JP2009175415A - Liquid crystal display device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a liquid crystal display device in which neither a stripe nor a flicker is seen, even if the illumination region of a backlight is divided into a plurality of regions. <P>SOLUTION: The liquid crystal display device has a liquid crystal panel 11 and a backlight 12, and a controller 10 which calculates luminance values of respective illumination regions of the backlight 12 on the basis of an image signal, and the controller 10 changes areas and arrangement positions of the respective illumination per frame. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a liquid crystal display device that displays an image illuminated by a backlight.

  As a backlight of a liquid crystal display device, a cold cathode tube or a light emitting diode (hereinafter referred to as an LED) is used as a light source, and in the display state, the backlight always emits light at a constant luminance over time. Was composed. However, recently, as the use of LEDs in the backlight has rapidly progressed, it has become easy to adjust the backlight, and at the same time, it has become possible to realize high-speed variation that can be synchronized with an image.

  Therefore, in order to further improve the contrast by applying backlight brightness control, the backlight brightness can be varied according to the image, and the displayed γ characteristic can be maintained in an ideal state even when the brightness is switched. A driving method for switching the gradation has been proposed.

  In this driving method, when it is determined that the image is bright, the luminance of the backlight is increased and the γ characteristic is switched to a direction in which the gradient from dark to light is laid down. On the other hand, when it is determined that the image is dark, the luminance of the backlight is lowered and the γ characteristic is switched to a direction in which the gradient from dark to light is increased. As a result, an image having a wider dynamic range can be expressed. In other words, the brightness displayed from the liquid crystal could be varied in the wide range from the maximum brightness of the image, the maximum brightness of the backlight to the minimum brightness of the image, and the minimum brightness of the backlight. .

  However, since the backlight brightness is controlled collectively over the entire screen, the backlight brightness is limited for images that contain many highlights that cause a large brightness gradient in the screen. The conventional method and the dynamic range, which are constant, are not different, and the improvement effect cannot be exhibited.

  For this reason, recently, as proposed in Patent Document 1, there is a technique in which the backlight is divided into a plurality of illumination areas, and the luminance is controlled according to the input image signal. In this method, since the brightness of each illumination area is controlled based on the image signal, the brightness is high for a display portion including a lot of bright image information in the entire screen, and conversely dark image information. Therefore, the luminance of the display portion including a large amount of can be lowered, and the dynamic range of the entire screen is further expanded.

Further, since this method changes the luminance of the backlight for each illumination area, when the image signal is supplied to the liquid crystal panel with the same gradation, the luminance of the display image is shifted between the illumination areas. . Therefore, in order to convert the image signal according to the brightness of the backlight for each illumination area, the brightness of the display image is shifted between each illumination area by the appropriate gradation converted according to the brightness of the backlight of each illumination area. Therefore, an appropriate display image can be obtained.
JP 2002-99250 A

  However, although the luminance deviation between the plurality of illumination areas can be eliminated as in Patent Document 1, the appropriate luminance as described above can be obtained when the luminance variable and gradation variable resolution is rough or the variable speed is different. There are cases where gradation cannot be set. In addition, since each illumination area is fixed, the boundary always exists at the same place, so that there is a problem that the place looks like a streak.

  Further, when there is not so much luminance gradient in the screen such as a raster screen and the gradation histogram is biased to the same gradation, there is a problem that the portion looks like a streak.

  Furthermore, when an image in which the gradation level of each illumination area varies is an image in which a fast-moving object moves across each illumination area, the gradation change of each illumination area catches up. As a result, the gradation changes every time the moving illumination area is crossed, and thus there is a problem that the image appears to flicker.

  Therefore, in view of the above problems, the present invention provides a liquid crystal display device that does not show streaks or flicker even when the illumination area of the backlight is divided into a plurality of areas.

  The present invention provides a liquid crystal panel that displays an image in a display area based on an image signal, a backlight that has a plurality of illumination areas and that illuminates the display area of the liquid crystal panel from the illumination areas, and the illumination areas. A backlight control unit that calculates a luminance of each of the illumination regions based on the image signal, wherein the backlight control unit is configured to change the area or the arrangement position of each illumination region at any change time. The liquid crystal display device is changed to

  The present invention also provides a liquid crystal panel that displays an image in a display area based on an image signal, a plurality of illumination areas, a backlight that illuminates the display area of the liquid crystal panel from each of the illumination areas, A backlight control unit that calculates the luminance of each illumination area based on the image signal, the backlight control unit has a luminance gradient in an arbitrary range calculated based on the image signal In the liquid crystal display device, the area of each illumination region increases as the size increases.

