JP2014219686A - Video processing circuit, processing method of the same, liquid crystal display device, and electronic apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress reduction in display quality affected by a lateral electric field.SOLUTION: A liquid crystal panel 100 comprises a liquid crystal element in which a liquid crystal 105 is held between a pixel electrode 118 provided at an element substrate 100a and a common electrode 108 provided at a counter substrate 100b. A video processing circuit 30 detects a boundary between a dark pixel in which, in a normally black mode, voltage to be applied to the liquid crystal element corresponding to a gradation level designated by a video signal Vid-in is less than a threshold Vth1 and a bright pixel in which the voltage is a threshold Vth2 or more. If voltage to be applied to the dark pixel in contact with the detected boundary is less than voltage Vc, the video processing circuit changes the voltage to be applied to the dark pixel from voltage to be applied corresponding to the gradation level designated by the video signal to the voltage Vc.

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 above configuration, only the component of the electric field acting on the liquid crystal molecules in the direction from the pixel electrode to the common electrode (or the opposite direction), that is, the vertical direction (vertical direction) with respect to the substrate surface is displayed control. It can be said that it contributes to.

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 the VA (Vertical Alignment) method or the TN (Twisted Nematic) method, liquid crystal alignment failure (reverse tilt domain) occurs. However, there has been a problem that a display defect occurs.
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 equal to or higher than a set value has a drawback that the brightness of the displayed image is limited to the set value.
The present invention has been made in view of the above-described circumstances, and one of its purposes is to provide a technique for reducing the reverse tilt domain while eliminating these drawbacks.

  In order to achieve the above object, in the video processing circuit according to the present invention, a video signal designating an application voltage of the liquid crystal element is input for each pixel, and the application of the liquid crystal element is performed based on the processed video signal. A video processing circuit for defining each voltage, wherein the applied voltage specified by the input video signal is lower than the first voltage, and the applied voltage is greater than or equal to the second voltage greater than the first voltage. When the applied voltage specified by the input video signal is lower than the third voltage lower than the first voltage with respect to the boundary detection unit for detecting the boundary with the second pixel and the first pixel in contact with the boundary, And a correction unit that corrects an applied voltage to the liquid crystal element corresponding to the first pixel from the applied voltage specified by the input video signal to the third voltage. According to the present invention, since it is not necessary to change the structure of the liquid crystal panel 100, the aperture ratio is not reduced. Further, the present invention can be applied to a liquid crystal panel already manufactured without devising the structure. Further, when the applied voltage specified by the input video signal is lower than the third voltage for the first pixel in contact with the detected boundary, the applied voltage to the liquid crystal element corresponding to the first pixel is changed to the third voltage. Since correction is performed, the influence of the correction is not exerted on other pixels. For this reason, the brightness of the displayed image is not limited to the set value.

In the present invention, when the applied voltage of the first pixel in contact with the detected boundary is equal to or higher than the third voltage, the correction unit converts the applied voltage to the liquid crystal element corresponding to the first pixel to the video signal. It is preferable to set the applied voltage specified by. As a result, it is possible to make it difficult to perceive a change in brightness due to correction for a pixel in which a reverse tilt domain is likely to occur.
In the present invention, it is preferable that the boundary detection unit detects the boundary when the first pixel and the second pixel are adjacent in the horizontal direction. Although the reverse tilt domain can be surely reduced in the configuration in which the detection is performed with the boundary in the vertical or horizontal direction as a boundary, the circuit scale tends to be complicated. For this reason, in consideration of the supply order of the video signals, it is easier to suppress the complexity of the circuit size in the configuration in which the detection is performed with the boundary in the horizontal direction as a boundary. In particular, the boundary detection unit is preferably configured to detect the boundary by comparing an input video signal with a signal obtained by delaying the input video signal by one pixel.
In the present invention, when the applied voltage is lower than the third voltage for one or more pixels located on the opposite side of the boundary with respect to the first pixel in contact with the boundary, the correction unit applies the pixel to the pixel. It is preferable that the applied voltage to the corresponding liquid crystal element is corrected from the applied voltage specified by the input video signal to the third voltage. Since the application period of the third voltage corrected to the third voltage becomes longer, the occurrence of the reverse tilt domain can be more reliably reduced. The third voltage is preferably 1.5 volts or less. This is because a change in brightness due to correction is hardly perceived and is less susceptible to the influence of a lateral electric field.
In addition to the video processing circuit, the present invention can be conceptualized as a video processing method, a liquid crystal display device, and an electronic device including the liquid crystal display device.

