WO2011092807A1

WO2011092807A1 - Projection type display device and method of controlling projection type display device

Info

Publication number: WO2011092807A1
Application number: PCT/JP2010/051032
Authority: WO
Inventors: タンテイミョー
Original assignee: Ｎｅｃディスプレイソリューションズ株式会社
Priority date: 2010-01-27
Filing date: 2010-01-27
Publication date: 2011-08-04

Abstract

Disclosed is a projection type display device comprising a reflection type image forming element (130), provided with a plurality of micro-mirrors actuated either ON or OFF in accordance with the video signal in one frame, which reflects the illumination from the ON actuated micro-mirrors and forms a projection image; a transmission type panel (14), configured to have variable transmissivity, which transmits OFF light from the OFF actuated micro-mirrors and outputs said OFF light as return light; a light source (110); an optical element (150) which irradiates onto the reflection type image forming element (130) a uniform distribution of the light that results from focusing the return light and the light from the light source; and a control unit (20) which stores a predetermined standard value as an initial value, compares the standard value and the absolute value of the difference in the luminance of the OFF light between the current frame and the next frame, determines the luminance of the OFF light in the next frame in order for the absolute value to become smaller than the standard value if the absolute value is larger than the standard value, and in order to obtain return light of the determined luminance, changes the transmissivity of the transmission type panel (14) and updates the standard value to a value based on the return light in the next frame.

Description

Projection display device and control method of projection display device

The present invention relates to a projection display device and a method for controlling the projection display device.

As one of the projection display devices, a digital light processing (DLP: registered trademark) projection display device is known. A configuration of a DLP projection display apparatus will be described. FIG. 1 is a block diagram showing a configuration example of a related projection display apparatus.

As shown in FIG. 1, the projection display apparatus includes an optical engine 100 and a control unit 200. The optical engine 100 includes a lamp 110 serving as a light source, a lens 120 that collects light from the lamp 110, a color wheel 140, a rod integrator 150, a reflective image forming element 130, and a reflective image forming element 130. A projection lens 160 that projects the reflected light onto the screen and an absorber (absorber) 170 that absorbs the light that is not projected onto the screen are included.

The control unit 200 includes an image signal input unit 230, an image signal processing unit 210, and a color wheel driving circuit 250. The image signal processing unit 210 includes a frame memory 211 and a scaling / gamma correction unit 215.

1 is provided with a digital micromirror device (DMD: registered trademark) element which is a kind of image forming element.

The DMD element has a configuration in which hundreds of thousands or more of micromirrors are arranged in a matrix on a rectangular plane. One pixel in one frame image corresponds to one micromirror. The micromirror operates in either ON or OFF according to a video signal including an ON / OFF signal that is a signal for instructing ON or OFF, and changes the direction of the mirror depending on whether it is ON or OFF.

The light incident on the micro mirror that is turned on is reflected by the micro mirror and sent to the projection lens 160. Hereinafter, the light reflected by the ON-operation micromirror is collectively referred to as ON light. The light incident on the micro mirror that is turned off is reflected by the micro mirror and sent to the absorber 170. Hereinafter, the light reflected by the micromirror that is turned off is collectively referred to as OFF light. ON / OFF of the micromirror is modulated by a pulse width modulation method based on the ON / OFF signal of the video signal.

In the color wheel 140, an area sandwiched between the outer periphery of the disk and a concentric circle on the center side of the disk is divided into three parts by a line passing through the central axis so that the center angle of the disk is equal. Each of the three divided parts is provided with a color filter for each of the three primary colors consisting of red (R), green (G), and blue (B). The color wheel 140 rotates in accordance with the control of the color wheel driving circuit 250 and irradiates the rod integrator 150 with the white light from the lamp 110 divided into the three primary colors in terms of time.

In the following, the case where the color of the filter provided on the color wheel 140 is three primary colors will be described. However, the color is not limited to the three primary colors, and may be four colors obtained by adding white to the three primary colors.

The rod integrator 150 is an optical element that irradiates the reflective image forming element 130 with light incident from the color wheel 140 in a uniform illuminance distribution.

The image signal input unit 230 is continuously input with a video signal that is a signal related to one frame of video, and a vertical synchronizing signal (Vsync) / horizontal synchronizing signal (Hsync) (in the figure, “ When a synchronization signal composed of “V / Hsync” is input, the input signal is decoded, converted from an analog signal to a digital signal, and the digitized signal is transmitted to the image signal processing unit 210.

The scaling / gamma correction unit 215 is configured to correct an error in scaling and video brightness for matching the video size of the video signal to the size of the DMD element with respect to the video signal received from the image signal input unit 230. A video signal that has been subjected to gamma correction is generated. The video signal includes an ON / OFF signal corresponding to each of the three primary colors, and the pulse width of the ON / OFF signal corresponds to color information indicating the gradation information. The scaling / gamma correction unit 215 transmits the generated video signal to the frame memory 211 one video at a time in synchronization with the synchronization signal.

The scaling / gamma correction unit 215 transmits a color filter synchronization signal indicating the color field switching timing of the color wheel 140 to the color wheel driving circuit 250 based on the vertical synchronization signal received from the image signal input unit 230. The color field is a period in which the color wheel 140 is irradiated with light from one of the three primary colors in one frame period.

The color wheel driving circuit 250 rotates the color wheel 140 in accordance with the color filter synchronization signal received from the image signal processing unit 210.

The frame memory 211 temporarily stores a video signal of one frame received from the scaling / gamma correction unit 215, and turns on / off each micromirror according to the color information of the video signal, the vertical synchronization signal, and the horizontal synchronization signal. An OFF signal is transmitted to the reflective image forming element 130.

The operation of the projection display device described above will be described.

