Projection video display

A projection video display that projects video image suppresses deterioration of its quality which is attributed to a change in an optical path of the video image. A video signal generator performs control such that a second subframe in an N-th frame in a left-eye image is displayed on DMDs and then a second subframe in an N-th frame in a right-eye image is displayed on the DMDs. Furthermore, the video signal generator performs control such that a displayed location is not changed on a screen and the same types of subframes are displayed at the time when frames are switched.

RELATED APPLICATIONS

This application claims the benefit of Japanese Application No. 2015-197267, filed on Oct. 5, 2015, the disclosure of which is incorporated by reference herein.

BACKGROUND

1. Technical Field

The present disclosure relates to a projection video display that has a three-dimensional (3D) video display function and employs a pixel shift technique to project high-density video.

2. Description of Related Art

Some conventionally known projection video displays have a wobbling element in order to achieve high-resolution, high-quality video. A wobbling element is an element that controls an optical path of video image generated by a video generator such as a liquid crystal display element, thus changing a location at which the video image is displayed on the projection surface.

With the above wobbling element, the projection video display can provide high-resolution video even when receiving a video input signal whose resolution is higher than that of the video generator (e.g., refer to Unexamined Japanese Patent Publication No. 2006-047414).

SUMMARY

A projection video display of the present disclosure includes a video generator, an optical system, an optical path changer, and a controller. The video generator generates video image. The optical system projects the video image onto a projection surface. The optical path changer is disposed in an optical path of the video image and changes a location at which the video image is displayed on the projection surface. The controller controls the video generator and the optical path changer, based on a video input signal. The controller generates a left-eye video signal and a right-eye video signal, which are viewpoint images for three-dimensional (3D) video, from the video input signal. The controller spatially splits signals indicating frames in each of the left-eye video signal and the right-eye video signal to generate signals indicating a plurality of types of subframes. The controller controls the optical path changer so as to maintain the location at which the video image is displayed on the projection surface before and after a time when a subframe in the left-eye video signal and a subframe in the right-eye video signal are switched. The controller controls the video generator such that, when a first frame is switched to a second frame, a last subframe in the first frame and a first subframe in the second frame have a same type and are related to different viewpoint images.

According to the present disclosure, a projection video display suppresses deterioration of its quality caused by optical path changes.

DETAILED DESCRIPTION

Some exemplary embodiments will be described below in detail with appropriate reference to the accompanying drawings. In some cases, excessive details will not be described. For example, details of a matter already known in the art will not be described, and components substantially the same as those already described will not be described again. The reason is to prevent the following description from being needlessly redundant, facilitating an understanding of those skilled in the art.

The applicant will provide the accompanying drawings and the following description for the purpose of helping those skilled in the art sufficiently understand the present disclosure, and therefore the accompanying drawings and the following description are not intended to limit a subject matter described in the claims.

First Exemplary Embodiment

1-1. Configuration of Projection Video Display

A configuration of a projection video display will be described with reference toFIG. 1andFIG. 2.FIG. 1is a perspective view of the exterior of projection video display100that can display 3D video, screen200, and liquid crystal shutter glasses103for use in watching a three-dimensional (3D) image.

Projection video display100projects, onto screen200in a temporally alternate manner, video image of viewpoint videos (left-eye image and right-eye image) generated in accordance with a video input signal. Projection video display100includes emitter101, which outputs control signals for use in controlling an open/close operation of liquid crystal shutter glasses103in synchronization with images to be displayed. Liquid crystal shutter glasses103are equipped with a receiver (not illustrated) that receives the control signals from emitter101. Liquid crystal shutter glasses103cause the liquid crystal shutters for left and right eyes to close in an alternate manner in response to the control signals, namely, in synchronization with images to be displayed by projection video display100.

FIG. 2Ais a block diagram illustrating a configuration of projection video display100. Projection video display100includes light source10, video generator20, optical guiding system50, and projection optical system60. Video generator20generates video image in accordance with a video input signal. Optical guiding system50guides light emitted from light source10to video generator20. Projection optical system60projects the video image generated in the above manner onto screen200. Projection video display100further includes command receiver102, emitter101, and controller70. Command receiver102receives a command generated through an operation of a button in a remote controller or a main body of projection video display100. Emitter101is used to output a control signal for use in controlling an open/close operation of liquid crystal shutter glasses103in synchronization with an image to be displayed. Controller70controls light source10, video generator20, and other components.FIG. 2Bis a block diagram illustrating a configuration of controller70. Controller70includes video signal generator74, display element driver76, and piezoelectric element driver72.

Command receiver102receives a result of selecting one of a normal video display mode and a 3D video display mode through an operation of a button in the remote controller or the main body. In the normal video display mode, video generator20generates video for a single viewpoint in accordance with a video input signal. In the 3D video display mode, video generator20generates a left-eye image and a right-eye image in accordance with a video input signal.

Projection video display100further includes optical path changer80, which changes the optical path of the video image generated by video generator20. More specifically, optical path changer80shifts the location at which the video image generated by video generator20is displayed on screen200, within the range of a pixel length or less (e.g., a half of a pixel length). Details of this operation will be described later. The above operation of optical path changer80enables projection video display100to provide video with its resolution perceived to be higher than that of the video image generated by video generator20.

1-2. Optical Configuration of Projection Video Display

An optical configuration of projection video display100will be described with reference toFIG. 3.FIG. 3is a schematic view of an optical configuration of projection video display100.

White light emitted from light source10enters optical guiding system50. When entering optical guiding system50, the white light passes through lens52and then is focused on or close to the incident surface of rod54. Then, the white light enters rod54and is reflected on the inner surface of rod54several times. As a result, the white light is output from rod54with its light intensity distribution being substantially uniform. The white light that has output from rod54is focused on mirror58by lens56. In this case, lens56may be a relay lens that causes an image on the output surface of rod54to be formed on DMDs (digital mirror devices), which will be described later. The white light that has been output from lens56is reflected by mirror58and then enters video generator20.

When entering video generator20, the white light passes through lens22and then is incident on total internal reflection prism24. In this case, lens22substantially collimates and focuses the incident light.

Total internal reflection prism24includes a first prism, a second prism, and thin air layer26formed between the opposing surfaces of the first and second prisms. When light is incident on air layer26at an angle equal to or greater than its critical angle, all the light is reflected. When the white light that has output from lens22enters total internal reflection prism24, all the white light is reflected by air layer26(total reflection surface) and then enters color prism28.

