JP2006276363A - Liquid crystal device and electronic equipment - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To control an angle of visibility by simple data processing in a liquid crystal device. <P>SOLUTION: The liquid crystal device has a wide visibility angle display mode and a narrow visibility angle display mode as display modes of image data. In the wide visibility angle display mode, input image data are outputted to a liquid crystal display part as display image data in a non-converted state and displayed. In the narrow visibility angle display mode, display image data are generated by shifting the gradation value of the input image data to the white gradation value side and displayed on the liquid crystal display part. Since contrast is reduced by shifting the gradation value of the input image data to the white gradation value side, visibility is reduced. Thereby visibility from the side direction can be reduced and a side visibility angle can be narrowed. Since the visibility angle can be limited by simple data conversion processing of the input image data, a change in the structure of the liquid crystal panel itself is not required and visibility angle control can be inexpensively realized. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to viewing angle control of a liquid crystal device.

  TN (Twisted Nematic) liquid crystal used in various types of liquid crystal devices has a property that the contrast and hue differ depending on the viewing direction, so-called viewing angle dependency, because the liquid crystal molecules are obliquely oriented when a voltage is applied. For this reason, various techniques for reducing the viewing angle dependency and widening the viewing angle have been proposed.

  As a method for widening the viewing angle, a method of improving the structure of the liquid crystal panel itself and a method of using an optical member such as a viewing angle compensation film are widely used. On the other hand, a method of controlling the viewing angle by signal processing of an image signal to be displayed without changing the structure of the liquid crystal panel itself has been proposed. For example, Patent Document 1 has a γ conversion circuit for independently converting RGB input data so as to obtain a desired viewing angle characteristic according to the VT characteristic of a liquid crystal panel, and a plurality of γ data so as to obtain a desired viewing angle characteristic. A method of switching between and using is disclosed.

Japanese Patent Application No. 2001-147673

  SUMMARY An advantage of some aspects of the invention is that it provides a liquid crystal device capable of controlling a viewing angle by simple data processing and an electronic apparatus using the liquid crystal device.

  In one aspect of the present invention, the liquid crystal device outputs input image data as display image data without conversion at the time of wide viewing angle display, and converts the gradation value of the input image data to a white gradation value at the time of narrow viewing angle display. A data processing unit that outputs the display image data shifted to the side, and a liquid crystal display unit that displays the display image data.

  The liquid crystal device displays input image data on a liquid crystal display unit. Here, the liquid crystal device has a wide viewing angle display mode and a narrow viewing angle display mode as image data display modes. At the time of wide viewing angle display, the input image data is output to the liquid crystal display unit as display image data without conversion and displayed. On the other hand, at the time of narrow viewing angle display, display image data in which the gradation value of the input image data is shifted to the white gradation value side is generated and displayed on the liquid crystal display unit. By shifting the gradation value of the input image data to the white gradation value side, the contrast is lowered, so that the visibility is lowered. As a result, the visibility from the left and right direction can be reduced, and the left and right viewing angles can be narrowed. Since the viewing angle can be limited by simple data conversion processing of input image data, it is not necessary to change the structure of the liquid crystal display panel itself, and viewing angle control can be realized at low cost.

  In one aspect of the liquid crystal device, the data processing unit changes a shift amount for shifting the gradation value of the input image data in accordance with a viewing angle control amount input from the outside. By changing the shift amount according to the required viewing angle control amount, the viewing angle control degree can be easily changed. In a preferred example, when the input image data is Din, the display image data is Dout, the shift amount is a, and the number of gradations of the input image data is b, the data processing unit Dout = Din / b + a The display image data is generated according to the following formula.

