WO2018020035A1

WO2018020035A1 - Seamless multi-screen projection display system

Info

Publication number: WO2018020035A1
Application number: PCT/EP2017/069238
Authority: WO
Inventors: Stefan VANDEMAELE; Simon SABBE; Tom Bert
Original assignee: Barco N.V.
Priority date: 2016-07-29
Filing date: 2017-07-28
Publication date: 2018-02-01
Also published as: CN107664910A

Abstract

A screen assembly for a front projection display system is described with a first, a second, and a third projection screen having surfaces on which images can be projected, there being an angle between the first and second screens wherein the surface of the third projection screen on which images can be projected extends over the surface of the first projection screen and the surface of the third projection screen is either adjacent to the surface of the second projection screen or extends over the surface of the second projection screen.

Description

Seamless Multi-Screen Projection Display system

Field of the Invention

The present invention relates to front projection display systems and in particular to a construction which minimizes the visual seam between adjacent screens of a front projection display system, as well as a method of constructing such a display system.

Description of the Prior Art

Motion pictures shown in movie theaters are generally in 35 mm or 70 mm film formats (sometimes referred to as "first-run" movies), which have become the current standard formats in the movie industry. In order to provide high-quality screen images having minimal distortion, movie screens are designed with a width and arcuate radius suitable for these film sizes.

Since the 1960s, specialized movie theaters began showing Cinerama-type motion pictures. Cinerama-type motion pictures provide wider screen images than first-run movies by using three projectors to project three separate screen images adjacently onto a wider movie screen, with the three screen images together forming a single frame or screen image for the motion picture. The three projectors are mounted in an arc which covers a very wide aggregate angle of view. A center projector projects images forward, and two projectors on either side of the center projector crisscross, with a right projector projecting an image on a left panel of the movie screen and a left projector projecting an image on a right panel of the movie screen.

In a typical Cinerama or IMAX™ projection system, the screens are fixed and the geometry of the projection surface is not modified in function of the film being projected.

An IMAX projection system comprises a single large projection screen. The projection screen consists of smaller screen fabric elements that are stitched or sealed together, leaving no space or seam visible between screen fabric elements. An example of how screen elements are assembled is given in US 5,130,846 "Screen Panel Fastener" that describes how screen panels are fastened to a support structure. Adjacent screen panels will typically overlap each other and be fastened mechanically together and to a support structure by the intermediary of a fastener. Once two panel elements have been fastened together, they cannot be disassembled rapidly (like during the 15 minutes between two successive projections in a theater).

In another technique, screen elements are fused together. Large quality screens require radio frequency heat sealing (also known as dielectric sealing) to create a quality seams. In dielectric sealing, two pieces of fabric are placed between two electrodes and fused together. The seaming is thus permanent.

In a Cinerama projection system, the screen is composed of more than a thousand screen elements. The seams between panels are usually noticeable. Enthusiasts say the seams are not obtrusive; detractors disagree. For instance, in his memoirs, Lowell Thomas, an investor in the company that exploited Cinerama, was still raving about it thirty years after and yet the seams are still there. A detailed description of a Cinerama screen and screen elements is given in US 2,476,521 "Screen for picture projections".

The screen described in US 2,476,521 comprises upper and lower foundation members 1 and 2, preferably channel shaped as shown, which said members may be supported and spaced by any suitable arrangement of structural supporting members (not shown). The foundation members are curved circularly, as shown in Figure 1 , to support the cylindrical projection surface and extend through any desired are. They are supported in parallel relationship spaced to provide whatever vertical screen expanse is desired. In applying the" invention to other single curved surfaces, the curvature of the foundation members would be altered to conform to the curve selected.

The projection surface, i.e. the surface against which the projected image impinges, is made up of a series of screen elements 3 consisting of spaced strips extending from one of the foundation members to the other. The said strips are anchored to the upper and lower foundation members by suitable brackets 4' and 5, which said brackets may be secured to the foundation members by suitable bolts.

It is desirable that the screen elements be easily and quickly attachable to or removable from the foundation members so as to permit the screen to be quickly assembled and disassembled. It is also desirable that the screen elements be maintained under tension while attached to the foundation members. For these purposes the upper brackets 4 are provided with studs 6 adapted to receive the slots in the upper ends of the strips and the lower brackets and the lower ends of the strips are provided with apertures 8 and 9, respectively, to receive the ends of the springs which subject the strips to tension.

The brackets 4 and 5 are spaced along the foundation members in such manner that when the screen is viewed from the point at which the pictures are projected, which point preferably coincides with or lies behind the center of curvature of the screen, one vertical edge of each screen element overlaps the opposite edge of the next adjacent element, so that the projected image falls entirely on the surfaces of the screen elements.

Since 2014 Barco Escape projection systems deliver a compelling immersive cinema experience. The Barco Escape system does not require replacing the screens installed in theaters. The Barco Escape system can be retrofitted and allows a seamless transition between regular projection on a single screen and projection in the Escape format on the existing central screen complemented by lateral screens on the left and on the right of the central screen. A schematics representation of an Escape theater can be seen on figure 1 A and 1 B.

The lateral screens in an Escape theater cannot be sealed or sticthed to the central screen and as a result, a visible seam exist between the central screen and the lateral screens.