Color prism28includes a first prism, a second prism, and a third prism. Blue-light reflection dichroic film30is formed between the first and second prisms, and red-light reflection dichroic film32is formed between the second and third prisms. When entering color prism28, the white light is separated into blue light, red light, and green light by both blue-light reflection dichroic film30and red-light reflection dichroic film32. Then, the blue light enters DMD34, the red light enters DMD36, and the green light enters DMD38. In this case, each of DMDs34,36,38changes angles of the micro mirrors in accordance with a video input signal, thereby reflecting incident light at different angles. As a result, the reflected light enters a projection lens in projection optical system60or is led to the outside of the active area of the projection lens.

The light that has been reflected by DMD34, the light that has been reflected by DMD36, and the light that has been reflected by DMD38pass through color prism28again. During the passage inside color prism28, the blue light, the red light, and the green light, into which the white light has been separated, are combined together and then this combined light enters total internal reflection prism24. In this case, when entering total internal reflection prism24, the combined light is incident on air layer26at an angle smaller than the critical angle. Thus, the incident light passes through air layer26and then enters projection optical system60. In this way, the video image created by DMDs34,36,38is projected onto the screen.

Using the DMDs34,36,38as video display elements enables a projection video display to exhibit higher light and heat resistance than by using liquid crystal display elements (liquid crystal panels). Moreover, using three DMDs for blue light, red light, and green light enables a projection video display to exhibit good color reproduction and to produce bright, high-resolution projection video.

1-3. Optical Configuration of Optical Path Changer

With reference toFIG. 4, a description will be given of a configuration of optical path changer80in projection video display100in this exemplary embodiment.FIG. 4is a schematic view of an optical configuration of the projection video display in this exemplary embodiment between video generator20and projection optical system60. Optical path changer80is disposed in front of projection optical system60.

Optical path changer80includes lens unit85and piezoelectric elements88,89. Lens unit85includes lenses86,87and cancels the refractive indices of lenses86,87. Each of piezoelectric elements88,89moves a corresponding one of the lenses in lens unit85in two directions within a plane perpendicular to the optical axis of projection optical system60. Piezoelectric elements88,89are electrically connected to piezoelectric element driver72. Piezoelectric element driver72supplies electricity to piezoelectric elements88,89, thereby controlling deformation of piezoelectric elements88,89. Lens unit85may include three or more lenses. Herein, each of piezoelectric elements88,89may be an exemplary actuator.

Lens86in lens unit85may be a plano-concave lens; the surface that faces total internal reflection prism24is flat and the surface that faces lens87functions as a concave surface. Lens86is fixed with the flat surface being in contact with total internal reflection prism24. Lens87in lens unit85may be a piano-convex lens; the surface that faces lens86functions as a convex lens and the surface that faces projection optical system60is flat. Lens87is disposed between projection optical system60and lens86, and predetermined spacings are provided between lens87and projection optical system60and between lens87and lens86.

Piezoelectric elements88,89in lens unit85are connected to piezoelectric element driver72. Each of piezoelectric elements88,89moves lens87in at least two directions within a plane perpendicular to the optical axis of projection optical system60, in accordance with a drive signal (applied voltage) from piezoelectric element driver72.

FIG. 5is a schematic view of an exemplary configuration of lens unit85. As illustrated inFIG. 5, piezoelectric elements88,89in lens unit85have lens outer frame201, lens inner frame202, and lens fixture203made of a glass substrate.

Lens inner frame202is provided with strut204, strut205, strut206, and strut207. Lens outer frame201is provided with reception hole208, reception hole209, reception hole210, and reception hole211. Strut204is inserted into reception hole208. Strut205is inserted into reception hole209. Strut206is inserted into reception hole210. Strut207is inserted into reception hole211. The cross-sectional area of reception holes208,209,210, and211is set to be larger than that of struts204,205,206, and207. Thus, lens inner frame202is supported by lens outer frame201so as to be movable relative to lens outer frame201.

Lens fixture203is provided with strut212, strut213, strut214, and strut215. Lens inner frame202is provided with reception hole216, reception hole217, reception hole218, and reception hole219. Strut212is inserted into reception hole216. Strut213is inserted into reception hole217. Strut214is inserted into reception hole218. Strut215is inserted into reception hole219. The cross-sectional area of reception holes216,217,218, and219is set to be larger than that of struts212,213,214, and struts215. Thus, lens fixture203is supported by lens inner frame202so as to be movable relative to lens inner frame202.

Each of piezoelectric elements88,89is an element that varies its length in response to applied voltage. More specifically, when a voltage is applied, each of piezoelectric elements88,89increases its length; when the application of the voltage is stopped, each of piezoelectric elements88,89decreases its length. Piezoelectric element89is fixed to lens outer frame201and is in contact with lens inner frame202. Piezoelectric element88is fixed to lens inner frame202and is in contact with lens fixture203. Piezoelectric elements88,89are electrically connected to piezoelectric element driver72. Piezoelectric element driver72individually supplies drive signals (voltages) to piezoelectric elements88,89. When supplied with a drive signal from piezoelectric element driver72, each of piezoelectric elements88,89increases its length.

Spring222is disposed close to piezoelectric element89with its first end fixed to lens outer frame201and with its second end fixed to lens inner frame202. Spring222resists a force generated in the direction in which piezoelectric element89increases its length and applies a tension to lens inner frame202and lens outer frame201so as to be attracted to each other. Piezoelectric element89pushes lens inner frame202when increasing its length, thereby moving lens inner frame202in the negative direction of the X axis, relative to lens outer frame201. Spring222attracts lens inner frame202when piezoelectric element89decreases its length, thereby moving lens inner frame202in the positive direction of the X axis, relative to lens outer frame201.

Spring223is disposed close to piezoelectric element88with its first end fixed to lens inner frame202and with its second end fixed to lens fixture203. Spring223resists a force generated in the direction in which piezoelectric element88increases its length and applies a tension to lens inner frame202and lens fixture203so as to be attracted to each other. Piezoelectric element88pushes lens fixture203when increasing its length, thereby moving both lens87and lens fixture203in the positive direction of the Y axis, relative to lens inner frame202. Spring223attracts lens fixture203when piezoelectric element88decreases its length, thereby moving both lens87and lens fixture203in the negative direction of the Y axis, relative to lens inner frame202.

Both piezoelectric element89and spring222are disposed close to center of gravity G1on the Y axis. Center of gravity G1on the Y axis corresponds to the center of gravity of a lens section on the Y axis; the lens section is constituted by: lens87; lens inner frame202that functions as a lens holder for lens87; and lens fixture203. Both piezoelectric element88and spring223are disposed close to center of gravity G2of the lens section on the X axis.

1-4. Operation of Projection Video Display

Projection video display100operates in two video projection modes; the first one is a 3D video display mode in which 3D video containing videos for a plurality of viewpoints is displayed, and the second one is a normal mode in which video for a single viewpoint is displayed.

