JP2012113226A - Video processing method, video processing circuit, liquid crystal display device, and electronic apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To remove conventional drawbacks from a technique for reducing a reverse tilt domain, while making overdrive effective.SOLUTION: A liquid crystal panel 100 includes a liquid crystal element with liquid crystals 105 sandwiched between a pixel electrode 118 provided on an element substrate 100a and a common electrode 108 provided on a counter substrate 100b. In a normally black mode, a video processing circuit 30 detects a risk boundary that is part of a boundary between a dark pixel in which a voltage applied to a liquid crystal element corresponding to a gradation level specified by a video signal Vid-in is below a first voltage and a bright pixel equal to or higher than a second voltage, and determined by a tilt azimuth of liquid crystal molecules. Then, the video processing circuit 30 corrects the video signal specifying the application of voltage to a liquid crystal element corresponding to at least either the dark pixel or bright pixel in contact with the detected risk boundary, to a voltage that restrains liquid crystal orientation failure caused by a lateral electric field, by removing an over-driven pixel from a correction target.

Description

  The present invention relates to a technique for reducing display defects in a liquid crystal panel.

  The liquid crystal panel has a configuration in which the liquid crystal is sandwiched between a pair of substrates held in a certain gap. Specifically, the liquid crystal panel is provided such that pixel electrodes are arranged in a matrix for each pixel on one substrate, and a common electrode is provided on the other substrate so as to be common to each pixel. It is the structure which clamped. When a voltage corresponding to the gradation level is applied and held between the pixel electrode and the common electrode, the alignment state of the liquid crystal is defined for each pixel, and thereby the transmittance or reflectance is controlled. Therefore, in the configuration described above, only the component in the direction from the pixel electrode to the common electrode (or the opposite direction) out of the electric field acting on the liquid crystal molecules, that is, the component perpendicular to the substrate surface (vertical direction) is used for display control. It can be said that it contributes.

By the way, when the pixel pitch is narrowed for miniaturization and high definition as in recent years, an electric field generated between adjacent pixel electrodes, that is, an electric field parallel to the substrate surface (transverse direction) is generated. The impact is becoming impossible to ignore. For example, when a horizontal electric field is applied to a liquid crystal to be driven by a vertical electric field such as a VA (Vertical Alignment) method or a TN (Twisted Nematic) method, the liquid crystal is poorly aligned (that is, reverse tilt domain). Has occurred, resulting in a problem in display.
In order to reduce the influence of the reverse tilt domain, a technique for devising the structure of the liquid crystal panel by defining the shape of the light shielding layer (opening) according to the pixel electrode (see, for example, Patent Document 1), video signal A technique (for example, refer to Patent Document 2) that clips a video signal that is equal to or greater than a set value by determining that a reverse tilt domain occurs when the average luminance value calculated from the above is below a threshold value has been proposed.

JP-A-6-34965 (FIG. 1) Japanese Patent Laying-Open No. 2009-69608 (FIG. 2)

However, the technique of reducing the reverse tilt domain depending on the structure of the liquid crystal panel has a drawback that the aperture ratio is liable to be lowered, and it cannot be applied to a liquid crystal panel that has already been manufactured without devising the structure. On the other hand, the technique of clipping a video signal that is equal to or higher than a set value has a drawback that the brightness of an image to be displayed is limited to the set value.
By the way, in an electro-optical device using a liquid crystal as an electro-optical material, the response speed of the liquid crystal is low, so that there is a problem that display characteristics of moving images are deteriorated. Specifically, problems such as a feeling of afterimage appearing in the displayed image and a moving cursor disappearing have occurred. To solve this problem, when there is a gradation change from the previous frame to the current frame, the gradation change for the pixel in the first field of the current frame is greater than the gradation specified in the current frame A technique called overdrive driving has been proposed in which a grayscale equivalent voltage that is excessively shifted in the direction is applied to increase the response speed of the liquid crystal.
The present invention has been made in view of the above-described circumstances, and one of its purposes is to eliminate the conventional drawbacks of a technique for reducing the reverse tilt domain while enabling overdrive driving.

In order to achieve the above object, in the video processing circuit according to the present invention, a video signal designating an applied voltage of the liquid crystal element is input for each pixel, and the liquid crystal element of the liquid crystal element is based on the corrected video signal. A video processing method for defining an applied voltage, wherein an input video signal is analyzed for each of a current frame and a frame immediately before the current frame, and overdrive is performed according to a change in the applied voltage of each pixel. An overdrive control step of generating and outputting a video signal of the current frame for driving; a first pixel in which the applied voltage is lower than the first voltage in the input video signal; and the applied voltage is the first voltage A first boundary that detects a boundary that changes from the previous frame to the current frame, among boundaries with a second pixel that is greater than or equal to a second voltage greater than A second boundary that detects a risk boundary that is a part of a boundary between the first pixel and the second pixel specified by the output step and the input video signal of the current frame and that is determined by a tilt direction of the liquid crystal In the video signal of the current frame output in the detection step and the overdrive control step, among the boundaries detected in the first boundary detection step, the first boundary that is in contact with the risk boundary detected in the second boundary detection step A video signal designating a voltage applied to a liquid crystal element corresponding to at least one of the first and second pixels is excluded from the correction target for a pixel in which the overdrive drive is performed, and the first and second pixels And a correction step of correcting so as to reduce the generated lateral electric field.
According to the present invention, since it is not necessary to change the structure of the liquid crystal panel, the aperture ratio is not reduced, and the present invention can be applied to a liquid crystal panel that has already been manufactured without devising the structure. Further, the voltage applied to the liquid crystal element corresponding to the second pixel among the pixels in contact with the risk boundary that has changed from the previous frame to the current frame is a value corresponding to the gradation level specified by the video signal. Therefore, the brightness of the image to be displayed is not limited to the set value. Furthermore, in the present invention, pixels for which overdrive driving is performed are excluded from correction targets, and therefore, overdrive driving is not invalidated by correction related to suppression of the reverse tilt domain.

In the present invention, in the correction step, for the first pixel whose applied voltage specified by the video signal of the previous frame is equal to or less than a predetermined first threshold, a liquid crystal element corresponding to the first pixel When the applied voltage to the voltage falls below a third voltage lower than the first voltage, the applied voltage of the first pixel may be corrected to be equal to or higher than the third voltage.
According to the present invention, it is possible to identify a dark pixel on which overdrive driving is performed in the current frame relatively easily by referring to the applied voltage specified by the video signal of the previous frame.

In the present invention, in the correction step, the applied voltage specified by the video signal of the previous frame output in the overdrive step is less than or equal to a predetermined first threshold value. When the applied voltage to the liquid crystal element corresponding to the first pixel is lower than the third voltage lower than the first voltage, the applied voltage of the first pixel is corrected to be equal to or higher than the third voltage. May be.
According to the present invention, by referring to the applied voltage specified by the video signal of the previous frame after control related to overdrive driving, it is possible to identify the dark pixel that is overdriven in the current frame relatively easily. it can.

Further, in the present invention, the correction unit, from the first pixel in contact with the risk boundary detected in the second boundary detection step among the boundaries detected in the first boundary detection step in the correction step, When the voltage applied to the liquid crystal elements corresponding to the pixels that are not subjected to the overdrive drive is less than the third voltage for two or more predetermined numbers of the first pixels continuous to the opposite side of the risk boundary In addition, the correction may be made so that the voltage is not less than the third voltage.
According to the present invention, the change in the applied voltage due to the correction of the video signal can be made inconspicuous. Further, it is possible to prevent the liquid crystal molecules from being unstable even after the next update (rewrite). Further, according to the present invention, it is possible to suppress the occurrence of the reverse tilt domain even when the response time of the liquid crystal element is longer than the time interval at which the display screen is updated.

In the present invention, in the correction step, the liquid crystal element corresponding to the second pixel for the second pixel whose applied voltage specified by the video signal of the previous frame is equal to or greater than a predetermined second threshold value. The applied voltage may be corrected to be a fourth voltage that is higher than the first voltage and lower than the second voltage.
According to the present invention, by referring to the applied voltage specified by the video signal of the previous frame, it is possible to identify a bright pixel that is overdriven in the current frame relatively easily.

In the present invention, in the correction step, the applied voltage specified by the video signal of the previous frame output in the overdrive step is greater than or equal to a predetermined second threshold value. The voltage applied to the liquid crystal element corresponding to the second pixel may be corrected to be a fourth voltage that is higher than the first voltage and lower than the second voltage.
According to the present invention, by referring to the applied voltage specified by the video signal of the previous frame after control related to overdrive driving, it is possible to identify a bright pixel that is overdriven in the current frame relatively easily. it can.

In the present invention, the correction unit may include, from the second pixel in contact with the risk boundary detected in the second boundary detection step among the boundaries detected in the first boundary detection step in the correction step. For two or more predetermined numbers of the second pixels that are continuous to the opposite side of the risk boundary, the voltage applied to the liquid crystal elements corresponding to the pixels that are not overdriven is greater than the first voltage. You may make it correct | amend so that it may become the 4th voltage lower than the said 2nd voltage.
According to the present invention, the change in the applied voltage due to the correction of the video signal can be made inconspicuous. Further, according to the present invention, it is possible to suppress the occurrence of the reverse tilt domain even when the response time of the liquid crystal element is longer than the time interval at which the display screen is updated. According to the present invention, the change in the applied voltage due to the correction of the video signal can be made inconspicuous.

In the present invention, it is preferable that the first boundary detection unit detects, in the first boundary detection step, a boundary moved by one pixel from the previous frame to the current frame as the changing boundary. .
According to the present invention, since the video signal is corrected by focusing on the portion where the tailing phenomenon is conspicuous due to the influence of the reverse tilt domain, it is possible to suppress the change of the input video signal.

  In addition to the video processing method, the present invention can be conceptualized as a video processing circuit, a liquid crystal display device, and an electronic device including the liquid crystal display device.

1 is a diagram showing a liquid crystal display device to which a video processing circuit according to an embodiment of the present invention is applied. 3 is a diagram showing an equivalent circuit of a liquid crystal element in the liquid crystal display device. FIG. The figure which shows the structure of the video processing circuit. The figure which shows the structure of the motion detection part and correction | amendment part of the video processing circuit. The figure explaining the principle of an overdrive drive. The figure explaining the principle of an overdrive drive. The figure which shows the VT characteristic of the liquid crystal panel which comprises the liquid crystal display device. FIG. 6 is a diagram showing a display operation in the liquid crystal panel. Explanatory drawing of the initial orientation when it is set as the VA system in the liquid crystal panel. The figure for demonstrating the motion of the image in the liquid crystal panel. Explanatory drawing of the reverse tilt which generate | occur | produces in the liquid crystal panel. The figure for demonstrating the motion of the image in the liquid crystal panel. Explanatory drawing of the reverse tilt which generate | occur | produces in the liquid crystal panel. The figure which shows the procedure of the motion detection in the video processing circuit. The figure which shows the detection procedure of the risk boundary in the video processing circuit. The figure which shows the correction process in the video processing circuit. The figure which shows the correction process in the video processing circuit. The figure when it is set as the other tilt azimuth angle in the same liquid crystal panel. The figure when it is set as the other tilt azimuth angle in the same liquid crystal panel. The figure which shows the correction process in the video processing circuit which concerns on 2nd Embodiment of this invention. The figure which shows the correction process in the video processing circuit. The figure which shows the structure of the video processing circuit which concerns on 3rd Embodiment of this invention. The figure which shows the correction process in the video processing circuit. The figure which shows the correction process in the video processing circuit which concerns on 4th Embodiment of this invention. The figure which shows the correction process in the video processing circuit. The figure which shows the structure of the video processing circuit which concerns on 5th Embodiment of this invention. The figure which shows the correction process in the video processing circuit. The figure which shows the correction process in the video processing circuit. The figure which shows the correction process in the video processing circuit which concerns on 6th Embodiment of this invention. The figure which shows the correction process in the video processing circuit. The figure which shows the correction process in the video processing circuit which concerns on 7th Embodiment of this invention. Explanatory drawing of the initial orientation when it is set as the TN system in the liquid crystal panel. Explanatory drawing of the reverse tilt which generate | occur | produces in the liquid crystal panel. Explanatory drawing of the reverse tilt which generate | occur | produces in the liquid crystal panel. The figure which shows the projector to which a liquid crystal display device is applied. The figure which shows the malfunction on a display etc. by the influence of a horizontal electric field.

Embodiments of the present invention will be described below with reference to the drawings.
<First Embodiment>
First, a first embodiment of the present invention will be described.
FIG. 1 is a block diagram showing an overall configuration of a liquid crystal display device to which a video processing circuit according to this embodiment is applied.
As shown in FIG. 1, the liquid crystal display device 1 includes a control circuit 10, a liquid crystal panel 100, a scanning line driving circuit 130, and a data line driving circuit 140. The video signal Vid-in is supplied to the control circuit 10 from the host device in synchronization with the synchronization signal Sync. The video signal Vid-in is digital data that designates the gradation level of each pixel in the liquid crystal panel 100, and is used as a vertical scanning signal, a horizontal scanning signal, and a dot clock signal (all not shown) included in the synchronization signal Sync. The images are supplied in the order of scanning.
The video signal Vid-in designates the gradation level, but since the applied voltage of the liquid crystal element is determined according to the gradation level, it can be said that the video signal Vid-in designates the applied voltage of the liquid crystal element. Absent.

  The control circuit 10 includes a scanning control circuit 20 and a video processing circuit 30. The scanning control circuit 20 generates various control signals and controls each unit in synchronization with the synchronization signal Sync. As will be described in detail later, the video processing circuit 30 processes the digital video signal Vid-in and outputs an analog data signal Vx.

In the liquid crystal panel 100, an element substrate (first substrate) 100a and a counter substrate (second substrate) 100b are bonded to each other while maintaining a certain gap, and a liquid crystal 105 driven by a vertical electric field is placed in this gap. It is a sandwiched configuration. In the element substrate 100a, a surface facing the counter substrate 100b is provided with a plurality of m rows of scanning lines 112 along the X (horizontal) direction in the figure, while a plurality of n columns of data lines 114 are provided with Y (vertical). ) Along the direction and so as to be electrically insulated from each scanning line 112.
In this embodiment, in order to distinguish the scanning lines 112, there are cases where they are referred to as 1, 2, 3,. Similarly, in order to distinguish the data lines 114, there are cases where they are referred to as 1, 2, 3,..., (N−1), n-th column in order from the left in the figure.

In the element substrate 100a, a set of an n-channel TFT 116 and a pixel electrode 118 having a rectangular shape and transparency is provided corresponding to each intersection of the scanning line 112 and the data line 114. The TFT 116 has a gate electrode connected to the scanning line 112, a source electrode connected to the data line 114, and a drain electrode connected to the pixel electrode 118. On the other hand, a transparent common electrode 108 is provided on the entire surface of the counter substrate 100b facing the element substrate 100a. A voltage LCcom is applied to the common electrode 108 by a circuit not shown.
In FIG. 1, since the facing surface of the element substrate 100a is the back side of the drawing, the scanning lines 112, the data lines 114, the TFTs 116, and the pixel electrodes 118 provided on the facing surface should be indicated by broken lines. Each line is shown as a solid line because it becomes difficult.