A method to minimize the visibility of seams between adjacent rear projection screens spaced apart from each other is disclosed In US 3,514,871 "Wide angle visual display". Large Lenses are positionned between the screens and a viewer. The screens are thus viewed through these lenses and are modified accordingly in at least two respects. First, the lenses function in a well understood manner to give the viewer the impression that the displays are considerably removed from the viewing position. Second, each lens cooperates with the lens next to it to function much in the same way as a pair of binoculars. The practical result of this is that whatever may be the separate visual impressions as seen by each of the two eyes of the viewer, these Visual impressions are fused in the viewer's brain into a single, clear visual impression. Thus, with no more care than merely duplicating the content of the screens along adjacent marginal edges and generally aligning the same, the viewer experiences a single, clear visual impression of the content projected along these marginal edges. In other words, the seam between adjacent screens is not perceived by the viewer. Adjacent screens not being fastened together, the lateral screens can be removed fairly rapidly. Unfortunately, the technique cannot be applied to existing theater settings. Indeed, lenses large enough to be used in a theater settings are not practical and require an additional support structure. Furthermore, the proposed solution operates only when the viewer occupies a favored position also known as sweet spot. In a regular theater setting most of the viewers will not be positioned at or near the sweet spot and they will perceive the seam.

In US 6,407,798 "Dual-screen theater", a first screen is used to project films in a first format and a second screen is used when films are projected in a second format.

The first and second screen are distinct, i.e. they have no portion in common as in an Escape projection system wherein a central screen is used to project films in a first format and said central screen is augmented by adjacent screens on its right and on its left. The solution proposed in US 6,407,798 is not only costlier and bulkier than what is required in an Escape display system, the problem of seams is not solved.

Indeed, as disclosed in US 6407798 "To the extent that there may be gaps between the sections of the wide-screen after the side panel sections are extended outwardly, the sections can be positioned tightly together to minimize any gaps, or the adjoining edges of the screen sections can be provided with overlapping flanges so that a substantially continuous arcuate surface results." Unfortunately, in an escape system, the central screen and a lateral screen cannot be positioned tightly together without risking scratching the coating of the central screen. Furthermore US 6,407,798 does not disclose how flanges should be deployed to avoid scratching the central portion of the wide-screen. It also remains silent on the geometry of flanges (shape and dimensions) that could be used in an Escape display system.

Alternatively, US 6407798 discloses a screen comprising a plurality of narrow strips stretched vertically from an upper strip rail to a lower strip rail. These strips provide the flexibility to allow the surface of the wide-screen to be curved easily to a desired arcuate radius. When positioned tightly or overlappingly against each other (e.g., similar to leaves of a Venetian blind), the row of strips gives the appearance of a substantially continuous and smooth screen surface. The strip rail guide the vertical strips and position them correctly with respect to each other. Unfortunately, such rails are neither available nor desirable in an Escape display system. How to position such strips without guiding rail with respect to the central screen is still an open question.

SUMMARY OF THE INVENTION A solution is required to make the seams between the lateral screens and the central screen of multiscreen display such as a Barco Escape™ display system less visible while retaining the possibility to easily dismantle or move the lateral screens. This should be done without deteriorating the coating on the central projection screen. The art needs improvement.

The present invention provides a screen assembly for a front projection display system comprising:

a first projection screen having top, bottom, left and right edges said edges delimiting a surface on which images can be projected; a second projection screen having top, bottom, left and right edges, said edges delimiting a surface on which images can be projected. The said first and second screens define an angle therebetween of less than 180°; with said left edge of said first projection screen and said right edge of said second projection screen, being separated by a seam wider than the pixel pitch of the images projected on the first and/or second projection screen. In order to decrease the visibility of the seam between the first and second projection screens, a third projection screen having top, bottom, left and right edges, said edges delimiting a surface on which images can be projected is used.

This screen assembly can avoid one or several of the problems of the prior art.

The surface of the third projection screen on which images can be projected extends over the surface of the first projection screen and; the surface of the third projection screen is either adjacent to the surface of the second projection screen or extends over the surface of the second projection screen.

It is an advantage of that aspect of the invention that the seam between the first and second projection screens will be less visible while avoiding another highly visible seam between the second and the third projection seam as would be e.g. the case if one vertical edge of each projection screen element overlapped the opposite edge of the next adjacent projection screen (i.e. if the second projection screen overlapped the third projection screen which overlaps the first projection screen).

In another aspect of the invention, the surface of the third projection screen and the surface of the second projection screen are flush along an edge of the third projection screen.

It is an advantage of that aspect of the invention that it will prevent visual artefacts.

In another aspect of the invention, the distance between the surface of the third projection screen and the surface of the first projection screen is smaller or equal to the distance that can be resolved by a viewer looking at the screen assembly.

It is an advantage of that aspect of the invention that it will render the screen assembly seamless.

In particular, the distance between the surface of the third projection screen and the surface of the first projection screen is inferior or equal to the pixel pitch of the images projected on the screen assembly.

In a further aspect of the invention, the third projection screen comprises a self- supporting substrate on which a coating is formed.

It is an advantage of that aspect of the invention that no closed frame is required. If a closed frame were required, this might limit the minimum distance being possible between the surface of the third projection screen on which images are projected and the surface of the first projection screen on which images are projected.

In a further aspect of the invention, the part of the third projection screen closest to the first projection screen is tangent or parallel to the surface of the third projection screen.

