JP2007241038A - Liquid crystal display device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a liquid crystal display device capable of separately displaying images different in feelings of luster. <P>SOLUTION: The liquid crystal display device has: a first liquid crystal panel (TN type liquid crystal panel) 19 capable of controlling optical transmissivity; a second liquid crystal panel (PDLC type liquid crystal panel) 20 capable of controlling a degree of light scattering; an image roughness detection means (spatial frequency judgment circuit) 31 for detecting roughness of an image displayed on the first liquid crystal panel 10 based on an image signal to be supplied to the first liquid crystal panel and a second liquid crystal panel control means (PDLC type liquid crystal panel drive circuit) 33 which controls a degree of the light scattering by the second liquid crystal panel based on a detection result of the image roughness detection means. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a liquid crystal display device.

In the conventional liquid crystal display device, the first liquid crystal layer in which the light absorption state and the transparent state can be controlled, the second liquid crystal layer in which the light scattering state and the transparent state can be controlled, and the reflective film are on the display surface side. Have been proposed (for example, see Patent Document 1). In this liquid crystal display device, a bright state is displayed by applying a voltage to each liquid crystal layer so that the first liquid crystal layer is in a transparent state and the second liquid crystal layer is in a scattering state. On the other hand, a voltage is applied to each liquid crystal layer so that the first liquid crystal layer is in a light absorbing state and the second liquid crystal layer is in a transparent state, thereby displaying a dark state. According to this configuration, the effective reflectance is increased by scattering the reflected light in the bright state display, and the effective reflectance is decreased by using only the regular reflection component as the reflected light in the dark state display. be able to. As a result, a bright display with high contrast can be obtained.
JP 9-318969 A

  By the way, recent liquid crystal display devices are required to obtain a more natural image for the user. For example, a glossy and smooth image and a glossy and rough image are displayed separately. May be required. However, conventionally, a liquid crystal display device that can satisfy such a requirement has not been provided. In the liquid crystal display device of Patent Document 1 described above, a bright reflective display with a high contrast can be obtained by using two liquid crystal layers, but the above requirement has not been met.

  The present invention has been made to solve the above problems, and an object thereof is to provide a liquid crystal display device capable of displaying and separately displaying images having different glossiness.

  In order to achieve the above object, a liquid crystal display device according to the present invention includes a first liquid crystal panel capable of controlling light transmittance, and the viewing side of the first liquid crystal panel or the viewing side of the first liquid crystal panel. And a second liquid crystal panel capable of controlling the degree of light scattering, and an image roughness for detecting the roughness of an image displayed on the first liquid crystal panel based on an image signal supplied to the first liquid crystal panel. And a second liquid crystal panel control means for controlling the degree of light scattering by the second liquid crystal panel based on the detection result of the image roughness detection means.

  The “image roughness” in the present invention means the degree of scattering of light forming an image. Specifically, in an “image with a high degree of roughness”, the image light is greatly scattered, and the observer feels a glossy and rough image. On the other hand, in an “image with a low degree of roughness”, the scattering of image light is small, and the observer feels that the image is glossy and slippery.

  In the liquid crystal display device of the present invention, the image roughness detecting means displays on the first liquid crystal panel based on the image signal supplied to the first liquid crystal panel which can control the light transmittance and substantially forms an image. The roughness of the image to be detected is detected. The second liquid crystal panel control means controls the degree of light scattering by the second liquid crystal panel based on the detection result from the image roughness detection means. At this time, when it is determined that the degree of roughness of the image is large, the degree of light scattering by the second liquid crystal panel is increased, and when it is determined that the degree of roughness of the image is small, the light by the second liquid crystal panel is Decrease the degree of scattering. As a result, the image is composed of light with different degrees of scattering according to the image displayed on the first liquid crystal panel, and the observer can feel the difference in glossiness of the image. Moreover, according to the structure of this invention, a bright image can be made brighter compared with the case where a scattering film etc. are used.

Moreover, it is good also as a structure provided with the illumination means which irradiates light to the said laminated body on the opposite side to the visual recognition side of the laminated body of a 1st liquid crystal panel and a 2nd liquid crystal panel.
The liquid crystal display device of the present invention can be applied to any of a reflective liquid crystal display device, a transmissive liquid crystal display device, or a transflective liquid crystal display device having both reflective display and transmissive display. However, it is desirable to apply the present invention to a transmissive liquid crystal display device having illumination means for irradiating light to the first liquid crystal panel and the second liquid crystal panel. The reason is that, in the reflective liquid crystal display device, the intensity and direction of incident light differ depending on the use environment, whereas in the transmissive liquid crystal display device, the intensity and direction of incident light from the illumination means can be fixed. This is because it becomes easy to optimally design the degree of light scattering.

