CA2003661A1 - Method and apparatus for presenting 3-d motion pictures - Google Patents

Abstract

Title: METHOD AND APPARATUS FOR PRESENTING

Inventors: William C. Shaw I. Graeme Ferguson Roman B. Kroitor Gordon W. Harris Ken T. Baker Paul D. Panabaker Marian F. Toporkiewicz ABSTRACT OF THE DISCLOSURE

A high fidelity 3-D immersion theatre experience is produced by alternately projecting corresponding left-eye and right-eye images onto a dome-shaped projection screen from two separate film strips and through separate wide-angle lenses. The lenses are positioned close together with their projection axes in a common vertical plane to achieve lateral co-incidence of the projected images and oriented in that plane to achieve vertical co-incidence of the images. Each person viewing the motion picture is provided with glasses that have lenses in the form of liquid crystal cells arranged to alternately block the left and right eyes of the person in synchronism with the projection of right-eye and left-eye images respectively, so that a stereoscopic effect is perceived.

Description

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FI~LD OF THE INVXNTION
Thi~ invention relates to a method and apparatus for presenting stereoscopic or three-dimensional motion pictures (hereafter called 3-D motion pictures).
BACKGROUND O~ THE INV~NTION
3-D motion pictures are generally made by simultaneously photographing a sub~ect using two motion picture cameras positioned to provide ~left eyeN and "right eye" views of the ~ub~ect. To present the motion picture, the images recorded by the camera6 are pro~ected onto a screen and are optically coded in some way ~o that the left eye of a viewer sees only the images that were recorded by the Nleft eye~' camera while the viewer~s right eye sees only the "right eye~ images. The viewer then perceives a stereoscopic or 3-D effect.
DESCRIPTION OF THE PRIOR ART
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One method~of coding the images involves using .. ...
colour filters (anaglypta). For example, the right eye ~
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images may be coloured blue and the left eye images red and - 20 the viewer provided ~ith spectacles having filters that are coloured 8e that the viewer~s right eye sees only blue images iand the' iefti eye sees only red images'. A -~
disadvantage of this technique i8 of course that it can be used with two colour images only. This method was used by i ~ -the ~ssignee of the present invention (Imax Systems Corporation) to present computer qenerated 3-D images in a - dome at the Tsukuba Expo '85 fair in Japan. ~ ;
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Full colour 3-D image~ may be coded by a technique referred to as ~lalternate eye~. This involves the use of what are in effect ~huttered spectacle~ worn by a viewer. The ~hutters effectively block and unblock the view from each eye alternately in timed relation to pro~ection of the images onto the screen so that the viewer' 3 right eye is blocked when left eye images appear and vice versa.
. .
This technique i~ di cu~sed, for example, in United States Patent No. 4,424,529 (Roese et al.).
Another coding technique involves the use of crossed polarized filters (axes of polarization at 90 to each other) on the pro~ection lenses for the respective images and correspondingly polarized filters in glasses worn by a viewer. Thi~ technique was used by Imax Systems Corporation to present full colour 3-D motion pictures at Expo '86 in Vancouver, Canada using large format films such as tho~e that are available under the registered trade marks INAX and ONNINAX. The use of large format films is possible as a result of development of the so-called "rolling loop~ film transport mechanism for cameras and pro~ectors. United States Patent No. 3,494,524 to Jones discloses the 'principle of a rolling ~loop transport mechanism and a number of improvements are disclosed in United States Patents Nos. 3,600,073, 4,365,877 and 4,441,796 (Shaw).
While the polarization technique may be the best c~rrently used commercial method of presenting full colour .
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3-D motion pictures, it does have some limitations. One of these ic that the viewer must keep his or her head erect in order to maintain proper polarizer orientation ~nd avoid ~Ighostl~ image3. A second limitation is that most materials u~ied for pro~ection screens significantly depolarize the pro~ected light which degrades the quality of the projected image. However, the present inventors have found that the single most significant limitation of the polarization technique is that the polarized light is effectively "rotatedN and the polarization effect severely impaired where a curved screen i8 used for wide field of view pre~ientations. Thi~i is due to an effect known as NBrewster's Law'.
BRI~F DESCRIPTION OF THE INVENTION
An ob~ect of the present invention is to provide an improved method and apparatus for presenting 3-D motion pictures.
In a broad method aspect, the invention involves the teps of providing a dome-shaped pro~ection screen and alternately pro~ecting corresponding left-eye and rlght-eye images onto the screen. The left and right eyes of each person viewinq the motion picture are alternately blocked in synchronism with the appearance of right-eye and left-eye images recpectively on the screen, so that a stereoscopic effect is perceived. Preferably, the images are pro~ected fro- two separate film strips through separate wide-angle lenses having respective pro~ection ~: :

