JP2004177575A - Liquid crystal display device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a liquid crystal display device capable of enhancing display picture quality of a moving image by controlling high speed display drive (frame frequency conversion rate) of a liquid crystal display panel in accordance with a temperature in the device. <P>SOLUTION: The liquid crystal display device is provided with a frame frequency conversion section 12 which converts frame frequency of a picture signal supplied to the liquid crystal display panel by interpolating subframes of a specified number to an input picture frame. Further, the liquid crystal display device is provided with a temperature detection section 5 which detects the temperature in the device and a control section 6 which performs variable control of the frame frequency conversion rate depending on the frame frequency conversion section 12 on the basis of the detected temperature. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a liquid crystal display device that displays an image using a liquid crystal display panel, and more particularly to a liquid crystal display device that prevents motion blur that occurs when displaying a moving image.
[0002]
[Prior art]
2. Description of the Related Art In recent years, flat panel display devices (FPDs) such as a liquid crystal display device (LCD) capable of realizing high definition, low power consumption, and space saving have been actively developed. Among them, a computer display device and a television display device have been particularly developed. The use of LCDs for such applications is remarkable. However, in contrast to a cathode ray tube (CRT) display device which has been mainly used for such a purpose, an LCD displays a moving image when displaying a moving image. It has been pointed out that it is perceived as being so-called "motion blur".
[0003]
It has been pointed out that the motion blur in displaying a moving image is caused not only by the delay of the optical response time of the liquid crystal but also by the display method of the LCD itself as described in, for example, JP-A-9-325715. In a CRT display device in which a phosphor is emitted by scanning an electron beam to perform display, the light emission of each pixel has a so-called impulse-type display system in which although there is some afterglow of the phosphor, the light emission is substantially impulse-shaped. I have.
[0004]
On the other hand, in an LCD display device, the electric charge stored by applying an electric field to the liquid crystal is held at a relatively high rate until the next electric field is applied. A TFT switch is provided for each dot to be stored, and an auxiliary capacitor is usually provided for each pixel, so that the ability to hold the stored charge is extremely high.) The liquid crystal pixels are based on the image information of the next frame. This is a so-called hold-type display system in which light emission is continued until rewritten by application of an electric field.
[0005]
In such a hold-type display device, since the impulse response of the image display light has a temporal spread, the time-frequency characteristics are deteriorated, and accordingly, the spatial frequency characteristics are also reduced, resulting in blurred viewing images. . Therefore, for example, Japanese Patent Application Laid-Open Nos. 4-302289 and 2001-42831 propose a device that raises the frame frequency of a display image and suppresses a decrease in the spatial frequency characteristic that causes the above-described motion blur. I have.
[0006]
This will be described with reference to FIG. In FIG. 6, reference numeral 1 denotes a motion vector detecting unit that detects motion vector information from an input image signal, and 2 denotes a sub-frame image generated by using the motion vector information obtained by the motion vector detecting unit 1, thereby obtaining an input image. A frame frequency conversion unit for converting the frame frequency of the signal to, for example, twice, 3 is an electrode drive for driving data electrodes and scanning electrodes of the liquid crystal display panel 4 based on the image signal frequency-converted by the frame frequency conversion unit 2. Reference numeral 4 denotes an active matrix type liquid crystal display panel having a liquid crystal layer and electrodes for applying a scanning signal and a data signal to the liquid crystal layer.
[0007]
In the above configuration, the motion vector detection unit 1 may obtain the motion vector information by using, for example, a matching method or a gradient method, or when the input image signal includes the motion vector information in some form, You may use it as it is. For example, since image data compressed and encoded using the MPEG method includes motion vector information of a moving image calculated at the time of encoding, a configuration may be adopted in which this motion vector information is acquired and output.
[0008]
Further, the frame frequency conversion unit 2 generates a frame interpolation image (sub-frame image) by motion interpolation using the motion vector information output from the motion vector detection unit 1, and converts the generated interpolation frame signal. The frame frequency (60 Hz) of the input image signal is doubled to 120 Hz by sequentially outputting the input image signal together with the input frame signal, and the image signal converted to the double speed is supplied to the liquid crystal display panel 4 via the electrode driving unit 3. Then, the liquid crystal display panel 4 is driven at double speed.
