JP2007065177A - Back projection type video display device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a back projection type video display device capable of appropriately controlling the luminance of a screen in accordance with both the luminance of external light and the luminance of projected light, projecting the light with relatively high luminance when it is bright on the surroundings, thereby showing the screen brightly, and restraining the luminance relatively according as it gets dark on the surroundings, thereby reducing glare concerning a signal having a high APL, while displaying a white video part having small area without lowering brightness, because it is projected with high luminance. <P>SOLUTION: By providing an optical sensor 200 capable of receiving stray light by the video light reflected on the back side of the screen 102 of a liquid crystal projection television 100 and stray light by external light made incident after it is transmitted through the screen 102 and provided at a prescribed position in a housing 101, the intensity of video light projected from a video light projection mechanism 110 is controlled based on the detection output of the optical sensor 200. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention supports a transmissive screen for video display, a video light projection mechanism that projects video light corresponding to a video signal representing a video to be observed from the front side of the screen, and the screen. In addition, the present invention relates to a so-called rear projection type video display apparatus using a so-called liquid crystal rear projection television receiver or the like, which includes a housing that houses the video light projection mechanism therein.

  2. Description of the Related Art Conventionally, a luminance limiter control using APL (Average Picture Level) is performed in a cathode ray tube television receiver or the like. In other words, CRT direct-view televisions and projectors are equipped with a configuration that detects the average value of the cathode current and protects the tube, and if it exceeds a certain value, negatively feeds back to the gain of the video signal amplification circuit or the DC reproduction level. ing. According to this configuration, even with the same white peak signal, a signal with a low APL such as a white window of a small area is displayed with the maximum luminance, but with a signal with a high APL such as a large white area, the luminance is increased. The display is lowered and it is also intended to suppress the viewer from feeling dazzling.

  On the other hand, in a conventional general rear projector (projector using a micro display such as a liquid crystal light valve, LCOS, or mirror device), the luminance is not controlled by APL as in the case of a direct-view liquid crystal television receiver, and the white peak The signal is always displayed at the maximum luminance regardless of the display area, and it is inevitable that the observer feels dazzling in a large area. In order to deal with such problems, it has already been proposed to adjust the gain of the amplifier by controlling the luminance by APL, as in the case of a cathode ray tube television receiver or the like.

  For example, in an image reproduction method for reproducing an image on a display device having a plurality of pixels based on an image signal including a pixel signal representing information for each pixel, an average of all pixel signal levels is calculated as an average signal level. Thereafter, an input signal-output luminance characteristic representing a change in luminance of the pixel with respect to the level of the pixel signal is set according to the average signal level, and then an image is reproduced so as to satisfy the set input signal-output luminance characteristic The method of doing is proposed (refer patent document 1).

  In this proposal, even if a display device (such as a liquid crystal display device) in which the input signal-output luminance characteristic is constant regardless of the average signal level, the input signal-output luminance characteristic is adjusted as the average signal level increases. Since the exponent value (gamma value) when approximated by an exponential function can be reduced, the dark portion of the overall dark image (image with low average brightness) has excellent visibility in the dark area, and the overall bright image ( It is said that it is possible to reproduce an image having excellent visibility of a bright part by preventing white-out and glare in an image having a high average luminance.

  Similarly to the above, in an image display device that includes a display unit having a plurality of pixels for displaying an image and receives an image signal including a pixel signal representing information for each pixel, the level of all the pixel signals is An average signal level calculation unit that calculates an average as an average signal level, and an input signal-output luminance characteristic that sets an input signal-output luminance characteristic representing a change in luminance of the pixel with respect to the level of the pixel signal in accordance with the average signal level There has been proposed an image display device including a setting unit and a signal correction unit that corrects an image signal so as to satisfy a set input signal-output luminance characteristic (see Patent Document 2).

In the proposed device, the input signal-output luminance characteristic is changed in accordance with the average signal level, so that the input signal-output luminance characteristic is constant regardless of the average signal level (such as a liquid crystal display device). Even if the image signal is used, an image value having a characteristic that an exponent value (gamma index in a CRT display device) when an nonlinear function of an input signal-output luminance characteristic is approximated by an exponential function increases as the average signal level increases A device can be realized. Therefore, it is possible to provide an image display device that is excellent in the visibility of dark portions in an overall dark image (image having a low average luminance) and the visibility of bright portions in an overall bright image (an image having a high average luminance). It is supposed to be possible.
JP 2001-296831 A (paragraph 0027 to paragraph 0028, FIG. 1) JP 2001-296855 A (paragraph 0028 to paragraph 0029, FIG. 1)