It is a figure which shows the liquid crystal display device to which the video processing circuit which concerns on 1st Embodiment is applied. It is a figure which shows the equivalent circuit of the liquid crystal element in the liquid crystal display device. It is a figure which shows the structure of the video processing circuit. It is a figure which shows the display characteristic in the liquid crystal display device. It is a figure which shows the display operation in the liquid crystal display device. It is a figure which shows the correction process in the video processing circuit. It is a figure which shows another correction process in the video processing circuit. It is a figure which shows the structure of the video processing circuit which concerns on 2nd Embodiment. It is a figure which shows the content of the correction process in the video processing circuit. It is a figure which shows the correction | amendment operation | movement in the video processing circuit. It is a figure which shows the correction | amendment operation | movement in the video processing circuit. It is a figure which shows the correction | amendment operation | movement in the video processing circuit. It is a figure which shows the correction | amendment operation | movement in the video processing circuit. It is a figure which shows the projector to which a liquid crystal display device is applied. It is a figure which shows the malfunction on a display etc. by the influence of a horizontal electric field.

<First Embodiment>
Embodiments of the present invention will be described below with reference to the drawings.
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 this figure, 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.
Among these, 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 includes a vertical scanning signal, a horizontal scanning signal, and a dot clock signal (all shown in FIG. 1) included in the synchronization signal Sync. Supplied in the order of scanning according to (omitted).
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. Among these, the scanning control circuit 20 generates various control signals and controls each unit in synchronization with the synchronization signal Sync. Although the details will be described 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 the 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 the present 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. Since it becomes difficult, each is shown by a solid line.

An equivalent circuit of the liquid crystal panel 100 is as shown in FIG. It becomes the composition which did.
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. 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. For this reason, 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 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 the present 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 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. 5A, the scanning line driving circuit 130 selects the scanning line 112 in the order of the first, second, third,. The scanning signal to the line is set to the selection voltage V _H (H level), and the scanning signal to the other scanning lines is set to 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.

In the present embodiment, the relationship between the applied voltage and the transmittance of the liquid crystal element 120 is represented by a VT characteristic as shown in FIG. 4A 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. is there.
However, if the voltage applied to the liquid crystal element 120 is simply defined in accordance with the gradation level specified by the video signal Vid-in, a display defect due to the reverse tilt domain may occur.

This defect is caused when the liquid crystal molecules sandwiched in the liquid crystal element 120 are in an unstable state and are disturbed by the influence of the transverse electric field, so that the alignment state according to the applied voltage is less likely to occur thereafter. It is considered as one.
When the voltage applied to the liquid crystal element 120 is equal to or higher than the black level voltage Vbk in the normally black mode and is in the voltage range A lower than the threshold value Vth1 (first voltage), the regulating force by the vertical electric field is regulated by the alignment film. Therefore, the alignment state of the liquid crystal molecules tends to be disturbed. This is when the liquid crystal molecules are in an unstable state.
For convenience, the transmittance range (gradation range) of the liquid crystal element in which the voltage applied to the liquid crystal element is in the voltage range A is “a”.

On the other hand, 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 a dark pixel close to a black level or a black level in an image to be displayed and a white level or This is a case where a bright pixel close to the white level is adjacent.
Among such dark pixels and bright pixels, the dark pixel is the liquid crystal element 120 in which the applied voltage is in the voltage range A in the normally black mode as shown in FIG. A bright pixel applies a lateral electric field to the dark pixel. In order to specify this bright pixel, the bright pixel is the liquid crystal element 120 in the voltage range B in which the applied voltage is not less than the threshold value Vth2 (second voltage) and not more 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”.
In the normally black mode, the threshold value Vth1 is an optical threshold voltage that makes the relative transmittance of the liquid crystal element 10%, and the threshold value Vth2 is an optical saturation voltage that makes the relative transmittance of the liquid crystal element 90%. You can think about it.