1-4-1. Normal Mode

Using optical path changer80configured above can display video with its resolution being four times that of DMDs34,36,38. More specifically, projection video display100splits a video input signal whose resolution is four times that of DMDs into a plurality of subframes, and then projects these subframes onto screen200at different locations. In this way, projection video display100can project a video input signal whose resolution is higher than that of DMDs onto screen200. A description will be given below of control that achieves a quadruple resolution, with reference toFIG. 6andFIG. 7.

To display video with its resolution being four times that of DMDs34,36,38, video signal generator74(spatially) splits a video input signal indicating a single frame (e.g., N-th frame) pixel by pixel, and then generates four subframes made up of pixels disposed at different locations. After that, video signal generator74outputs the four subframes in order within the period of the single frame.

More specifically, as illustrated inFIG. 6, for example, video signal generator74handles four (2×2) pixels as a single block and then splits the video input signal into a plurality of subframes by using a single pixel in each block. As an example, video signal generator74selects the upper left pixel in each block from among the pixels contained in the video input signal, and then generates a video signal indicating a first subframe from the signals related to the selected upper left pixels. In other words, video signal generator74selects a quarter of all the pixels in the video input signal, and then generates a video signal indicating a first subframe from the selected pixels. In this case, the resolution of the video signal indicating the first subframe is equal to a quarter of that of the video input signal. Likewise, a video signal indicating a second subframe is related to the upper right pixel in each block in the video input signal. A video signal indicating a third subframe is related to the lower right pixel in each block in the video input signal. A video signal indicating a fourth subframe is related to the lower left pixel in each block in the video input signal. Then, video signal generator74outputs the video signal indicating the first subframe, the video signal indicating the second subframe, the video signal indicating the third subframe, and the video signal indicating the fourth subframe to the display element driver76in this order. Furthermore, video signal generator74outputs a synchronization signal to piezoelectric element driver72, which is used to make the timing at which a subframe is switched to another subframe coincide with the timing at which optical path changer80shifts a location at which video image is displayed on screen200(changes an optical path of video image).

As illustrated inFIG. 7, while DMDs34,36,38are displaying the video of the first subframe, optical path changer80causes the video image to be projected onto screen200at a predetermined location (reference location). While DMDs34,36,38are displaying the video of the second subframe, optical path changer80changes the optical path of the video image such that the video image is projected onto screen200at the location denoted by the solid line, which is shifted rightward by a half of the pixel length from the reference location denoted by the broken line. In this case, piezoelectric element89increases its length, and lens unit85bends the optical path of the video image. While DMDs34,36,38are displaying the video of the third subframe, optical path changer80changes the optical path of the video image such that the video image is further moved downward by a half of the pixel length and thus projected onto screen200at the location denoted by the solid line, which is shifted rightward by a half of the pixel length and downward by a half of the pixel length from the reference location. While DMDs34,36,38are displaying the video of the fourth subframe, optical path changer80changes the optical path of the video image such that the video image is further moved leftward by a half of the pixel length and thus projected onto screen200at the location denoted by the solid line, which is shifted downward by a half of the pixel length from the reference location. In this way, projection video display100can display the video with its pixels arranged in conformity with those of an original video input signal and with its resolution perceived to be four times that of DMDs34,36,38.

Next, a description will be given of control over which video of an N-th frame is switched to video of an (N+1)-th frame.FIG. 8illustrates waveforms of drive voltages applied to piezoelectric elements88,89in this exemplary embodiment. The part (a) illustrates a waveform of a drive voltage applied to piezoelectric element89when lens87moves in the directions of the X axis. The part (b) illustrates a waveform of a drive voltage applied to piezoelectric element88when lens87moves in the directions of the Y axis. The part (c) illustrates locations at which the video image is displayed on screen200when the video image shifted by optical path changer80is projected onto screen200.

Video signal generator74generates video output signals indicating a first subframe, a second subframe, a third subframe, and a fourth subframe from a video input signal indicating a single frame. More specifically, the first subframe is generated from the signal indicating the upper left pixels in blocks, each of which contains 2×2 pixels in the video input signal. The second subframe is generated from the signal indicating the upper right pixel in each block. The third subframe is generated from the signal indicating the lower right pixel in each block. The fourth subframe is generated from the signal indicating the lower left pixel in each block. After that, video signal generator74outputs the video output signals indicating the first subframe, the second subframe, the third subframe, and the fourth subframe to display element driver76in this order. Moreover, video signal generator74outputs a synchronization signal to piezoelectric element driver72, which is used to make the timing at which DMDs34,36,38switch subframes coincide with the timing at which optical path changer80shifts a location at which the video image is displayed on screen200.

When switching the video of the N-th frame to the video of the (N+1)-th frame, video signal generator74displays the fourth subframe for the N-th frame, which is the subframe in the N-th frame displayed at last, and then displays the first subframe for the (N+1)-th frame, which is the subframe in the (N+1)-th frame displayed at first. In this case, piezoelectric element driver72causes optical path changer80to change a location at which the video image is to be displayed on screen200to a location related to the first subframe.

1-4-2. 3D Video Display Mode

In the 3D video display mode, controller70alternately outputs two respective subframes for left-eye video and right-eye video in relation to their displayed locations. Then, controller70drives optical path changer80so as to display video with its resolution being twice that of DMDs34,36,38. In addition, controller70controls optical path changer80and the timing of an open/close operation of liquid crystal shutter glasses to be worn by the viewer when a viewer watches 3D video.

Video signal generator74(spatially) splits a video input signal indicating a single frame (e.g., N-th frame) pixel by pixel, and then generates two subframes made up of pixels disposed at different locations. After that, video signal generator74outputs the two subframes in order within the period of the single frame.

First, video signal generator74generates a video signal indicating a first subframe and a video signal indicating a second subframe, as a video input signal indicating an N-th frame for the left-eye video. Then, video signal generator74outputs the generated video signals to display element driver76in a predetermined sequence. As illustrated inFIG. 9, for example, the video signal indicating the first subframe is related to the upper left pixels (marked with a circle) in blocks, each of which contains four (2×2) pixels. In other words, the video signal indicating the first subframe is related to the upper left pixels in the blocks in a video input signal indicating the left-eye video. The video signal indicating the second subframe is related to the lower right pixels (marked with a triangle) in the blocks in the video input signal indicating the left-eye video.

Next, similar to the case of the left-eye video, video signal generator74generates a video signal indicating a first subframe and a video signal indicating a second subframe, as a video input signal indicating the N-th frame for the right-eye video. Then, video signal generator74outputs the generated video signals to display element driver76in a predetermined sequence. The video signal indicating the first subframe is related to the upper left pixels in blocks in the video input signal for the right-eye video. The video signal indicating the second subframe is related to the lower right pixels in the blocks in the video input signal for the right-eye video.

