JP2007148331A - Liquid crystal display element and its driving method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a liquid crystal display element which has excellent display quality and can make power consumption of a lighting device less than that in the conventional art, and its driving method. <P>SOLUTION: The driving method of the liquid crystal display element includes: a first stage of performing degamma processing of image data; a second stage of detecting a value P<SB>n</SB>obtained by finding maximum values by frames as to the degamma-processed data and smoothing the maximum values; a third stage of processing the degamma-processed data so that P<SB>n</SB>reaches transmissivity of 100%; and a fourth stage of performing gamma processing of the degamma-processed data to restore the original image data. The image data obtained at the fourth stage are input to a driving circuit. Further, light emission luminance of the lighting device is controlled from data of P<SB>n</SB>detected at the second stage so that the lighting device has luminance corresponding to P<SB>n</SB>. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a liquid crystal display element including a lighting device and a driving method thereof.

  In general, a liquid crystal display element is composed of a very thin liquid crystal layer of about several μm oriented in a predetermined direction, a pair of thin substrates sandwiching the liquid crystal layer, and a polarizer and an analyzer sandwiching the substrate. And a pair of polarizing plates. A pair of transparent electrodes facing each other with the liquid crystal layer interposed therebetween are formed on the substrate. When a voltage is applied to the transparent electrode, an electric field is generated between the electrodes, and the alignment of liquid crystal molecules changes. Thereby, the amount of light transmitted through the liquid crystal display element can be changed.

  Such a liquid crystal display element can be easily reduced in thickness and weight by selecting components, and can be driven at a low voltage. Therefore, liquid crystal display elements such as televisions, instrument panels for vehicles, and cellular phones are used. It is widely used for display elements for portable information terminals.

  The liquid crystal display element is mainly configured by an illumination device such as a backlight or a front light, a liquid crystal panel, and a drive circuit. The illumination device illuminates the liquid crystal panel from the viewing direction or the opposite direction. On the other hand, the drive circuit applies a voltage to the liquid crystal layer via the electrodes in the liquid crystal panel to change the alignment of the liquid crystal. As a result, the light transmission characteristics determined by the product (Δn · d) of the refractive index anisotropy (Δn) of the liquid crystal and the liquid crystal layer thickness (d) are different between the portion where the voltage is applied and the portion where the voltage is not applied. Occurs. While the liquid crystal display element is in operation, the lighting device is lit continuously, but this difference in the transmission characteristics of the light transmitted through the liquid crystal layer creates light and darkness on the liquid crystal panel. Desired display.

  The luminance of such a liquid crystal display element is determined by the transmittance of the liquid crystal panel and the brightness of the illumination device. Here, the transmittance of the liquid crystal panel is determined by the mode of the liquid crystal, the characteristics of the polarizing plate, the characteristics of the color filter, and the like. Therefore, it is easiest to brighten the lighting device in order to improve the luminance. For this reason, in recent years, development of lighting devices with low power consumption and high emission luminance has been promoted.

  However, when the light emission luminance of the lighting device is increased in order to improve the luminance, there is a problem that the black color becomes bright and the display quality of the image decreases.

To solve this problem, the peak level V _p is detected at a constant period for the video signal V _in supplied from the outside, and the gain G _s = V _p / V ₀ (V ₀ : video signal V _in is calculated from this value. (Standard peak level) is calculated, and then the video signal level is modulated as V _c = V _in / G _s (see Patent Document 1). In this method, the spatial modulation element is driven by the modulated video signal V _c , and the light output level of the light emitting unit is set to L _out = G _s × L _o (L _o : reference light output level of the light emitting unit). Then, it is said that the display quality of the image can be improved by repeating this series of processes at regular intervals.

JP-A-6-102484

  However, the method described in Patent Document 1 has a problem that the screen flickers.

  On the other hand, when an image such as a movie is displayed by a liquid crystal display element, the screen generally has a dark tone. In such a case, the lighting device is always lit at 100% output, but the screen is darkened by blocking the light of the lighting device by liquid crystal. For this reason, there also existed a problem that the illuminating device wasted power consumption.

