KR20030038897A - Adaptive gamma curve correction apparatus and method for a liquid crystal display - Google Patents

Abstract

PURPOSE: A correcting device of an adaptive gamma curve for a liquid crystal display and a method thereof are provided to improve the performance of the liquid crystal display according to various display modes or conditions by selecting and switching the gamma curve optimally in the display mode. CONSTITUTION: An adaptive gamma curve correcting device includes a controller(32) receiving an image signal and generating display data and scan signals; a data driving unit(26) receiving the display data signal from the controller and generating the data voltage to the image gray level to drive the supply source of a thin film transistor array of a liquid crystal display panel(28); a scan driving unit(24) receiving the scan signal from the controller, and generating the scan voltage for driving the gate of the thin film transistor array; backlight(29) projected to the liquid crystal display panel; and reflection and transmission display mode R-V and T-V curves(36,38). The gamma curve correcting device supplies the gamma curve to the data driving unit to correct nonlinearity of the liquid crystal display panel.

Description

ADAPTIVE GAMMA CURVE CORRECTION APPARATUS AND METHOD FOR A LIQUID CRYSTAL DISPLAY}

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to liquid crystal displays (LCDs), and more particularly, to an adaptive gamma curve correction device and method for LCDs having multiple display modes or various display states.

LCD comes in two types: reflective and transmissive. In a reflective LCD, the ambient light 10 passes through the LCD 12 at the front of the LCD and is reflected back through the LCD 12 by the reflector 14 so that the display light is displayed to the viewer as shown in FIG. 1A. do. If the ambient light 10 is weak or the ambient environment is not bright enough for the observer, clear image display is not obtained. In addition, if the modulation effect in the LCD is weak, the ambient light intensity for clear image display is more strictly demanded. As shown in FIG. 1B, the transmissive LCD can overcome the disadvantages of low light intensity with the backlight 18 provided by the light source. In a transmissive LCD, the backlight 18 passes through the LCD 12 to display the display light 16 on the viewer. However, the light source providing the backlight 18 consumes power. It also has the drawback of reducing the size and weight of the LCD array. Moreover, when the environment is bright, the transmissive LCD cannot save power for the backlight as in a reflective LCD. As a solution, a transflective LCD combining a reflective LCD and a transmissive LCD has been proposed. In a transmissive LCD, as shown in FIG. 1C, ambient light 10 passing through the LCD 12 is partially reflected by the transducer 20, which also allows passage of the backlight 18. The transparent LCD has two display modes, a reflective display mode and a transmissive display mode. If the ambient light 10 is strong enough, power to the backlight 18 can be saved. In contrast, the backlight source is turned on when the environment is dark.

However, introducing a transparent LCD has a problem in that a reflective LCD and a transmissive LCD have different optical characteristics. A typical display system is shown in FIG. 2, in which a controller 22 for receiving an image signal has a scan driver 24 for driving the LCD panel 28 and the display data signal D transmitted to the data driver 26. Generates a scan signal S sent to. In order to correct the nonlinearity of the transmittance / reflectivity of the driving voltage of the LCD panel 28, the gamma curve correcting apparatus is supplied to the data driver 26 to supply correction data called the gamma curve 30 depending on the LCD panel 28. Is provided. Unfortunately, if both types of LCDs are optimized, the gamma curves for reflective LCDs and the gamma curves for transmissive LCDs are different. When the optical effect or performance is optimized in the transmissive LCD, the gamma curve for the image gray level in the reflective display mode is different from the gamma curve for the image gray level in the transmissive display mode. As a result, the display quality deteriorates in the transparent LCD.

In addition, the performance of the LCD with a pre-fixed gamma curve is also worsened because the optical properties of the liquid crystal depend on the temperature when the ambient temperature changes. Therefore, the gamma curve correction device of the prior art is not adaptable to ambient conditions.

Accordingly, an apparatus and method for adaptive gamma curve correction for LCDs having multiple display modes or various display states are desirable.

It is an object of the present invention to provide adaptive correction for gamma curves provided in LCDs with multiple display modes or various display states.

1A, 1B, 1C show three different types of LCDs;

2 is a block diagram of an exemplary display system for an LCD;

3 is a block diagram of a display system for an LCD having multiple display modes according to the present invention;

4 is a diagram showing an R-V curve and a T-V curve for a gamma curve in an LCD display system according to the present invention;

5 is a circuit diagram of a first embodiment of a gamma curve correction device according to the present invention;

6 is a block diagram of a second embodiment of a gamma curve correction device according to the present invention;

7 is a block diagram of a third embodiment of a gamma curve correction device according to the present invention; And

8 is a block diagram of a display system for LCD with thermal adaptation according to the present invention.