The conventional technology described above still has various problems as described below. That is, in any of the above-described techniques described in the literatures, a configuration in which the circuit characteristics are changed by an input signal is disclosed. However, since the gamma characteristics of the display device are taken into consideration, the configuration is complicated. Is inevitable.
In general, the screen brightness that is easy to see varies depending on the ambient brightness (external light), and it is desirable that the brighter the screen is, the higher the screen brightness is, and the lower the brightness is. For example, the maximum brightness may be used during bright days, but dazzling may be felt if the brightness is not lowered at night. For this reason, a sensor is provided on the front of a direct-view television to detect ambient brightness, and screen brightness is controlled according to the brightness. In particular, recent liquid crystal television receivers are configured to adjust the screen brightness by controlling the brightness of the backlight to achieve desirable characteristics from the standpoint of energy saving. Since the mounting position is restricted, it is difficult to optimally detect the ambient brightness.

  The present invention has been made paying attention to the problems in the prior art as described above, has a simple configuration, and appropriately controls the screen brightness according to both the brightness of the external light and the brightness of the projection light. When the surroundings are bright, the screen is projected with a relatively high brightness to make the screen brighter, and the brightness is relatively suppressed as the surroundings become darker. An object of an image such as a white area is projected with a high luminance, and therefore it is an object of the present invention to provide a rear projection type image display device capable of displaying without reducing a sense of brightness.

In order to solve the above-described problems, the present application proposes the following techniques.
(1) A transmissive screen for video display, a video light projection mechanism for projecting video light corresponding to a video signal representing a video to be observed from the front side of the screen to the back side, and the screen are supported. And a housing that houses the image light projection mechanism inside the image display device, wherein the image light projected from the image light projection mechanism reaches the back side of the screen. Provided at a predetermined position in the housing near the light projection optical path and capable of receiving stray light due to image light reflected on the back side and capable of receiving stray light due to external light incident through the screen. And a projection light intensity control means for controlling the intensity of the image light projected from the image light projection mechanism based on the detection output from the light sensor. The video display device.

  According to the rear projection type image display device of (1), the optical sensor receives stray light from the image light reflected on the back surface of the screen and stray light from outside light incident through the screen. The image light projected from the image light projection mechanism by the projection light intensity control means detects the intensity of the light by both the image light and the outside light, and according to the detected intensity by both the image light and the outside light. Therefore, when the intensity of the image light is relatively strong, the intensity of the image light is relatively suppressed, and when the outside light is relatively bright, the image light is accordingly adjusted. By controlling the intensity of the image light projected from the image light projection mechanism in the direction of increasing the intensity of the image, while avoiding the possibility that the observer of the image will feel dazzling, it also supports the brightness of the surroundings Adjusted to appropriate brightness It is possible to display an image.

(2) A transmissive screen for video display, a video light projection mechanism for projecting video light corresponding to a video signal representing a video to be observed from the front side of the screen to the back side, and the screen are supported. And a housing that houses the image light projection mechanism inside the image display device, wherein the image light projected from the image light projection mechanism reaches the back side of the screen. Provided at a predetermined position in the housing near the light projection optical path and capable of receiving stray light due to image light reflected on the back side and capable of receiving stray light due to external light incident through the screen. An optical sensor, detection output separation means for separating a detection output by the optical sensor into a component by the image light and a component by the external light, and the video light separated by the detection output separation means And a projection light intensity control means for controlling the intensity of the image light projected from the image light projection mechanism by relying on both of the component and the component due to the external light in a predetermined relationship. A rear projection type image display device.

  According to the rear projection type image display device of (2), the optical sensor receives stray light due to the image light reflected on the back surface of the screen and stray light due to external light incident through the screen, The intensity of the light by both the image light and the external light is detected, respectively, and the projection light intensity control means according to each intensity of the image light and the external light separated from the detection value by the detection output separation means Since the intensity of the image light projected from the image light projection mechanism can be controlled, the intensity of the image light projected from the image light projection mechanism is relatively suppressed when the intensity of the image light is relatively strong. Adjusting to avoid the risk of glare for the viewer of the image, while increasing the intensity of the image light accordingly to increase the brightness of the image displayed on the screen when the external light is relatively bright Clear display In the so that, it is possible to perform display of the adjusted image to the appropriate brightness.

