamma correction on the four-color display data; And (D) displaying the gamma corrected four-color data on the display panel.

According to the solution of the above-mentioned problems, the organic light emitting display according to the present invention and its image quality control method have the following effects.

First, by reproducing the gradation according to the dithering algorithm and the error diffusion algorithm using the dithering mask, the uniformity of the image quality can be improved while eliminating the screen unevenness in the low gradation region.

The threshold value of the dithering mask is set based on the driving characteristics of the white, red, green, and blue pixels constituting the second unit pixel, thereby preventing image quality deterioration due to pattern noise and / or flicker according to the dither pattern.

1 is a view schematically showing an organic light emitting display according to an embodiment of the present invention.
2 is a block diagram for explaining a data conversion unit according to an embodiment of the present invention shown in FIG.
FIG. 3 is a block diagram for explaining the tone reproduction section shown in FIG. 2. FIG.
4 is a diagram showing a dithering mask according to the present invention.
5 is a diagram for explaining a threshold setting process of a white dithering mask according to the present invention.
6 is a view for explaining a threshold setting process of a green dithering mask according to the present invention.
FIG. 7 is a view for explaining a threshold setting process of a red dithering mask according to the present invention.
FIG. 8 is a diagram for explaining a threshold setting process of a blue dithering mask according to the present invention.
9 is a flowchart illustrating a method of controlling an image quality of an OLED display according to an exemplary embodiment of the present invention.

The meaning of the terms described herein should be understood as follows.

The word " first, "" second," and the like, used to distinguish one element from another, are to be understood to include plural representations unless the context clearly dictates otherwise. The scope of the right should not be limited by these terms.

It should be understood that the terms "comprises" or "having" does not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, or combinations thereof.

It should be understood that the term "at least one" includes all possible combinations from one or more related items. For example, the meaning of "at least one of the first item, the second item and the third item" means not only the first item, the second item or the third item, but also the second item and the second item among the first item, Means any combination of items that can be presented from more than one.

Hereinafter, preferred embodiments of the organic light emitting display and the image quality control method according to the present invention will be described in detail with reference to the accompanying drawings.

1 is a view schematically showing an organic light emitting display according to an embodiment of the present invention.

Referring to FIG. 1, an OLED display according to an embodiment of the present invention includes a display panel 100, a data conversion unit 200, and a panel driver 300.

The display panel 100 includes a plurality of data lines DL formed to intersect with each other and a plurality of sub pixels P formed in a pixel region defined by a plurality of gate lines GL. A plurality of driving power lines PL for supplying driving power to each sub pixel P and a cathode electrode layer (not shown) for supplying a cathode power to each sub pixel P are formed in the display panel 100 .

Each of the plurality of sub-pixels P includes an organic light emitting diode (OLED) and a pixel circuit (PC).

The organic light emitting diode OLED is connected between the pixel circuit PC and the cathode electrode layer and emits a predetermined color light by emitting light in proportion to the amount of data current supplied from the pixel circuit PC.

The pixel circuit PC responds to the data voltage Vdata supplied from the panel driver 300 to the data line DL in response to the gate signal GS supplied from the panel driver 300 to the gate line GL And supplies the data current to the organic light emitting diode OLED. To this end, the pixel circuit PC comprises a switching transistor, a driving transistor, and at least one capacitor formed on a substrate by a thin film transistor forming process.

The switching transistor is switched according to a gate signal GS supplied to the gate line GL to supply a data voltage Vdata supplied from the data line DL to the driving transistor. The driving transistor is switched according to the data voltage Vdata supplied from the switching transistor to generate a data current based on the data voltage Vdata and supplies the data current to the organic light emitting diode OLED, . The at least one capacitor holds the data voltage supplied to the driving transistor for one frame.

In the pixel circuit PC of each sub-pixel P, a characteristic difference of driving transistors such as a threshold voltage Vth and a mobility of the driving transistor occurs due to process variations or the like, The amount of current flowing varies, and a luminance deviation occurs between the pixels, which may result in deterioration of image quality. Accordingly, the organic light emitting display according to the present invention includes an external compensation circuit for sensing a characteristic change of the driving transistor of each sub-pixel P, compensating for display data to be supplied to each sub-pixel, .

The external compensation circuit charges the sensing line SL with the current flowing through the driving transistor of each sub-pixel P using a sensing line SL connected to each sub-pixel P, And senses a voltage charged in the sensing line SL through the sensing line SL and derives a current flowing in the driving transistor of each sub pixel P according to the sensed voltage.