It is an advantage of that aspect of the invention that it will prevent or limit damages to the surface of the first projection screen if the third projection screen bumps against the first projection screen. In a further aspect of the invention an edge of the third projection screen is coated in a light absorbing material

Alternatively, an edge of the third projection screen is coated in a material with optical properties similar or identical to the optical properties of the surface of the second or first projection screen. It is an advantage of that aspect of the invention that it will further reduce the visibility of the seam that can exist between the third projection screen and the first or second projection screen.

A screen assembly according to any of the preceding claims further characterized in that the directrix that defines the cylindrical surface of the third screen (on which images can be projected) is a segment of a conic section (includes circle, ellipse, parabola, hyperbola and intersecting straight lines.,

In a further aspect of the invention the third projection screen has a ridge. It is an advantage of that aspect of the invention that it will increase the capacity of the substrate of the third projection screen to be self-supporting. It is a further advantage of that aspect of the invention that it can modify the resonance frequency of the third projection screen. Modifying the resonance frequency of the third projection screen can be used to prevent or limit the risk of contact between the third projection screen and the surface of the first projection screen. In yet another aspect of the invention, the third projection screen is fastened to the second projection screen.

The fastening can be done by means of screws and/or magnets.

It is an advantage of that aspect of the invention that it does not require alignment of the third and second projection screen.

DEFINITIONS

"Angle". In planar geometry, an angle is the figure formed by two rays, called the sides of the angle, sharing a common endpoint, called the vertex of the angle. Angles formed by two rays lie in a plane, but this plane does not have to be a Euclidean plane. Angles are also formed by the intersection of two planes in Euclidean and other spaces. These are called dihedral angles. Angles formed by the intersection of two curves in a plane are defined as the angle determined by the tangent rays at the point of intersection.While The angle between two planes (such as two adjacent faces of a polyhedron) is usually defined as the acute angle between two lines normal to the planes, the definition we will use is different. Since we will illustrate the invention with a number of planar section (in a plane substantially perpendicular to the projection screens), we will measure the angle between two adjacent projection screens based on the tangents to the trace of the projection screens in the plane of the section.

In this patent application, figure 12A shows the angle between two planar projection screen and figure 12B shows the angle between two non-planar projection screen. In figure 12A, the angle between the lateral projection screen 1 1 1 and the central projection screen 1 10 is Θ1 . The angle between the lateral projection screen 1 12 and the central projection screen 1 10 is Θ2. The projection screen being planar in the example of figure 12A, the angle between the screen 1 1 1 and 1 10 on one hand and 1 12 ans 1 10 on the other hand can be determined in the plane of the figure. The angle Θ1 is determined by the rays P1 and P3 which meets at the vertex V1 . The angle Θ2 is determined by the rays P2 and P3 which meets at the vertex V2. In figure 12B, the angle Θ1 is the angle between the tangent T1 to the screen 1 1 1 and the tangent T2 to the screen 1 10. The angle Θ2 between the central screen and the lateral screen 1 12 is the angle between the tangent T3 to the screen 1 12 and the tangent T4 to the screen 1 10. "Conic section". Ellipse, circle parabola, hyperbola (including intersecting straight lines) and segments thereof. Some examples of segments of conical section are given on figure 13A (segments of parabola), 13B (segments of ellipse) and 13C (segments of hyperbola including degenerate hyperbola i.e. segments of intersecting straight lines).

"Cylindrical surface". A cylindrical surface is generated by a straight line which moves along a fixed curve and remains parallel to a fixed straight line. The fixed curve is called the directrix of the surface and the moving line is called the generatrix (or generator) of the surface. A cylindrical surface does not need to have a circuiar section. The cross-section can be polygonal for example square, a pentagon, hexagonal or more sides.

"Flange". A flange is an external or internal ridge, or rim (lip), for strength, as the flange of an iron beam such as an I-beam or a T-beam; or for attachment to another object, as the flange on the end of a pipe, steam cylinder, etc., or on the lens mount of a camera; or for a flange of a rail car or tram wheel. Thus flanged wheels are wheels with a flange on one side to keep the wheels from running off the rails. An example is given in figure 14. A flange is a projecting rim or collar on an object, e.g. for keeping it in place.

"Flush". In mechanichs, means even or level (having the same height) with another surface. "Nominal", is being according to a plan, satisfactory, or as expected or typical.

"Pixel Pitch". Pixel pitch is a measure of the resolution of a fixed format display in general and a projection display in particular. In a modern front projection device, pixel pitch is very close to the size of the pixel projected on the projection screen. In cinema, the size of a pixel on screen varies from a fraction of a mm to several mm depending on the size of the screen, the projector and the distance between projector and screen.

"Projection Cone" or "Light-Emission Cone". Is the region of space reached in straight line by the rays of light coming out of the projection lens of a projector as shown on figure 15. A projector 1910 projects light on a projection screen 1910. In the example of figure 15, the projection cone 1920 forms a truncated pyramid. The base of the pyramid lies in the plabe of the projection screen 1910 and the faces of the pyramid are delimited by the adjacent dotted lines (which correspond sto rays of light) 1921 , 1922, 1923 and 1924.

"Ridge". An edge or ledge or lip which protrudes beyond the normal face of an object.

"Rim", the outer often curved or circular edge or border of something.

"Tangent". In geometry, the tangent line (or simply tangent) to a plane curve at a given point is the straight line that "just touches" the curve at that point. Leibniz defined it as the line through a pair of infinitely close points on the curve. The tangent plane to a surface at a given point is the plane that contains the tangent lines to all the curves on the surface at the given same point. "Theater". Refers to a building or room in which movies are shown.

