KR102218460B1 - Display device and visibility enhancement method thereof - Google Patents

Abstract

The present invention relates to a display device, and includes a calculation unit, a gain selector, a PWM selector, a data modulator, and a display panel driver. The calculation unit calculates a Max Color Brightness Level (MCBL) representing the brightness of the brightest color in the pixel data of the input image. The gain selector selects a gain based on the MCBL. The PWM selector selects a PWM (Pulse width modulation) value according to the illuminance input from the illuminance sensor. The data modulator modulates the pixel data with the gain.

Description

Display device and its visibility improvement method {DISPLAY DEVICE AND VISIBILITY ENHANCEMENT METHOD THEREOF}

The present invention relates to a display device with improved visibility.

Liquid Crystal Display Device (LCD), Organic Light Emitting Diode Display (hereinafter referred to as "OLED Display"), Plasma Display Panel (PDP), field emission display device ( Field Emission Display, FED) and other flat panel display devices are used.

The liquid crystal display displays an image by controlling an electric field applied to liquid crystal molecules according to a data voltage. Active matrix type liquid crystal display devices have been applied to almost all display devices, from small mobile devices to large TVs, and are widely used because of lower cost and higher performance thanks to the development of process technology and driving technology.

Since the OLED display is a self-luminous device, power consumption is lower than that of a liquid crystal display device that requires a backlight, and can be manufactured thinner. In addition, the OLED display has a wide viewing angle and a fast response speed. OLED display devices are expanding the market while competing with liquid crystal display devices.

Visibility of an image reproduced in a display image may deteriorate depending on the illuminance of the external environment. A method of improving the visibility of a display device is adjusting a gamma curve according to an average image level ("APL") or illuminance. This prior art is disclosed in Korean Patent Publication 10-2012-0042004 (2012. 05. 03.). However, since this method does not consider the difference in grayscale distribution in images with the same or similar APL, grayscale aggregation occurs in high gradations and the quality improvement effect is small in low gradations.

APL is calculated as Equation 1 below.

Here, n is the number of pixels per screen.

In a one-frame image, if the grayscale of all pixel data is 33 and the number of pixels is 1920×1080, APL = 13 (%) as follows.

In FIG. 1, the left image and the right image partially have different gradation distributions, but the APL is the same as 13 (%). This is because the APL is simply calculated as the average value of the grayscale without considering the difference in the grayscale distribution in a single frame image.

The APL of the left image of FIG. 1 is

이다.

to be.

The APL of the right image of FIG. 1 is

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to be.

In FIG. 1, the left image and the right image are the same as APL = 13 (%), but the grayscale distributions are different from each other. When the gamma curve is modified by the gamma curve adjustment method, the gamma curve is applied to all pixels. Accordingly, when the same gamma curve is applied to an image having the same APL as in the left image and the right image of FIG. 1, the difference in brightness distribution of the image is not considered, and thus the visibility felt by the observer is deteriorated.

The present invention provides a display device capable of improving visibility by adjusting pixel data based on human brightness perception characteristics, and a method for improving visibility thereof.

The display device of the present invention includes a calculation unit, a gain selector, a PWM selector, a data modulator, and a display panel driver.

The calculation unit calculates an index representing the brightness of the brightest color in the pixel data of the input image. The gain selector selects a gain based on the above index. The PWM selector selects a PWM (Pulse width modulation) value according to the illuminance input from the illuminance sensor. The data modulator modulates the pixel data with the gain, and the display panel driver writes the modulated pixel data to pixels of the display panel to reproduce the input image on the display panel.

The method for improving visibility of the display device includes: calculating an index representing the luminance of the brightest color from pixel data of an input image; Selecting a gain based on the index; Selecting a PWM value according to the illuminance input from the illuminance sensor; Modulating the pixel data with the gain; And reproducing the input image on the display panel by writing the modulated pixel data to pixels of the display panel.

The present invention modulates pixel data by calculating an index (MCBL) representing the luminance of the brightest color from pixel data, and selecting a pixel gain based on the result. In addition, the present invention selects the optimum PWM value according to the illuminance. As a result, the present invention can improve visibility by optimizing the brightness of pixel data according to the gradation distribution even in an image with the same APL based on the brightness perception characteristics of humans, and by optimizing the PWM value according to the illuminance I can.

1 is a diagram showing an example of an image having different grayscale distributions and the same APL.
2 is a flow chart showing a method for improving visibility according to an embodiment of the present invention.
3 is a graph defining PWM for each illuminance.
4 is a graph defining k for each gray level of pixel data.
5 is a diagram showing MCBL for images having the same APL and different grayscale distributions.
6 shows a display device according to an exemplary embodiment of the present invention.
7 is a diagram showing in detail the apparatus for improving visibility of the timing controller shown in FIG. 6.
8 is a circuit diagram showing a pixel configuration of a liquid crystal display device.
9 is a circuit diagram showing a pixel configuration of an OLED display.

