JPH03196790A - Liquid crystal projector - Google Patents

Abstract

PURPOSE:To adjust the difference of the gamma property between plural liquid crystal panels well and to improve the reproduction picture quality by providing respective gamma compensation circuits corresponding to the plural liquid crystal panels. CONSTITUTION:gamma compensation circuits 56, 58, 60 set with independent compensation properties are respectively connected to the picture signal input side of the respective liquid crystal panels 50, 52, 54 of R, G and B, and the respective picture signals of the R, G and B are inputted to these. By the compensation by these gamma compensation circuits 56, 58, 60, the gamma properties of all R, G and B of the picture reception side with the liquid crystal panels 50, 52, 54 at its center is made to become the same as a cathode ray tube (gamma=2.2). Thus, the difference of the gamma properties between the liquid crystal panels 50, 52, 54 is well adjusted, and the reproduction picture quality can be improved.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a liquid crystal projector using a plurality of liquid crystal panels, and particularly relates to γ correction of the liquid crystal panel.

[Prior Art] As a liquid crystal projector using a liquid crystal panel, there is one shown in FIG. 8, for example. In the figure, light emitted from a halogen lamp 12 having a reflector lO is
First, the light enters the interference filter 14. This cuts infrared rays, making it difficult for heat from the light source 38 to be transmitted to the front.

The light that has passed through the interference filter 14 is incident on the blue gicroic mirror 16, where the blue (B) light is separated. The separated blue light is reflected by the reflection mirror 18 and enters the blue TFT-liquid crystal panel 20 . A blue image signal is input to the liquid crystal panel 20, and a blue image is formed based on this.

Next, the light transmitted through the blue glaucroic mirror 16 is
The light enters a green (G) gicchroic mirror 22, where the green light is separated. The separated green light enters the green liquid crystal panel 24. A green image signal is input to the liquid crystal display panel 24, and based on this,
A green image is formed.

Next, the red color (
R) The light is sequentially reflected by the reflecting mirrors 26 and 28 and enters the red liquid crystal panel 30. A red image signal is input to the liquid crystal panel 30, and a red image is formed based on this.

Next, the blue, green, and red images formed by the blue, green, and red liquid crystal panels 20, 24, and 30 are combined by the color compositing gicroic prism 32, and the combined color image is Screen 36 by projection lens 34
is shown in the image.

By the way, in television broadcasting, video software, etc.
As is well known, a γ correction of 1/2.2 is given in advance at the time of converting the image into an electrical signal. This is to compensate for the γ characteristic (γ=22) of a cathode ray tube, which is a television receiver or playback device. In other words, the video signal of γ=l/2.2 on the transmitting side is γ=2.2
Since the signal is reproduced on a cathode ray tube, the overall γ characteristic is γ=(1/2.2)x2°2=1.

However, when images are played back on a liquid crystal panel like the liquid crystal projector mentioned above, the γ characteristic of the liquid crystal is γ≠2.2, so the γ compensation on the transmitting side and the γ characteristic on the receiving side are will no longer match, and the playback quality will deteriorate. Therefore, it is necessary to provide an appropriate γ correction circuit on the receiving side.

Note that in some liquid crystal televisions and the like in which R, G, and B pixels are arranged in a mosaic pattern, gamma correction is performed only on the luminance signal during video signal processing, and in some cases gamma correction is not performed.

[Problem to be Solved by the Invention] However, in the above-mentioned liquid crystal projector that uses 83 R, G, and 83 liquid crystal panels, due to differences in manufacturing processes and variations in characteristics between panels, problems such as those shown in FIG. The γ characteristics are different for each type. Same figure fA+, +8
), fcl is the γ of each R, G, and H liquid crystal panel.
Characteristic examples are shown, with the horizontal axis representing the applied voltage and the vertical axis representing the illuminance. As shown in these figures, for the same applied voltage, the edge liquid crystal panel has the highest illuminance (and the blue one has the lowest illuminance).

Furthermore, in the liquid crystal projector, if the characteristics of the lamp 12 are flat and always produce perfect white light, R, G, B
The color balance is easy to maintain. However, 1. Depending on the characteristics of the lamp 12, it is difficult to emit perfect white light, resulting in color imbalance. The γ characteristics become different between R, G, and B due to such a color imbalance in the optical system.