[0009]
As described above, by performing the motion adaptive frame interpolation processing using the motion vector information and increasing the display frame frequency, the display state of the hold-type drive can be approximated to the display of the impulse-type drive such as a CRT in a pseudo manner. As a result, it is possible to improve image quality deterioration due to motion blur generated when displaying a moving image.
[0010]
[Patent Document 1]
Japanese Patent Application Laid-Open No. 9-325715 [Patent Document 2]
JP-A-4-302289 [Patent Document 3]
Japanese Patent Application Laid-Open No. 2002-42831
[Problems to be solved by the invention]
According to the above-described conventional technique, in order to improve image quality degradation due to motion blur generated when a moving image is displayed on a hold-type display device, at least one or more signals are generated within one frame period (for example, 16.7 msec for a 60 Hz progressive scan). The motion compensation interpolation of these sub-frames and the supply of these to the liquid crystal display panel reduce the display frame period. However, in order to prevent image quality deterioration due to motion blur, the display frame period (sub-frame It is desirable to make the image display period as short as possible.
[0012]
By the way, as shown in FIG. 7, it is known that the response speed of the liquid crystal has a very large temperature dependency, and the response to an input signal at a low temperature becomes extremely poor, and the response time increases. That is, in the conventional technique described above, when the frame frequency of the display image signal is increased, when the temperature in the device is low, the writing of the next sub-frame image is started before the liquid crystal completely responds and reaches the target luminance. As a result, there is a problem that the image quality of a displayed image is deteriorated, such as a more serious afterimage such as tailing.
[0013]
The present invention has been made in view of the above problems, and improves the display image quality of a moving image by variably controlling high-speed display driving (frame frequency conversion rate) of a liquid crystal display panel according to the internal temperature of the device. It is intended to provide a liquid crystal display device capable of performing the above.
[0014]
[Means for Solving the Problems]
The present invention relates to a liquid crystal display device provided with a frame frequency conversion means for converting a frame frequency of an image signal supplied to a liquid crystal display panel by interpolating a predetermined subframe with respect to an input image frame. A temperature detecting means for detecting the internal temperature, and a control means for variably controlling a frame frequency conversion rate by the frame frequency converting means based on the detected temperature.
[0015]
According to the liquid crystal display device of the present invention, when converting the display frame frequency to a high frequency in order to prevent motion blur, the frame frequency conversion rate is automatically switched appropriately in accordance with the internal temperature of the device. After the liquid crystal has completely reached the target luminance in response, the next image display can be performed, and a high-quality moving image display in which the occurrence of an afterimage as well as the motion blur is suppressed can be realized.
[0016]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, an embodiment of the present invention will be described in detail with reference to FIGS. 1 to 5. The same reference numerals will be given to the same portions as those in the above-described conventional example, and the description thereof will be omitted. Here, FIG. 1 is a functional block diagram showing a schematic configuration of a main part in the liquid crystal display device of the present embodiment, FIG. 2 is a timing chart showing an operation of a frame frequency converter in the liquid crystal display device of the present embodiment, and FIG. FIG. 4 is a schematic explanatory view for explaining the operation of the frame frequency conversion unit in the liquid crystal display device of the embodiment, FIG. 4 is a flowchart showing the basic operation principle of the liquid crystal display device of the present embodiment, and FIG. FIG. 4 is an explanatory diagram for describing a basic operation principle in FIG.
[0017]
As shown in FIG. 1, the liquid crystal display device of the present embodiment has a temperature detector 5 for detecting the temperature inside the device and a temperature detector 5 for detecting the temperature inside the device, in addition to the conventional example described above with reference to FIG. A control CPU 6 for outputting a control signal for variably controlling the frame frequency conversion rate in the frame frequency conversion unit 12 based on the temperature data thus obtained. It is desirable that the temperature detector 5 be provided so as to detect the temperature of the liquid crystal display panel 4 as accurately as possible.