The data conversion unit 200 converts the three-color input data RGB of red, green, and blue into four-color input data of white, red, green, and blue, The four-color display data (W'R'G'B ') is generated by correcting the four-color input data according to the dithering algorithm using the set dithering mask and the error diffusion algorithm to reproduce the gradation, Thereby improving the uniformity of image quality. Specifically, the data converter 200 converts the three-color input data (RGB) of red, green, and blue inputted from an external system body (not shown) or a graphics card (not shown) Green, and blue, and generates four-color correction data that reflects the error diffusion value propagated from the peripheral pixels to the four-color input data, and outputs the four-color correction data to the respective dithering masks of white, red, Color display data (W'R'G'B ') according to a result of comparison between the color-by-color threshold value and the four-color correction data that are set differently from each other and supplies the four-color display data W'R'G'B' to the panel driver 300, And calculates the error diffusion value based on the error between the correction data and the four-color display data (W'R'G'B '). The specific configuration of the data conversion unit 200 will be described later.

The panel driver 300 drives the display panel 100 based on white, red, green and blue four-color display data W'R'G'B 'supplied from the data converter 200 . The panel driver 300 may control the gate control signal GCS and the data control signal DCS based on a timing synchronization signal TSS input from an external system body (not shown) or a graphics card (not shown) And sequentially generates the gate signal GS according to the gate control signal and sequentially supplies the generated gate signal GS to the gate line GL and outputs the four color display data W to be displayed in each unit pixel supplied from the data conversion unit 200 'R'G'B') into a data voltage (Vdata) and supplies it to the corresponding data line (DL). The panel driver 300 includes a timing controller 310, a gate driver 320, and a data driver 330.

The timing controller 310 controls the driving timings of the gate driver 320 and the data driver 330 according to the timing synchronization signal TSS. That is, the timing controller 310 generates a gate control signal GCS and a data control signal DCS based on a timing synchronization signal TSS such as a vertical synchronization signal, a horizontal synchronization signal, a data enable signal, and a clock signal Controls the driving timing of the gate driving unit 320 through the gate control signal GCS and controls the driving timing of the data driving unit 330 through the data control signal DCS synchronized with the timing.

The timing controller 310 receives the four-color display data W'R'G'B 'supplied from the data converter 200 and outputs the four-color display data W'R'G'B' as white, red, green, and blue to be suitable for driving the display panel 100. [ Blue, and supplies the aligned four-color display data (Ra, Ga, Ba, Wa) to the data driver 330 through the set data interface method.

The data conversion unit 200 may be embedded in the timing control unit 310. In this case, the data conversion unit 200 may be embedded in the timing control unit 310 in the form of a program.

The gate driver 320 generates a gate signal GS according to a gate control signal GCS supplied from the timing controller 310 and sequentially supplies the gate signal GS to a plurality of gate lines GL.

The data driver 330 may operate in a display mode or an external sensing mode under the control of the timing controller 310. [

First, in the display mode, the data driver 330 receives the four-color display data (Ra, Ga, Ba, Wa) and the data control signal DCS aligned from the timing controller 310, (Not shown) to receive a plurality of reference gamma voltages. The data driver 330 sequentially samples and latches the four-color display data Rd, Gd, Bd, and Wd according to the data control signal DCS, A data voltage Vdata to be supplied to each subpixel P of one horizontal line is generated in a unit of one horizontal period through digital-analog conversion in which the gamma voltage is selected as the data voltage Vdata, Supply.

Next, in the external sensing mode, the data driver 330 supplies a data voltage for sensing to each data line DL under the control of the timing controller 310, and is connected to each sub pixel P Generates sensing data (Sdata) by sensing the characteristic change of the driving transistor included in each sub-pixel (P) through each sensing line SL and provides the generated sensing data (Sdata) to the timing control unit 310 . The specific operation of the organic light emitting diode display according to the display mode or the external sensing mode is disclosed in Korean Patent Laid-Open Nos. 10-2010-0047505, 10-2012-0061522, 10-2013-0066449 , Or 10-2013-0066450.

FIG. 2 is a block diagram for explaining a data conversion unit according to the embodiment of the present invention shown in FIG. 1, and FIG. 3 is a block diagram for explaining the tone reproduction unit shown in FIG.

2 and 3, the data conversion unit 200 according to the embodiment of the present invention includes an inverse gamma correction unit 210, a four-color data generation unit 220, a gray level representation unit 230, (240).