In the liquid crystal display device of the present invention, either the first liquid crystal panel or the second liquid crystal panel may be arranged on the viewing side, but the first liquid crystal panel is placed on the viewing side with respect to the second liquid crystal panel. It is better to place it.
The reason is that when the second liquid crystal panel is arranged on the viewer side, for example, when used as a transmissive liquid crystal display device, when the degree of light scattering by the second liquid crystal panel is increased, the reflected light of outside light Is also strongly scattered, and there is a risk of adverse effects such as difficulty in viewing the display.

Further, the image roughness detection means detects the roughness of the image for each of the divided areas obtained by dividing the display screen of the first liquid crystal panel, and the second liquid crystal panel control means detects the division from the image roughness detection means. Based on a plurality of detection results for each region, the degree of light scattering may be controlled for each region of the second liquid crystal panel that planarly overlaps each of the divided regions of the first liquid crystal panel.
When the above processing is performed without dividing the display screen of the first liquid crystal panel, when the video scene is switched, for example, when the overall glossy image is switched to the less glossy image, etc. The effect of the invention can be exhibited. In contrast, the roughness of the image is detected for each divided area of the display screen of the first liquid crystal panel, and the degree of light scattering is controlled for each area of the second liquid crystal panel that overlaps each of the divided areas in a plane. In this case, even if an image with high glossiness and an image with low glossiness are mixed in one screen, the degree of light scattering is controlled according to each image within one screen. Optimal display can be performed.

The image roughness detection means can detect the roughness of the image by the wavelet transform method.
According to this configuration, unlike the case where the Fourier transform method is used, image processing can be performed in real time, and an image with a more uncomfortable feeling can be obtained.

Alternatively, the image roughness detection means can detect the roughness of the image based on the luminance distribution of the image signal.
According to this configuration, the roughness of the image can be obtained more easily, and the burden on the image processing circuit can be reduced.

The second liquid crystal panel can be composed of a polymer dispersed liquid crystal panel.
According to this configuration, the degree of scattering of transmitted light can be easily and accurately controlled by using the polymer dispersion type liquid crystal panel.

Hereinafter, an embodiment of the present invention will be described with reference to FIGS.
The liquid crystal display device of this embodiment is an example of a transmissive liquid crystal display device provided with a backlight.
FIG. 1 is a cross-sectional view showing a schematic configuration of the liquid crystal display device of the present embodiment. FIG. 2 is a plan view showing a pixel configuration of each panel constituting the liquid crystal display device. FIG. 3 is a diagram for explaining the operation of the liquid crystal display device. FIG. 4 is a block diagram showing a configuration of a drive circuit unit of the liquid crystal display device. FIG. 5 is a flowchart for explaining the operation of the spatial frequency determination circuit described later of the drive circuit unit. In each drawing used for the following description, the scale of each member is appropriately changed to make each member a recognizable size.

  As shown in FIG. 1, the liquid crystal display device 1 of this embodiment includes a TN (Twisted Nematic) type liquid crystal panel (first liquid crystal panel) 10, a polymer dispersed liquid crystal (Polymer Dispersed Liquid Crystal) in order from the viewer side (viewing side). , Hereinafter referred to as PDLC) type liquid crystal panel (second liquid crystal panel) 20 and backlight (illuminating means) 30 are stacked. The light emitted from the backlight 30 is incident on the TN liquid crystal panel 10 after the degree of scattering (directivity) is controlled by the PDLC liquid crystal panel 20, and the transmittance is modulated by the TN liquid crystal panel 10. Thus, an image is formed. The backlight 30 includes a light source such as a cold cathode tube, an LED, a reflector, a light guide plate, and the like.

  The TN type liquid crystal panel 10 has an indium tin oxide (hereinafter referred to as ITO) on the inner surface (surface on the liquid crystal layer side) of a lower substrate (substrate opposite to the viewing side) 11 made of a transparent substrate such as glass. A plurality of pixel electrodes 12 made of a transparent conductive film such as abbreviated) are formed, and an alignment film 13 made of polyimide or the like is formed so as to cover the pixel electrode 12. The plurality of pixel electrodes 12 are arranged in a matrix on the lower substrate 11, and thin film transistors, data lines, scanning lines, and the like that supply image signals to the pixel electrodes 12 are formed. To do. On the other hand, a common electrode 16 made of a transparent conductive film such as ITO is formed on the inner surface of an upper substrate (viewing side substrate) 15 made of a transparent substrate such as glass, and an alignment film made of polyimide or the like so as to cover the common electrode 16 17 is formed. The liquid crystal layer 5 is sandwiched between the lower substrate 11 and the upper substrate 15. The liquid crystal layer 5 is a TN mode liquid crystal layer 5 in which liquid crystal molecules are twisted by 90 ° between the lower substrate 11 and the upper substrate 15. Polarizers 14 a and 14 b are arranged on the outer surfaces (surfaces opposite to the liquid crystal layer) of the lower substrate 11 and the upper substrate 15 so that the transmission axes are orthogonal to each other.