The present invention has been made in view of these points, and is
It is an object of the present invention to provide a liquid crystal projector that can improve the reproduced image quality by properly adjusting the γ characteristics between liquid crystal panels of tl.

[Means for Solving the Problems] The present invention provides a liquid crystal projector including a plurality of liquid crystal panels, in which a small number of γ correction circuits (having compensation characteristics corresponding to the γ characteristics of each of the liquid crystal panels) are installed in each liquid crystal panel. The feature is that a plurality of them are provided corresponding to the following.

[Operation] In a liquid crystal projector, for example, liquid crystal panels are provided for each color of R, G, and B, and the γ characteristics of these liquid crystal panels do not necessarily match, and are also different from those of a cathode ray tube. Such differences in γ values are corrected by γ correction circuits independently provided for each liquid crystal panel. According to the main aspect, the characteristics of the γ correction circuit are set so as to compensate for the γ characteristics of the optical system including the liquid crystal panel.

[Example 1] Hereinafter, an example of a liquid crystal projector according to the present invention will be described with reference to the accompanying drawings. Figure 1 shows 1
The main configuration of this embodiment is shown. As shown in the figure, γ correction circuits 56, 58, and 60, each having independently set correction characteristics, are connected to the image signal input side of each of the R, G, and H liquid crystal panels 50, 52, and 54. and these are R
2G and H image signals are input. Through correction by these γ correction circuits 56, 58, 60, the γ characteristics on the image receiving side centering on the liquid crystal panel 50, 52, 54 are adjusted to R.
, G, and B are all similar to the Brownian distance (γ=2.2).

FIG. 2 shows a detailed configuration example of such a γ correction circuit 56.58°60. Although these circuits have different characteristics, they have the same connection configuration, so the γ correction circuit 56 will be explained as a representative. In the figure, the input side of the γ correction circuit 56 is the input side of the contrast gain adjustment section 62. A control signal SC is input to this contrast gain adjustment section 62 via a variable resistor 64. By adjusting this variable resistor 64, the amplifier gain of the contrast gain adjustment section 62 is changed, thereby adjusting the contrast.

Next, the output of the contrast gain adjustment section 62 is 1 μm1.
is connected to the input side of the bright DC (direct current) adjustment section 66. A control signal SB is input to the bright DC:A adjusting section 66 via a variable resistor 68. By adjusting the variable resistor 68, the DC level of the rOJIRE signal is changed, thereby adjusting the brightness. Note that these adjustment circuits are usually constructed from appropriate integrated circuits.

Next, the output side of the bright DC adjustment section 66 is connected to the input side of a gain variable section 70 whose amplifier gain changes depending on the DC level of the signal. More specifically, the gain variable section 70 includes NPN transistors Q1. Q2
．． Q3, and the base of the transistor Q3 is the input side of the gay 21 transformer 70. A collector resistor RC is connected to the power supply V at the collector of this transistor Q3.
cc, and on the emitter side, an emic resistor R5 is connected between the earth and the resistor R5.
,,R2 is a transistor Ql.

and each emitter of Q2.

Next, resistors R, , R are connected to the base side of the transistor Ql.
4. A divided voltage of the power supply voltage VCC by a variable resistor VR is applied, and a stabilizing capacitor C8 is connected between it and the ground. Also, transistor Q
A divided voltage of the power supply voltage VC (by resistors R5, R6 and variable resistor VR2) is applied to the base side of 2, and a stabilizing capacitor C2 is connected between it and ground. A power supply voltage Vcc is applied to the collector sides of these transistors Q1 and Q2, and the collector side of the transistor Ql is connected to the output of the gain variable section 70.
That is, it is the output side of the γ correction circuit 56.

Next, the procedure for adjusting the γ correction circuit 56 as described above will be explained with reference to FIGS. 3 to 6. For example, assume that the overall characteristic of γ=2.2 that is desired to be obtained as a whole is as shown in FIG. 3 [Al. That is, as shown in FIG.
Assume that the characteristics shown in the figure fAl are required as a whole. Here, assuming that the liquid crystal panel 50 has the characteristics shown in FIG. The result is as shown in fDl in the same figure.