The inverse gamma correction unit 210 performs inverse gamma correction on the three-color input data (RGB) so as to linearly change the luminance value according to the gray-scale values of the three-color input data RGB of red, Gamma correction, and supplies the linearized three-color input data to the four-color data generation unit 220. The four-

The four-color data generator 220 generates the four-color data based on the three-color input data RGB of red, green, and blue corrected by the inverse gamma correction unit 210, Color input data WRGB of white, red, green, and blue to be displayed on each of the sub-pixels P of the display device. Specifically, the four-color data generation unit 220 extracts white data W from the three-color input data RGB of red, green, and blue for each unit pixel, Color input data (WRGB) of white, red, green and blue can be generated by correcting the three-color input data (RGB) of red, green and blue. For example, the white data W in the four-color input data WRGB may be set to a common tone value (or minimum tone value) among the three color input data RGB of red, green, and blue. The red, green, and blue data in the four-color input data WRGB are set to gray-level values obtained by subtracting the white data W from each of three-color input data RGB of red, green, . As another example, the four-color data generation unit 220 may generate three-color input data RGB (RGB) according to the data conversion method disclosed in detail in Korean Patent Laid-Open Publication No. 10-2013-0060476 or No. 10-2013-0030598 ) Into four-color input data WRGB.

The gradation reproducing unit 230 generates 4 gradations of white, red, green and blue based on the 4-color input data WRGB provided from the 4-color data generator 220, the error diffusion value, The color input data WRGB is corrected to generate the four-color display data W'R'G'B 'in which no screen unevenness occurs in the low gradation region. That is, the gradation reproducing unit 230 generates four-color display data W'R'G'B 'by correcting the four-color input data according to a dithering algorithm and an error diffusion algorithm Thereby improving the uniformity of the picture quality while eliminating screen unevenness in the low gradation area. To this end, the gray level representation unit 230 may include an error addition unit 231, a dithering mask unit 233, a dithering unit 235, an error calculation unit 237, and an error diffusion unit 239 have.

The error adding section 231 adds the error correction information to the error diffusion section 239 to the four-color input data WRGB of white, red, green and blue provided from the four-color data generation section 220, The four color correction data (Wedv, Redv, Gedv, Bedv) of white, red, green and blue are generated by reflecting the error diffusion value Pedv of the pixel P. For example, the error addition unit 231 adds the four-color input data WRGB and the error diffusion value Pedv of the corresponding sub-pixel P to obtain four-color correction data of white, red, green, and blue Wedv, Redv, Gedv, Bedv).

The dithering mask unit 233 selects the white, red, green, and blue dithering masks to be applied to the current frame from among a plurality of dithering masks for each color individually set for white, red, green, and blue, (Wth, Rth, Gth, and Bth) set for each dithering mask of white, red, green, and blue. Here, the dithering mask unit 233 may select the white, red, green, and blue dithering masks to be applied to the current frame based on the vertical synchronization signal Vsync among the input timing synchronization signals.

Each of the plurality of dithering masks for each color may be a 4x4 Bayer dithering mask. The threshold values (Wth, Rth, Gth, Bth) set in each cell of the plurality of dithering masks for each color are determined by the process variations of the driving transistors and the organic light emitting devices OLED included in each subpixel P and / Or a driving characteristic deviation to eliminate a screen unevenness that occurs in a low gradation region, and can be set differently for each color of white, red, green, and blue. At this time, the white threshold values Wth set in each cell of the white dithering mask are different from the green threshold values Gth set in each cell of the green dithering mask, and each cell of the red dithering mask The red threshold values Rth set in the blue dithering mask are different from the threshold values Bth set in each cell of the blue dithering mask. The thresholds set for the white dithering mask and the green dithering mask may be set to form a bayer pattern. The thresholds set for the red dithering mask and the blue dithering mask, respectively, The value may also be set to form a Bayer pattern.

FIG. 4 is a diagram illustrating a dithering mask according to the present invention, wherein the dithering mask has a 4 × 4 matrix and each cell (C (1, 1) to C (4, 4) A different threshold value is set through the threshold value. Each of the white, red, green, and blue dithering masks is set to have a different threshold value for each of the i-th to j-th frames individually.

5 to 8 as an example, it is assumed that each cell C (1, 1) to C (4, 4) of the white, red, green and blue dithering masks applied to the i- A threshold value of each cell is set to a cell at a different position. First, threshold values of the white, red, green, and blue dithering masks applied to the i-th frame are determined based on the same data as the white dithering mask, the green dithering mask, the red dithering mask And a blue dithering mask.