BRIEF DESCRIPTION OF THE FIGURES Figure 1 is an illustration of an example multi-screen cinema environment having front, left and right screens as in e.g. an Escape™ system according to an embodiment of the present invention.

Figure 2 shows a detail of multi-screen cinema environment of Figure 1 . Figure 3 is a schematic representation of multi-screen environment seen from above according to an embodiment of the present invention.

Figure 4 is an illustration of a projection system for providing an immersive display experience on multiple screens according to an embodiment of the present invention. Figures 5A to C shows views of display systems with the screen extensions according to embodiments of the present invention. Figure 5D shows a projection cone of a projector used to project images mainly on a central projection screen according to an embodiment of the present invention. Figure 5E shows a lateral extension element extending at least until a region delimited by the line joining the edge of the central projection screen and the projection lens of the projector and the limit of the area where viewers will be positioned. Figure 5F shows how viewers positioned at the opposite of the right edge of the screen extension element and closest to the central screen will see the space between the screen extension element and the central screen more clearly than other viewers. Figures 6A, B, C, D and E show curved screen extension elements made of a curved substrate laminated with screen material according to embodiments of the present invention.

Figures 7A, 7B, 7C, and 7D show a screen fabric spanned on a metallic frame by means of spanners to form a lateral screen according to embodiments of the present invention.

Figures 8A and B show how a part of the screen extension element that is closest to the central screen can be at a tangent to the surface of the central screen or merely parallel to the surface of the central screen without touching it according to embodiments of the present invention. Figures 9A and B show a directrix that allows a screen extension element to approach the surface of a central screen in a tangent or parallel fashion according to embodiments of the present invention.

Figure 10 shows a cross section of a screen extension element; whereby the thickness of the substrate decreases from one edge according to an embodiment of the present invention.

Figures 1 1 A and 1 1 B show a viewer looking at an edge from an angle of approximately 45 degrees and a checkerboard pattern is projected on the central screen, the side screen and on the screen extension element according to embodiments of the present invention. Figure 12A shows the angle between two planar projection screens and figure 12B shows the angle between two non-planar projection screen according to embodiments of the present invention.

Figure 13 shows examples of segments of conical section. Figure 13A shows segments of parabola. Figure13B shows segments of ellipse and 13C shows segments of a hyperbola including a degenerate hyperbola i.e. segments of intersecting straight lines as used in embodiments of the present invention.

Figure 14 shows an example of a flange.

Figure 15 shows rays of light coming out of the projection lens of a projector.

DETAILED DESCRIPTION OF EMBODIMENTS

The present invention will be described with reference to certain embodiments which are examples from which the skilled person is able to learn the principle advantages and features of embodiments of the present invention. Figure 1 shows a multiscreen projection display system comprising a first or front screen 1 10 located in front of the audience. Left side or second screen 1 1 1 and right side or third screen 1 12 are screens located to the sides of the audience. Screens may also be mounted above and/or below screen 1 10. Front screen 1 10 has four edges, including top edge 142, bottom edge 143, left edge 140 and right edge 141 . Left side screen 1 1 1 and right side screen 1 12 also have four edges. For example, left side screen has front edge 1 1 6, which is the edge closest to front screen 1 10. It has rear edge 1 18, which is the edge farthest away from front screen 1 10. It has top edge 1 17, which is the edge closest to the ceiling. It also has bottom edge 1 19, which is the edge closest to the floor. Right side screen has similar edges.

Early Barco EscapeTM systems that were installed, a seam or "black bar" 144 is visible between the central screen 1 10 and the left side screen 1 1 1 as well as between the central screen 1 10 and the right side screen 1 12.

Figure 2 shows a detail of figure 1 in the dashed circle. Figure 3 is a schematic representation of the example multi-screen environment seen from above (i.e. a top view of the example multi-screen environment). It also illustrates an example seating arrangement for the multi-screen cinema environment of figure 1 .

Audience members in immersion zone 1 13 may be immersed by front screen 1 10, left side screen 1 1 1 , and right side screen 1 12. The audience in immersion zone 1 13 may be seated in seats such as seat 123. In the multi-screen environment, immersion zone 1 13 may span from front screen 1 10 to boundary 121 , which is an illustrative line connecting the rear edges of the left side screen 1 1 1 and right side screen 1 12. Beyond boundary 121 to the rear is viewing zone 1 14. Seats such as seat 122, in viewing zone 1 14 may not be fully immersed in the multi-screen cinema environment, but can still view front screen 1 10, left side screen 1 1 1 , and/or right side screen 1 12.

Figure 4 is an illustration of a projection system for providing an immersive display experience on multiple screens. The projector system 200a can be configured to be the master projector system. As used herein, the master projector system or the master media server provides synchronization signal to which the slave projector systems 200b and 200c synchronize their output. The master projector system 200a receives, decodes and/or provides the main audiovisual presentation in the immersive display 100. As used herein, a slave projector system or slave media server provides images synchronized to the master system wherein synchronization is based at least in part on the synchronization signal provided by the master projector system. A slave projector system may provide video that is projected peripheral, adjacent, near and/or otherwise complementary to the video provided by the master system.

