WO2012147602A1

WO2012147602A1 - Liquid crystal display apparatus

Info

Publication number: WO2012147602A1
Application number: PCT/JP2012/060555
Authority: WO
Inventors: 勇司田中
Original assignee: シャープ株式会社
Priority date: 2011-04-26
Filing date: 2012-04-19
Publication date: 2012-11-01

Abstract

In order to obtain a configuration capable of displaying a smooth image close to an original image while improving the viewing angle of a liquid crystal panel in a liquid crystal display apparatus, a liquid crystal display apparatus (1) is provided with a liquid crystal panel (11) in which a plurality of pixels are arranged in a matrix, and a viewing angle adjustment device (13) which adjusts the viewing angle of the liquid crystal panel (11) by changing the tone of an image signal inputted to each of the pixels. The viewing angle adjustment device (13) comprises a tone conversion unit (21) which performs black display when the tone of the inputted signal is less than or equal to a lower limit, performs white display when the tone of the inputted signal is greater than or equal to an upper limit, and performs tone conversion in at least part of a halftone range, an error calculation unit (22) which finds the error between the tone of a signal outputted from the tone conversion unit (21) and the tone of the signal inputted to the tone conversion unit, and an error correction unit (24) which, using the error, corrects the tone of a signal for the next pixel to be inputted to the tone conversion unit (21).

Description

Liquid crystal display

The present invention relates to a liquid crystal display device having a liquid crystal panel.

Conventionally, a liquid crystal display device having a liquid crystal panel is known. In such a liquid crystal display device, as disclosed in, for example, Japanese Patent Laid-Open No. 6-222740, a predetermined unit for improving the viewing angle of the liquid crystal panel with respect to a display unit (pixel group) composed of a plurality of pixels of the liquid crystal panel is disclosed. The gradation of the pixel is corrected with this pattern. As described above, a method of correcting the gradation of a pixel with a predetermined pattern for a display unit composed of a plurality of pixels is generally called a dither method.

By the way, when the tone of each pixel is corrected by using the dither method as in the configuration disclosed in the above-mentioned Japanese Patent Application Laid-Open No. 6-222740, the number of pixels for white display and black display is increased and the image is displayed in a dot shape. The For this reason, the corrected image is difficult to see. In addition, when the dither method as described above is used, the resolution is lowered, so that it may be particularly difficult to recognize characters and the like.

An object of the present invention is to obtain a configuration capable of displaying a smooth image close to the original image while improving the viewing angle of the liquid crystal panel in the liquid crystal display device.

A liquid crystal display device according to one aspect of the present invention includes a liquid crystal panel in which a plurality of pixels are arranged in a matrix, and a change in gradation of a video signal input to each of the pixels. A viewing angle adjusting device that adjusts the viewing angle, wherein the viewing angle adjusting device sets the gradation of the input signal to black display below the lower limit value and white display above the upper limit value, and to the lower limit value. A gradation conversion unit that performs gradation conversion in at least a part of the intermediate gradation range between the upper limit value and the upper limit value, a gradation of the signal that is output after gradation conversion by the gradation conversion unit, and the gradation conversion An error calculation unit for obtaining an error from the gradation of the signal input to the unit, and an error calculated by the error calculation unit, the gradation of the signal for the next pixel input to the gradation conversion unit is determined. An error correction unit for correcting.

According to an embodiment of the present invention, a configuration capable of displaying a smooth image close to the original image while improving the viewing angle of the liquid crystal panel can be obtained.

FIG. 1 is a block diagram showing a schematic configuration of the liquid crystal display device according to the first embodiment. FIG. 2 is a diagram illustrating a schematic configuration of the viewing angle adjustment circuit according to the first embodiment. FIG. 3 is a diagram illustrating an example of the relationship between the gradation of the video signal and the transmittance of the liquid crystal panel when the liquid crystal panel is viewed from the front. FIG. 4 is a diagram illustrating an example of the relationship between the gradation of the video signal and the transmittance of the liquid crystal panel when the liquid crystal panel is viewed from an oblique direction. FIG. 5 is a diagram illustrating an example of a difference in transmittance of the liquid crystal panel when the liquid crystal panel is viewed from the front and when viewed from an oblique direction. FIG. 6 is an example of various signals input to the viewing angle adjustment circuit. FIG. 7 is a diagram showing the relationship between the gradation of the video signal input to the viewing angle adjustment circuit and the gradation of the video signal output from the viewing angle adjustment circuit in the liquid crystal display device according to the first embodiment. It is. FIG. 8 is a diagram illustrating an example in which the input video is subjected to gradation conversion by the dither method and the configuration of the first embodiment. FIG. 9 is a diagram illustrating a schematic configuration of a viewing angle adjustment circuit of the liquid crystal display device according to the second embodiment. FIG. 10 is a diagram showing the relationship between the gradation of the video signal input to the viewing angle adjustment circuit and the gradation of the video signal output from the viewing angle adjustment circuit in the liquid crystal display device according to the second embodiment. It is. FIG. 11 shows an example in which the input video is subjected to gradation conversion by the configuration of the second embodiment. FIG. 12 is a block diagram illustrating a schematic configuration of a liquid crystal display device according to the third embodiment. FIG. 13 is a diagram illustrating a schematic configuration of a viewing angle adjustment circuit according to the third embodiment. FIG. 14 shows an example in which the input video is tone-converted without an initial error value and tone-converted with an error initial value. FIG. 15 is a block diagram illustrating a schematic configuration of a liquid crystal display device according to the fourth embodiment. FIG. 16 is a diagram illustrating a schematic configuration of a viewing angle adjustment circuit according to the fourth embodiment. FIG. 17 shows an example in which the input video is subjected to gradation conversion by the configuration of the fourth embodiment. FIG. 18 is a block diagram illustrating a schematic configuration of a liquid crystal display device according to the fifth embodiment. FIG. 19 is a diagram illustrating a schematic configuration of a viewing angle adjustment circuit according to the fifth embodiment. FIG. 20 shows an example in which the input video is subjected to gradation conversion by the configuration of the fifth embodiment. FIG. 21 is a block diagram illustrating a schematic configuration of a liquid crystal display device according to a modification of the fifth embodiment. FIG. 22 is a diagram illustrating a schematic configuration of a viewing angle adjustment circuit according to a modification of the fifth embodiment. FIG. 23 is a block diagram showing a schematic configuration of the liquid crystal display device according to the sixth embodiment. FIG. 24 is a diagram illustrating a schematic configuration of a viewing angle adjustment circuit according to the sixth embodiment. FIG. 25 shows an example in which the input video is subjected to gradation conversion by the configuration of the sixth embodiment. FIG. 26 is a block diagram showing a schematic configuration of the liquid crystal display device according to the seventh embodiment. FIG. 27 is a block diagram showing a schematic configuration of the liquid crystal display device according to the eighth embodiment. FIG. 28 is a block diagram showing a schematic configuration of the liquid crystal display device according to the ninth embodiment.

A liquid crystal display device according to an embodiment of the present invention includes a liquid crystal panel in which a plurality of pixels are arranged in a matrix, and the liquid crystal panel by changing a gradation of a video signal input to each pixel. A viewing angle adjusting device that adjusts the viewing angle of the input signal, wherein the viewing angle adjusting device sets the gradation of the input signal to black display below the lower limit value and white display above the upper limit value. A gradation conversion unit that performs gradation conversion in at least a part of an intermediate gradation range between the value and the upper limit value, a gradation of a signal that is output after gradation conversion by the gradation conversion unit, and the gradation An error calculation unit for obtaining an error from the gradation of the signal input to the conversion unit, and a signal gradation for the next pixel input to the gradation conversion unit using the error calculated by the error calculation unit An error correction unit for correcting Adult).

With the above configuration, an error between the gradation of the signal input to the viewing angle adjustment device that adjusts the viewing angle of the liquid crystal panel and the gradation of the signal output after gradation conversion by the viewing angle adjustment device is considered. Thus, the gradation of the signal of the next pixel input to the viewing angle adjusting device can be corrected. Thereby, it is possible to correct an error of gradation conversion in the viewing angle adjusting device and display an image closer to the original image on the liquid crystal panel.