FIG. 2 is a diagram showing an equivalent circuit in the liquid crystal panel 100.
As shown in FIG. 2, the liquid crystal panel 100 has a configuration in which liquid crystal elements 120 each having a liquid crystal 105 sandwiched between a pixel electrode 118 and a common electrode 108 are arranged corresponding to the intersection of a scanning line 112 and a data line 114. . Although omitted in FIG. 1, in the equivalent circuit in the liquid crystal panel 100, an auxiliary capacitor (storage capacitor) 125 is actually provided in parallel to the liquid crystal element 120 as shown in FIG. 2. The auxiliary capacitor 125 has one end connected to the pixel electrode 118 and the other end commonly connected to the capacitor line 115. The capacitor line 115 is maintained at a constant voltage over time.
Here, when the scanning line 112 becomes H level, the TFT 116 having the gate electrode connected to the scanning line is turned on, and the pixel electrode 118 is connected to the data line 114. Therefore, when a data signal having a voltage corresponding to the gradation is supplied to the data line 114 when the scanning line 112 is at the H level, the data signal is applied to the pixel electrode 118 via the turned-on TFT 116. When the scanning line 112 becomes L level, the TFT 116 is turned off, but the voltage applied to the pixel electrode 118 is held by the capacitive element of the liquid crystal element 120 and the auxiliary capacitor 125.
In the liquid crystal element 120, the molecular alignment state of the liquid crystal 105 changes according to the electric field generated by the pixel electrode 118 and the common electrode 108. For this reason, if the liquid crystal element 120 is a transmission type, it has a transmittance corresponding to the applied / holding voltage. In the liquid crystal panel 100, since the transmittance varies for each liquid crystal element 120, the liquid crystal element 120 corresponds to a pixel. The pixel array area is the display area 101.
In this embodiment, the liquid crystal 105 is a VA system, and a normally black mode in which the liquid crystal element 120 is in a black state when no voltage is applied.

The scanning line driving circuit 130 supplies the scanning signals Y1, Y2, Y3,..., Ym to the scanning lines 112 in the 1, 2, 3,..., M-th row in accordance with the control signal Yctr from the scanning control circuit 20. Specifically, as shown in FIG. 8A, the scanning line driving circuit 130 selects the scanning line 112 in the order of 1, 2, 3,..., (M−1), m-th row over the frame. The scanning signal for the selected scanning line is set as the selection voltage V _H (H level), and the scanning signal for the other scanning lines is set as the non-selection voltage V _L (L level).
The frame means a period required to display one frame of an image by driving the liquid crystal panel 100. If the frequency of the vertical scanning signal included in the synchronization signal Sync is 60 Hz, the frame is the reciprocal thereof. It is 16.7 milliseconds.

The data line driving circuit 140 samples the data signal Vx supplied from the video processing circuit 30 as data signals X1 to Xn on the data lines 114 in the 1st to nth columns according to the control signal Xctr from the scanning control circuit 20.
It should be noted that in this description, with respect to the voltage, except for the voltage applied to the liquid crystal element 120, the ground potential not shown is used as a reference for zero voltage unless otherwise specified. The voltage applied to the liquid crystal element 120 is a potential difference between the voltage LCcom of the common electrode 108 and the pixel electrode 118, and is for distinguishing from other voltages.

  Now, the relationship between the applied voltage and the transmittance of the liquid crystal element 120 is represented by, for example, a VT characteristic as shown in FIG. 7A in the normally black mode. For this reason, in order to make the liquid crystal element 120 have a transmittance corresponding to the gradation level specified by the video signal Vid-in, a voltage corresponding to the gradation level should be applied to the liquid crystal element 120. . However, if the voltage applied to the liquid crystal element 120 is simply defined according to the gradation level specified by the video signal Vid-in, a display defect due to the reverse tilt domain may occur.

An example of display defects caused by the reverse tilt domain will be described. For example, as shown in FIG. 36, when the image indicated by the video signal Vid-in moves to the right one pixel at a time in a black pattern in which black pixels continue with a white pixel as a background, the left edge of the black pattern This manifests as a kind of tailing phenomenon in which a pixel that should change from a black pixel to a white pixel at the edge (the trailing edge of motion) does not become a white pixel due to the occurrence of a reverse tilt domain.
Note that when the liquid crystal panel 100 is driven at the same speed as the supply speed of the video signal Vid-in as in this embodiment, the black pixel region with the white pixel as the background has two or more pixels for each frame. When moving, if the response time of the liquid crystal element is shorter than the time interval at which the display screen is updated, such a tailing phenomenon does not become obvious (or is hardly visible). The reason is considered as follows. That is, when a white pixel and a black pixel are adjacent to each other in a certain frame, a reverse tilt domain may occur in the white pixel, but considering the movement of the image, the pixels in which the reverse tilt domain occurs are discrete. This is because it is considered visually inconspicuous.
36, when a white pattern in which white pixels continue with a black pixel as a background moves to the right by one pixel for each frame, the right edge of the white pattern (the tip of movement) It can also be said that a pixel to be changed from a black pixel to a white pixel does not become a white pixel due to the occurrence of a reverse tilt domain.
In FIG. 36, for convenience of explanation, the vicinity of the boundary of one line is extracted from the image.

This defect on display due to the reverse tilt domain is disturbed by the influence of the lateral electric field when the liquid crystal molecules sandwiched in the liquid crystal element 120 are in an unstable state, and thereafter the alignment state according to the applied voltage is obtained. One of the causes is thought to be difficult.
Here, the case of being affected by a lateral electric field is a case where the potential difference between adjacent pixel electrodes becomes large. This is because black pixels (or close to the black level) dark pixels in an image to be displayed. This is a case where a bright pixel of white level (or close to the white level) is adjacent.
Among these, the dark pixel is a pixel of the liquid crystal element 120 in the voltage range A in which the applied voltage is equal to or higher than the black level voltage Vbk in the normally black mode and lower than the threshold value Vth1 (first voltage). For convenience, the transmittance range (gradation range) of the liquid crystal element in which the applied voltage of the liquid crystal element is in the voltage range A is “a”.
Next, for the bright pixel, the liquid crystal element 120 is in the voltage range B where the applied voltage is equal to or higher than the threshold Vth2 (second voltage) and equal to or lower than the white level voltage Vwt in the normally black mode. For convenience, the transmittance range (gradation range) of the liquid crystal element in which the applied voltage of the liquid crystal element is in the voltage range B is “b”.

  The liquid crystal molecules are in an unstable state when the applied voltage of the liquid crystal element is lower than Vc1 in the voltage range A. When the applied voltage of the liquid crystal element is lower than Vc1, since the regulating force of the vertical electric field by the applied voltage is weaker than the regulating force by the alignment film, the alignment state of the liquid crystal molecules is easily disturbed by a few external factors. Further, when the applied voltage becomes Vc1 or higher after that, even if the liquid crystal molecules are inclined according to the applied voltage, it takes time to respond. In other words, if the applied voltage is Vc1 or more, the liquid crystal molecules start to tilt according to the applied voltage (the transmittance starts to change), so that the alignment state of the liquid crystal molecules is in a stable state. . For this reason, the voltage Vc1 is lower than the threshold value Vth1 defined by the transmittance.

When thinking in this way, the pixels in which the liquid crystal molecules were unstable before the change were reverse tilted due to the influence of the lateral electric field when the dark pixels and the bright pixels were adjacent due to the movement of the image. It can be said that the domain is likely to occur. However, considering the initial alignment state of the liquid crystal molecules, the reverse tilt domain may or may not occur depending on the positional relationship between the dark pixel and the bright pixel.
Next, we will consider each of these cases.

FIG. 9A is a diagram showing 2 × 2 pixels adjacent to each other in the vertical direction and the horizontal direction in the liquid crystal panel 100, and FIG. 9B shows the liquid crystal panel 100 in FIG. It is a simplified sectional view when fractured at a vertical plane including a -q line.
As shown in FIG. 9, the VA liquid crystal molecules have a tilt angle of θa and a tilt azimuth angle of θb (when the potential difference between the pixel electrode 118 and the common electrode 108 (voltage applied to the liquid crystal element) is zero. = 45 degrees) and the initial orientation. Here, since the reverse tilt domain is generated due to the lateral electric field between the pixel electrodes 118 as described above, the behavior of the liquid crystal molecules on the element substrate 100a side where the pixel electrodes 118 are provided becomes a problem. Therefore, the tilt azimuth angle and tilt angle of the liquid crystal molecules are defined with reference to the pixel electrode 118 (element substrate 100a) side.

Specifically, as shown in FIG. 9B, the tilt angle θa is a common electrode with one end on the pixel electrode 118 side as a fixed point out of the major axis Sa of the liquid crystal molecules with reference to the substrate normal Sv. The angle formed by the major axis Sa of the liquid crystal molecules when the other end on the 108 side is inclined.
On the other hand, the tilt azimuth angle θb is a substrate vertical plane (pq) including the major axis Sa of the liquid crystal molecules and the substrate normal Sv with reference to the substrate vertical plane along the Y direction that is the arrangement direction of the data lines 114. The angle formed by the vertical plane including the line. The tilt azimuth angle θb is different from the upper direction of the screen (opposite to the Y direction) with one end of the major axis of the liquid crystal molecule as a starting point when viewed in plan from the pixel electrode 118 side toward the common electrode 108. The direction toward the end (upper right direction in FIG. 9A) is defined as an angle defined clockwise.
Similarly, when viewed in plan from the pixel electrode 118 side, the direction from one end to the other end of the liquid crystal molecules on the pixel electrode side is referred to as the downstream side of the tilt direction for the sake of convenience, and conversely from the other end to the one end. The direction (the lower left direction in FIG. 9A) will be referred to as the upstream side of the tilt direction for convenience.

In the liquid crystal panel 100 using the liquid crystal 105 having such an initial alignment, attention is paid to 2 × 2 four pixels surrounded by a broken line, for example, as shown in FIG. FIG. 10A shows a case where a pattern composed of black level pixels (black pixels) moves one pixel at a time in the upper right direction with an area composed of white level pixels (white pixels) as a background.
That is, as shown in FIG. 11 (a), when 2 × 2 4 pixels are all black pixels in the (n−1) frame and only the lower left one pixel is changed to a white pixel in the n frame. Suppose. As described above, in the normally black mode, the applied voltage, which is the potential difference between the pixel electrode 118 and the common electrode 108, is larger in the white pixel than in the black pixel. For this reason, in the lower left pixel that changes from black to white, as shown in FIG. 11B, the liquid crystal molecules change from a state indicated by a solid line to a state indicated by a broken line, which is perpendicular to the electric field direction (horizontal of the substrate surface). Direction).

However, the potential difference generated in the gap between the pixel electrode 118 (Wt) of the white pixel and the pixel electrode 118 (Bk) of the black pixel is the same as the potential difference generated between the pixel electrode 118 (Wt) of the white pixel and the common electrode 108. In addition, the gap between the pixel electrodes is narrower than the gap between the pixel electrode 118 and the common electrode 108. Therefore, when compared in terms of electric field strength, the lateral electric field generated in the gap between the pixel electrode 118 (Wt) and the pixel electrode 118 (Bk) is larger than the vertical electric field generated in the gap between the pixel electrode 118 (Wt) and the common electrode 108. strong.
Since the lower left pixel is a black pixel in which the liquid crystal molecules are unstable in the (n−1) frame, it takes time for the liquid crystal molecules to tilt according to the strength of the vertical electric field. On the other hand, the horizontal electric field from the adjacent pixel electrode 118 (Bk) is stronger than the vertical electric field due to the white level voltage applied to the pixel electrode 118 (Wt). Therefore, in the pixel that is going to become white, as shown in FIG. 11B, the liquid crystal molecules Rv on the side adjacent to the black pixel are more temporally than other liquid crystal molecules that are inclined according to the vertical electric field. The reverse tilt state is entered first.
The liquid crystal molecules Rv that have previously entered the reverse tilt state adversely affect the movement of other liquid crystal molecules that attempt to tilt in the horizontal direction of the substrate as indicated by a broken line in accordance with the vertical electric field. For this reason, as shown in FIG. 11C, the region where the reverse tilt occurs in the pixel that should change to white is not limited to the gap between the pixel that should change to white and the black pixel, but changes from the gap to white. It spreads over a wide range in the form of eroding the pixels to be.
Thus, from FIG. 11, when the periphery of the target pixel to be changed to white is a black pixel, when the black pixel is adjacent to the target pixel on the upper right side, the right side, and the upper side, It can be said that the reverse tilt occurs in the inner peripheral region along the right side and the upper side.
Note that the pattern change shown in FIG. 11 (a) is not limited to the example shown in FIG. 10 (a), but the pattern composed of black pixels is changed in the right direction for each frame as shown in FIG. 10 (b). This also occurs when moving one pixel at a time, or when moving one pixel at a time in the upward direction as shown in FIG. In addition, when the view is changed in the description of FIG. 36, when a pattern of white pixels moves in the upper right direction, the right direction, or the upper direction one frame at a time for each frame with the background of black pixels as the background. Also occurs.

Next, in the liquid crystal panel 100, as shown in FIG. 12A, when a pattern of black pixels moves in the lower left direction by one pixel for each frame with a background of white pixels as a background, it is surrounded by a broken line. Focus on 2 × 2 4 pixels.
That is, as shown in FIG. 13A, when 2 × 2 4 pixels are all black pixels in the (n−1) frame and only the upper right one pixel is changed to a white pixel in the n frame. Suppose.
Even after this change, in the gap between the pixel electrode 118 (Bk) for the black pixel and the pixel electrode 118 (Wt) for the white pixel, the horizontal electric field stronger than the vertical electric field in the gap between the pixel electrode 118 (Wt) and the common electrode 108. An electric field is generated. Due to this lateral electric field, as shown in FIG. 13B, the liquid crystal molecules Rv on the side adjacent to the white pixels in the black pixel are aligned in time ahead of the other liquid crystal molecules to be inclined according to the vertical electric field. Changes to a reverse tilt state. However, since the vertical electric field does not change from the (n−1) frame in the black pixel, it hardly affects other liquid crystal molecules. For this reason, as shown in FIG. 13C, the region where the reverse tilt occurs in the pixel that does not change from the black pixel is narrow enough to be ignored as compared with the example of FIG.
On the other hand, among the 2 × 2 pixels, in the pixel that changes from black to white in the upper right, the initial alignment direction of the liquid crystal molecules is a direction that is not easily affected by the horizontal electric field. There are almost no liquid crystal molecules in a state. For this reason, in the upper right pixel, as the vertical electric field strength increases, the liquid crystal molecules are correctly tilted in the horizontal direction of the substrate surface as indicated by the broken line in FIG. As a result, display quality will not deteriorate.
Note that the pattern change shown in FIG. 13 (a) is not limited to the example shown in FIG. 12 (a), but the pattern consisting of black pixels is changed to the left for each frame as shown in FIG. 12 (b). This occurs even when moving one pixel at a time, or when moving one pixel downward for each frame as shown in FIG. In addition, when the view is changed in the description of FIG. 36, when a pattern composed of white pixels is moved one pixel at a time in the lower left direction, the left direction, or the lower direction for each frame with a background composed of black pixels as a background. Also occurs.