It can be said that when the applied voltage is in the voltage range A, the liquid crystal element is likely to generate a reverse tilt domain due to a lateral electric field when adjacent to the liquid crystal element in the voltage range B. However, it cannot be said that the reverse tilt domain is surely generated.
Conversely, the liquid crystal element in the voltage range B is in a stable state because the influence of the vertical electric field is dominant even if it is adjacent to the liquid crystal element in the voltage range A. Thus, the reverse tilt domain does not occur.

An example of a display defect caused by the reverse tilt domain will be described. As shown in FIG. 15A, for example, an image indicated by the video signal Vid-in has a black pixel area as a frame with a white pixel as a background. When the pixel moves one pixel at a time, for example, in the left direction, a pixel that should change from a black pixel to a white pixel is manifested as a kind of tailing phenomenon in which a reverse tilt domain does not become a white pixel. In the figure, for convenience of explanation, the vicinity of the boundary of one line is extracted from the frame image.
One of the causes of this phenomenon is that when a white pixel and a black pixel are adjacent to each other, the lateral electric field between these pixels becomes strong, and a reverse tilt domain easily occurs in the black pixel. This is considered to be because the region in this state becomes continuous as the black pixel moves.
Note that when the black pixel region moves by two or more pixels for each frame with the white pixel as the background, this tailing phenomenon does not become apparent or is hardly visible. The reason is considered as follows. When a white pixel and a black pixel are adjacent to each other in a certain frame, a reverse tilt domain is likely to occur in the black pixel. However, in this state, the black pixel moves by two or more pixels. This is considered to be continuous.

In order to suppress the occurrence of display defects caused by the reverse tilt domain, first, even when dark pixels and bright pixels are adjacent to each other in the image indicated by the video signal Vid-in, In the liquid crystal panel 100, it is important that dark pixels and bright pixels are not adjacent to each other.
In order to prevent the dark pixel and the bright pixel from being adjacent to each other in the liquid crystal panel 100, the voltage applied to the liquid crystal element corresponding to the dark pixel in the normally black mode may be increased. This is because the video signal Vid-in This means that the black level of the dark pixel adjacent to the bright pixel is brightened while ignoring the gradation level defined by. Therefore, secondly, it is important to correct the applied voltage of the liquid crystal element corresponding to the dark pixel adjacent to the bright pixel so that the change in the black level is not perceived as much as possible.
On the other hand, even if the liquid crystal element (dark pixel) whose applied voltage is in the voltage range A is adjacent to the liquid crystal element (bright pixel) in the voltage range B, it cannot be said that the reverse tilt domain is surely generated.

Therefore, in the present embodiment, in order to suppress the occurrence of display defects caused by the reverse tilt domain, first, when the dark pixel and the bright pixel are adjacent to each other in the image indicated by the video signal Vid-in, the reverse is performed. The dark pixel is listed as a correction candidate as a situation in which a tilt domain is likely to occur. Next, when the applied voltage of the liquid crystal element is lower than Vc in the dark pixel listed as the correction candidate. The configuration in which the voltage Vc is forcibly applied to the liquid crystal element in the dark pixel, more specifically, the gradation level of the dark pixel is corrected (replaced) to the gradation level c corresponding to the applied voltage Vc as described later. The configuration.
Here, the liquid crystal molecules in the VA mode are perpendicular to the substrate surface when the voltage applied to the liquid crystal element is zero, but the voltage Vc is lower than the threshold value Vth1 and gives an initial tilt angle to the liquid crystal molecules. The voltage is such that almost no change in transmittance is perceived with respect to a voltage change near the voltage Vc.
The voltage Vc is in the range of 0 to 1.5 volts from the viewpoint of hardly perceiving a change in transmittance in the vicinity of the black level of the normally black mode, but from the viewpoint of a voltage at which liquid crystal molecules start to tilt. In other words, it is 1.5 volts. Therefore, the voltage Vc is preferably 1.5 volts or less.

  In the present embodiment, a case where a dark pixel and a bright pixel are adjacent to each other in the image indicated by the video signal Vid-in is detected, and the applied voltage of the liquid crystal element in the dark pixel is at a gradation level at which the voltage falls below Vc. The video processing circuit 30 in FIG. 1 is a configuration that corrects the gradation level of the dark pixel to the gradation level c at some time.