The process of setting the threshold value (Wth) for each cell of the white dither mask (W-DM) applied to the i-th frame in conjunction with FIG. 4 and FIG. 5 will be described below.

4 and 5A, a threshold of 0 is set in the cell of (1, 1), and a threshold of 1 is set in the cell of (3, 3). Next, as can be seen from Figs. 4 and 5 (b), in the cell of (1,3) forming a 3x3 square with the cell of (1,1) and the cell of (3,3) 2 is set, and a threshold of 3 is set in the cell of (3, 1). Accordingly, in the white dithering mask (W-DM), the position of each cell in which the threshold value of 0 to 3 is set is a 3 × 3 square.

4 and 5 (c), a threshold of 4 is set in the cell of (2,2), and a threshold of 5 is set in the cell of (4,4). 4 and 5 (d), in the cell of (2, 4) and the cell of (2, 4) forming a 3 × 3 square with a cell of 6 is set, and a threshold value of 7 is set in the cell of (4, 2). Thus, in the white dithering mask (W-DM), the position of each cell in which the threshold value of 4 to 7 is set is a 3 × 3 square.

Then, as shown in FIGS. 4 and 5E, a threshold of 8 is set in the cell of (1,2), and a threshold of 9 is set in the cell of (3,4). Next, as shown in FIGS. 4 and 5 (f), in the cell of (1, 4) forming a 3 × 3 square with the cell of (1, 2) A threshold of 10 is set, and a threshold of 11 is set in the cell of (3, 2). Accordingly, in the white dither mask (W-DM), the positions of the cells having the threshold values of 8 to 11 are formed into a square of 3 × 3.

Next, as shown in FIGS. 4 and 5 (g), a threshold of 12 is set in the cell of (2,1) and a threshold of 13 is set in the cell of (4,3). Finally, as can be seen from FIGS. 4 and 5 (h), the cells of (2, 1) and (2, 3) And a threshold of 15 is set in the cell of (4, 1). Accordingly, in the white dithering mask (W-DM), the positions of the respective cells having the threshold values of 12 to 15 are formed into a 3 × 3 square.

The process of setting the threshold value (Gth) for each cell of the green dithering mask (G-DM) applied to the i-th frame by referring to FIGS. 4 to 6 will be described below. First, a threshold value Gth for each cell of the green dithering mask G-DM applied to the i-th frame is set to a predetermined value in each cell of the white dithering mask W-DM applied to the i-th frame Is set so as to form a Bayer pattern different from the set threshold value (Wth).

First, as can be seen from FIGS. 4, 5A and 6A, the cell of (1,1) and (3,3) of the white dithering mask W- (1, 3) cells of the green dithering mask (G-DM) forming a 3 × 3 square with a threshold of 0, and a threshold of 1 . 4 and 6 (b), a cell of (1, 1) forming a 3 × 3 square with a cell of (1, 3) and a cell of (3, 1) 14 is set, and a threshold of 15 is set in the cell of (3, 3). Accordingly, in the green dithering mask (G-DM), the positions of the cells having the thresholds of 0, 1, 14, and 15 are set to a square of 3 × 3.

Then, as can be seen from Figs. 4, 5C and 6C, the (2,2) cells of the white dithering mask W-DM and the A threshold value of 4 is set in a cell of (2,4) of the green dithering mask (G-DM) forming a 3 × 3 square with a cell, and a threshold of 4 is set in a cell of (4,2) Set the value. 4 and 6 (d), a cell of (2, 2), which forms a 3 × 3 square with a cell of (2,4) and a cell of (4,2) 2 is set, and a threshold value of 3 is set in the cell of (4, 4). Accordingly, the position of each cell in which the threshold value of 2 to 5 is set is a 3x3 square.

Then, as can be seen from Figs. 4, 5 (e) and 6 (e), the cell of (1, 2) of the white dithering mask W- (1, 4) cells of the green dithering mask (G-DM) forming a 3 × 3 square with the cell are set to a threshold of 8, and a cell of (3, 2) Set the value. Next, as shown in FIGS. 4 and 6 (f), in the cell of (1, 2) forming a 3 × 3 square with a cell of (1,4) and a cell of (3,2) 6 is set, and a threshold value of 7 is set in the cell of (3, 4). Accordingly, the position of each cell in which the threshold value of 6 to 9 is set becomes a 3x3 square.