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axes. In this event the lenses are positioned with their pro~ection axe~ in a common vertical or horizontal plane for co-incidence of the pro~ected images on the screen in a direction at right angles to said plane. The lenses are oriented within the said common plane to achieve co-incidence of the pro~ected images on the ~creen in the direction of the plane.
In its apparatus aspect, the invention preferably provides a dome-&haped pro~ection screen and means for alternately pro~ecting corresponding left-eye and right-eye images onto said screen from two ~eparate film strips. The pro~ection means includes separate wide-angle lenses for the respective film strips, the lenses having respective pro~ection axes and being positioned directly ad~acent one another with their respective axes in a common vertical or horizontal plane for co-incidence of the pro~ected images on the screen in a direction at right angles to that plane and with the lens axes oriented within the said common plane to achieve co-incidence of the images on the screen in the direction of that plane. The apparatus also includes mean~ for alternately blocking the left and right eyes of ~each person viewing the motion picture in synchronism with~
the appearance of right-eye and left-eye images respectively on the screen, so that a stereoscopic effect ~ 25 is perceived.
; Presentation of images on a dome-shaped pro~ection screen coupled with pro~ection through wide~

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angle lenseis allow~ the production of 3-D images that can occupy a wide field of view and thus fill the visual field of the audience. Alternate eye 3-D pro~ection allow~ the uce of full-colour images without the disadvantages associated with polarization techniquei. Pro~ectlon of the respective series of images from two separate film strips through separate lenses has been found to minimize eye strain because any unsteadine~s in the pro~ected images will be random and this has been found to be much more tolerable to a viewer than what might be termed co-incident unsteadiness if both images were pro~ected from the 3ame filmstrip. ~ ~ :
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Further, by orienting the lenses as defined previously, it is pos~ible to ensure a high level of co~
incidence of left-and right-eye images over a wide area of the screen. This also further minimizes eye strain and i8 particularly important where high resolution film is u~ed (see later). .
It has been found that attention to all of the~e criteria coupled with the use of high-quality equ1pment and film stock and high and uniform illumination levels can lead td the présefftation of a high fidelity stereoscopic motion picture and a superior theatrical experience for the ~:~ audience. It is pos6ible to display full-colour 3-D images -: 25 in a large volume of space that fill the vi~ual field of ~he audience while causing minimal eye strain, to the point ;~ at which members of the audience may not realize that they '' ~' ~:
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are watching a motion picture.
Exceptionally high quality presentation may be achiaved by using high resolution film, for example of IMAX
or ONNIMAX format. Thi~ format i~ characterized by a large frame ~ize (so-called 70 millimeter 15 perf. film) and high quality film ~tock. Nhile thi 8 particular format i8 not essential to the invention, it i8 believed that a large frame size should be used having a usable image area of at lea~t 1200 square millimeter~ (approximately two square inches).
BRIFF Dl~SCRIPTION OF T~IE DRAWIlæS :
In order that the invention may be more clearly understood, reference will now be made to the accompanying ~-drawings which illustrate a particular preferred embodiment of the invention by way of example, and in which: -Fig. 1 is a schematic vertical sectional view through a theatre for pro~ecting motion pictures in accordance with the invention;
Fig. 2 is a simplified perspective view showing the principal components of a 3-D motion picture pro~ector used in the theatre of Fig. l;
Fig. 3iis!a sdhematic view showing the two rotors ;
of the pro~ector of Fig. 2; -Fig. 4 is a somewhat schematic side elevational . .. ...
view of the pro~ection lenses of the pro~ector of Fig. 2;
Figs ! 5 and 6 are schematic perspective views . . .
illustrating alternate eye 3-D pro~ection; and, ~ ~-, -20036fil.

Fig. 7 shows a typical frame format for a filmstrip used in the method of the invention.
D13 SCRIPTION OF PREFERRI~D EIIBODIlll~N~
Referring first to Fig. 1, a motion picture .pro~ection theatre i8 ~hown to include a dome-shaped structure 10, the internal surface of which forms a pro~ection screen 12. Within the theatre i8 a ~tructure generally indicated at 14 that defines seating areas for the audience and a pro~ection room 16 for a pro~ector 20.
As will be described in more detail later, the pro~ector i8 designed to alternately pro~ect corresponding left-eye and right-eye images onto the screen 12 from two separate filmstrips through separate wide-angle lenses having respective pro~ection axes oriented to promote a high degree of lateral and vertical co-incidence of the projected images. The viewing audience is provided with glasses that operate in synchronism with the pro~ector to alternately block the left and right eyes of each person in synchronism with the sppesrance of right-eye and left-eye images on the screen 12, 80 that a stereoscopic effect is perceived.
~ Referring to Fig. 2, the pro~ector 20 has a $rame 22 which includes three horizontally disposed baseplates 24, 26 and 28 supported in vertically spaced positions by various legs 30. Baseplates 24 and 26 support respective upper and lower rolling loop transport mechanisms that are generally indicated at 32 and 34 respectively. Part3 of . ~.: ~..