In addition, in the viewing angle adjusting device, the input signal is displayed in black when the gradation is lower than the lower limit value and is displayed in white when the gradation is higher than the upper limit value. Can be spread. Thereby, the viewing angle characteristic of the liquid crystal panel can be improved.

Therefore, with the above configuration, a smooth image closer to the original image can be displayed on the liquid crystal panel while improving the viewing angle characteristics of the liquid crystal panel.

In the first configuration, the gradation conversion unit is configured to convert a gradation of a signal input to the gradation conversion unit into a gradation proportional to the gradation in the intermediate gradation range. (Second configuration).

Thus, a signal having a gradation within the intermediate gradation range is not converted into a signal having a greatly different gradation. Therefore, it is possible to display an image closer to the original image on the liquid crystal panel.

In the first configuration, the gradation conversion unit converts the gradation of the signal input to the gradation conversion unit into a constant gradation in at least a part of the gradation range in the intermediate gradation range. (Third configuration).

This makes it possible to convert a signal having a gradation within the intermediate gradation range into a signal having a clearer gradation. Therefore, the viewing angle characteristics of the liquid crystal panel can be improved with the above-described configuration.

In any one of the first to third configurations, the liquid crystal panel includes a plurality of lines in which a plurality of pixels are arranged in an example. An error initial value setting unit is further provided for setting different error initial values for each adjacent line with respect to the gradation of the video signal of the pixel on which the gradation conversion is performed (fourth configuration).

In this way, by giving an initial error value to the gradation of the pixel that is first subjected to gradation conversion in each line of the liquid crystal panel, the gradation of the pixel on the line is changed to a clear gradation. It becomes possible to change. In addition, since the error initial value is different for each adjacent line, the entire liquid crystal panel can display an image with clearer contrast. Thereby, the viewing angle characteristic of the liquid crystal panel can be further improved.

In the fourth configuration, the error initial value setting unit sets an error initial value for each line so that the magnitude relationship between the error initial values given to the adjacent lines is switched for each display frame of the liquid crystal panel ( Fifth configuration).

As a result, the brightness changes for each display frame at each pixel, so that the viewer sees the image of the average gradation, that is, the image close to the input image. On the other hand, since an error initial value is given in each frame, the gradation of each pixel changes to improve the viewing angle characteristics of the liquid crystal panel.

Therefore, the viewing angle characteristics of the liquid crystal panel can be improved while displaying an image closer to the input image by the above-described configuration.

In the fifth configuration, the error initial value setting unit has an error initial value that is different from positive to negative for each display frame of the liquid crystal panel with respect to each line so that the sum of error initial values in each line becomes zero. Is set (sixth configuration).

By doing so, the viewer can visually recognize the image displayed with an average gradation while improving the viewing angle in each display frame. Thereby, the viewing angle characteristic of the liquid crystal panel can be improved while displaying an image close to the original image.

In any one of the first to sixth configurations, a predetermined error pattern in a pixel group composed of a plurality of pixels is generated by a signal input to the gradation conversion unit and the error calculation unit. An error addition unit for adding to any one of the calculated errors is further provided (seventh configuration).

As described above, the viewing angle characteristics of the liquid crystal panel can be further improved by further combining the dither method for correcting the gradation with a predetermined error pattern in a pixel group composed of a plurality of pixels.

In the seventh configuration, the error adding unit changes the error pattern for each display frame of the liquid crystal panel so that the error due to the error pattern becomes zero in each pixel in the pixel group (eighth). Configuration). In this way, since the gradation is corrected by the dither method of the error pattern that is different for each display frame in each pixel, the viewer visually recognizes the image displayed with the average gradation. This makes it possible to improve the viewing angle characteristics of the liquid crystal panel in each display frame while displaying an image closer to the original image.

In any one of the first to eighth configurations, a gradation range changing unit that changes at least one of the lower limit value and the upper limit value is further provided (9th configuration).

This makes it possible to change the lower limit value that serves as a reference for black display and the upper limit value that serves as a reference for white display, so that the viewing angle characteristics of the liquid crystal panel can be improved and smooth images close to the original image can be displayed. Can be easily realized. That is, by increasing the lower limit value and decreasing the upper limit value, the range of the gradation area for black display and white display becomes wider, so that the viewing angle characteristics of the liquid crystal panel can be improved efficiently. On the other hand, by decreasing the lower limit value and increasing the upper limit value, the range of the gradation area for black display and white display becomes narrower, so that it is possible to display with gradation close to the original image. Smooth images close to the images can be displayed.

The ninth configuration further includes a visible number detection unit that detects the number of viewers who are viewing the liquid crystal panel, and the gradation range changing unit is configured to detect the number of visible numbers by the visible number detection unit. Accordingly, at least one of the lower limit value and the upper limit value is changed (tenth configuration).

By doing so, since at least one of the lower limit value and the upper limit value can be changed according to the number of viewers viewing the liquid crystal panel, the viewing angle characteristics of the liquid crystal panel can be improved according to the number of viewers. That is, as the number of viewers of the liquid crystal panel increases, the number of viewers viewing from the oblique direction with respect to the display surface of the liquid crystal panel increases, and accordingly, the viewing angle characteristics need to be improved accordingly. On the other hand, when the number of viewers of the liquid crystal panel is small, since there are few viewers viewing from the oblique direction with respect to the display surface of the liquid crystal panel, it is possible to restore the original image rather than improving the viewing angle characteristics. It is preferable to display a close smooth image. By changing at least one of the lower limit value and the upper limit value according to the request inferred from the number of viewers, video is output under more suitable conditions for viewers viewing the liquid crystal panel. can do.

The ninth configuration further includes a visual position detection unit that detects a position of a viewer viewing the liquid crystal panel and obtains an angle between the viewer and a normal line of the display surface of the liquid crystal panel. The gradation range changing unit is configured to change at least one of the lower limit value and the upper limit value according to a detection result of the angle by the visual recognition position detection unit (an eleventh configuration).

Accordingly, at least one of the lower limit value and the upper limit value is changed according to the angular position of the viewer viewing the liquid crystal panel, that is, the angle formed by the viewer and the normal line of the display surface of the liquid crystal panel. Can do. In other words, when there is a viewer who is viewing the liquid crystal panel from an oblique direction, it is necessary to improve the viewing angle characteristics of the liquid crystal panel, while the viewer is viewing the liquid crystal panel from substantially the front. When there is only one person, a smooth image display closer to the original image is required. By changing at least one of the lower limit value and the upper limit value according to the viewer's angular position with respect to such a liquid crystal panel, an image is output under more suitable conditions for a viewer viewing the liquid crystal panel. be able to.

Hereinafter, preferred embodiments of the liquid crystal display device of the present invention will be described with reference to the drawings. In addition, the dimension of the structural member in each figure does not represent the dimension of an actual structural member, the dimension ratio of each structural member, etc. faithfully.

FIG. 1 is a block diagram showing a schematic configuration of a liquid crystal display device 1 according to the first embodiment of the present invention. The liquid crystal display device 1 includes a liquid crystal panel 11, a backlight 12, and a viewing angle adjustment circuit 13 (viewing angle adjustment device). As will be described in detail later, the liquid crystal display device 1 is configured to improve the viewing angle characteristics of the display surface of the liquid crystal panel 11 by changing the gradation of each pixel of the liquid crystal panel 11 from the gradation of the input image. Has been. In FIG. 1, illustration of source drivers, gate drivers, and the like for driving the liquid crystal panel 11 and various signals such as vertical synchronization signals and horizontal synchronization signals input to these drivers are omitted. . The liquid crystal display device 1 of this embodiment can be used as a display unit of a television, a game machine, a personal computer, a portable information terminal, or the like, for example.

