JP2007033855A - Device and method for adjusting luminance of display device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide "a device and a method for adjusting the luminance of a display device" that can make back light luminance different between right and left sides of a dual-view display and display only a picture of one side with low luminance. <P>SOLUTION: The device for adjusting the luminance is equipped with a liquid crystal shutter 2 configured to vary light transmissivity and a view angle in response to application of a voltage and a voltage control section 4 which controls the voltage applied to the liquid crystal shutter 2, and performs control to dim a polarized light traveling from a back light 1 in a specified direction and then make the luminance lower in the specified direction by applying the voltage to the liquid crystal shutter 2, so that a display image viewed from the specified direction becomes dark. Consequently, only one picture of the dual-view display can be displayed with the low luminance. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a brightness adjusting device and a brightness adjusting method for a display device, and for example, relates to brightness adjustment of a so-called dual view display configured such that different images can be seen depending on the viewing direction on one display screen. .

2. Description of the Related Art Conventionally, there has been provided a dual view display configured such that different images can be seen depending on the viewing direction on one display screen (see, for example, Patent Document 1). For example, when a dual-view display is used as an in-vehicle display device for a car navigation system, navigation information is displayed on the driver side, and television images and DVD (Digital Versatile Disk) images are displayed to passengers other than the driver. It can be displayed.
JP 2004-233816 A

  By the way, LCD (liquid crystal display device) often used as an in-vehicle display device changes the visibility (visibility) of display contents depending on the brightness of the surroundings. For this reason, in an in-vehicle display device, in order to improve visibility, the backlight brightness of the LCD is controlled to a predetermined value based on the ambient illuminance that changes according to the driving situation and the driving time zone. ing. In addition, since the vehicle travels with the headlights turned on at night, the backlight brightness is controlled to a predetermined value in accordance with the lighting of the headlights. An automatic light control device is used for the automatic adjustment of the backlight luminance.

  In this automatic light control device, for example, PWM (Pulse Width Modulation) control is performed so that the backlight luminance is most suitable for a certain ambient illuminance. That is, the pulse width of the PWM signal is determined in real time according to the ambient illuminance detected by the sensor and the presence / absence of lighting of the headlight, and the drive unit of the backlight is subjected to switching control according to the pulse width. This allows the backlight brightness to be linear so that the backlight is dark when the ambient illuminance is low (when the headlight is on) and bright when the ambient illuminance is high (when the headlight is off). adjust.

  However, in the dual view display, since one backlight is shared by the left and right images, the backlight luminance is always the same in the left and right. For this reason, when the surroundings become dark and the backlight brightness is lowered, not only the navigation image on the driver side but also the brightness of the television image on the passenger side is lowered. However, when the backlight luminance is low, the gradation of the video cannot be accurately expressed, and in the case of the video originally having low luminance, there is a problem that the dark portion is crushed black.

  Note that only the image on the driver's seat side can be adjusted to be darker by adjusting the contrast and brightness of the image itself displayed on the driver's seat side. However, with this method, the brightness of absolute black (black 100%) cannot be changed. That is, there is a problem that the brightness of absolute black cannot be reduced unless the backlight brightness is reduced.

Further, as a means for controlling the brightness of the image, a dark filter comprising a liquid crystal shutter or the like is disposed on the LCD, and the light transmittance of the dark filter is controlled by a voltage applied to the dark filter, thereby displaying the image. A technique has also been proposed in which the brightness of the entire image can be controlled from a low luminance level to a high luminance level (see, for example, Patent Document 2).
JP-A-7-123342

  However, the technique described in Patent Document 2 controls the brightness of the entire display image, and cannot control only the brightness of one image in the dual view display.

  The present invention has been made to solve such a problem, and can realize different backlight luminances on the left and right sides of the dual view display so that only one image can be displayed with reduced luminance. For the purpose.

  In order to solve the above-described problems, in the present invention, a liquid crystal shutter configured to change a transmissivity and a viewing angle in response to application of a voltage, and a voltage control unit that controls an applied voltage to the liquid crystal shutter; By applying a voltage to the liquid crystal shutter, the light passing through the polarizing filter from the light source of the liquid crystal display device is dimmed and the luminance in the predetermined direction is reduced.

  According to the present invention configured as described above, in the state where no voltage is applied to the liquid crystal shutter, since all the polarized light that has passed through one polarizing filter passes through the other polarizing filter, the entire display image is bright. Is displayed. On the other hand, when a voltage is applied to the liquid crystal shutter, the alignment of the liquid crystal molecules changes, and polarized light that has passed through one polarization filter and entered from a specific direction cannot pass through the other polarization filter. For this reason, the image seen from this direction becomes dark. Therefore, when a voltage is applied to the liquid crystal shutter, only one image of the dual view display can be darkened, and only one image can be displayed with reduced brightness.