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20~)36fil respective film strips to be transported by the mechani~m~
are indicated at 38 and 40. Corre~ponding pro~ection len~es are indicated at 42 and 44, while a common lamphouse containing pro~ection lamps, mirror~ and a~sociated lenses . i8 generally indicated at 46. Lenses 42 and 44 are identical wide-angle ~fisheye~ lenses.
The drawings show only the principal components of the respective rolling loop mechanisms. Reference may be made to the Shaw ~073 patent (supra) for a fuller description of the rolling loop film transport mechanism.
The two mechanisms 32 and 34 of pro~ector 20 are each essentially the same as the mechanism disclosed in the Shaw patent, except for the features described specifically herein. The disclosure of the Shaw patent i8 incorporated herein by reference.
Fig. 2 ~hows that the rollinq loop mechanism 32 includes stator means made up of an inlet stator assembly 48 and outlet ~tator assembly 50 with an aperture plate 52 between the two stator assemblies. Part of a rotor of the mechanism is visible at 54. The rotor co-operate~ with the ~. ~ .......
stator to define a film passage, and has gaps for receiving film loops, all asldescribed in the Shaw patent. Rotor 54 is supported for rotation about a vertical axis indicated at X in Fig. 2.
- 25Mechanism 32 also includes means for moving film strip 38 through the passage between the rotor and stator, in the form of driven inlet and outlet sprockets 56 and 58 '` '`'`' ''`.', ' '~ "

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respectively. Mechanism 32 also includes means for locating the filmstrip in registration with the aperture in aperture plate 52, in the form of fixed fil~ regi~tration pins that are located ad~acent the film pro~ection aperture for engagement in the marginal perforations typically provided in motion picture film (see Fig. 7).
In accordance with the teaching of the Shaw patent, the film is decelerated as it is located on these registration pins, by a cam unit immediately ad~acent to and upstream of the aperture plate 52. The cam unit of mechanism 32 is generally indicated at 60 in Fig. 2.
The lower rolling loop transport mechanism 34 is essentially identical with mechanism 32 and includes a film decelerating cam unit 62. The two cam units are driven by a common drive ~haft 63. The other components of mechanism 34 are denoted by primed reference numeral6 corresponding to the numerals used for the components of mechanism 32.
The rotors 54 and 54~ of the two mechanisms are identical and are positively coupled together for rotation about axis X. ;
The two rotors are rotationally offset from one another (see Fig.l 3)i to an extent sufficient to cauæe alternate projection of images from the respective filmfitrips 38 and 40. However, all of the other components of the two mechaniqms will be aligned with one another. For example, as can be seen from Fig. 2, the two input sprockets 56 and 56~ are aligned and are mounted on a '~ ~'"'.,`''.

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common driven shaft 64. Similarly, the output sprocket 58 and the corresponding sprocket for mechanism 34 (not visible) are mounted on a common drive shaft 66. Although not visible in Fig. 1, the two drive shafts 64 and 66 are driven from the main drive motor of the pro~ector 80 that the sprockets are driven in synchronism with the other component~ of the projector.
Two separate aperture plates are in fact used for the respective mechanisms but the plates are mounted in a common housing indicated at 68. Similarly, the two pro~ection lenses 42 and 44 are vertically aligned and mounted in a common housing 70.
Referring to Fig. 3, the two rotors 54 and 54' are shown as seen in plan but with the lower rotor 54' shown as being of larger diameter than the upper rotor simply for the purpose of illustrating the rotor offset discussed previously; in fact, the two rotors are of -~
identical diameter. The gaps in the two rotors are denoted respectively by the letters G and G' and the lines denoted A and B indicate the gap offset between the respective rotors. ~ach of the rotors is provided with a curved plate behind each gap that forms a main shutter, and with a "flicker~ shutter midway between each pair of gap~, again as de~cribed in Shaw '073 patent. As a result of this shutter configuration, each frame in each filmstrip is ,: ~
pro~ected twice. ~ -Fig. 3 shows a practical pro~ector in which each ~-': . ~ :, - XO~)3661.