The master projector system 200a transmits a synchronization signal over the cabled connection 130a to a first slave projector system 200b that then transmits the same synchronization signal over the cabled connection 130b to a second slave projector system 200c. The synchronization signal is the same or substantially the same for all projector systems to enable globally synchronized video in the immersive display system. Accordingly, due at least in part to the projector systems 200a-c projecting video based on the synchronization signal, a synchronized video presentation is provided on the screens 1 10, 1 1 1 and 1 12.

The projectors 200a, b and c each project an image on one of the screen 1 10, 1 1 1 , 1 12.

The spaces 144 and 145 between the central screen 100 and side screens 1 1 1 and 1 12 prevents the blending of the images projected on screens adjacent to each other.

It is an advantage or a purpose of the present invention to reduce the visibility of the seams 144 and 145.

In order to hide the seams or black bars 144 and 145; extension elements such as curved screen extension elements 150 are added to the lateral screens 1 1 1 and 1 12 as illustrated on the perspective view of figure 5A.

A top view of the display system 100 with the screen extensions 150 is given on figure 5B. As seen on figure 5B, the screen extension element 150 can hide part of the front screen 1 10. The inventors realized that it would be an easier solution as well as a more robust one (i.e. less prone to failure) to position the screen extension element 150 in front of the front screen 1 10 instead of adjacent to the left edge 140 or right edge 141 of the front screen 1 10. Furthermore, positioning the extension elements 150 next to the central screen instead of in front of the central screen still leaves a black seam between the central screen and the extension elements 150. This seam being "frontal" i.e. in a plane directly facing the audience, it is very visible. The situation where screen extension elements 150 are positioned adjacent to the edges of the front screen is illustrated on figure 5C to stress the difference with figure 5A and 5B. Tests were made to evaluate the impact of the screen extension elements on user experience. As long as the screen extension elements were positioned in front of the central screen 1 10; users reported having hardly perceived the space between the screen extension element 150 and the surface of the central screen 1 10. This was true whether the viewers looked at the central screen from a central viewing position or from an off-center viewing position.

Better overall results were obtained when the right edge 157 of the screen extension element 150 was in the projection cone of the projector 200a used to project images mainly on the central projection screen 1 10 as illustrated on figure 5D. Similarly, on the right side of the display system, the results were better when the left edge 157B of the screen extension element 150B was in the projection cone of the projector 200a used to project images mainly on the central projection screen 1 10.

Based on that observation, it is possible to determine the positions allowed for the edge 157 of the screen extension element 150 for a given central screen 1 10 and a given projector 200a. For instance, on the example of figure 5E, the lateral extension 150 should extend at least until the hashed region. In a first approximation, the hashed region is delimited by the line L joining the edge 140 of the central projection screen 1 10 and the projection lens of the projector 200a and the limit of the area where viewers will be positioned When the nominal distance between the right edge157 of the screen extension element 150 must be at a distance of DO or less from the central projection screen 1 10, a novel boundary condition is necessary and the screen extension element should be in the double hashed region.

The nominal distance can be evaluated in function of the projection settings (position of the viewers, size of the screens ...).

For instance, as seen on figure 5F, the viewers positioned at the opposite of the right edge 157 of the screen extension element 150 and closest to the central screen (position P0 on figure 5F) will see the space between the screen extension element 150 and the central screen 1 10 more clearly than other viewers at other positions like e.g. at P1 and at P2. The average human eye not being able to resolve details smaller than 1 mm when viewed at a distance of plus or minus 3 meters and a half and the distance between P0 and the right edge 157 of the screen extension element being 10 meters or more in a typical theater setting, the distance DO can be as large as 3 mm and the seam will be invisible to a viewer positioned at P0. Other viewers are even less likely to see the seam, either because they are farther away from it or because they see it at an angle as illustrated on figure 5F.

In a first embodiment seen on figure 6A, B and C, the curved screen extension element 150 is made of a curved substrate 151 laminated with screen material 152 with similar or identical optical properties as the screen material used for the front screen 1 10. In particular the screen material 152 is white and has an optical gain in the range 1 .30 to 1 .80. The screen material 152 can be different from the screen material used for the side screens 1 1 1 and 1 12. The substrate can be made of a flexible material like e.g. PVC (polyvinyl chloride), PET (polyethylene terephthalate), acrylic or any other material that can be shaped in the required geometry. The material is advantageously flexible enough in order not to damage the surface of front screen 1 10 if the screen extension element 150 bumps against front screen 1 10 during positioning (together or independently of the lateral screens) . If PVC is used for the substrate 151 , the thickness Th1 of the substrate is for instance 0.3mm although a thickness of 0.2, 0.5 mm or more will give acceptable results as well.

The screen material 152 can for instance be identical to the screen material used for the front screen 1 10 and/or the lateral screens 1 1 1 , 1 12.

The projection surface determined by the screen extension element 150 can be a cylindrical surface with a directrix D as indicated on figure 6A, 6B and 6C and a generatrix G parallel to the edge 1 1 6 of side screen 1 1 1 . When the central screen 1 10 is planar; the generatrix G can be parallel to the plane of the central screen and in particular, parallel to the left and right edges of the central screen. Figure 6A shows a section of a screen extension element 150 in a plane P1 perpendicular to the projection surface of the side screen and extension element 150.

Figure 6B shows a view of projection of a screen extension element in the plane of the screen 1 1 1 when the screen extension element 150 is fastened to the side screen 1 1 1 in nominal position.