Although not specifically shown, the liquid crystal panel 11 includes an active matrix substrate in which a large number of pixels are arranged in a matrix, a counter substrate disposed to face the active matrix substrate, and a liquid crystal sealed between these substrates. With layers. The liquid crystal panel 11 may be, for example, a transmissive liquid crystal panel, or a reflective or semi-reflective liquid crystal panel. That is, the liquid crystal panel 11 may have any configuration as long as it can display video.

Although not particularly shown, the active matrix substrate is provided with a thin film transistor as a switching element, a pixel electrode, and a plurality of rows of gate lines and a plurality of columns of source lines arranged in a grid so as to surround them. Yes.

The counter substrate is disposed at a position facing at least the pixel electrode of the active matrix substrate. The counter substrate is provided with a counter electrode. Each pixel is formed by the counter electrode, the pixel electrode of the active matrix substrate, and the liquid crystal layer disposed therebetween.

The gate electrode of the thin film transistor in the active matrix substrate is connected to the above gate driver through a gate line. Therefore, when a gate voltage is output from the gate driver to the gate line, the thin film transistor connected to the gate line is selected. The gate driver outputs a gate voltage with reference to the vertical synchronization signal.

On the other hand, the source electrode of the thin film transistor is connected to the above-described source driver via a source line. The source driver generates a gradation display signal necessary for gradation display of a video based on the input video signal. Therefore, when a grayscale display signal is output as a drive voltage from the source driver to the source line, a voltage is applied to the liquid crystal of each pixel through the thin film transistor connected to the gate line selected by the gate driver. That is, the source driver outputs a driving voltage corresponding to each gate line based on the video signal, thereby enabling gradation display of each pixel. The source driver outputs a drive voltage with reference to the horizontal synchronization signal.

The backlight 12 is arranged on one side in the thickness direction of the liquid crystal panel 11 although not particularly shown. As the backlight 12, for example, a direct type, an edge light type, or a planar light source type can be used. Moreover, as a light source of the backlight 12, a cold cathode tube, a light emitting diode, etc. can be used, for example.

The viewing angle adjustment circuit 13 converts the gradation of the video signal input to the liquid crystal panel 11 so as to improve the viewing angle characteristics on the display surface of the liquid crystal panel 11. That is, the viewing angle adjustment circuit 13 is configured to convert the gradation of the original video signal and output it to the liquid crystal panel 11 so that the viewing angle characteristics are improved on the display surface of the liquid crystal panel 11.

Here, the viewing angle characteristics of the liquid crystal panel 11 will be described with reference to FIGS. The liquid crystal panel 11 adjusts the light transmittance by applying a voltage to the liquid crystal layer to change the alignment state of the liquid crystal molecules in the liquid crystal layer. The liquid crystal panel 11 has a narrow viewing angle compared to other display devices because the alignment state of liquid crystal molecules changes relatively depending on the viewing direction with respect to the display surface. For example, in the case of a liquid crystal panel in which the transmittance of the liquid crystal is proportional to the gradation of the video signal as shown in FIG. As shown in FIG. 4, as shown in FIG. 4, it seems that the transmittance is increased in some gradations. In FIG. 3 and FIG. 4, normalization is performed so that the transmittance of the liquid crystal panel becomes 1 when the gradation of the video signal is 256.

For example, as shown in FIG. 3, when the gradation of the video signal is 128, the transmittance is 0.5 when the display surface of the liquid crystal panel 11 is viewed from the front. On the other hand, as shown in FIG. 4, when the display surface is viewed obliquely (45 degrees with respect to the normal of the display surface), the transmittance is 0.75. This will be described with an example of an image displayed on the liquid crystal panel 11 (an image having a transmittance of 0.5 when viewed from the front). As shown by an image 1 in FIG. When viewed from 45 [deg.] With respect to the normal of the surface, the transmittance is 0.75, and it looks whitish.

On the other hand, as shown in video 2 in FIG. 5, when the liquid crystal panel 11 is viewed from the front, the gradation of the video signal is zero (so that the average transmittance is 0.5, which is the same as that of video 1. Pixels (hatched portions) that are black) are arranged in a staggered pattern. Then, even when the liquid crystal panel 11 is viewed from an oblique direction (45 degrees with respect to the normal of the display surface), the average transmittance is 0.5.

As described above, when an image having an intermediate gradation (for example, gradation 128) is displayed on the liquid crystal panel 11 (image 1 in FIG. 5), the transmittance of the liquid crystal panel 11 greatly varies depending on the viewing direction. Therefore, the viewing angle is improved as shown in video 2 in FIG. Examples of such a viewing angle improvement method include a dither method.

However, when video display such as video 2 in FIG. 5 is performed, pixels in which the gradation is zero (black display) and pixels in which the gradation is maximum (white display) are mixed. Therefore, unlike the original image, the image 2 looks like a dotted image as shown in the image 2 of FIG. For this reason, the original video and the video to be displayed are greatly different, and the display image quality is deteriorated.

In the present embodiment, the viewing angle adjustment circuit 13 is configured to display an image closer to the original image while improving the viewing angle of the liquid crystal panel 11. Specifically, as shown in FIGS. 1 and 2, the viewing angle adjustment circuit 13 converts an input video signal (hereinafter referred to as an input video signal) into an output video signal that improves viewing angle characteristics. Is configured to do. Moreover, the viewing angle adjustment circuit 13 is configured to use a so-called error diffusion method in which an error between the gradation of the output video signal and the gradation of the input video signal is used for gradation conversion of the next pixel. .

More specifically, as shown in FIGS. 1 and 2, the viewing angle adjustment circuit 13 includes a gradation conversion unit 21 that converts the gradation of the input video signal, and the level of the signal converted by the gradation conversion unit 21. An error calculating unit 22 for obtaining an error between the tone and the gradation of the signal before conversion, an error holding unit 23 for storing the error, and an error correcting unit 24 for correcting the input signal of the next pixel using the error. Have. In addition to the signals (not shown) input to the liquid crystal panel 11, various signals as shown in FIGS. 1 and 6 are input to the viewing angle adjustment circuit 13. That is, as shown in FIGS. 1 and 6, the viewing angle adjustment circuit 13 receives a clock signal (clock), a video signal, a vertical synchronization signal, a horizontal synchronization signal, and an effective signal as reference signals. The valid signal is a signal that is output during a period in which the video signal is output, and is generally used to erase a blanking period provided between the video signals.

As shown in FIG. 2, the gradation converting unit 21 is configured to obtain the gradation y of the output signal according to the gradation x of the input signal. Specifically, the gradation converting unit 21 compares the gradation x of the input signal with a minimum value (MIN) that is a predetermined lower limit value and a maximum value (MAX) that is an upper limit value. When the value is smaller than the value (MIN), y = 0 (black display in this embodiment), and when it is larger than the maximum value (MAX), y = 256 (white display in this embodiment). Further, the gradation converting unit 21 sets y = R (set value) when the gradation x of the input signal is between the minimum value (MIN) and the maximum value (MAX). In other words, the gradation conversion unit 21 sets the minimum value (MIN) and the maximum value (MAX) to thereby display an intermediate gradation for displaying an image other than the black indication (gradation 0) and the white display (gradation 256). A range is defined.

FIG. 7 shows an example of the relationship between the gradation x of the input signal and the gradation y of the output signal in the gradation conversion unit 21. In the example of FIG. 7, the minimum value (MIN) of the intermediate gradation range is set to 64, the maximum value (MAX) is set to 192, and the gradation of the output signal is converted to 192 for the gradation of 128 or more. ing. As shown in FIG. 7, an input signal having a gradation of the minimum value (= 64) or less is converted into an output signal having a gradation of zero, while an input signal having a gradation of the maximum value (= 192) or more is It is converted into an output signal of gradation 256. An input signal having a gradation of 128 or more is converted into an output signal having a gradation 192.

As described above, in the present embodiment, the gradation conversion unit 21 converts the gradation of the video signal into a signal whose gradation changes stepwise according to the value of the gradation. In addition, as described above, the minimum value and the maximum value are determined, and a signal having a gradation below the minimum value is converted to an output signal having a gradation of zero, while a signal having a gradation above the maximum value is changed to the maximum gradation. By doing so, the gradation of black display and white display can each be increased. Thereby, the viewing angle characteristic of the liquid crystal panel 11 can be improved.