(3) The detection output separation means is provided so as to detect that the output of the photosensor is stored and that the video signal is in an all black state, and the stored contents of the storage means at the time of the detection. All-black state detecting means for emitting a timing signal for rewriting, a storage value in the storage means rewritten in synchronization with the timing signal as a component value by external light, and an output value of the photosensor and a storage value in the storage means And a separation processing unit that obtains a difference value as a component value by the video projection light, respectively.

  According to the rear projection type video display device of (3) above, in particular, in the operation by the rear projection type video display device of (2), when the video signal becomes an all black state, it is detected that this state has been reached. In synchronism with the timing signal generated by the all black state detection means, the output of the optical sensor at that time is stored in the storage means, so that the stored value becomes the component value by the external light, while the video signal is all black. It is possible to obtain the difference between the output value of the optical sensor when it is not in the state and the stored value as the component value by the image projection light. The detected component values can be obtained, and an image adjusted to an appropriate brightness can be displayed based on these values.

(4) The detection output separation means includes a storage means for storing the output of the photosensor, an all black signal generation means for generating a signal corresponding to the all black state of the video signal, and a timing according to an external operation. An operation for updating the storage contents of the storage means and a circuit for generating video light of the video light projection mechanism by replacing a signal corresponding to the all black state generated by the all black signal generating means with the video signal An operation means for simultaneously performing the supply operation, the updated storage value in the storage means as a component value by external light, and a difference value between the output value of the optical sensor and the storage value in the storage means (2) a rear projection type image display device, comprising: a separation processing unit that obtains each component value by light.

  According to the rear projection type video display device of the above (4), in particular, in the operation by the rear projection type video display device of (2), an operation to the operation unit is performed, for example, an external operation to a corresponding operation part of the remote controller or the main body. If the external light changes at the timing when the external light changes, the component value by the external light, which is the stored value in the storage means, is updated at a timing synchronized with this, and the stored value with the value in accordance with the situation at the present time point is updated. While the component value by the external light can be obtained as the component value by the image projection light as the difference between the output value of the optical sensor and the stored value, respectively, therefore, such an external operation is appropriately performed to obtain the image light. The value of the detection component corresponding to the intensity of each of the external light and the external light can be obtained, and the image adjusted to the brightness suitable for the external light and the image light at that time can be displayed. Kill.

Hereinafter, embodiments of the present invention will be described with reference to the drawings. In the drawings to be referred to below, for the sake of convenience, the main part that is the subject of the description is exaggerated as appropriate, and other than the main part is appropriately simplified or omitted.
FIG. 1 is a diagram showing an optical configuration of a liquid crystal rear projection television receiver (hereinafter abbreviated as “liquid crystal projection television”) as an embodiment of the present invention. Note that the liquid crystal projection television is originally provided with a tuner circuit for receiving television broadcasts, but is not essential in the present invention, and thus illustration thereof is omitted.

  In FIG. 1, a video display screen 102 is supported by a housing 101 of a liquid crystal projection television 100 by a support mechanism (not shown), and corresponds to a video signal representing an image to be observed from the front side of the screen 102. An image light projection mechanism 110 that projects image light onto the back side of the screen 102 is accommodated. The image light representing the display image generated by the image light projection engine 111 (1110) of the image light projection mechanism 110 is arranged along the inner surface of the inclined portion above the rear surface of the housing 101 with the image light emitted from the projection lens 112. The image is reflected by the mirror 113 and projected so as to form an image on the back side of the screen 102.

  An enlarged display 1-A in FIG. 1 shows a cross-sectional structure of the screen 102 in the horizontal direction. In this screen 102, a hard coat layer 102a, a diffusing plate 102b, a black stripe 102c, and a lenticular lens 102d are laminated or bonded together in order from the front side (outermost side), and are thus integrally formed. A Fresnel lens 102f is provided so as to face the lenticular lens-equipped diffuser plate 102e, which is a plate-like body, from the back side.

  FIG. 2 is a perspective view showing an arrangement relationship of each element shown in the enlarged display FIG. 1-A in FIG. In FIG. 2, the elements corresponding to those in FIG. 1 are denoted by the same reference numerals, but the hard coat layer 102a is omitted. Note that the viewpoint of the arrangement in FIG. 2 is represented by a relationship in which the left and right sides are opposite to those in the enlarged display FIG. 1-A in FIG. The Fresnel lens 102f on the back side is for directing light rays spreading toward the four corners of the screen 102 to the center, and prevents the periphery of the screen 102 from becoming dark when viewed from the viewer side.