In the example of figure 6A, the thickness of both the substrate 151 and the screen material 152 are constant along the directrix D. As will be discussed later, it can be advantageous to let the thickness of the substrate 151 and/or the screen material 152 vary from a first edge 159 of the screen extension element 150 to a second edge 157 of the screen extension element 150. In the example of figure 5A, 5B, 6A, 6B and 6C; the edges 157 and 159 are parallel to the edge 1 16 of side screen 1 1 1 . Edge 159 is closest to edge 1 1 6 of side screen 1 1 1 than edge 157. Edge 157 is closer to the central screen 1 10 than edge 159. When the substrate is too thin to allow spanning screen fabric on it, a sprayed coating or "paint-on-screen" can be used.

A ridge 1 60 along part or whole of the top and bottom edges of the screen extension element 150 (as seen on figure 6D) can be used to increase its rigidity.

In one embodiment of the invention, the screen extension element 150 can be fastened to the support structure that supports the lateral screen 1 1 1 or 1 12. The extension 150 is adjacent to the edge 1 16 of lateral screen 1 1 1 . The ridge 1 60 can then also be used to change the resonance frequency of the extension element. This is useful when the lateral screens 1 1 1 and 1 12 being driven by (electrical) motors when they are positioned, vibrations are likely to be transmitted to the screen extension elements 150. If those vibrations have a frequency that matches the resonance frequency of the screen extension element, the extremity of the screen extension element may oscillate severely enough to slap the central screen repeatedly. Uncontrolled oscillations of the screen extension element have thus the potential to alter the coating of the central screen By modifying the resonance frequency of the screen extension element, ridges along the top and bottom edges of the screen extension elements can be used to mitigate the risk of altering the coating of the central screen when positioning the lateral screens close to the central screen.

The ridge can extend inside and / or outside of the curvature of the screen extension element as seen on figure 6E. To allow easy modification of the resonance frequency on site, the thickness of the ridge can be varied by piling one or more sheet-like component 161 on the ridge(s)

1 60 as seen on figure 6D. The sheet like component 1 61 can be made of the same material as the substrate 151 or it can be made of a different material, thereby increasing the range of the correction to the resonance frequency. Alternatively, the screen extension elements could be positioned independently from side screen 1 1 1 and 1 12. For instance, the screen extension element 150 could hang from the ceiling or be supported by a support structure like e.g. a tripod.

In the example of figure 7A, 7B, 7C and 7D; a screen fabric 1 1 1 1 is spanned on a metallic frame 305 by means of spanners 306 to form the lateral screen 1 1 1 . The spanners and the frame can be invisible when the screen fabric 1 1 1 1 is in place as is the case for e.g. Cinescreen™ from ShowTex. On figure 7A, the screen extension element 150 is positioned adjacent to edge 1 1 6 of side screen 1 1 1 by means of a frame extension 307 fastened to the frame 305. If one or more elements

1 61 are used, they can be fastened to the frame extension 307. The screen extension 150 can be positioned adjacent to edge 1 1 6 of side screen 1 1 1 or screen extension element 150 can overlap the edge 1 1 6 and the screen fabric 1 1 1 1 of side screen 1 1 1 .

The extension frame 307 can then be as represented in perspective view on figure 7B. The extension frame 307 can be fastened to frame 305 by means of e.g. screws 309 or strong magnets. When the screen extension element 150 is made of a rigid or semi-rigid substrate 151 , it can be glued or screwed to frame extension 307. Alternatively, the screen extension element 150 can be a screen fabric spanned on a closed frame extension 307 (not shown).

Alternatively, magnets 31 1 and 308 are used to position the screen extension element 150 as illustrated on figure 7C and 7D. If the metal frame 305 is made of ferromagnetic material, it is also possible to fasten the screen extension element 150 by means of the magnets 31 1 alone as illustrated on figure 7C. To increase stability, the magnets 31 1 are preferably as long as the trusses 310 of frame 305 are wide. The magnets 31 1 can be embedded in the substrate 151 or between the substrate 151 and the screen fabric 152. The magnets 308 can be positioned behind the screen fabric 1 1 1 1 of side screen 1 1 1 as seen on figure 7D.

In another embodiment the extension 150 is an integral part of the lateral screen 1 1 1 or 1 12. The screen material 1 1 1 1 of lateral screen 1 1 1 and 1 12 can be stitched to the screen material 152 of the screen extension element 150 either before or after the screen material 152 is laminated on the substrate 151 . If a standard screen fabric is used for the screen extension element, the fabric can be seamed to the screen fabric of the lateral screen 1 1 1 or 1 12.

The part of the screen extension element 150 that is closest to the central screen 1 10 can be tangent to the surface of the central screen 1 10 or merely parallel to the surface of the central screen 1 10 without touching it as seen on the top view on figure 8A and 8B.

If the screen extension element is tangent to the surface of the central screen, the backside of the screen extension element can be coated in e.g. Teflon or covered with a micro-fiber rag used for cleaning the surface of the central screen.

Examples of directrix D that allows the screen extension element to approach the surface of the central screen in a tangent or parallel fashion are represented on figure 9A and 9B.

On figure 9A, the directrix is formed by a segment of a straight line SL and an arc of circle AC with radius Rc and center C.

Instead of an arc of circle, the segment AC can be a segment of a conic section including a degenerate hyperbola.