* Explanation of symbols for the main parts of the drawings

24: scan driver 26: data driver

28: LCD panel 29: backlight

32 controller 36 R-V curve

38: T-V curve 39: light sensor

In an LCD having multiple display modes or various display states according to the present invention, each gamma curve is prepared for each display mode or state, and the corresponding gamma curve is provided to the LCD when the display mode or state is switched.

In a hardware related embodiment, two voltage dividers are employed to generate the R-V curve for the reflective display mode and the T-V curve for the transmissive display mode selected by the switch controlled by the mode signal to provide an appropriate gamma curve. In the digital related embodiment, a memory is employed to store the digital display RV curve for the reflection display mode and the TV curve for the transmission display mode, and the addresser is controlled by the mode signal to read out an appropriate gamma curve from the memory. . In a software related embodiment, the memory stores parameters corresponding to the RV curve for the reflective display mode and the TV curve for the transmissive display mode, wherein the gamma curve generator controlled by the mode signal is based on the appropriate parameters stored in the memory. Calculate

In a temperature adaptable embodiment, thermal couples are employed to sense the ambient temperature and to select an appropriate gamma curve from a plurality of gamma curves prepared at various temperature conditions.

By preparing a plurality of gamma curves prepared in the multiple display mode or state in advance, the present invention can make the LCD suitable for display execution by switching the gamma curve.

The invention will be more clearly understood by the embodiments described below with reference to the accompanying drawings.

In the display system of the present invention, FIG. 3 shows a block diagram for a transmissive LCD similar to the conventional one shown in FIG. The controller 32 receives the image signal to generate the display data signal D and the scan signal S. FIG. The data driver 26 receives the display data signal D from the controller 32 and sets the data voltage for the image gray level to drive a source of a thin film transistor (TFT) array (not shown) of the LCD panel 28. Create On the other hand, the scan driver 24 receives the scan signal S from the controller 34 and generates a scan voltage SV for the scan line to drive the gate of the TFT array in the LCD panel 28. The backlight 29 is prepared to be projected onto the LCD panel 28 for the transmissive display mode. To correct the nonlinearity of the LCD panel 28, the gamma curve correction device 34 supplies the gamma curve γ to the data driver 26. However, two gamma curves are prepared by the gamma curve correction device 34, which are the RV curve 36 for the reflection display mode and the TV curve 38 for the transmission display mode, and the output of the gamma curve correction device 34. γ is converted to the RV curve 36 and the TV curve 38. The selection of the R-V curve 36 and the T-V curve 38 is controlled by the mode signal M from the controller 32. When the LCD panel 28 is operated in the reflective display mode, the controller 32 selects the RV curve 36 in the gamma curve corrector 34 by the mode signal M and supplies it to the data driver 936. do. When the transmissive display mode is desired, the controller 32 turns on the backlight 29 and switches the gamma curve γ to the TV curve 38 in the gamma curve correction device 34 by the mode signal M. do. In this embodiment, the mode signal M is also used to turn the backlight 29 on / off, so that the gamma curve correction device 34 is switched from the reflective display mode to the transmissive display mode. Is switched to the TV curve 38 simultaneously.

To further enhance the automatic adaptability, the optical sensor 39 is used to monitor the light intensity of the surrounding environment, such as the manner in which the transmissive display mode is operated by the optical sensor 39 according to one or more predetermined thresholds. When the environment is cloudy, the signal sensed by the sensor 39 reaches a predetermined threshold, so that the illuminance is switched to the transmissive display mode in which the backlight 29 is turned on and the gamma curve correction is switched to the TV curve 38. Generate a notification signal (I). The optical sensor 38 may directly turn on the backlight 29 to trigger the mode signal M by another signal, or the optical sensor 39 may turn on the backlight 29 to simultaneously switch to the TV curve 38. The controller 32 can be operated to trigger the mode signal M. In addition, the threshold value for switching the display mode may be designed in consideration of the ambient illumination and its change over time.

For a typical implementation, FIG. 4, which provides the R-V curve 36 and the T-V curve 38 measured on the actual transflective LCD, shows their features and the distinction between them. As is well known in the art, the reflectance is less than the transmittance for each particular voltage in the transition region between the black and white display voltage levels. This difference between the R-V curve 36 and the T-V curve 38 will lower the display performance even if each gamma curve is based on a different display mode. Therefore, display performance cannot be improved if only one gamma curve is used for both the reflective display mode and the transmissive display mode.