  The lenticular lens 102d is a minute convex lens in the vertical direction, and widens the viewing angle in the horizontal direction by spreading light rays in the horizontal direction. The diffuser plate 102b is a ground glass plate, and the projection light forms an image here. The surface is provided with a plurality of black stripes 102c and 102c made of a low-reflective black material so as to coincide with the position of the lenticular valley, and the contrast is lowered by absorbing the outside light without blocking the projection light. I try not to let you.

  FIG. 3 is a diagram showing the configuration of the image light projection engine 1110 in FIG. The light emitted from the lamp 1111 that is the light source is made uniform in the amount of light within the illumination range by the two integrators 1112a and 1112b, and then the deflection direction thereof is aligned in one direction by the polarization conversion element 1113, and the condenser lens 1114 is Then, the light is emitted to an R reflecting dichroic mirror 1115R for color separation.

  The R component light reflected by the R reflecting dichroic mirror 1115R configured to reflect the R component and transmit the G and B components is transmitted to the R transmissive liquid crystal panel 1118R via the reflecting mirror 1116R and the R field lens 1117R. Irradiated. On the other hand, the G and B component lights transmitted by the R reflecting dichroic mirror 1115R are separated by the G reflecting dichroic mirror 1115G, and the G component light is irradiated to the G transmissive liquid crystal panel 1118G via the G field lens 1117G. .

  Similarly, the B component light transmitted by the R reflecting dichroic mirror 1115R also passes through the G reflecting dichroic mirror 1115G, and relay lens 1119a, reflecting mirror 1116B-1, relay lens 1119b, reflecting mirror 1116B-2, and B field lens. The transmissive liquid crystal panel 1118B for B is irradiated through 1117B. In addition, since polarizing plates having a polarization axis at a predetermined angle are provided on both surfaces of each of the transmissive liquid crystal panels for R, G, and B, the light radiated on each panel is transmitted through each panel and then R, G , B are formed, synthesized by the cross dichroic prism 1120, projected by the projection lens 112, and projected onto the screen 102 (FIG. 1) via the mirror 113 (FIG. 1).

  FIG. 4 is a perspective view of the liquid crystal rear projection television 100 of FIG. 1 viewed from the front side. In FIG. 4, the elements corresponding to those in FIG. 1 are denoted by the same reference numerals. Also, in FIG. 4, the outermost four corners of the optical path of the image light projected by the projection lens 112 and projected onto the screen 102 (FIG. 1) via the mirror 113 (FIG. 1) are indicated by dashed lines. Has been. In this embodiment, the image light (projection light) projected from the projection lens 112 of the image light projection mechanism 110 is in the vicinity of the image light projection optical path reaching the back side of the screen 102 and is reflected on the back side. The optical sensor 200 is disposed at a predetermined position in the housing 101 that can receive the stray light caused by the external light and can receive the stray light caused by the incident external light that passes through the screen 102.

  The optical sensor 200 has a diffusing material on the surface so as not to have a specific directivity, and is provided at a position slightly off the optical path of the projection light. By detecting the stray light due to the projection light and the stray light due to the external light by the optical sensor 200, it is possible to obtain detection outputs proportional to the average value of the projection light and the external light. In the present embodiment, the above-mentioned predetermined position relating to the arrangement of the optical sensor 200 is a position suitable for detecting both stray light of both image light (projection light) and external light, as shown in the figure. Is set at a substantially central position viewed in the left-right direction in the vicinity of the lower end edge.

  Instead of setting the optical sensor 200 to the position as described above, the optical sensor 200 is arranged on the rear surface of the video light projection unit of the video light projection mechanism 110 (such as an appropriate place on the side peripheral surface of the video light projection mechanism 110). You may comprise as follows. In this case, when the optical sensor 200 is attached, a long wiring connecting to the subsequent circuit is not necessary, and the optical sensor 200 can be attached at the time of assembling the image light projection mechanism 110 alone. This is advantageous.

  FIG. 5 is a block diagram showing the configuration of the luminance adjustment circuit in the image light projection mechanism 110 of FIG. The black level of the video signal supplied from the input terminal 501 is reproduced by the DC reproduction circuit 502. Thereafter, the signal is amplified by the variable gain amplifier circuit 503 and is provided as a gamma correction circuit 504 (corresponding to each of R, G, and B, such as 504R, 504G, and 504B. The gamma (1 / 2.2) originally applied to the video signal and the gamma of the liquid crystal light valve 506 (represented as one representative for each of R, G, and B). Are collectively corrected, and the driving circuit 505 drives the liquid crystal light valve.