If the side screens 1 1 1 and 1 12 must form an angle different from 90 degrees with the central screen 1 10, the angle alpha characterizing the directrix D on figure 9A and 9B are adapted accordingly. For instance, if the side screen 1 1 1 must form an angle of 90 degrees + beta ,the angle alpha becomes 90 degrees - beta for the directrix of figure 9A and 90 degrees + beta for the directrix of figure 9B.

It can be an advantage to have the outermost portion of the screen extension parallel to the central screen when its position is nominal. Indeed, in case of a collision between the screen extension element and the central screen, the force will be spread across a larger area and the risk that the coating of the central screen be damaged is reduced.

The distance DO between the substrate 151 of the screen extension 150 in the vicinity of its edge 157 and the central screen 1 12 is preferably kept below the pixel pitch of images projected on the lateral screen. This is to ensure that the seam existing between the central screen 1 12 and the lateral screen 1 1 1 is hardly noticeable when the viewers are sitting in one of the seats 123 in the theater. The nominal distance DO can be less than 1 cm, less than 5 mm or preferably less than 2.5 mm. If the combined thickness of the substrate 151 and screen material 152 is larger than the pixel pitch, some viewers are likely to see that seam.

To mitigate this, the thickness of the screen extension element 150 can decrease from the nominal value ThO = Th1 + Th2 to a lower value Th3 (Th1 < ThO) where Th3 will be less than the pixel pitch. Decreasing the thickness of the screen extension element 150 can be advantageous to further mitigate the risk of deteriorating the coating of the central screen 1 10.

Indeed, as the substrate 150 gets thinner, it is easier to bend. In the eventuality of a collision between the screen extension element 150 and the central screen, the portion of screen extension element that would come in contact with the surface of the screen will bend more easily. By bending more easily, the thinner part of the screen extension element will not be able to transmit as much force as otherwise, thereby decreasing the probability that the coating of the central screen be scratched. If a ridge 1 61 is used, it should be narrower or absent from the region of the screen extension element that would contact the surface of the central screen in the event of a collision. This can mean that there is no ridge in the terminal part of the screen extension element or that the ridge extends from the substrate away from the central screen. To further decrease the risk of deteriorating the coating of the central screen, the back side of the screen extension element can be coated in a material like e.g. Teflon or a micro-fiber rag, at least in the vicinity of the edge 157 of the screen extension element.

An example of cross section of the screen extension element 150 can be seen on figure 10. On figure 10, the thickness of the substrate 150 decreases from edge 159, where it is equal to Th1 , to edge 157, where it has decreased to the value Th1 '.

The lateral side 158 of edge 157 can be coated in black to further decrease its perceptibility by viewers. If it is not possible to decrease Th1 so that it becomes smaller than the pixel pitch, it may be advantageous to coat the lateral side 158 of edge 157 with a coating whose optical properties are identical or similar to the optical properties of the screen material 152 instead of black.

In another aspect of the embodiment, the screen material 152 is bent around the edge 157 In that fashion, the lateral side 158 is covered with screen material 152.

When side 158 is covered with screen material 152 or coated with a material with optical properties identical or similar to those of screen 1 10, the visibility off the lateral side 158 is decreased.

Reflection of pixels projected on the central screen 1 10 close to the edge 157 on the screen material covering the lateral side 158 of the screen extension element 150 will decrease visibility of the vestigial seam that can still exist between the screen element 150 and the central screen 1 10. This is illustrated on figure 1 1 A and 1 1 B. On those figures, a viewer looks at the edge 159 from an angle of approximately 45 degrees. On figure 1 1 A, a checkerboard pattern is projected on the central screen 1 10 and the side screen 1 1 1 and screen extension element 150. The lateral side 158 of screen extension element 150 is coated in black.

On figure 1 1 B, the same checkerboard pattern is projected on the central screen 1 10 and the side screen 1 1 1 and screen extension element 150. The lateral side 158 of screen extension element 150 is covered by e.g. screen material 152. The screen fabric used for screens 1 1 1 and 1 10 behaving like a Lambertian emitter, some of the light reflected by the screen 1 10 in the vicinity of edge 157 reaches the lateral side of the screen extension element and is reflected back towards the viewers. The exact end result depends on the screen fabric used for the central screen and the screen extension element 150. Tests also indicate that the visibility of the lateral side 158 depends on the colors projected on the screen extension element 150 and the central screen 1 10 in the vicinity of the lateral side 158.

Depending on the position of the projector 200b that projects images on the side screen 1 1 1 , the image can also be projected on the lateral side 158 and the visibility of the lateral side is decreased further. The invention allows rendering the display system 100 seamless or as close to seamless as possible without using costlier and more complex techniques.

When the directrix D is an arc of a circle, tests showed that the radius of curvature Rc could be as little as 5 cm when the screens 1 10, 1 1 1 and 1 12 are typically 8 meters long and 3 to 4 meters high.

Claims

Claims.

1 . A screen assembly for a front projection display system comprising: a first projection screen (1 10) having top, bottom, left and right edges said edges delimiting a surface on which images can be projected; a second projection screen (1 1 1 ) having top, bottom, left and right edges, said edges delimiting a surface on which images can be projected; said first and second screens defining an angle therebetween of less than 180°; with said left edge of said first projection screen and said right edge of said second projection screen, being separated by a distance greater than the pixel pitch of the images projected on the first and/or second projection screen, a third projection screen having top, bottom, left and right edges, said edges delimiting a surface on which images can be projected wherein the surface of the third projection screen on which images can be projected extends over the surface of the first projection screen and the surface of the third projection screen is either adjacent to the surface of the second projection screen or extends over the surface of the second projection screen.

