EP0140963A1 - Stereoscopic video systems - Google Patents

Abstract

In order to allow the observation of the Pulfrich effect in images projected on a two-dimensional screen, filters (10, 12) are placed before the eyes of the observer. The filter in front of one eye is denser than the filter in front of the other eye. To increase the impression of depth, a dark border (30) may surround the screen.

Description

Description Stereoscopic Video Systems

Technical Field

The subject invention is related to improved stereoscopic video systems. More particularly, improved stereoscopic projection and viewing systems are described for use in television, motion pictures or video games.

Background Art In the prior art, a number of systems have been developed for creating and viewing stereoscopic images. One such system , described in detail in U . S . Patent No. 4,131,342, issued December 26, 1978 to Dudley and incorporated herein by reference, relies on the Pulfrich phenomenon. The Pulfrich phenomenon was discovered in 1922 and is based on a psychophysiological characteristic of the human visual system. The phenomenon manifests itself when an observer places a neutral filter over one eye and views a moving object with both eyes. under these conditions, the object will appear to

.travel a path different from its actual path of travel. The effect can be easily observed by viewing the harmonic oscillations of a pendulum. If an observer covers one eye with a neutral density filter, the bob of the pendulum will appear to follow an elliptical path. The direction of rotation of the elliptical path is dependent upon which eye of the observer has been covered by the filter.

The Pulfrich illusion appears to be based upon the difference in time required to assimilate visual impressions of objects having different degrees of brightness. More particularly, the signal transmitted along the optic nerve is thought to be delayed when the image perceived is dimmed due to the filter. Where the object is stationary, the time lag will not affect the perception of the location of the object. However, when the object is moving, right and left eye images received in the brain will correspond to different locations and generate a retinal disparity. The brain interprets the retinal disparity by locating the object at a point either closer to or farther from the actual distance of observer. The effect is increased as the horizontal velocity component of the viewed object is increased.

The Pulfrich illusion can be utilized to generate pleasing and powerful stereographic images. However, commercial use of the illusion has been limited due to a variety of shortcomings associated witn the systems in the prior art. The subject disclosure is intended to provide solutions for overcoming a variety of these shortcomings. Furthermore, some of the solutions presented herein may also be applicable to other stereoscopic systems.

One of the most significant problems of the prior art systems concerns the method of viewing the Pulfrich images. As described in the above cited Dudley patent, in the prior art, Pulfrich. images are observed by placing a neutral density filter over one eye of the observer. Dudley suggests that the filter should have a neutral density (ND) of .9 to 1.1. For purposes of background, a neutral-density filter having a density of 1.0 transmits 10% of the light energy which it receives. As discussed above, the filter is used to produce a visual time lag that induces the brain to impart a stereoscopic effect to the moving image.

One problem that arises with this method of viewing relates to the large imbalance of image intensity between the two eyes of the observer that results when the brightness of the image reaching one eye is attenuated. This viewing imbalance creates headaches and visual fatigue in the observer over a period of time. As discussed more fully hereinbelow, this problem is overcome in the subject invention by covering both eyes of the observer with filters in a manner to reduce the viewing imbalance.

Another shortcoming of the prior art viewing systems relates to the cost of producing the filter. In order to be commercially feasible, it would be necessary to distribute a large number of filters at no charge to viewers. As can be appreciated, distributing many filters, having sufficient clarity to be acceptable to an observer, can be relatively costly. This problem was addressed in the Dudley patent which disclosed the use of a filter defined by a shield having a large number of pin holes formed therein. However, it is quite difficult to accurately form a large number of pin holes in a shield without generating some distortion in the viewed image. Accordingly, it would be desirable to provide an alternate means for viewing the Pulfrich illusion which is relatively lowin cost.

Another shortcoming of prior art systems, which applies to both the Pulfrich illusion and other stereoscopic techniques, concerns confusing or conflicting visual cues. As can be appreciated, in stereoscopic systems, the intent is to create the illusion of three dimensions on a two-dimensional screen. When the mind is simultaneously presented witn conflicting information, the stereoscopic effects will be diminished or eliminated entirely.

One of the stronger visual cues is that of interposition. Stated simply, where an object appears to move in front of a second object, the object in the foreground should obscure the view of the background object. This type of visual cue can be used to enhance stereoscopic effects. For example, when moving objects are generated by computer for video display in a video game, the foreground objects can be made to electronically obscure the background objects.