Video signal generator74subsequently subjects the same process to a video input signal indicating an (N+1)-th frame for the left-eye video and a video input signal indicating an (N+1)-th frame for the right-eye video.

Video signal generator74also outputs a synchronization signal to piezoelectric element driver72, which is used to make the timing at which DMDs34,36,38switch subframes coincide with the timing at which optical path changer80shifts a location at which the video image is displayed on screen200.

Next, a description will be given of control over which optical path changer80configured above displays 3D video with its resolution being twice that of DMDs34,36,38, with reference toFIG. 10.

While DMDs34,36,38are displaying the video of the first subframe, optical path changer80projects video image onto screen200at a predetermined location (reference location) denoted by the broken line. While DMDs34,36,38are displaying the video of the second subframe, optical path changer80changes the optical path of the video image such that the video image is projected onto screen200at the location denoted by the solid line, which is shifted rightward by a half of the pixel length and downward by a half of the pixel length from the reference location denoted by the broken line. In this case, piezoelectric element88and piezoelectric element89increase their lengths, and lens unit85bends the optical path of the video image.

In the above way, projection video display100can display video with its resolution perceived to be twice that of DMDs34,36,38.

Next, a description will be given of control over which video of an N-th frame is switched to video of an (N+1)-th frame.FIG. 11illustrates waveforms of drive voltages applied to piezoelectric elements88,89. The part (a) illustrates a waveform of a drive voltage applied to piezoelectric element89when lens87moves in the directions of the X axis. The part (b) illustrates a waveform of a drive voltage applied to piezoelectric element88when lens87moves in the directions of the Y axis. The part (c) illustrates a timing waveform (synchronization signal) that causes shutter glasses to switch a light shielding state between the right side and the left side. The part (d) illustrates locations at which the video image is displayed on screen200when the video image shifted by optical path changer80is projected onto screen200.

Next, a description will be given of control over which video of an N-th frame in the left-eye image is switched to video of an N-th frame in the right-eye image (N is any natural number). As illustrated inFIG. 11, video signal generator74controls optical path changer80so as to maintain a location at which the video image is displayed on screen200at the time when video of an N-th frame for the left-eye image is switched to video of an N-th frame for the right-eye image.

A signal related to the upper left pixels in blocks in a video input signal for the left-eye image is referred to as first subframe L1. Likewise, a signal related to the lower right pixels in the blocks is referred to as second subframe L2. Video signal generator74generates first subframe L1and second subframe L2as video output signals, based on a video input signal indicating the N-th frame for the left-eye image. Then, video signal generator74outputs generated first subframe L1and second subframe L2to display element driver76in this order. Moreover, video signal generator74generates a synchronization signal used to make the timing at which the display of DMDs34,36,38is switched from the first subframe to the second subframe coincide with the timing at which optical path changer80shifts a location at which video image is displayed on screen200. Then, video signal generator74outputs the synchronization signal to piezoelectric element driver72.

Next, video signal generator74generates first subframe R1and second subframe R2as video output signals, based on a video input signal indicating the N-th frame for the right-eye image. The first subframe R1corresponds to a signal related to the upper left pixels in blocks in a video input signal for the right-eye image. The second subframe R2corresponds to a signal related to the lower right pixels in the blocks in the video input signal for the right-eye image. Video signal generator74outputs generated second subframe R2and first subframe R1to display element driver76in this order. Moreover, video signal generator74generates a synchronization signal used to make the timing at which the display of DMDs34,36,38is switched from the second subframe to the first subframe coincide with the timing at which optical path changer80shifts a location at which video image is displayed on screen200. Then, video signal generator74outputs the synchronization signal to piezoelectric element driver72.

In short, video signal generator74controls DMDs34,36,38so as to display second subframe L2of the N-th frame for the left-eye image and then to display second subframe R2of the N-th frame for the right-eye image. In addition, video signal generator74controls DMDs34,36,38so as to display first subframe R1of the N-th frame for the right-eye image and then to display first subframe L1of an (N+1)-th frame for the left-eye image. In this case, video signal generator74controls DMDs34,36,38to display the same type of subframes at the time when frames are switched, in order to eliminate the need to change a location at which video image is displayed on screen200. As an example, if a first subframe (or a second subframe) is displayed immediately before frames are switched, a first subframe (or a second subframe) for a different viewpoint image is displayed immediately after the frames have been switched. In other words, piezoelectric element driver72does not drive piezoelectric elements88,89at the time when frames are switched.

Controller70generates a synchronization signal used to drive liquid crystal shutter glasses103. The synchronization signal is at the High level during the display of the N-th frame for the left-eye image and is at the Low level during the display of the N-th frame for the right-eye image. When the synchronization signal is at the High level, the liquid crystal shutter glasses set its left-eye liquid crystal glass to a light transmission state and its right-eye liquid crystal glass to a light shielding state, in response to the synchronization signal. As a result, the viewer can observe the left-eye image with his/her left eye. When the synchronization signal is at the Low level, the liquid crystal shutter glasses set the left-eye liquid crystal glass to the light shielding state and the right-eye liquid crystal glass to the light transmission state. As a result, the viewer can observe the right-eye image with his/her right eye.

As described above, video signal generator74and controller70set a frequency at which a displayed location of the video image on screen200is changed to be the same as a frequency at which liquid crystal shutter glasses103switch the light shielding state between the left side and the right side, with their phase difference controlled to be 90 degrees.

FIG. 12illustrates waveforms of drive voltages applied to piezoelectric elements88,89when piezoelectric elements88,89are driven every time a first subframe and a second subframe are switched. In a method for driving piezoelectric elements88,89in order to display video of an N-th frame as illustrated inFIG. 12, the videos of first subframe L1for the left-eye image, second subframe L2for the left-eye image, second subframe R2for the right-eye image, and first subframe R1for the right-eye image are displayed in this order. This driving method involves changing a displayed location at a higher frequency than the driving method in this exemplary embodiment illustrated inFIG. 11.

The driving method in this exemplary embodiment as illustrated inFIG. 11can reduce a frequency at which piezoelectric elements88,89are driven to a half that at which piezoelectric elements88,89are driven every time the first subframe and the second subframe are switched as illustrated inFIG. 12. When a piezoelectric element is driven at a high speed, the piezoelectric element may make loud noise. So, by driving piezoelectric elements at a low frequency, noise made by the driving of the piezoelectric elements can be reduced. In addition, the quality of the resultant video can be maintained.

The piezoelectric elements are driven at the same frequency both in the 3D video display mode as illustrated inFIG. 11and in the normal mode as illustrated inFIG. 8. This can suppress mode-dependent variation in noise.

