JPH07162791A - Video projector - Google Patents

Abstract

PURPOSE:To automatically adjust the luminance of a screen corresponding to surrounding brightness. CONSTITUTION:A voltage corresponding to the surrounding brightness is generated in a sensor 6, it is compared with a prescribed reference level in a comparator circuit 7 and a resistance value for an electronic variable resistor 8 or 9 is adjusted by the voltage corresponding to the difference. The contrast or brightness of video signals to be supplied to a liquid crystal panel 2 is adjusted by the electronic variable resistor 8. Also, the voltage to be supplied to a lamp 4 for projecting video images on the liquid crystal panel 2 is adjusted by the electronic variable resistor 9.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a video projection device such as a liquid crystal projection display device, and more particularly to a video projection device characterized by means for controlling the brightness of a projected screen.

[0002]

2. Description of the Related Art As a display capable of displaying a large screen image, there is an image projection device for enlarging and projecting an image of a visualized video signal on a screen. The image projection device includes a CRT projection display device that projects an image on the phosphor screen of a CRT, a liquid crystal projection display device that projects an image on a liquid crystal panel, and the like.

[0003]

In such a video projection apparatus, the larger the screen, the lower the screen brightness. Therefore, it was necessary to view the video with the surroundings darkened. In addition, it is difficult to obtain optimum brightness in an environment where the ambient brightness constantly changes. Further, in a video projection device having a constant projection angle such as a rear projection type video projection device (rear projector), if the brightness of the screen is constant, the screen may be too bright and difficult to see at night when the surroundings are dark. .

The present invention has been made in order to solve such a problem, and provides a video projection device in which the brightness of the screen is automatically adjusted according to the ambient brightness. With the goal.

[0005]

SUMMARY OF THE INVENTION In order to solve the above problems, the present invention provides a video projection device such as a liquid crystal projection display with a means for detecting ambient brightness and a predetermined output for this means. Means for comparing with a reference value and means for controlling the brightness of the projected image according to the output of this means are provided.

Here, as the reference value, a predetermined value or an output value of the means for detecting the brightness of the projected screen is used.

Further, the control of the brightness of the projected image is
(1) Control of level of video signal input to image projection device (contrast control, brightness control), (2)
It is realized by adopting at least one of the control of the brightness of the light source of the projection device.

The means for detecting the ambient brightness is provided, for example, on the back surface or the side surface of the image projection apparatus main body.

[0009]

According to the present invention, since the screen brightness is controlled according to the difference between the detected ambient brightness and the reference value, the screen is automatically optimized even if the ambient brightness changes. The brightness is controlled to a certain level.

If a fixed value is set in advance as the reference value, the brightness of the screen is controlled according to the result of comparing the ambient brightness and the fixed value. Further, when a value obtained by detecting the brightness of the projected screen is used as the reference value, the brightness of the screen is controlled according to the result of comparing the ambient brightness with the brightness of the projected screen.

[0011]

Embodiments of the present invention will now be described in detail with reference to the drawings. (First Embodiment) FIG. 1 is a block diagram showing the configuration of a first embodiment of a liquid crystal projection display device to which the present invention is applied.

In this figure, C input from the S terminal
The signal and the Y signal are input to the liquid crystal drive signal circuit 1, where they are converted into R, G, B signals and applied to signal electrodes (not shown) of the liquid crystal panel 2. Also, the liquid crystal drive signal circuit 1
Separates the composite sync signal (SYNC) from the input Y signal and supplies it to the liquid crystal control signal circuit 3. The liquid crystal control signal circuit 3 generates a scanning signal from this composite synchronizing signal and applies it to the scanning electrodes (not shown) of the liquid crystal panel 2, and also generates a field inversion pulse (FRP) and supplies it to the liquid crystal drive signal circuit 2. To do. Field inversion pulse is on liquid crystal panel 2
It is a pulse for inverting the polarities of R, G, B signals applied to each field. The light generated by the lamp 4 passes through the liquid crystal panel 2 and is projected onto a screen (not shown) by a projection optical system (not shown). This allows
An image formed on the liquid crystal panel 2 based on the video signal is projected on the screen. Power supply circuit 5 is AC100
A voltage to be supplied to each part of the liquid crystal projection display device is generated from a power source such as V or DC 12V (only the voltage V to be supplied to the lamp 4 necessary for explaining the present invention is shown here).

Next, the point of automatically controlling the brightness of the projected screen according to the ambient brightness will be described. The brightness of the screen is realized by performing at least one of (1) control of the level of the video signal in the liquid crystal drive signal circuit 1 (contrast control or brightness control) and (2) control of the emission brightness of the lamp 4. .

First, the method (1) will be described. The sensor 6 generates a voltage according to the ambient brightness of the liquid crystal projection display device and supplies it to the level comparison circuit 7. The level comparison circuit 7 has a predetermined reference voltage (R
EF) is input, the difference between the output voltage of the sensor 6 and the reference voltage is supplied to the electronic variable resistor 8, and the resistance value is controlled. The electronic variable resistor 8 is adjusted so that the resistance value becomes the center value when the output of the level comparison circuit 7 is a predetermined value, for example, 0. Then, the electronic variable resistor 8 is connected to the contrast adjustment terminal or the brightness adjustment terminal of the liquid crystal drive signal circuit 1, and the contrast or brightness is adjusted according to the difference between the output of the sensor 6 and the reference value.
As a result, for example, when the surroundings are bright, the contrast or brightness can be increased accordingly.