When the video signal and the synchronization signal are input from the outside via the image signal input unit 230, the image signal processing unit 210 converts the video signal into a video signal that matches the size and color of the image to be projected. The micromirror ON / OFF signal corresponding to the signal is transmitted to the reflective image forming element 130 in accordance with the synchronization signal via the frame memory 211 for each frame. In addition, the image signal processing unit 210 supplies a color filter synchronization signal to the color wheel driving circuit 250.

The color wheel driving circuit 250 controls the rotation of the color wheel 140 according to the color filter synchronization signal, so that the light of the white light source is temporally divided into three primary colors, and the reflective image forming element 130 is passed through the rod integrator 150. Is irradiated.

When an ON / OFF signal is input from the image signal processing unit 210 to the reflective image forming element 130, each micromirror operates ON or OFF according to the ON / OFF signal. Of the light irradiated to the reflective image forming element 130, the light reflected by the micromirror that is turned on is sent to the projection lens 160, and the light reflected by the micromirror that is turned off is absorbed by the absorber 170. The light sent to the projection lens 160 is projected on the screen, and an image corresponding to the video signal is displayed on the screen.

In the projection display apparatus shown in FIG. 1, the OFF light reflected by the reflective image forming element 130 is absorbed by the absorber 170. The absorber 170 absorbs the OFF light, and converts the energy of the OFF light into heat and releases it. One example is disclosed in Japanese Patent Application Laid-Open No. 2004-163876 (hereinafter referred to as Patent Document 1).

As another method, a configuration in which an air-cooled radiator (heat radiating plate) is provided on the light absorbing plate in order to improve the heat radiating property of the light absorbing plate is disclosed in Japanese Patent Application Laid-Open No. 2008-292953 (hereinafter referred to as Patent Document 2). It is disclosed in the following. Furthermore, a configuration using a liquid-cooled radiator is disclosed in Japanese Unexamined Patent Application Publication No. 2007-127856 (hereinafter referred to as Patent Document 3).

In any of the methods disclosed in Patent Documents 1 to 3, OFF light is processed as heat, and energy of OFF light is wasted.

In contrast to the fact that the OFF light has been wasted, a method for effectively using the OFF light has been studied. An example of a projection television that can use the OFF light is disclosed in Japanese Patent Laid-Open No. 2002-287250 ( Hereinafter, it is disclosed in Patent Document 4).

In the technique disclosed in Patent Document 4, as shown in FIG. 2 of this document, OFF light reflected by the light receiving plane 3 of the optical deflector 400 is received by the mirror 7 and returned to the light receiving plane 3, and reflected by the light receiving plane 3. To return to the vicinity of the light emitting point of the light source. In this way, the intensity of light applied to the light receiving plane 3 is increased by reciprocating the OFF light in the propagation path of the light source → the light receiving plane 3 → the mirror 7 → the light receiving plane 3 → the light source.

Further, Patent Document 4 defines an average ON rate that indicates an average ratio of ON light in one frame, and discloses a graph that indicates the relationship between the intensity of light irradiated on the light receiving plane 3 and the average ON rate. . From this graph, it can be seen that the smaller the average ON rate, the greater the intensity of the light that reciprocates the OFF light and joins the light of the light source.

It is necessary to prevent the screen brightness from fluctuating with changes in the average ON rate. For this reason, Patent Document 4 adopts a CRT television technology that limits the luminance of a high average luminance image exceeding the normal luminance level, determines a predetermined value Q corresponding to the normal average luminance level, and determines the average ON rate. Is less than Q, the light intensity applied to the light receiving plane 3 is controlled to be constant, and when the average ON rate is greater than Q, the intensity of the light obtained by reciprocating the OFF light along the propagation path. Control to maximize

The OFF light that is not used in the projected image depends on the content of the projected image, and the luminance changes from frame to frame. Therefore, if the luminance difference between frames is large, the blinking (flickering) phenomenon becomes noticeable. . When the flickering phenomenon becomes prominent, flicker is perceived by a person viewing the image, and it is difficult to reuse OFF light as a light source.

In the technique disclosed in Patent Document 4, the flickering phenomenon is not taken into consideration, and when the average ON rate is less than Q, even if the flickering phenomenon is suppressed, the average ON rate is larger than Q. May cause a noticeable flickering phenomenon, in which case the person viewing the image will perceive the flicker.

One of the objects of the present invention is to provide a projection display apparatus that suppresses the occurrence of flicker and can use OFF light that is not used for projection as light of a light source.

A projection display device according to one aspect of the present invention includes a plurality of micromirrors arranged in a matrix that operates either on or off in response to a video signal indicating one frame of video, and illuminates the micromirror. Reflective image forming element that forms a projected image by the reflected light reflected by the ON-operation micromirror, and the transmittance can be changed, and the OFF light that is reflected from the OFF-operation micromirror is transmitted. Optics that illuminates the reflective image forming element as illumination light with uniform illuminance distribution, by making the transmission panel that emits the feedback light, the light source, and the light collected from the feedback light and the light from the light source. The device includes a memory that stores a predetermined reference value as an initial value, and compares the absolute value of the difference in brightness of the OFF light between the current frame and the next frame with the reference value. Is larger than the reference value, the brightness of the OFF light of the next frame is obtained, and the transmittance of the transmissive panel is switched to obtain the feedback light of the obtained brightness, and in the next frame, the absolute value is smaller than the reference value. A control unit that calculates a new reference value based on the feedback light and stores the new reference value in a memory.