  The present invention has been made in view of these problems. That is, an object of the present invention is to provide a liquid crystal display element that is excellent in display quality and can reduce the power consumption of a lighting device as compared with the related art, and a driving method thereof.

  Other objects and advantages of the present invention will become apparent from the following description.

  According to a first aspect of the present invention, there is provided a liquid crystal panel driven by a drive circuit, an illuminating device for irradiating the liquid crystal panel with predetermined light, an illuminating device driver for driving the illuminating device, and degamma processing of image data. Then, after detecting the maximum value for each predetermined period and processing the data so that the maximum value becomes 100% transmittance, the image data processing means returns the original image data by gamma processing the de-gamma processed data A liquid crystal display element, wherein the image data output from the image data processing means is input to the drive circuit, and the maximum value data detected by the image data processing means is input to the driver for the illumination device. About.

According to a second aspect of the present invention, in a method for driving a liquid crystal display element having a liquid crystal panel driven by a driving circuit and an illuminating device that irradiates the liquid crystal panel with predetermined light, a first degamma process is performed on image data. A second step of obtaining a maximum value for each frame of the degamma processed data and detecting a value P _n obtained by smoothing the maximum value, and for the degamma processed data, P a third step of processing data so that _n becomes 100% transmittance, and a fourth step after the third step, gamma processing the de-gamma processed data to return it to the original image data The image data obtained in the fourth step is input to the driving circuit, and the lighting device is configured so that the lighting device has a luminance corresponding to P _n from the data of P _n detected in the second step. Luminance brightness The present invention relates to a method for driving a liquid crystal display element.

In the second aspect of the present invention, the smoothing may be a method of recursively processing the maximum value. Further, the smoothing may be a method of calculating an average value for a plurality of frames with respect to the maximum value. In this case, the plurality of frames are preferably 32 or more frames.
The light emission luminance of the lighting device is preferably controlled according to a smooth curve connecting a predetermined minimum luminance to a maximum luminance. In this case, when the maximum luminance is 100, the minimum luminance is preferably in the range of 25-50.

  According to the first aspect of the present invention, the image data is degamma processed to detect the maximum value for each predetermined period, and after the data processing is performed so that the maximum value becomes the transmittance of 100%, the degamma processing is performed. By providing image data processing means for performing gamma processing on the data and returning it to the original image data, it is possible to provide a liquid crystal display element that is excellent in display quality and can reduce the power consumption of the lighting device as compared with the conventional case.

Further, according to the second aspect of the present invention, the maximum value for each frame is obtained for the degamma processed data, the value P _n obtained by smoothing the maximum value is detected, and the lighting device changes to P _n . Since the light emission luminance of the lighting device is controlled so as to achieve a corresponding luminance, it is possible to provide a method for driving a liquid crystal display element that is excellent in display quality and that can reduce power consumption of the lighting device as compared with the related art.

  As described above, in the conventional liquid crystal display element, an image having a dark color tone is displayed by blocking the light of the illumination device with the liquid crystal. In this case, the light emission luminance of the lighting device is not changed. Therefore, the present inventor has considered that when the image is dark, the display is performed by improving the transmittance of the liquid crystal while lowering the light emission luminance of the lighting device accordingly. According to this method, it is possible to reduce the power consumption of the lighting device without degrading the display quality.

  FIG. 1 is a flowchart showing a method for driving a liquid crystal display element in the present embodiment. In this embodiment, the case where a backlight is used as the lighting device is illustrated.

  As shown in FIG. 1, first, degamma processing is performed on image data in order to facilitate data processing (step 1). Specifically, the data is converted so that the image data and the luminance are proportional. In this embodiment, for example, when the input signal is 6 bits for each color of R, G, and B, the degamma processing can be performed with 6 bits or more and 10 bits or less.

Next, a maximum value for each frame is obtained for the degamma processed data, and a value P _n obtained by smoothing the maximum value is detected (step 2).

Next, the data after de-gamma process, Step 2 P _n detected by the data processing so that the transmittance of 100% (step 3).

  Thereafter, the data is gamma processed to return to the original image data (step 4), and this data is sent to the drive circuit for controlling the liquid crystal panel (step 5).