From the description of FIG. 9 to FIG. 13, when focusing on a certain n frame in the assumed VA (normally black mode) liquid crystal, the following pixel is satisfied in the n frame when the following requirements are satisfied. It can be said that it is affected by the reverse tilt domain. That is,
(1) When focusing on the n frame, a dark pixel and a bright pixel are adjacent to each other, that is, a pixel having a low applied voltage is adjacent to a pixel having a high applied voltage, and the lateral electric field becomes strong. And
(2) In the n frame, the bright pixel (applied voltage high) is positioned on the lower left side, the left side, or the lower side corresponding to the upstream side of the tilt direction in the liquid crystal molecules with respect to the adjacent dark pixel (applied voltage low). If you want to
(3) When the pixel that changes to the bright pixel in the n frame is in an unstable state in the (n-1) frame one frame before,
This means that reverse tilt occurs in the bright pixel in n frames.
The reason has already been explained. In (2), when the boundary indicating the portion where the dark pixel and the bright pixel are adjacent has moved by one pixel from the previous frame, it is more susceptible to the reverse tilt domain. It is considered to be.

  Incidentally, FIG. 10 illustrates a case where 2 × 2 4 pixels are black pixels in the (n−1) frame and only the lower left is a white pixel in the next n frames. However, generally, not only (n-1) frames and n frames but also a plurality of frames before and after these frames are accompanied by similar movements. For this reason, as shown in FIGS. 10A to 10C, in the dark pixels (pixels with white circles) in which the liquid crystal molecules are unstable in the (n−1) frame, the image pattern From the movement, it is considered that the bright pixel is often adjacent to the lower left side, the left side, or the lower side.

Therefore, in the (n-1) frame in advance, the dark pixel and the bright pixel are adjacent to each other in the image indicated by the video signal Vid-in, and the dark pixel is located on the upper right side and the right side with respect to the bright pixel. Alternatively, when a voltage is applied to the liquid crystal element corresponding to the dark pixel when it is positioned on the upper side so that the liquid crystal molecules do not become unstable, the requirements (1) and ( Even if the condition 2) is satisfied, the requirement (3) is not satisfied, so that the reverse tilt domain does not occur in n frames.
With this as a premise, consideration will be given from n frames to (n + 1) frames. In n frames, when a dark pixel and a bright pixel are adjacent to each other in the image indicated by the video signal Vid-in, and the dark pixel is located on the upper right side, the right side, or the upper side with respect to the bright pixel. If measures are taken so that the liquid crystal molecules of the liquid crystal element corresponding to the dark pixel do not become unstable, the image pattern is moved by one pixel. As a result, the requirements (1) and (2) ) Does not satisfy requirement (3). Therefore, when viewed from the n frame, the occurrence of the reverse tilt domain can be suppressed in the future (n + 1) frame.

Next, in the n frame, when the dark pixel and the bright pixel are adjacent to each other in the image indicated by the video signal Vid-in, and the dark pixel is in the positional relationship with respect to the bright pixel, Consider how to prevent liquid crystal molecules from becoming unstable in dark pixels. As described above, the liquid crystal molecules are in an unstable state when the applied voltage of the liquid crystal element is lower than Vc1 (third voltage). For this reason, if the applied voltage of the liquid crystal element specified by the video signal Vid-in is lower than Vc1 for the dark pixels satisfying the above positional relationship, this is forcibly corrected and applied to a voltage of Vc1 or higher. It will be good.
Then, what kind of value is preferable as the voltage to be corrected will be examined. When the applied voltage specified by the video signal Vid-in is lower than Vc1, when the voltage is corrected to a voltage higher than Vc1 and applied to the liquid crystal element, the liquid crystal molecules are made more stable, or a reverse tilt domain occurs. A higher voltage is preferable if priority is given to the more reliable suppression of the problem. However, in the normally black mode, the transmittance increases as the applied voltage of the liquid crystal element is increased. Since the gradation level specified by the original video signal Vid-in is a dark pixel, that is, the lower transmittance, increasing the correction voltage means that an image not based on the video signal Vid-in is displayed. Leads to.
On the other hand, if a priority is given to preventing a change in transmittance due to the correction when a voltage corrected to Vc1 or higher is applied to the liquid crystal element, the lower limit voltage Vc1 is preferable. . In this way, what value should be used as the correction voltage should be determined depending on what is prioritized. In this embodiment, Vc1 is adopted as the correction voltage, but a higher voltage may be used.
Note that the liquid crystal molecules in the VA mode are in a state closest to the substrate surface when the applied voltage of the liquid crystal element is zero, but the voltage Vc1 is a voltage that gives an initial tilt angle to the liquid crystal molecules. Yes, liquid crystal molecules begin to tilt from the application of this voltage. In general, the voltage Vc1 at which the liquid crystal molecules are in a stable state is not generally determined due to various parameters in the liquid crystal panel. However, in the liquid crystal panel in which the gap between the pixel electrodes 118 is narrower than the gap (cell gap) between the pixel electrode 118 and the common electrode 108 as in the present embodiment, the voltage is approximately 1.5 volts. . Therefore, as the correction voltage, 1.5 volts is the lower limit, so that it is sufficient if it is equal to or higher than this voltage. Conversely, if the applied voltage of the liquid crystal element is less than 1.5 volts, the liquid crystal molecules are in an unstable state.

By the way, in the case of an image with motion, even if the pixel is in contact with the boundary in the current frame indicated by the video signal Vid-in, the frame immediately before the current frame (hereinafter referred to as “previous frame”). Considering the movements included, there are a case where the video signal needs to be corrected and a case where there is no need to correct it. The present invention suppresses the occurrence of a reverse tilt domain in consideration of the state of the previous frame when correcting the current frame.
Based on this idea, the video processing circuit 30 in FIG. 3 is a circuit for processing the n-frame video signal Vid-in and preventing the occurrence of the reverse tilt domain in the liquid crystal panel 100 in advance.

Next, details of the video processing circuit 30 will be described with reference to FIG.
As shown in FIG. 3, the video processing circuit 30 includes a frame memory 302, an overdrive control unit 304, a motion detection unit 306, a delay circuit 308, an OR circuit 310, a risk boundary detection unit 312, a previous frame state determination unit 314, a correction 316, a D (Digital) / A (Analog) converter 318, and a delay circuit 320.
The scanning control circuit 20 controls accumulation and reading of video data in the frame memory 302, delay timing of the delay circuits 308 and 320, accumulation of the video signal Vid-in in the motion detection unit 306 and the risk boundary detection unit 312, and the like. Is done.

The frame memory 302 has a storage area corresponding to the pixel arrangement of the liquid crystal panel 100 of, for example, vertical m rows × horizontal n columns. The frame memory 302 stores one frame of video data indicating the image indicated by the video signal Vid-in, and each storage area of the frame memory 302 designates the gradation level of the corresponding pixel 110. Store video data. The video data stored in the frame memory 302 is shared by the overdrive control unit 304, the motion detection unit 306, and the risk boundary detection unit 312 in order to acquire the video signal Vid-in of the previous frame. Is.
Note that the video data is written in the storage area of the frame memory 302 in accordance with the video signal Vid-in supplied from the host device. Further, under the control of the control circuit 10, video data for one row of pixels positioned on the scanning line selected by the selection signal Xctr is read from the frame memory 302.

  The overdrive control unit 304 analyzes the video signal Vid-in input to the video processing circuit 30 for each of the current frame and the previous frame, and performs overdrive driving according to a change in applied voltage specified for each pixel. The video signal Vid-ove for the current frame is generated and output (overdrive control step). In the overdrive drive, when the gradation level indicated by the video signal Vid-in of the current frame is higher than the gradation level indicated by the video signal Vid-in of the previous frame, the gradation that is higher than this gradation level. This includes an operation of outputting a video signal corresponding to the level and applying an excessive voltage to the liquid crystal element based on the video signal. The overdrive driving is further lower than the gradation level when the gradation level indicated by the video signal Vid-in of the current frame is lower than the gradation level indicated by the video signal Vid-in of the previous frame. It includes an operation of outputting a video signal corresponding to the gradation level and applying an undervoltage to the liquid crystal element based on the video signal.

  Specifically, the overdrive control unit 304 includes a lookup table and an arithmetic circuit. The overdrive control unit 304 obtains the video signal Vid-in of the previous frame by obtaining the video signal Vid-in of the current frame from the host device and reading out the video data stored in the frame memory 302. Then, when the current frame video data Vid-in and the previous frame video data Vid-in are input to the lookup table, the overdrive control unit 304 compensates for the change in the gradation level of the pixel. Is supplied to the computing unit. Specifically, the lookup table corresponds to each combination of the gradation level specified by the video signal Vid-in of the current frame and the gradation level specified by the video signal Vid-in of the previous frame. It is a table in which compensation values for compensating the response of the liquid crystal element 120 are stored in advance, and is a two-dimensional conversion table that outputs a compensation value β corresponding to a combination of gradation levels specified by these two data. The arithmetic circuit adds the compensation value β supplied from the lookup table to the video data Vid-in of the current frame, and outputs it as a video signal Vid-ove.

Here, the compensation value β supplied by the lookup table of the overdrive control unit 304 will be described with reference to FIGS. Here, as shown by the solid line in FIG. 5A, paying attention to a certain pixel, the gradation level of the current frame specified by the video signal Vid-in is changed from G10 of the gradation level of the previous frame. Assume a change to brighter G11.
In this assumption, the focus of the liquid crystal layer having a relatively low response even when applied to the pixel electrode 118 of the focus pixel by selecting the scanning line corresponding to the focus pixel based on the video signal Vid-in of the current frame. The actual transmittance in the pixel (liquid crystal capacitor) depends on the target gradation level G11 by the timing when the scanning line is next selected, as shown by a two-dot chain line in FIG. It does not reach the transmittance, and the transmittance becomes closer to that.
Therefore, as shown in FIG. 5B, the target pixel is corrected by correcting the gradation level G11 specified by the video data Vid-in of the current frame to a value excessively shaken slightly in the gradation change direction. Is compensated for so that the actual transmittance at is equal to the transmittance according to the gradation level G11 by the next selection timing of the scanning line. A value excessively shaken in the gradation changing direction at this time is set as a compensation value β1.

Similarly, it is assumed that the gradation level of the current frame specified by the video signal Vid-in has changed from the gradation level G11 of the previous frame to a darker G10.
In this assumption, the focus of the liquid crystal layer having a relatively low response even when applied to the pixel electrode 118 of the focus pixel by selecting the scanning line corresponding to the focus pixel based on the video signal Vid-in of the current frame. The actual transmittance in the pixel (liquid crystal capacitor) depends on the target gradation level G10 by the next timing when the scanning line is selected, as shown by a two-dot chain line in FIG. It does not reach the transmittance, and the transmittance before this is also reached.
Therefore, as shown in FIG. 6B, the target pixel is corrected by correcting the gradation level G10 specified by the video signal Vid-in of the current frame to a value excessively shaken slightly in the gradation change direction. Is compensated for so that the actual transmittance at is equal to the transmittance according to the gradation level G10 before the next selection timing of the scanning line. A value excessively shaken in the gradation changing direction at this time is set as a compensation value β2.
Here, the case where the gradation level changes from G10 to G11 or G11 to G10 is described, but the actual compensation values β1 and β2 are designated by the video signal Vid-in of the previous frame and the current frame. It is a value obtained in advance by experiments or the like for each combination of gradation levels. A compensation value β for each of these combinations is stored in a lookup table. Such overdrive driving is performed when the change in gradation level from the previous frame to the current frame is relatively large. The change is small and the liquid crystal element 120 of the pixel of interest (liquid crystal capacitance) When it is not necessary to compensate for the response (that is, when low response is not a problem), the pixel is not overdriven. A pixel that is not overdriven is, for example, a pixel that reaches the transmittance corresponding to the target gradation level by the next timing when the scanning line is selected without overdriving.

Returning to FIG.
The motion detection unit 306 acquires the video signal Vid-in of the current frame, reads out the video data of the previous frame stored in the frame memory 302, acquires the video signal Vid-in, and obtains the dark signal in the gradation range a. It is determined whether or not there is a boundary (hereinafter referred to as “applied boundary”) that has changed from the previous frame to the current frame among the boundaries where the pixel and the bright pixel in the gradation range b are adjacent to each other. The application boundary is a boundary that does not exist in the previous frame and exists in the current frame between pixels.
When it is determined that there is an application boundary, the motion detection unit 306 detects the application boundary and outputs boundary information indicating the position (first boundary detection step). That is, the motion detection unit 306 functions as a first boundary detection unit.
Note that the motion detection unit 306 cannot detect the boundary in the vertical or horizontal direction in the image to be displayed unless a certain amount (at least three or more rows) of video signals is accumulated. Therefore, a delay circuit 320 for delaying the video signal Vid-ove supplied from the overdrive control unit 304 to the correction unit 316 is provided in order to adjust the supply timing of the video signal Vid-ove from the overdrive control unit 304. It has been.

A more detailed configuration of the motion detection unit 306 will be described with reference to FIG.
In this embodiment, the motion detection unit 306 includes a current frame detection unit 3062, a previous frame detection unit 3064, a storage unit 3066, and an application boundary determination unit 3068.
The current frame detection unit 3062 analyzes the image indicated by the video signal Vid-in of the current frame, and determines whether there is a portion where a dark pixel in the gradation range a and a bright pixel in the gradation range b are adjacent to each other. Is determined. When the current frame detection unit 3062 determines that there is an adjacent portion, the current frame detection unit 3062 detects the adjacent portion as a boundary and outputs boundary information.
Note that the boundary here refers to a portion where a dark pixel in the gradation range a and a bright pixel in the gradation range b are adjacent, that is, a portion where a strong lateral electric field is generated. For this reason, for example, a portion where a pixel in the gradation range a and a pixel in another gradation range d (see FIG. 7A) that is neither the gradation range a nor the gradation range b are adjacent to each other, A portion where a pixel in the gradation range b and a pixel in the gradation range d are adjacent is not treated as a boundary.
The previous frame detection unit 3064 analyzes the image indicated by the video signal Vid-in of the previous frame and detects a portion where a pixel in the gradation range a and a pixel in the gradation range b are adjacent to each other as a boundary. Here, the definition of the boundary detected by the previous frame detection unit 3064 is the same as that of the current frame detection unit 3062.