In addition, a control method for a projection display apparatus according to one aspect of the present invention includes a plurality of micromirrors arranged in a matrix that operates either ON or OFF in response to a video signal indicating one frame of video. Reflective image forming element that forms a projection image with reflected light reflected by the micromirrors that are turned on for illumination light that illuminates the micromirrors, and the reflected light of the micromirrors that are turned off and configured to change the transmittance. Reflection-type image formation as illumination light by making the transmissive panel that transmits OFF light and emitting it as feedback light, the light source, and the light collected from the feedback light and light from the light source, making the illuminance distribution uniform A method for controlling a projection display apparatus having an optical element for irradiating an element and a memory for storing a reference value set in advance as an initial value, wherein the current frame and the next frame are turned off. When the absolute value of the difference in brightness is compared with the reference value, and the absolute value is greater than the reference value, the brightness of the OFF light of the next frame in which the absolute value is smaller than the reference value is obtained, and the obtained brightness In order to obtain the feedback light, the transmittance of the transmissive panel is switched, a new reference value is calculated based on the feedback light in the next frame, and the new reference value is stored in the memory.

FIG. 1 is a block diagram showing a configuration example of a related projection display apparatus. FIG. 2 is a block diagram illustrating a configuration example of the projection display apparatus according to the first embodiment. FIG. 3 is a view for explaining the operation of the optical engine shown in FIG. FIG. 4 is a diagram for explaining a method of combining the light from the lamp and the OFF light. FIG. 5 is a block diagram for explaining the configuration of the control unit shown in FIG. FIG. 6 is a flowchart showing the procedure of the OFF light adjustment method for suppressing flicker. FIG. 7 is a graph showing the utilization ratio of the primary light quantity. FIG. 8 is a block diagram illustrating a configuration example of the projection display apparatus according to the second embodiment. FIG. 9 is a diagram for explaining the configuration of the control unit shown in FIG.

(First embodiment)
The configuration of the projection display device of this embodiment will be described.

FIG. 2 is a block diagram showing an example of the configuration of the projection display device of the present embodiment. The same components as those shown in FIG. 1 are denoted by the same reference numerals, and detailed description thereof is omitted.

As shown in FIG. 2, the projection display device of the present embodiment includes an optical engine 10 and a control unit 20. The optical engine 10 includes a configuration obtained by removing the absorber 170 from the optical engine 100 illustrated in FIG. 1, an OFF light feedback unit 11, and a light merging unit 30. The optical confluence unit 30 includes reflection mirrors 31 and 32 and a condensing lens 35.

The OFF light feedback unit 11 includes a condenser lens 12 that condenses the OFF light, a transmissive liquid crystal panel 14, and an optical fiber 13 that guides the light focused by the condenser lens 12 to the liquid crystal panel 14. The optical path until the OFF light reflected by the reflective image forming element 130 reaches the light combining unit 30 via the OFF light feedback unit 11 corresponds to a feedback path for returning the OFF light to the light source side.

It should be noted that a cooling mechanism for absorbing heat may be provided in the optical fiber 13 and the liquid crystal panel 14 when heat is released when the intensity of OFF light attenuates in the return path. In the present embodiment, the cooling mechanism is not shown in the drawing.

As shown in FIG. 2, the control unit 20 includes an image signal input unit 230, an image signal processing unit 21, a color wheel drive circuit 25, and a liquid crystal panel control unit 27. The image signal processing unit 21 includes a current image frame memory 212, a next image frame memory 213, and a scaling / gamma correction unit 215.

The image signal input unit 230 is connected to the scaling / gamma correction unit 215 of the image signal processing unit 21 through a signal line. The scaling / gamma correction unit 215 is connected to the color wheel driving circuit 25 through a signal line. The liquid crystal panel control unit 27 is connected to each of the liquid crystal panel 14, the current image frame memory 212 and the next image frame memory 213 of the image signal processing unit 21, and the color wheel driving circuit 25 via signal lines.

The color wheel drive circuit 25 controls the rotation of the color wheel 140 according to the color filter synchronization signal received from the scaling / gamma correction unit 215 and transfers the color filter synchronization signal to the liquid crystal panel control unit 27.

Note that a power supply circuit (not shown) for supplying power to the lamp 110 and the control unit 20 is not directly related to the features of the present invention, and thus description thereof is omitted.

Next, the configuration of the optical engine 10 shown in FIG. 2 will be described in detail. In the present embodiment, when the lamp 110 is a primary light source, the OFF light is used as the light of the secondary light source.

FIG. 3 is a block diagram for explaining the operation of the optical engine shown in FIG. 2, and FIG. 4 is a diagram for explaining a method of joining the light from the lamp and the OFF light.

As shown in FIG. 3, the reflection mirror 31 is disposed at a position where the OFF light transmitted through the liquid crystal panel 14 of the optical engine 10 is incident. Hereinafter, the light after the OFF light has transmitted through the liquid crystal panel 14 is referred to as feedback light. The mirror surface of the reflection mirror 31 is inclined by about 45 degrees with respect to the optical axis of the return light, reflects the return light and irradiates the condenser lens 35.

The reflection mirror 32 is disposed at a position where light emitted from the lamp 110 and focused by the lens 120 is incident. The mirror surface of the reflection mirror 32 is inclined about 45 degrees with respect to the optical axis of the light from the lens 120, and reflects incident light to irradiate the condenser lens 35.

The condenser lens 35 is disposed between the reflection mirror 31 and the reflection mirror 32 and the color wheel 140, and collects the light reflected by the reflection mirror 31 and the light reflected by the reflection mirror 32 to the color wheel 140. Irradiate.

As shown in FIG. 3, the return light reaches the reflection mirror 31 via the condenser lens 12, the optical fiber 13 and the liquid crystal panel 14. On the other hand, the light emitted from the lamp 110 and collected by the lens 120 reaches the reflection mirror 32. Then, as shown in FIG. 4, the optical axes of the light from the lamp 110 and the feedback light are adjusted in parallel by the reflecting mirror 31 and the reflecting mirror 32, and these lights are converged by being joined by the condenser lens 35. Then, the color wheel 140 is irradiated as light from one light source.