As shown in FIGS. 1 and 2, the error calculation unit 22 obtains an error z between the gradation x of the signal input to the gradation conversion unit 21 and the gradation y of the output signal. In other words, the error calculation unit 22 is configured to obtain a tone error when the tone is converted by the tone conversion unit 21.

The error holding unit 23 is configured by, for example, a memory device, and is configured to hold the error z calculated by the error calculation unit 22. As shown in FIG. 2, the error holding unit 23 receives a clock signal and a valid signal. The error holding unit 23 outputs the error z to the error correction unit 24 according to the valid signal so as to match the input of the video signal while synchronizing with the clock signal.

As shown in FIG. 2, the error correction unit 24 is configured to correct the gradation of the video signal based on the error z output from the error holding unit 23. In other words, the error correction unit 24 uses the gradation error z generated in the gradation conversion unit 21 to correct the gradation i of the video signal for the next pixel. The signal corrected by the error correction unit 24 is input to the gradation conversion unit 21.

With the configuration of the viewing angle adjustment circuit 13 as described above, it is possible to converge the error in the gradation converting unit 21 and display an image closer to the original image on the liquid crystal panel 11. That is, the viewing angle adjustment circuit 13 can realize viewing angle improvement by an error diffusion method which is one of pseudo halftone processing methods.

Next, an example of converting the gradation of the input video will be described. In FIG. 8, when the entire display surface is displayed with an intermediate gradation (for example, gradation 126) (the upper part of FIG. 8), the character “A” is displayed with an intermediate gradation (for example, gradation 126). FIG. 8 shows an example in which tone conversion is performed by the conventional dither method and the method of the present embodiment.

First, in the dither method, calculation was performed using a dither pattern corresponding to a pixel group consisting of four pixels. Specifically, in the example of FIG. 8, four pixels surrounded by a thick line are defined as one pixel group, and calculation is performed using a dither pattern for this pixel group. In the dither pattern in the example of FIG. 8, the gradation after conversion of each pixel is calculated by, for example, the following equation according to the position of the pixel in the pixel group (see the bottom diagram in FIG. 8).

(1) Position of “1” in the dither pattern of FIG. 8 y = x × 4 (0 ≦ x <64), 256 (64 ≦ x)
(2) Position of “2” in the dither pattern of FIG. 8 y = 0 (x <64), (x−64) × 4 (64 ≦ x <128), 256 (128 ≦ x)
(3) Position of “3” in the dither pattern of FIG. 8 y = 0 (x <128), (x−128) × 4 (128 ≦ x <192), 256 (192 ≦ x)
(4) Position of “4” in the dither pattern of FIG. 8 y = 0 (x <192), (x−192) × 4 (192 ≦ x)

When the gradation of each pixel is converted using the dither method as described above, as shown in FIG. 8, when the entire display surface is an intermediate gradation image (for example, a gradation of 126), a black display level is obtained. Tone zero (shaded area) appears in a staggered pattern. Therefore, although the viewing angle characteristic of the liquid crystal panel 11 can be improved, it becomes difficult to see as a dotted image. Further, when gradation conversion is performed by the dither method, the character “A” becomes difficult to be recognized as a character as shown in FIG.

On the other hand, the gradation conversion of this embodiment using the viewing angle adjustment circuit 13 having the above-described configuration is performed using the relationship between the gradation of the input signal and the gradation of the output signal as shown in FIG. . That is, assuming that MIN = 64 and MAX = 192, the gradation conversion unit 21 calculates the gradation in each pixel by the following equation.

y = 0 (x ≦ 64), 64 (64 <x <128),
192 (128 ≦ x <192), 256 (192 ≦ x)

As described above, an error between the gradation of the signal on the input side and the gradation of the signal on the output side of the gradation conversion unit 21 is obtained by the error calculation unit 22, and the error is held by the error holding unit 23. Then, at the timing when the video signal of the next pixel is input to the viewing angle adjustment circuit 13, the error correction unit 24 corrects the gradation of the video signal with the error. In the present embodiment, the error corrected by the error correction unit 24 is set to zero in the pixel to be calculated first. Further, the error obtained at the last pixel of the line in the liquid crystal panel 11 is used for correcting the video signal of the first pixel of the next line.

When the gradation of each pixel is converted by the method of the present embodiment, as shown in FIG. 8, in the case of an image in which the entire display surface is displayed with an intermediate gradation (for example, the gradation is 126), the entire display surface is displayed. Although each pixel has a variation in gradation, it becomes an intermediate gradation (for example, gradation is 64, 192). That is, in the method of this embodiment, unlike the dither method, a display in which black display pixels are present in a zigzag manner does not occur, so that an image closer to the original display image can be displayed. This is more remarkable in the case where the character “A” is displayed. That is, when the gradation of the character “A” displayed with the intermediate gradation (for example, the gradation is 126) is converted by the method of the present embodiment, the gradation is different for each pixel (for example, the gradation is 64, 192). However, unlike the dither method, it is not difficult to recognize as a character.

Further, by performing the gradation conversion as described above, as shown as image 3 in FIG. 5, the liquid crystal panel 11 is obliquely oriented with respect to the transmittance 0.5 when the liquid crystal panel 11 is viewed from the front ( When viewed from 45 degrees with respect to the normal of the display surface, the average transmittance is 0.6. Therefore, by performing the gradation conversion as described above, the viewing angle characteristics of the liquid crystal panel 11 can be improved as compared with the case where the gradation conversion is not performed (video 1). Note that the image 3 in FIG. 5 is also an example in which the transmittance is calculated using FIGS. 3 and 4.

In this embodiment, the gradation of the video signal in the range larger than the gradation 64 and smaller than the gradation 128 is converted into the gradation 64, and at the same time, the gradation is greater than the gradation 128 and smaller than the gradation 192. The gradation of the video signal is converted to gradation 192. However, only one gradation may be converted in the intermediate gradation range, or the intermediate gradation range may be divided into three or more ranges and converted into different gradations.

(Effects of the first embodiment)
In this embodiment, gradation conversion of the next pixel is performed using an error between the gradation of the signal on the input side and the gradation of the signal on the output side of the gradation conversion unit 21. Thereby, it is possible to display an image closer to the original image while improving the viewing angle characteristics of the liquid crystal panel 11.

In addition, the gradation conversion unit 21 converts gradations below the minimum value (MIN) to gradations 0 (black display) and converts gradations above the maximum value (MAX) to maximum gradations (white display). Therefore, the gradation range of black display and white display can be increased, and the viewing angle characteristics of the liquid crystal panel 11 can be improved.

[Second Embodiment]
FIG. 9 shows a schematic configuration of the viewing angle adjusting circuit 30 (viewing angle adjusting device) of the liquid crystal display device according to the second embodiment of the present invention. The viewing angle adjustment circuit 30 of this embodiment is different from the first embodiment in the configuration of the gradation conversion unit 31. In the following description, the same parts as those of the first embodiment are denoted by the same reference numerals, and the description thereof is omitted. The parts different from the first embodiment will be mainly described.

Specifically, the gradation conversion unit 31 outputs an output signal according to the following expression if the gradation x of the input signal is between the minimum value (MIN) and the maximum value (MAX) (intermediate gradation range). The tone y of the signal to be obtained is obtained. In the gradation conversion unit 31 of the present embodiment, if the gradation x of the input signal is less than the minimum value (MIN), the gradation y of the output signal is changed to zero, while the input signal If the gradation x is equal to or greater than the maximum value (MAX), the gradation y of the output signal is changed to the maximum gradation.

Y = (x-MIN) × 256 / (MAX-MIN)

That is, in this embodiment, as shown in FIG. 10, the gradation converting unit 31 has a gradation x of the input signal between the minimum value (MIN) and the maximum value (MAX) (intermediate gradation range). In this case, the gradation x is converted to a gradation y proportional to the gradation x. That is, in the present embodiment, in the intermediate gradation range, the gradation of the input signal (x) is converted using a linear function as shown in FIG.