  In the PDLC type liquid crystal panel 20, a plurality of divided region electrodes 22 made of a transparent conductive film such as ITO are formed on the inner surface of a lower substrate 21 made of a transparent substrate such as glass, and polyimide or the like is formed so as to cover the divided region electrode 22. An alignment film 23 is formed. The arrangement of the divided region electrodes 22 will be described later. Further, the plurality of divided region electrodes 22 are arranged in a matrix on the lower substrate, and a control signal is individually supplied to the divided region electrodes 22 via wiring or the like (not shown). . On the other hand, a common electrode 26 made of a transparent conductive film such as ITO is formed on the inner surface of an upper substrate 25 made of a transparent substrate such as glass, and an alignment film 27 made of polyimide or the like is formed so as to cover the common electrode 26. . The liquid crystal layer 8 is sandwiched between the lower substrate 21 and the upper substrate 25. The liquid crystal layer 8 includes a network of polymer polymers and liquid crystal molecules, and the refractive index difference between the network phase and the liquid crystal phase is changed by driving the liquid crystal molecules, and the degree of scattering of transmitted light can be controlled. It has become.

In the case of the present embodiment, as shown in FIG. 2A, the TN type liquid crystal panel 10 includes 4m pixel electrodes 12 arranged in the horizontal direction of the screen and 3n pixel electrodes 12 arranged in the vertical direction of the screen. A total of 4m × 3n pixel electrodes 12 are provided. Assume that the pixel region having the plurality of pixel electrodes 12 is virtually divided into four regions in the horizontal direction of the screen and three regions in the vertical direction of the screen, and is divided into 12 regions as a whole. Here, each divided region is represented as A _{11 to} A ₃₄ . On the other hand, as shown in FIG. 2B, the PDLC type liquid crystal panel 20 corresponds to the divided areas A _{11 to} A ₃₄ of the TN type liquid crystal panel 10 and overlaps with the divided areas A _{11 to} A ₃₄ in a plane. Divided region electrodes B _{11 to} B ₃₄ are provided in the region. Therefore, each of the divided region electrodes B _{11 to} B ₃₄ of the PDLC type liquid crystal panel 20 is responsible for controlling light scattering in the m × n pixels of the TN type liquid crystal panel 10.

  The relationship between the operation of the TN type liquid crystal panel 10 and the PDLC type liquid crystal panel 20 and the display image is as shown in FIG. Here, without considering halftone, the “bright state” (denoted as “ON” in FIG. 3), “dark state” (denoted as “OFF” in FIG. 3) of the TN liquid crystal panel 10, and the PDLC type liquid crystal panel Only four combinations of 20 “scattering states” (denoted as “ON” in FIG. 3) and “non-scattering states” (denoted as “OFF” in FIG. 3) are considered.

  When the PDLC liquid crystal panel 20 is in the “scattering state” when the TN liquid crystal panel 10 is in the “bright state” (second from the left in FIG. 3), most of the light sufficiently scattered by the PDLC liquid crystal panel 20 Is transmitted through the TN type liquid crystal panel 10, so that an image is formed by light with low directivity, and a rough image with a weak glossiness is obtained. On the other hand, when the PDLC liquid crystal panel 20 is set to the “non-scattering state” when the TN liquid crystal panel 10 is in the “bright state” (fourth from the left in FIG. 3), the PDLC liquid crystal panel 20 is substantially scattered without being scattered. Since the straight light passes through the TN liquid crystal panel 10, an image is formed by light having strong directivity, and a smooth image with a strong glossiness is obtained. Further, when the TN liquid crystal panel 10 is in the “dark state” (third from the left end and the left in FIG. 3), the PDLC liquid crystal panel 20 is almost the same in both the “scattering state” and the “non-scattering state”. The black display is obtained.