rotor has eight gaps and ~ixteen ~hutters. In this configuration, the rotor offset necessary to achieve alternate eye pro~ection (with two images being pro~ected twice) i8 one quarter of the gap spacing. The angular 5amount of the offset will therefore amount to one quarter of 45 (the angular spacing of the gaps). If no ~econdary shutters were used, the offset should be one half of the gap spacing. This amount should be further divided by two for each secondary shutter added between each ad~acent pair of gaps.
The two lenses 42 and 44 are vertically aligned in a plane of aLignment indicated at P in Fig. 2. This len~
orientation ensures that the pro~ected images are laterally co-incident on the pro~ection s~reen 12 (Fig. 1). Vertical 15co-incidence i8 achieved by appropriate orientation of the pro~ect$on axes of the two lenses as shown in Fig. 4. That view is a schematic illu~tration taken in plane P. The two lenses 42 and 44 are shown as are their respective axes 42a and 44a. In this particular embodiment, image co-incidence 20in the vertical direction is accomplished by shifting the two lenses towards one another as indicated by arrows 64.
This has the effect df dèflecting the images that are pro~ected through lens 42 so that they meet at the screen.
The normal "straight ahead" positions of the 25lenses 42 and 44 are indicated in ghost outline in Fig. 4.
In these positions, the pro~ection axes 42a and 44a would be co-incident with the respective centreline~ 66 of the : ' .

; ;~C03 _ 13 --apertures through which the images are projected. However, the lense~ are ~hifted towards one another to the off~et positions shown in Fig. 4. The offset between the aperture centrelines 66 and the re~pective projection axes 42a, 44a is generally denoted by arrows 68 in Fig. 4. The extent of this offset will depend on the particular dimensions of the theatre and the spacing between the two projection lenses but in one practical embodiment was 0.102 millimeters (per len~). The offset will normally be fixed once set and may be applied at either or both of the lenses a~ Yhown or at only one lens.
In addition to this lens offset, it may be desirable to impart to one or both of the lenses a programmable lens shift in order to correct for inaccuracies in the location of the images on the two filmstrips. A technique for accomplishing this lens shift i~ dlsclosed in United States patent application Serial No.
365,633 filed June 13, 1989.
Figs. 5 and 6 illustrate schematically the step of alternately blocking the left and right eyes of each person viewing the motion picture in synchronism with the appearancè of right-eye and left-eye images respectively on the screen. The pro~ector is generally indicated by a cylinder denoted 20 and the two views may be taken as illustrating projection of sequential frames, namely a -~ right-eye frame 70 from the upper filmstrip 38 through~ projection lens 42 (Fig. 5) and a left-eye frame 72 from " ...
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Z(~'~)3661 - 14 _ the lower filmstrip 40 through pro~ection len~ 44. Each viewer of the motion picture is provided with a pair of glasses 74 comprising a headband 76 and respective left-eye and right-eye len~e~ 78 and 80 carried in a frame 82 which is suspended from the headband 76. The two lenses 78 and 80 are liquid crystal cells that can be electrically actuated to alternate between an opaque state and a transmissive state. In Fig. 5, the left-eye lens 78 is shown as opaque while the right-eye len3 80 is transmissive 80 that the , ~ . .:,, .
viewer will see the right-eye image 70 on the screen. In Fig. 6 on the other hand, the lens states have been reversed so that the viewer can see the left-eye image 72.
.
Electrical circuitry for actuating the lenses i8 accommodated within a housing 84 carried by the headband 76. The circuitry includes an infrared receiver which receives infrared synchronizing signals illustrated at 86 from a transmitter 88 that is triggered in synchronism with the~ pro~ection of right-eye and left-eye images from pro~ector 20. In Figs. 5 and 6, this synchronization is shown ~chematically as being derived from a rotary tim$ng chutter 90 that is driven by a mechanical drive mechanism 92 from the main drivo shaft of the pro~ector. Shutter 90`
has peripheral notches 94 and has associated therewith an : , optical detector 96 that is respectively blocked and ~ . ~
~ 25 unblocked as the shutter rotates and the notches 94 move , ~
through the detector.
Neither the infrared transmission and receiving :