In this way, in this embodiment, the condensing lens 12 is provided instead of the absorber 170 shown in FIG. 1, and the OFF light focused by the condensing lens 12 is guided to the liquid crystal panel 14 by the optical fiber 13. The feedback light after passing through 14 is combined with the light from the lamp 110 via the reflection mirror 31 and the condenser lens 35 and irradiated to the color wheel 140.

So far, the configuration of the optical engine 10 for returning the OFF light and using it as the light of the secondary light source has been described.

If the luminance when the OFF light reflected by the reflective image forming element 130 is uniformly irradiated to a predetermined area is defined as the luminance of the OFF light in this embodiment, the luminance of the OFF light is the content of the image to be projected or It varies greatly depending on the ON / OFF status of the micromirror. For example, when the brightest all-white screen is projected, there is no OFF light. Conversely, when the all-black screen is projected, all the light supplied from the lamp 110 is OFF light. Since the brightness of the OFF light varies greatly depending on the projected image, it is necessary to appropriately adjust the amount of OFF light to be returned.

The control unit 20 adjusts the amount of the return light in accordance with the timing of the color filter synchronization signal based on the brightness of the OFF light of two consecutive frames. Hereinafter, the configuration of the control unit 20 for using OFF light having different luminance for each frame as stable light will be described in detail. In the present embodiment, the same control is performed for each of the three primary colors. Here, the case of one color will be described.

FIG. 5 is a block diagram for explaining the configuration of the control unit shown in FIG.

The current image frame memory 212 shown in FIG. 5 corresponds to the frame memory 211 shown in FIG. 1, and the image signal processing unit 21 has a configuration in which a next image frame memory 213 is added to the image signal processing unit 210 shown in FIG. It is. Currently, the video signal of the current frame image that is the image of the frame to be projected is stored in the current image frame memory 212, and the video signal of the next frame image that is the image of the frame to be projected next is the next image frame memory 213. Stored in

When the ON / OFF signal based on the video signal of the current frame image is transmitted to the reflective image forming element 130, the video signal of the next frame image is overwritten in the current image frame memory 212, and the video signal of the next frame is further transferred to the next frame. The image frame memory 213 is overwritten. By increasing the frame memory in the image signal processing unit from one screen to two screens, video signals of two consecutive frames of video are sequentially stored in the frame memory.

As shown in FIG. 5, the liquid crystal panel control unit 27 includes a luminance comparison unit 271 that compares the OFF light luminances of two consecutive frames, and a synchronization / adjustment circuit 272 that controls luminance adjustment and luminance adjustment timing. A memory 273 that stores a reference value for determining whether or not to perform brightness adjustment, a decoder 274 that supplies a synchronization signal to the synchronization / adjustment circuit 272, and a liquid crystal drive circuit 275 that controls the transmittance of the liquid crystal panel 14.

The memory 273 is a nonvolatile memory. The memory 273 calculates the luminance for determining the luminance of the feedback light based on the reference value as a criterion for determining whether or not to adjust the luminance of the OFF light to be fed back, and the luminance difference between the OFF lights of two consecutive frames. The formula, the transmittance calculation formula indicating the relationship between the brightness of the feedback light and the transmittance of the liquid crystal panel 14, and the reference value calculation formula for obtaining the reference value corresponding to the brightness of the feedback light are registered in advance. .

Here, a reference value that is a criterion for determining whether or not to adjust the brightness of the OFF light and a reference value calculation formula will be described.

The reference value serving as a criterion for determining whether or not to adjust the brightness of the OFF light is a limit brightness difference that humans can recognize as flicker, and a brightness difference smaller than the reference value is not recognized as flicker by humans. This reference value is a limit value at which the human eye starts to perceive blinking due to a luminance difference that occurs every frame period (for example, 16.67 ms when the frame frequency is 60 Hz) as “flickering”. According to the Ferry-Porter law, it varies depending on the luminance of the target. Here, the visual target is a projected image.

According to the Ferry-Porter law, if the luminance of the target is I, the critical fusion frequency (CFF), which is the limit frequency at which a person can detect flicker, is expressed by the following equation.

CFF = a · log I + b (1)
However, a and b in Formula (1) are constants.

From equation (1), the CFF increases as the luminance increases, and the CFF decreases as the luminance decreases. From this, the relationship between the luminance and the reference value is as follows. As the luminance increases, the flicker becomes conspicuous and the reference value decreases. On the other hand, when the luminance is reduced, the flicker is less noticeable and the reference value is increased. The reference value calculation formula described above is a formula for obtaining the reference value from the brightness of the feedback light based on the relationship between the brightness and the reference value.

Actually, whether or not there is flicker is determined by whether or not a person feels “flickering” by looking at the projected image, so the brightness of the light collected from the return light and the lamp and the reference value A relational expression is obtained. The above-described reference value calculation formula is a relational expression between the brightness of the light collected from the feedback light and the lamp light and the reference value, and the lamp light is made constant, and the lamp light is subtracted from the collected light. This is an expression showing the relationship between the luminance of the remaining feedback light and the reference value.

The luminance calculation formula registered in advance in the memory 273 will be described later.

The luminance comparison unit 271 shown in FIG. 5 includes a decoder (not shown) and a comparator (not shown). The decoder converts the video signal stored in each of the current image frame memory 212 and the next image frame memory 213 into a value indicating the brightness of the OFF light as follows. Based on the relationship that the brightness of the OFF light is proportional to the number of micromirrors that are turned off during one frame period, an equation for obtaining the brightness of the OFF light from the number of micromirrors that are turned off is stored in advance in the decoder circuit. The decoder reads out the number of micromirrors operating OFF from the video signal for one frame, and calculates the brightness of the OFF light based on the number.