Then, as can be seen from Figs. 4, 5 (g) and 6 (g), the cell of (2,1) and the cell of (4,3) of the white dithering mask W- (2, 3) cells of the green dithering mask (G-DM) forming a 3x3 square with the cell are set to a threshold of 12, and a cell of (4, 1) Set the value. 4 and 6 (h), a cell of (2, 1) forming a 3 × 3 square with a cell of (2, 3) and a cell of (4, 1) A threshold value of 10 is set, and a threshold value of 11 is set in the cell of (4, 3). Accordingly, the position of each cell in which the threshold value of 10 to 13 is set becomes a 3x3 square.

The process of setting the threshold value (Rth) for each cell of the red dither mask (R-DM) applied to the i < th > frame will be described with reference to FIGS. First, the threshold Gth for each cell of the red dither mask R-DM applied to the i-th frame is calculated using the white and green dithering masks W-DM, G- DM are set to be different from the threshold value Wth set in each cell.

4 and 7A, a threshold of 0 is set in the cell of (2, 2), and a threshold of 1 is set in the cell of (4, 4). Next, as can be seen from Figs. 4 and 7 (b), the cells of (2, 2) and (4, 4) 2 is set, and a threshold value of 3 is set in the cell of (4, 2). Accordingly, in the red dither mask (R-DM), each cell having a threshold value of 0 to 3 is formed into a square having a size of 3 × 3.

4 and 7C, a threshold value of 4 is set in the cell of (1, 2), and a threshold of 5 is set in the cell of (3,4). 4 and 7 (d), a cell of (1, 4) forming a 3 × 3 square with a cell of (1, 2) and a cell of (3, 4) 6 is set, and a threshold value of 7 is set in the cell of (3, 2). Accordingly, in the red dithering mask (R-DM), the position of each cell in which the threshold value of 4 to 7 is set is a 3 × 3 square.

Then, as shown in FIGS. 4 and 7E, a threshold of 8 is set in the cell of (2,1), and a threshold of 9 is set in the cell of (4,3). 4 and 7 (f), a cell of (2, 1) and a cell of (4, 3) together with a cell of (3, 3) 10 is set, and a threshold of 11 is set in the cell of (4, 1). Accordingly, in the red dither mask (R-DM), the position of each cell in which the threshold value of 8 to 11 is set is a 3 × 3 square.

Next, as shown in FIGS. 4 and 7 (g), a threshold of 12 is set in the cell of (1, 1) and a threshold of 13 is set in the cell of (3, 3). Finally, as can be seen from FIGS. 4 and 7 (h), the cells of (1, 1) and (3, 3) And a threshold of 15 is set in the cell of (3, 1). Thus, in the red dither mask (R-DM), the positions of the cells having the thresholds of 12 to 15 are set to a square of 3 × 3.

The process of setting the threshold value (Gth) for each cell of the blue dithering mask (B-DM) applied to the i-th frame by referring to FIGS. 4 to 8 will be described below. First, the threshold value Gth for each cell of the blue dithering mask (B-DM) applied to the i-th frame is calculated by using the dithering mask (W-DM) of white, green, DM) and a Bayer pattern which are different from a threshold value Wth set in each cell of the G-DM, R-DM, and G-DM.

First, as can be seen from FIGS. 4, 7A and 8A, the cell of (2,2) of the red dithering mask W-DM and the cell of (3,3) (2, 4) of the blue dithering mask (B-DM) forming a 3 × 3 square with a threshold value of 0 is set in the cell of (4, 2) . Next, as can be seen from Figs. 4 and 8 (b), in the cell of (2, 2) forming a square of 3 x 3 size together with the cell of (2,4) 14 is set, and a threshold of 15 is set in the cell of (4, 4). Accordingly, in each of the blue dithering masks (B-DM), the positions of the cells having the thresholds of 0, 1, 14, and 15 are set to a square of 3 × 3.

Then, as can be seen from Figs. 4, 7C and 8C, the (1, 2) cells of the red dithering mask (R-DM) A threshold value of 4 is set in a cell of (1,4) of the blue dithering mask (B-DM) forming a 3 × 3 square with a cell, and a threshold of 4 is set in a cell of (3, 2) Set the value. Then, as can be seen from FIGS. 4 and 8 (d), in the cells (1, 2) forming the square of 3 × 3 together with the cells of (1, 4) 2, and sets a threshold value of 3 in the cell of (3, 4). Accordingly, the position of each cell in which the threshold value of 2 to 5 is set is a 3x3 square.