Next, the method (2) will be described. The output of the level comparator 7 is supplied to the electronic variable resistor 9. The electronic variable resistor 9 is adjusted so that the resistance value becomes a center value when the output of the level comparison circuit 7 is a predetermined value, for example, 0. Then, the electronic variable resistor 9 is supplied to the power supply circuit 5, and the voltage V applied to the lamp 4 is controlled according to the difference between the output of the sensor 6 and the reference value. As a result, for example, when the surroundings are dark, the emission brightness of the lamp 4 can be reduced accordingly.

The user is allowed to select either (1) or (2) described above, or both of them are used.

FIG. 2 shows an example in which the liquid crystal projection type display device of the present invention is attached to an overhead console of an automobile. This liquid crystal projection type display device is constructed so that it can be folded when not in use, and FIG. 2 (a) shows the time of use and FIG. 2 (b) shows the time of folding.

In FIG. 2A, the liquid crystal projection type display device 11 is mounted inside an overhead console exterior 13 provided under the roof 12. Then, the projection unit 1 on the front surface of the liquid crystal projection display device 11
The light emitted from 1a is projected on the screen 14.

Then, when the overhead console exterior 13 is rotated counterclockwise around the open / close center axis 15 by an open / close mechanism (not shown), the upper end of the liquid crystal projection display device 11 is displayed as shown in FIG. 2 (b). Has a roof 1
The screen 14 is brought into contact with a fixed portion 12a formed so as to project into the vehicle, and the screen 14 is rotated clockwise about the rotary shaft 14a, and is folded and stored in the overhead console exterior 13. At this time, the movable pin 17 provided on the side surface of the liquid crystal projection display device 11 moves in the cam groove 16 formed in the overhead console exterior 13, and the fixed spring 18 contracts.

In this example, the sensor 6 for detecting the ambient brightness may be attached at a position not affected by the projection light, for example, on the back surface or the side surface of the liquid crystal projection display device 12.

(Second Embodiment) FIG. 3 is a block diagram showing a main configuration of a second embodiment of a liquid crystal projection display device to which the present invention is applied.

In this figure, the first sensor 21 is shown in FIG.
It is a sensor that outputs a voltage corresponding to the brightness of the surroundings, which is the same as that of the sense6. The second sensor 22 is a sensor that outputs a voltage according to the brightness of the screen projected on the screen. For example, in the case of FIG. 2, the second sensor 22 is preferably attached to the front surface side (viewer side) of the screen 13. The level comparison circuit 23 outputs the difference voltage between the first sensor 21 and the second sensor 22, and the first electronic variable resistor 2
The resistance values of the fourth and second electronic variable resistors 25 are controlled. As in the case of FIG. 1, the resistance values of these resistors are adjusted so as to be the center value when the difference voltage is a predetermined value, for example, 0. Then, the level of the video signal is adjusted by the first electronic variable resistor 24, and the drive voltage of the lamp is adjusted by the second electronic variable resistor 25. However, in the case of the present embodiment, the output of the level comparison circuit 23 is set to a predetermined initial value when the control operation is started up.

The present invention is not limited to the above-mentioned embodiments, and various modifications can be made based on the spirit of the present invention, and these modifications are not excluded from the scope of the present invention. For example, in FIG. 1, the reference value (REF) of the level comparison circuit 7 may be manually adjusted. Further, a switch is provided on the input side of the electronic variable resistors 8 and 9, and the signal from the level comparison circuit 7 or the manual adjustment signal is selected by this switch to select the electronic variable resistor 8
Alternatively, it may be configured to input to 9. Further, the present invention can be applied to a CRT projection type display device.

[0024]

As described in detail above, according to the present invention, in a video projection device such as a liquid crystal projection display device, the brightness of the screen is automatically adjusted according to the ambient brightness. Optimal brightness can be obtained even in an environment where the ambient brightness constantly changes (eg, in a car).

[Brief description of drawings]

FIG. 1 is a block diagram showing the configuration of a first embodiment of a liquid crystal projection display device to which the present invention is applied.

FIG. 2 is a configuration diagram showing an example in which the liquid crystal projection display device of the present invention is attached to an overhead console of a vehicle.

FIG. 3 is a block diagram showing the configuration of a second embodiment of a liquid crystal projection display device to which the present invention is applied.

[Description of Reference Signs] 1 ... Liquid crystal drive signal circuit, 2 ... Liquid crystal panel, 3 ... Liquid crystal control signal circuit, 4 ... Lamp, 5 ... Power supply circuit, 6, 21 ... Sensor for detecting ambient brightness, 7, 23 ... Level comparison circuit, 8, 9, 24, 25 ... Electronic variable resistor, 22 ... Sensor for detecting brightness of projected screen

Claims (4)

[Claims] 1. An image projection apparatus for converting an input video signal into an image and projecting it on a screen, comprising: (a) means for detecting ambient brightness; and (b) output of the means to a predetermined reference value. And a means for controlling the brightness of the image projected on the screen according to the output of the means, 2. The image projection apparatus according to claim 1, further comprising means for detecting the brightness of the image projected on the screen, wherein the output of the means is used as a reference value. 3. The image projection apparatus according to claim 1, wherein the means for controlling the brightness of the projected image is a means for controlling the brightness of a light source for projecting the image. 4. The image projection apparatus according to claim 1, wherein the means for controlling the brightness of the projected image is a means for controlling the level of the video signal.