A comparator (not shown) of the luminance comparison unit 271 compares the luminances of the two OFF lights calculated by the decoder, and calculates the absolute value of the luminance difference between the two OFF lights. Then, the comparator transmits luminance information including information on the luminance of OFF light of each of the two consecutive frames and information on the absolute value of the luminance difference between the two OFF lights to the synchronization / adjustment circuit 272.

When the decoder 274 receives the color filter synchronization signal from the color wheel driving circuit 25, the decoder 274 transmits a color filter synchronization signal for notifying the timing of the color field of the color to be adjusted to the synchronization / adjustment circuit 272.

When the liquid crystal driving circuit 275 receives the adjustment signal including the transmittance information of the liquid crystal panel 14 and the color filter synchronization signal from the synchronization / adjustment circuit 272, the control signal including the transmittance information in accordance with the color filter synchronization signal. Is transmitted to the liquid crystal panel 14 to switch the transmittance of the liquid crystal panel 14. Here, the color filter synchronization signal is information indicating the timing of changing to the transmittance included in the adjustment signal.

Next, the configuration of the synchronization / adjustment circuit 272 will be described.

FIG. 6 is a flowchart showing a procedure of an OFF light adjustment method for suppressing flicker. The procedure described here is also performed for each of the three primary colors. However, since the description is redundant, the description will be given for the case of one color. A reference value serving as a criterion for determining whether or not to adjust the OFF light luminance is T, the OFF light luminance of the current frame is P, and the OFF light luminance of the next frame is N. The luminance information includes information of | P−N |, P, and N.

When the synchronization / adjustment circuit 272 receives the brightness information from the brightness comparison unit 271, the synchronization / adjustment circuit 272 reads T from the memory 273 and compares | PN | with T (step 1001). When the absolute value of the difference between P and N is smaller than the T value, the synchronization / adjustment circuit 272 transmits an adjustment signal including information indicating that the transmittance of the liquid crystal panel 14 is maintained as it is to the liquid crystal drive circuit 275. (Step 1002). Alternatively, the synchronization / adjustment circuit 272 does not transmit an adjustment signal to the liquid crystal drive circuit 275.

In step 1001, if the absolute value of the difference between P and N is equal to or greater than the T value, the synchronization / adjustment circuit 272 compares the magnitudes of P and N (step 1003). When P is smaller than N, it is necessary to reduce the transmittance of OFF light in the liquid crystal panel 14 in order to make the absolute value of the difference between P and N smaller than the reference value. The synchronization / adjustment circuit 272 refers to the luminance calculation formula registered in the memory 273 in order to make the absolute value of the difference between P and N smaller than the reference value, and the absolute value of the difference between P and N is the reference value. The maximum brightness of N that is less than Subsequently, the synchronization / adjustment circuit 272 obtains the transmittance of the liquid crystal panel 14 corresponding to the obtained luminance based on the transmittance calculation formula registered in the memory 273 and an adjustment signal including information on the obtained transmittance. Is transmitted to the liquid crystal driving circuit 275 (step 1004).

Thereafter, the synchronization / adjustment circuit 272 obtains a reference value for the luminance of the feedback light of the next frame from the reference value calculation formula, and registers the new reference value in the memory 273 to update the reference value. The reference value is updated because the brightness of the feedback light changes as the transmittance of the liquid crystal panel 14 changes. Therefore, the reference value calculation formula based on the Ferry-Porter law based on the brightness after the change of the feedback light This is because it is necessary to re-determine a reference value that satisfies the above.

When changing the brightness of the feedback light, the reference value is changed according to the brightness after the change of the feedback light, so that the OFF light is maximized against the change in the brightness of the feedback light of the images projected one after another. And the occurrence of flicker can be suppressed.

On the other hand, if P is larger than N in step 1003, it is necessary to increase the transmittance of OFF light in the liquid crystal panel 14 in order to make the absolute value of the difference between P and N smaller than the reference value. The synchronization / adjustment circuit 272 refers to the luminance calculation formula registered in the memory 273 in order to make the absolute value of the difference between P and N smaller than the reference value, and the absolute value of the difference between P and N is the reference value. The minimum brightness of N that is less than. Subsequently, the synchronization / adjustment circuit 272 obtains the transmittance of the liquid crystal panel 14 corresponding to the obtained luminance based on the transmittance calculation formula registered in the memory 273 and an adjustment signal including information on the obtained transmittance. Is transmitted to the liquid crystal driving circuit 275 (step 1005).

Thereafter, the synchronization / adjustment circuit 272 obtains a reference value for the luminance of the feedback light of the next frame from the reference value calculation formula, and registers the new reference value in the memory 273 to update the reference value.

Further, in

steps

1002, 1004, and 1005, the synchronization / adjustment circuit 272 transmits the color filter synchronization signal received from the decoder 274 to the liquid crystal drive circuit 275. By using the color filter synchronization signal as a switching timing for changing the transmittance of the liquid crystal panel 14, the transmittance of each color is adjusted to correspond to the period of the color field of each color.

Here, an example of the luminance calculation formula described above will be described.

The relationship between the light amount (F) of the return light after the OFF light passes through the liquid crystal panel 14 and the light amount (S) of the ON light is the light amount that is incident on the reflective image forming element 130 and supplied from the lamp 110. When the primary light quantity is used as a reference, the following formula F = (1−S) −LA−t (t) (2)
Can be expressed as

In Expression (2), L is an amount corresponding to the invariable loss in the return path including the optical fiber 13, the liquid crystal panel 14, and the reflection mirror 31. For example, if the optical fiber 13 having a loss of 20 dB / km or less in the visible light region and the liquid crystal panel 14 having a transmittance of 90% or more are used, the constant loss of the return path can be suppressed to 20% or less. A (t) is the amount corresponding to the variable loss due to the luminance adjustment of the synchronization / adjustment circuit 272, and is the amount of light shielded by the liquid crystal panel 14. A (t) is a parameter that is determined by the reference value calculation formula and changes for each frame. Here, A (t) is expressed as a function of time t because the frame changes at a constant period.