  The present invention also provides a liquid crystal panel that displays an image in a display area based on an image signal, a plurality of illumination areas, a backlight that illuminates the display area of the liquid crystal panel from each of the illumination areas, A backlight control unit that calculates the luminance of each illumination area based on the image signal, wherein the backlight control unit moves the object on the image calculated based on the image signal In the liquid crystal display device, the area of each illumination region is increased as the vector speed increases.

  According to the present invention, streaks and flickers are not seen by changing the area and arrangement position of each illumination region.

  Hereinafter, the liquid crystal display device 2 of the embodiment of the present invention will be described, but before that, the liquid crystal display device 1 which is a reference form of the liquid crystal display device 2 of the present embodiment will be described.

(Reference form)
A liquid crystal display device 1 according to a reference embodiment of the present invention will be described with reference to FIGS.

(1) Configuration of Liquid Crystal Display Device 1 The configuration of the liquid crystal display device 1 according to the present embodiment will be described.

  FIG. 1 is a block diagram of a liquid crystal display device 1 of the present embodiment.

  The liquid crystal display device 1 includes a controller 10, a liquid crystal panel 11, a backlight 12, a source driver circuit 22, and a gate driver circuit 23.

  The liquid crystal panel 11 uses OCB type liquid crystal and has a size of 20 to 30 inches. The liquid crystal panel 11 includes an array substrate and a counter substrate. The array substrate is wired so that signal lines and scanning lines are orthogonal to each other, and TFTs (thin film transistors) are provided at the intersections thereof. OCB mode liquid crystal is sandwiched between the substrate and the counter substrate.

  A source driver circuit 22 and a gate driver circuit 23 are connected to the liquid crystal panel 11, and a signal from the controller 10 is received by the source driver circuit 22 and the gate driver circuit 23 to display an image on the liquid crystal panel 11.

  The backlight 12 is disposed on the back surface of the liquid crystal panel 11, and the backlight 12 includes a plurality of white LEDs 24, which are point light sources, arranged in a lattice pattern.

  The controller 10 stores the RGB image signal in the frame memory 13 and then receives it, and controls the source driver circuit 22, the gate driver circuit 23, and the backlight 12 based on an external timing signal.

  As shown in FIG. 2, the liquid crystal panel 11 and the backlight 12 are each divided into a plurality of regions. Hereinafter, the divided areas are referred to as “display areas” in the liquid crystal panel 11 and “illumination areas” in the backlight 12.

(2) Controller 10
Next, the controller 10 will be described.

  As shown in FIG. 1, the controller 10 includes an image luminance calculation unit 14, an image luminance data holding unit 15, a backlight luminance calculation unit 16, a backlight luminance data holding unit 17, a backlight luminance control unit 18, and a gradation conversion unit. 19, a tone correction lookup table (tone correction LUT) 20, and a tone correction unit 21.

  The controller 10 converts the image information input to the liquid crystal panel 11 based on the luminance distribution information of the backlight 12 so that correct gradation reproduction can be obtained in the screen.

  First, the input image signal is analyzed for each illumination area of the backlight 12, and the average or most frequent gradation, the maximum gradation, and the minimum gradation are extracted. Based on these pieces of image information, the luminance distribution of the backlight 12 is determined. That is, when the image information includes a lot of bright luminance information, the luminance of the backlight 12 is set high, and when the image information includes a lot of dark luminance information, the luminance of the backlight 12 is set low.

  Next, based on the control result of the backlight 12, the gradation shift amount is determined for each smaller display area in the liquid crystal panel 11. At this time, even if the luminance control value of the backlight 12 that illuminates the display area is the same, the gradation shift amount is not the same. The reason is that even if the brightness control value that directly illuminates the display area is the same, the brightness control value around the illumination area changes depending on the surrounding image information, and the brightness value that illuminates the display area due to crosstalk between the illumination areas Because changes. Accordingly, an appropriate gradation shift amount is determined based on matrix information of luminance control values that illuminate the image. The gradation shift amount is also generally not linear, and is nonlinearly shifted according to the γ characteristic that relates the gradation and the display luminance level.

(3) Description of Liquid Crystal Panel 11 and Backlight 12 FIG. 2 is an explanatory diagram of the liquid crystal panel 11 and the backlight 12.

  In the liquid crystal panel 11, the RGB image signal is modulated and controlled for each pixel based on the RGB gradation conversion data for each region.

  In the backlight 12, brightness control is performed based on image brightness information for each display area of the liquid crystal panel 11.