Then, as can be seen from Figs. 4, 7 (e) and 8 (e), the (2, 1) cell of the red dithering mask R- (2, 3) cells of the blue dithering mask (B-DM) forming a 3 × 3 square with the cell are set to a threshold of 8, and a cell of (4, 1) Set the value. Next, as can be seen from Figs. 4 and 8 (f), a cell of (2, 1) forming a 3x3 square with a cell of (2,3) and a cell of (4,1) 6 is set, and a threshold value of 7 is set in the cell of (4, 3). Accordingly, the position of each cell in which the threshold value of 6 to 9 is set becomes a 3x3 square.

Then, as can be seen from Figs. 4, 7 (g), and 8 (g), the (1, 1) cell of the red dithering mask R- A threshold of 12 is set in the (1,3) cell of the blue dithering mask (B-DM) forming a 3 × 3 square with the cell, and a threshold of 12 is set in the cell of (3,1) Set the value. Next, as can be seen from FIGS. 4 and 8 (h), a cell of (1, 1) forming a 3 × 3 square with a cell of (1, 3) A threshold value of 10 is set, and a threshold value of 11 is set in the cell of (3, 3). Accordingly, the position of each cell in which the threshold value of 10 to 13 is set becomes a 3x3 square.

In this manner, in order to prevent the same threshold value from being set in the same cell position as the threshold value set in each dithering mask applied to the i-th frame, the position of the cell where the threshold value of 0 is set is shifted to the periphery, A threshold value is set in each cell of the dithering mask selectively applied to each of the +1 th to jth frames. For example, the dithering mask unit 233 may have first to eighth dithering masks of white, green, red, and blue applied to the first to eighth frames, respectively, and the dithering mask unit Green, red and blue dither masks set in the frame corresponding to the current frame among the first to eighth frames in accordance with the vertical synchronization signal Vsync, and outputs the selected white, green, red and blue (Wth, Rth, Gth, and Bth) set in each of the dithering masks of the respective pixels.

The threshold of each of the white, green, red and blue first dithering masks applied to the first frame is set in the same manner as each of the dithering masks of the i-th frame described above. The threshold value of each of the second to eighth dithering masks of white, green, red and blue applied to each of the first to eighth frames is set such that the threshold value set in the dithering mask applied to the previous frame is leftward, Direction, and the diagonal direction, respectively.

As described above, in the threshold setting method for each cell of the dithering mask, a different threshold value is individually set for each of a plurality of frames, and a threshold value set at the same cell position of the color-dependent dithering mask is set differently Thereby preventing occurrence of pattern noise and / or flicker based on the dither pattern during dithering using the dithering mask.

2 and 3, the dithering unit 235 receives the four-color correction data (Wedv, Redv, Gedv, Bedv) of white, red, green and blue supplied from the error adding unit 231, (Wth, Rth, Gth, and Bth) of white, red, green, and blue supplied from the dithering mask unit 233 are compared with each other, and the white, red, green, and blue four- Dithering is performed to change data (Wedv, Redv, Gedv, Bedv) into the set smoothing compensation data or pixel off data, so that four-color display data of white, red, green and blue in which no screen unevenness occurs in the low- (W'R'G'B '). More specifically, when the four-color correction data (Wedv, Redv, Gedv, Bedv) is greater than the corresponding threshold value (Wth, Rth, Gth, Bth), the dithering unit 235 outputs the four- Redv, Gedv, and Bedv) to the smear compensation data to generate four-color display data (W'R'G'B '). On the other hand, if the four-color correction data Wedv, Redv, Gedv, and Bedv are smaller than the corresponding threshold values Wth, Rth, Gth, and Bth, the dithering unit 235 outputs the four- Redv, Gedv, Bedv) to the pixel off data to generate the four-color display data (W'R'G'B ').

The smear compensation data may be set to data to be applied to each subpixel P when the same current flows to each of the subpixels P. [ In this case, the smear compensation data may be set to a uniform gray level value for each sub-pixel by performing the external sensing mode described above. In this case, the smear compensation data may be stored in real time or periodically Or may be set to a fixed gray level value that does not cause screen unevenness through a preliminary experiment or in a low gray level region.

The pixel off data is set to a gray level value that does not cause the organic light emitting element OLED of each subpixel P to emit light. For example, the pixel off data may be a tone value of zero.

The error calculator 237 calculates the difference between the four color correction data (Wedv, Redv, Gedv, Bedv) of white, red, green and blue supplied from the error adder 231, And the error (Pev) between the red, green and blue four-color display data (W'R'G'B '). That is, the error calculator 237 calculates the deviation between the correction data (Wedv, Redv, Gedv, Bedv) and the display data (W'R'G'B ') for each of the sub- (Pev) of each sub-pixel (P) generated in accordance with the dithering of the sub-pixel (235).