From Equation (2), the amount of OFF light in one frame is (1-S), and the value obtained by subtracting the amount lost in the feedback path from that value is {(1-S) -L}. If the light quantity of {(1-S) -L} is used as it is as the secondary light source, flicker may occur. Therefore, by subtracting A (t) from {(1-S) -L} so that flicker does not occur, the amount of light F transmitted through the liquid crystal panel 14 becomes {(1-S) -LA (t). }.

A luminance calculation formula obtained by replacing the light quantity of the formula (2) with the luminance is registered in the memory 273 in advance. When adjusting the brightness of the OFF light of the next frame, the synchronization / adjustment circuit 272 obtains the transmittance of the liquid crystal panel 14 corresponding to the brightness obtained from the brightness calculation formula from the transmittance calculation formula, and information on the transmittance Is sent to the liquid crystal drive circuit 275.

FIG. 7 is a graph showing the utilization ratio of the primary light quantity, and is a graph visually representing the expression (2). The initial reference value T may be an arbitrary value, but when the brightness of the feedback light and the brightness of the ON light coincide with each other, the value obtained from the reference value calculation formula is set as the initial T value. It is written as a point.

As shown in FIG. 7, the primary light quantity is classified into four types: ON light, feedback light, variable loss due to brightness adjustment, and invariant loss due to the feedback path. FIG. 7 shows that A (t) increases so that the brightness difference does not become larger than the reference value because the brightness due to the OFF light increases as the amount of OFF light increases.

Referring to FIG. 7, when OFF light is not used, almost the same amount of light as ON light was treated as a loss. According to the present embodiment, the lost feedback light can be used as a light source, and depending on the content of the projected image, the light loss can be reduced by up to about 50% (ON light) compared to the case where OFF light is not used. = 0).

In this way, by adjusting the transmittance of the liquid crystal panel 14 in accordance with the increase or decrease in the brightness difference of the OFF light between two consecutive frames, the amount of the OFF light that is used as the light source. The luminance change is maintained within the reference value. Further, the reference value is updated to a value corresponding to the brightness of the feedback light of the next frame. As a result, the OFF light luminance change between successive frames is suppressed within the reference value obtained from the reference value calculation formula, and the occurrence of the flickering phenomenon can be prevented.

Next, the operation of the projection display device of this embodiment will be described. The initial reference value registered in advance in the memory 273 is a value obtained from the reference value calculation formula when the luminances of the ON light and the feedback light match. Further, the case of one color among the three primary colors will be described.

The user connects an information processing apparatus (not shown) storing image data to be projected onto the screen to the projection display apparatus of the present embodiment with a cable. Subsequently, when the user activates the information processing apparatus and the projection display apparatus and turns on the power of the lamp 110, the light from the lamp 110 enters the condenser lens 35 via the lens 120 and the reflection mirror 32. The light condensed by the condenser lens 35 enters the reflective image forming element 130 via the color wheel 140 and the rod integrator 150.

When a user operates the information processing apparatus and inputs an instruction to send image data from the information processing apparatus to the projection display apparatus, a synchronization signal and a video signal of the image data are transmitted from the information processing apparatus to the image of the projection display apparatus. The signal is input to the signal input unit 230. Upon receiving the video signal and the synchronization signal from the image signal input unit 230, the image signal processing unit 21 receives the first frame (hereinafter referred to as the current frame) and the next frame (hereinafter referred to as the next frame). ) Are stored in the current image frame memory 212 and the next image frame memory 213, respectively. The image signal processing unit 21 transmits an ON / OFF signal based on the video signal stored in the current image frame memory 212 to the reflective image forming element 130 in accordance with the synchronization signal, so that the reflective image forming element 130 is transmitted. An image based on the video signal of the current frame by the ON light from is projected onto the screen, and the OFF light is projected onto the condenser lens 12.

The liquid crystal panel control unit 27 adjusts the brightness of the OFF light from the respective video signals of the current image frame memory 212 and the next image frame memory 213 while an image based on the video signal stored in the current image frame memory 212 is being projected. calculate. Further, the liquid crystal panel control unit 27 calculates the absolute value of the difference in luminance of OFF light between two successive frames of the current frame and the next frame. Subsequently, the liquid crystal panel control unit 27 determines whether it is necessary to adjust the brightness of the OFF light of the next frame in accordance with the procedure shown in FIG.

When the liquid crystal panel control unit 27 determines that the brightness of the OFF light of the next frame needs to be adjusted, the absolute value of the difference in the brightness of the OFF light of the two consecutive frames is smaller than the reference value, and the next frame is turned off. The luminance of light is obtained, and the transmittance of the liquid crystal panel 14 for obtaining feedback light of that luminance is obtained. Subsequently, the liquid crystal panel control unit 27 uses the color filter synchronization signal to match the start timing of the color field of the color filter of the color wheel 140 corresponding to the color information of the video signal of the next frame image. Is switched to the obtained transmittance. Thereafter, the liquid crystal panel control unit 27 obtains a reference value corresponding to the feedback light of the next frame and registers it in the memory 273.

When the image projected on the screen is switched from the current frame image to the next frame image, OFF light enters the liquid crystal panel 14 via the condenser lens 12 and the optical fiber 13. When the OFF light is transmitted through the liquid crystal panel 14 whose transmittance has been adjusted as described above, the feedback light that is the light that has passed through the liquid crystal panel 14 is reflected by the reflection mirror 31, and the lamp 110 is reflected by the condenser lens 35. Merge with the light.