Z00~661 means nor the electrical circuitry for actuating the gla~ses len~ have been explained in detail since they may be accomplished in accordance with the teachings of the prior art, for example the Roe~e, et al. Patent No.
4,424,529 discussed previously. Preferably, however, proprietary technology is utilized for example in accordance with the teachings of a co-pending patent application entitled ~Pro~ection Synchronization Sy8tem" of Imax Systems Corporation. It should also be noted that, while infrared triggering of glasses containing liquid crystal cells is believed preferable, there is no restriction to this particular technology. In principle, . .
mechanically shuttered glasses could be used and/or a different synchronization technique could be employed (e.g.
through an electrical cord).
In summary pro~ector 20 pro~ects alternate left~
and right-eye images and at the same time transmits infrared synchronizing signals to the glaisses 74 ~o that the viewer's eyes are alternately blocked and unblocked in synchronism with the pro~ection of the left- and right-eye images onto the screen 80 that a ~tereoscopic effect is perceived.
Referring back to Fig. 1, the images are pro~ected onto the pro~ection ~creen 12 at the inside :: ! , surface of the dome 10. The dome has the shape of a segment of a hemisphere, the centre of which is indicated at 98.
The o~verall size of the dome will depend on audience Z0036~.~
_ 16 -seating capacity and other factors and may, for example, be of approximately 24 metres in diameter (d). In this embodiment, the dome has an angular extent about centre 98 of 160 defined by the two chain-dotted line~ denoted 100 and 102 respectively, each of a length d/2. The dome is inclined at an angle of approximately 28 indicated at 104 in Fig. 1 and defined between the horizontal and a line 106 between diametrally opposed points at the bottom of the dome-shaped surface. As mentioned previously, the audience ......
will be seated on ~tructure 14; as such, the dome i~ in effect tilted down in front of the audience for better viewing the pro~ected images. In an actual theatre, each of the steps 14a of structure 14 will accommodate a row of seats.
Pro~ector 20 is located within pro~ection room 16 and is oriented so that the pro~ection axis 108 is tilted upwardly, in this case at an angle 110 of 13.5 to a horizontal reference line R. The particular wide-angle pro~ection lenses used are designed to give a field of view represented by angle 112 of 123 comprising 35 below the pro~ection axis 108 and 88 above that axis. The lateral field of view (not illustrated) is 180.
., . ~ .:
Pro~ector 20 is located laterally so that its ~ --pro~eotions lenses ~2 and 44 are located in the common vertical plane P referred to previously with plane P
extending through the centre 98 of the dome. The len~es are ~paced from one another so that the separation between the ~-, - ~
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lens axes i~ 101.6 millimeters. It is believed that the lenses should be positioned as close together as pos~ible pre$erably at a spacing in the range 100 to 160 millimeters. The pro~ector itself is positioned slightly above the geometric centre of the dome. Specifically, the pro~ector i8 located 80 that the pro~ection point (the ~
midpoint of a line ~oining the rear ~'nodal" points of the ~ ~;
two pro~ection lenses is located a distance (a) above centre point 98 and a distance (b) forward of that point (closer to the screqn). It is believed that the ratios of these distances relative to the diameter of the dome (d) .. ..
should be approximately a:d = 1:35 and b:d = 1:60. In this particular embodiment (a) is 690 millimeters, (b) is 400 millimeters and (d) is 24000 millimeters (24m).
The Nnodal~ points of a lens are two points on the optical axis of the lens 50 80 located that any incident ray directed at one such point will produce a paralleI emergent ray directed through the other point. In a pro~ector, the rear nodal point is the point closest to the film.
Preferably, the light reflecting properties of the screen 12 are selected to provide highi~gainli (defined as the relationship between the intensity of the incident and reflected light rays). This can be accompllshed by a combination of surface texture and metallic paint. The on-axis gain (normal to the screen surface) should preferably be in the range of 1.5 - 2.0 and the off-axis gain should Z0036~1 , ~, taper off to levels of le~s than 0.5 at angles of about 40.
At angles greater than 45, the gain should quickly decrease to avoid unwanted reflection of light onto other locations of the screen. Techniques for achieving high gain pro~ection are known in the art. For example, reference may be made to United States Patent No. 3,354,738 (Forehand, et al.) entitled "Front Pro~ection Screen with Precision Gain Control~. A high gain screen is at least highly desirable, particulary where the liquid crystal cells used in the viewing glas~es (74) have relatively low light transmission properties in the transmissive state. However, high screen gain may be of less importance where the transmission properties of the cells are higher.
Fig. 7 shows a typical frame format that might be used for the filmstrips 38 and 40 in accordance with the method of the invention. The format shown is the existing ONNIMAX format of Imax Systems Corporation. The filmstrip itself is generally denoted by reference numeral 114; only one frame on the filmstrip is shown and i8 denoted 116. In ~ . .
this embodiment, the imayes on the filmstrip were shot ; ~ ~-using fisheye lenses, as a result of which the actual image recorded on the fiim has an overall shape~which'resembles' '~
a circle that has been flattened at the bottom as shown by the area denoted 118 in Fig. 7. If the film is shot using fisheye lenses and then pro~ected using fisheye lenses, . ~ ~ :,.;., .
distortion of the pro~ected image is minimized. However, in ~ome cases, such distortion may be acceptable or even ';~

