GB2442019A - Large field of view image projection apparatus with beam splitting means - Google Patents

Abstract

An image projection apparatus for projecting light onto a screen medium to present an image to a user, comprising first and second substantially collocated projection means, the first projection means 42 being operable to project light in a first divergent beam and the second projection means 44 being operable to project light in second and third divergent beams using a beam splitting device (60), said second and third divergent beams being respectively juxtaposed on either side of the first.

Description

[MAGE DISPLAY SYSTEM AND METHOD The invention relates to a system for

displaying an image on a display medium and an associated method.

It is often necessary to generate an image on a display, wherein the displayed image is a composite image formed from a number of discrete images. This is particularly the case where a large field of view (FOV) is desired. Such a display might commonly be required in the field of simulation displays, and particularly in flight simulators. In such cases, the use of several projectors may be necessary to achieve a given FOV.

In a flight simulator, the main aim is to present the user or users with visual and other stimuli which, as far as possible, replicate the stimuli that would be evident in the real-life scenario being simulated. In order to present the users with a visual stimulus across a large FOV, an extensive display medium is required. In practice, this is typically achieved by means of a plurality of juxtaposed display devices, and scene generation means operable to provide cooperating image data to these display devices which enables, as far as possible, a continuous scene to be presented to the users.

In a flight simulator, the objects depicted in the scene will normally be at a far larger distance from the user than can actually be accommodated within the physical confines of the simulator apparatus. Therefore, in addition to a large FOV, a further important feature of the display system in a flight simulator is that the display should appear to show a scene that is situated a large distance from the user of the apparatus. This will give visual cues that give the correct perception of distance for the scene that is being shown.

The illusion of distance is usually accomplished by ensuring that light rays emanating from each particular point on the display system are substantially collimated, as would be the case in a real scene that is situated a large distance from an observer. Optical systems to accomplish this are well known in the field, and an example of a system is shown schematically in figures 1, 2a and 2b. Figure 1 shows a side view of the system, and figures 2a and 2b show a plan view.

In figure 1, a composite image from a plurality of image projectors 10 is formed on a curved back-projection screen 15. The projectors 10 are placed a suitable distance behind the screen 15 so that they produce a focused image on the screen 15. A concave mirror 25 is placed some distance in front of the screen 15. The user 20 will normally be positioned on the same side of the mirror 25 as the screen 15. Usually, both the screen 15 and mirror 25 are curved in profile, with the profiles being dependent on the collimation requirements of the system.

An alternative to the above configuration is given in US5253 116. Here, the projector(s) are placed such that the front surface of the screen is illuminated. The present invention is equally applicable to this configuration.

The user position, a suitable location in order to view the reflection of the screen 15 in the mirror 25, is further selected to present the user 20 with substantially collimated image rays 32. An image composed of collimated rays 32 is desirable, since this will provide the user 20 with a relatively realistic viewing experience, with an impression of depth provided by the substantially parallel rays of light. Since the most common location for the user 20 to be situated in is at, or near to, the vertical axis passing through the centre of curvature 12 of the mirror 25, the screen 15 is often offset vertically from the axis of the mirror 25 to allow the user 20 an uninterrupted view. The choice of architecture is a function of the required FOV and spatial restrictions such as the cockpit size and shape.

Within the apparatus, light rays 30 emanating from any particular point 31 on the screen will be reflected by the mirror 25 into substantially parallel reflected rays 32, and thus the user 20 is given a perception of light having travelled from a distant object, rather than from a relatively close projector 10. Generally, a greater FOV is required in the horizontal than in the vertical direction. Thus in the vertical direction, the required FOV can be generated using a single projector 10, whereas in the horizontal direction multiple projectors 10 are required.

Figures 2a and 2b show plan views of the system shown in figure 1. Figure 2a shows the overlapping projected images, whilst in figure 2b this detail has been omitted for clarity. Figure 2b instead shows the collimated images rays 32 as observed by the user 20. The image projectors 10 are arranged side-by-side so that, in the horizontal direction, their combined output produces a continuous composite image on the screen with a large FOV. Each projector 10 produces an image on the screen 15 with a FOV 11 that overlaps the FOV 11 of each adjacent projector 10. The overlap 13 between adjacent projectors' FOVs 11 will result in a seam being present in the composite image. As with the horizontal direction, in the vertical direction the optical system is arranged such that light rays 30 emanating from any particular point 31 will become substantially collimated image rays 32 when presented to the user 20.

The overall FOV is, with regard to the above, intended to provide the user with sufficient visual stimulus that the simulation equipment can, as far as possible, replicate the simulated experience. For this, it may be impractical to provide a single display device to deliver a sufficient FOV. For example, common industry standards for such displays systems give an overall horizontal FOV of between 150 and 225 . This is presently impractical to achieve using a single display projection device projecting an image onto a screen, and thus more than one device is inevitable.

To avoid dead space between the various portions of the overall image, the image portions are overlapped andlor blended. This can lead to the perception of edges in the image, which can be distracting to the user. While the appearance of such edges can be mitigated to some extent by the application of electronic andlor mechanical edge blending techniques, a visible seam often still remains visible.