[0018]
The frame frequency conversion unit 12 includes, for example, a frame memory. After storing an image of one frame of the input image signal in the frame memory, the image is converted at a predetermined frame frequency based on a control signal from the control CPU 6. By reading the signal to compress the time axis and performing the motion adaptive frame interpolation process using the motion vector information obtained by the motion vector detection unit 1, the sub-frame image (shaded in FIG. 3) is obtained. Generate and convert the frame frequency of the display image signal to a high frequency.
[0019]
In the present embodiment, for example, as shown in FIGS. 2B and 3A, the input image signal shown in FIG. 2 (c) and 3 (b) as shown in FIGS. 2 (c) and 3 (b), and FIG. 2 (d) and FIG. 3 (c). As shown, a mode for outputting an image signal whose frame frequency is tripled is provided, and each mode can be switched in accordance with a control signal from the control CPU 6. That is, the frame frequency conversion rate by the frame frequency conversion unit 12 can be varied between 1 and 3 times.
[0020]
Here, the input image signal is a progressive scan signal of 60 Hz. Therefore, the frame frequency output by the frame frequency conversion unit 12 in each mode is 60 Hz, 120 Hz, and 180 Hz, respectively, and the frame period is 1/60 second (16.7 msec). ), 1/120 second (8.3 msec), and 1/180 second (5.6 msec). By switching between these modes in accordance with the internal temperature of the apparatus, a period during which the temperature-dependent liquid crystal responds (liquid crystal response time) is sufficiently ensured.
[0021]
Next, the operation of the present embodiment configured as described above will be described with reference to the flowchart of FIG. First, it is determined whether or not the temperature inside the device detected by the temperature detecting unit 5 is higher than M ° C. (for example, 20 ° C.) (step 1). If the temperature is higher than M ° C., it is determined that the response speed of the liquid crystal is sufficiently fast. Therefore, the liquid crystal display panel 4 is driven at triple speed with the frame frequency conversion rate by the frame frequency converter 12 being tripled (step 2).
[0022]
In this case, as shown in FIG. 5A, the image display period of each sub-frame can be 5.6 msec, and it is possible to sufficiently prevent the occurrence of motion blur. In addition, the response speed of the liquid crystal is sufficiently fast, and the liquid crystal completely responds to the target luminance within this image display period (5.6 msec), so that an afterimage such as tailing does not occur.
[0023]
If it is determined in step 1 that the temperature in the apparatus is lower than M ° C., it is determined whether the detected temperature is lower than N ° C. (for example, 10 ° C.) (step 3). If the temperature inside the device is higher than N ° C. (ie, N ° C. <temperature inside the device <M ° C.), the response speed of the liquid crystal is considered to be slightly slower, so that the frame frequency conversion rate by the frame frequency converter 12 is doubled. Then, the liquid crystal display panel 4 is driven at double speed (step 4).
[0024]
In this case, as shown in FIG. 5B, the image display period of each sub-frame is 8.3 msec, so that it is possible to reduce the occurrence of motion blur, and even if the response speed of the liquid crystal is somewhat slow, this image is displayed. Since the liquid crystal can be expected to completely respond to the target luminance within the display period (8.3 msec), the occurrence of an afterimage such as tailing can be reduced.
[0025]
Further, if it is determined in step 3 that the temperature inside the device is lower than N ° C., the response speed of the liquid crystal is considered to be considerably slow. Therefore, the frame frequency conversion by the frame frequency conversion unit 12 is stopped, and the through output (frame output) is performed. By setting the frequency conversion rate to 1), the liquid crystal display panel 4 is driven at the same speed (ie, high-speed display driving is turned off) (step 5).
[0026]
In this case, as shown in FIG. 5C, the image display period of each frame can be secured for 16.7 msec, and the occurrence of motion blur cannot be prevented, but this image display period (16.7 msec) It is expected that the liquid crystal will completely respond to the target brightness and reach the target brightness, so it is possible to prevent the occurrence of afterimages such as tailing due to incomplete response of the liquid crystal, which has a greater effect on image quality degradation than motion blur It becomes.