FIG. 11 shows an example of gradation change when the gradation conversion unit 31 of the present embodiment is used. As shown in FIG. 11, the character “A” is displayed in an intermediate gradation (for example, 128 gradations) even when an image having an intermediate gradation (for example, a gradation of 128) is displayed on the entire screen. Even in this case, when the gradation of the input video is converted by the viewing angle adjustment circuit 30 of the present embodiment, the output video is also displayed with an intermediate gradation. Therefore, according to the configuration of the present embodiment, an image closer to the original image can be displayed on the liquid crystal panel 11.

(Effect of 2nd Embodiment)
In this embodiment, if the gradation of the input signal is within an intermediate gradation range between the minimum value (MIN) and the maximum value (MAX), gradation conversion is performed using a linear function. This makes it possible to display an image closer to the original image on the liquid crystal panel 11.

[Third Embodiment]
FIG. 12 is a block diagram showing a schematic configuration of a liquid crystal display device 40 according to the third embodiment of the present invention. In this embodiment, the configuration of the viewing angle adjustment circuit 41 (viewing angle adjustment device) of the liquid crystal display device 40 is different from that of the second embodiment described above. In the following description, the same components as those in the above-described second embodiment are denoted by the same reference numerals, description thereof is omitted, and differences from the second embodiment are mainly described.

Specifically, as shown in FIGS. 12 and 13, the viewing angle adjustment circuit 41 includes an error calculation unit 22, an error holding unit 23, an error correction unit 24 similar to those in the first embodiment, and the same as in the second embodiment. A gradation conversion unit 31. That is, also in this embodiment, as in the above-described second embodiment, the gradation converting unit 31 can input the input signal if the gradation of the input signal is between the minimum value (MIN) and the maximum value (MAX). The gradation of the received signal is converted by a linear function and output.

In addition, the viewing angle adjustment circuit 41 of the present embodiment includes an error initial value setting unit 42 that gives an error initial value to the error holding unit 23 when performing gradation conversion of pixels at the beginning of each line in the liquid crystal panel 11. Have. The error initial value setting unit 42 is configured to identify the first pixel of each line based on the input horizontal synchronization signal. Then, the error initial value setting unit 42 sets the error initial value to the error holding unit when it is detected that the pixel to be subjected to gradation conversion next is the first pixel of each line based on the horizontal synchronization signal. Output to 23. Note that the initial value of the error output by the error initial value setting unit 42 is preferably different for each line, and more preferably a value such that the initial value of the error becomes zero in adjacent lines. For example, as shown in FIG. 14, when the initial error value is 32 for the first pixel of a certain line, the initial error initial value of the next line is preferably -32.

The initial value of the error output from the error initial value setting unit 42 is held by the error holding unit 23, and then when the video signal is input according to the valid signal, the error correction unit is synchronized with the clock signal. 24 (see FIGS. 12 and 13). Thus, the error correction unit 24 corrects the video signal for the first pixel of the line in the liquid crystal panel 11 using the initial value of the error.

In the present embodiment, the error holding unit 23 is held in the error holding unit 23 every time the line of the liquid crystal panel 11 changes, that is, every time an error initial value is input from the error initial value setting unit 42. The error is changed to the initial value. The error holding unit 23 may add the error at that time and the initial value of the error output from the error initial value setting unit 42 when the line changes.

As described above, FIG. 14 shows the change in gradation when the initial value of the error is given to the video signal for the first pixel of each line. As shown in the center portion of FIG. 14, when the initial value of the error is not added to the video signal for the first pixel of each line, the output video may be almost the same as the input video. Such a phenomenon is often observed in the case of a regular still image in which there is almost no difference in transmittance between adjacent pixels.

On the other hand, as shown on the right side of FIG. 14, by adding the initial value of the error to the video signal for the first pixel of each line, a difference occurs in the gradation after conversion for each line, and conversion of each pixel is performed. Later gradation changes from the input video. Therefore, with the configuration of the present embodiment, it is possible to prevent the output video from being substantially equivalent to the input video, and to improve the viewing angle characteristics of the liquid crystal panel 11.

Further, even when the configuration of this embodiment is used, black display pixels do not appear in a staggered manner or cannot be recognized as characters unlike the dither method. Therefore, even with the configuration of the present embodiment, it is possible to display an image closer to the original image on the liquid crystal panel 11 while improving the viewing angle characteristics of the liquid crystal panel 11.

(Effect of the third embodiment)
In this embodiment, an initial error value is assigned to the video signal for the first pixel in each line. As a result, even in the case of a still image in which there is almost no difference in transmittance between adjacent pixels, the input video can be prevented from being output as it is as an output video.

Therefore, according to the configuration of the present embodiment, even in the case of a still image, it is possible to display an image closer to the original image on the liquid crystal panel 11 while improving the viewing angle of the liquid crystal panel 11.

[Fourth Embodiment]
FIG. 15 is a block diagram showing a schematic configuration of a liquid crystal display device 50 according to the fourth embodiment of the present invention. In the liquid crystal display device 50 of this embodiment, the configuration of the viewing angle adjustment circuit 51 (viewing angle adjustment device) is different from the configuration of the third embodiment described above. In the following description, the same components as those of the above-described third embodiment are denoted by the same reference numerals, description thereof is omitted, and differences from the third embodiment are mainly described.

Specifically, as shown in FIGS. 15 and 16, the viewing angle adjustment circuit 51 includes a gradation conversion unit 31, an error calculation unit 22, an error holding unit 23, and an error correction unit 24 similar to those in the third embodiment. . The viewing angle adjustment circuit 51 of the present embodiment also has an error initial value setting unit 52 as in the third embodiment. Further, the viewing angle adjustment circuit 51 of the present embodiment includes a display frame determination unit 53 that determines display frame switching.

When the vertical synchronization signal is input, the display frame determination unit 53 determines that the display frame has been switched, and outputs a display frame switching signal to the error initial value setting unit 52. The display frame determination unit 53 determines display frame switching by detecting the rising or falling edge of the vertical synchronization signal.

The error initial value setting unit 52 is configured to give an initial value of error to the video signal for the first pixel of each line based on the horizontal synchronization signal, as in the third embodiment. Further, the error initial value setting unit 52 is configured to invert the initial value of the error from the initial value of the error in the previous display frame based on the signal output from the display frame determination unit 53. Yes. That is, when a signal is output from the display frame determination unit 53, the error initial value setting unit 52 reverses the sign of the initial value of the error output to each line in the previous display frame, and converts it after conversion. Output the value to each line of the next display frame.

FIG. 17 shows the gradation conversion result of the input video when the viewing angle adjustment circuit 51 of the present embodiment is used. As shown in FIG. 17, when the display frame is switched, the sign of the initial value of the error to be added to the input signal of the first pixel of each line is inverted, so that the level of each pixel of the output video is displayed for each display frame. Tone changes. As a result, the viewer visually recognizes the average value of the gradation to be converted for each display frame in each pixel, and thus visually recognizes an image closer to the original image than the configuration of each of the embodiments described above. can do. In addition, in each display frame, since the gradation of each pixel is converted by the gradation converting unit 31, the viewing angle characteristics of the display panel 11 can be improved.

(Effect of the fourth embodiment)
In this embodiment, the sign of the initial value of the error given to the input signal of the first pixel of each line in the liquid crystal panel 11 is inverted for each display frame. As a result, the viewer can visually recognize each pixel at an average value of gradations that change for each display frame, and thus can visually recognize an image closer to the original image. In addition, since the gradation of each pixel is converted in each display frame, the viewing angle characteristics of the liquid crystal panel 11 can be improved.

Therefore, according to the configuration of this embodiment, it is possible to make the viewer visually recognize an image closer to the original image while improving the viewing angle characteristics of the liquid crystal panel 11.