  Hereinafter, an embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a diagram illustrating a schematic configuration example of a liquid crystal display device including the brightness adjusting device according to the present embodiment. In FIG. 1, 1 is a backlight (corresponding to the light source of the present invention) disposed on the back surface of the liquid crystal display, and 2 is configured such that the transmissivity and the viewing angle change according to the application of voltage. A liquid crystal shutter, 3 is a liquid crystal panel used as a dual view display, and 4 is a voltage control unit for controlling a voltage applied to the liquid crystal shutter 2. The liquid crystal shutter 2 is disposed between the backlight 1 and the liquid crystal panel 3.

  FIG. 2 is a diagram for explaining the principle of a dual view display using a parallax barrier. As shown in FIG. 2, the dual view display is configured by a combination of a switch liquid crystal 101 and a TFT (Thin Film Transistor) liquid crystal 102.

  The switch liquid crystal 101 is provided with a plurality of optical parallax barriers 103 at equal intervals. The parallax barrier 103 controls the traveling direction of the light from the backlight 1 and separates the light so that different lights reach the left and right observation positions 106 and 107. Further, in the TFT liquid crystal 102, the left image and the right image are alternately displayed on the left pixel group 104 and the right pixel group 105 which are alternately arranged.

  Light that passes through the parallax barrier 103 and passes through the left pixel group 104 reaches the left observation position 106, and light that passes through the parallax barrier 103 and passes through the right pixel group 105 reaches the right observation position 107. Thereby, on the display screen of one TFT liquid crystal 102, different images can be seen depending on the viewing direction.

  FIG. 3 is a diagram showing a cross-sectional structure of the liquid crystal shutter 2. In FIG. 3, 11a and 11b are polarizing filters, 12a and 12b are glass substrates, 13a and 13b are transparent electrodes, 14a and 14b are alignment films, 15 is a spacer, and 16 is a liquid crystal. In this way, the polarizing filters 11a and 11b, the glass substrates 12a and 12b, the transparent electrodes 13a and 13b, and the alignment films 14a and 14b each form a pair, and these layers sandwich the central liquid crystal 16 in a sandwich shape. Is configured.

  The polarizing filters 11a and 11b control light entering and exiting and are arranged so that their polarization directions are twisted by 90 degrees. The alignment films 14a and 14b are films for aligning the molecules of the liquid crystal 16 in a certain direction, and are arranged so that the direction of each groove is twisted by 90 degrees.

  FIG. 4 is a diagram showing the arrangement of liquid crystal molecules. As shown in FIG. 4, when the liquid crystal 16 is brought into contact with the alignment films 14a and 14b having fine grooves in a certain direction, the liquid crystal molecules are aligned along the grooves. By sandwiching the liquid crystal 16 between the two alignment films 14a and 14b whose groove directions are changed by 90 degrees, the liquid crystal molecules are twisted by 90 degrees and arranged in the layer secured by the spacer 15, as shown in FIG.

  When light passes through the liquid crystal 16 in which the molecular arrangement is twisted 90 degrees in this way, the light is twisted 90 degrees along the gap where the liquid crystal molecules are arranged. When the twisted liquid crystal 16 is sandwiched between two polarizing filters 11a and 11b whose polarization directions are orthogonal, light from the backlight 1 entering from one polarizing filter 11a is 90 degrees along the gap between the liquid crystal molecules. Since it reaches the other polarizing filter 11b in a twisted state, it can pass through the other polarizing filter 11b.

  On the other hand, when a voltage is applied to the liquid crystal shutter 2, the arrangement of the liquid crystal molecules changes. That is, the liquid crystal molecules are arranged with an angle corresponding to the magnitude of the applied voltage with respect to the polarizing filters 11a and 11b. In the present embodiment, the voltage control unit 4 controls the magnitude of the applied voltage, so that the molecules of the liquid crystal 16 are 0 degrees (parallel) to 90 degrees (with respect to the polarizing filters 11a and 11b) as shown in FIG. A predetermined angle (for example, about 45 degrees).

  In FIG. 5, arrow A indicates the transmission axis of one polarizing filter 11a, and arrow B indicates the transmission axis of the other polarizing filter 11b, which are twisted by 90 degrees. Arrows C and D indicate vibration directions of polarized light that passes through one polarizing filter 11a, and arrows E and F indicate vibration directions of polarized light that reaches the other polarizing filter 11b.

  When the applied voltage to the liquid crystal 16 is off, the liquid crystal molecules are parallel to the polarizing filters 11a and 11b. Therefore, the light emitted from the backlight 1 passes through the liquid crystal 16 from any direction and passes through the liquid crystal 16 and is twisted 90 degrees and passes through the other polarizing filter 11b. Thereby, the whole display image is displayed brightly.