[0027]
As described above, as the temperature in the apparatus, that is, the detected temperature of the liquid crystal display panel 4 decreases, the frame frequency conversion rate in the frame frequency conversion unit 12 is reduced, so that the image scanning period (the liquid crystal response period) is sufficiently ensured. After the liquid crystal completely reaches the target luminance in response, the next image can be displayed. Therefore, it is possible to appropriately suppress the occurrence of motion blur and an afterimage in accordance with the usage environment, and to realize a high-quality moving image display. Here, the variable control of the frame frequency conversion rate is performed for each input image frame.
[0028]
In the present embodiment, an example in which the frame frequency of the display image signal is switched and converted to 1 to 3 times in accordance with the temperature in the apparatus has been described. However, the present invention is not limited to this. Obviously, the switching conversion may be employed. This may be appropriately designed depending on the optical response characteristics of the liquid crystal display panel. In addition, since the perception of motion blur differs depending on the image content and the image content and varies greatly from person to person, a configuration that allows the user to select and instruct an arbitrary frame frequency conversion rate may be added.
[0029]
Further, as is clear from FIG. 7, the response time of the liquid crystal differs depending on the gradation transition before and after one frame, and generally, the time required to change from one halftone to another halftone becomes longer. The conversion frame frequency may be determined in consideration of the gradation transition of the current frame data with respect to the previous frame data in addition to the temperature. As a result, it is possible to further realize appropriate moving image display according to the optical response characteristics of the liquid crystal.
[0030]
As described above, in the liquid crystal display device of the present embodiment, by interpolating a predetermined number of subframes with respect to an input image frame and driving the liquid crystal display panel at high speed, the display state of the liquid crystal display panel can be approximated to the display state of impulse type driving. When preventing motion blur, the display drive speed (frame frequency conversion rate) is controlled in accordance with the temperature inside the device, so that motion blur is prevented and the occurrence of afterimages such as tailing is prevented. And the image quality of the displayed image can be improved.
[0031]
【The invention's effect】
Since the liquid crystal display device of the present invention is configured as described above, the liquid crystal completely responds to the target brightness by automatically switching the frame frequency conversion rate appropriately in accordance with the internal temperature of the device. After that, it is possible to display the next image, and it is possible to realize a high-quality moving image display in which the occurrence of afterimages and the occurrence of afterimages are suppressed in accordance with the usage environment.
[Brief description of the drawings]
FIG. 1 is a functional block diagram showing a schematic configuration of a main part in an embodiment of a liquid crystal display device of the present invention.
FIG. 2 is a timing chart showing an operation of a frame frequency converter in one embodiment of the liquid crystal display device of the present invention.
FIG. 3 is a schematic explanatory diagram for explaining an operation of a frame frequency converter in one embodiment of the liquid crystal display device of the present invention.
FIG. 4 is a flowchart showing a basic operation principle in one embodiment of the liquid crystal display device of the present invention.
FIG. 5 is an explanatory diagram for explaining a basic operation principle in one embodiment of the liquid crystal display device of the present invention.
FIG. 6 is a functional block diagram showing a schematic configuration of a main part of a conventional liquid crystal display device (high-speed drive type).
FIG. 7 is an explanatory diagram showing an example of optical response characteristics of a liquid crystal display panel.
[Explanation of symbols]
Reference Signs List 1 motion vector detecting unit 3 electrode driving unit 4 liquid crystal display panel 5 temperature detecting unit 6 control CPU
12 Frame frequency converter

Claims (1)

A liquid crystal display device including a frame frequency conversion unit that converts a frame frequency of an image signal supplied to a liquid crystal display panel by interpolating a predetermined number of subframes with respect to an input image frame,
Temperature detection means for detecting the temperature inside the device,
A liquid crystal display device comprising: control means for variably controlling a frame frequency conversion rate by the frame frequency conversion means based on the detected temperature.

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