On the other hand, the light emission luminance of the backlight is controlled from the data of _Pn detected in step 2 so that the backlight has luminance corresponding to _Pn (step 6). In the present embodiment, a minimum value (minimum luminance) of luminance when dimming the backlight is obtained, and linear interpolation is performed from this value to the maximum luminance of the backlight (luminance corresponding to 100% output), It is preferable to modulate the luminance of the backlight according to the obtained curve.

  By repeating Steps 1 to 6, the same video as that obtained from the image data that is not subjected to these processes can be displayed with the power consumption of the backlight suppressed.

In the present embodiment, _Pn is detected from the transmitted image data without using a memory, and the previously detected data of _Pn is applied to the next transmitted image data. Can do. It is also possible to use the memory to detect the _Pn of the transmitted image data, temporarily store it in the memory, and apply the detected _Pn data to the data read from the memory.

P _n in step 2 is preferably determined as follows.

  First, the maximum value for every fixed period is calculated | required about the value by which the degamma process was performed (step 2011). Here, the fixed period refers to a period corresponding to one-screen display, and in this embodiment refers to one frame period.

Subsequently, _Pn is calculated | required from Formula (1) by making the calculated | required maximum value into M (step 2012-2013). Here, P _n is the maximum value used in the nth frame. It should be noted that the value calculated by Equation (1) is rounded up to the nearest decimal point. The obtained value of P _n is stored in the memory and used when calculating P _n in the next frame.

P _n = (1−α) M + αP _n−1 (0 ≦ α <1) (1)

  The greater the value of α, the greater the degree of smoothing, so that the flicker on the screen can be reduced. In the present embodiment, 0.80 ≦ α is preferable, 0.92 ≦ α is more preferable, and 0.97 ≦ α is further preferable. α = 0.80 is an allowable level of flicker. If the value of α is 0.92 or more, it can be set to a level with almost no flicker. Further, if the value of α is 0.97 or more, the flicker can be at a level where it cannot be visually recognized at all.

P _n can also be determined as in step 2 ′ of FIG. Note that step 1 and steps 3 to 6 in FIG. 2 are the same as those described in FIG.

  First, with respect to the value subjected to the degamma process, a maximum value for each fixed period is obtained (step 2021). Here, the fixed period refers to a period corresponding to one-screen display, and in this embodiment refers to one frame period. In addition, in FIG. 2, memory 1 → memory 2 → memory 3 →... → memory n, for each frame, data in memory 1 is moved to memory 2 and data in memory 2 is moved to memory 3. Eventually, the data is transferred to the memory n.

Then, by calculating the average value for each of a plurality of frames for the maximum value obtained, it is possible to determine the value of _{P n} (step 2022 to 2025).

Thus, in the present embodiment, the value of P _n obtained by smoothing can be obtained by a method of recursively processing the maximum value for each frame, as shown in FIG. As shown in FIG. 2, the maximum value for each frame can be obtained by a method of calculating an average value for each of a plurality of frames. In addition, according to the method of recursively processing, since a division process is not required, it can be set as a simpler circuit structure compared with the method of calculating an average value. In the case of recursive processing, the degree of smoothing can be changed simply by changing the value of α. For example, if α is increased, the degree of smoothing can be increased. On the other hand, when calculating the average value, the degree of smoothing can be changed by changing the number of frames to be averaged. However, in this case, since a different circuit is required depending on the number of frames, the circuit scale is changed. For example, when the number of frames is changed to 3, 4 and 5, a circuit for dividing by 3, a circuit for dividing by 4, and a circuit for dividing by 5 are separately required.

On the other hand, _if the value of _Pn in step 2 is obtained by the following method, the image quality is degraded.

For example, when the maximum value is detected for each frame, the maximum value is set as _Pn , and the data processing in step 3 is updated for each frame, flickering occurs on the screen every time the maximum value changes. (Comparative Example 1). Further, when a plurality of frames are considered as one unit and the maximum value detected for each unit is set to _Pn , the same flicker occurs (Comparative Example 2).