  In another aspect of the liquid crystal device, the data processing unit may perform a predetermined gradation display method when a gradation value of the display image data does not match a gradation value that can be displayed by the liquid crystal display unit. Means for converting a gradation value of the display image data into a gradation value that can be displayed by the liquid crystal display unit. By shifting the gradation value of the input image data to the white gradation value side, the liquid crystal display panel may become a gradation value that cannot be originally displayed. In this case, for example, error diffusion method, dither method, etc. Through this process, the gradation value of the display image data may be converted into a gradation value that can be displayed by the liquid crystal display unit and displayed. As a result, it is possible to prevent a specific gradation from being unable to be expressed.

  In addition, an electronic device including the above liquid crystal device can be formed.

  Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings.

[Liquid Crystal Display]
A schematic configuration of a liquid crystal device to which the present invention is applied is shown in FIG. The liquid crystal device 100 includes a data processing unit 10, a controller 15, and a display unit 20. The data processing unit 10 performs data processing for viewing angle control on input image data Din supplied from the outside, generates display image data Dout, and supplies the display image data Dout to the display unit 20. The display unit 20 displays the supplied display image data Dout on the liquid crystal panel 23.

The data processing unit 10 includes a data conversion unit 11 and a conversion control unit 12. The data converter 11 performs data processing for controlling the viewing angle. Specifically, during wide viewing angle display, the input image data Din is output as it is, that is, without conversion, as display image data Dout. On the other hand, at the time of narrow viewing angle display, the input image data Din is converted to shift the gradation value to the white gradation value side to generate display image data Dout. Specifically, the input image data is Din, the display image data is Dout, the amount by which the gradation value of the input image data is shifted (referred to as “shift amount”) is a, and the number of gradations of the input image data is b. When the data processing unit,
Dout = f (Din) + a (Formula 1)
= Din / b + a (Formula 2)
Then, the conversion process is performed to generate display image data. In addition, Formula 1 is a general formula, and f (Din) is a monotonically increasing function of Din in this case. Data conversion in the data converter 11 will be described in detail later.

  The conversion control unit 12 responds to the control signals S1 and S2 supplied from the controller 15 with parameters used for data conversion in the data conversion unit 11, specifically, the shift amount a and the level of the input image data in the above equation 2. The coefficient b is determined and supplied to the data converter 11. Specifically, the controller 15 supplies the conversion control unit 12 with a control signal S1 indicating the viewing angle control amount and a control signal S2 indicating the number of gradations of the input image data. The conversion control unit 12 supplies the data conversion unit 11 with the gradation number b of the input image data indicated by the control signal S2. Further, the conversion control unit 12 determines the shift amount a based on the viewing angle control amount indicated by the control signal S <b> 1 and supplies the shift amount a to the data conversion unit 11.

  The controller 15 is connected to an input device (not shown) and the like, and supplies the viewing angle control amount input by the user via the input device to the conversion control unit 12 as a control signal S1. For example, when the liquid crystal device has two display modes of a wide viewing angle display mode and a narrow viewing angle display mode, the user inputs a selection or switching instruction for one of the modes using the input device. The controller 15 receives this instruction and generates a control signal S1 as a viewing angle control amount.

  A multi-stage narrow viewing angle display mode can also be prepared. For example, a narrow viewing angle display mode and an ultra narrow viewing angle control mode in which the viewing angle is further limited may be prepared. In this case, the viewing angle control amount in the ultra-narrow viewing angle control mode is set larger than the viewing angle control amount in the narrow viewing angle control mode. Further, the input device may be a device capable of inputting a continuous amount such as a jog dial, for example, so that the user can input a desired viewing angle restriction degree. In that case, the controller 15 supplies a viewing angle control amount corresponding to the operation amount of the input device by the user to the conversion control unit 12 as the control signal S1.

  The display unit 20 includes an X driver 21, a Y driver 22, and a liquid crystal panel 23. The Y driver 22 supplies a selection signal to the scanning lines of the liquid crystal panel 23. The X driver 21 receives the display image data Dout supplied from the data processing unit 10 and writes the display image data Dout to the scanning line selected by the Y driver 22. Thereby, the display image data Dout is displayed on the liquid crystal panel 23. Note that various methods can be adopted as a display control method for the display image data Dout in the liquid crystal panel 23, and application of the present invention is not limited to a specific display control method.

