JPH0943577A - Video signal processing circuit and display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enlarge an apparent visual field angle by making a device a constitution in which a halftone reproducibility correcting means performs a halftone reproducibility correction with respect to luminance signal lower than a reference level to improve the deterioration of visibility accompanying black inversion and black paint out phenomenons. SOLUTION: This device detects parts continously having luminance information of luminance lower than the luminance signal in a video signal and applys different half-one reproducibility correction pixel to the parts every pixel. That is, a pixel (a) and a pixel (b) are parts continously having luminance information of luminance lower than the luminance signal in the video signal and at this time, when an area having information of low luminance is large in a screen (in one frame)., a black inversion and a black paint out effect the degrading of picture guality for viewers. Then, when pixels (a), (b) continously having information of low luminance exist, it prevented from occurring that the black inversion and the black paint out occur simultaneously by applying different halftone reproducibility correction every pixels (a), (b). Consequently, the apparent visual field angle is enlarged.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a video signal processing circuit configured to suppress image quality deterioration of a display device due to a change in a viewing azimuth angle of a viewer, and a liquid crystal display device or a CRT display equipped with the video signal processing circuit. The present invention relates to a display device such as a device. In particular, when the viewing azimuth angle of the viewer changes not only from the front, it is possible to suppress a reduction in visibility, and when the viewing azimuth angle of the viewer is in the front, the video signal has gradation information. However, when the viewing azimuth angle of the viewer changes, the brightness becomes constant (black shadow) and the brightness inversion phenomenon (black inversion) in which the magnitude of the brightness in the low brightness area is switched occurs (EN) Provided are a video signal processing circuit and a display device which can alleviate the drawback of damage.

[0002]

2. Description of the Related Art As a liquid crystal display device using a liquid crystal panel, a structure shown in FIG. 4 is conventionally known. This liquid crystal display device includes a Y / C separation circuit 5 and a sync separation circuit 7 for inputting a composite video signal from a video signal input terminal 1 to which a composite video signal is applied. The Y / C separation circuit 5 separates the composite video signal into a luminance signal and a color difference signal. The sync separation circuit 7 extracts horizontal and vertical sync signals from the composite video signal.

The output of the Y / C separation circuit 5 is the signal demodulation circuit 6
Further, to the signal demodulation circuit 6, a hue control signal is input from the input terminal 2, and a color gradation control signal by varying the amplitude of the color difference signal is input from the input terminal 3. The signal demodulation circuit 6 demodulates the signals separated by the Y / C separation circuit 5 and other input signals into RGB signals. This demodulated signal is the polarity inversion circuit 8
The signal is inverted at 1, is supplied to the RGB amplifier 10 for each of the RGB color signals, and is then input to the clamp circuit 11. A contrast control signal is input to the clamp circuit 11 from the input terminal 4. The output signal of the clamp circuit 11 is input to the X driver circuit 12.

The output signal from the sync separation circuit 7 is supplied to the clock generation circuit 9 and then to the X driver circuit 12 and the Y driver circuit 13. These X
The driver circuit 12 and the Y driver circuit 13 drive the liquid crystal panel 14 to display.

In the liquid crystal display device having such a configuration, the composite video signal input to the input terminal 1 is applied to the Y / C separation circuit 5, where it is separated into a luminance signal and a color difference signal, and then the signal demodulation circuit 6 At R (red), G (green), B
Demodulated to each color signal of (blue). This signal demodulation circuit 6
The input terminal 2 receives a hue control signal by phase adjustment of the color difference signal in the signal demodulation circuit, and the input terminal 3 receives a color tone control signal by amplitude adjustment of the color difference signal. A viewer can arbitrarily set these control signals.

Next, R output from the signal demodulation circuit 6
The G and B signals are given to the polarity inverting circuit 8. Here, in order to secure long-term reliability in the liquid crystal panel 14 and prevent application of a DC voltage, the polarity of the applied voltage is switched every 1H (one horizontal period) and converted into r, g and b signals.