The light obtained by combining the return light and the light from the lamp 110 enters the reflective image forming element 130 via the color wheel 140 and the rod integrator 150, and is used for projection of the next frame image switched from the current frame image.

As in this embodiment, when ON light expresses a color gradation in the PWM method, the pulse time of the ON operation of the micromirror is about several tens of μs in the case of 256 gradations. Further, the time required for the OFF light reflected by the reflective image forming element 130 to return to the reflective image forming element 130 again through the return path is several considering the general size and speed of light of the projection display device. It is about ns. Since OFF light generated in the time of several tens of μs from the start of projection of the next frame image is irradiated to the reflective image forming element 130 via the feedback path in several ns, for example, one frame period of 16.67 ms is This is a sufficient time to use the OFF light as a secondary light source for projecting an image using a video signal of the same frame as the frame that generates the OFF light.

The operation in the processing of step 1004 and step 1005 of the flowchart shown in FIG. 6 will be described in detail.

In step 1003, when the brightness of the OFF light of the current frame is smaller than the OFF light of the next frame, the next frame image projected on the screen becomes an image darker than the current frame image. When the next frame image is projected, the brightness of the OFF light becomes larger than that in the case of the current frame image. However, the liquid crystal panel control unit 27 reduces the transmittance of the liquid crystal panel 14 (step 1004), so that the second order The brightness of the light source is suppressed, and the person viewing the projected image on the screen does not feel flicker.

On the other hand, when the brightness of the OFF light of the current frame is larger than the OFF light of the next frame in step 1003, the next frame image projected on the screen becomes an image brighter than the current frame image. When the next frame image is projected, the brightness of the OFF light becomes smaller than that in the case of the current frame image, but the liquid crystal panel control unit 27 increases the transmittance of the liquid crystal panel 14 (step 1005), so that the second order The brightness of the light source increases, and the person viewing the projected image on the screen does not feel flicker.

In this way, by adjusting the brightness of the OFF light within the reference value based on the reference value calculation formula for each frame, the flickering phenomenon due to the change in the brightness of the OFF light between frames is suppressed to an inconspicuous level. , Do not let the person who sees the image feel flicker.

As described in the case of one color in the description of the configuration and operation described above, for each color, the luminance comparison unit 271, the synchronization / adjustment circuit 272, and the liquid crystal driving circuit 275 perform the color filter synchronization signal based on the color information of the video signal. The transmittance of the liquid crystal panel 14 is adjusted at the timing of the color field of the color to be adjusted.

The projection display apparatus according to the present embodiment effectively reuses the OFF light that is not used when the image is modulated by the DMD element as the secondary light source, compared with the case where the OFF light is not used. The light use efficiency of the projector can be improved and a bright image can be provided.

In addition, the light obtained by returning the OFF light as a secondary light source has an effect of improving the brightness of the projected image. If the brightness of the primary light source is lowered by that amount, the life of the primary light source is further increased. The length can be increased, and the power consumption can be substantially reduced. For this reason, it is possible to increase the brightness of the projected image and to save energy in the power supplied to the projection display device.

Select a power saving mode for a projection display device that is preset so that a power saving mode that makes the power supplied to the lamp 80 to 90% normal is selectable, and then apply the control method of this embodiment This not only extends the life of the lamp, but also improves the brightness of the image projected on the screen. As a result, the life of the light source can be improved and the power can be saved.

Also, by using OFF light as the secondary light source, an effect of improving the contrast ratio and brightness of the image can be obtained.

In the DLP projection display apparatus, it has been considered extremely difficult to use OFF light whose luminance changes from frame to frame. However, by introducing the method of using OFF light described in this embodiment, the OFF light is turned off. It is expected that the light use efficiency will be about 1.5 times that in the case where light is not used.

Briefly explain why the light usage efficiency is expected to be about 1.5 times. Assuming that the light incident on the DMD element is 100%, when the OFF light is not used, the light that is effectively used is only 50%, and the remaining 50% is lost as the OFF light. In this embodiment, if the remaining 80% obtained by subtracting 20% of the constant loss from 100% is used to the maximum, the light utilization efficiency is about 1.6 times from the calculation result of 0.5 × 0.8. Can be estimated. In consideration of the variable loss at the time of adjustment for suppressing the flickering phenomenon in this estimated value, the light use efficiency is expected to be about 1.5 times.

(Second Embodiment)
In the present embodiment, the power of the lamp is controlled in accordance with the change in the brightness of the OFF light.

FIG. 8 is a block diagram showing an example of the configuration of the projection display device of the present embodiment. In addition, the same code | symbol is attached | subjected about the structure similar to the projection type display apparatus of 1st Embodiment, and the detailed description is abbreviate | omitted.

As shown in FIG. 8, the control unit 20a of the projection display device according to the present embodiment is provided with a panel / lamp control unit 51 instead of the liquid crystal panel control unit 27 of the projection display device according to the first embodiment. The lamp driving circuit 52 is further added. The panel / lamp controller 51 is connected to the lamp driving circuit 52 through a signal line.

FIG. 9 is a diagram for explaining the configuration of the control unit shown in FIG.

Since the method of extending the life varies depending on the type of lamp such as LED, LASER, halogen lamp, metal halide lamp, xenon lamp, etc., each lamp type corresponds to the brightness difference of OFF light of two consecutive frames. A power calculation formula for determining supply power is registered in the memory 273 in advance.

The synchronization / adjustment circuit 272 operates in the same manner as in the first embodiment, obtains power supplied to the lamp based on a preset lamp power calculation formula, and includes power information including information on power supplied to the lamp. The color filter synchronization signal is transmitted to the lamp driving circuit 52.