The hardware approach to gamma curve correction device 34 is shown in FIG. In this apparatus, the two voltage dividers 40 and 42 for the reflective display mode and the transmissive display mode are connected in parallel and have two end nodes connected to the high voltage source Vh and the low voltage source Vl, respectively. . In other embodiments, the high and low voltage sources may be different for voltage dividers corresponding to different display modes. In the embodiment of the present invention, the voltage divider 40 for the reflective display mode is composed of five resistors Rr1, Rr2, Rr3, Rr4, Rr5 connected in series, and the voltage divider 42 for the transmissive display mode is It consists of five resistors (Rt1, Rt2, Rt3, Rt4, Rt5) connected in series. Both sides of the voltage divider 40, 42 are tapered to provide a gamma curve voltage coupled to the switches SW1, SW2, SW3, SW4. The switches SW1-SW4 are controlled by the mode signal to simultaneously switch the voltage divider 40 or the voltage divider 42. Thus, each of the two gamma curves can be controlled to be provided for the reflective display mode and the transmissive display mode.

6 shows another embodiment of the present invention for supplying a digital gamma curve. The R-V curve 46 and the T-V curve 48 are stored in the read memory (RAM) 44 in a digital form in which values of both the gamma curves 36 and 38 are previously sampled and stored in the ROM 44. The addresser 50 is controlled by the mode signal M to generate an appropriate address ADDR for reading the data of the R-V curve 46 or the T-V curve 48 to be output. If necessary, the digital gamma curve γ 'from the ROM 44 can be converted into an analog voltage by digital with an analog converter (DAC) 52. In this way, the gamma curve to be supplied is retrieved from a look-up table suitable for the digital display system as a whole.

A software related embodiment of the present invention is shown in FIG. In this approach, the basic parameters for the R-V curve 56 and the T-V curve 58 are stored only in the ROM 54, and the amount of storage can be reduced. Gamma curve generator 60 is controlled by mode signal M to get the appropriate parameter P from ROM 54. In gamma curve generator 60, processing is executed to calculate a gamma curve value based on the imported parameter. The software in gamma curve generator 60 may be updated for other systems. As in the prior art, the actual gamma curve can be accessed by a limited method, so only certain point data and equations are required for parameters that can simplify the calculations performed by the gamma curve generator 60. As shown in Figure 4, the curve can be derived directly from the actual R-V curve and the T-V curve.

8 shows a block diagram of a display system for an LCD with temperature adaptation. In this system, the reflective LCD panel 62 is optimized by the gamma curve correction device 66 switched by the controller 64 with the support of the thermal couple 74. The gamma curve corrector 66 is a high temperature (HT) gamma curve 68, an intermediate temperature (MT) gamma curve 70 and a low temperature (LT) gamma curve (for the LCD panel 62 operating in different temperature ranges). It is prepared to have a gamma curve according to the three temperatures of 72). Thermal couple 74 monitors the ambient temperature and generates a notification signal T to controller 64 to select the appropriate gamma curve from gamma curves 68, 70, 72. In another embodiment, gamma curve correction device 66 may be switched directly by column couple 74 with signal T acting as mode signal M. As shown in FIG.

Multiple gamma curves are reflective LCD, transmissive LCD, partially reflective LCD, transflective LCD, twisted nematic (TN) LCD, super-twisted nematic (STN) LCD, thin film transistor (TFT) LCD, thin film diode (TFD) ) It is applied to LCD, metal insulation metal (MIM) LCD and various processing temperature.

The embodiments and drawings are described by way of example only, and various modifications and changes may be made by those skilled in the art to which the present invention pertains without departing from the technical spirit of the present invention. All changes and modifications within the spirit of the present invention are defined by the appended claims.

As described above, according to the present invention, it is possible to provide adaptive correction for a gamma curve provided to an LCD having multiple display modes or various display states.