[Fifth Embodiment]
FIG. 18 is a block diagram showing a schematic configuration of a liquid crystal display device 60 according to the fifth embodiment of the present invention. The liquid crystal display device 60 of this embodiment is different from the above-described second embodiment in the configuration of the viewing angle adjustment circuit 61 (viewing angle adjustment device). In the following description, the same components as those of the second embodiment are denoted by the same reference numerals, description thereof is omitted, and components different from those of the second embodiment are mainly described.

Specifically, as shown in FIGS. 18 and 19, the viewing angle adjustment circuit 61 includes a gradation conversion unit 31, an error calculation unit 22, an error holding unit 23, and an error correction unit 24 similar to those in the second embodiment. Have Furthermore, the viewing angle adjustment circuit 61 of the present embodiment includes a dither pattern generation unit 62 that generates a dither pattern used for the dither method, and the dither pattern generated by the dither pattern generation unit 62 as an error. And an error adder 63 for adding to the input signal.

The dither pattern generation unit 62 is configured to generate a dither pattern based on the horizontal synchronization signal, the valid signal, and the clock signal. That is, the dither pattern generation unit 62 generates an error pattern for a pixel group (for example, four pixels) according to the video signal.

More specifically, the dither pattern generation unit 62 obtains the X coordinate of each pixel from the input clock signal and valid signal, and obtains the Y coordinate of each pixel from the input horizontal synchronization signal. Then, the dither pattern generation unit 62 generates an error dither pattern by setting an error according to the coordinates of each pixel obtained in this way. In the example of the present embodiment, the dither pattern generation unit 62 is, for example, +8 for pixels where both the X coordinate and the Y coordinate are odd, and +4 for pixels where the X coordinate is even and the Y coordinate is odd. A pattern is generated that gives an error of −4 for pixels with an odd X coordinate and an even Y coordinate, and −8 for pixels with an even X coordinate and Y coordinate.

It should be noted that the error dither pattern generated by the dither pattern generation unit 62 is preferably a pattern in which the error of each pixel differs within the pixel group to which the dither pattern is assigned. Further, the dither pattern described above is preferably a pattern in which the error is zero in the pixel group. The error value in the above-described dither pattern is an example, and naturally, other values may be used.

19, the error adding unit 63 is configured to add the dither pattern of the error d generated by the dither pattern generating unit 62 to the input signal v of the gradation converting unit 31. As a result, the error signal d of the dither pattern is added to the error z between the output side and the input side of the gradation converter 31 in the input signal of the gradation converter 31.

FIG. 20 shows an example of gradation conversion when the viewing angle adjustment circuit 61 having the above-described configuration is used. In FIG. 20, dither pattern errors as shown in the lower part of FIG. 20 are used to facilitate the calculation of the gradation of the output video. In practice, as described above, it is preferable to use an error smaller than the error of the dither pattern shown in FIG.

As shown in FIG. 20, the gradation change at each pixel is further increased as compared with the configuration of the second embodiment described above. That is, the viewing angle characteristics can be further improved by providing the dither pattern generation unit 62 and the error addition unit 63 so that errors due to the dither pattern can be added to the configuration of the second embodiment as in the present embodiment. .

(Effect of 5th Embodiment)
In this embodiment, the tone conversion unit 31 adds the error of the dither pattern to the error between the tone of the signal on the output side and the tone of the signal on the input side of the tone conversion unit 21 in the second embodiment. Input signal. Thereby, the viewing angle characteristic of the liquid crystal panel 11 can be improved by the amount of the dither pattern error.

Therefore, with the configuration of the present embodiment, the viewing angle characteristics of the liquid crystal panel 11 can be further improved while displaying an image closer to the original image.

In addition, by using the dither pattern, it is possible to reduce the unique pattern that occurs in the configuration of the second embodiment. That is, when tone conversion of a video is performed using the configuration of the second embodiment, a pattern peculiar to the output video may be formed, but such a pattern can be reduced by a dither pattern, The display quality of output video can be improved.

(Modification of the fifth embodiment)
FIG. 21 shows a liquid crystal display device 70 according to a modification of the fifth embodiment. In this modification, the error dither pattern generated by the dither pattern generation unit 62 is added to the error between the gradation of the signal on the output side of the gradation conversion unit 31 and the gradation of the signal on the input side. This is different from the fifth embodiment. In the following description, the same components as those in the above-described fifth embodiment are denoted by the same reference numerals, description thereof is omitted, and differences from the fifth embodiment are mainly described.

Specifically, as shown in FIGS. 21 and 22, the error adder 63 calculates an error for calculating an error between the tone of the signal on the output side of the tone converter 31 and the tone of the signal on the input side. The error dither pattern generated by the dither pattern generation unit 62 is added to the signal output from the unit 22.

Also with this configuration, the gradation converter 31 can take into account the error of the dither pattern in addition to the error between the output signal gradation and the input signal gradation, and the viewing angle of the liquid crystal panel 11 The characteristics can be further improved.

[Sixth Embodiment]
FIG. 23 is a block diagram showing a schematic configuration of a liquid crystal display device 80 according to the sixth embodiment of the present invention. In the liquid crystal display device 80 of this embodiment, the configuration of the viewing angle adjustment circuit 81 (viewing angle adjustment device) is different from the configuration of the fifth embodiment. In the following description, the same components as those in the fifth embodiment are denoted by the same reference numerals, description thereof is omitted, and differences from the fifth embodiment are mainly described.

Specifically, as shown in FIGS. 23 and 24, the viewing angle adjustment circuit 81 is similar to the fifth embodiment in the gradation conversion unit 31, the error calculation unit 22, the error holding unit 23, and the error correction unit 24. And an error adder 63. Furthermore, the viewing angle adjustment circuit 81 of this embodiment includes a display frame determination unit 82 that determines display frame switching, and an error dither pattern (error) for each display frame in accordance with an output signal from the display frame determination unit 82. A dither pattern generation unit 83 for generating (pattern).

When the vertical synchronization signal is input as shown in FIG. 24, the display frame determination unit 82 determines that the display frame has been switched, and outputs a display frame switching signal. The display frame determination unit 82 determines display frame switching by detecting the rising or falling edge of the vertical synchronization signal.

The dither pattern generation unit 83 is configured to generate a dither pattern based on the horizontal synchronization signal, the valid signal, and the clock signal, as in the fifth embodiment. That is, the dither pattern generation unit 83 obtains the X coordinate of each pixel from the input clock signal and valid signal, and obtains the Y coordinate of each pixel from the input horizontal synchronization signal. Then, the dither pattern generation unit 83 generates an error dither pattern by setting an error according to the coordinates of each pixel thus obtained.

In addition, the dither pattern generation unit 83 is configured to be able to generate at least two dither patterns. In the present embodiment, the dither pattern generation unit 83 sets, for example, as the first pattern, +8 for pixels where both the X coordinate and the Y coordinate are odd, and pixels where the X coordinate is even and the Y coordinate is odd. On the other hand, a pattern that gives an error of +4, an X coordinate that is odd and a Y coordinate that is even -4, and an X that is an even number of pixels that both X and Y coordinates are -8. Generate. In addition, the dither pattern generation unit 83, for example, as a second pattern, for pixels where both the X coordinate and the Y coordinate are odd, -8, and for pixels where the X coordinate is even and the Y coordinate is odd. Generates a pattern that gives an error of -4, +4 for pixels with an odd X coordinate and an even number of Y coordinates, and +8 for an even number of pixels with both X and Y coordinates.

Furthermore, the dither pattern generation unit 83 is configured to generate and output different dither patterns in accordance with the display frame switching signal output from the display frame determination unit 82. For example, in the present embodiment, the dither pattern generation unit 83 switches and outputs the first pattern and the second pattern described above in accordance with a display frame switching signal output from the display frame determination unit 82.

FIG. 25 shows an example of gradation conversion when the viewing angle adjustment circuit 81 having the above-described configuration is used. In FIG. 25, an error of a dither pattern as shown on the right side of FIG. 25 is used to facilitate the calculation of the gradation of the output video. In practice, it is preferable to use an error smaller than the error of the dither pattern shown in FIG.