Further, if the maximum value is detected for each frame and the average value among a plurality of frames is _Pn in step 2, flickering is reduced, but a sudden change in brightness (dark → light) It becomes difficult to display the accompanying image with high responsiveness (Comparative Example 3). In this case, although the responsiveness can be improved by reducing the number of frames when calculating the average value, on the contrary, flickering occurs on the screen.

It is also conceivable that the maximum value detected for each frame is multiplied by an appropriate coefficient, and the average value of these values in a plurality of frames is set to _Pn in Step 2 (Comparative Example 4). In this case, for example, the value of the coefficient to be applied to the immediately preceding frame is 10, the value of the coefficient to be applied to the second previous frame is 5, and the value of the coefficient to be applied to the third previous frame is 2, etc. Weight data. According to this method, flicker is reduced, but as described above, it is difficult to display an image with a rapid change in brightness (dark → light) with high responsiveness. In addition, although the responsiveness can be improved by reducing the number of frames when calculating the average value, flickering occurs on the screen as described above.

The flicker which becomes a problem in the above Comparative Examples 1 to 4 becomes remarkable when the luminance of the liquid crystal panel is low. Thus, flickering can be reduced by obtaining the minimum value of the light emission luminance of the backlight so that the luminance is not lower than this value. Therefore, flickering is reduced by calculating _{Pn in the same} manner as in Comparative Example 3 and then modulating the luminance of the backlight so that the luminance does not become lower than a predetermined value (Comparative Example 5). ). However, it is difficult to display images with sudden changes in brightness (dark → light) with high responsiveness. Specifically, when the display image becomes bright, it becomes discontinuous, such as starting to brighten after a certain period of time. The sex issue is still not resolved. In this case, although the responsiveness can be improved by reducing the number of frames when calculating the average value, flickering occurs on the screen as in Comparative Example 3.

  On the other hand, when hysteresis is added to the relationship between the image data and the luminance, and the luminance of the backlight is modulated accordingly, flickering occurs when the data or luminance changes suddenly (Comparative Example 6).

  Thus, in any of Comparative Examples 1 to 6, flickering occurs on the screen. Although the reason for this is not necessarily clear, it is considered that one reason is that there is an error between the actual display brightness and the display brightness assumed by the calculation. In addition, all of the above calculations are based on the assumption that the liquid crystal panel is observed from the front. However, since the liquid crystal has a viewing angle dependency, the calculation is assumed if the liquid crystal panel is observed off the assumed position. It is expected to be different from the displayed brightness. Therefore, this is also considered to be one of the reasons described above.

If the flicker on the screen is due to the above reason, it is difficult to completely eliminate the flicker. However, as described above, (1) the maximum value for each frame of the degamma-processed value is obtained, and the value obtained by smoothing the maximum value is set as _Pn in Step 2, and (2) By linearly interpolating from the minimum luminance to the maximum luminance of the backlight and modulating the luminance of the backlight according to the obtained curve, it is possible to make the flicker on the screen inconspicuous to a level that hardly causes a problem.

  In the above (2), the reason why linear interpolation is performed from the minimum luminance to the maximum luminance is that flickering occurs when the data and the luminance change suddenly as described in the comparative example 6. However, in the present embodiment, the minimum luminance and the maximum luminance need only be connected by a smooth curve, and linear interpolation is not necessarily required.

  When applying the method of calculating the average value of FIG. 2 to the smoothing in step 2, the number of frames used for calculating the average value is preferably 32 or more, and 64 or more. Is more preferable, and it is more preferable that it is 128 or more. This is because as the number of frames is larger, flicker can be made inconspicuous. As described in Comparative Examples 3 and 4, when the number of frames increases, it becomes difficult to display an image with a rapid change in brightness (dark → light) with high responsiveness. However, the decrease in responsiveness that occurs when the number of frames is 128 is not so large as to be visually recognized on the screen, so it is considered that there is almost no problem.

  In addition, the minimum luminance of the backlight in this embodiment is preferably about 25 to 50 when the maximum luminance of the backlight is 100. When the minimum luminance is lower than this range, flickering increases, and it becomes difficult to display an image with a rapid change in luminance (dark → light) with high responsiveness. On the other hand, when the minimum luminance is higher than this range, the power consumption increases. For example, when the number of frames is 128 and the luminance is about 25, a liquid crystal display element in a low power consumption mode in which flicker is an allowable lower limit can be obtained. Further, when the number of frames is 128 and the luminance is about 50, a liquid crystal display element in a low power consumption mode with little flickering and high response can be obtained.