Next, details of the video processing circuit 30 will be described with reference to FIG.
As shown in this figure, the video processing circuit 30 includes a boundary detection unit 302, a delay circuit 312, a correction unit 314, and a D / A converter 316.
Among these, the delay circuit 312 accumulates the video signal Vid-in supplied from the host device, reads out the video signal Vid-d after a predetermined time, and outputs it as a video signal Vid-d. FIFO (FastIn Fast Out) Consists of a memory and multi-stage latch circuit. The accumulation and reading in the delay circuit 312 are controlled by the scanning control circuit 20.

The boundary detection unit 302 includes a detection unit 304 and a determination unit 306 in the present embodiment. Among these, the detection unit 304 first analyzes the frame image indicated by the video signal Vid-in, and the pixels in the gradation range a and the pixels in the gradation range b are adjacent in the vertical or horizontal direction. It is determined whether or not there is a part to be processed. Secondly, when it is determined that there is an adjacent part, a boundary (edge) that is the adjacent part is detected.
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 to each other. Therefore, for example, a portion where a pixel in the gradation range a and a pixel in another gradation range d that is neither the gradation range a nor the gradation range b are adjacent, or a pixel in the gradation range b A portion adjacent to a pixel in the adjustment range d is not treated as a boundary.

The determination unit 306 determines whether or not the pixel indicated by the video signal Vid-d output with delay is a dark pixel in contact with the boundary detected by the detection unit 304, and the determination result is “ If “Yes”, the flag Q of the output signal is set to “1”, for example, and “0” if the determination result is “No”.
Note that the detection unit 304 cannot detect the boundary in the vertical or horizontal direction in the image to be displayed unless a certain amount of video signals are accumulated. Therefore, a delay circuit 312 is provided in order to adjust the supply timing of the video signal Vid-in from the host device.
Since the timing of the video signal Vid-in supplied from the host device and the timing of the video signal Vid-d supplied from the delay circuit 312 are different, strictly speaking, the horizontal scanning periods of the two do not match. However, the following description will be made with no particular distinction.
Further, the scanning control circuit 20 controls the accumulation of the video signal Vid-in for detecting the supply in the detection unit 304.

When the flag Q supplied from the determination unit 306 is “1”, the correction unit 314 specifies the gray level if the gray level specified by the video signal Vid-d is darker than c. It is replaced with a video signal of level c and output as a video signal Vid-out.
Even if the flag Q supplied from the determination unit 306 is “1”, the correction unit 314 specifies a bright level in which the gradation level specified by the video signal Vid-d is c or higher. And when the flag Q is “0”, the gradation level specified by the video signal Vid-d is output as the video signal Vid-out without correction.

The D / A converter 316 converts the video signal Vid-out, which is digital data, into an analog data signal Vx.
In order to prevent the direct current component from being applied to the liquid crystal 105, the voltage of the data signal Vx is, for example, frame-by-frame with a positive voltage on the higher side and a negative voltage on the lower side with respect to the voltage Vcnt that is the video amplitude center. Can be switched alternately.
Note that the voltage LCcom applied to the common electrode 108 may be considered to be substantially the same voltage as the voltage Vcnt, but is adjusted to be lower than the voltage Vcnt in consideration of off-leakage of the n-channel TFT 116 and the like. Sometimes.

According to the video processing circuit 30, when the pixel indicated by the video signal Vid-d is a dark pixel in contact with the boundary and the gradation level specifies a level darker than c, this video processing circuit 30 In the embodiment, since the flag Q is “1”, the gradation level of the pixel indicated by the video signal Vid-d is replaced with c and output as the video signal Vid-out.
On the other hand, when the pixel indicated by the video signal Vid-d is not a dark pixel that is in contact with the boundary, or even when it is in contact with the pixel, the gradation level specifies a bright level of c or higher. In this embodiment, since the flag Q is “0”, the video signal Vid-d is output as the video signal Vid-out without correcting the gradation level.