Next, r, g, which have been demodulated and subjected to polarity inversion,
The b signal and the R, G, and B signals are input to the RGB amplifier 10, where each signal is amplified and finely adjusted to adjust the white balance. In the clamp circuit 11 of the next stage,
The black level of each color signal is clamped to a constant voltage. The liquid crystal panel 14 is adjusted by adjusting the clamp voltage.
You can set the brightness of. The contrast of the liquid crystal panel 14 is adjusted by changing the amplitude level of the signal applied to the liquid crystal panel 14.

Next, in order to obtain a timing signal for displaying an image on the liquid crystal panel 14, a clock generator 8
Inputs the horizontal and vertical sync signals obtained by separating the composite video signal from the input terminal 1 by the sync separation circuit 6, generates horizontal and vertical clocks in synchronization with these, and outputs the X driver circuit 12
And to each of the Y driver circuits 13. The X driver circuit 12 and the Y driver circuit 13 display an image on the liquid crystal panel 14 based on the input signal.

With this configuration, the viewer can arbitrarily set the optimum display screen.

[0010]

However, the conventional liquid crystal display device constructed as described above has the following drawbacks. That is, the liquid crystal panel is significantly deteriorated in image quality depending on the viewing azimuth angle with respect to the viewer. Especially when the brightness of the image is low, when the viewing azimuth of the viewer is in front, the brightness is constant when the viewing azimuth of the viewer changes, even though the video signal has gradation information. However, there is a drawback that the visibility is deteriorated due to a phenomenon (black crushing) and a so-called luminance inversion phenomenon (black inversion) in which the magnitude of the luminance in the low luminance portion is switched.

Next, the reason why the above-mentioned drawbacks occur will be described.

FIG. 5 shows changes in halftone reproduction characteristics when the viewing azimuth angle of the viewer changes with respect to the liquid crystal display device.
Reference numeral 71 in the figure denotes a case where the viewer views the liquid crystal display device from the front. As shown in FIG. 6 (perspective view) and FIG. 7 (right side view), 72 is 10 ° down when the viewer views the liquid crystal display device from a direction 5 ° below the front. This is the case when viewed from the side direction. As shown in FIGS. 8 (perspective view) and 9 (right side view), 74 is the same as 10 ° above when the viewer views the liquid crystal display device from a direction 5 ° above the front. This is the case when viewed from the direction.

6 to 9, reference numeral 31 is a viewer, and 32 is a displacement angle θDOWN of the viewing azimuth angle. Further, 33 is a liquid crystal display device in front of the viewer, 3
4 is a liquid crystal display device at a viewing azimuth displacement angle θ DOWN, 41 is a viewer, 42 is a viewing azimuth displacement angle θ DO
WN, 43 is a liquid crystal display device in front of the viewer, 44 is a liquid crystal display device at a viewing azimuth displacement angle θ DOWN, 5
1 is a viewer, 52 is a viewing azimuth displacement angle θUP, 53
Is a liquid crystal display device from the viewer's front, 54 is a liquid crystal display device at a viewing azimuth displacement angle θUP, 61 is a viewer, 6
2 is a viewing azimuth displacement angle θUP, 63 is a liquid crystal display device in front of the viewer, and 64 is a viewing azimuth displacement angle θU.
It is a liquid crystal display device in P.

FIG. 10 is a diagram showing the relationship between the video signal voltage value on the horizontal axis and the brightness on the vertical axis, and the dotted line 81 shows the γ curve of the conventional liquid crystal display device.
The solid line 82 shows the γ curve when the viewing azimuth angle of the viewer changes by 10 ° in the direction in which black reversal or blackout occurs.

As can be understood from both of these figures, the halftone reproduction characteristics of the conventional liquid crystal display device show a remarkable change in visibility as the viewing azimuth angle of the viewer changes. In the case of 73 or 82 in FIG. 10, black reversal in which the γ curve reverses the luminance with respect to changes in the video signal amplitude, and black crushing where the luminance becomes constant occur, and the visibility is impaired. The present invention has been made to solve such problems of the prior art, and provides a video signal processing circuit and a display device capable of reducing black reversal and blackout and increasing the apparent viewing angle. The purpose is to do.