  In this embodiment, as shown in FIG. 2, the liquid crystal panel 11 is divided into a 6 × 8 display area (FIG. 2A), and the backlight 12 is divided into a 3 × 4 illumination area (FIG. 2B). ). For convenience, the display area on the liquid crystal panel 11 is indicated by (i, j), and the illumination area on the backlight 12 is indicated by [i, j].

(4) Operation of Liquid Crystal Display Device 1 The operation of the liquid crystal display device 1 will be described with reference to FIG.

  The RGB image signals are stored in the frame memory 13 and then read out for each display area.

  The image luminance calculation unit 14 calculates a luminance value for each display region based on the read image signal, and sends the calculated luminance data for each display region to the image luminance data holding unit 15.

  The backlight luminance calculation unit 16 calculates the backlight luminance level for each illumination region based on the luminance data for each display region from the image luminance data holding unit 15. The calculated backlight luminance data for each illumination area is sent to the backlight luminance data holding unit 17.

  The backlight luminance control unit 18 calculates the backlight luminance for each illumination area based on the calculation result of the backlight luminance calculation unit 16.

  The gradation converting unit 19 sequentially reads out image signals stored in the frame memory 13 for each pixel, and performs gradation modulation based on the luminance data of the backlight 12 that illuminates the display area.

  The gradation correction unit 21 performs appropriate gradation correction using the data of the gradation correction LUT 20 based on the backlight luminance data around the display area, and finally the RGB input to the source driver circuit 22 Image signal (R "G" B ").

(5) Gradation Correction Method Next, the gradation correction method performed after the gradation conversion process will be specifically described together with the backlight luminance level determination method described so far.

FIG. 4 is a diagram showing an example of the result of calculating the average luminance gradation for each display area in FIG. 2A for the RGB image signal levels corresponding to the images stored in the frame memory. The relationship between the RGB image signal and the signal luminance level Y takes into account the visibility of each RGB image signal.

Y = 0.30R + 0.59G + 0.11B (1)

It can be expressed as The coefficient of equation (1) is determined by the RGB chromaticity points and the white point, that is, the display system specifications.

  In the present embodiment, the 2 × 2 display area corresponds to the illumination area (see FIG. 2), and the average luminance can be calculated for each illumination area from FIG. 4 as shown in FIG. Similarly, the maximum value and the minimum value of the RGB signal on the illumination area can be calculated from the maximum value and the minimum value of the signal level for each display area.

(6) Luminance Level Determination Procedure The luminance level of each illumination area is determined from the average, maximum, and minimum luminance signal levels according to the procedure shown in FIG.

  That is, for example, an appropriate backlight luminance level is selected based on the average luminance signal level, and other parameters (here, maximum value and minimum value) fall within the displayable signal level range at the selected backlight luminance level. Judge whether.

  If any parameter is out of range, the backlight brightness level is selected by iterative processing.

  When all parameters are not included in the displayable signal level range at any backlight luminance level, a backlight luminance level that includes either the minimum value or the maximum value is selected.

(7) Gradation correction processing In the present embodiment, the backlight luminance level as shown in FIG. 6B is selected from the RGB display average luminance signal level for each illumination area as shown in FIG. To do.

  The RGB image signal levels sequentially read from the frame memory 13 are subjected to gradation conversion from the backlight luminance level information (see FIG. 6B) of each illumination area.

  However, it is necessary to perform tone correction processing for the following reasons.

  FIG. 7 shows a region [2, 2] in which the luminance level 1 is selected in FIG. 6B and a region [3, 2] in which the luminance level 3 is selected, which is located on the lower side of the screen of [2, 2]. It is the figure which showed typically the spatial distribution of the brightness | luminance at the time of white display.

  When the backlight brightness is modulated for each illumination area, the backlight brightness that illuminates a certain display area is superposed not only on the illumination area directly below but also on the adjacent illumination area due to crosstalk between the illumination areas. . That is, a phenomenon occurs in which the actual backlight luminance is deviated from the backlight luminance used for the gradation conversion due to the illuminating light from the adjacent area. That is, an illumination error phenomenon occurs.

  In FIG. 7, for the sake of simplification, the slot loss talk between the two regions is shown, but actually, as shown in FIG. 6B, the region around the [2, 2] region, that is, [1, 1], [1 , 2], [1,3], [2,1], [2,3], [3,1], [3,2], and [3,3] Is determined. Since the crosstalk is determined by the number of divisions of the illumination area, the area of the area, the design of the backlight, and the like, depending on the conditions, it may be affected by a change in the luminance level in the illumination area other than the adjacent area. For example, if the actual brightness of the backlight with brightness level 1 selected for a certain display area includes an error of 20% with respect to the brightness data at the time of gradation conversion (20% brightness is high), the second to fifth floors A gradation conversion error of about a tone occurs, and is visually recognized as an obstacle such as a pseudo contour between the display areas and gradation inversion.