- Z(~036fi1 -- 19 -- ~ ~

desirable, in which case the film could be shot using lenses of longer focal length which would result in a rectangular image on the film.
The u~able image area of the frame is the rectangular area 120 between the marginal perforations 122 and within which the image area 118 i~ located. The particular frame format sho~m is known as 70 mm 15 perf.
because the film is 70 millimeters wide and the length of each frame corresponds to fifteen of the perforations 122 (which are of standard size and pitch). The usable image .
area 120 for each frame in OMNIMUC format i8 3,376 sq. mm and the actual image area 118 is 2,653 sq. m~. The dimensions of the usable image area 120 are 69.6 mm x 48.5 mm.
By way of comparison, so-called 4 perf. 35 mm film has a usable image area of 306 sq. mm (20.1 mm x 15.2 mm) and the actual image where a fisheye lens is used to shoot the film is 241 sq. mm. It has been found that this frame format is unacceptable for use in the method of the invention and that the u~able image area (as area 120 in Fig. 7) should be at least 1,200 8q. mm in order to achieve satisfa'ctory resolution of the pro~ected i~mage.
In summary, it has been found that certain specific criteria must be adopted in order to achieve a high fidelity 3-D immer~ion theatre having high resolution full-colour 3-D images that can occupy a large volume of space and thus fill the visual field of the audience. These 200366~

criteria include the u8e of a dome-shaped pro~ection ~creen (e.g. as shown in Fig. 1), coupled with alternate eye image presentation, pro~ection of the images through wide-angle lenses and accurate positioning of the lenses to achieve lateral and vertical image co-incidence. The images ~hould be projected from separate filmstrips preferably having a large frame format. The pro~ection len~es should be closely spaced, preferably at a maximum separation of 100 to 160 mm (4-6 inches) and the pro~ector should preferably be positioned clo~e to the geometric centre of the dome-~haped pro~ection screen.
It should finally be noted that the preceding description relates to a particular preferred emhodiment of the invention and that many modifications are pos~ible within the broad scope of the invention. Some of those modifications have been specifically indicated and others , :.
will be apparent to a person skilled in the art.
For example, while the disclosure refers specifically to use of OMNIMAX format film pro~ected using a twln stacked rotor rolling loop pro~ector, and while this film format and method of pro~ection is preferred, others may be ~sed. For exampie, two separate pro~ectors cou~d be employed (rolling loop or conventional) and the pro~ected images could be brought together for pro~ection by optical means. The particular pro~ector illustrated has the - significant practical advantage that the two rotors are rigidly coupled together 80 that there is no possibility Z(~036fil of loss or delay in synchronization of the pro~ected images such as could occur if two synchronized pro~ectors were used.
The pro~ection screen itself should be dome-shaped as deisicribed previo~sly, preferably but notessentially a segment of a true hemisphere. The dome itself can be a non-structural screen erected within a larger building or can form a structural enclosure for the audience. Preferably, the images are pro~ected from a pro~ection point in the vicinity of the geometrical centre of the dome as discussed previously. However, within the broad scope of the invention, the images could be pro~ected into the dome from outciide, for example from below the bottom edge of the dome in the embodiment illu3trated in Fig. 1.
It should finally be noted that references to the pro~ection lenses being located in a "vertical" plane are to be interpreted as meaning that the plane is vertical relative to the normal orientation of the pro~ector when isupported on a horizontal surface. For example, if the : ~ . . ~:, . .
pro~ector were to be located on an inclined surface, the "verticll" plane would be at right angles to that surface.
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Claims (37)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A method of presenting a 3-D motion pictures, comprising the steps of:
providing a dome-shaped projection screen;
alternately projecting corresponding left-eye and right-eye images onto said screen; and, alternately blocking the left and right eyes of each person viewing the motion picture, in synchronism with the appearance of right-eye and left-eye images respectively on the screen, so that a stereoscopic effect is perceived.

2. A method of presenting a 3-D motion pictures, comprising the steps of:
providing a dome-shaped projection screen;
alternately projecting corresponding left-eye and right-eye images onto said screen from two separate filmstrips bearing said images, each image being located within a usable image area on the relevant filmstrip of at least 1,200 square millimeters, the images being projected through separate lenses having respective projection axes;
positioning the lenses at a spacing from one another within the range of 100 to 160 millimeters and with their respective projection axes in a common vertical or horizontal plane for co-incidence of the projected images on the screen in a direction at right angles to said plane;

prior to presenting the motion picture shifting at least one of said lenses in said vertical plane to achieve co-incidence of the projected images on the screen in the direction of said plane; and, alternately blocking the left and right eyes of each person viewing the motion picture, in synchronism with the appearance of right-eye and left-eye images respectively on the screen, so that a stereoscopic effect is perceived.