One method of reducing the potential for distraction caused by the seams is to ensure that seams, if formed, will appear at points in the display with relatively low interest to the user. Thus a seam forming in the straight ahead' direction of a pilot in a simulator would be undesirable. Such a straight ahead' direction is defined as an angular range in the FOV on a display around the principal axis defined by the seating position of the user. It will be appreciated that this forward direction will be defined with reference to the apparatus and thus not with regard to the potential user of the apparatus. The forward direction of the user would be defined with reference to the apparatus, such as by alignment of controls and alignment of the user's seat. The manufacturer of the apparatus is thus able to define with some certainty the preferred FOV of a user.

Usually, the overall scene is delivered using an odd number of projection devices, commonly three or five. The advantage of using an odd, as opposed to even, number of projectors is that any potential seams in the image can be placed such that they are either side of the field of maximum interest. Using an even number of projectors on the other hand would tend to result in an undesirable seam being present substantially in the

centre of the field of maximum interest.

Despite arranging for the seams to be located away from the centre of the user's FOV, seams are still undesirable in any part of the image. A primary cause of the visibility of seams is often the differential aging of components in the projection system. Over time, the output from projectors will vary, and the outputs from different projectors used in a single simulator system may vary in different ways. For instance, the variation may be as a result of deterioration of optical and/or electronic components over time. Since aging will affect different display devices in different ways, it is possible that the luminance and/or chrominance of different portions of the overall display will be different if their respective projectors have deteriorated at different rates. This will advance the visibility of seams in the overall display. Slight damage may also occur, which may be undetectable by inspection of the device itself. One example of this would be dislodging of an optical element (e.g. a lens) of the device. This may also give rise to a seam, which may be difficult to resolve by repair.

Matching projectors is a task that increases in complexity rapidly with an increase in the number of projectors used in the simulator system. Additionally, the range of available adjustment tends to be reduced for a large number of projectors since there will tend to be a large natural spread of luminances and chrominances to be compensated.

Advances in projection teclmology mean that it is now feasible to cover the required FOV with the output of two projection devices rather than three, or four projectors rather than five. For example, whereas a previous system might have used three projectors projecting at a resolution of 1600x 1200 pixels, two projectors projecting at 4096x2 160 projectors can be used instead. This therefore provides not only a better image in that it is generated by fewer projectors (and thus with fewer seams) but also the advances in projector resolution mean that the number of pixels in the total image has increased from 5.76 Mega pixels (1600x1200x3) to 17.69 Mega pixels (4096x2160x2). The use of fewer projectors reduces the effect of non-uniform luminance and chrominance across the total FOV in the system, and thereby reduces the problem of matching the different projectors. Further, fewer projectors have a direct impact on maintenance time. This is thus attractive to a manufacturer, and also to a user.

However, a problem with using only two projectors is that the resultant seam will appear in substantially the forward direction, and thus in the field of maximum interest.

According to the invention therefore, there is provided a display apparatus for projecting light onto a screen medium to present an image to a user, the display apparatus comprising first and second substantially collocated projection means, the first projection means being operable to project light in a first divergent beam and the second projection means being operable to project light in second and third divergent beams, said second and third divergent beams being respectively juxtaposed on either side of the first.

The second projection means may be operable to generate light in a single beam, and comprise splitting means operable to split said single beam into said second and third divergent beams. The splitting means may comprise reflecting means operable to receive incident light from said single means and to reflect one portion of said incident light in a first direction and another portion of said incident light in a second direction.

The reflecting means may comprise a mirror wedge, the mirror wedge comprising reflecting faces defining a wedge apex at which the single beam is directed.

The reflecting means may further comprise second and third mirror means, each operable to receive incident light directed thereto by the reflecting faces of the mirror wedge, and to reflect light to form said second and third divergent beams.

The reflecting means may be arcuate. In that way, beam shaping to conform with the shape of a screen to which light is to be projected, can be achieved.

The second projection may further comprise beam shaping means to shape at least one of the single beam and the second and third divergent beams.

At least one of the first and second projector may comprise blend masking means for blending the edges of each beam output therefrom. The blend masking means may comprise a mechanical or optical blend mask.

Further aspects and advantages will be appreciated by the reader from the following description of a specific embodiment of the invention, with reference to the accompanying drawings: Figure 1 is a schematic side view of a known method of composite image projection in a flight simulator system.

Figure 2 is a schematic plan view of the image projection method shown in figure 1.

Figure 3 is a schematic plan view of a flight simulator including projection apparatus in accordance with a specific embodiment; and Figure 4 is a schematic plan view of a second projector of the projection apparatus illustrated in figure 3.

Figure 3 illustrates an image projection system within a flight simulator, comprising an arcuate back-projection screen 15 and a projector apparatus 40 operable to emit light for incidence on the screen 15. The remaining parts of the flight simulator system may be identical to the prior art, as shown in figures 1 and 2, and so are not shown here.