The display device of the present invention may be implemented as a flat panel display device such as a liquid crystal display device (LCD), an OLED display device, a plasma display panel (PDP), and a field emission display device (FED). This display device includes an illuminance sensor for real-time sensing of illuminance of an external environment. The illuminance refers to the illuminance of the external environment in which the display device is used.

The present invention does not adjust the gamma curve according to the illuminance, but adjusts the luminance of each of the pixels in consideration of the luminance level of the pixels felt by the observer when the illuminance changes.

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. The same reference numerals throughout the specification mean substantially the same constituent elements. In the following description, when it is determined that detailed descriptions of known functions or configurations related to the present invention may unnecessarily obscure the subject matter of the present invention, detailed descriptions thereof will be omitted.

Referring to FIG. 2, the method of improving visibility of the present invention receives data of an input image and determines illuminance using an illuminance sensor (S1 and S2).

In the method for improving visibility of the present invention, as shown in FIG. 3, an optimized PWM value is selected based on a preset PWM (Pulse width modulation) data for each illumination intensity. The PWM value is proportional to the illuminance and is set to the maximum value (MAX) in the outdoor environment illuminance. Accordingly, in the method for improving visibility of the present invention, a PWM value optimized for each illuminance is selected, and the PWM value is selected as the maximum value at illuminance equal to or higher than the outdoor environment illuminance (S3, S7). The PWM value for each illuminance shown in FIG. 3 may be implemented as a look-up table (LUT).

The PWM value controls the brightness of the pixels. The PWM value means the duty ratio (%) of the PWM signal. The PWM signal adjusts the brightness of the backlight light source of the liquid crystal display device or the voltage of the pixel power supply (ELVDD) in the OLED display device. The backlight light source of the liquid crystal display emits light at a lighting ratio defined by the duty ratio of the PWM signal. The higher the duty ratio of the PWM signal, the higher the backlight luminance. The maximum luminance of the pixels is proportional to the luminance of the backlight light source.

The pixel power EVDD of the OLED display device is commonly applied to all pixels. The pixel power EVDD is output from a power integrated circuit (PWIC). The power IC increases the voltage of the pixel power supply EVDD as the duty ratio of the PWM signal increases. The pixels of an OLED display emit light with higher luminance as the voltage of the pixel power supply (EVDD) increases.

In the method for improving visibility of the present invention, a PWM is selected according to illuminance and a Max Color Brightness Level (MCBL) is calculated in order to estimate the luminance level of pixels felt by a human. Expressed as a percentage, it is shown in Equation 2 below.

The pixels may include a red (R) subpixel, a green (G) subpixel, and a blue subpixel. MCBL is a new concept index that is calculated as the maximum color value from data of n (n is a positive integer) pixels and refers to the brightness of the brightest color among RGB colors of a pixel. MCBL reflects the difference in gradation distribution perceived by humans by considering the characteristics of human brightness perception, not APL. It should be noted that MCBL is not simply an average of gray scales, but a luminance level perceived by humans.

The method for improving visibility of the present invention derives an MCBL-based optimal pixel gain for visibility enhancement, and modulates pixel data with the pixel gain (S5). The pixel gain is multiplied by the pixel data of the input image. The pixel gain may be calculated as in Equation 3 based on the MCBL and k defined in FIG. 4. k is a brightness compensation adjustment parameter for the entire image and is set differently for each gray level in consideration of differences in human perception characteristics for each gray level. k has a value between 0 and 1.

In FIG. 4, parameters are defined as shown in Table 1 below. NP _LOW and NP _HIGH are the low and high gradation inflection points of the curve.

MCBL is high when the input image is generally bright. On the other hand, when the input image is generally dark, the MCBL is low. The k-curve of FIG. 4 is an optimal k value at which no other artifact occurs while the brightness of an image increases in a cognitive quality experiment. In FIG. 4, k is defined along a nonlinear curve that decreases as the gray level increases. 4 may be implemented as a lookup table. Meanwhile, k is not limited to FIG. 4. The curve of FIG. 4 may be changed according to the type of display device, driving characteristics, and manufacturer.

On the other hand, if the pixel gain is determined based on the APL rather than the brightness felt by humans, the effect of increasing the brightness perceived by the observer is small. On the contrary, the present invention can optimize the brightness of an image felt by an observer by determining a pixel gain based on MCBL, a new index for evaluating the brightness felt by a human.

In the method for improving visibility, the modulated pixel data is written to pixels of the display panel to reproduce an input image on the display panel (S6).