  In FIG. 5, one drive system circuit is provided for each of the R, G, and B colors of the liquid crystal light valve (transmission type liquid crystal panel). 3, the transmissive liquid crystal panel 1118R, the transmissive liquid crystal panel 1118G for G, the transmissive liquid crystal panel 1118B for B, and the transmissive liquid crystal panel 1118B for B are applied. Each one drive system circuit is provided corresponding to each.

The detection signal from the optical sensor 200 described with reference to FIG. 4 is output by averaging the period of at least one frame (or field) by the low-pass filter 201. The output signal of the low-pass filter 201 that is averaged and output in this way is supplied to one input terminal of the adder circuit 202 and also supplied to the storage circuit 203.
An all black state detection circuit 507 is provided for detecting that the video signal supplied to the input terminal 501 is in an all black state based on the output of the DC reproduction circuit 502 and generating a detection signal in the detection state. Stores and holds the output signal of the low-pass filter 201 supplied to itself at the timing synchronized with the detection signal of the all black state detection circuit 507 in its own trigger terminal 203a. Accordingly, the storage circuit 203 holds data corresponding to the output of the optical sensor 200 when the video signal is at the all black level, that is, the external light component of the detection output. Specifically, since the output of the optical sensor 200 is delayed by the low-pass filter 201, for example, after the detection signal of the all-black state detection circuit 507 is output, it is held at the timing when the all-black state disappears and then returns. What is necessary is just to comprise.

  The value (external light component data) stored in the storage circuit 203 is supplied to the other input terminal (differential input terminal) of the adder circuit 202 and also supplied to the amplifier circuit 204. As a result, data of the component corresponding to the luminance of the image light obtained by subtracting the value of the external light component from the output of the optical sensor 200 is obtained from the output terminal of the adder circuit 202, and the amplifier circuit 204 outputs the value of the external light component. A value Se subjected to appropriate amplification is output.

  A component corresponding to the image light output from the adder circuit 202 is supplied to the inverting amplifier circuit 205 to form a signal in which the direction of the increase / decrease change is reversed, and this signal has an appropriate DC level at the other input terminal. The constant voltage E1 for setting the value is supplied to one input terminal of the adding circuit 206. As a result, at the output terminal of the adder circuit 206, an output ISv is obtained in which the direction of change in increase / decrease of the luminance of the image light is reversed and the direct current level is appropriately adjusted.

  The output corresponding to the above-mentioned external light component (appropriate amplification is applied to the value) and the output of the luminance of the video light with the direction of change of the increase / decrease reversed and the DC level adjusted appropriately Are supplied to the adder circuit 207, and an output value (Se + ISv) obtained by adding the two is obtained. A gain control terminal of the variable gain amplifying circuit 503 uses the output signal Gcs subjected to the process of limiting the upper limit of the output value (Se + ISv) of the adder circuit 207 to a constant value by the limiter circuit 208 as a gain control signal. To be supplied.

  6 shows the output of the low-pass filter (LPF) 201 based on the average value of the brightness of the projection light from the projection lens 112 of the image light projection mechanism 110 of FIG. 4 and the detection signal from the optical sensor 200 of FIG. 5 (and FIG. 4). It is a figure which shows the relationship. When there is no outside light, an output substantially proportional to the average value of the projection light as in the characteristic 6001 is obtained. When there is outside light, an offset b is superimposed as in the characteristic 6002. Note that the average value of the projected light is an output that is substantially proportional to the APL when the amplifier circuit operates at the maximum gain.

  FIG. 7 is a diagram illustrating the relationship of the output of the low-pass filter (LPF) 201 based on the detection signal from the optical sensor 200 with respect to external light when the video signal is all black. The output b of the low-pass filter 201 when the external light is a corresponds to the offset in FIG. Therefore, if the outside light is bright, the characteristic 6002 in FIG. 6 tends to have a larger offset.

  In the circuit of FIG. 5, when the video signal is all black, the all black state detection circuit 507 detects this and sends a trigger signal to the storage circuit 203 connected as described above, and the output value of the low pass filter 201. Remember. That is, the output of the low-pass filter 201 at the timing when all black or no signal is present, such as when no input signal is input to the projector (image light projection mechanism 110), when switching an external tuner, when switching content scenes, etc. Is stored, it is possible to extract only the output component due to external light. Although it is conceivable that the outside light changes frequently even if it is not so large, such as when the sun is clouded, a stable level can be obtained by providing such a memory circuit 203.