[0016]

The video signal processing circuit of the present invention is a video signal processing circuit for processing a video signal including a luminance signal, and comprises a halftone reproducibility correction means for performing a halftone reproduction correction on the video signal. The halftone reproducibility correcting means is configured to perform the halftone reproducibility correction on the luminance signal lower than the reference level, thereby achieving the above object.

In the video signal processing circuit of the present invention, a comparator for detecting the luminance signal lower than the reference level, a reference voltage input terminal for applying a reference voltage to the comparator,
A γ converter for performing two or more different types of halftone reproduction corrections on the luminance signal of the reference voltage or less detected by the comparator can be provided.

In the video signal processing circuit of the present invention, the comparator may be configured to include an AND gate, and the γ converter may be configured to have at least two types of halftone reproduction characteristics. it can.

The display device of the present invention includes one of the above-mentioned video signal processing circuits in a display device which causes image quality deterioration when the viewing azimuth angle changes, and thereby the above object is achieved.

In the display device of the present invention, the halftone reproducibility correcting means can reproduce two or more kinds of halftone reproduction characteristics for each pixel in one frame of an image.

In the display device of the present invention, the halftone reproducibility correcting means can reproduce two or more kinds of halftone reproduction characteristics in one frame of the image.

The operation of the present invention will be described below.

The black reversal and the black crushing have a large effect on the deterioration of the image quality for the viewer when a large area having low-luminance information in the screen (between one frame). Therefore, when there are pixels having low-luminance information continuously, it is possible to prevent black reversal and blackout from occurring at the same time by applying different halftone reproduction corrections to these pixels. As a result, it is possible to expand the apparent viewing angle.

The liquid crystal display device of the present invention detects portions having luminance information of lower luminance continuously than the luminance signal in the video signal, and applies different halftone reproduction correction to these portions for each pixel. .

Pixels a and b shown in FIG. 2 (c) are portions having luminance information of lower luminance continuously than the luminance signal in the video signal. At this time, as shown in FIGS. 2A and 2B, the halftone reproduction correction is performed on the luminance information lower than the reference level. A solid line 101 in FIG. 3 shows the result of halftone reproduction correction performed on the γ curve of the solid line 103 given to the pixel a, and a dotted line 102 shows a γ curve of the dotted line 104 given to the pixel b. Is the result of performing halftone reproduction correction.

Therefore, even when the pixel a and the pixel b have low-luminance information, different halftone reproduction is performed, black inversion and black crushing do not occur at the same time, and the image quality is degraded to the viewer. It becomes difficult to be recognized. Therefore, the apparent viewing angle is widened.

[0027]

Embodiments of the present invention will be described below.

FIG. 1 shows an example of a liquid crystal display device according to this embodiment. This liquid crystal display device has a video signal input terminal 1 for inputting a composite video signal, an input terminal 2 for a hue control signal, an input terminal 3 for a color gradation control signal by varying the amplitude of a color difference signal, and a contrast control. A signal input terminal 4, a Y / C separation circuit 5 that separates the composite video signal into a luminance signal and a color difference signal, a signal demodulation circuit 6 that demodulates the composite video signal into an RGB signal, and a horizontal and vertical direction from the composite video signal. A sync separation circuit 7 for extracting a sync signal and a polarity inversion circuit 8
, Clock generation circuit 9, and R for each RGB color signal
GB amplifier 10, clamp circuit 11, X driver circuit 12, Y driver circuit 13, liquid crystal panel 14,
A / D for analog / digital conversion of luminance signal
A converter 15, a comparator 16 used to detect a low brightness portion, a reference level input terminal 17 for inputting a reference level to the comparator, and a low brightness portion of a video signal detected by the comparator for each pixel. Γ for applying different halftone reproduction correction
And a converter 18.

In such a structure, the portion excluding the liquid crystal panel 14 is the video signal processing circuit, and the portion surrounded by A is the main part of the present invention. Further, circuits and the like having the same numbers as those of the conventional device have the same functions.

Next, the operation contents of the liquid crystal display device provided with the video signal processing circuit having such a configuration will be described.

The composite video signal input to the video input terminal 1 is given to the Y / C separation circuit 5 and the sync separation circuit 7. The Y / C separation circuit 5 separates the composite video signal into a luminance signal and a color difference signal. The separated luminance signal and chrominance signal are supplied to the A / D converter 15 and the signal demodulation circuit 6, respectively.