The storage unit 3066 stores the boundary information detected by the previous frame detection unit 3064 and outputs the information with a delay of one frame period.
Therefore, the boundary detected by the current frame detection unit 3062 relates to the current frame, whereas the boundary detected by the previous frame detection unit 3064 and stored in the storage unit 3066 relates to the previous frame. .
The application boundary determination unit 3068 determines, as the application boundary, the boundary of the current frame image detected by the current frame detection unit 3062 excluding the same part as the boundary of the previous frame image stored in the storage unit 3066. Is.

Returning to FIG. 3, the description will be continued.
The delay circuit 308 includes a FIFO (Fast In Fast Out) memory, a multistage latch circuit, and the like, accumulates boundary information supplied from the motion detection unit 306, and after a predetermined time has passed (here, one frame) It is read out and output after (period).
The OR circuit 310 adds the boundary information of the current frame supplied from the motion detection unit 306 and the boundary information of the previous frame supplied from the delay circuit 308, and outputs the result to the correction unit 316 as boundary information mov_edge. That is, the OR circuit 310 outputs boundary information mov_edge indicating an application boundary that has changed from the previous frame at least one of the current frame and the previous frame.

  The risk boundary detection unit 312 detects a risk boundary that is a part of the boundary between the dark pixel and the bright pixel specified by the input video signal Vid-in of the current frame and is determined by the tilt direction of the liquid crystal 105 ( Second boundary detection step). Specifically, the risk boundary detection unit 312 analyzes the image indicated by Vid-in of the current frame, and the dark pixel in the gradation range a and the bright pixel in the gradation range b are in the vertical or horizontal direction. It is determined whether or not there is an adjacent part. The risk boundary detection unit 312 is a part of the boundary between the dark pixel and the bright pixel, where the dark pixel is located on the upper side and the bright pixel is located on the lower side, and the dark pixel is located on the right side and the bright pixel. Is extracted on the left side, and this is detected as a risk boundary. The risk boundary detection unit 312 outputs boundary information rsk_edge indicating the risk boundary. That is, the risk boundary detection unit 312 functions as a second boundary detection unit.

  The previous frame state determination unit 314 reads the video data of the previous frame stored in the frame memory 302 and acquires the video signal Vid-in. Then, the previous frame state determination unit 314 determines whether or not the applied voltage specified by the video signal Vid-in of the previous frame acquired from the frame memory 302 is equal to or lower than the first threshold, and an output indicating the determination result. The signal vol_sig is output. This voltage called the first threshold is an applied voltage corresponding to the gradation level PXLV. The gradation level PXLV is a gradation level corresponding to a predetermined voltage level, but overdrive driving is performed on the dark pixels in the gradation range a of the current frame in a direction that lowers the applied voltage. It is a value that serves as an indicator of whether or not That is, the previous frame state determination unit 314 does not perform overdrive driving when the gradation level of the video signal of the previous frame is equal to or lower than PXLV so that overdrive driving is not performed in the current frame. The output signal vol_sig indicating is output. The gradation level PXLV is the same as, for example, the gradation level c1, but may be determined in advance to an appropriate value obtained through experiments or the like.

  The correction unit 316 is a darker one that touches the risk boundary detected by the risk boundary detection unit 312 among the application boundaries detected by the motion detection unit 306 in the video signal Vid-ove of the current frame output from the delay circuit 320. The video signal Vid-ove that specifies the voltage applied to the liquid crystal element 120 corresponding to at least one of the pixel and the bright pixel is excluded from the correction target, and the dark signal in contact with the risk boundary is excluded from the correction target. Correction is performed so as to reduce the lateral electric field generated in the pixel and the bright pixel (correction step). Specifically, the correction unit 316 touches the risk boundary corresponding to the application boundary, and for a dark pixel that is not overdriven, the gradation level designated for the dark pixel is a level darker than c1. In some cases, the video signal Vid-ove is corrected to a video signal of gradation level c1 and output as a video signal Vid-out. On the other hand, the correction unit 316 outputs the video signal Vid-ove as it is as the video signal Vid-out without correcting the video signal for the other pixels.

Next, a more detailed configuration of the correction unit 316 will be described with reference to FIG.
The correction unit 316 includes a determination unit 3162 and a replacement unit 3164 in the present embodiment.
The determination unit 3162 determines whether or not the pixel indicated by the video signal Vid-ove output from the delay circuit 320 satisfies the correction condition for the video signal. The determination unit 3162 sets the output signal flag Q to, for example, “1” when the determination result is “Yes”, and outputs “0” when the determination result is “No”. Specifically, the determination unit 3162 is (I) the pixel indicated by the video signal Vid-ove from the overdrive control unit 304 is a dark pixel, and is output from the (II) OR circuit 310 (motion detection unit 306). (III) indicates that the boundary information rsk_edge output from the risk boundary detection unit 312 is a risk boundary, and (IV) specifies the video signal of the previous frame. When the output signal vol_sig indicates that the applied voltage is equal to or lower than the first threshold value corresponding to the gradation level PXLV (that is, overdrive driving is not performed), it is determined that the pixel of interest satisfies the correction condition. .
As described above, in the present invention, overdrive driving is performed in correspondence with (I) to (III) and the condition that the pixel is in contact with the risk boundary corresponding to the application boundary, and (IV). There are two correction conditions that are roughly classified as non-pixels. In the following, the former condition is referred to as “boundary correction condition”, and the latter condition is referred to as “OD correction condition”. is there.

In the replacement unit 3164, the flag Q supplied from the determination unit 3162 is “1”, that is, the pixel indicated by the video signal Vid-ove is a dark pixel in contact with the risk boundary corresponding to the application boundary, and In the case where the pixel is not driven, when the gradation level specified for the dark pixel indicated by the video signal Vid-ove is darker than c1, the gradation level is replaced with c1. Then, the video signal Vid-out is output.
On the other hand, when the pixel indicated by the video signal Vid-ove is not a dark pixel in contact with the risk boundary, the replacement unit 3164 does not replace the gradation level with c1 because the flag Q is “0”, and the flag Q Even when “1” is set, if a bright level with a gradation level of c1 or higher is designated, the video signal Vid-ove is output as the video signal Vid-out without replacing the gradation level with c1. To do.

  The D / A converter 318 converts the video signal Vid-out, which is digital data, into an analog data signal Vx. In this embodiment, the surface inversion method is used. In this case, the polarity of the data signal Vx is switched every time one frame is rewritten on the liquid crystal panel 100.

Next, the display operation of the liquid crystal display device 1 will be described. The video signal Vid-in is transmitted from the host device over the frame from the first row and the first column to the first row and the nth column, the second row and the first column to the second row and the nth column, and the third row and the first row. Supplied in the order of pixels from column to 3 rows and n columns,..., M rows and 1 columns to m rows and n columns. The video processing circuit 30 performs processing such as delay and correction on the video signal Vid-in and outputs it as a video signal Vid-out.
Here, when viewed in the horizontal effective scanning period (Ha) in which the video signal Vid-out of 1 row 1 column to 1 row n column is output, the processed video signal Vid-out is converted into a D / A converter 318. By this, as shown in FIG. 8 (b), it is converted into a positive or negative data signal Vx. Here, it is converted into, for example, a positive data signal Vx. The data signal Vx is sampled as data signals X1 to Xn on the data lines 114 in the 1st to nth columns by the data line driving circuit 140.
On the other hand, in the horizontal scanning period in which the video signal Vid-out of 1 row 1 column to 1 row n column is output, the scanning control circuit 20 controls the scanning line driving circuit 130 so that only the scanning signal Y1 becomes H level. To do. If the scanning signal Y1 is at the H level, the TFT 116 in the first row is turned on, so that the data signal sampled on the data line 114 is applied to the pixel electrode 118 via the TFT 116 in the on state. As a result, the positive voltage corresponding to the gradation level specified by the video signal Vid-out is written in the liquid crystal elements in the first row and first column to the first row and n column, respectively.

Subsequently, the video signal Vid-in in the 2nd row and the 1st column to the 2nd row and the nth column is similarly processed by the video processing circuit 30 and is output as the video signal Vid-out. Then, the data line driving circuit 140 samples the data line 114 in the 1st to nth columns.
In the horizontal scanning period in which the video signal Vid-out of the 2nd row and the 1st column to the 2nd row and the nth column is output, only the scanning signal Y2 is set to the H level by the scanning line driving circuit 130. Is applied to the pixel electrode 118 via the TFT 116 in the second row in the on state. As a result, the positive voltage corresponding to the gradation level designated by the video signal Vid-out is written in the liquid crystal elements in the 2nd row and the 1st column to the 2nd row and the nth column.
Thereafter, a similar writing operation is executed for the third, fourth,..., M-th rows, whereby a voltage corresponding to the gradation level specified by the video signal Vid-out is written to each liquid crystal element. A transmission image defined by the video signal Vid-in is created.
In the next frame, a similar writing operation is executed except that the video signal Vid-out is converted into a negative polarity data signal by polarity inversion of the data signal.

FIG. 8B is a voltage waveform showing an example of the data signal Vx when the video signal Vid-out of 1 row 1 column to 1 row n column is output from the video processing circuit 30 over the horizontal scanning period (H). FIG. In the present embodiment, since the normally black mode is used, if the data signal Vx is positive, the voltage higher than the reference voltage Vcnt by the amount corresponding to the gradation level processed by the video processing circuit 30. In the case of negative polarity, the voltage is lower than the reference voltage Vcnt by the amount corresponding to the gradation level (indicated by ↓ in the figure).
Specifically, if the voltage of the data signal Vx is positive, the voltage ranges from the voltage Vw (+) corresponding to white to the voltage Vb (+) corresponding to black. In the range from the voltage Vw (−) corresponding to 1 to the voltage Vb (−) corresponding to black, the voltages are shifted from the reference voltage Vcnt by the amount corresponding to the gradation.
The voltage Vw (+) and the voltage Vw (−) are in a symmetric relationship with respect to the voltage Vcnt. The voltages Vb (+) and Vb (−) are also in a symmetrical relationship with respect to the voltage Vcnt.
FIG. 8B shows the voltage waveform of the data signal Vx, which is different from the voltage applied to the liquid crystal element 120 (potential difference between the pixel electrode 118 and the common electrode 108). Further, the vertical scale of the voltage of the data signal in FIG. 8B is enlarged as compared with the voltage waveform of the scanning signal or the like in FIG.

A specific example of correction processing by the video processing circuit 30 will be described.
As described above, the video processing circuit 30 determines whether each pixel in the video signal of the current frame satisfies both the boundary correction condition and the OD correction condition, and determines a correction target pixel. Yes. In order to simplify the description, first, a specific example regarding the boundary correction condition will be described.
For example, the image indicated by the video signal Vid-in of the previous frame is as shown in FIG. 14 (1), and the image indicated by the video signal Vid-in of the current frame is as shown in FIG. 14 (2), for example. In other words, that is, when a pattern composed of dark pixels in the gradation range a moves leftward with a bright pixel in the gradation range b as a background, the pattern is detected by the previous frame detection unit 3064 and stored in the storage unit 3066. The boundary of the previous frame image and the boundary of the current frame image detected by the current frame detection unit 3062 are as shown in FIG. 14 (3), respectively.
Therefore, the application boundary determined by the motion detection unit 306 is as shown in FIG. On the other hand, the risk boundary detected from the video signal Vid-ove of the current frame by the risk boundary detection unit 312 is as shown in FIG. Therefore, as shown in FIG. 15 (6), of the application boundaries detected by the motion detection unit 306, the dark pixel is located on the upper side and the bright pixel is located on the lower side, and the dark pixel is located on the right side. The dark pixel adjacent to the portion corresponding to the risk boundary, which is the portion where the bright pixel is located on the left side, satisfies the boundary correction condition of the present embodiment.

Next, a specific example regarding the OD correction condition will be described.
When all dark pixels satisfying the boundary correction condition satisfy the OD correction condition and a darker level than the gradation level c1 is designated for these dark pixels, as shown in FIG. In addition, the correction unit 316 corrects the video signal Vid-ove for these dark pixels to the video signal Vid-out of the gradation level c1. For this reason, an image indicated by the video signal Vid-in has a portion that changes from a black pixel to a white pixel by moving a black pixel region by one pixel in either the upper right direction, the right direction, or the upper direction. Even if it exists, in the liquid crystal panel 100, the liquid crystal molecules do not change directly from an unstable state to a white pixel, but once the voltage Vc1 corresponding to the gradation level c1 is applied, the liquid crystal molecules are forcibly stabilized. After passing through this state, the pixel changes to a white pixel.
In FIG. 16A, the dark pixel indicated by * 1 is in contact with the risk boundary because the risk boundary that is continuous vertically and horizontally is located in the lower left corner. It is determined whether or not a darker level than the gradation level c1 is designated. This is to cope with a case where the pattern corresponding to the bright pixel located at the lower left moves one pixel in the diagonally upper right direction with respect to the dark pixel indicated by * 1. On the other hand, the dark pixel indicated by * 2 has a risk boundary that is torn only in the vertical or horizontal direction at one corner, and has no continuous risk boundary in the vertical and horizontal directions. It is not subject to judgment. This concept can be adopted regardless of the tilt azimuth angle θb. Therefore, the description thereof is omitted below.

By the way, for the dark pixels that are overdriven, the video signal is corrected in the darkening direction as indicated by β2 in FIG. 6B. On the other hand, the correction for suppressing the reverse tilt domain (in order to reduce the lateral electric field) is to correct the video signal in the brightening direction as indicated by the arrow v2 shown in FIG. Since the correction direction of the video signal is contradictory in this way, when the correction unit 316 performs correction to suppress the reverse tilt domain for the dark pixel on which overdrive driving is performed, the action of overdrive driving is canceled out. As a result, the display quality of the liquid crystal panel 100 is degraded due to the responsiveness of the liquid crystal 105. Therefore, the correction unit 316 excludes dark pixels that are overdriven from the correction target without performing correction for reducing the lateral electric field on the dark pixels that satisfy the boundary correction condition.
The above is the basis for considering the OD correction condition in the present invention.