As shown in FIG. 1, when the MCBL of the left image and the right image are calculated with the same APL = 13 (%), but the grayscale distribution is mutually, as shown in FIG. 5, the MCBL of the left image is 18 (%) and the MCBL of the right image is 71 (%). to be. MCBL is calculated as a higher value as the color area in the image is brighter. In a one-frame image, if the grayscale of all pixel data is 33 and the number of pixels is 1920×1080, the MCBL is 13 (%) equal to the APL if the grayscale values of each RGB are the same as shown below.

In FIG. 1, the left image has a higher grayscale value of green data than other colors. Therefore, as shown in FIG. 5, the MCBL of the left image is 18 (%).

In FIG. 2, the image on the right has a higher grayscale value of yellow data compared to other colors. Therefore, as shown in FIG. 5, the MCBL of the right image is 71 (%).

As can be seen from the above, the MCBL can distinguish between the presence or absence of a partially bright image in an image having the same APL and its level. In the method for improving visibility of the present invention, since an image of the same APL can be classified in consideration of human brightness perception characteristics, an optimum pixel gain can be derived from each of the left image and the right image.

6 shows a display device according to an exemplary embodiment of the present invention.

Referring to FIG. 6, the display device of the present invention includes a display panel 100, a display panel driver that writes pixel data of an input image to a pixel array of the display panel 100, and an illuminance sensor (not shown).

The display panel driver includes a data driver 102, a gate driver 104, a timing controller (TCON) 110, and the like.

A plurality of data lines 11 and a plurality of scan lines (or gate lines) 12 cross the pixel array of the display panel 100. The pixel array of the display panel 100 includes pixels that are arranged in a matrix form to display an input image. Each of the pixels includes an R sub-pixel, a G sub-pixel, and a B sub-pixel. Each of the pixels may further include a white (W) sub-pixel.

The data driver 102 converts the pixel data received from the timing controller 110 into an analog gamma compensation voltage, generates a data voltage, and outputs the data voltage to the data lines 11. Pixel data input to the data driver 102 is digital video data of an input image.

The gate driver 104 supplies scan pulses (or gate pulses) synchronized with the output voltage of the data driver 102 to the scan lines 12 under the control of the timing controller 110. The gate driver 104 sequentially selects pixels to which data is written by sequentially shifting the scan pulses in line units.

The timing controller 110 receives pixel data of an input image and timing signals synchronized therewith from a host system (not shown). The timing controller 110 selects the optimum PWM and pixel gain according to the illuminance using the visibility improving device as shown in FIG. 7. PWM adjusts the backlight brightness of a liquid crystal display device or the pixel power supply (ELVDD) of an OLED display device according to the illuminance. The pixel gain optimizes the luminance of the pixel data felt by the observer for each illuminance. The timing controller 110 transmits the pixel data R'G'B' modulated by the visibility improving device to the data driver 102. The apparatus for improving visibility may be built into the timing controller 110.

The timing controller 110 controls operation timings of the data driver 102 and the gate driver 104 based on timing signals input in synchronization with pixel data of an input image. The timing signals include a vertical synchronization signal (Vsync), a horizontal synchronization signal (Hsync), and a data enable signal (DE). The timing controller 110 generates a data timing control signal and a gate timing control signal based on the timing signals to synchronize the data driving unit 102 and the gate driving unit 104. The data timing control signal defines the operation timing and output timing of the data composition unit 102. The gate timing control signal defines the operation timing and output timing of the gate driver 104.

The timing controller 110 may control the backlight light source and the pixel power ELVDD based on the PWM selected according to the MCBL.

The host system may be implemented as any one of a TV (Television) system, a set-top box, a navigation system, a DVD player, a Blu-ray player, a personal computer (PC), a home theater system, and a phone system.

The method for improving visibility shown in FIG. 2 may be implemented in hardware as shown in FIG. 7.

Referring to FIG. 7, the apparatus for improving visibility includes a data receiving unit 72, an MCBL calculating unit 74, a gain selecting unit 76, a PWM selecting unit 78, a data modulating unit 80, and a data transmitting unit 82. Include.

The data receiver 72 receives pixel data (R, G, B) of an input image and timing signals (Vsync, Hsync, DE) from the host system. The pixel data is delayed by the operation time of the MCBL calculation unit 74 and the gain selection unit 76. The data receiving unit 72 delays the pixel data and timing signals input to the data modulating unit 80 to synchronize the MCBL calculation unit 74, the gain selector 76, and the data modulator 80.

The MCBL calculator 74 calculates the MCBL of pixel data as shown in Equation 1. The gain selector 76 selects a pixel gain based on the MCBL. The PWM selector 78 selects a PWM value according to the illuminance value received from the illuminance sensor and outputs a PWM signal.

The data modulator 80 outputs the modulated pixel data R'G'B' by multiplying the pixel data by a pixel gain. The data transmission unit 82 transmits the pixel data R'G'B' and a data timing control signal to the data driver 102.