In other words, when the characteristics of f8), fcl, and TDI in the same figure are combined, the characteristic of fAl in the same figure is obtained.
The γ correction amount fDl in the figure is set, and the gain adjustment of the γ correction circuit 56 is performed as follows so that an input/output relationship corresponding to this is obtained. In this example, the fifth
As shown in the figure, such correction characteristics can be obtained using a line graph.

Next, the gain adjustment of the γ correction circuit 56 is performed using, for example, an apparatus configuration as shown in FIG. In the figure, an IRE signal for adjustment output from a signal generator 74 is input to a liquid crystal projector 76, and an image based on this is projected onto a screen 78. The illuminance of this reproduced video is measured by an illumination meter 80, and the measurement result is
-Y is output to block 82. That is, the reproduced video illuminance corresponding to the change in the IRE signal of the signal generator 74 is
- It is designed to be outputted by a Y plotter 82.

a. Liquid crystal panel illuminance range measurement First, the R, G,
BThe maximum opening degree and minimum illuminance are measured for each LCD panel.Next, an appropriate color balance is determined from these measurement results, and the black level, brightness level, and contrast are each set. Ru. Specifically, the level a of each liquid crystal panel is determined to a value that is approximately 80 to 90% of the maximum resolution of the three liquid crystal panels and provides an appropriate color balance. In addition, the minimum illuminance of the δ liquid crystal panel and the white level pa
Contrast is commonly determined from the degree. Further, the black level illuminance of each liquid crystal panel is determined so that white level illuminance ÷ contrast = black level illuminance.

b. Black level adjustment Next, the rO' IRE signal is inputted from the signal generator 74 to the liquid crystal projector 76, and the brightness is adjusted so that the reproduced image has black level illuminance. As mentioned above, this adjustment is performed by the variable resistor 68 of the γ correction circuit 56.

C4 low brightness level adjustment Next, UO'' ~ r40J IRE (No. 5) is manually adjusted in the same way, and the contrast is adjusted so that it rides the characteristic curve of γ = 2.2. As mentioned above, this adjustment is This is done by the variable resistor 64 of the γ correction circuit 56.

d. Medium brightness level adjustment Next, the r40J to r80JIRE signals are input in the same way, and the transistor Ql is adjusted so that it rides the characteristic curve of γ=2,2.
rONJ - DC level and amplifier gain are adjusted.

e. High brightness level adjustment Next, the ``80'' to rloOJ IRE signals are similarly input, and the rONJ -DC level and amplifier gain of the transistor Q2 are adjusted so as to ride the characteristic curve of γ=2.2.

FIG. 5 shows the input/output characteristics of the gain variable section 70 adjusted as described above, that is, the relationship between the base voltage vIl and the collector voltage Vc of the transistor 03. As shown in this figure, as the base voltage VIl rises, the emitter voltage v6 gradually rises along the graph Gl, and the collector voltage ve becomes VCC (Rc'Vtl
/RE and gradually decreases along G2.

Then, the base voltage VB of transistor Q3 is Vllll
Then, the above-mentioned medium brightness level adjustment point is reached, transistor Q1 turns "ON", and collector voltage VC becomes V.
cc-I RC-V): l /I RE// R gradually decreases along G3. Furthermore, when the base voltage v6 of the transistor Q3 becomes vR□, the above-mentioned high brightness level adjustment point is reached, the transistor Q2 becomes r ON J, and the collector voltage vc becomes VLC-f Rc'VE) /
IR, /noR, //R21 gradually decreases along G4.

As described above, the characteristics of the gain variable section 70 of the γ correction circuit 56 are set. As a result, the human output characteristics of the γ correction circuit 56 as a whole become as shown in FIG. In the figure, if the input image signal voltage V+s of the γ correction circuit 56 gradually decreases as shown in the graph GA, then the γ
Image signal voltage V after correction. UT becomes like graph GB. In the figure, the fluctuation indicated by arrow Fl is an adjustment needle caused by the control signal SR, the fluctuation indicated by arrow F2 is an adjustment needle caused by control signal SC, the variation indicated by arrow F3 is an adjustment needle caused by resistor R1, and the variation indicated by arrow F4 is an adjustment needle caused by control signal SC. The fluctuation shown is an adjustment needle due to resistor R2.