FIG. 13illustrates waveforms of drive voltages applied to piezoelectric elements88,89when piezoelectric elements88,89are driven alternately every time a first subframe and a second subframe are switched. InFIG. 13, the videos of first subframe L1for the left-eye image, first subframe R1for the right-eye image, second subframe L2for the left-eye image, and second subframe R2for the right-eye image are displayed in this order.

The driving method in this exemplary embodiment as illustrated inFIG. 11can reduce a frequency at which liquid crystal shutter glasses103are driven to a half that of the driving method illustrated inFIG. 13. This can cause liquid crystal shutter glasses103to switch the light shielding state between the left side and the right side at a low frequency, thereby reducing a crosstalk, which is an incident in which the left video and the right video simultaneously appear when the left video and the right video are switched. To suppress crosstalk which is attributed to the switching, both of the left and the right sides of liquid crystal shutter glasses103may be temporarily set to the light shielding state at the same time. In this case, the driving method in this exemplary embodiment can shorten a time over which both the sides are set to the light shielding state for each frame. This can reduce the risk of the resultant video being darkened.

As described above, controller70controls video generator20in the following manner. First, controller70generates viewpoint images for 3D video, namely, a left-eye video signal and a right-eye video signal, from a video input signal. Then, controller70spatially splits signals indicating frames in each of the left-eye video signal and the right-eye video signal, thereby generating multiple types of signals indicating subframes. Furthermore, controller70controls optical path changer80so as to keep a location at which video image is displayed on a projection surface before and after the time when a subframe for the left-eye video signal is switched to a subframe for the right-eye video signal. In this case, controller70controls video generator20such that, when a first frame is switched to a second frame, the last subframe in the first frame and the first subframe in the second frame have the same type and are related to different viewpoint images. As an example, if the last subframe in an N-th frame to be displayed is first subframe R1for the right-eye image, the first subframe in the (N+1)-th frame to be displayed at the next time to the N-th frame is first subframe L1in the (N+1)-th frame for the left-eye image. In this example, both the subframes are related to different viewpoint images, more specifically the last subframe in the N-th frame is related to a right-eye image, and the first subframe in the (N+1)-th frame is related to a left-eye image. In addition, both the subframes have the same subframe type, more specifically are the first subframe. Since both the subframes have the same subframe type, these subframes are displayed on screen200at the same location before and after the time when the N-th frame is switched to the (N+1)-th frame.

A description will be given of a process of video to be input to video signal generator74.

1-5-1. Quadruple Density Video

Each of the left-eye video and the right-eye video has a resolution which is the four times that of each DMD. Video signal generator74generates a video output signal indicating a first subframe from the upper left pixels in blocks in a video input signal for each viewpoint video; each block contains 4 (2×2) pixels. Likewise, video signal generator74generates a video output signal indicating a second subframe from the lower right pixels in the blocks.

In the above case, the upper right pixel and the lower left pixel in each block are not used. Therefore, pixels may be lacked at corresponding points between the left video and the right video. For example, the pixel in the left-eye video at the coordinates (A0, B0) and the pixel in the right-eye video at the coordinates (A1, B1) are designated as corresponding points in the 3D video. The pixel in the left-eye video at the coordinates (A0, B0) corresponds to the upper left pixel in a block; the pixel in the left-eye video at the coordinates (A1, B1) corresponds to the upper right pixel in the block. In this case, the pixel in the left-eye video at the coordinates (A0, B0) is displayed as the video of the first subframe, but the pixel in the right-eye video at the coordinates (A1, B1) is not displayed in the subframes. Thus, the left video and the right video are not combined together within a region in which no corresponding points are present, in which case the viewer may feel that the resultant video looks strange.

To prevent the above disadvantage, a video signal generator may add pixel information regarding upper right pixels and lower left pixels not to be used to pixel information regarding upper left pixels and lower right pixels to be used. Before adding the pixel information, video signal generator may disperse the pixel information by processing input quadruple density video with a low-pass filter.

Alternatively, pixel information regarding upper right pixels and lower left pixels not to be used may be added in advance to pixel information regarding upper left pixels and lower right pixels to be used, and then the resultant pixel information may be input to video signal generator74.

Each of the right-eye video and the left-eye video has a resolution which is the twice that of each DMD. A video signal generator uses an entire input video to generate a first subframe and a second subframe.

The video signal generator may generate double density video by using CG (computer graphics).

To generate frame video, first, the video signal generator stops time on the CG.

Then, the video signal generator generates a first subframe for a left eye with its resolution being the same as that of each DMD. Here, the location of the viewpoint is referred to as the first viewpoint location, and the location of the projection surface is referred to as the first projection location. Then, the video signal generator generates a second subframe for a left eye with its resolution being the same as that of each DMD. In this case, the viewpoint is maintained at the first viewpoint location, but the projection surface is shifted rightward by a half of the pixel length and downward by a half of the pixel length from the viewpoint location. Here, the location of the projection surface is referred to as the second projection location. Continuing, the video signal generator generates a first subframe for a right eye with its resolution being the same as that of each DMD. Here, the location of the viewpoint is referred to as the second viewpoint location. The projection surface is positioned at the first projection location. Finally, the video signal generator generates a second subframe for a right eye with its resolution being the same as that of each DMD. In this case, the viewpoint is maintained at the second viewpoint location, but the projection surface is positioned at the second projection location.

Each of the right-eye video and the left-eye video has a resolution which is the twice that of each DMD. A video signal generator uses an entire input video to generate a first subframe and a second subframe.

The video signal generator may generate double density video by using computer graphics (CG).

At a first timing, the video signal generator generates a first subframe for a left eye with its resolution being the same as each DMD. Here, the location of the viewpoint is referred to as the first viewpoint location, and the location of the projection surface is referred to as the first projection location. Then, at a second timing when a predetermined time has elapsed on the CG, the video signal generator generates a second subframe for a left eye with its resolution being the same as each DMD. In this case, the viewpoint is maintained at the first viewpoint location, but the location of the projection surface is shifted rightward by a half of the pixel length and downward by a half of the pixel length with respect to the viewpoint location. Here, the location of the projection surface is referred to as the second projection location. Continuing, at a third timing when a predetermined time has further elapsed on the CG, the video signal generator generates a second subframe for a right eye with its resolution being the same as each DMD. In this case, the location of the viewpoint is referred to as the second viewpoint location. The projection surface is maintained at the second projection location without changing the location. Finally, at a fourth timing when a predetermined time has elapsed on the CG, the video signal generator generates a first subframe for a right eye with its resolution being the same as each DMD. In this case, the viewpoint is maintained at the second viewpoint location, but the projection surface is positioned at the first projection location.