Therefore, the correction unit 316 selects dark pixels for which overdrive driving is performed according to the control of the overdrive control unit 304 among dark pixels that are candidates for correction as indicated by “c1” in FIG. Does not correct the video signal Vid-ove.
Here, the correction processing of the correction unit 316 will be described with reference to FIG. FIG. 17 exemplifies a pixel column in a part of a row in the (n−1) -frame video signal Vid-ove and the n-frame video signal Vid-ove, and the pixels in the left-right direction (horizontal direction) in the figure. Are arranged. 17A illustrates the case where the n-frame video signal Vid-ove is not corrected, and FIG. 17B illustrates the case where the n-frame video signal Vid-ove is corrected. is there. In FIG. 17, “□” represents a bright pixel whose video signal Vid-ove has not been corrected by the correction unit 316, and “■” represents a dark pixel whose video signal Vid-ove has not been corrected by the correction unit 316. To express.
As shown in FIG. 17, the dark pixels Pix1 to Pix3 that are in contact with the risk boundary corresponding to the application boundary satisfy the boundary correction condition. However, the dark pixel Pix2 indicated as “OD drive” in FIG. 17B is an object of overdrive drive and does not satisfy the OD correction condition. Since the dark pixel Pix2 is overdriven to increase the response speed of the liquid crystal 105, the dark pixel Pix2 is excluded from the correction target by the correction unit 316 in order to enable the overdrive driving.
Therefore, the correcting unit 316 assumes that the dark pixel whose gradation level of the video signal Vid-in of the previous frame is equal to or lower than the gradation level PXLV satisfies the OD correction condition, and sets the dark pixel gradation level satisfying the boundary correction condition. The video signal Vid-out is corrected (shown by “◯”) so as to be c1 (however, the gradation level before correction is darker than c1). On the other hand, the correction unit 316 assumes that the dark pixel in which the gradation level of the video signal Vid-in of the previous frame exceeds the gradation level PXLV does not satisfy the OD correction condition, and even if the boundary pixel satisfies the boundary correction condition. The signal Vid-out is not corrected (indicated by “x”). Therefore, in the example shown in FIG. 17, the correction unit 316 corrects the video signals of the dark pixels Pix1 and Pix3 to c1, but does not correct the video signal of Pix2.
Here, the case where the arrangement direction of the pixels is the left-right direction has been described, but correction is excluded for the pixels for which overdrive driving has been performed regardless of whether the arrangement direction is the vertical direction or the diagonal direction. There is no change in respect.

  Since the video processing circuit 30 includes the delay circuit 308 and the OR circuit 310, pixels that satisfy the boundary correction condition but do not satisfy the OD correction condition are excluded from correction in the current frame (n frame). However, if overdrive driving is not performed even in a frame (n + 1 frame) after one frame, it is a correction target. Since this content is common to each embodiment described later, this description will be omitted hereinafter.

As described above, in this embodiment, it is only necessary to detect a boundary and a risk boundary between pixels instead of the entire image for one frame, and therefore, motion is detected by analyzing an image for two frames or more. Compared to the configuration, the image processing circuit can be prevented from becoming large and complicated. Furthermore, it is possible to prevent the region in which the reverse tilt domain is likely to occur from becoming continuous as the black pixel moves.
Further, in the present embodiment, in the image defined by the video signal Vid-ove, the pixel whose video signal is corrected is a dark pixel adjacent to the bright pixel and has a gradation level darker than the gradation level c1. Among the dark pixels to which is designated, only the pixels located on the downstream side of the tilt direction with respect to the dark pixel. For this reason, the portion where the display not based on the video signal Vid-ove occurs is a dark pixel adjacent to the bright pixel without considering the tilt azimuth, and a gradation level darker than the gradation level c1 is designated. Compared to a configuration in which all dark pixels are uniformly corrected, the number of dark pixels can be reduced. In the present embodiment, the pixels for which overdrive driving is performed are excluded from the correction target for reducing the lateral electric field, so that the effect of overdrive driving is not canceled.
Furthermore, in the present embodiment, since the video signal equal to or higher than the set value is not clipped uniformly, the contrast ratio is not adversely affected by providing a voltage range that is not used. In addition, since it is not necessary to change the structure of the liquid crystal panel 100, the aperture ratio is not reduced, and the present invention can be applied to a liquid crystal panel that has already been manufactured without devising the structure.

<Other examples of tilt azimuth>
In the embodiment described above, the case where the tilt azimuth angle θb is 45 degrees in the VA method has been described as an example. Next, an example where the tilt azimuth angle θb is other than 45 degrees will be described.
First, an example in which the tilt azimuth angle θb is 225 degrees as shown in FIG. In this example, when the liquid crystal molecules in the self pixel and the peripheral pixels change from the unstable state to the bright pixel only by the self pixel, the reverse tilt in the self pixel is on the left side and the bottom side as shown in FIG. Occurs in the inner peripheral area along. Note that this example is equivalent to the case where the tilt azimuth angle θb shown in FIG. 9 is 45 degrees and rotated by 180 degrees.
When the tilt azimuth angle θb is 225 degrees, among the requirements (1) to (3) in which the reverse tilt domain occurs when the tilt azimuth angle θb is 45 degrees, the requirement (2) is as follows: Correct it. That is,
(2) In the n frame, the bright pixel (applied voltage high) is located on the upper right side, the right side or the upper side corresponding to the upstream side of the tilt direction in the liquid crystal molecules with respect to the adjacent dark pixel (applied voltage low). In case,
And correct. There is no change to requirement (1) and requirement (3).
Therefore, when the tilt azimuth angle θb is 225 degrees, in the n frame, a dark pixel and a bright pixel are adjacent to each other, and the dark pixel is opposed to the bright pixel on the lower left side, the left side, or the lower side. If it is located on the side, measures may be taken to prevent the liquid crystal molecules from becoming unstable with respect to the liquid crystal element corresponding to the dark pixel.
For this purpose, the correction unit 316 in the video processing circuit 30 includes a portion where the dark pixel is located on the lower side and the bright pixel is located on the upper side of the application boundary detected by the motion detection unit 306, and the dark pixel is located on the left side. The video signal may be corrected based on the risk boundary of the portion where the bright pixel is located on the right side.
When the tilt azimuth angle θb is 225 degrees, when the image shown in FIG. 14 (2) satisfies the correction condition related to overdrive driving, the black pixels in contact with the risk boundary shown in FIG. The gradation level may be corrected to the gradation level c1. The correction unit 316 specifies dark pixels to be corrected depending on whether or not the correction condition relating to overdrive driving is satisfied, and this specifying method is as described above.

Next, an example in which the tilt azimuth angle θb is 90 degrees as shown in FIG. In this example, when the liquid crystal molecules in the self pixel and the peripheral pixels are changed from the unstable state to the bright pixel only by the self pixel, the reverse tilt in the self pixel is along the right side as shown in FIG. Occurs intensively in the area. For this reason, it can be said that the reverse tilt domain occurs in the self-pixel near the right side of the upper side and the right side of the lower side by the width generated on the right side.
Therefore, when the tilt azimuth angle θb is 90 degrees, among the requirements (1) to (3) that the reverse tilt domain occurs when the tilt azimuth angle θb is 45 degrees, the requirement (2) Is corrected as follows. That is,
(2) In the n frame, the bright pixel (applied voltage high) is generated not only on the left side corresponding to the upstream side of the tilt direction in the liquid crystal molecules but also on the left side of the adjacent dark pixel (applied voltage low). When located on the upper or lower side affected by the area to be
And correct. There is no change to requirement (1) and requirement (3). Therefore, if the tilt azimuth angle θb is 90 degrees, the dark pixel and the bright pixel are adjacent to each other in the n frame, and the dark pixel is opposite to the bright pixel on the right side, the lower side, or the upper side. In the case where the liquid crystal element is located at the position, the liquid crystal element corresponding to the dark pixel may be subjected to measures so that the liquid crystal molecules do not become unstable.

For this purpose, the correction unit 316 in the video processing circuit 30 includes a portion where the dark pixel is located on the right side and the bright pixel is located on the left side and the dark pixel is located on the upper side of the application boundary detected by the motion detection unit 306. The video signal may be corrected based on the risk boundary risk boundary of the portion where the bright pixel is located on the lower side and the portion where the dark pixel is located on the lower side and the bright pixel is located on the upper side.
When the tilt azimuth angle θb is 90 degrees, the image shown in FIG. 14 (2) has black pixels in contact with the risk boundary shown in FIG. 16 (b) when the correction condition related to overdrive driving is satisfied. The gradation level is to be corrected to the gradation level c1. The correction unit 316 specifies dark pixels to be corrected depending on whether or not the correction condition relating to overdrive driving is satisfied, and this specifying method is as described above.
According to this configuration, when the tilt azimuth angle θb is 90 degrees, the area composed of black pixels in the image defined by the video signal Vid-in is in the upward direction, the upper right direction, the right direction, the lower right direction, or the lower direction. Even if there is a portion that changes from a black pixel to a white pixel by moving only one pixel, the liquid crystal panel 100 does not change directly from an unstable state to a white pixel, Once the liquid crystal molecules are forced to pass through a stable state by the application of the voltage Vc1 corresponding to the gradation level c1, the pixel changes to a white pixel, so that the occurrence of a reverse tilt domain can be suppressed.

Second Embodiment
Next, a second embodiment of the present invention will be described. This embodiment will also be described on the assumption that it is a normally black mode. This is the same in the following embodiments unless otherwise specified. In the following description, the same components as those in the first embodiment are denoted by the same reference numerals, and detailed description thereof is omitted as appropriate. In the first embodiment described above, the video processing circuit 30 corrects only the dark pixels satisfying the boundary correction condition to the gradation level c1. Also, two or more predetermined number of dark pixels continuous to the opposite side are also targets to be corrected to the gradation level c1.
As described above, the video processing circuit 30 of the present embodiment is different from the configuration of the first embodiment in that the number of dark pixels to be corrected in the correction unit 316 is changed.

As in the first embodiment described above, the determination unit 3162 of the correction unit 316 is (I) the pixel indicated by the video signal Vid-ove from the overdrive control unit 304 is a dark pixel, and (II) the OR circuit 310 ( The boundary information mov_edge output from the motion detection unit 306) indicates that it is an applicable boundary, (III) the boundary information rsk_edge output from the risk boundary detection unit 312 indicates that it is a risk boundary, and (IV ) When the output signal vol_sig indicates that the applied voltage specified by the video signal of the previous frame is equal to or lower than the first threshold value corresponding to the gradation level PXLV (that is, overdrive driving is not performed), Is determined to satisfy the correction condition.
When both of these determination results are “Yes”, the determination unit 3162 outputs the flag Q of the output signal as “1”, and when any one of the determination results is “No”, “0” is output. "Is output. Further, when the determination unit 3162 of this embodiment determines “Yes”, the gradation level of the pixel indicated by the video signal Vid-ove that is a dark pixel continuous in the opposite direction of the risk boundary corresponding to the application boundary. Are in the gradation range a, and the dark pixel whose distance from the risk boundary to the pixel is within (K + 1) pixels is treated as satisfying the boundary correction condition. Then, the determination unit 3162 outputs the value of the flag Q as “1” for a pixel that does not perform overdrive driving among dark pixels that satisfy the boundary correction condition (that is, a pixel that satisfies the OD correction condition). In this embodiment, K = 1.
For the pixels other than those that are in contact with the risk boundary, the determination unit 3162 determines whether or not the OD correction condition is satisfied based on the output signal vol_sig from the previous frame state determination unit 314.
If the flag Q is “1” and the darker level is specified for the dark pixel than the gradation level c1, the replacement unit 3164 replaces the dark pixel with the gradation level c1.

A specific example of processing by the video processing circuit 30 will be described.
For example, the image indicated by the video signal Vid-in of the previous frame is as shown in FIG. 14 (1), and the image indicated by the video signal Vid-in of the current frame is as shown in FIG. 14 (2), for example. When θb = 45 degrees, pixels satisfying the boundary correction condition are as shown in FIG.

The correction unit 316 does not correct the video signal Vid-ove for the dark pixels that are overdriven according to the control of the overdrive control unit 304 among the dark pixels indicated by “c1” in FIG. . The correction process of the correction unit 316 will be described with reference to FIG. FIG. 21 corresponds to FIG. 17, and illustrates one row of pixel columns in the (n−1) -frame video signal Vid-ove and the n-frame video signal Vid-ove. Pixels) in the direction). FIG. 21A illustrates the case where the n-frame video signal is not corrected, and FIG. 21B illustrates the case where the n-frame video signal is corrected. As shown in FIG. 21, the dark pixels Pix1 to Pix6 that are in contact with the risk boundary corresponding to the application boundary satisfy the boundary correction condition. However, the dark pixels Pix3, Pix4, and Pix6 indicated as “OD drive” in FIG. 21 are objects of overdrive drive and do not satisfy the OD correction condition. Therefore, the dark pixels Pix3, Pix4, and Pix6 are excluded from correction targets of the correction unit 316.
Therefore, in the example shown in FIG. 21, the correction unit 316 corrects the video signals of the dark pixels Pix1, Pix2, and Pix5 to c1 (only when the gradation level is darker than c1 before correction) (indicated by “◯”). ), The video signals of Pix3, Pix4, and Pix6 are not corrected (illustrated by “x”).

Further, in the same way as in the first embodiment, when θb = 90 degrees, pixels satisfying the boundary correction condition in the image shown in FIG. 14 (2) are as shown in FIG. 20 (b). When θb = 225 degrees, pixels satisfying the boundary correction condition in the image shown in FIG. 14 (2) are as shown in FIG. 20 (c).
According to the present embodiment, even when the response time of the liquid crystal element is longer than the time interval at which the display screen is updated, such as when the liquid crystal panel 100 is doubled or faster, the number of dark pixel groups to be corrected is reduced. By appropriately setting, it is possible to avoid in advance the occurrence of display defects due to the reverse tilt domain described above. Further, according to the present embodiment, the change in the applied voltage due to the correction of the video signal can be made inconspicuous.
According to the structure of this embodiment, there exists an effect equivalent to 1st Embodiment besides the above.

<Third Embodiment>
Next, a third embodiment of the present invention will be described.
In this embodiment, in the configuration of the first embodiment, a video signal of a bright pixel that satisfies the boundary correction condition is corrected instead of a dark pixel that satisfies the boundary correction condition. In this embodiment, dark pixels are not corrected. Therefore, in this embodiment, in order to suppress the above-described “(3) a pixel that changes to the bright pixel in the n frame is in an unstable state of liquid crystal molecules in the (n−1) frame one frame before”. Instead of increasing the gradation level of the dark pixel, “(1) When focusing on the n frame, the dark pixel and the bright pixel are adjacent to each other, that is, the pixel with the low applied voltage and the pixel with the high applied voltage The horizontal electric field is suppressed by paying attention to the requirement that the horizontal electric field becomes stronger. That is, the video processing circuit 30 corrects the applied voltage to the liquid crystal element 120 corresponding to the bright pixel in contact with the risk boundary to be low, thereby generating a horizontal electric field generated between the bright pixel and the dark pixel adjacent to each other across the risk boundary. Suppress. The contents regarding the OD correction condition are the same as those in the first and second embodiments described above.