Next, in order to detect a portion having luminance information of lower luminance continuously than the luminance signal in the video signal, the luminance signal is input from the Y / C separation circuit 5 to the A / D converter 15, where At, each pixel is sampled and analog-to-digital conversion is performed. The converted data is input to the comparator 16 at the next stage.

The comparator 16 includes a reference level input terminal 17
The reference value is input from. The output of the comparator 16 becomes H level when the data value is smaller than the reference value,
At other times, it becomes L level. This output is given to the 16-and-gate 16a provided in the comparator and converted to the TTL level. As the other signal, the dot clock used when sampling the pixel is given to the AND gate 16a. When the dot clock and the L level signal are input, the AND gate 16a controls the γ converter. Generate a signal. The γ converter control signal is given to the γ converter 18. Further, the γ converter 18 has
The signal passed through the A / D converter 15 is input.

The γ converter 18 uses a ROM (Read Only Memory) and has a look-up table in which at least two or more kinds of halftone reproduction characteristics are written in advance. The γ converter control signal is used to switch the halftone reproduction characteristic. Here, the value of the halftone reproduction correction that the liquid crystal display device should have can be arbitrarily set, but in the present invention, the γ value is set to a value within the range of 1.9 or more and 3.2 or less. In the embodiment, two types of γ value of the γ converter, 1.9 and 2.2, are used. Note that the γ value is not limited to 1.9 and 2.2, and any binary value of 1.9 or more and 3.2 or less, or three or more values can be used. The reason why the γ value is in the range of 1.9 or more and 3.2 or less is that within this range,
This is because in a display device such as a liquid crystal display device, black deviation or black inversion can be less likely to occur even if the viewing direction is greatly deviated, specifically within 15 °.

The digital signal processed by the γ converter 18 is converted into an analog signal by the D / A converter 19 and given to the signal demodulation circuit 6.

FIG. 2 shows a state in which γ correction (halftone reproduction correction) is performed. Pixels a and pixels b on the liquid crystal panel shown in FIG. 2C are portions having luminance information continuously lower in luminance than the luminance signal in the video signal, as shown in FIG. 2B. In this case, a γ converter control signal is generated as shown in FIG. 2C, and halftone reproduction correction (γ correction) is performed accordingly. Specifically, when the γ converter control signal is at L level, γ
A lookup table having a value of 2.2 is used, and a lookup table having a γ value of 1.9 is used at the H level. By this operation, when the luminance signal is lower than the reference level of the comparator 16, the halftone reproduction characteristic can be changed for each pixel.

The luminance signal subjected to the halftone reproduction correction is digitally converted by the D / A converter 19 as described above.
The signal is analog-converted and demodulated by the signal demodulation circuit 6 into color signals of R (red), G (green), and B (blue) together with color difference signals. To this signal demodulation circuit 6, a hue control signal by phase adjustment of the color difference signal in the signal demodulation circuit and a signal for color shading control by amplitude adjustment of the color difference signal are input from the input terminal 2 and adjusted. Can be arbitrarily set by the viewer.

Next, the R, G and B signals are supplied to the liquid crystal panel 14.
In order to secure long-term reliability and prevent DC voltage application, 1
It is input to the polarity inversion circuit 8 for switching the polarity of the applied voltage every H (one horizontal period), and is converted into r, g, b signals.

Next, demodulated and polarity-reversed r, g,
The b signal and the R, G, B signals are input to the RGB amplifier 10, and the white balance is adjusted by amplifying and finely adjusting each signal.

Next, the clamp circuit 11 at the next stage clamps the black level of each color signal to a constant voltage. The brightness of the liquid crystal panel 14 can be set by adjusting the clamp voltage.

On the other hand, the sync separation circuit 7 which has received the composite video signal from the video signal input terminal 1 outputs the composite video signal horizontally,
The signal is separated into a vertical synchronizing signal and output to the clock generator 9.
The clock generator 9 generates horizontal / vertical clocks synchronized with these, and outputs each to the X driver circuit 12 and the Y driver circuit 13. These clocks are used as timing signals for displaying an image on the liquid crystal panel 14.