The display operation of the liquid crystal display device 1 will be described. From the host device, the video signal Vid-in is transmitted from the first row and the first column to the first row and the n column, the second row and the first column, the second row and the first column, the third row and the first column, from the first row. Supplied in the order of pixels of 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 replacement on the video signal Vid-in and outputs it as the video signal Vid-out.
Here, when viewed in the horizontal effective scanning period (Ha) in which the video signal Vid-out of the 1st row and 1st column to the 1st row and the nth column is output, the processed video signal is processed by the D / A converter 316. 5B, the data signal Vx is converted into a positive or negative data signal Vx, for example, positive polarity here. 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, and the D / A converter 316 has a positive polarity. 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. 5B shows a voltage indicating 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). It is a waveform diagram. 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.
5B 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. 5B is enlarged as compared with the voltage waveform of the scanning signal or the like in FIG.

A specific example of processing by the video processing circuit 30 according to the first embodiment will be described.
Detected when the frame image (part of) indicated by the video signal Vid-in is an image displaying a window area of black pixels with white pixels as the background, as shown in FIG. 6 (1), for example. The boundary is shown in (2) of FIG.
The video processing circuit 30 replaces the video signal with the gradation level c when a darker level than the gradation level c is designated for the dark pixel in contact with the detected boundary. Accordingly, the image shown in (1) of FIG. 6 is corrected by the video processing circuit 30 as shown in (3) of FIG.

For this reason, even if the window region of the black pixel moves by one pixel in any direction, there is no portion where the black pixel adjacent to the white pixel directly changes to the white pixel. For example, as shown in FIG. 15B, even if the window area of the black pixel moves one pixel in the left direction, the black pixel adjacent to the white pixel in the video signal Vid-in once has the gradation level c ( After changing to the applied voltage Vc), it changes to a white pixel.
Therefore, according to the present embodiment, 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 image defined by the video signal Vid-in, since the gradation level of the dark pixel in contact with the boundary is locally replaced, the possibility that the correction of the display image by the replacement is perceived by the user is small. . In addition, in this embodiment, since it is not necessary to change the structure of the liquid crystal panel 100, the aperture ratio does not decrease, and it is also possible to apply to an already manufactured liquid crystal panel without devising the structure. It is.

<Application / Modification of First Embodiment>
In the first embodiment described above, various applications and modifications are possible.

<Part 1>
In the first embodiment, when a dark pixel and a bright pixel are adjacent to each other in the image indicated by the video signal Vid-in, one of the two pixels whose applied voltage Vc is lower (dark in the normally black mode) The pixel) is corrected to the gradation level c and applied with the voltage Vc. However, the pixel to be replaced may be two or more.
For example, when the image indicated by the video signal Vid-in is as shown in (1) of FIG. 6, for example, and the detected boundary is as shown in (2) of FIG. As shown in FIG. 7A, when a darker pixel than the gradation level c is designated for each dark pixel in contact with the dark pixel and a dark pixel adjacent to the dark pixel in the direction opposite to the boundary, respectively. Alternatively, it may be replaced with a video signal of gradation level c.

When the gradation levels of the two pixels are replaced in this way, when the window area of the black pixel moves by one pixel in any direction, the period of the gradation level c is 2 frames.
For example, as shown in FIG. 15C, when the window area of the black pixel moves one pixel to the left, the black pixel adjacent to the white pixel in the video signal Vi d-in is changed to the black level for each frame. ) → gradation level c → gradation level c → white level. For this reason, the period during which the initial tilt angle is given to the liquid crystal molecules is two frames, which is doubled compared to the first embodiment, so that the effect of suppressing the reverse tilt domain can be increased.
Further, the number of candidate pixels to be replaced is not limited to “2”, and may be “3” or more. For example, “6” may be used as in a second embodiment described later.

<Part 2>
In the first embodiment, a dark pixel and a bright pixel are detected as a boundary in a vertical or horizontal adjacent portion. The reason is that the moving direction of the black pixel region may be any. Because.
However, considering movement such as a cursor, for example, it may be sufficient to assume only the horizontal (X) direction as the moving direction of the black (dark) pixel region. In particular, the video signal Vid-in includes 1 row 1 column to 1 row n column, 2 rows 1 column to 2 rows n column, 3 rows 1 column to 3 rows n column, ..., m row 1 column to m row n column. If only the horizontal direction is assumed as the moving direction, there is room for simplifying the configuration of the boundary detection unit 302 as in the second embodiment described below.