[Viewing angle control]
Next, the viewing angle control will be described in detail. There is a correlation between the viewing angle of the liquid crystal panel and the contrast. If the contrast is lowered, the visibility is lowered. As a result, the viewing angle is limited. Therefore, in the present invention, at the time of narrow viewing angle display, data conversion is performed to shift the gradation value of the input image data to the white gradation value side, thereby reducing the contrast and narrowing the viewing angle.

  FIG. 2 is a graph showing the angle dependence of the transmittance at each gradation of the liquid crystal panel. Note that the graph of FIG. 2 is an example of a vertical alignment type liquid crystal panel capable of 64 gradation display with gradation values of 0 to 63. In FIG. 2, the horizontal axis represents the viewing angle in the left-right direction. The vertical axis represents the transmittance of the liquid crystal panel, with the upper side corresponding to white and the lower side corresponding to black. Further, “n / 63” in the figure shows a transmittance graph when n gradations of 0 to 63 are displayed on the liquid crystal panel. As shown in the figure, the transmittance increases as the gradation value increases in the front direction (viewing angle 0 degree), but as the viewing angle increases to the left and right, the increase in transmittance with respect to the increase in the gradation value decreases. The transmittance is saturated at a certain gradation value. That is, when the gradation value of certain display data increases, the transmittance increases in the front direction, and thus there is no problem in visibility. On the other hand, when the viewing angle exceeds a predetermined angle (about ± 40 degrees in the example of FIG. 2), the transmittance is saturated and the visibility is lowered when the number of gradations of the image data is increased. Therefore, by increasing the gradation value of the image data, that is, by shifting the gradation value to the white side, the visibility from the left and right direction can be reduced while maintaining the front direction visibility. It is understood that the viewing angle of direction can be limited.

  FIG. 3 shows the relationship between the viewing angle and contrast when the data conversion unit 11 performs data conversion on input image data and when it does not. In FIG. 3, the graph of “0/63” is a graph when data conversion is not performed, and it can be seen that sufficient contrast can be obtained with a wide viewing angle. The graph “7/63” is a graph when the gradation value of the input image data is converted so that black has a gradation value “7”. The brightness of white does not change in the front direction, and is about 100. Sufficient contrast is obtained. On the other hand, contrast decreases in the left-right direction. It is generally said that the contrast that human beings feel easy to see is “5” or more, and when the contrast is “5” or less, the visibility is drastically lowered. Using this criterion, when the gradation value of the input image data is converted so that the gradation value of black is “7”, the left and right viewing angles can be limited to about ± 40 degrees.

  Further, as shown by the graph of “16/63”, when the gradation value of the input image data is converted so that the gradation value of black is “16”, the contrast is reduced to about 20 in the front direction, but the brightness is increased. The visibility does not deteriorate so much because it does not change. On the other hand, the viewing angle in the left-right direction is limited to about ± 25 degrees. This is particularly effective in securing the confidentiality of display information by limiting the viewing angle in the left-right direction in a portable electronic device or the like.

  Thus, by converting the gradation value of the input image data so that black is shifted to the white side, it is possible to limit the viewing angle in the left-right direction. In the present embodiment, the data conversion unit described above is used. 11 performs this conversion according to Equation 2 above. In Equation 2 above, the shift amount “a” indicates the amount by which the black gradation value is shifted to the white side. Since the normal (ie, the black gradation value is not shifted) black gradation value is “0”, the black gradation value is converted to “7” as in the example of FIG. In this case, the shift amount a in Expression 2 is 7. In Expression 2, the term “Din / b” is required to assign each gradation value of the converted image data to the gradation width between black and white after the shift amount a is shifted. . For example, when the shift amount a = 7, each gradation value of 0 to 63 of the input image data is converted into each gradation value obtained by dividing the gradation width of 7 to 63 into 64 after the data conversion process according to Equation 2. Will be assigned.