The video signal generator generates subframe video signals for a left-eye video and a right-eye video in the above manner, and then a video display of the present disclosure displays a 3D video. In this way, it is possible to display time-compensated video, as opposed to double density video1.

1-6. Function and Effect

As described above, projection video display100includes video generator20, optical guiding system50, projection optical system60, and optical path changer80. Video generator20generates video image. Both optical guiding system50and projection optical system60project the video image onto screen200. Optical path changer80is disposed in the optical path of the video image and changes a location at which the video image is displayed on screen200. Projection video display100further includes liquid crystal shutter glasses103and controller70. Liquid crystal shutter glasses103switch a light shielding state between its left side and right side. Controller70controls video generator20, optical path changer80, and liquid crystal shutter glasses103, based on a video input signal. Controller70spatially splits signals indicating frames in each of video input signals for a left eye and a right eye, and then generates signals indicating multiple types of subframes. Controller70controls optical path changer80so as to maintain a location at which the video image is displayed on screen200before and after the time when frames in the video signals for a left eye and a right eye are switched. Moreover, controller70controls video generator20so that, when a first frame is switched to a second frame, the last subframe in the first frame and the first subframe in the second frame have the same type (first/second subframe) and are related to different viewpoint videos.

The video signal generator74and the controller70control piezoelectric elements88,89, which are used to change a location at which the video image is displayed on screen200, and liquid crystal shutter glasses103, such that a driving frequency of piezoelectric element88,89coincides a driving frequency at which liquid crystal shutter glasses103switch a light shielding state between the left side and the right side. Furthermore, a phase difference between a drive waveform of piezoelectric elements88,89and a drive waveform of liquid crystal shutter glasses103are set to 90 degrees.

The above configuration can cause the optical path of the video image to be changed at a low frequency, thereby maintaining a quality of video. Thus, this configuration is effective in improving reliability of piezoelectric elements and reducing making of noise. In addition, the configuration can cause liquid crystal shutter glasses103to switch a light shielding state between its left side and right side at a low frequency, thereby effectively reducing an occurrence of a crosstalk and suppressing resultant video from being darkened.

Second Exemplary Embodiment

A projection video display in a second exemplary embodiment basically has substantially the same configuration as the projection video display in the first exemplary embodiment, but their methods for controlling a shift of a displayed location differ from each other.

In a 3D video display mode, the projection video display in the second exemplary embodiment shifts its displayed location in a different direction at regular intervals.FIG. 11illustrates an exemplary control over which images are projected onto a screen at an upper left location and at a lower right location.FIG. 14illustrates an exemplary control over which images are projected onto a screen at an upper right location and at a lower left location. In this case, a phase difference between drive waveforms of piezoelectric elements88,89is set to 180 degrees.

In this exemplary embodiment, every time the normal mode is switched to a 3D video display mode, the projection video display switches between the control over which images are projected at an upper left location and at a lower right location and the control over which images are projected at an upper right location and at a lower left location. Switching the driving method in this manner causes the mechanism to move in different directions. Consequently, it is possible to prevent the mechanism from deteriorating unevenly, enabling optical path changer80to operate stably in the normal mode.

Video signal generator74uses different pixels to generate subframes. Under the control over which an image is projected onto a screen at an upper left location and at a lower right location, video signal generator74generates a first subframe video from upper left pixels and a second subframe video from lower right pixels. Under the control over which an image is projected onto a screen at an upper right location and at a lower left location, video signal generator74generates a first subframe video from upper right pixels and a second subframe video from lower left pixels.

Third Exemplary Embodiment

A projection video display in a third exemplary embodiment has substantially the same configuration as the projection video displays described in the first and second exemplary embodiments. A description will be given, especially regarding a video input signal and video signals indicating subframes (referred to below as subframe signals).

FIG. 19,FIG. 20,FIG. 21,FIG. 22,FIG. 24each illustrate a relationship between subframe signals and signals indicating pixels in blocks in frames of a video input signal. For example, signal L00_1is related to the upper left pixel in each block in the video input signal indicating an (N+1)-th frame illustrated inFIG. 19. Likewise, signal L10_1is related to the upper right pixel in each block. Signal L11_1is related to the lower right pixel in each block. Signal L01_1is related to the lower left pixel in each block. Signal L00_2is related to the upper left pixel in each block in the video input signal indicating an (N+2)-th frame illustrated inFIG. 19. Video generator20outputs signal L00_1as a subframe signal indicating a first subframe illustrated inFIG. 19. Likewise, video generator20outputs signal L10_1as a subframe signal indicating a second subframe. Video generator20outputs signal L11_1as a subframe signal indicating a third subframe. Video generator20outputs signal L01_1as a subframe signal indicating a fourth subframe. In this case, video generator20outputs subframe signal L00_1indicating the first subframe, subframe signal L10_1indicating the second subframe, subframe signal L01_1indicating the fourth subframe, and subframe signal L11_1indicating the third subframe in this order in accordance with the temporal axis illustrated inFIG. 19.

Exemplary subframe signals according to the third exemplary embodiment will be described with reference toFIG. 20. As illustrated inFIG. 20, video generator20generates a subframe signal by making interpolation based on video input signals indicating two successive frames and then outputs this subframe signal. InFIG. 20, video generator20outputs signal L00_1related to the upper left pixel in each block in the video input signal, as a subframe signal indicating the first subframe. Then, video generator20generates signal L10_1aby making interpolation based on a video input signal L10_1indicating an (N+1)-th frame and a video input signal L10_2indicating an (N+2)-th frame, and outputs the signal L10_1aas a subframe signal indicating a second subframe in the (N+1)-th frame. Likewise, video generator20generates signal L11_1aby making interpolation based on signals L11_1and L11_2and then outputs signal L11_1aas a subframe signal indicating a fourth subframe. Video generator20generates signal L01_1aby making interpolation based on signals L01_1and L01_2and then outputs signal L01_1aas a subframe signal indicating a third subframe. In the third exemplary embodiment, video generator20outputs these subframe signals at different timings on a time-series basis. In the configuration illustrated inFIG. 19, the subframes for the (N+1)-th frame are signals corresponding to the same timing of the video input signal. In this case, if timing at which the subframes are displayed on screen200does not match the timing of the video signal, a viewer may feel something strange. The configuration in the third embodiment causes subframe images in the same frame to be displayed at different timings, suppressing the viewer from feeling something strange.