When only the horizontal direction is assumed as the moving direction of the dark pixel, in addition to the second embodiment, focusing on the vertical component among the detected boundaries, the dark pixel ( And dark pixels adjacent thereto) may be used as correction candidates.
For example, when the frame image indicated by the video signal Vid-in is as shown in (1) of FIG. 6 and the detected boundary is as shown in (2) of FIG. When a darker level than the gradation level c is designated for a dark pixel in contact with the boundary, the video signal of the gradation level c may be replaced (see FIG. 7B). Further, when a darker level than the gradation level c is designated for a dark pixel in contact with the vertical boundary and a dark pixel adjacent thereto, the image signal of the gradation level c may be replaced ( (See (c) of FIG. 7).

Second Embodiment
Next, a video processing circuit according to the second embodiment will be described. In the second embodiment, in the normally black mode, the boundary between the dark pixel and the bright pixel adjacent to each other in the horizontal direction is detected, and the dark pixel in contact with the boundary and the dark pixel are A total of six dark pixels including five dark pixels continuous in the opposite direction are set as correction candidates.

FIG. 8 is a block diagram showing the configuration of the video processing circuit 30 according to the second embodiment, in which the boundary detection unit 302 is changed to specialize the detection of the boundary.
In this figure, a delay circuit (D) 308 outputs a video signal D1 obtained by delaying the video signal Vid-in supplied from the host device by one period of the dot clock signal Clk, that is, by one pixel. It is. The delay circuit (D) 309 outputs a video signal D2 obtained by delaying the video signal D1 by one period of the dot clock signal Clk. Therefore, the video signal D1 has a relationship that precedes the video signal D2 by one pixel in time.
In this example, the delay circuit 312 outputs a video signal D8 obtained by delaying the video signal Vid-in by eight periods (eight pixels) of the dot clock signal Clk.

The determination unit 310 compares the gradation level of the video signal D1 with the gradation level of the video signal D2,
(1) In the first case where the gradation level of the video signal D1 is in the gradation range a and the gradation level of the video signal D2 is in the gradation range b, or vice versa.
(2) In the second case where the gradation level of the video signal D1 is in the gradation range b and the gradation level of the video signal D2 is in the gradation range a,
Are determined to be boundaries, and an H level determination signal Jdg is output.
When the determination unit 310 determines the second case, the determination signal Jdg is set to the H level from the time of detection. However, when the first case is detected, the determination signal Jdg is changed to the dot clock signal from the time of determination. The H level is delayed by 6 cycles of Clk (the number of pixels to be corrected).

The counter 311 resets the count value Pc to “0” when the determination signal Jdg falls from H to L level, and then counts up the count value Pc with the dot clock Clk.
The correction unit 315 replaces the gradation level c with the gradation level c when the count value Pc is an effective value and the gradation level of the video signal D8 is lower than the gradation level c. The correction unit 315 sets the valid value of the count value Pc from “0” to “5” in this example.

Next, the operation of the video processing circuit according to the second embodiment will be described with reference to FIGS. Here, in the image indicated by the video signal Vid-in, the display content of a certain line is the content indicated by (1) in FIG. 9, more specifically, white pixels in the columns from a to d. Assume that black pixels are in the columns up to v and white pixels are in the columns from w to z. Although omitted in FIG. 9, white pixels continue on the left side of the a column, black pixels continue between the m and n columns, and black pixels continue on the right side of the z column. To do.
In such an image, boundaries are detected at two locations, between the d and e columns and between the v and w columns. For this reason, when viewed in the temporal supply order, the pixel that is a correction candidate is on the rear side (right side of the boundary in the spatial arrangement) at the boundary between the d and e columns, whereas v and The boundary between the w columns is the front side (left side of the boundary in terms of spatial arrangement).
In this example, as shown in (2) of FIG. 9, the number of pixels that are candidates for correction from the boundary is set to “6”.