The error diffusion unit 239 diffuses the error Pev of each subpixel P supplied from the error calculation unit 237 to the spatial subpixel P, Calculates the error diffusion value Pedv and provides the error diffusion value Pedv of each of the calculated sub-pixels P to the error addition section 231 described above.

The gamma correction unit 240 performs gamma correction on the four-color display data (W'R'G'B ') of white, red, green, and blue supplied from the gray scale generator 230 to nonlinearize And supplies the non-linearized white, red, green and blue four-color display data W'R'G'B 'to the panel driving unit 300, i.e., the timing control unit 310. [

9 is a flowchart illustrating a method of controlling an image quality of an organic light emitting display according to an embodiment of the present invention.

Referring to FIG. 9, a method of controlling image quality of an organic light emitting display according to an exemplary embodiment of the present invention will be described step by step.

The input three-color input data of red, green, and blue is linearized by inverse gamma correction (S100).

Then, the four-color input data of white, red, green, and blue are generated based on the inverse gamma corrected three-color input data of red, green, and blue (S200). Here, the four-color input data is generated by the four-color data generator 220 shown in FIG. 2, and a duplicate description thereof will be omitted.

Then, the white, red, green, and blue four-color input data are corrected according to a dithering algorithm using a dithering mask in which different threshold values are individually set for white, red, green, and blue data, and an error diffusion algorithm Four-color display data of white, red, green, and blue is generated (S300). Step S300 will be described in more detail as follows.

First, an error diffusion value of each sub-pixel P to be described later is added to the white, red, green, and blue four-color input data to generate four-color correction data of white, red, green, and blue ). Here, the four-color correction data is generated by the error addition unit 231 shown in FIG. 3, and a duplicate description thereof will be omitted.

Then, the white, red, green, and blue dithering masks to be applied to the current frame are selected from a plurality of dithering masks for each color corresponding to white, red, green, and blue, respectively, and the dithering mask of the selected white, red, green, And outputs a color-by-color threshold value set for each color (S320). Here, the threshold value for each color is generated by the dithering mask unit 233 shown in FIG. 3, and a duplicate description thereof will be omitted.

Then, the four-color correction data of white, red, green, and blue are compared with corresponding threshold values for respective colors, and the four-color correction data of white, red, green, Dithering for changing the pixel off data is performed to generate four-color display data of white, red, green, and blue (S330). Here, the four-color display data is generated by the dithering unit 235 shown in FIG. 3, and a duplicate description thereof will be omitted.

Subsequently, an error of each sub-pixel generated in accordance with the dithering is calculated by calculating a deviation between the white, red, green and blue four-color correction data and the white, red, green and blue four-color display data (D340) .

Subsequently, the error of each sub-pixel is diffused by spatial diffusion, that is, neighboring sub-pixels, and the error diffusion value of each sub-pixel is calculated (S350).

Then, the four-color display data of white, red, green, and blue are subjected to gamma correction so as to be non-linear (S400).

Then, the non-linearized white, red, green, and blue four-color display data are aligned to fit the pixel arrangement structure of the display panel, the aligned data is converted into a data voltage and displayed on the corresponding sub-pixel (S500) .

As described above, the organic light emitting display device and its image quality control method according to the embodiment of the present invention are applicable to four color input data (WRGB) of white, red, green and blue, And the four-color input data WRGB is corrected according to a dithering algorithm using a dithering mask in which different threshold values are set for white, red, green, and blue data, respectively, and an error diffusion algorithm, W'R'G'B ') to reproduce the gradation, thereby eliminating the screen unevenness in the low gradation region and improving the image quality uniformity.

It will be apparent to those skilled in the art that various modifications and variations can be made in the present invention without departing from the spirit or scope of the general inventive concept as defined by the appended claims and their equivalents. Will be clear to those who have knowledge of. Therefore, the scope of the present invention is defined by the appended claims, and all changes or modifications derived from the meaning and scope of the claims and their equivalents should be interpreted as being included in the scope of the present invention.