  In order to compensate for the gradation conversion error due to the illumination error phenomenon, in this embodiment, as shown in FIG. 3, the gradation correction unit 21 uses the gradation correction LUT 20 and the final image signal to the source driver circuit 22 is supplied. Is output. The gradation correction LUT 20 stores gradation correction data corresponding to a combination of the luminance level of a certain illumination area and the luminance level of the adjacent illumination area for each display area, and the luminance level of the backlight 12 is stored. The gradation correction amount is determined while referring to it.

(First embodiment)
Next, the liquid crystal display device 2 according to the first embodiment of the present invention will be described with reference to FIGS.

(1) Outline of the liquid crystal display device 2 As shown in the column of the problem to be solved by the invention, the liquid crystal display device 1 according to the above-mentioned reference embodiment has a variable luminance and variable gradation, or a variable speed. As a result, the appropriate brightness of the backlight 12 cannot be set, and the position of each illumination area is fixed, so that a streak appears at that position. Therefore, the liquid crystal display device 2 according to the present embodiment provides a device that does not show such a streak.

(2) Configuration of the liquid crystal display device 2 The difference between the reference embodiment and the present embodiment is the structure of the controller 10.

  The controller 10 of the present embodiment has a region conversion unit 9. When the RGB image signal is sent from the frame memory 13, the area conversion unit 9 changes the area and arrangement position of the illumination area 30 for each frame.

(3) Configuration of Backlight 12 The backlight 12 in the present embodiment has a plurality of white LEDs 28 arranged in a grid pattern as shown in FIG. The four LEDs 28 are arranged in each illumination area 30. A diffusion plate 121 is disposed on the backlight 12 on the liquid crystal panel 11 side.

(4) Operation of Liquid Crystal Display Device 2 Next, the operation of the liquid crystal display device 2 will be described with reference to FIG.

  The area converting unit 9 alternately changes the 4 × 4 illumination area 30 shown in FIG. 10A and the 3 × 4 illumination area 30 shown in FIG. 10B every frame. The arrangement and number of these illumination areas 30 are stored in advance in the area conversion unit 9.

  In the n frame, based on the 4 × 4 illumination area 30, an image is displayed while performing the gradation correction processing as described in the reference embodiment for each display area. In the (n + 1) frame, the image is displayed in the 3 × 4 illumination area 30 in the same manner. In the (n + 2) frame, the image is displayed again in the 4 × 4 illumination area 30.

  In addition, since it is necessary to perform the gradation correction processing described in the above reference form for each display area, the display area of the liquid crystal panel 11 needs to be divided more finely than the illumination area 30 that is divided most finely.

(5) Effect According to the present embodiment as described above, by changing the area and arrangement position of the illumination area 30 for each frame, the position of the illumination area 30 is not fixed as in the reference embodiment. There is no occurrence of streaks at the border of the illumination area 30.

(6) Modification Example In the above embodiment, the illumination area 30 is changed for each frame. However, the present invention is not limited to this, and the illumination area 30 may be changed for every several frames.

  Further, as shown in FIG. 11, the display area having a large area and the display area having a small area may be changed. That is, the first arrangement pattern of the illumination area 30 as shown in FIG. 11A and the second arrangement pattern as shown in FIG. 11B may be alternately changed.

(Second Embodiment)
Next, the liquid crystal display device 2 of the second embodiment will be described with reference to FIG.

  In the liquid crystal display device 1 of the reference embodiment, since each illumination region 30 is fixed, the boundary always exists in the same place, so that there is not so much luminance inclination in the screen such as a raster screen, and the gradation histogram is also the same. In the case of being biased toward gradation, the place looks like a streak.

  Therefore, in the present embodiment, the area conversion unit 9 of the controller 10 shown in FIG. 8 obtains a change in gradation within a preset range in the display image based on the histogram, and a large scale is displayed on the display image. When it is determined that there is no change in tone, that is, there is no luminance gradient, the area of the illumination region 30 is increased as shown in FIG.

  Specifically, the area conversion unit 9 obtains the luminance gradient in the entire screen, and when the luminance inclination is lower than the first threshold, that is, in the case of a raster screen with almost no luminance inclination, the area conversion unit 9 divides the plurality of illumination areas 30. Then, the illumination area 30 is enlarged as the threshold values of the second threshold value and the third threshold value are exceeded. When the luminance gradient is maximum, the illumination area 30 is set to one on the entire screen.