As shown in FIG. 8, the pixels of the OLED display include a switch TFT (SWTFT), a driving TFT (DRTFT), an organic light emitting diode (OLED), a storage capacitor (Cst), and the like.

The switch TFT (SWTFT) supplies the data voltage (DATA) to the gate of the driving TFT (DRTFT) in response to the gate pulse. The driving TFT (DRTFT) is connected between the power line to which the pixel power source ELVDD is supplied and the OLED and controls the current flowing through the OLED according to the data voltage applied to its gate. OLED is a hole injection layer (HIL), a hole transport layer (HTL), an emission layer (EML), an electron transport layer (ETL), and an electron injection layer (EIL). ) Has a structure in which organic compound layers such as are stacked. OLED emits light when electrons and holes combine in a light emitting layer. The storage capacitor Cst maintains the gate-source voltage Vgs of the driving TFT DRTFT for one frame period.

The pixel may further include an internal compensation circuit. The internal compensation circuit includes one or more switch TFTs and one or more capacitors to initialize the gate of the driving TFT DRTFT, and then sense the threshold voltage and mobility of the driving TFT DRTFT to compensate the data voltage DATA. This compensation circuit (PIXC) can be applied to any known one.

The pixel power ELVDD is generated from a PWM-controlled power IC to adjust the luminance of the pixel according to the illuminance.

As shown in FIG. 9, the pixels of the liquid crystal display include a liquid crystal cell Clc, a storage capacitor Cst, a thin film transistor (TFT), and the like. The liquid crystal cell Clc uses liquid crystal molecules driven by an electric field between a pixel electrode to which a data voltage (DATA) is applied through a TFT and a common electrode to which a common voltage (Vcom) is applied to delay the phase of light according to data. Adjust the transmittance. The storage capacitor Cst maintains the voltage of the liquid crystal cell Clc for one frame period. The TFT is turned on in response to a gate pulse (or scan pulse, SCAN) from the gate line 12 to transfer the data voltage from the data line 11 to the pixel electrode of the liquid crystal cell Clc. Supply.

The liquid crystal display may be implemented in any known liquid crystal mode such as a twisted nematic (TN) mode, a vertical alignment (VA) mode, an in plane switching (IPS) mode, and a fringe field switching (FFS) mode. In addition, the liquid crystal display device may be implemented in various forms such as a transmissive liquid crystal display, a transflective liquid crystal display, and a reflective liquid crystal display. A transmissive liquid crystal display device or a transflective liquid crystal display device includes a backlight unit and a backlight driver.

The backlight unit may be implemented as an edge type backlight unit or a direct type backlight unit. The backlight unit is disposed under the rear surface of the display panel 100 of the liquid crystal display device and irradiates light to the display panel 100. The backlight driver supplies current to light sources of the backlight unit to emit light. Light sources may be implemented with a light emitting diode (LED). The backlight driver adjusts the luminance of light sources with PWM control selected according to the illuminance.

It will be appreciated by those skilled in the art through the above description that various changes and modifications can be made without departing from the technical idea of the present invention. Therefore, the technical scope of the present invention should not be limited to the content described in the detailed description of the specification, but should be determined by the claims.

100: display panel 102: data driver
104: gate driver 106: timing controller
72: data receiving unit 74: MCBL calculation unit
76: gain selector 78: PWM selector
80: data modulator 82: data transmitter

Claims (7)

A calculation unit that calculates an index representing the luminance of the brightest color in the pixel data of the input image;
A gain selector for selecting a gain based on the index;
A PWM selector for outputting a PWM signal by selecting a pulse width modulation (PWM) value according to the illuminance input from the illuminance sensor;
A data modulator that modulates the pixel data with the gain; And
A display panel driver for reproducing the input image on the display panel by writing modulated pixel data to pixels of the display panel,
The display device in which the index is an MCBL defined by the following equation.

delete The method of claim 1,
A display device in which the gain is calculated by the following equation.

Here, k is a compensation parameter defined by a nonlinear curve that decreases as the gray level increases. The method of claim 3,
A display device in which the PWM value is selected as the maximum value in the illuminance of an outdoor environment. The method of claim 4,
A display device in which the PWM signal controls backlight brightness of a liquid crystal display. The method of claim 4,
A display device in which the PWM signal controls pixel power of an organic light emitting diode display. Calculating an index representing the luminance of the brightest color in the pixel data of the input image;
Selecting a gain based on the index;
Selecting a pulse width modulation (PWM) value according to the illuminance input from the illuminance sensor;
Modulating the pixel data with the gain; And
Reproducing the input image on the display panel by writing modulated pixel data to pixels of the display panel,
A method for improving visibility of a display device in which the index is an MCBL defined by the following equation.

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