  As described above, the addition circuit 202 subtracts the output of the storage circuit 203 from the output of the low-pass filter 201, and therefore only depends on the brightness of the average value of the projection light (image light) excluding the influence of external light. The output of the characteristic 6001 (FIG. 6) can be obtained. This output is inverted and amplified to match the DC level (output ISv), the output of the memory circuit is added to the amplified output (Se), and the limiter circuit 208 limits the output at a constant DC level A.

  FIG. 8 is a diagram illustrating the characteristics of the limiter circuit 208. As described above, the output signal Gcs subjected to the process of limiting the upper limit to a constant value by the limiter circuit 208 is supplied to the gain control terminal of the variable gain amplifier circuit 503 as a gain control signal. The variable gain amplifying circuit 503 in which the signal Gcs whose characteristics are shown in FIG. 8 is supplied to its own gain control terminal is adjusted to the maximum gain when the signal Gcs is level A. This maximum gain is set so as to correspond to the state in which the projector (image light projection mechanism 110) is operating at the maximum luminance.

  In FIG. 8, when the outside light is bright, as shown by the characteristic 8004, the operation is performed independently of the projection light, and the brightness of the white peak is always maximized. When the outside light becomes darker and the average value of the projected light gradually becomes brighter, the gain of the variable gain amplifier circuit 503 is adjusted to decrease as shown by the characteristics 8003, 8002, and 8001. As a result of such adjustment, it is possible to reduce glare when the average value of the projection light is high, that is, when the APL of the video signal is high. Actually, when the gain is lowered, the brightness of the projection light is suppressed. As a result, the output of the optical sensor 200 is also lowered, so that it becomes stable when balanced.

  To summarize one aspect of the above configuration and operation from the viewpoint of the idea of the present invention, the storage means (storage circuit 203) for storing the output of the optical sensor 200 and the fact that the video signal is in an all-black state. All black state detecting means (all black state detecting circuit 507) which is provided to detect and rewrites the stored contents of the storage means 203 at the time of the detection (updates the existing stored contents by a new input); The stored value in the storage unit 203 rewritten in synchronization with the timing signal is used as a component value by external light, and the difference value between the output value of the optical sensor 200 and the stored value in the storage unit 203 is used as a component value by video projection light. It can be considered that the detection output separation means is configured to include separation processing means (adder circuit 202) obtained respectively.

  Further, the component of the image light projection light separated by the detection output separation means, that is, the component obtained as the output of the adder circuit 202 is inverted in polarity by the inverting amplifier circuit 205, and the level E1 is added by the adder circuit 206. By adjusting the operating point, the value ISv whose polarity is inverted and weighted corresponding to the gain of the inverting amplifier circuit 205 is obtained, while on the other hand, the component due to the external light separated by the detection output separation means, that is, the storage As for the component obtained as the stored value (output) in the means 203, a value Se with a weight corresponding to the gain of the amplifier circuit 204 is obtained, and both of these components are used in the “predetermined relationship” of each weighting described above. The image light projection mechanism 11 is based on the value obtained by performing the limiter processing by the limiter circuit 208 to the value synthesized by the adder circuit 207. Projection light intensity control means for controlling the intensity of the image light projected from the can see what is configured.

  It should be noted that “each predetermined relationship” can be set to a desired design value, specifically by the gain of the amplifier 204, the gain of the inverting amplifier 205, and the DC level E1 added by the adder circuit 206. Alternatively, a wide range of static, simple, or dynamic and adaptive relationships can be set as desired by other appropriate known methods depending on the processing algorithm in the digital circuit. .

  In the present embodiment, with the configuration as described above, the luminance of the screen (screen 102) can be controlled according to the average value of projection light and external light, so that the maximum luminance is obtained when the surroundings (external light) are bright. Can be projected and viewed with the brightest screen. In addition, as the surroundings become darker, projection is performed with a reduced brightness corresponding to the average value of the projection light, so that a signal with a high APL can not only reduce glare but also a signal such as a small area of white. Since the projection is performed with high luminance, it is possible to display the image without reducing the brightness.

  Such an effect occurs because the output of the optical sensor 200 is controlled based on the output obtained by integrating the low-pass filter 201 for one frame (or field) period. That is, in FIG. 8 showing the characteristics of the output of the limiter circuit 208 (accordingly, the gain control signal supplied to the gain control terminal of the variable gain amplifier circuit 503), a characteristic such as 8001 is obtained when the brightness of the external light decreases. However, the small white area is a signal with a high luminance level peak value but a low APL. Therefore, the output level of the low-pass filter 201 is low, and therefore corresponds to the region on the left side of the characteristic curve 8001. This is because the output of the limiter circuit 208 is close to the maximum value, the peak value of the luminance level of white having a small area is hardly suppressed, and the luminance can be maintained.