The X driver circuit 12 and the Y driver circuit 13 display an image on the liquid crystal panel 14 based on the respective input signals. The contrast of the display screen of the liquid crystal panel 14 can be adjusted by changing the amplitude level of the signal applied to the liquid crystal panel 14.

With the above configuration, when the brightness of the image due to the viewing azimuth angle to the viewer of the liquid crystal panel 14 is low, it is possible to improve the deterioration of the visibility due to the black reversal and the blackout phenomenon.

FIG. 3 is a diagram showing the relationship between the video signal amplitude and the luminance obtained by the liquid crystal display device of the above embodiment.
A solid line 101 in FIG. 3 indicates a halftone reproduction correction with respect to the γ curve of the solid line 103 given to the pixel a when the viewer views the image with a tilt of 10 ° in the direction in which black inversion or blackout occurs. The result is shown. The dotted line 102 indicates the pixel b.
It is the result of performing halftone reproduction correction on the γ curve of the dotted line 104 given to.

In the figure, when the pixel a and the pixel b have low luminance information, different halftone reproduction is performed, black inversion and black underexposure do not occur at the same time, and the image quality deterioration occurs to the viewer. It becomes difficult to be recognized. As described above, the apparent viewing angle can be expanded.

Although not explicitly stated in the above embodiment, the present invention may have a structure in which a predetermined look-up table used for correcting the halftone reproduction characteristic is incorporated in advance, or the γ value is 1. It goes without saying that a range of 9 or more and 3.2 or less, and 2 or more various γ-correction lookup tables may be incorporated in advance and the lookup table to be actually used may be manually selected. This is preferable because the viewer can manually select the γ value that is most visually recognizable while actually viewing the display screen.

In the above embodiment, a high frequency γ converter control signal shown in FIG. 2C is used to perform γ correction for each pixel. In that case, the power consumption is high. Therefore, it is preferable to use a low frequency. In order to use that low frequency,
It is preferable to perform γ correction for each source bus line or gate bus line provided in the liquid crystal panel 14 instead of performing correction.

Although not explicitly stated in the above embodiment, in the present invention, the unit period for performing the γ correction is one frame, and the γ correction is performed when the luminance signal becomes lower than the reference level during that period. Alternatively, γ correction may be performed for each gate line, each pixel, each source line, or in a random state for the entire one frame.

Further, although the liquid crystal display device has been described in the above embodiment, the present invention is not limited to this, and it is needless to say that the present invention can be similarly applied to other types of display devices such as a CRT display device. is there.

[0050]

In the case of the present invention, γ
Since it is corrected, even if the image brightness due to the viewing azimuth angle with respect to the viewer is low, it is possible to improve the deterioration of visibility due to the phenomenon of black reversal and blackout, and to expand the apparent viewing angle. It is possible.

[Brief description of drawings]

FIG. 1 is a circuit configuration diagram showing an example of a liquid crystal display device according to an embodiment.

2A and 2B are diagrams used for explaining operation contents of the liquid crystal display device according to the present embodiment, FIG. 2A is a schematic diagram showing a luminance signal and a reference level, FIG. 2B is a partially enlarged view thereof, and FIG. FIG. 3 is a diagram showing a positional relationship between pixels on a liquid crystal panel and various signals.

FIG. 3 is a diagram showing a γ curve obtained by the liquid crystal display device according to the present embodiment and a γ curve before halftone reproduction correction.

FIG. 4 is a circuit configuration diagram showing a conventional liquid crystal display device.

FIG. 5 shows the input video signal amplitude on the horizontal axis and the luminance (bilogarithmic axis) on the vertical axis, and shows the change in the halftone reproduction characteristic with the change in the viewing azimuth angle of the viewer in the conventional liquid crystal display device. It is a figure.

FIG. 6 is a perspective view showing a positional relationship between a line of sight of a viewer and a liquid crystal display device.

7 is a right side view showing the positional relationship between the line-of-sight position of the viewer and the liquid crystal display device in the case of FIG.

FIG. 8 is a perspective view showing the positional relationship between the line of sight of the viewer and the liquid crystal display device.