In this way, by approximation using a polygonal line, the γ correction circuit 5
6 characteristics are set as shown in FIG. 3 IDI. The above operation is similarly performed for the γ correction circuits 58 and 60, and γ correction characteristics corresponding to the characteristics of each of the G and B liquid crystal panels 52 and 54 are set.

Next, the overall operation of the above embodiment will be explained. As described above, the γ value of the image signal input to the liquid crystal projector 76 is set to γ:l/2.2 in accordance with the cathode ray tube. When the H signal of such video signals is input to the γ correction circuit 56, γ correction is performed with the characteristics shown in FIGS. 5 and 6, which approximate the characteristics shown in FIG. 3 CD+.

This corrected image signal is input to the liquid crystal panel 50. However, since the characteristics of the liquid crystal panel 50 are as shown in FIG.
becomes. However, the γ characteristic of the input image signal is γ=1/2
．． 2, the resulting γ characteristic of the reproduced R video is (1/2.2)X2 2=1. The same applies to G and H images. In this way, the γ characteristics between the plurality of liquid crystal panels are well adjusted, and the reproduced video image quality, together with the γ compensation 1 on the transmitting side, has a natural and good gradation.

<Other Examples> Note that the present invention is not limited to the above-mentioned Examples. For example, according to the embodiment described above, it is possible to apply γ correction independently according to the γ characteristics of each of the R, G, and H liquid crystal panels. It is also possible to set the characteristics of For example, as shown in graph GC in Figure 7, the illuminance is set to γ=2 at low brightness.
．． If the so-called black extension characteristic is lowered from 2 (graph GD), a deep image can be obtained. Furthermore, it is also possible to make the color balance between the black and white levels of the image signal constant at an arbitrary ratio.

Furthermore, in the above embodiment, γ of each R, G, and H liquid crystal panel
Although only the characteristics were considered, the gamma characteristics of the entire optical system including the liquid crystal panel are shown in Figure 3 (so that the characteristics of Al can be obtained,
The compensation characteristics of the γ correction circuit may be set.

The other one circuit configuration is not limited to the above-mentioned embodiment, and may be appropriately modified in design so as to achieve the same effect.

[Effects of the Invention] As explained above, according to the present invention, since a γ correction circuit is provided for each of a plurality of liquid crystal panels,
This has the effect that the difference in γ characteristics between a plurality of liquid crystal panels can be satisfactorily adjusted to improve the reproduced image quality.

[Brief explanation of drawings]

FIG. 1 is an explanatory diagram showing an embodiment of the liquid crystal projector according to the present invention, FIG. 2 is a circuit diagram showing a detailed configuration example of the main part of the embodiment, and FIG. 3 is an example of the γ characteristic to be compensated. FIG. 4 is an explanatory diagram showing an adjustment device for the γ correction circuit,
FIG. 5 is a graph showing an example of the characteristics of the gain variable section 70;
FIG. 7 is a graph showing the human output characteristics of the γ correction circuit in the embodiment, FIG. 7 is a graph showing the γ characteristics of another embodiment in which black expansion is performed, and FIG. 8 is a configuration diagram showing an example of a liquid crystal projector. FIG. 9 is a graph showing an example of γ characteristics of a liquid crystal panel. 50.52.54...LCD panel, 56.58°60
. . . γ correction circuit, 62 . . . Gain adjustment section for contrast, 64. 68 . . . Variable resistor, 66 . Q2. Q3...NPN type transistor, 74...
Signal generator, 76...LCD projector, 78...
Screenshot, 80...! In degree meter 1B 2-X -Y
Plotter.

Claims (1)

[Claims] A liquid crystal projector including a plurality of liquid crystal panels, characterized in that a plurality of γ correction circuits having compensation characteristics corresponding to at least the γ characteristics of each of the liquid crystal panels are provided corresponding to each liquid crystal panel.