2. A screen assembly according to claim 1 , wherein the surface of the second projection screen and the surface of the third projection screen are flush along an edge of the third projection screen.

3. A screen assembly according to claim 1 or 2, wherein a seam between the first and second projection screens is not highly visible while there is no highly visible seam between the second and the third projection seam.

4. A screen assembly according to any preceding claim, wherein a distance between the surface of the third projection screen and the surface of the first projection screen is smaller or equal to the distance that can be resolved by a viewer looking at the screen assembly.

5. A screen assembly according to any preceding claim, wherein a distance between the surface of the third projection screen and the surface of the first projection screen is inferior or equal to the pixel pitch of the images projected on the screen assembly.

6. A screen assembly according to any preceding claim, wherein the third projection screen comprises a self-supporting substrate on which a coating is formed.

7. A screen assembly according to any preceding claim, without a closed frame so that there is no limit to the minimum distance between the surface of the third projection screen on which images are projected and the surface of the first projection screen on which images are projected.

8. A screen assembly according to any preceding claim, wherein a part of the third projection screen closest to the first projection screen lies at a tangent or parallel to the surface of the third projection screen.

9. A screen assembly according to any preceding claim, wherein an edge of the third projection screen is coated in a light absorbing material.

10. A screen assembly according to any of the claims 1 to 8, wherein an edge of the third projection screen is coated in a material with optical properties similar or identical to the optical properties of the surface of the second or first projection screen.

1 1 . A screen assembly according to any preceding claim, wherein a directrix that defines a cylindrical surface of the third screen on which images can be projected is a segment of a conic section.

12. A screen assembly according to claim 1 1 , wherein the directrix is one of a circle, an ellipse, a parabola, a hyperbola and intersecting straight lines.

13. A screen assembly according to any preceding claim, wherein the third projection screen has a ridge.

14. A screen assembly according to any preceding claim, adapted to modify the resonance frequency of the third projection screen.

15. A screen assembly according to claim 14, wherein the resonance frequency of the third projection screen prevents or limits the risk of contact between the third projection screen and the surface of the first projection screen.

1 6. A screen assembly according to any preceding claim, wherein the third projection screen is fastened to the second projection screen.

1 7. A screen assembly according to claim 1 6, wherein the fastening comprises screws and/or magnets.

1 8. A method of screen assembling for a front projection display system, the method comprising: obtaining a first projection screen (1 1 0) having top, bottom, left and right edges said edges delimiting a surface on which images can be projected; obtaining a second projection screen (1 1 1 ) having top, bottom, left and right edges, said edges delimiting a surface on which images can be projected; placing said first and second screens at an angle there between of less than 1 80°; with said left edge of said first projection screen and said right edge of said second projection screen, being separated by a distance greater than the pixel pitch of the images projected on the first and/or second projection screen,

obtaining a third projection screen having top, bottom, left and right edges, said edges delimiting a surface on which images can be projected wherein the surface of the third projection screen on which images can be projected extends over the surface of the first projection screen and the surface of the third projection screen is placed either adjacent to the surface of the second projection screen or extends over the surface of the second projection screen.

1 9. A method according to claim 1 8, wherein the surface of the second projection screen and the surface of the third projection screen are placed flush along an edge of the third projection screen.

20. A method according to claim 18 or 19, further comprising reducing the visibility of a seam between the first and second projection screens while there is no highly visible seam between the second and the third projection seam.

21 . A method according to any of the claims 18 to 20, wherein a distance between the surface of the third projection screen and the surface of the first projection screen is set to be smaller or equal to the distance that can be resolved by a viewer looking at the screen assembly.

22. A method according to any of the claims 18 to 21 , wherein a distance between the surface of the third projection screen and the surface of the first projection screen is made inferior or equal to the pixel pitch of the images projected on the screen assembly.

23. A method according to any of the claims 18 to 22, wherein the third projection screen comprises a self-supporting substrate on which a coating is formed.

24. A method according to any of the claims 18 to 23, providing no limit to the minimum distance between the surface of the third projection screen on which images are projected and the surface of the first projection screen on which images are projected without having a closed frame.

25. A method according to any of the claims 18 to 24, a part of the third projection screen closest to the first projection screen being located at a tangent or parallel to the surface of the third projection screen.

26. A method according to any of the claims 18 to 25, further comprising coating an edge of the third projection screen in a light absorbing material.

27. A method according to any of the claims 18 to 25, wherein an edge of the third projection screen is coated in a material with optical properties similar or identical to the optical properties of the surface of the second or first projection screen.

28. A method according to any of the claims 18 to 27, wherein a directrix that defines a cylindrical surface of the third screen on which images can be projected is a segment of a conic section.

29. A method according to claim 28, wherein the directrix is one of a circle, an ellipse, a parabola, a hyperbola and intersecting straight lines.

30. A method according to any of the claims 18 to 29, providing the third projection screen with a ridge.

31 . A method according to any of the claims 18 to 30, further comprising modifying the resonance frequency of the third projection screen.

32. A method according to claim 31 , wherein the resonance frequency of the third projection screen prevents or limits the risk of contact between the third projection screen and the surface of the first projection screen.

33. A method according to any of the claims 18 to 32, further comprising fastening the third projection screen to the second projection screen.

34. A method according to claim 33, wherein the fastening comprises screws and/or magnets.