As shown in FIG. 25, two types of output video can be obtained for the same input video, depending on the dither pattern switched for each display frame. That is, since the gradation changes for each display frame in each pixel, the viewer visually recognizes the gradation of the average value of those gradations. Therefore, the viewing angle adjustment circuit 81 outputs a video signal that is closer to the original video than the configuration in which the dither pattern is combined with the configuration of the second embodiment as in the fifth embodiment described above. be able to.

(Effect of 6th Embodiment)
In this embodiment, a dither pattern different for each display frame is added to the error between the output side and the input side of the gradation converting unit 31. Thereby, the viewer visually recognizes the gradation of each pixel as an average value of gradation when the dither pattern is added. Therefore, the viewer can visually recognize the video as almost the same as the original video. In addition, since the video with improved viewing angle characteristics is displayed in each display frame, the viewing angle characteristics of the liquid crystal panel 11 can be improved.

[Seventh Embodiment]
FIG. 26 is a block diagram showing a schematic configuration of a liquid crystal display device 90 according to the seventh embodiment of the present invention. The liquid crystal display device 90 of this embodiment includes a MAX and MIN changing unit 91 (tone range changing unit) that changes the minimum value (MIN) and the maximum value (MAX) when the tone conversion unit 31 performs tone conversion. Is different from the configuration of the second embodiment. In the following description, the same components as those of the second embodiment are denoted by the same reference numerals, description thereof is omitted, and differences from the second embodiment are mainly described. In FIG. 26, the viewing angle adjustment circuit 30 is simplified, but the configuration of the viewing angle adjustment circuit 30 is the same as the configuration of the second embodiment.

Specifically, as shown in FIG. 26, the MAX and MIN changing unit 91 outputs a minimum value (MIN) that is a threshold value for black display to the gradation converting unit 31 and white according to a mode input from the outside. A signal for determining a maximum value (MAX) which is a display threshold value is output.

Although not particularly illustrated, the liquid crystal display device 90 is provided with a mode selection switch capable of selecting, for example, a viewing angle improvement mode and an image quality priority mode. When mode selection is performed by the mode selection switch, a mode signal corresponding to the selected mode is input to the MAX and MIN changing unit 91.

In the MAX and MIN changing unit 91, the gradation range in which the gradation converting unit 31 of the viewing angle adjusting circuit 30 converts to a gradation other than black and white, that is, the minimum value of the intermediate gradation range, according to the input mode signal. Set (MIN) and maximum value (MAX). The minimum value (MIN) means a threshold value for converting the gradation below it to black display, and the maximum value (MAX) means a threshold value for converting the gradation above it to white display. .

For example, in the viewing angle improvement mode, the MAX and MIN changing unit 91 increases the minimum value (MIN) and the maximum value (MAX) of the intermediate gradation range compared to the image quality priority mode. On the other hand, for example, in the image quality priority mode, the MAX and MIN changing unit 91 decreases the minimum value (MIN) and increases the maximum value (MAX) of the intermediate gradation range as compared with the viewing angle improvement mode.

As described above, the minimum value (MIN) and the maximum value (MAX) of the gradation conversion range in the gradation adjustment unit 31 of the viewing angle adjustment circuit 30 are changed according to the selected mode, so that it is suitable for each mode. Video display can be performed. In other words, in the viewing angle improvement mode, the viewing angle of the liquid crystal panel 11 is improved by expanding the gradation range to be converted into white display and black display. On the other hand, in the image quality priority mode, the display image on the liquid crystal panel 11 can be made closer to the original image by narrowing the gradation range for conversion to white display and black display.

(Effect of 7th Embodiment)
In this embodiment, the minimum value (MIN) and the maximum value (MAX) of the intermediate gradation range in the gradation conversion unit 31 of the viewing angle adjustment circuit 30 are changed according to the selected mode. Thereby, it is possible to perform screen display suitable for the selected mode.

[Eighth Embodiment]
FIG. 27 is a block diagram showing a schematic configuration of a liquid crystal display device 100 according to the eighth embodiment of the present invention. The liquid crystal display device 100 according to this embodiment detects the number of people viewing the liquid crystal panel 11, and changes the minimum value (MIN) and maximum value (MAX) of the intermediate gradation range according to the number of people. The configuration is different from that of the seventh embodiment. In the following description, the same components as those in the seventh embodiment are denoted by the same reference numerals, description thereof is omitted, and differences from the seventh embodiment are mainly described.

Specifically, as illustrated in FIG. 27, the liquid crystal display device 100 includes a camera unit 101 that captures an image of a person who is viewing the liquid crystal panel 11, and viewing that detects the number of viewers from an image acquired by the camera unit 101. And a number detection unit 102. The camera unit 101 may be provided integrally with the liquid crystal display device 100, for example, or may be provided separately from the liquid crystal display device 100.

The viewer number detection unit 102 performs image processing using an image photographed by the camera unit 101 and detects the number of viewers located on the display surface side of the liquid crystal panel 11. The viewer number detection unit 102 detects a person viewing the liquid crystal panel 11 by recognizing a human face in the image, for example. Then, the viewing number detection unit 102 outputs the number of people viewing the liquid crystal panel 11 as a signal.

The liquid crystal display device 100 changes the minimum value (MIN) and maximum value (MAX) of the intermediate gradation range in the gradation conversion unit 31 of the viewing angle adjustment circuit 30 according to the number of people viewing the liquid crystal panel 11. A MAX and MIN changing unit 103 is included. The MAX / MIN changing unit 103 increases the minimum value (MIN) and decreases the maximum value (MAX) when the number of people viewing the liquid crystal panel 11 is large compared to when the number of viewers is small. The viewing angle of the liquid crystal panel 11 is improved. On the other hand, the MAX and MIN changing unit 103 reduces the minimum value (MIN) and increases the maximum value (MAX) when the number of viewers of the liquid crystal panel 11 is small compared to when the number of viewers is large. Give priority to display quality.

For example, if the number of viewers of the liquid crystal panel 11 is one, the MAX and MIN changing unit 103 sets the maximum value (MAX) to the gradation 256 and sets the minimum value (MIN) to the gradation zero. If the number of viewers of the liquid crystal panel 11 is two, the MAX and MIN changing unit 103 sets the maximum value (MAX) to the gradation 224 and sets the minimum value (MIN) to the gradation 32. Further, if the number of viewers of the liquid crystal panel 11 is three or more, the maximum value (MAX) is set to the gradation 192 and the minimum value (MIN) is set to the gradation 64. Since the above-described gradation and number of people are examples, the minimum value (MIN) and the maximum value (MAX) may be changed based on the number of people other than this.

Thus, by changing the minimum value (MIN) and the maximum value (MAX) of the intermediate gradation range in the gradation adjustment unit 31 of the viewing angle adjustment circuit 30 according to the number of viewers of the liquid crystal panel 11, the viewer's It is possible to display an image suitable for the position. That is, when the number of viewers of the liquid crystal panel 11 is small, it is presumed that the viewer is viewing from almost the center of the display surface of the liquid crystal panel 11, so display image quality is given priority. On the other hand, when the number of viewers of the liquid crystal panel 11 is large, it is estimated that there are many viewers viewing from the oblique direction with respect to the display surface of the liquid crystal panel 11. Priority.

(Effect of 8th Embodiment)
In this embodiment, the minimum value (MIN) and maximum value (MAX) of the intermediate gradation range in the gradation conversion unit 31 of the viewing angle adjustment circuit 30 are changed according to the number of people viewing the liquid crystal panel 11. Accordingly, the position of the viewer viewing the liquid crystal panel 11 can be estimated based on the number of viewers of the liquid crystal panel 11, and optimal video display can be performed on the liquid crystal panel 11.

That is, when the number of viewers is small, it is estimated that the viewer is viewing the liquid crystal panel 11 from the front of the display surface, and the display image quality is prioritized without unnecessarily improving the viewing angle characteristics of the liquid crystal panel 11. can do. On the other hand, when the number of viewers is large, it is estimated that the viewer is viewing the liquid crystal panel 11 from an oblique direction with respect to the display surface, and the viewing angle characteristics are improved more than the display image quality of the liquid crystal panel 11. Priority can be given.