9 is a right side view showing the positional relationship between the line of sight of the viewer and the liquid crystal display device in the case of FIG.

FIG. 10 is a conventional liquid crystal display device, in which the distribution of the video signal amplitude of an image in one frame when the viewing azimuth angle of the viewer is front, the conventional γ curve and the viewing of the viewer. It is a figure which shows the conventional (gamma) curve when an azimuth is 10 degrees in the direction which black reversal or black crushing occurs.

[Explanation of symbols]

1 video signal input terminal 2 input terminal 3 input terminal 4 input terminal 5 Y / C separation circuit 6 signal demodulation circuit 7 sync separation circuit 8 polarity inversion circuit 9 clock generation circuit 10 RGB amplifier circuit 11 clamp circuit 12 X driver circuit 13 Y driver Circuit 14 Liquid crystal panel 15 A / D converter 16 Comparator 16a AND gate 17 Comparison reference level input terminal 18 γ converter 19 D / A converter 31 Viewer 32 Viewing azimuth displacement angle θ DOWN 33 From the viewer Liquid crystal display device in front 34 Displacement angle of viewing azimuth angle θ DOWN Liquid crystal display device 41 Viewer 42 Displacement angle of viewing azimuth angle θ DOWN 43 Liquid crystal display device in front of viewer 44 Viewing azimuth angle Liquid crystal display device at displacement angle θ DOWN 51 Viewer 52 Viewing azimuth displacement angle θ UP 53 Liquid crystal in front of the viewer Display device 54 Liquid crystal display device at viewing azimuth displacement angle θUP 61 Viewer 62 Viewing azimuth displacement angle θUP 63 Liquid crystal display device in front of viewer 64 At viewing azimuth displacement angle θUP Liquid crystal display device 71 Viewing azimuth angle ± 0 ° (θUP = 0 °, θDOWN =
Halftone reproduction characteristics of conventional liquid crystal display device at 0 °) 72 Viewing azimuth angle + 5 ° (θDOWN = 0 °) Halftone reproduction characteristics of conventional liquid crystal display device 73 Viewing azimuth angle + 10 ° (θDOWN = Halftone reproduction characteristics of conventional liquid crystal display device at 0 °) 74 Viewing azimuth angle −5 ° (θUP = 0 °) Halftone reproduction characteristics of conventional liquid crystal display device 75 Viewing azimuth angle −10 ° ( θUP = 0 °) halftone reproduction characteristic of a conventional liquid crystal display device 81 low luminance part of luminance signal in video signal 82 pixel 101 when video signal is displayed on liquid crystal panel 101 given to pixel a Γ of halftone reproduction characteristics
Curve 102 γ of halftone reproduction characteristics given to pixel b
Curve 103 10 ° in the direction in which visual inversion or blackout occurs
Γ curve of 101 at the time of 10 4
Gamma curve of 102 when

Claims (7)

[Claims] 1. A video signal processing circuit for processing a video signal including a luminance signal, comprising halftone reproducibility correction means for performing halftone reproduction correction on the video signal, wherein the halftone reproducibility correction means is higher than a reference level. A video signal processing circuit configured to perform halftone reproducibility correction on low luminance signals. 2. A comparator for detecting the luminance signal lower than the reference level, a reference voltage input terminal for supplying a reference voltage to the comparator, and a luminance signal detected by the comparator and having a reference voltage or less. The video signal processing circuit according to claim 1, further comprising: a γ converter that performs two or more different halftone reproduction corrections. 3. The video signal processing circuit according to claim 2, wherein the comparator comprises an AND gate. 4. The video signal processing circuit according to claim 2, wherein the γ converter has at least two kinds of halftone reproduction characteristics. 5. A display device which causes image quality deterioration when the viewing azimuth angle is changed, the display device comprising the video signal processing circuit according to claim 1. 6. The halftone reproducibility correction means sets the image 1
The display device according to claim 5, wherein two or more types of halftone reproduction characteristics can be reproduced for each pixel between frames. 7. The halftone reproducibility correction means sets the image 1
The display device according to claim 5, wherein the display device is configured to reproduce two or more types of halftone reproduction characteristics in the entire frame.