Claims (38)

An LCD panel having a plurality of display modes or states; A plurality of voltage dividers each corresponding to a plurality of gamma curves for the plurality of display modes or states; And And a means controlled by a signal mode to switch between the plurality of voltage dividers to provide an adaptive gamma curve for the LCD panel. The method of claim 1, And said LCD panel is selected from the group of reflective LCD, transmissive LCD, partially reflective LCD, and transflation LCD. The method of claim 1, Adaptive gamma curve correction device for LCD, characterized in that the LCD panel is selected from the group of TN-LCD and STN-LCD. The method of claim 1, And said LCD panel is selected from the group of TFT-LCD, TFD-LCD, and MIM-LCD. The method of claim 1, And said display mode comprises a reflective display mode and a transmissive display mode. The method of claim 1, And the display state includes various temperature states. The method of claim 6, And a thermal couple for monitoring an ambient temperature to automatically switch between the plurality of gamma curves corresponding to the various temperature conditions. The method of claim 1, Adaptive gamma curve correction device for an LCD, characterized in that it further comprises a backlight projected on the LCD panel. The method of claim 8, And an optical sensor for monitoring the ambient light intensity to automatically turn on / off the backlight according to at least one threshold value corresponding to the ambient light intensity. The method of claim 7, wherein And the mode signal is derived from a switch signal for turning on / off the backlight. An LCD panel having a plurality of display modes or states; Means for storing a plurality of gamma curves for the plurality of display modes or states; And And an addresser controlled by a mode signal to read a digital gamma curve among the plurality of gamma curves. The method of claim 11, And said LCD panel is selected from the group of reflective LCD, transmissive LCD, partially reflective LCD, and transflation LCD. The method of claim 11, Adaptive gamma curve correction device for LCD, characterized in that the LCD panel is selected from the group of TN-LCD and STN-LCD. The method of claim 11, And said LCD panel is selected from the group of TFT-LCD, TFD-LCD, and MIM-LCD. The method of claim 11, And said display mode comprises a reflective display mode and a transmissive display mode. The method of claim 11, And the display state includes various temperature states. The method of claim 16, And a thermal couple for monitoring an ambient temperature to automatically switch between the plurality of gamma curves corresponding to the various temperature conditions. The method of claim 11, Adaptive gamma curve correction device for an LCD, characterized in that it further comprises a backlight projected on the LCD panel. The method of claim 18, And an optical sensor for monitoring the ambient light intensity to automatically turn on / off the backlight according to at least one threshold value corresponding to the ambient light intensity. The method of claim 17, And the mode signal is derived from a switch signal for turning on / off the backlight. The method of claim 11, And an analog converter for converting the digital gamma curve into an analog signal. An LCD panel having a plurality of display modes or states; Means for storing a plurality of gamma curve parameters for the plurality of display modes or states; And And a gamma curve generator controlled by a mode signal to generate a gamma curve signal based on the plurality of gamma curve parameters. The method of claim 22, And said LCD panel is selected from the group of reflective LCD, transmissive LCD, partially reflective LCD, and transflation LCD. The method of claim 22, Adaptive gamma curve correction device for LCD, characterized in that the LCD panel is selected from the group of TN-LCD and STN-LCD. The method of claim 22, And said LCD panel is selected from the group of TFT-LCD, TFD-LCD, and MIM-LCD. The method of claim 22, And said display mode comprises a reflective display mode and a transmissive display mode. The method of claim 22, And the display state includes various temperature states. The method of claim 27, And a thermal couple for monitoring an ambient temperature to automatically switch between the plurality of gamma curves corresponding to the various temperature conditions. The method of claim 22, Adaptive gamma curve correction device for an LCD, characterized in that it further comprises a backlight projected on the LCD panel. The method of claim 29, And an optical sensor for monitoring the ambient light intensity to automatically turn on / off the backlight according to at least one threshold value corresponding to the ambient light intensity. The method of claim 28, And the mode signal is derived from a switch signal for turning on / off the backlight. Preparing an LCD panel having a plurality of display modes or states; Preparing a plurality of gamma curves for the plurality of display modes or states; And And switching between the plurality of gamma curves to supply a gamma curve signal. The method of claim 32, And monitoring an ambient temperature to automatically switch between the plurality of gamma curves corresponding to various temperature conditions. The method of claim 32, Adaptive gamma curve correction method for the LCD further comprises the step of projecting a backlight on the LCD panel. The method of claim 34, wherein And monitoring said ambient intensity intensity to automatically turn on / off said backlight depending on at least one threshold value corresponding to ambient light intensity. The method of claim 32, Storing the plurality of gamma curves and reading one of the plurality of gamma curves. The method of claim 36, And converting one of the plurality of gamma curves into an analog gamma curve signal. The method of claim 32, Storing a plurality of gamma curve parameters and generating the gamma curve signal based on one of the plurality of gamma curve parameters.