  By the way, for a bright pixel to be overdriven, the gradation level is corrected in a brighter direction as indicated by β1 in FIG. On the other hand, the correction for suppressing the reverse tilt domain (in order to reduce the lateral electric field) corrects the video signal in the darkening direction as indicated by the arrow v1 shown in FIG. As described above, since the video signal correction directions are contradictory to each other, when the correction unit 316 corrects the reverse tilt domain for a bright pixel on which overdrive driving is performed, the action of overdrive driving is canceled out. As a result, the display quality of the liquid crystal panel 100 is degraded due to the responsiveness of the liquid crystal 105. Therefore, the correction unit 316 excludes a bright pixel to be overdriven from a correction target without performing correction for reducing the lateral electric field on the bright pixel that satisfies the boundary correction condition.

The video processing circuit 30 of this embodiment is different from the configuration of the first embodiment in that the configuration related to the previous frame state determination unit 314, the gradation level input to the correction unit 316, and the determination of the determination unit 3162 The content is changed.
The previous frame state determination unit 314 reads the previous frame video data stored in the frame memory 302 and acquires the previous frame video signal Vid-in. Then, the previous frame state determination unit 314 determines whether or not the applied voltage specified for the pixel indicated by the video signal Vid-in output from the frame memory 302 is greater than or equal to the second threshold. An output signal vol_sig indicating the result is output. This voltage called the second threshold is an applied voltage corresponding to the gradation level PXHV. The gradation level PXHV is a gradation level corresponding to a predetermined voltage level, but overdrive driving is performed on a bright pixel in the gradation range b of the current frame so as to increase the applied voltage. The value is used as an index of whether or not That is, the previous frame state determination unit 314 performs overdrive when the gradation level of the video signal Vid-in of the previous frame is equal to or higher than the gradation level PXHV so that overdrive driving is not performed in the current frame. An output signal vol_sig indicating that driving is not performed is output. Note that the gradation level PXHV is the same as the gradation level c2, for example, but it is preferable that the gradation level PXHV is determined in advance to an appropriate value obtained through experiments or the like.

In the determination unit 3162, (I) the pixel indicated by the video signal Vid-ove from the overdrive control unit 304 is a bright pixel, and (II) the boundary information mov_edge output from the OR circuit 310 (motion detection unit 306) is (III) The boundary information rsk_edge output from the risk boundary detection unit 312 indicates a risk boundary, and (IV) the applied voltage specified by the video signal of the previous frame When the output signal vol_sig indicates that it is equal to or higher than the second threshold value corresponding to the gradation level PXHV (that is, overdrive driving is not performed), it is determined that the focused pixel satisfies the correction condition. Among these, (I) to (III) are boundary correction conditions, and (IV) is an OD correction condition. The determination unit 3162 outputs the flag Q of the output signal as, for example, “1” when all the determination results are “Yes”, and “0” when any one of the determination results is “No”. "Is output.
When the flag Q supplied from the determination unit 3162 is “1”, the replacement unit 3164 is a bright pixel designated by the video signal Vid-ove with respect to a bright pixel when the flag Q is “1”. Is replaced with a video signal of the gradation level c2 and output as a video signal Vid-out. The gradation level c2 corresponds to the applied voltage Vc2 (fourth voltage) to the liquid crystal element 120, and is obtained by any applied voltage that is below the threshold Vth2 and above the threshold Vth1. However, it is preferable that the applied voltage Vc2 falls within a change of 10% from the brightness when correction is not performed.
The replacement unit 3164 designates a darker level than the gradation level c2 for the bright pixel when the flag Q supplied from the determination unit 3162 is “0” or when the flag Q is “1”. If it is, the video signal Vid-ove is output as it is as the video signal Vid-out without replacing the gradation level.

A specific example of processing by the video processing circuit 30 will be described.
An image indicated by the video signal Vid-in one frame before the current frame is, for example, as shown in FIG. 14 (1), and an image indicated by the video signal Vid-in of the current frame is, for example, FIG. ) And θb = 45 degrees, the pixels that satisfy the boundary correction condition are as shown in FIG. 22A.

Of the bright pixels that are candidates for correction as indicated by “c2” in FIG. 22A, the correction unit 316 performs video for the bright pixels that are overdriven according to the control of the overdrive control unit 304. Do not correct the signal.
Here, the correction processing of the correction unit 316 will be described with reference to FIG. FIG. 23 corresponds to FIG. 17, and illustrates a pixel column in a part of a row in the (n−1) -frame video signal Vid-ove and the n-frame video signal Vid-ove. Pixels are arranged in the (horizontal direction). FIG. 23A illustrates the case where the n-frame video signal Vid-ove is not corrected, and FIG. 23B illustrates the case where the n-frame video signal Vid-ove is corrected. is there. As shown in FIG. 23, the bright pixels Pix1 to Pix3 that are in contact with the risk boundary corresponding to the application boundary satisfy the boundary correction condition. However, the bright pixels Pix1 and Pix3 indicated as “OD drive” in FIG. 23 are overdrive drive targets and do not satisfy the OD correction condition. The bright pixels Pix1 and Pix3 are excluded from correction targets of the correction unit 316 because overdrive driving is performed to increase the response speed of the liquid crystal.
Therefore, the correction unit 316 assumes that the bright pixel whose gradation level of the video signal Vid-in of the previous frame is PXHV or higher satisfies the OD correction condition, and sets the gradation level of the bright pixel satisfying the boundary correction condition to c2. Thus, the video signal Vid-out is corrected (indicated by “◯”). On the other hand, the correction unit 316 assumes that the dark pixel whose gradation level of the video signal Vid-in of the previous frame is lower than PXHV does not satisfy the OD correction condition, and even if the video signal Vid- Out is not corrected (illustrated by “x”). Therefore, in the example shown in FIG. 23, the correction unit 316 corrects the gradation level of the bright pixel Pix2 to c2, but does not correct the video signals of Pix1 and Pix3.

Further, in the same way as in the first embodiment, when θb = 90 degrees, pixels satisfying the boundary correction condition in the image shown in FIG. 14 (2) are as shown in FIG. 22 (b). When θb = 225 degrees, the pixels that satisfy the boundary correction condition in the image shown in FIG. 14 (2) are as shown in FIG. 22 (c).
This suppresses the potential difference between adjacent bright and dark pixels across the risk boundary and reduces the lateral electric field, thereby reducing the occurrence of reverse tilt domains caused by the lateral electric field. Moreover, there exists an effect equivalent to the structure of 1st Embodiment mentioned above.

<Fourth embodiment>
Next, a fourth embodiment of the present invention will be described.
In the third embodiment described above, the video processing circuit 30 corrects only the bright pixels satisfying the boundary correction condition to the gradation level c2, but continues from the bright pixels in contact with the risk boundary to the opposite side of the risk boundary. A predetermined number of bright pixels of 2 or more are also targets to be corrected to the gradation level c2.
As described above, the part of the video processing circuit 30 of the present embodiment that is different from the configuration of the third embodiment is that the number of bright pixels to be corrected in the correction unit 316 is changed.
In this embodiment, correction for dark pixels is not performed.

In the correction unit 316, as in the third embodiment described above, the determination unit 3162 is (I) the pixel indicated by the video signal Vid-ove from the overdrive control unit 304 is a bright pixel, and (II) the OR circuit 310. The boundary information mov_edge output from the (motion detection unit 306) indicates that it is an applicable boundary, and (III) the boundary information rsk_edge output from the risk boundary detection unit 312 indicates that it is a risk boundary. IV) When the output signal vol_sig indicates that the applied voltage specified by the video signal of the previous frame is equal to or higher than the second threshold corresponding to the gradation level PXHV (that is, overdrive driving is not performed), attention is paid It is determined that the pixel satisfies the correction condition.
When both of these determination results are “Yes”, the determination unit 3162 outputs the flag Q of the output signal as “1”, and when any one of the determination results is “No”, “0” is output. "Is output. Further, when the determination unit 3162 determines “Yes”, the gradation level of the pixel that is a bright pixel continuous in the opposite direction of the risk boundary corresponding to the application boundary and indicated by the video signal Vid-ove is within the gradation range. A bright pixel that belongs to b and whose distance from the risk boundary to the pixel is within (K + 1) pixels is treated as satisfying the boundary correction condition. Then, the determination unit 3162 outputs the value of the flag Q as “1” for a pixel that does not perform overdrive driving among bright pixels that satisfy the boundary correction condition (that is, a pixel that satisfies the OD correction condition). In this embodiment, K = 1.
For the pixels other than those that are in contact with the risk boundary, the determination unit 3162 determines whether or not the OD correction condition is satisfied based on the output signal vol_sig from the previous frame state determination unit 314.
The replacement unit 3164 replaces the bright pixel with the gradation level c2 when the flag Q is “1”.

A specific example of processing by the video processing circuit 30 will be described.
An image indicated by the video signal Vid-in one frame before the current frame is, for example, as shown in FIG. 14 (1), and an image indicated by the video signal Vid-in of the current frame is, for example, FIG. ), When θb = 45 degrees, pixels that satisfy the boundary correction condition are represented as shown in FIG.

Of the bright pixels that are candidates for correction as indicated by “c2” in FIG. 24A, the correction unit 316 performs video for the bright pixels that are overdriven according to the control of the overdrive control unit 304. The signal Vid-ove is not corrected. The correction process of the correction unit 316 will be described with reference to FIG. FIG. 25 corresponds to FIG. 17 and illustrates one row of pixel columns in the (n−1) -frame video signal Vid-ove and the n-frame video signal Vid-ove. Pixels) in the direction). FIG. 25A illustrates the case where the n-frame video signal Vid-ove is not corrected, and FIG. 25B illustrates the case where the n-frame video signal Vid-ove is corrected. Is. As shown in FIG. 25, the bright pixels Pix1 to Pix6 that are in contact with the risk boundary corresponding to the application boundary satisfy the boundary correction condition. However, the bright pixels Pix2, Pix5, and Pix6 indicated as “OD drive” in FIG. 25 are objects of overdrive drive and do not satisfy the OD correction condition. Therefore, the bright pixels Pix2, Pix5, and Pix6 are excluded from correction targets of the correction unit 316.
Therefore, in the example shown in FIG. 25, the correction unit 316 corrects the video signals of the bright pixels Pix1, Pix3, and Pix4 to c2 (shown by “◯”), but does not correct the video signals of Pix2, Pix5, and Pix6 (“ X ”).

Further, in the same way as in the first embodiment, when θb = 90 degrees, pixels satisfying the boundary correction condition in the image shown in FIG. 14 (2) are as shown in FIG. 24 (b). When θb = 225 degrees, pixels satisfying the boundary correction condition in the image shown in FIG. 14 (2) are as shown in FIG. 24 (c).
As described above, since dark pixels determined by the tilt orientation of the liquid crystal element 120 are targeted for correction, the occurrence of reverse tilt domains can be suppressed while suppressing changes from the original image. Further, even when the response time of the liquid crystal element is longer than the time interval at which the display screen is updated, it is possible to suppress the occurrence of the reverse tilt domain. Play.

<Fifth Embodiment>
Next, a fifth embodiment of the present invention will be described.
In the following description, the same components as those in the first embodiment are denoted by the same reference numerals, and the description thereof is omitted as appropriate. In this embodiment, both the dark pixel correction described in the first embodiment and the bright pixel correction described in the third embodiment are performed. That is, the video processing circuit 30 of this embodiment corrects the video signal so as not to satisfy the conditions (1) and (3).

FIG. 26 is a block diagram showing the configuration of the video processing circuit 30 according to this embodiment. The difference between the video processing circuit 30 and the video processing circuit 30 of the first embodiment described above is that the calculation unit 322 is added, the configuration related to the previous frame state determination unit 314, and the determination contents of the determination unit 3162 are changed. The point is.
Specifically, taking the normally black mode as an example, if the pixel indicated by the video signal Vid-ove is in contact with the risk boundary, the calculation unit 322 first determines that the pixel is a dark pixel. The tone level c1 is calculated and output for the dark pixel. Second, if the pixel is a bright pixel, the tone level c2 is calculated and output for the bright pixel.
In the correction unit 316, the determination unit 3162, specifically, the determination unit 3162, (I) the pixel indicated by the video signal Vid-ove from the overdrive control unit 304 is a bright pixel or a dark pixel (II ) Indicates that the boundary information mov_edge output from the OR circuit 310 (motion detection unit 306) is an applicable boundary, and (III) indicates that the boundary information rsk_edge output from the risk boundary detection unit 312 is a risk boundary. Further, (IV) when the output signal vol_sig indicates that the applied voltage specified by the video signal of the previous frame is not overdriven, it is determined that the focused pixel satisfies the correction condition. When both of these determination results are “Yes”, the determination unit 3162 outputs the flag Q of the output signal as “1”, and when any one of the determination results is “No”, “0” is output. "Is output. Among these, (I) to (III) are boundary correction conditions, and (IV) is an OD correction condition.

  The previous frame state determination unit 314 reads the video data of the previous frame stored in the frame memory 302 and acquires the video signal Vid-in. If the pixel indicated by the video signal Vid-ove of the current frame is a dark pixel, the previous frame state determination unit 314 determines the level of the pixel indicated by the video signal Vid-in of the previous frame output from the frame memory 302. It is determined whether the adjustment level is equal to or lower than PXLV (the applied voltage is equal to or lower than the first threshold value). On the other hand, if the pixel indicated by the video signal Vid-ove of the current frame is a bright pixel, the previous frame state determination unit 314 determines the level of the pixel indicated by the video signal Vid-in of the previous frame output from the frame memory 302. It is determined whether or not the adjustment level is PXHV or higher (the applied voltage is higher than or equal to the second threshold value). When the determination result is “Yes”, the previous frame state determination unit 314 outputs an output signal vol_sig indicating that overdrive driving is performed. Also in this embodiment, the determination unit 3162 determines whether or not the OD correction condition is satisfied based on the output signal vol_sig.

  If the flag Q output from the determination unit 3162 is “1”, the replacement unit 3164 replaces the dark pixel or the bright pixel of the video signal Vid-ove with the gradation level output from the calculation unit 322, and replaces this with the video. Output as signal Vid-out. That is, the correction unit 316 corrects the video signal Vid-ove to the gradation level c1 output from the calculation unit 322 when the gradation level of the dark pixel when the flag Q is “1” is lower than c1. This is output as a video signal Vid-out. The correction unit 316 corrects the video signal Vid-ove of the bright pixel when the flag Q is “1” to the gradation level c2 output from the calculation unit 322, and outputs this as the video signal Vid-out. To do.

A specific example of processing by the video processing circuit 30 will be described.
For example, the image shown by the video signal Vid-in one frame before the current frame is as shown in FIG. 14A, and the image shown by the video signal Vid-in of the current frame is shown in FIG. ), When θb = 45 degrees, pixels that satisfy the boundary correction condition are represented as shown in FIG.