As shown in FIG. 4, the liquid crystal display device 1 of the present embodiment includes a spatial frequency determination circuit (image roughness detecting means) 31, a TN liquid crystal panel drive circuit 32, and a PDLC liquid crystal panel drive circuit (second liquid crystal). Drive circuit section 30 provided with a panel control means) 33. The TN liquid crystal panel drive circuit 32 is the same as a conventional general liquid crystal panel drive circuit, and supplies an externally input image signal to the TN liquid crystal panel 10 as a drive voltage. As shown in FIG. 2A, the spatial frequency determination circuit 31 detects the roughness of the image for each of the divided areas A _{11 to} A ₃₄ obtained by dividing the screen of the TN liquid crystal panel 10 into twelve areas. The PDLC driving voltage supplied to each of the divided region electrodes B _{11 to} B ₃₄ of the PDLC type liquid crystal panel 20 corresponding to A _{11 to} A ₃₄ is determined according to the control flow of FIG. Here, only the luminance signal is focused on among the image signals.

As shown in FIG. 5, the spatial frequency determination circuit 31 first divides the screen of the TN type liquid crystal panel 10 into a plurality of regions (step S1). For example, when the division method is fixed in advance, such as horizontal 4-division and vertical 3-division in this embodiment, the procedure of step S1 can be omitted. Or it is good also as a structure which changes how to divide | segment a screen according to an image. In the case of this configuration, it is necessary to control the degree of light scattering of the PDLC type liquid crystal panel 20 for each divided region that changes from time to time. Therefore, in this case, the divided region electrodes B _{11 to} B ₃₄ of the PDLC type liquid crystal panel 20 are not roughly provided as in the present embodiment, but are provided finely in the same manner as the TN type liquid crystal panel 10 side, and the division at that time is performed. The divided region electrode 22 in the region may be similarly driven.

  Next, a luminance signal wavelet transform process is performed for each divided region (step S2). The wavelet transform process is known as one of frequency analysis techniques, and extracts a high frequency component (high spatial frequency component, that is, strong scattering component) by a high pass filter.

  Next, an average value in each divided region of the high spatial frequency obtained by the wavelet transform process in step S2 is calculated (step S3). In this step S3, the amount of the high-frequency component of the luminance signal constituting the image is calculated, and as a result, the intensity of image light scattering in each divided region is quantified.

  Next, based on the average value of the high spatial frequency obtained in step S3, the PDLC driving voltage value applied to each divided region electrode 22 of the PDLC type liquid crystal panel 20 in comparison with the lookup table (LUT) is determined for each divided region. (Step S4). In this case, the correlation between the average value of the high spatial frequency and the PDLC driving voltage value that realizes the optimum light scattering at that time is obtained in advance and stored as an LUT. Specifically, an LUT is created such that the higher the average value of the spatial frequency, the higher the PDLC drive voltage value. Further, the PDLC type liquid crystal panel 20 used in the present embodiment has a higher degree of light scattering as the drive voltage value is higher. The PDLC drive voltage value determined in step S4 is sent as a signal to the PDLC type liquid crystal panel drive circuit 33, and the drive voltage is supplied from the PDLC type liquid crystal panel drive circuit 33 to the PDLC type liquid crystal panel 20.

  Thus, in the liquid crystal display device 1 of the present embodiment, the average value of the high spatial frequency obtained by the wavelet transform processing in the spatial frequency determination circuit 31 is large, and the roughness of the image displayed on the TN type liquid crystal panel 10 is large. If it is determined that the degree of light scattering is large, the degree of light scattering of the PDLC-type liquid crystal panel 20 is increased. On the other hand, when it is determined that the average value of the high spatial frequency is small and the degree of roughness of the image is small, the degree of light scattering of the PDLC type liquid crystal panel 20 is weakened. As a result, images displayed on the TN liquid crystal panel 10, such as a glossy metal surface and a non-glossy paper surface, are generated with light having different degrees of scattering according to images having different glossiness. As a result, the observer can feel the difference in glossiness of the image. Further, since a liquid crystal panel capable of controlling the scattering property is used, a bright image can be made brighter than when a scattering film or the like is used.

Furthermore, in the case of this embodiment, the average value (image roughness) of the high spatial frequency is detected for each of the divided areas A _{11 to} A ₃₄ of the display screen of the TN liquid crystal panel 10, and the PDLC corresponding to each of the divided areas. The degree of light scattering is controlled for each formation region of the divided region electrodes B _{11 to} B ₃₄ of the liquid crystal panel 20. According to this configuration, even when an image having a high glossiness and an image having a low glossiness are mixed in one screen, light scattering is caused according to a local position in one screen. By controlling the degree, it is possible to perform fine display with optimized glossiness.