  On the other hand, when a voltage is applied to the liquid crystal 16 to change the alignment of the liquid crystal molecules, when the polarized light emitted from one polarizing filter 11a passes through the liquid crystal 16 in this state, the polarized light is polarized in a specific direction as indicated by the solid line arrow X. Is twisted 90 degrees and completely passes through the other polarizing filter 11b (see arrows C and F). As a result, when the light coming from the direction of the solid line arrow X is viewed from the opposite direction, the portion looks bright to the observer.

  On the other hand, polarized light coming from a specific direction such as the dotted arrow Y passes through the liquid crystal 16 without twisting up to 90 degrees (see arrows D and E). Therefore, polarized light in such a direction cannot completely pass through the other polarizing filter 11b. As a result, when the light coming from the direction of the dotted arrow Y is viewed from the opposite direction, the portion looks dark to the observer.

  As described above, in the present embodiment, the transmittance of the polarized light and the viewing angle are controlled to change by applying a voltage to the liquid crystal shutter 2 to change the alignment of the liquid crystal molecules. That is, by applying a voltage to the liquid crystal shutter 2, the polarized light traveling from the backlight 1 through the one polarizing filter 11a in a predetermined direction is dimmed to reduce the luminance in the predetermined direction. .

  Thereby, as shown in FIG. 6, while using one backlight 1, it is possible to realize different backlight luminances on the left and right of the dual view display. For example, it is possible to reduce the backlight luminance only for the image on the driver seat side without reducing the backlight luminance for the image on the passenger seat side. Since the luminance is not reduced by adjusting the video signal, the absolute black luminance can also be reduced.

  The viewing angle dependence when a voltage is applied to the liquid crystal shutter 2 is increased when a liquid crystal 16 having a viewing angle that is not originally wide is used. Therefore, the liquid crystal 16 used in the liquid crystal shutter 2 has a narrower viewing angle than the active matrix driving TFT (Thin Film Transistor) type or MIM (Metal-Insulator-Metal) type, and the passive matrix driving type TN (Twisted Nematic). ) Type liquid crystal and STN (Super Twisted Nematic) type liquid crystal.

  In addition, although the said embodiment demonstrated the example which arrange | positions the liquid-crystal shutter 2 between the backlight 1 and the liquid crystal panel 3 (dual view display), this invention is not limited to this. For example, the backlight 1, the liquid crystal panel 3, and the liquid crystal shutter 2 may be arranged in this order.

  In the above embodiment, an example in which the brightness adjusting device of the present invention is applied to a transmissive liquid crystal display including the backlight 1 has been described. However, a reflective liquid crystal display that performs display by reflecting external light, a reflective liquid crystal display, The present invention may be applied to a transflective liquid crystal display using a backlight in a dark place and outside light in a bright place by merging transmissive types.

  In addition, each of the above-described embodiments is merely an example of implementation in carrying out the present invention, and the technical scope of the present invention should not be construed in a limited manner. In other words, the present invention can be implemented in various forms without departing from the spirit or main features thereof.

  The present invention is useful for an apparatus that adjusts the brightness of a display image by controlling light from a light source.

It is a figure which shows the example of schematic structure of the liquid crystal display device provided with the luminance adjusting apparatus by this embodiment. It is a figure which shows the structural example of a dual view display. It is a figure which shows the cross-section of the liquid-crystal shutter by this embodiment. It is a figure which shows the arrangement | sequence of a liquid crystal molecule when the voltage is not applied to a liquid-crystal shutter. It is a figure which shows the arrangement | sequence of a liquid crystal molecule when a voltage is applied to a liquid-crystal shutter. It is a figure which shows the example of the display state of a dual view display.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Backlight 2 Liquid crystal shutter 3 Liquid crystal panel 4 Voltage control part 11a, 11b Polarizing filter 14a, 14b Alignment film 16 Liquid crystal

Claims (5)

A liquid crystal shutter configured to change the transmissivity and the viewing angle in response to application of a voltage;
A brightness adjusting apparatus for a display device, comprising: a voltage control unit that controls an applied voltage to the liquid crystal shutter. 2. The brightness adjusting apparatus for a display device according to claim 1, wherein the liquid crystal shutter is disposed between a light source and a liquid crystal panel. The liquid crystal shutter includes two polarizing filters arranged in a relationship in which the polarization direction is twisted by 90 degrees,
A liquid crystal disposed between the two polarizing filters,
The brightness adjusting device for a display device according to claim 1, wherein polarization is controlled by changing an arrangement of liquid crystal molecules according to a voltage applied to the liquid crystal. 4. The brightness adjusting apparatus for a display device according to claim 3, wherein the liquid crystal is a TN liquid crystal. In a liquid crystal display device provided with a liquid crystal shutter configured to change the transmissivity and the viewing angle according to the application of voltage,
By applying a voltage to the liquid crystal shutter, the polarized light from the light source of the liquid crystal display device passing through a polarizing filter and traveling in a predetermined direction is dimmed to reduce the luminance in the predetermined direction. A brightness adjustment method for a display device.

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