FIG. 10 is a diagram illustrating an operation when the rear side of the boundary is a correction candidate, and FIG. 11 is a diagram illustrating an operation when the front side of the boundary is a correction candidate.
First, with reference to FIG. 10, the operation when the rear side of the boundary is a correction candidate will be described.
The video signal Vid-in is supplied in the order of a, b, c,..., In accordance with the dot clock signal Clk.
The video signal D1 is delayed by one period (one pixel) of the dot clock signal Clk with respect to the video signal Vid-in by the delay circuit 308, and the video signal D2 is delayed from the video signal D1 by the delay circuit 309. Furthermore, it is delayed by one pixel.
In the video signals D1 and D2 thus delayed, the e column of the video signal D1 is in the gradation range a, and the d column of the video signal D2 is in the gradation range b. It is determined that this is the boundary. Therefore, the discrimination signal Jdg becomes H level at a timing delayed by 6 pixels from the timing at which the boundary is discriminated, that is, at a timing at which the pixel indicated by the video signal D8 is in the d column where the pixel contacts the front side. The counter 311 up-counts the count value Pc from “0” to “5” during a period of 6 pixels as correction candidates after the determination signal Jdg falls to the L level.

Therefore, in the correction unit 315, six pixels from the e column to the j column next to the d column in the video signal D8 are correction candidates. If the gradation level is lower than c in the six pixels from the e column to the j column that are candidates for correction, the gradation level is replaced with c, and if it is greater than or equal to c, the gradation level of the video signal D8 is not replaced.
The video signal Vid-out output from the correction unit 315 is output with a delay of one pixel with respect to the video signal D8 in consideration of replacement.

Next, an operation when the front side of the boundary is a correction candidate will be described with reference to FIG.
The video signal Vid-in is supplied in the order of..., X, y, z columns in accordance with the dot clock signal Clk.
The video signal D1 is delayed by one pixel with respect to the video signal Vid-in, and the video signal D2 is further delayed by one pixel with respect to the video signal D1 by the delay circuit 309. In the video signals D1 and D2 thus delayed, the w column of the video signal D1 is in the gradation range b and the v column of the video signal D2 is in the gradation range a. It is determined that this is the boundary. Therefore, the discrimination signal Jdg becomes H level at the timing when this boundary is discriminated, that is, at the timing when the pixel indicated by the video signal D8 becomes the p column 7 pixels before the border in the second case.
The counter 311 up-counts the count value Pc from “0” to “5” during a period of 6 pixels that are candidates for correction after the determination signal Jdg falls to the L level. Among D8, 6 pixels from the q column to the v column next to the p column are correction candidates. If the gradation level is lower than c in the six pixels from the q column to the v column that are correction candidates, it is replaced with the gradation level c, and if it is greater than or equal to c, the gradation level of the video signal D8 is not replaced.

In the configuration in which the dark pixel and the bright pixel are detected as a boundary in the horizontal or vertical direction as in the first embodiment, the pixels adjacent in the same row and the pixels adjacent in the same column are compared. In particular, the circuit scale of the boundary detection unit 302 tends to increase. Further, the delay amount of the delay circuit 312 is also required for a plurality of lines.
On the other hand, in the configuration in which the portion where the dark pixel and the bright pixel are adjacent in the horizontal direction is detected as a boundary as in the second embodiment, the adjacent pixels in the same row may be compared, and the delay amount is also an example of this. Since only 8 pixels are required, the circuit scale can be easily reduced.

<Application / Modification of Second Embodiment>
In the second embodiment described above, the number of pixels to be corrected is set to “6”, but is not limited thereto, and may be set to “1” as illustrated in (3) of FIG. When the number of pixels to be corrected is set to “1”, for example, the correction unit 315 sets the effective value of the count value Pc to “0” only, and the determination unit 310 determines the boundary in the second case. The discrimination signal Jdg is set to the H level by delaying the dot clock signal Clk by five cycles from the discrimination time.
In such a configuration, when the rear side of the boundary is a correction candidate, as shown in FIG. 12, the discrimination signal Jdg becomes H level at the timing when the video signal D8 becomes the d-th column, so the count value Pc is The video signal D8 becomes “0” at the timing when the video signal D8 is in the e column that contacts the rear side of the boundary. Therefore, in the correction unit 315, only the pixel in the e column next to the d column in the video signal D8 is a correction candidate.
On the other hand, when the front side of the boundary is a correction candidate, as shown in FIG. 13, the discrimination signal Jdg is at the H level at the timing when the video signal D8 becomes the u row, so that the count value Pc is the video signal D8. Becomes “0” at the timing when becomes the v-th line that touches the front side of the boundary. Therefore, in the correction unit 315, only the pixels in the v column next to the u column in the video signal D8 are candidates for correction.
Note that the e or v column that is a correction candidate is replaced with the gradation level c if the gradation level is lower than c, and the gradation level of the video signal D8 is not replaced if it is greater than or equal to c.
The number of pixels to be corrected can be set as appropriate other than “1” and “6”.