The projector apparatus 40 generates first, second and third image beams, the respective angular extent of which are indicated by arrow spans 22, 24, 26 in figure 3. For this, the projector apparatus 40 comprises first and second projectors 42, 44. The first projector 42 is an image projector of conventional construction and operable to project the first image beam 22 as indicated. This first image projector 42 thus projects an image beani to the screen at a position wherein the main area of interest in the field of view is located.

The second image projector 44 is operable to project the second and third image beams 24, 26 as indicated. To achieve this, the projector 44 comprises a beam splitting device as illustrated in figure 4.

As shown in figure 4, the projector 44 is essentially a conventional image projector as per the first projector 42, with the addition of a beam splitting device 60. The beam splitting device comprises a mirror wedge 62 defining two reflection faces 64, 66 and a wedge apex 68. The wedge apex 68 is aligned with the principal axis of projection of the projector, to ensure that substantially half of the light of the projected beam is incident on each reflection face of the wedge 62.

While the electronic and data processing aspects of the projector are not specifically part of the invention, it will be understood that most currently available projectors accept only one data source at a time and project an image on the basis of that single source of data. The double' image for output at the projector 44 and then for splitting at the mirror wedge 62, may in this case be defined by data input to the projector, the data being formulated by data processing means (not shown) from data defining the two separate images eventually projected.

In another case, the projector itself may be capable of receiving the two data streams and to formulate a single image beam therefrom for splitting into the two images. An example of such a projector currently available is the SONY SRXI 10 projector.

The beam splitting device further comprises first and second reflecting mirrors 70, 72, arranged opposite the reflection faces 64, 66, to redirect back the split beams into the directions defined by the second and third beam directions indicated in figure 3. These mirrors also have the effect of counteracting image reversal caused by reflection at the reflecting wedge: the light incident on the screen will have been reflected twice.

In the illustration, the reflection faces 64, 66 and the mirrors 70, 72 are planar.

However, it will be appreciated that some or all of these may be arcuate to provide beam shaping to compensate for the curvature of the screen 15.

The mirrors 70, 72 further each comprise a blend mask 74, 76, each positioned at the edge of the respective mirror adjacent the projector, to provide a blending effect at the edge of the reflected beam at the edge thereof which will overlap with the first image beam. In that way, while it is acknowledged that the presence of a seam cannot be discounted, its impact can be reduced.

It will be appreciated that the position of the projector 44 is advantageously equidistant between the two corresponding screen sections on which the two parts of the split image are projected. This maintains focus of both images.

The mirror arrangement shown in the example will inevitably introduce additional optical path length as the beam 22 from the first projector 42 project to the screen directly whereas the split beams 24, 26 project via the wedge and the mirrors.

Therefore, the magnification of the images formed by the split beams would, without compensation, be larger than those formed by the directly incident beams.

Various ways of achieving this compensation may be provided, either singly or in combination. A simple approach would be to place the second projector forward of the first projector, thus shortening the optical path to be substantially equal to the direct optical path.

In contrast, electronic magnification could be applied, such as electronic warping tools, but these have a tendency to cause loss of resolution.

It will be appreciated that light directly incident on the point of the wedge apex 68 will not be reflected into either split beam. The described embodiment envisages that this loss will not be significant.

The specific embodiment is described by way of example only, and should not be read as implying any restriction on the scope of protection sought, which should be determined from the accompanying claims.

Claims (9)

1. I

   CLAIMS: I. A display apparatus for projecting light onto a screen medium to present an image to a user, the display apparatus comprising first and second substantially collocated projection means, the first projection means being operable to project light in a first divergent beani and the second projection means being operable to project light in second and third divergent beams, said second and third divergent beams being respectively juxtaposed on either side of the first.
2. 2. A display apparatus in accordance with claim 1 wherein the second projection means is operable to generate light in a single beam, the apparatus comprising splitting means operable to split said single beam into said second and third divergent beams.
3. 3. A display apparatus in accordance with claim 2 wherein the splitting means comprises reflecting means operable to receive incident light of said single beam and to reflect one portion of said incident light in a first direction and another portion of said incident light in a second direction.
4. 4. A display apparatus in accordance with claim 3 wherein the reflecting means comprises a mirror wedge, the mirror wedge comprising reflecting faces defining a wedge apex at which the single beam is directed.
5. 5. A display apparatus in accordance with claim 4 wherein the reflecting means further comprises second and third mirror means, each presenting a reflecting face operable to receive incident light directed thereto by the reflecting faces of the mirror wedge, and to reflect light to form said second and third divergent beams.
6. 6. A display apparatus in accordance with claim 4 or claim 5 wherein the or each reflecting face is arcuate. (2
7. 7. A display apparatus in accordance with any preceding claim wherein the second projection means comprises beam shaping means opreable to shape at least one of the single beam and the second and third divergent beams.
8. 8. A display apparatus in accordance with any preceding claim wherein at least one of the first and second projection means comprises blend masking means for blending the edges of the or each beam output therefrom.
9. 9. A display apparatus in accordance with claim 8 wherein the blend masking means comprises a mechanical blend mask.