When the lamp driving circuit 52 receives the color filter synchronization signal and the power information from the panel / lamp control unit 51, the lamp driving circuit 52 determines the power to the lamp 110 according to the power information, and matches the determined power with the color field of the color filter synchronization signal. Supplied to the lamp 110.

In the present embodiment, the power supplied to the lamp is controlled according to the type of the lamp as the brightness of the OFF light changes, so that the life of the primary light source is further improved and the power is saved. Promoted.

In the first and second embodiments, the case where there is one reflective image forming element 130 has been described. However, the projection display apparatus provided with the reflective image forming elements 130 corresponding to the three primary colors. In addition, the present invention may be applied. In this case, instead of the color wheel driving circuit 25 and the color wheel 140, filters corresponding to the three primary colors may be provided in the respective reflective image forming elements 130. Since an example of an apparatus similar to a projection display apparatus provided with reflective image forming elements corresponding to the three primary colors is disclosed in Patent Document 4, detailed description thereof is omitted here.

In addition, as a method of condensing the OFF light of the reflective image forming element 130 and the light from the lamp 110 and irradiating the color wheel 140, the method using the OFF light feedback unit 11 and the light confluence unit 30 has been described. The OFF light feedback unit 11 and the optical merging unit 30 are an example of the method, and other methods may be used.

In addition, although the case where the video signal input from the outside is an analog signal has been described, it may be a digital signal. In this case, the image signal input unit 230 may not be provided with a function for converting an analog signal into a digital signal.

Although the present invention has been described with reference to the embodiments and examples, the present invention is not limited to the above embodiments and examples. Various changes that can be understood by those skilled in the art can be made to the configuration and details of the present invention within the scope of the present invention.

DESCRIPTION OF SYMBOLS 10 Optical engine 11 OFF light feedback part 14 Liquid crystal panel 20 Control part 21 Image signal processing part 25 Color wheel drive circuit 27 Liquid crystal panel control part 30

Optical confluence part

31, 32 Reflection mirror 35 Condensing lens 110 Lamp 120 Lens 130 Reflective image Forming element 140 Color wheel 150 Rod integrator 160 Projection lens

Claims

A plurality of micromirrors arranged in a matrix that operates either ON or OFF according to a video signal indicating one frame of video is provided, and illumination light that illuminates the micromirror is reflected by the micromirror that is ON A reflective image forming element that forms a projected image by reflected light; and
A transmissive panel configured to change the transmittance and transmit the OFF light, which is the reflected light of the micromirror in the OFF operation, and emit it as feedback light;
A light source;
An optical element that receives the condensed light of the feedback light and the light from the light source, irradiates the reflective image forming element as the illumination light with a uniform illuminance distribution;
A memory for storing a predetermined reference value as an initial value, and comparing the absolute value of the difference in luminance of OFF light between the current frame and the next frame with the reference value, and the absolute value is greater than the reference value In this case, the absolute value is smaller than the reference value, the brightness of the OFF light of the next frame is obtained, the transmittance of the transmissive panel is switched to obtain the feedback light having the obtained brightness, and the A control unit that calculates a new reference value based on the feedback light in the next frame and stores the new reference value in the memory;
A projection display device.
The projection display device according to claim 1,
The controller is
When switching the transmittance of the transmissive panel, if the brightness of the OFF light of the current frame is smaller than the brightness of the OFF light of the next frame, the transmittance of the transmissive panel is lowered and the OFF light of the current frame is reduced. A projection display device that increases the transmittance of the transmissive panel when the luminance is larger than the luminance of OFF light of the next frame.
The projection display device according to claim 1 or 2,
The controller is
The projection display apparatus, wherein the new reference value is set to a smaller value as the luminance of the feedback light in the next frame increases.
The projection display device according to any one of claims 1 to 3,
A color wheel that includes a plurality of color filters and that irradiates the optical element through the plurality of color filters by dividing the period of the one frame into time by collecting the light collected from the feedback light and the light from the light source Is further provided,
The memory stores a reference value corresponding to each color of the plurality of colors as an initial value,
The video signal includes an ON / OFF signal corresponding to each of the plurality of colors, which is a signal for instructing ON or OFF for each micromirror,
The controller is
The brightness of the OFF light and the ON / OFF of the video signal of the next frame calculated by the ON / OFF signal of the video signal of the current frame corresponding to the color of the light emitted from the color wheel to the optical element. The absolute value of the difference with the brightness of the OFF light calculated by the OFF signal is compared with the reference value, and based on the result, the transmittance of the transmissive panel is switched and the new reference value is calculated. A projection display device.
A plurality of micromirrors arranged in a matrix that operates either ON or OFF according to a video signal indicating one frame of video is provided, and illumination light that illuminates the micromirror is reflected by the micromirror that is ON A reflective image forming element that forms a projected image by reflected light, a transmissive panel that is configured so that the transmittance can be changed, and that transmits OFF light, which is reflected light of the micromirror in the OFF operation, and emits it as feedback light; A light source, an optical element that receives light collected from the feedback light and the light from the light source, irradiates the reflective image forming element as the illumination light with a uniform illuminance distribution, and an initial value A control method for a projection display device having a memory for storing a predetermined reference value,
Comparing the absolute value of the difference in brightness of the OFF light between the current frame and the next frame and the reference value
If the absolute value is larger than the reference value, obtain the brightness of the OFF light of the next frame, the absolute value is smaller than the reference value,
The transmittance of the transmissive panel is switched in order to obtain the feedback light having the calculated luminance, and a new reference value is calculated based on the feedback light in the next frame, and the new reference value is stored in the memory. And control method of projection display device.