3. A method of presenting a 3-D motion pictures, comprising the steps of:
providing a projection screen having a dome-shape extending about a geometric centre;
alternately projecting corresponding left-eye and right-eye images onto said screen from two separate filmstrips bearing said images, each image being located within a maximum usable image area on the relevant filmstrip of at least 1,200 square millimeters, and the images being projected through separate lenses, the lenses having respective projection axes and defining a projection point mid-way between the rear nodal points of the lenses;
positioning the lenses closely adjacent one another with said projection point adjacent said geometric centre but between said centre and the screen; and, alternately blocking the left and right eyes of each person viewing the motion picture, in synchronism with the appearance of right-eye and left-eye images respectively on the screen, so that a stereoscopic effect is perceived.

4. A method of presenting 3-D motion pictures, comprising the steps of:
providing a dome-shaped projection screen;
alternately projecting corresponding left-eye and right-eye images onto said screen from two separate filmstrips bearing said images, the images being projected through separate wide-angle lenses having respective projection axes;
positioning the lenses directly adjacent one another with their respective projection axes in a common vertical or horizontal plane for co-incidence of the projected images on the screen in a direction at right angles to said plane;
orienting the lenses within said common plane to achieve co-incidence of the projected images on the screen in the direction of said plane;
alternately blocking the left and right eyes of each person viewing the motion picture, in synchronism with the appearance of right-eye and left-eye images respectively on the screen, so that a stereoscopic effect is perceived.

5. A method as claimed in claim 1, wherein said lenses are positioned with their projection axes parallel to one another but spaced by a distance in the range 100-160 millimeters.

6. A method as claimed in claim 4, wherein the images carried by the respective filmstrips each having a usable image area of at least 1,200 square millimeters.

7. A method as claimed in claim 4, wherein said step of orienting the lenses to achieve vertical co-incidence of the projected images on the screen is accomplished prior to presenting the motion picture, by positioning the lenses with their respective projection axes co-incident with the centrelines of the respective projection apertures, and shifting at least one of said lenses towards the other while maintaining the projection axes parallel to one another, to an extent sufficient to achieve said vertical image co-incidence.

8. A method as claimed in claim 4, wherein said step of alternately blocking the left and right eyes of each person viewing the motion picture is performed by providing each said person with a pair of glasses for viewing the motion picture, each said pair of glasses having left and right lenses each comprising a liquid crystal cell capable of actuation to alternate between an opaque state and a transmissive state, and causing the respective states of the two lenses to alternate in synchronism with the appearance of right-eye and left-eye images respectively on the screen.

9. A method as claimed in claim 8, wherein said alternation of the transmissive states of the glasses lenses is accomplished by transmitting infrared synchronizing signals in synchronism with the projection of right eye and left-eye images, and using said synchronizing signals to alternate the transmissive states of the lenses.

10. A method as claimed in claim 4, wherein the projector is located above the geometric centre of the dome.

11. A method as claimed in claim 10, wherein the projector is located so that the midpoint of a line joining the rear nodal points of the projection lenses is located a distance (a) above the geometric centre of the dome and a distance (b) closer to the screen than said centre, wherein (a) and (b) are defined relative to the diameter (d) of the dome by the approximate ratios a:d = 1:35 and b:d = 1:60.

12. A method as claimed in claim 4, wherein said projection screen is formed by a dome having the shape of a 160° segment of a sphere.

13. A method as claimed in claim 12, wherein said dome is arranged in a tilted orientation with respect to a horizontal plane so that persons viewing a motion picture from within the dome can comfortably look towards the centre of the dome.

14. A method as claimed in claim 13, wherein the dome is tilted at an angle of approximately 28° with respect to the horizontal.

15. A method as claimed in claim 13, wherein the projector is located so that the projection axes of the respective lenses are inclined upwardly with respect to a horizontal reference plane.

16. A method as claimed in claim 15, wherein the said projection axes are tilted at an angle of approximately 13.5° to said horizontal reference plane.

17. A method as claimed in claim 16, wherein said projection lenses are selected to project images within a field of view extending approximately 35° below and 88°
above said projection axes.