100: display panel 200: data conversion unit
210: reverse gamma correction unit 220: four-color data generation unit
230: gradation reproduction unit 231: error addition unit
233: Dithering mask unit 235: Dithering unit
237: error calculating unit 239: error diffusion unit
240: gamma correction unit 300: panel driving unit
310: timing control unit 320: gate driving unit
330: Data driver

Claims (11)

A display panel including a plurality of unit pixels including white, red, green and blue sub-pixels;
The three-color input data of red, green, and blue is converted into four-color input data of white, red, green, and blue, and the error diffusion value propagated from the surrounding pixels is reflected in the corresponding four- Green, and blue, and compares the four-color correction data corresponding to the color-by-color threshold individually set for each of the white, red, green, and blue dithering masks to obtain white, red, A data conversion unit which generates blue four-color display data and calculates the error diffusion value based on an error between the four-color correction data and the four-color display data; And
And a panel driver for displaying white, red, green, and blue four-color display data supplied from the data converter on the display panel. The method according to claim 1,
Wherein the data conversion unit comprises:
An inverse gamma correction unit for performing inverse gamma correction on the three-color input data of red, green, and blue;
A four-color data generator for converting the three-color input data of the inverse gamma corrected red, green, and blue into the four-color input data of the white, red, green, and blue;
A gradation reproducing unit for generating four-color display data by correcting four-color input data of white, red, green, and blue based on the four-color input data, the error diffusion value, and the threshold value for each color; And
And a gamma correction unit that gamma-corrects the four-color display data and provides the gamma correction data to the panel driving unit. 3. The method of claim 2,
Wherein the gradation reproducing section comprises:
An error addition unit for adding the error diffusion value to the 4-color input data to generate the 4-color correction data;
A dithering mask for each of the white, red, green and blue colors to be applied to a current frame among a plurality of dithering masks for each color to be applied to each of a plurality of frames, A dithering mask unit for outputting a threshold value for each color;
The four-color correction data is compared with the corresponding threshold value for each color, and dither is performed to change the four-color correction data to the set smear compensation data or pixel off data according to the comparison result to generate the four-color display data A dithering unit;
An error calculator for calculating an error between the four-color correction data and the four-color display data; And
And an error diffusion unit for calculating the error diffusion value by diffusing the error calculated by the error calculation unit into peripheral sub-pixels. The method of claim 3,
Wherein the dithering mask is a 4 × 4 Bayer dither mask. 5. The method of claim 4,
Wherein each of the plurality of dithering masks for each color to be applied to each of the plurality of frames has different threshold values of white, red, green, and blue,
Wherein threshold values of white, red, green, and blue are set for each of the white, red, green, and blue dithering masks to be applied to the same frame. The method of claim 3,
Wherein the smear compensation data is set to data applied to each sub-pixel when the same current flows through each of the sub-pixels. A method of controlling an image quality of an organic light emitting display device having a display panel including a plurality of unit pixels including white, red, green and blue sub-pixels,
A step (A) of performing inverse gamma correction on the three-color input data of red, green, and blue;
(B) generating four-color input data of white, red, green, and blue based on the inverse gamma corrected three-color input data of red, green, and blue;
The four-color correction data is generated by reflecting the error diffusion value propagated from the peripheral pixels to the corresponding four-color input data, and the four-color correction data is generated by using the threshold value for each color individually set for each of the white, red, green, and blue dithering masks, And generating the four-color display data of white, red, green, and blue, and calculating the error diffusion value based on the error between the four-color correction data and the four-color display data C);
(D) performing gamma correction on the four-color display data; And
And (D) displaying the gamma-corrected four-color data on the display panel. 8. The method of claim 7,
The step (C)
Adding the error diffusion value to the 4-color input data to generate the 4-color correction data;
A dithering mask for each of the white, red, green and blue colors to be applied to a current frame among a plurality of dithering masks for each color to be applied to each of a plurality of frames, Outputting a color-specific threshold value;
The four-color correction data is compared with the corresponding threshold value for each color, and dither is performed to change the four-color correction data to the set smear compensation data or pixel off data according to the comparison result to generate the four-color display data step;
Calculating an error between the four-color correction data and the four-color display data; And
And diffusing the calculated error into peripheral sub-pixels to calculate the error diffusion value. 9. The method of claim 8,
Wherein the dithering mask is a 4 × 4 Bayer dither mask. 10. The method of claim 9,
Wherein each of the plurality of dithering masks for each color to be applied to each of the plurality of frames has different threshold values of white, red, green, and blue,
Wherein threshold values of white, red, green, and blue are set for each of the white, red, green, and blue dithering masks to be applied to the same frame. 10. The method of claim 9,
Wherein the smear compensation data is set to data applied to each sub-pixel when the same current flows through the sub-pixels.

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