The interpolation made by video generator20may be weighted interpolation in which different weights are added to successive frames based on the timing at which subframes are projected onto screen200. For example, the timing at which the subframe signal L10_1indicating the second subframe in the (N+1)-th frame is output is closer to the timing at which the subframe signal L00_1indicating the first subframe in the (N+1)-th frame is output than the timing at which the subframe signal L00_2indicating the first subframe in the (N+2)-th frame is output. Thus, video generator20generates subframe signal L10_1aby making interpolation in which a heavier weight is added to the subframe signal L10_1and a lighter weight is added to the subframe signal L10_2. In this case, the ratio of a first timing difference to a second timing difference is set to 1:3; the first timing difference is defined as the difference between the timing at which subframe signal L00_1is output and the timing at which subframe signal L10_1ais output, and the second timing difference is defined as the difference between the timing at which subframe signal L10_1ais output and the timing at which subframe signal L00_2. In this way, the ratio of the weight added to subframe signal L10_1to the weight added to subframe signal L10_2is preferably set to 3:1. By making the interpolation in which weights based on the difference between the displayed timings are added to subframe signals, it is possible to reduce the risk of the viewer feeling something strange.

Exemplary subframe signals according to the third exemplary embodiment will be described with reference toFIG. 21. In the configuration illustrated inFIG. 21, each video input signal contains a left-eye video signal and a right-eye video signal. Video generator20generates first subframe L1related to the upper left pixel in each block and second subframe L2related to the lower right pixel in each block, based on the left-eye video signal. Likewise, video generator20generates first subframe R1related to the upper left pixel in each block and second subframe R2related to the lower right pixel in each block, based on the right-eye video signal. Similar to the generation of the subframe signals using interpolation as illustrated inFIG. 20, video generator20generates the second subframe L2for the left-eye video, the second subframe R2for the right-eye video, and the first subframe R1for the right-eye video through interpolation using video input signals indicating two successive frames. Generating subframe signals in this manner can reduce the risk of the viewer feeling something strange at a displayed timing.

Video generator20may further use a spatial correction. For example, video generator20may correct subframe signal L00_1indicating first subframe L1by referring to video signal L01_1related to the pixel on the under side and video signal L10_1related to the pixel on the right side. Subsequently, video generator20may correct second subframe L2, first subframe R1, and second subframe R2in the same manner. In this case, video generator20generates subframe signals by making interpolation based on a video signal acquired through the interpolation of a video input signal. Combining temporal interpolation and spatial correction in this manner enables the viewer to perceive the video as being in higher resolution when a viewer watches video projected onto screen200and reduces the risk of the viewer feeling something strange at a displayed timing.

Exemplary subframe signals according to the third exemplary embodiment will be described with reference toFIG. 22. Video generator20illustrated inFIG. 22generates video at a higher frame rate than a video input signal. More specifically, video generator20generates subframe signals for an (N+1)-th frame by making interpolation using a video input signal indicating the (N+1)-th frame and a video input signal indicating an (N+2)-th frame (not illustrated). For example, video generator20generates subframe signal L00_1bindicating first subframe L1by making interpolation using the subframe signals L00_1and L00_2(not illustrated). Video generator20outputs two subframe signals L00_1and L00_1bindicating first subframe L1within the period of the (N+1)-th frame. Likewise, video generator20generates and outputs subframe signals indicating second subframe L2, first subframe R1, and second subframe R2. In this way, video generator20can output a signal at a higher frame rate than the video input signal. Consequently, projection video display100can project video onto screen200at high time-resolution, thereby enabling the viewer to perceive the video as being of higher quality and reducing the risk of the viewer feeling something strange at a displayed timing.

InFIG. 22, the video input signal contains the left-eye video signal and the right-eye video signal. However, projection video display100can also output a signal at a higher frame rate even when displaying 2D video as in the case ofFIG. 20.

Exemplary subframe signals according to the third exemplary embodiment will be described with reference toFIG. 23andFIG. 24. As illustrated inFIG. 24, video generator20receives video input signals in each of which a left-eye video signal and a right-eye video signal are combined together. Each video input signal contains the combination of the left-eye video signal and the right-eye video signal, as illustrated inFIG. 23. InFIG. 23, video signal L00is generated by extracting only signals related to the upper left pixels in blocks of the left-eye video signal. Likewise, video signal L11is generated by extracting only signals related to the lower right pixels in blocks of the left-eye video signal. This scheme is also applied to the right-eye video signal. The video input signal contains the combination of video signals L00, L11, R00, and R11. In a vertical direction, the resolution of each of video signals L00, L11, R00, and R11is a half that of the left-eye video signal and the right-eye video signal. Likewise, in a horizontal direction, the resolution of each of video signals L00, L11, R00, and R11is a half that of the left-eye video signal and the right-eye video signal. In short, the resolution of each of video signals L00, L11, R00, and R11is a quarter that of the left-eye video signal and the right-eye video signal. As illustrated inFIG. 24, video generator20generates subframe signals, based on the video input signal generated in the above manner. The video input signal illustrated inFIG. 23andFIG. 24differs from that in other exemplary embodiments, in that video signals L00, L11, R00, and R11are arranged spatially separated from one another. This arrangement eliminates the need for video generator20to generate video signals individually related to pixels in blocks, each of which contains 4 (2×2) pixels, thereby reducing computing complexity of video generator20. In which case, information contained in the video input signal to be input to video generator20, which is a video signal used to display 3D video, is smaller in amount than the video input signal as illustrated inFIG. 21. Thus, using this video input signal leads to reductions in a volume of data traffic and a capacity required to store video data.

Other Exemplary Embodiments

In the foregoing exemplary embodiments, light source10is not specified; however, a lamp light source, a solid light source, or more preferably a light source including a laser light source and a fluorescent substance may be used. The configuration of video generator20described above is provided with three DMDs; however, this configuration is not limited. Alternatively, a video generator may be provided with a single DMD. Moreover, instead of the DMD(s), a video generator may be provided with a light transmission type or light reflection type of liquid crystal display element as a display element.

In the foregoing exemplary embodiments, piezoelectric elements are used as an actuator that vibrates optical path changer80; however, this configuration is limited. Alternatively, for example, a VCM (voice coil motor) may be used. Although optical path changer80is disposed between video generator20and projection optical system60, optical path changer80may be disposed at any midway point between video generator20and screen200. For example, optical path changer80may be interposed between lenses in projection optical system60. The plano-concave lens (lens86) and the plano-convex lens (lens87) are disposed in lens unit85in this order with reference to video generator20; however, this configuration is not limited. The two lenses in lens unit85may be disposed in any fashion so as to cancel their refractive indices. Alternatively, for example, the piano-convex lens (lens87) and the plano-concave lens (lens86) may be disposed in this order with reference to video generator20.