The correction unit 316 includes dark pixels that are overdrive driven according to control of the overdrive control unit 304 among dark pixels that are candidates for correction as indicated by “c1” in FIG. Of the bright pixels that are candidates for correction as shown by “c2” in FIG. 27A, the bright pixels that are overdriven in accordance with the control of the overdrive control unit 304. The video signal Vid-ove is not corrected.
Here, the correction processing of the correction unit 316 will be described with reference to FIG. FIG. 28 corresponds to FIG. 17 and illustrates an example of a pixel column in a part of a row in the (n−1) -frame video signal Vid-ove and the n-frame video signal Vid-ove. Pixels are arranged in the (horizontal direction). FIG. 28 (a) illustrates the case where the n-frame video signal Vid-ove is not corrected, and FIG. 28 (b) illustrates the case where the n-frame video signal Vid-ove is corrected. is there. As shown in FIG. 28, dark pixels and bright pixels Pix1 to Pix1 to P that are in contact with the risk boundary corresponding to the application boundary satisfy ix6 and the boundary correction condition. However, the bright pixels Pix1 and Pix5 and the dark pixel Pix4 indicated as “OD drive” in FIG. 28 are objects of overdrive drive and do not satisfy the OD correction condition.
Therefore, the correction unit 316 does not correct the video signal for reducing the horizontal electric field for the bright pixels Pix1 and Pix5 and the dark pixel Pix4 (illustrated by “x”), and applies the horizontal electric field to the other pixels. The video signal is corrected for reduction (indicated by “◯”).

Further, in the same way as in the first embodiment, when θb = 90 degrees, pixels satisfying the boundary correction condition in the image shown in FIG. 14B are as shown in FIG. When θb = 225 degrees, pixels satisfying the boundary correction condition in the image shown in FIG. 14 (2) are as shown in FIG. 27 (c).
According to this embodiment, an effect equivalent to that of both the first and third embodiments described above can be obtained, and a lateral electric field generated between adjacent bright pixels and dark pixels can be further suppressed across the risk boundary, and a reverse tilt can be achieved. Generation of domains can be further suppressed.

<Sixth Embodiment>
Next, a sixth embodiment of the present invention will be described.
In the fifth embodiment described above, the video processing circuit 30 corrects the gradation levels c1 and c2 only for the dark pixels and the bright pixels that satisfy the boundary correction conditions. Two or more predetermined numbers of dark pixels / bright pixels continuous to the opposite side of the risk boundary are also targets for correcting the video signal.
In the following description, the same components as those in the fifth embodiment are denoted by the same reference numerals, and the description thereof is omitted as appropriate. The video processing circuit 30 of this embodiment is different from the video processing circuit 30 of the fifth embodiment described above in that the calculation content of the calculation unit 322 and the determination content of the determination unit 3162 are changed.

In the correction unit 316, the determination unit 3162 includes (I) a pixel indicated by the video signal Vid-ove from the overdrive control unit 304 is a bright pixel or a dark pixel, and (II) an OR circuit 310 (motion detection unit 306). (III) indicates that the boundary information rsk_edge output from the risk boundary detection unit 312 is a risk boundary, and (IV) the image of the previous frame. When the output signal vol_sig indicates that the applied voltage specified by the signal does not perform overdrive driving, it is determined that the focused pixel satisfies the correction condition.
When both of these determination results are “Yes”, the determination unit 3162 outputs the flag Q of the output signal as “1”, and when any one of the determination results is “No”, “0” is output. "Is output. Further, when the determination unit 3162 determines “Yes”, the gradation level of the pixels indicated by the video signal Vid-ove, which are dark pixels / bright pixels continuous in the opposite direction of the risk boundary corresponding to the application boundary, is determined. A dark pixel / bright pixel that belongs to the gradation range a / b and whose distance from the risk boundary to the pixel is within (K + 1) pixels is treated as satisfying the boundary correction condition. Then, the determination unit 3162 outputs the value of the flag Q as “1” for a pixel that does not perform overdrive driving among dark pixels / bright pixels that satisfy the boundary correction condition (that is, pixels that satisfy the OD correction condition). To do. In this embodiment, K = 1.
When the flag Q is “1” and the video signal Vid-ove specifies a darker level than the gradation level c1 for the dark pixel, the replacement unit 3164 calculates the dark pixel from the calculation unit 322. This is replaced with the output gradation level c1, and this is output as the video signal Vid-out. Further, when the flag Q is “1”, the replacement unit 3164 replaces the gray level c2 output from the calculation unit 322 with respect to the bright pixel in the video signal Vid-ove, and replaces this with the video signal Vid−. Output as out.

A specific example of processing by the video processing circuit 30 will be described.
For example, the image shown by the video signal Vid-in one frame before the current frame is as shown in FIG. 14A, and the image shown by the video signal Vid-in of the current frame is shown in FIG. ), When θb = 45 degrees, pixels that satisfy the boundary correction condition are represented as shown in FIG.

  Then, the correction unit 316 outputs the video signal Vid for the pixels that are overdriven according to the control of the overdrive control unit 304 among the dark pixels and the bright pixels that are correction candidates illustrated in FIG. -ove is not corrected. The correction process of the correction unit 316 will be described with reference to FIG. FIG. 30 corresponds to FIG. 17, and illustrates an example of a pixel column for one row in the (n−1) -frame video signal Vid-ove and the n-frame video signal Vid-ove. Are arranged. FIG. 30A illustrates the case where the n-frame video signal Vid-ove is not corrected, and FIG. 30B illustrates the case where the n-frame video signal Vid-ove is corrected. Is. As shown in FIG. 30, among the dark pixels and bright pixels that are in contact with the risk boundary corresponding to the application boundary, those indicated as Pix1 to Pix12 satisfy the boundary correction condition. However, the bright pixels Pix2, Pix9, and Pix10 and the dark pixels Pix7, Pix8, and Pix12 shown as “OD drive” in FIG. 30 are objects of overdrive drive. Therefore, the correction unit 316 does not correct the video signal for reducing the horizontal electric field for the bright pixels Pix2, Pix9, Pix10 and the dark pixels Pix7, Pix8, Pix12 (illustrated by “x”), and other pixels. Is corrected for the video signal to reduce the transverse electric field (indicated by “◯”).

Further, based on the same concept as in the first embodiment, when θb = 90 degrees, pixels satisfying the boundary correction condition in the image shown in FIG. 14B are as shown in FIG. When θb = 225 degrees, the pixels that satisfy the boundary correction condition in the image shown in FIG. 14 (2) are as shown in FIG. 29 (c). Thus, since the pixel determined by the tilt azimuth of the liquid crystal element 120 is a correction target, the occurrence of the reverse tilt domain can be suppressed while suppressing the change from the original image.
According to the configuration of this embodiment, the same effect as that of the fifth embodiment is obtained, and for the same reason as in the second and fourth embodiments, the response time of the liquid crystal element is longer than the time interval at which the display screen is updated. Even in this case, it is possible to suppress the occurrence of reverse tilt domains.

<Seventh embodiment>
Next, a seventh embodiment of the present invention will be described.
In the following description, the same components as those in the sixth embodiment are denoted by the same reference numerals, and description thereof will be omitted as appropriate. The video processing circuit 30 of this embodiment is different from the video processing circuit 30 of the sixth embodiment described above in that the detection content of the motion detection unit 306 is changed.
In the sixth embodiment described above, video signals are corrected for a plurality of bright pixels and a plurality of dark pixels adjacent to each other across a risk boundary corresponding to an application boundary. On the other hand, in this embodiment, the motion detection unit 306 detects the boundary where the dark pixel and the bright pixel are adjacent in the current frame, and moves by one pixel from the boundary one frame before the detected boundary. Determined as the application boundary. As already described with reference to FIG. 36, when the liquid crystal panel 100 is driven at the same speed as the supply speed of the video signal Vid-in, the dark pixel region with the bright pixel in the background has two pixels for each frame. Such tailing phenomenon does not become apparent (or difficult to be visually recognized) when moving by the above. Therefore, the correction unit 316 sets the adjacent pixels on the risk boundary moved by one pixel as a correction target. For this purpose, the motion detection unit 306 applies the boundary moved by one pixel from the boundary of the image indicated by the video signal Vid-in of the previous frame among the boundaries of the image indicated by the video signal Vid-in of the current frame. And a boundary that has not moved from the previous frame and a boundary that has moved by two or more pixels are not detected as application boundaries. As a result, the correction unit 316 can correct the correction unit 316 by narrowing down to a place where the reverse tilt domain is more likely to occur. Thereby, it is possible to effectively suppress the occurrence of the reverse tilt domain while further suppressing the change of the video signal.
Note that the motion detection unit 306 may operate in the same manner as in the above-described sixth embodiment, and the correction unit 316 may specify adjacent pixels on the risk boundary that has moved by the amount of pixels.

The correction unit 316 includes a pixel that does not touch the application boundary, or a pixel that does not touch the application boundary among dark pixels and bright pixels that are correction candidates illustrated in FIG. The video signal Vid-ove is not corrected for pixels that are overdriven in accordance with the control of the unit 304. The correction process of the correction unit 316 will be described with reference to FIG. FIG. 31 corresponds to FIG. 17, and illustrates an example of a pixel column for one row in the (n−1) -frame video signal Vid-ove and the n-frame video signal Vid-ove. Are arranged. FIG. 31A illustrates the case where the n-frame video signal Vid-ove is not corrected, and FIG. 31B illustrates the case where the n-frame video signal Vid-ove is corrected. Is. As shown in FIG. 31, among dark pixels and bright pixels that are in contact with the risk boundary corresponding to the application boundary, Pix1 to Pix4 satisfy the boundary correction condition including contact with the risk boundary moved by one pixel. . Further, the bright pixel Pix2 indicated as “OD drive” in FIG. 31 is an object of overdrive drive and does not satisfy the OD correction condition. Accordingly, the correction unit 316 corrects the video signals of the other bright pixels Pix1 and dark pixels Pix3 and Pix4 without correcting the video signal for reducing the horizontal electric field for the bright pixel Pix2 (illustrated by “x”). To do.
The configuration of this embodiment also has the same effect as that of the sixth embodiment described above. The configuration in which only the boundary moved by one pixel is used as the application boundary is also applicable to the configurations of the first to fifth embodiments described above.

<Modification>
(Modification 1) TN Method In the embodiment described above, an example in which the VA method is used for the liquid crystal 105 has been described. Next, an example in which the liquid crystal 105 is a TN mode will be described.
FIG. 32A is a diagram showing 2 × 2 pixels in the liquid crystal panel 100, and FIG. 32B is a simplified cross-section when fractured along a vertical plane including the pq line in FIG. FIG.
As shown in these figures, the TN liquid crystal molecule has a tilt angle of θa and a tilt azimuth angle of θb (= 45 degrees) in a state where the potential difference between the pixel electrode 118 and the common electrode 108 is zero. It is assumed that the initial alignment is performed. In contrast to the VA system, the TN system tilts in the horizontal direction of the substrate, so the tilt angle θa of the TN system is larger than the value of the VA system.

In an example in which the TN mode is used for the liquid crystal 105, a normally white mode in which the liquid crystal element 120 is in a white state when no voltage is applied is often used because of a high contrast ratio or the like.
Therefore, when the TN mode is used for the liquid crystal 105 and the normally white mode is set, the relationship between the applied voltage and the transmittance of the liquid crystal element 120 is expressed by a VT characteristic as shown in FIG. As the applied voltage increases, the transmittance decreases. However, it is not different from the normally black mode in that the liquid crystal molecules are in an unstable state when the applied voltage of the liquid crystal element 120 is lower than the voltage Vc1.

In such a TN type normally white mode, as shown in FIG. 33A, in the (n−1) frame, all of the 2 × 2 four pixels are in a state where the liquid crystal molecules are unstable white pixels. Assume that in the frame, only the upper right pixel changes to a black pixel. As described above, in the normally white mode, the potential difference between the pixel electrode 118 and the common electrode 108 is larger in the black pixel than in the white pixel, contrary to the normally black mode. For this reason, in the upper right pixel that changes from white to black, as shown in FIG. 33B, the liquid crystal molecules change from the state indicated by the solid line to the state indicated by the broken line (in the direction perpendicular to the substrate surface). Try to stand in the direction).
However, the potential difference generated in the gap between the pixel electrode 118 (Wt) of the white pixel and the pixel electrode 118 (Bk) of the black pixel is the same as the potential difference generated between the pixel electrode 118 (Bk) of the black pixel and the common electrode 108. In addition, the gap between the pixel electrodes is narrower than the gap between the pixel electrode 118 and the common electrode 108. Therefore, when compared with the strength of the electric field, the horizontal electric field generated in the gap between the pixel electrode 118 (Wt) and the pixel electrode 118 (Bk) is larger than the vertical electric field generated in the gap between the pixel electrode 118 (Bk) and the common electrode 108. strong.
Since the upper right pixel is a white pixel in which the liquid crystal molecules are unstable in the (n-1) frame, it takes time for the liquid crystal molecules to tilt according to the strength of the vertical electric field. On the other hand, the horizontal electric field from the adjacent pixel electrode 118 (Wt) is stronger than the vertical electric field due to the black level voltage applied to the pixel electrode 118 (Bk). As shown in FIG. 31 (b), the liquid crystal molecules Rv on the side adjacent to the white pixel are in a reverse tilt state earlier in time than other liquid crystal molecules that are to be tilted according to the vertical electric field.
The liquid crystal molecules Rv that have been in the reverse tilt state adversely affect the movement of other liquid crystal molecules that attempt to stand in the horizontal direction of the substrate as indicated by the broken line in accordance with the vertical electric field. For this reason, as shown in FIG. 33C, the region where the reverse tilt occurs in the pixel that should change to black is not limited to the gap between the pixel that should change to black and the white pixel, but changes from the gap to black. It spreads over a wide range in the form of eroding the pixels to be.
Therefore, from the contents shown in FIG. 33, when the periphery of the target pixel to be changed to black is a white pixel, when the white pixel is adjacent to the target pixel on the lower left side, the left side, and the lower side, In the pixel of interest, reverse tilt occurs in the inner peripheral area along the left side and the lower side.

On the other hand, as shown in FIG. 34 (a), in the (n−1) frame, all 2 × 2 four pixels are in an unstable white pixel state of liquid crystal molecules, and in the n frame, only the lower left one pixel is black. Assume that the pixel changes. Even in this change, the horizontal electric field stronger than the vertical electric field in the gap between the pixel electrode 118 (Bk) and the common electrode 108 in the gap between the pixel electrode 118 (Bk) of the black pixel and the pixel electrode 118 (Wt) of the white pixel. Will occur. Due to this lateral electric field, as shown in FIG. 34 (b), the liquid crystal molecules Rv on the side adjacent to the black pixels in the white pixel are aligned ahead of the other liquid crystal molecules to be inclined according to the vertical electric field. Changes to a reverse tilt state, but in the white pixel, the strength of the vertical electric field does not change from the (n−1) frame, and thus hardly affects other liquid crystal molecules. For this reason, as shown in FIG. 34C, the region where the reverse tilt occurs in the pixel that does not change from the white pixel is narrow enough to be ignored as compared with the example of FIG.
On the other hand, among the 2 × 2 pixels, in the pixel that changes from white to black in the lower left, the initial alignment direction of the liquid crystal molecules is a direction that is not easily affected by the horizontal electric field. There are almost no liquid crystal molecules in a state. For this reason, in the lower left pixel, as the vertical electric field strength increases, the liquid crystal molecules rise correctly in the direction perpendicular to the substrate surface as indicated by the broken line in FIG. As a result, display quality will not deteriorate.