  In addition, since it is necessary to perform the gradation correction processing described in the above reference form for each display area, the display area of the liquid crystal panel 11 needs to be divided more finely than the illumination area 30 that is divided most finely.

  By doing in this way, when the brightness | luminance inclination becomes large, the streak between the illumination areas 30 does not appear.

(Third embodiment)
Next, the liquid crystal display device 2 of the third embodiment will be described.

  In the liquid crystal display device 1 of the reference form, when a fast-moving object operates across the illumination areas 30 in an image in which the gradation levels of the illumination areas 30 vary, the floor of each illumination area 30 is displayed. The tone change may not catch up, and as a result, the moving object may straddle the flickering area 30 every time it crosses the illumination area 30 and flicker.

  Therefore, in the present embodiment, a motion vector detection unit is provided in the region conversion unit 9 of the controller 10 in FIG. 8, and when the speed of the motion vector detected by the motion vector detection unit exceeds the reference speed, the illumination region 30 Increase

  That is, as shown in FIG. 13, the illumination area 30 is increased as the moving image speed, which is the speed of the motion vector, increases.

  In addition, since it is necessary to perform the gradation correction processing described in the above reference form for each display area, the display area of the liquid crystal panel 11 needs to be divided more finely than the illumination area 30 that is divided most finely.

  By doing in this way, a fast-moving object does not straddle the illumination area 30, and flicker does not occur.

(Example of change)
The present invention is not limited to the above-described embodiments, and various modifications can be made without departing from the gist thereof.

  For example, in the above embodiment, the OCB mode liquid crystal has been described, but the present invention is not limited to this, and other mode liquid crystal may be used.

It is the block diagram which showed the structural example of the liquid crystal display device of the reference form of this invention. It is the figure which showed an example of the area | region division of a screen and a backlight. It is the figure which showed the correspondence of the brightness | luminance level of a backlight, a brightness | luminance, and a gradation signal. It is the figure which showed an example of the result of having calculated the average luminance gradation of the input signal level for every display area. It is the figure shown about the selection method of a backlight luminance level. It is the figure which showed an example of the result of having calculated the average luminance gradation of the input signal level for every illumination area. It is the figure which showed the illumination error by the crosstalk between illumination areas. 1 is a block diagram of a liquid crystal display device according to a first embodiment. It is the block diagram of a backlight similarly. It is the figure which showed the change state of the illumination area in a backlight. It is the figure which showed the change of the illumination area in the example of a change of 1st Embodiment. It is the figure which showed the change state of the illumination area in 2nd Embodiment. It is the figure which showed the change state of the illumination area in 3rd Embodiment.

Explanation of symbols

2 Liquid crystal display device 9 Region changing unit 10 Controller 11 Liquid crystal panel 12 Backlight 13 Frame memory 14 Image luminance calculating unit 15 Image luminance data holding unit 16 Backlight luminance calculating unit 17 Backlight luminance data holding unit 18 Backlight luminance control unit 19 Tone converter 20 Tone correction LUT
21 gradation correction unit 22 source driver circuit 23 gate driver circuit 28 LED
30 Illumination area

Claims (4)

A liquid crystal panel for displaying an image in a display area based on an image signal;
A backlight having a plurality of illumination areas and illuminating a display area of the liquid crystal panel from each illumination area;
A backlight control unit that calculates the brightness of each illumination area based on the image signal;
In a liquid crystal display device having
The backlight control unit
Change the area of each illumination region, or the arrangement position at any change time,
Liquid crystal display device. The backlight control unit
For each illumination area, the area of the illumination area, or a plurality of arrangement patterns with different arrangement positions are stored,
Switch the arrangement pattern at each change time,
The liquid crystal display device according to claim 1. A liquid crystal panel for displaying an image in a display area based on an image signal;
A backlight having a plurality of illumination areas and illuminating a display area of the liquid crystal panel from each illumination area;
A backlight control unit that calculates the brightness of each illumination area based on the image signal;
In a liquid crystal display device having
The backlight control unit
As the luminance gradient in an arbitrary range calculated based on the image signal increases, the area of each illumination region increases.
Liquid crystal display device. A liquid crystal panel for displaying an image in a display area based on an image signal;
A backlight having a plurality of illumination areas and illuminating a display area of the liquid crystal panel from each illumination area;
A backlight control unit that calculates the brightness of each illumination area based on the image signal;
In a liquid crystal display device having
The backlight control unit
The area of each illumination region is increased as the speed of the motion vector of the object on the image calculated based on the image signal increases.
Liquid crystal display device.

Images