  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 designates the applied voltage of the liquid crystal element, the boundary may be determined based on the designated applied voltage to correct the voltage.

  In each embodiment, the liquid crystal element 120 is not limited to a transmissive type, and may be a reflective type. Furthermore, the liquid crystal element 120 is not limited to the normally black mode, but may be a normally white mode in which the liquid crystal element 120 is in a white state when no voltage is applied, for example, as a TN method. In the normally white mode, 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. 4B, and the transmittance increases as the applied voltage increases. Decrease. Since the pixel affected by the lateral electric field is the pixel having the lower applied voltage, the applied voltage to the pixel lower than the voltage Vc is replaced with Vc.

<Electronic equipment>
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 apparatus using the liquid crystal display device according to the above-described embodiment. FIG. 14 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 circuits, 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 group 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.

  As electronic devices, in addition to the projector described with reference to FIG. 14, 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 ... Boundary detection Units, 314, 315 ... correction unit, 316 ... D / A converter, 2100 ... projector.

Claims (9)

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 processed video signal,
A boundary detection unit that detects a boundary between a first pixel in which an applied voltage specified by an input video signal is lower than the first voltage and a second pixel in which the applied voltage is greater than or equal to a second voltage greater than the first voltage. When,
When the applied voltage specified by the input video signal is lower than the third voltage lower than the first voltage for the first pixel in contact with the boundary, the applied voltage to the liquid crystal element corresponding to the first pixel is A correction unit that corrects the applied voltage specified by the input video signal to the third voltage;
A video processing circuit comprising: The correction unit is
When the applied voltage of the first pixel in contact with the detected boundary is equal to or higher than the third voltage, the applied voltage to the liquid crystal element corresponding to the first pixel is set to the applied voltage specified by the video signal. The video processing circuit according to claim 1. The boundary detection unit
The video processing circuit according to claim 1, wherein the boundary is detected when the first pixel and the second pixel are adjacent to each other in the horizontal direction. The boundary detection unit
The video processing circuit according to claim 3, wherein the boundary is detected by comparing an input video signal with a signal obtained by delaying the input video signal by one pixel. The correction unit is
When the applied voltage is lower than the third voltage with respect to one or more pixels located on the opposite side of the first pixel in contact with the boundary, the applied voltage to the liquid crystal element corresponding to the pixel is The video processing circuit according to claim 1, wherein the applied voltage specified by the input video signal is corrected to the third voltage. The video processing circuit according to claim 1, wherein the third voltage is 1.5 volts or less. A video processing method for inputting a video 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 the processed video signal,
Detecting a boundary between a first pixel in which an applied voltage specified by an input video signal is lower than a first voltage and a second pixel in which the applied voltage is greater than or equal to a second voltage greater than the first voltage;
When the applied voltage specified by the input video signal is lower than the third voltage lower than the first voltage for the first pixel in contact with the boundary, the applied voltage to the liquid crystal element corresponding to the first pixel is A video processing method, wherein the applied voltage specified by the input video signal is corrected to the third voltage. 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 processing circuit that inputs a video signal designating an applied voltage of the liquid crystal element for each pixel and defines an applied voltage of the liquid crystal element based on the processed video signal;
The video processing circuit includes:
A boundary detection unit that detects a boundary between a first pixel in which an applied voltage defined by an input video signal is lower than the first voltage and a second pixel in which the applied voltage is equal to or greater than a second voltage that is greater than the first voltage. When,
When the applied voltage specified by the input video signal is lower than the third voltage lower than the first voltage for the first pixel in contact with the boundary, the applied voltage to the liquid crystal element corresponding to the first pixel is A correction unit that corrects the applied voltage specified by the input video signal to the third voltage;
A liquid crystal display device comprising:   An electronic apparatus comprising the liquid crystal display device according to claim 8.

Images