[Ninth Embodiment]
FIG. 28 is a block diagram showing a schematic configuration of a liquid crystal display device 110 according to the ninth embodiment of the present invention. The liquid crystal display device 110 of this embodiment is different from the configuration of the eighth embodiment described above in that the viewing position is detected. In the following description, the same components as those in the eighth embodiment are denoted by the same reference numerals, description thereof is omitted, and only different portions are described.

Specifically, as illustrated in FIG. 28, the liquid crystal display device 110 includes a camera unit 101 similar to that in the eighth embodiment, and a viewing position detection that detects a viewer position from an image acquired by the camera unit 101. Part 111.

The viewing position detection unit 111 performs image processing using an image captured by the camera unit 101 and detects a viewer located on the display surface side of the liquid crystal panel 11. The viewer number detection unit 102 detects a person viewing the liquid crystal panel 11 by recognizing a human face in the image, for example. The viewer number detection unit 102 is the person who is viewing the liquid crystal panel 11 and is located most diagonally with respect to the display surface (the person located at the largest angular position with respect to the normal of the display surface). The angle position (angle with respect to the normal to the display surface) is output as a signal.

The liquid crystal display device 110 changes the minimum value (MIN) and maximum value (MAX) of the intermediate gradation range in the gradation conversion unit 31 of the viewing angle adjustment circuit 30 according to the angular position of the viewer of the liquid crystal panel 11. A MAX and MIN changing unit 112 is included. The MAX and MIN changing unit 112 has a minimum value (MIN) = θ and a maximum value (MAX) = 255−θ (0 ≦ θ ≦ 90), where θ is the angle position of the viewer of the liquid crystal panel 11, and the minimum value. A value (MIN) and a maximum value (MAX) are obtained. Note that the relationship between the angular position θ and the minimum value and the maximum value is not limited to the above-described relationship, and may be a relationship in which the minimum value increases and the maximum value decreases as the angular position θ increases.

Thereby, the intermediate gradation range of the liquid crystal panel 11 can be changed according to the angular position of the viewer of the liquid crystal panel 11. Therefore, when the viewer is viewing from a position close to the normal to the display surface of the liquid crystal panel 11, the minimum value (MIN) decreases and the maximum value (MAX) increases, so display image quality is given priority. be able to. On the other hand, when the viewer is viewing from a position at a large angle with respect to the normal line of the liquid crystal panel 11, the minimum value (MIN) increases and the maximum value (MAX) decreases. The adjustment area increases. Thereby, priority can be given to the improvement of the viewing angle characteristic of the liquid crystal panel 11. FIG.

(Effect of 8th Embodiment)
In this embodiment, the minimum value (MIN) and the maximum value (MIN) of the intermediate gradation range in the gradation conversion unit 31 of the viewing angle adjustment circuit 30 according to the angular position of the viewer with respect to the normal line of the display surface of the liquid crystal panel 11 ( MAX) is changed. As a result, an optimal video display can be performed on the liquid crystal panel 11 in accordance with the angular position of the viewer of the liquid crystal panel 11.

[Other Embodiments]
While the embodiments of the present invention have been described above, the above-described embodiments are merely examples for carrying out the present invention. Therefore, the present invention is not limited to the above-described embodiment, and can be implemented by appropriately modifying the above-described embodiment without departing from the spirit thereof.

In each of the above embodiments, an example of a liquid crystal display device that displays an image with gradations 0 to 256 is shown. However, the present invention is not limited to this, and the liquid crystal display device displays an image with different gradations other than gradations 0 to 256. It may be configured to perform.

In each of the above embodiments, an example in which the liquid crystal display device performs monochrome display is shown. However, the present invention is not limited to this, and the liquid crystal display device may be configured to be capable of color display. In this case, gradation conversion as in each of the above embodiments may be performed for each color.

In the first embodiment, the gradation of the output signal is changed stepwise with respect to the gradation of the video signal input to the viewing angle adjustment circuit 13 in the intermediate gradation range. In the second embodiment, the gradation of the signal is converted so as to be proportional to the gradation of the video signal input to the viewing angle adjustment circuit 30 in the intermediate gradation range. However, by combining these, the gradation of the output signal is changed stepwise in a part of the intermediate gradation range, and is proportional to the gradation of the input video signal in the other range. The gradation may be converted.

In each of the fifth and sixth embodiments, an example of the dither pattern is shown. However, the error value constituting the dither pattern may be other than the values shown in the above-described embodiments. Also, the dither pattern may be a pattern different from the above-described embodiment, or may be a pattern for a pixel group other than four pixels.

In the seventh to ninth embodiments, the MAX and

MIN changing units

91, 103, and 112 are provided in the second embodiment. However, the present invention is not limited to this, and the MAX and

MIN changing units

91, 103, and 112 may be provided for the first, third to sixth embodiments.

The liquid crystal display device according to the present invention can be used to improve the viewing angle of a liquid crystal panel.

Claims

A liquid crystal panel in which a plurality of pixels are arranged in a matrix;
A viewing angle adjustment device that adjusts the viewing angle of the liquid crystal panel by changing the gradation of the video signal input to each pixel,
The viewing angle adjusting device includes:
The gradation of the input signal is black when it is lower than the lower limit value and white when it is higher than the upper limit value, and gradation conversion is performed in at least a part of the intermediate gradation range between the lower limit value and the upper limit value. A gradation conversion unit;
An error calculation unit for obtaining an error between the gradation of the signal output after gradation conversion by the gradation conversion unit and the gradation of the signal input to the gradation conversion unit;
Using the error calculated by the error calculation unit, an error correction unit that corrects the gradation of the signal for the next pixel input to the gradation conversion unit;
A liquid crystal display device.
The gradation conversion unit is configured to convert a gradation of a signal input to the gradation conversion unit into a gradation proportional to the gradation in the intermediate gradation range. A liquid crystal display device according to 1.
The gradation converting unit is configured to convert a gradation of a signal input to the gradation converting unit into a constant gradation in at least a part of the gradation range in the intermediate gradation range. The liquid crystal display device according to claim 1.
The liquid crystal panel has a plurality of lines in which a plurality of pixels are arranged in an example,
An error initial value setting unit that sets a different error initial value for each adjacent line with respect to the gradation of a video signal of a pixel that is first subjected to gradation conversion by the gradation conversion unit in the line. The liquid crystal display device according to any one of 1 to 3.
5. The liquid crystal according to claim 4, wherein the error initial value setting unit sets an error initial value for each line such that a magnitude relationship between error initial values given to the adjacent lines is switched for each display frame of the liquid crystal panel. Display device.
6. The error initial value setting unit sets an error initial value having a different sign for each display frame of the liquid crystal panel for each line so that the sum of error initial values in each line becomes zero. A liquid crystal display device according to 1.
An error adding unit that adds a predetermined error pattern in a pixel group composed of a plurality of pixels to either the signal input to the gradation converting unit or the error calculated by the error calculating unit; 7. A liquid crystal display device according to any one of claims 1 to 6.
The liquid crystal display device according to claim 7, wherein the error adding unit changes the error pattern for each display frame of the liquid crystal panel so that an error due to the error pattern becomes zero in each pixel in the pixel group. .
The liquid crystal display device according to claim 1, further comprising a gradation range changing unit that changes at least one of the lower limit value and the upper limit value.
A visual number detection unit that detects the number of viewers viewing the liquid crystal panel;
10. The liquid crystal display device according to claim 9, wherein the gradation range changing unit is configured to change at least one of the lower limit value and the upper limit value in accordance with a result of detection of the number of viewers by the viewer number detection unit. .
A visual position detector that detects a position of a viewer viewing the liquid crystal panel and obtains an angle formed by the viewer and a normal line of the display surface of the liquid crystal panel;
The liquid crystal display device according to claim 9, wherein the gradation range changing unit is configured to change at least one of the lower limit value and the upper limit value according to a detection result of the angle by the visual recognition position detection unit. .