Note that the reaction time (response characteristics) of the luminance change can be arbitrarily set by changing the characteristics of the low-pass filter 201 on the output side of the optical sensor 200 or adding a delay circuit in series. it can.
FIG. 9 is a block diagram illustrating a configuration of a luminance adjustment circuit according to another embodiment. In FIG. 9, parts corresponding to those in FIG. 5 described above are denoted by the same reference numerals, and description of these parts is omitted. In the embodiment of FIG. 9, a double switch 600 is provided between the DC regeneration circuit 502 and the variable gain amplifier circuit 503, and the direct current and the electrode to which the black level E2 is applied by the first contact 601 are connected. The output terminal of the reproduction circuit 502 is selectively connected to the input terminal of the variable gain amplifier circuit 503. The ground contact level signal is synchronized with the timing at which the first contact 601 connects the all black level E2 to the input terminal of the variable gain amplifier circuit 503 by the second contact 602 linked to the first contact 601 described above. Is applied to the trigger terminal 203a of the memory circuit 203 to trigger the memory operation. Specifically, since the output of the optical sensor 200 is delayed by the low-pass filter 201, it may be stored, for example, when the switch 600 returns.

  The switch 600 can operate an operator (not shown) outside the casing 101 of the liquid crystal rear projection television 100 or with a remote controller. By pressing this switch, the level E2 of all black can be changed by the first contact 601. At the same time as being connected to the input terminal of the gain amplifier circuit 503, a ground level signal is applied to the trigger terminal 203a of the memory circuit 203, and data corresponding to the external light at that time can be stored in the memory circuit 203. .

  To summarize one aspect of the configuration and operation of the embodiment of FIG. 9 from the viewpoint of the present invention, the storage means 203 for storing the output of the optical sensor 200 and the signal corresponding to the all black state of the video signal. Corresponding to the all black state generated by the all black signal generating means (E2), the operation of updating the stored contents of the storage means 203 at the timing according to the external operation, and the all black signal generating means (E2). An operation means (switch 600) for simultaneously performing an operation of changing the signal into a video signal and supplying it to a circuit (variable gain amplification circuit 503) for generating video light of the video light projection mechanism 110, and the updated memory The separation processing unit obtains the stored value in the means as the component value by the external light and the difference value between the output value of the optical sensor 200 and the stored value in the storage means 203 as the component value by the image projection light. And (addition circuit 202), can be viewed as it is configured for detecting an output separating means comprises a.

  Note that the component of the image light projection light separated by the detection output separation means, that is, the component obtained as the output of the adder circuit 202 is inverted in polarity by the inverting amplifier circuit 205, and the level E1 is added by the adder circuit 206. By adjusting the operating point, a value ISv whose polarity is inverted and weighted corresponding to the gain of the inverting amplifier circuit 205 is obtained. On the other hand, a component due to external light separated by the detection output separation means, that is, a storage As for the component obtained as the stored value (output) in the means 203, a value Se with a weight corresponding to the gain of the amplifier circuit 204 is obtained, and both of these components are used in the “predetermined relationship” of each weighting described above. The image light projection mechanism 110 is based on the value obtained by performing the limiter processing by the limiter circuit 208 to the value synthesized by the adder circuit 207. The projection light intensity control means for controlling the intensity of the projected image light can be regarded as being configured, and this “predetermined relationship” can be appropriately set by various methods. Is the same as the embodiment of FIG.

In the embodiment of FIG. 9, in addition to the same effects as those of the embodiment of FIG. 5, for example, when the illumination light in the room is artificially changed or the curtain is pulled, the outside light is relatively In the case of a large and sudden change, the switch 600 can be artificially operated to make it easy to see even after the outside light changes.
Although the liquid crystal rear projection television has been described in the present embodiment, it is obvious that the same effect can be obtained even in a liquid crystal rear projector (liquid crystal rear monitor) that does not include a tuner circuit.