18. A method as claimed in claim 4, wherein said screen has a projection surface selected to provide an on-axis gain in the range of 1.5 to 2Ø

19. A method as claimed in claim 4, wherein said step of alternately projecting corresponding left-eye and right-eye images is performed by providing a rolling loop projector having two rotors stacked vertically one above the other and rotatable about a common vertical axis, for transporting the respective said filmstrips, and wherein one of said rotors is rotationally offset with respect to the other rotor to cause said alternate image projection.

20. A method as claimed in claim 19, wherein each said filmstrip has a large frame format having a usable image area of at least 1,200 square millimeters, and wherein the images on said filmstrips are of a shape produced by recording each said image through a wide-angle lens and occupy less than said usable image area.

21. An apparatus for presenting 3-D motion pictures comprising:
a dome-shaped projection screen;
means for alternately projecting corresponding left-eye and right-eye images onto said screen from two separate filmstrips, said projecting means including separate wide-angle lenses for each said filmstrip, having respective projection axes, and said lenses being posi-tioned directly adjacent one another with their respective projection axes in a common vertical or horizontal plane for co-incidence of the projected images in a direction at right angles to said plane, the lenses being oriented in said common plane to achieve co-incidence of the projected images in the direction of said plane; and, means for alternately blocking the left and right eyes of each person viewing the motion picture in synchronism with the appearance of right eye and left-eye images respectively on the screen, so that a stereoscopic effect is perceived.

22. An apparatus as claimed in claim 21, wherein said lenses are positioned With their projection axes parallel to one another but spaced by a distance in the range 100-160 millimeters.

23. An apparatus as claimed in claim 21, wherein the images carried by the respective filmstrips each having a usable image area of at least 1,200 square millimeters.

24. An apparatus as claimed in claim 21, wherein said lenses are positioned with their respective projection axes co-incident with the centrelines of the respective projection apertures, and wherein at least one of said lenses is shifted towards the other while maintaining the projection axes parallel to one another, to an extent sufficient to achieve said vertical image co-incidence.

25. An apparatus as claimed in claim 21, wherein said means for alternately blocking the left and right eyes of each person viewing the motion picture comprises a pair of glasses for each said person, each said pair of glasses having left and right lenses each comprising a liquid crystal cell capable of actuation to alternate between an opaque state and a transmissive state, and means for causing the respective states of the two lenses to alternate in synchronism with the appearance of right-eye and left-eye images respectively on the screen.

26. An apparatus as claimed in claim 25, wherein said means for causing alternation of the transmissive states of the glasses lenses comprises means for transmitting infrared synchronizing signals in synchronism with the projection of right-eye and left-eye images, and receiver means in each pair of glasses for causing said synchronizing signals to affect the transmissive states of the lenses.

27. An apparatus as claimed in claim 21, wherein the projector is located above the geometric centre of the dome.

28. An apparatus as claimed in claim 27, wherein the projector is located so that the midpoint of a line joining the rear nodal points of the projection lenses is located a distance (a) above the geometric centre of the dome and a distance (b) closer to the screen than said centre, wherein (a) and (b) are defined relative to the diameter (d) of the dome by the approximate ratios a:d = 1:35 and b:d = 1:60.

29. An apparatus as claimed in claim 21, wherein said projection screen is formed by a dome having the shape of a 160° segment of a sphere.

30. An apparatus as claimed in claim 29, wherein said dome is arranged in a tilted orientation with respect to a horizontal plane so that persons viewing a motion picture from within the dome can comfortably look towards the centre of the dome.

31. An apparatus as claimed in claim 30, wherein the dome is tilted at an angle of approximately 28° with respect to the horizontal.

32. An apparatus as claimed in claim 30, wherein the projector is located so that the projection axes of the respective lenses are inclined upwardly with respect to a horizontal reference plane.

33. An apparatus as claimed in claim 32, wherein the said projection axes are tilted at an angle of approximately 13.5° to said horizontal reference plane.

34. An apparatus as claimed in claim 33, wherein said projection lenses are selected to project images within a field of view extending approximately 35° below and 88°
above said projection axes.

35. An apparatus as claimed in claim 21, wherein said screen has a projection surface selected to provide an on-axis gain in the range of 1.5 to 2Ø

36. An apparatus as claimed in claim 21, wherein said projector comprises a rolling loop projector having two rotors stacked vertically one above the other and rotatable about a common vertical axis, for transporting the respective said filmstrips, and wherein one of said rotors is rotationally offset with respect to the other rotor to cause said alternate image projection.

37. An apparatus as claimed in claim 36, wherein each said filmstrip has a large frame format having a usable image area of at least 1,200 square millimeters, and wherein the images on said filmstrips are of a shape produced by recording each said image through a wide-angle lens and occupy less than said usable image area.