  In addition, the present embodiment is a transmissive liquid crystal display device, and includes a backlight 30 on the back side of the PDLC liquid crystal panel 20. Therefore, unlike the reflective liquid crystal display device, the intensity and direction are controlled from the backlight 30. The incident light is incident on the PDLC type liquid crystal panel 20 to facilitate optimization of the degree of light scattering by the PDLC type liquid crystal panel 20. Furthermore, since the TN type liquid crystal panel 10 is arranged closer to the viewing side than the PDLC type liquid crystal panel 20, the influence of scattered light of external light when the PDLC type liquid crystal panel 20 is arranged on the viewing side can be reduced. There are no problems such as difficulty in viewing the display. The image roughness detection means detects the roughness of the image using the wavelet transform method. Therefore, unlike the case where the Fourier transform method is used, image processing can be performed in real time and the image is more comfortable. Can be obtained.

  The technical scope of the present invention is not limited to the above embodiment, and various modifications can be made without departing from the spirit of the present invention. For example, in the above-described embodiment, the TN liquid crystal panel 10 is used as the first liquid crystal panel for controlling the light transmittance. However, the liquid crystal panel is not limited to the TN liquid crystal panel 10 and any other mode liquid crystal panel can be used. In addition, although the appearance of the display is deteriorated, the PDLC type liquid crystal panel (second liquid crystal panel) 20 may be arranged closer to the viewing side than the TN type liquid crystal panel (first liquid crystal panel) 10. Further, the present invention can be applied not only to a transmissive liquid crystal display device but also to a reflective liquid crystal display device and a transflective liquid crystal display device. In addition, the specific configuration of each liquid crystal panel can be changed as appropriate.

  In the above embodiment, wavelet transform processing is used as means for detecting the roughness of the image. However, instead of this method, the roughness of the image can be detected based on the luminance distribution of the image signal. For example, the average value and variance of the luminance values are obtained from the luminance distribution of the image signal supplied to a plurality of pixels in a predetermined horizontal line (or all pixels in the divided region) in each divided region, and the variance is averaged. Calculate the value divided by the value. If the value is large, it can be determined that the scattering property is strong, that is, the image is rough, and if the value is small, it can be determined that the scattering property is weak, that is, the image is not rough. In this method, the roughness of the image can be obtained more easily, and the burden on the image processing circuit can be reduced.

It is sectional drawing which shows schematic structure of the liquid crystal display device of one Embodiment of this invention. It is a top view which shows the pixel structure of each panel which comprises the liquid crystal display device. It is a figure for demonstrating the effect | action of the liquid crystal display device. It is a block diagram which shows the structure of the drive circuit part of the liquid crystal display device. It is a flowchart which shows operation | movement of the spatial frequency determination circuit of the drive circuit part.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Liquid crystal display device, 10 ... TN type | mold liquid crystal panel (1st liquid crystal panel), 20 ... PDLC type | mold liquid crystal panel (2nd liquid crystal panel), 30 ... Backlight (illuminating means), 31 ... Spatial frequency determination circuit (image coarseness) Detection means), 33... PDLC type liquid crystal panel drive circuit (second liquid crystal panel control means)

Claims (7)

A first liquid crystal panel capable of controlling light transmittance;
A second liquid crystal panel that is laminated on the viewing side of the first liquid crystal panel or on the opposite side of the viewing side of the first liquid crystal panel, and capable of controlling the degree of light scattering;
Image roughness detecting means for detecting roughness of an image displayed on the first liquid crystal panel based on an image signal supplied to the first liquid crystal panel;
And a second liquid crystal panel control means for controlling a degree of light scattering by the second liquid crystal panel based on a detection result of the image roughness detection means.   2. The liquid crystal according to claim 1, wherein illumination means for irradiating light to the multilayer body is provided on a side opposite to a viewing side of the multilayer body including the first liquid crystal panel and the second liquid crystal panel. Display device.   The liquid crystal display device according to claim 1, wherein the first liquid crystal panel is disposed on a viewing side of the second liquid crystal panel. The image roughness detecting means detects the roughness of the image for each divided area obtained by dividing the display screen of the first liquid crystal panel into a plurality of areas,
The second liquid crystal panel control means is configured to planarly overlap each of the divided areas of the first liquid crystal panel based on a plurality of detection results for each of the divided areas from the image roughness detecting means. The liquid crystal display device according to any one of claims 1 to 3, wherein the degree of light scattering is controlled for each region of the panel.   5. The liquid crystal display device according to claim 1, wherein the image roughness detection unit detects the roughness of the image by a wavelet transform method. 6.   5. The liquid crystal display device according to claim 1, wherein the image roughness detection unit detects the roughness of the image based on a luminance distribution of the image signal. 6. The liquid crystal display device according to any one of claims 1 to 6, wherein the second liquid crystal panel is configured by a polymer dispersion type liquid crystal panel.

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