  In the case of providing a plurality of stages of narrow viewing angle modes, the shift amount a in Equation 2 may be changed. For example, the shift amount in the narrow viewing angle display mode may be set to a1, and the shift amount in the ultra narrow viewing angle display mode may be set to a2 (> a1). In addition, when the viewing angle control amount is continuously changed, the shift amount a may be continuously changed.

  Normally, the gradation value of the output image data is set to the number of gradations that can be displayed on the liquid crystal display panel. That is, if the liquid crystal display panel can display 64 gradations, the output image data is expressed in 64 gradations. However, in the present invention, the black gradation value is shifted to the white side by the shift amount a according to Equation 2, and the gradation range after the shift is divided into 64 to express 64 gradations. The gradation value may actually correspond to a gradation value that cannot be displayed by the liquid crystal display panel. In that case, an intermediate gradation that the liquid crystal display panel cannot originally display may be displayed by a known method such as an error diffusion method or a dither method.

  In the above embodiment, the data processing unit 10 is configured independently of the display unit 20 as shown in FIG. 1, but the data processing unit 10 may be provided in the X driver 21.

[Electronics]
Next, specific examples of electronic devices to which the liquid crystal display device 100 according to the present invention can be applied will be described with reference to FIG.

  First, an example in which the liquid crystal display device 100 according to the present invention is applied to a display unit of a portable personal computer (so-called notebook personal computer) will be described. FIG. 4A is a perspective view showing the configuration of this personal computer. As shown in the figure, the personal computer 710 includes a main body 712 having a keyboard 711 and a display 713 to which the liquid crystal display panel according to the present invention is applied.

  Next, an example in which the liquid crystal display device 100 according to the present invention is applied to a display unit of a mobile phone will be described. FIG. 4B is a perspective view showing the configuration of this mobile phone. As shown in the figure, the cellular phone 720 includes a plurality of operation buttons 721, a reception port 722, a transmission port 723, and a display unit 724 to which the liquid crystal display device 100 according to the present invention is applied.

  Note that, as an electronic device to which the liquid crystal display device 100 according to the present invention can be applied, in addition to the personal computer shown in FIG. 4A and the mobile phone shown in FIG. Type / monitor direct-view type video tape recorder, car navigation device, pager, electronic notebook, calculator, word processor, workstation, videophone, POS terminal, digital still camera, etc.

It is a block diagram which shows schematic structure of the liquid crystal display device which concerns on embodiment. The angle dependence of the transmittance | permeability in each gradation of a certain liquid crystal display panel is shown. It is a graph which shows the relationship between the viewing angle at the time of data conversion, and contrast. It is the schematic which shows the electronic device to which the liquid crystal display device of this invention is applied.

Explanation of symbols

10 data processing unit, 11 data conversion unit, 12 conversion control unit, 15 controller, 20 display unit, 21 X driver, 22 Y driver, 23 liquid crystal panel

Claims (5)

Data that outputs input image data without conversion during wide viewing angle display, and outputs display image data in which the gradation value of the input image data is shifted to the white gradation value side during narrow viewing angle display A processing unit;
And a liquid crystal display unit for displaying the display image data.   The liquid crystal device according to claim 1, wherein the data processing unit changes a shift amount for shifting a gradation value of the input image data in accordance with a viewing angle control amount input from the outside. When the input image data is Din, the display image data is Dout, the shift amount is a, and the gradation number of the input image data is b, the data processing unit is
Dout = Din / b + a
The liquid crystal device according to claim 2, wherein the display image data is generated according to the formula:   When the gradation value of the display image data does not match the gradation value that can be displayed by the liquid crystal display unit, the data processing unit converts the gradation value of the display image data into the liquid crystal by a predetermined gradation display method. The liquid crystal device according to any one of claims 1 to 3, further comprising means for converting the display unit into a displayable gradation value.   An electronic apparatus comprising the liquid crystal device according to claim 1.

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