It is a figure showing the optical composition of the liquid crystal rear projection television receiver as an embodiment of the invention. FIG. 2 is a perspective view showing an arrangement relationship of each element shown in enlarged display FIG. 1-A in FIG. 1. It is a figure showing the structure of the image light projection engine in FIG. It is the perspective view which looked at the liquid-crystal rear projection television receiver of FIG. 1 from the front side. It is a block diagram showing the structure of the luminance adjustment circuit in the light projection mechanism in FIG. It is a figure which shows the relationship between the average value of the brightness | luminance of the projection light from the projection lens of the imaging light projection mechanism in FIG. 4, and the output of the low-pass filter based on the detection signal by the optical sensor of FIG. It is a figure which shows the relationship of the output of the low-pass filter based on the detection signal by the optical sensor with respect to external light when a video signal is all black. It is a figure which shows the characteristic of the limiter circuit in FIG. It is a block diagram showing the structure of the luminance adjustment circuit in other embodiment.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 100 ... Liquid crystal projection television 101 ... Case 102 ... Screen 102a ... Hard-coat layer 102b ... Diffuser 102c ... Black stripe 102d ... Lenticular lens 102e ... Diffusion plate with lenticular lens 102f ... Fresnel lens 110 ... Image light projection mechanism 111 ... Image light Projection engine 112 ... Projection lens 113 ... Mirror 200 ... Optical sensor 201 ... Low pass filter 202 ... Adder circuit 203 ... Memory circuit 203a ... Trigger terminal 204 ... Amplifier circuit 205 ... Inverting amplifier circuit 206 ... Adder circuit 207 ... Adder circuit 208 ... Limiter circuit 501 ... Input terminal 502 ... DC regeneration circuit 503 ... Variable gain amplifier circuit 504 ... Gamma correction circuit 505 ... Drive circuit 506 ... Liquid crystal light valve 507 ... All black state detection circuit DESCRIPTION OF SYMBOLS 600 ... Switch 601 ... 1st contact 602 ... 2nd contact 1110 ... Image light projection engine 1111 ... Light source 111a, 1112b ... Integrator 1113 ... Polarization conversion element 1114 ... Condenser lens 1115R ... R reflection dichroic mirror 1115G ... G reflection dichroic mirror 1116R ... Reflective mirrors 1116B-1, 1116B-2 ... Reflective mirror 1117R ... R field lens 1117G ... G field lens 1117B ... B field lens 1118R ... R transmissive liquid crystal panel 1118G ... G transmissive liquid crystal panel 1118B ... B Transmission type liquid crystal panel 1119a ... relay lens 1120 ... cross dichroic prism

Claims (4)

  A transmissive screen for video display, a video light projection mechanism for projecting video light corresponding to a video signal representing a video to be observed from the front side of the screen to the back side, and supporting the screen and the video A rear projection type display device having a housing for accommodating the light projection mechanism therein, wherein the image light projection optical path through which the image light projected from the image light projection mechanism reaches the back side of the screen An optical sensor provided at a predetermined position in the housing that is capable of receiving stray light due to image light reflected near the back side and is capable of receiving stray light due to external light that has passed through the screen and is incident thereon And a projection light intensity control means for controlling the intensity of the image light projected from the image light projection mechanism based on the detection output by the optical sensor. Display devices.   A transmissive screen for video display, a video light projection mechanism for projecting video light corresponding to a video signal representing a video to be observed from the front side of the screen to the back side, and supporting the screen and the video A rear projection type display device having a housing for accommodating the light projection mechanism therein, wherein the image light projection optical path through which the image light projected from the image light projection mechanism reaches the back side of the screen An optical sensor provided at a predetermined position in the housing that is capable of receiving stray light due to image light reflected near the back side and is capable of receiving stray light due to external light that has passed through the screen and is incident thereon A detection output separating means for separating a detection output by the optical sensor into a component by the video light and a component by the external light, and by the video light separated by the detection output separation means And a projection light intensity control means for controlling the intensity of the image light projected from the image light projection mechanism by relying on both components of the minute and the component due to the external light in a predetermined relationship. A rear projection type image display device.   The detection output separation means is provided to detect that the output of the photosensor is stored, and to detect that the video signal is in a completely black state, and the timing of rewriting the storage contents of the storage means at the time of the detection A difference between the output value of the photosensor and the stored value in the storage means, with the stored value in the storage means rewritten in synchronization with the timing signal as a component value by external light The rear projection type image display device according to claim 2, further comprising separation processing means for obtaining values as component values by the image projection light.   The detection output separating means includes a storage means for storing the output of the photosensor, an all black signal generating means for generating a signal corresponding to the all black state of the video signal, and the storage means at a timing according to an external operation. The operation of updating the stored content and the operation of supplying a signal corresponding to the all black state generated by the all black signal generating means to the circuit for generating the image light of the image light projection mechanism in place of the image signal And the difference between the output value of the optical sensor and the stored value in the storage means is the component by the image projection light. The rear projection type image display device according to claim 2, further comprising separation processing means for obtaining each value.

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