For this reason, in the normally white mode in which the tilt azimuth angle θb is 45 degrees in the TN method, the requirement (1) is left as it is.
(2) In the n frame, when the dark pixel (applied voltage high) is located on the upper right side, the right side or the upper side with respect to the adjacent bright pixel (applied voltage low),
(3) A pixel that changes to the dark pixel in the n frame has a reverse tilt in the dark pixel in the n frame when the liquid crystal molecules are in an unstable state in the (n-1) frame one frame before. ,It turns out that.
Therefore, when this occurrence state is reconsidered with reference to the (n + 1) frame, even if the dark pixel satisfies the positional relationship in the (n + 1) frame due to the motion of the image, in the n frame before the change, This means that measures should be taken so that the liquid crystal molecules of the pixel do not become unstable.
In the normally white mode, in contrast to the normally black mode, considering that the applied voltage of the liquid crystal element is lower as the gradation level is higher (brighter), the configuration of the video processing circuit 30 is as follows. Change to.
That is, in n frames, the risk boundary detection unit 312 in the video processing circuit 30 has a dark pixel located on the lower side and a bright pixel located on the upper side, a dark pixel located on the left side, and a bright pixel located on the right side. Any part may be extracted and detected as a risk boundary. The pixels for which the correction unit 316 corrects the video signal based on the risk boundary are as described in the first to seventh embodiments.
In this example, an example in which the tilt azimuth angle θb is 45 degrees in the TN method has been described. However, considering that the reverse tilt domain generation direction is opposite to that in the VA method, the tilt azimuth angle θb is 45 degrees. Measures in the case of angles other than the above, and the configuration for that, should be easily analogized from the above explanation.

Assuming that only the horizontal direction is assumed as the moving direction of the image pattern in this way, the configuration can be simplified as compared with the configuration assumed for the vertical direction and the oblique direction.
Here, the case where the VA system is used and the tilt azimuth angle θb is 45 degrees has been described as an example, but the same applies to the case where the VA system is used and the tilt azimuth angle θb is 225 degrees.

(Modification 2) Discrimination of Pixels to be Driven by Overdrive In the above-described embodiment, the video processing circuit 30 performs an overshoot when the gradation level of the video signal Vid-in of the previous frame is equal to or lower than PXLV for dark pixels. It is determined that drive driving is not performed, and it is determined that overdrive driving is not performed when the gradation level of the video signal Vid-in of the previous frame is equal to or higher than PXHV for a bright pixel. Instead, the pixel that is the target of overdrive driving may be determined as follows.
Based on the applied voltage (in other words, the gradation level specified by the video signal) specified by the video signal Vid-ove of the previous frame output from the overdrive control unit 304, the correction unit 316 performs overdrive. Bright pixels and dark pixels to be driven may be determined. Also in this case, as in the above-described embodiment, the correction unit 316 performs overdrive driving when the applied voltage of the liquid crystal element specified by the video signal Vid-ove of the previous frame is equal to or lower than the first threshold for dark pixels. A pixel that is the target of overdrive driving when the applied voltage of the liquid crystal element specified by the video signal Vid-ove of the previous frame is equal to or higher than the second threshold value. Good. The gradation level of the video signal corresponding to the applied voltage of the first and second thresholds may be different from the gradation levels PXLX and PXHV described above. Further, the correction unit 316 may determine the presence / absence of overdrive using the video signal of a frame before the previous frame.
In the present invention, it is only necessary to perform correction for suppressing the lateral electric field by excluding the pixel to be overdriven, and the method for determining the pixel is not limited to the method described above.

(Modification 3) Video signal used for boundary detection In the above-described embodiment, the motion detection unit 306 and the risk boundary detection unit 312 set a predetermined boundary based on the video signal Vid-ove output by the overdrive control unit 304. Although detected, it may be detected using the video signal Vid-in input to the video processing circuit 30 instead of after the overdrive control. In this case, in the video processing circuit 30, the video signal Vid-ove is not used for detection of the application boundary or the risk boundary.

(Modification 4) Other Modifications In the above-described embodiment, the video processing circuit 30 includes the delay circuit 308 and the OR circuit 310. This is not only the current frame (n frame) but also the subsequent frames ( The correction is made to prevent the lateral electric field from being reduced at the same location over (n + 1 frame and thereafter). On the other hand, in the present invention, configurations corresponding to these are not essential and may be omitted.
In each of the embodiments described above, the video signal Vid-in designates the gradation level of the pixel, but it may also designate the voltage applied to the liquid crystal element directly. When the video signal Vid-in specifies the applied voltage of the liquid crystal element, the boundary may be determined based on the specified applied voltage, and the voltage may be corrected.
In each of the second, fourth, sixth, and seventh embodiments described above, the gradation levels of the bright pixels and dark pixels that are correction targets may not be the same. In the sixth and seventh embodiments, the number of bright pixels to be corrected and the number of dark pixels (value of K) may be different.
In each embodiment, the liquid crystal element 120 is not limited to a transmissive type, and may be a reflective type.

(Modification 5) Electronic Device Next, a projection display device (projector) using the liquid crystal panel 100 as a light valve will be described as an example of an electronic device using the liquid crystal display device according to the above-described embodiment. FIG. 35 is a plan view showing the configuration of the projector.
As shown in this figure, a projector 2100 is provided with a lamp unit 2102 made of a white light source such as a halogen lamp. The projection light emitted from the lamp unit 2102 is provided with three primary colors of R (red), G (green), and B (blue) by three mirrors 2106 and two dichroic mirrors 2108 disposed therein. And led to the light valves 100R, 100G and 100B corresponding to the respective primary colors. Note that B light has a longer optical path than other R and G colors, and therefore, in order to prevent the loss, B light passes through a relay lens system 2121 including an incident lens 2122, a relay lens 2123, and an exit lens 2124. Led.

In the projector 2100, three sets of liquid crystal display devices including the liquid crystal panel 100 are provided corresponding to each of R color, G color, and B color. The configuration of the light valves 100R, 100G, and 100B is the same as that of the liquid crystal panel 100 described above. In order to specify the gradation levels of the primary color components of R color, G color, and B color, video signals are supplied from the external higher-level circuit, and the light valves 100R, 100G, and 100 are driven. .
The lights modulated by the light valves 100R, 100G, and 100B are incident on the dichroic prism 2112 from three directions. In the dichroic prism 2112, the R and B light beams are refracted at 90 degrees, while the G light beam travels straight. Therefore, after the images of the respective primary colors are combined, a color image is projected onto the screen 2120 by the projection lens 2114.

  Since light corresponding to each of R color, G color, and B color is incident on the light valves 100R, 100G, and 100B by the dichroic mirror 2108, it is not necessary to provide a color filter. In addition, the transmission images of the light valves 100R and 100B are projected after being reflected by the dichroic prism 2112, whereas the transmission image of the light valve 100G is projected as it is, so the horizontal scanning direction by the light valves 100R and 100B is The image is reversed in the horizontal scanning direction by the light valve 100G and displayed in an inverted image.

  In addition to the projector described with reference to FIG. 35, the electronic devices include a television, a viewfinder type / monitor direct view type video tape recorder, a car navigation device, a pager, an electronic notebook, a calculator, a word processor, a workstation. Video phones, POS terminals, digital still cameras, mobile phones, devices equipped with touch panels, and the like. Needless to say, the liquid crystal display device can be applied to these various electronic devices.

DESCRIPTION OF SYMBOLS 1 ... Liquid crystal display device, 30 ... Video processing circuit, 100 ... Liquid crystal panel, 100a ... Element substrate, 100b ... Opposite substrate, 105 ... Liquid crystal, 108 ... Common electrode, 118 ... Pixel electrode, 120 ... Liquid crystal element, 302 ... Frame memory , 304 ... Overdrive control unit, 3062 ... Current frame detection unit, 3064 ... Previous frame detection unit, 3066 ... Storage unit, 3068 ... Application boundary determination unit, 308 ... Delay circuit, 310 ... OR circuit, 312 ... Risk boundary detection unit 314: Previous frame state determination unit, 316 ... Correction unit, 3162 ... Determination unit, 3164 ... Replacement unit, 318 ... D / A converter, 320 ... Delay circuit, 322 ... Calculation unit, 2100 ... Projector

Claims (11)

An image processing method for inputting an image signal designating an applied voltage of a liquid crystal element for each pixel and defining an applied voltage of the liquid crystal element based on a corrected image signal,
The input video signal is analyzed for each of the current frame and the frame immediately before the current frame, and a video signal of the current frame for performing overdrive driving according to the change of the applied voltage of each pixel is generated. Output overdrive control step,
Of the boundary between the first pixel in which the applied voltage is lower than the first voltage and the second pixel in which the applied voltage is greater than or equal to the second voltage in the input video signal, the previous one A first boundary detection step of detecting a boundary that changes from the current frame to the current frame;
A second boundary detecting step for detecting a risk boundary which is a part of a boundary between the first pixel and the second pixel specified by the input current frame video signal and is determined by a tilt direction of the liquid crystal;
In the video signal of the current frame output in the overdrive control step, the first and second touching the risk boundary detected in the second boundary detection step among the boundaries detected in the first boundary detection step. A video signal designating an applied voltage to a liquid crystal element corresponding to at least one of the pixels is excluded from a pixel to be corrected, and a horizontal electric field generated in the first and second pixels is excluded. A video processing method comprising: a correction step of correcting so as to reduce. In the correction step,
For the first pixel in which the applied voltage specified by the video signal of the previous frame is equal to or less than a predetermined first threshold, the applied voltage to the liquid crystal element corresponding to the first pixel is the first voltage. 2. The video processing method according to claim 1, wherein when the voltage is lower than a lower third voltage, the applied voltage of the first pixel is corrected to be equal to or higher than the third voltage. In the correction step,
To the liquid crystal element corresponding to the first pixel, the applied voltage specified by the video signal of the previous frame output in the overdrive step is equal to or less than a predetermined first threshold value. 2. The video processing according to claim 1, wherein when the applied voltage is lower than a third voltage lower than the first voltage, the applied voltage of the first pixel is corrected to be equal to or higher than the third voltage. Method. In the correction step,
Among the boundaries detected in the first boundary detection step, two or more predetermined values that are continuous from the first pixel in contact with the risk boundary detected in the second boundary detection step to the opposite side of the risk boundary. The number of the first pixels is corrected so as to be equal to or higher than the third voltage when an applied voltage to a liquid crystal element corresponding to a pixel not subjected to the overdrive driving is lower than the third voltage. The video processing method according to claim 2 or 3. In the correction step,
For the second pixel in which the applied voltage specified by the video signal of the previous frame is equal to or greater than a predetermined second threshold, the applied voltage to the liquid crystal element corresponding to the second pixel is the first voltage. The video processing method according to claim 1, wherein the correction is performed so that the fourth voltage is higher than the voltage and lower than the second voltage. In the correction step,
For the second pixel in which the applied voltage specified by the video signal of the previous frame output in the overdrive step is greater than or equal to a predetermined second threshold value, to the liquid crystal element corresponding to the second pixel The video processing method according to claim 1, wherein the applied voltage is corrected to be a fourth voltage that is higher than the first voltage and lower than the second voltage. In the correction step,
Among the boundaries detected in the first boundary detection step, two or more predetermined values that are continuous from the second pixel in contact with the risk boundary detected in the second boundary detection step to the opposite side of the risk boundary. Correcting a voltage applied to a liquid crystal element corresponding to a pixel not subjected to the overdrive drive to a fourth voltage that is higher than the first voltage and lower than the second voltage. The video processing method according to claim 1, wherein the video processing method is a video processing method. In the correction step,
Among the boundaries detected in the first boundary detection step, pixels that are in contact with the risk boundary moved by one pixel from the previous frame to the current frame are set as correction targets for reducing the lateral electric field. The video processing method according to claim 1, wherein: A video processing circuit that inputs a video signal designating an applied voltage of a liquid crystal element for each pixel and defines an applied voltage of the liquid crystal element based on the corrected video signal,
The input video signal is analyzed for each of the current frame and the frame immediately before the current frame, and a video signal of the current frame for performing overdrive driving according to the change of the applied voltage of each pixel is generated. An overdrive control unit that outputs
Of the boundary between the first pixel in which the applied voltage is lower than the first voltage and the second pixel in which the applied voltage is greater than or equal to the second voltage in the input video signal, the previous one A first boundary detector that detects a boundary that changes from the current frame to the current frame;
A second boundary detection unit that detects a risk boundary that is a part of a boundary between the first pixel and the second pixel specified by the input video signal of the current frame and is determined by a tilt direction of the liquid crystal;
In the video signal of the current frame output by the overdrive control unit, the first and second touching risk boundaries detected in the second boundary detection step among the boundaries detected by the first boundary detection unit. A video signal designating an applied voltage to a liquid crystal element corresponding to at least one of the pixels is excluded from a correction target for a pixel in which the overdrive driving is performed, and a horizontal electric field generated in the first and second pixels is determined. A video processing circuit comprising: a correction unit that performs correction so as to reduce. A liquid crystal panel having a liquid crystal element in which a liquid crystal is sandwiched between a pixel electrode provided corresponding to each of the plurality of pixels on the first substrate and a common electrode provided on the second substrate;
A video signal that specifies the voltage applied to the liquid crystal element for each pixel, and a video processing circuit that defines the voltage applied to the liquid crystal element based on the corrected video signal,
The video processing circuit includes:
The input video signal is analyzed for each of the current frame and the frame immediately before the current frame, and a video signal of the current frame for performing overdrive driving according to the change of the applied voltage of each pixel is generated. An overdrive control unit that outputs
Of the boundary between the first pixel in which the applied voltage is lower than the first voltage and the second pixel in which the applied voltage is greater than or equal to the second voltage in the input video signal, the previous one A first boundary detector that detects a boundary that changes from the current frame to the current frame;
A second boundary detection unit that detects a risk boundary that is a part of a boundary between the first pixel and the second pixel specified by the input video signal of the current frame and is determined by a tilt direction of the liquid crystal;
In the video signal of the current frame output by the overdrive control unit, the first and second touching risk boundaries detected in the second boundary detection step among the boundaries detected by the first boundary detection unit. A video signal designating an applied voltage to a liquid crystal element corresponding to at least one of the pixels is excluded from a correction target for a pixel in which the overdrive driving is performed, and a horizontal electric field generated in the first and second pixels is determined. A liquid crystal display device comprising: a correction unit that performs correction so as to reduce.   An electronic apparatus comprising the liquid crystal display device according to claim 10.

Images