  In the gamma processing performed in this embodiment, the γ value can be set to an arbitrary value of 2 to 3 so as to match the relationship between the gradation and luminance of the liquid crystal display element. Generally, the γ value is set to 2.2. Further, the relationship between gradation and luminance may be obtained by actual measurement, and degamma processing and gamma processing may be performed from this relationship. Since the latter is closer to the actual mode, flicker can be reduced than the former.

  FIG. 2 is an example of a block diagram of a circuit of the liquid crystal display element in this embodiment. As shown in this figure, the liquid crystal panel 1 is driven by a drive circuit composed of a gate driver 2 and a source driver 3. Here, the gate driver 2 and the source driver 3 are driven by the power supply circuit 4. In addition, the drive timing of the gate driver 2 and the source driver 3 is determined by the timing controller 5.

When the image data is input to the backlight trimming 6 as the image data processing means, the processing of steps 1 to 4 described in FIG. 1 or FIG. 2 is performed. Then, by sending the processed image data to the source driver 3, a predetermined image is displayed on the liquid crystal panel 1. On the other hand, the luminance signal of the backlight 7 corresponding to the image data is sent to the backlight driver 8, and the emission luminance of the backlight 7 is controlled so as to have the luminance corresponding to _Pn detected in step 2. As the backlight in the present embodiment, for example, an LED (Light Emitting Diode) is used.

  The present invention is not limited to the above-described embodiment, and various modifications can be made without departing from the spirit of the present invention.

It is an example of the flowchart which shows the drive method of the liquid crystal display element in this Embodiment. It is another example of the flowchart which shows the drive method of the liquid crystal display element in this Embodiment. It is an example of the block diagram of the circuit of the liquid crystal display element in this Embodiment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Liquid crystal panel 2 Gate driver 3 Source driver 4 Power supply circuit 5 Timing controller 6 Backlight trimming 7 Backlight 8 Backlight driver

Claims (7)

A liquid crystal panel driven by a drive circuit;
An illumination device for irradiating the liquid crystal panel with predetermined light;
A lighting device driver for driving the lighting device;
The image data is degamma processed to detect the maximum value for each predetermined period, and after the data processing is performed so that the maximum value becomes 100% transmittance, the degamma processed data is gamma processed to obtain the original image data. Image data processing means for returning to
The liquid crystal display element, wherein the image data output from the image data processing means is input to the drive circuit, and the maximum value data detected by the image data processing means is input to the driver for the lighting device. A liquid crystal panel driven by a drive circuit;
In a driving method of a liquid crystal display element having an illumination device that irradiates the liquid crystal panel with predetermined light,
A first step of degamma processing image data;
A second step of obtaining a maximum value for each frame of the degamma processed data and detecting a value P _n obtained by smoothing the maximum value;
A third step of processing the degamma processed data so that P _n has a transmittance of 100%;
After the third step, there is a fourth step of gamma-processing the degamma processed data and returning it to the original image data,
The image data obtained in the fourth step is input to the drive circuit, and the illumination device is configured so that the illumination device has a luminance corresponding to _Pn from the data of _Pn detected in the second step. A method for driving a liquid crystal display element, characterized by controlling light emission luminance of the device.   The method of driving a liquid crystal display element according to claim 2, wherein the smoothing is a method of recursively processing the maximum value.   The method of driving a liquid crystal display element according to claim 2, wherein the smoothing is a method of calculating an average value for each of a plurality of frames with respect to the maximum value.   5. The method of driving a liquid crystal display element according to claim 4, wherein the plurality of frames are 32 or more frames.   6. The method of driving a liquid crystal display element according to claim 2, wherein the light emission luminance of the illumination device is controlled according to a smooth curve connecting a predetermined minimum luminance to a maximum luminance. .   7. The method of driving a liquid crystal display element according to claim 6, wherein the minimum luminance is in a range of 25 to 50 when the maximum luminance is 100.

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