In the foregoing exemplary embodiments, a signal indicating upper left pixels is set as a first subframe and a signal indicating lower right pixels is set as a second subframe in order to display double density video; however, a configuration of subframes is not limited. Alternatively, for example, a signal indicating upper right pixels may be set as a first subframe and a signal indicating lower left pixels may be set as a second subframe. In this case, an optical path changer may control an optical path of video image such that a location at which the video image is displayed on a projection surface moves in an upper right direction and in a lower left direction in accordance with a location of a pixel to be sampled.

In the foregoing exemplary embodiments, when video signal generator generates video signals indicating subframes, a signal indicating the upper left pixel in each block is set as a first subframe; however, this configuration is not limited. Alternatively, a signal indicating a pixel disposed at another location may be set as a first subframe. Moreover, an interpolation signal between pixels may be generated and set as a first subframe.

In the foregoing exemplary embodiments, as illustrated inFIG. 4andFIG. 5, an optical path of video image is changed by shifting lens87in two axial directions (X and Y directions); however, a configuration of an optical path changer is not limited. For example, an optical path changer may be made of a flat glass member.FIG. 15illustrates an exemplary configuration of this optical path changer. An optical path changer80aincludes glass member82and piezoelectric element84; glass member82refracts an optical path of video image from video generator20by means of its varying refractive index, and piezoelectric element84varies an angle at which glass member82is disposed. When an angle at which glass member82is disposed is varied, a location at which light is emitted is shifted due to a refractive effect. As a result, the video image is displayed on screen200at a shifted location. Piezoelectric element84is driven by piezoelectric element driver72. By disposing a plurality of piezoelectric elements, an optical path changer that can shift an optical path in two axial directions may be configured. Piezoelectric element84may include another type of actuator. For example, an actuator may have a coil. Optical path changer80may include two actuators provided in a glass member at respective locations, and these actuators may shift an optical path in two axial directions. In this way, optical path changer80can be configured with a simple structure.

An optical path changer may include a plurality of glass members that can shift an optical path in two axial directions.FIG. 16illustrates an exemplary configuration of these glass members. An optical path changer80cincludes glass members82a,82band piezoelectric elements84a,84b. Each of glass members82a,82brefracts an optical path of video image from video generator20by means of its varying refractive index. Piezoelectric element84avaries an angle at which glass member82ais disposed, and piezoelectric element84bvaries an angle at which glass member82bis disposed. Glass member82ashifts locations at which pixels are projected in the Y direction, whereas glass member82bshifts locations at which pixels are projected in the X direction. Piezoelectric elements84a,84bare driven by piezoelectric element driver72. By combining two glass members82a,82b, an optical path can be shifted in the X and Y directions.

In the foregoing exemplary embodiments, an optical path changer is made of a lens; however, an optical path changer may be made of a liquid crystal display element. In this case, the liquid crystal display element can shift an optical path by varying its refractive index.FIG. 17illustrates a configuration of an optical path changer including a liquid crystal display element. Optical path changer80bincludes: liquid crystal display element83; and drive circuit72bthat drives liquid crystal display element83. Drive circuit72bvaries a refractive index of a liquid crystal display element by controlling a voltage applied to liquid crystal display element83, thereby shifting an optical path of the transmitted light in a desired direction. The optical path changer with this configuration can also shift an optical path.

An optical path changer may include two liquid crystal display elements that shift an optical path of video image in two axial directions.FIG. 18illustrates a configuration of an optical path changer that includes two liquid crystal display elements that shift an optical path in two axial directions. Optical path changer80dincludes liquid crystal display element83a, liquid crystal display element83b, and drive circuit72b. Liquid crystal display element83ashifts the optical path in the Y direction. Liquid crystal display element83bshifts the optical path in the X direction. Drive circuit72bdrives liquid crystal display elements83a,83b.

In the foregoing exemplary embodiments, an optical path changer shifts an optical path along two axes. However, an optical path changer may shift the optical path along a single axis. Even the optical path changer that shifts an optical path along a single axis can also display high-quality 3D video. However, an optical path changer that shifts an optical path along two axes can display video other than 3D video with its resolutions in the vertical and horizontal directions being twice that of each of DMDs34,36,38.

In the foregoing exemplary embodiments, liquid crystal shutter glasses103are used; however, this configuration is not limited. Alternatively, the foregoing exemplary embodiments may be achieved by any other field sequential 3D system. If a system using polarized glasses is employed, for example, a device that modulates a polarization direction of video image to be projected can be driven at a half the frequency. In this case, the polarized glasses and the device that modulates a polarization direction configure a shutter device. If a wavelength division system using wavelength selection glasses is employed, a device that switches between multi-layer filters can be driven at a half the frequency. In this case, the wavelength selection glasses and the device that switches multi-layer filters configure a shutter device.

In the foregoing second exemplary embodiment, controller70switches between the control over which video image is projected at the upper left and lower right locations and the control over which video image is projected at the upper right and lower left locations every time the normal mode is switched to the 3D video display mode. However, the switching timing is not limited. Controller70may measure an operational time in 3D video display mode and switch between both the controls every time a preset time comes. Alternatively, controller70may switch between both the controls every time projection video display100is powered up. Moreover, controller70may employ the combination of a plurality of parameters.

For example, suppose when an operational time in the 3D video display mode measured by controller70reaches a preset time, projection video display100switches from the normal mode to the 3D video display mode. In response to this, controller70may switch between the control over which video image is projected at the upper left and lower right locations and the control over which video image is projected at the upper right and lower left locations. After an operational time in the 3D video display mode measured by controller70has reached a preset time, controller70may switch between both the controls when projection video display100is powered next time.

In the foregoing second exemplary embodiment, when controller70switches between the control over which video image is projected at the upper left and lower right locations and the control over which video image is projected at the upper right and lower left locations, video signal generator74generates subframes from different pixels. However, this configuration is not limited.

Alternatively, when controller70switches between the control over which video image is projected at the upper left and lower right locations and the control over which video image is projected at the upper right and lower left locations, video signal generator74may generate subframes from the same pixels and may change a displayed location on a display element. For example, when controller70performs the control over which video image is projected at the upper left and lower right locations, video signal generator74may generate first subframe video from upper left pixels and second subframe video from lower right pixels. After controller70has switched this control to the control over which video image is projected at the upper right and lower left locations, video signal generator74may still generate first subframe video from upper left pixels and second subframe video from lower right pixels. Then, optical path changer80shifts a location at which the video of the second subframe is displayed on a display element, leftward by one pixel length while maintaining the location at which the video of the first subframe is displayed on the display element. In this way, the relationship of a displayed location on a screen between subframes is maintained.

The foregoing exemplary embodiments are examples of the technique of the present disclosure; therefore, the exemplary embodiments can undergo various modifications, substitutions, additions, and omissions without the scopes of the claims and their equivalents.

The present disclosure is applicable to projection video displays that have a 3D video display function and employ a pixel shift technique to project high-density video.