Conflicting cues of interposition arise when the moving object passes one of the vertical side edges of the screen. More particularly, when a moving object crosses a vertical side edge of the screen, it will be obscured by the frame of the screen. This visual cue tends to indicate that the object is actually behind the plane of the screen. The latter visual cue will result in a visual conflict if the moving object had appeared to the observer to be in front of the screen before it crossed the vertical side edge. This conflicting visual cue will substantially diminish the stereoscopic effect. Accordingly, it would be desirable to provide a means to diminish the effects of conflicting visual cues.

The use of the Pulfrich illusion in commercial systems also appears to have been limited due to the .complexities of creating Pulfrich images. For example, in the above cited patent to Dudley, stereoscopic images are prepared through an expensive and time- consuming cell animation technique. Therefore, it would be desirable to provide improved methods for generating Pulfrich images for use in television, movie and arcade game applications. Accordingly, it is an object of the subject invention to provide a new and improved means for viewing Pulfrich images.

It is another object of the subject invention to provide a new and improved means for viewing Pulfrich images that reduces eye strain and fatigue. It is a further object of the subject invention to provide a new and improved means for viewing Pulfrich images that is relatively inexpensive to manufacture. It is still another object of the subject invention to provide new and improved means for reducing conflicting visual cues associated with stereoscopic images.

It is still a further object of the subject invention to provide a means, mountable in front of a viewing screen, to reduce conflicting depth cues of stereopsis and interposition.

It is still another object of the subject invention to provide a new and improved means for altering the horizontal velocity component of a moving object for reducing the conflicting cues of interposition. It is still a further object of the subject invention to provide new and improved means for creating stereoscopic images relying on the Pulfrich effect. It is still another object of the subject invention to provide a means for utilizing the Pulfrich effect to impart stereoscopic characteristics to an apparently stationary objects.

It is still a further object of the subject invention to provide a new and improved system for supplying stereoscopic foreground and background images utilizing the Pulfrich effect.

It is still another object of the subject invention to provide a new and improved system particularly adapted for video games capable of producing complex stereographic images utilizing a minimum of memory space.

Disclosure of the Invention

The subject invention provides for a variety of improvements associated with the generation of stereoscopic images. One group of improvements includes means for enhancing viewing of Pulfrich images. In accordance with the subject invention, in order to reduce eye strain and fatigue, spectacles are provided for covering both eyes of the observer. The spectacles include a first filter element adapted to be aligned with one eye of the observer and a second filter element adapted to be aligned with the remaining eye of the observer. One of the filter elements is provided with a density greater than the other filter element. The density difference functions to produce a time lag for inducing the retinal disparity necessary for viewing Pulfrich images. In addition, and discussed more fully below, use of two filter elements reduces eye strain and fatigue. Another viewing means is also disclosed that allows the viewing of Pulfrich images and is manufactured at relatively low cost. The latter means is defined by an opaque shield adapted to be aligned with one eye of the observer. The shield is provided with a single opening, preferably in the shape of an elongated, rectangular slit. The elongated slit functions to reduce the light transmitted to the observer's eyecreating the time lag necessary to generate the Pulfrich image. The subject invention also includes improved systems for reducing conflicting visual cues. The first system includes a border or surround having a central opening aligned with the viewing area of a two-dimensional screen. The border is mounted in front of and in spaced relationship to the screen in a manner such that objects which appear to an observer to be in front of the screen also appear behind the border. As described more fully hereinbelow, by using the border, the conflicting visual cue of interposition which can arise when an object crosses a vertical side edge of the screen, is substantially reduced. The latter conflicting cue of interposition can also be attenuated by reducing the speed of an object as it approaches a vertical side edge of the screen. More particularly, in the Pulfrich illusion, the stereoscopic effect of an image is enhanced when its horizontal velocity component is increased. Accordingly, by reducing the object's speed as it approaches the vertical side edges of the screen, the object will appear to move towards the surface of the screen. By this arrangement contrary cues such as interposition are attenuated enhancing the overall stereoscopic effects.

The subject application also discloses improved systems for creating Pulfrich effect images. In one embodiment, Pulfrich images are generated by rotating the image field relative to a camera. The plane of rotation of the field is perpendicular to the camera. As discussed below, this arrangement permits the generation of highly realistic stereoscopic effects. The subject invention also includes a means for providing stereoscopic foreground and background images utilizing the Pulfrich illusion. This result isachieved by having one image move relative to the other images in a manner such that the background will appear to be behind the foreground image. In one embodiment of the subject invention, this arrangement is carried out using a chroma-key system with the moving image generated by computer or travelling matte. In another embodiment of this sytem, background images are formed on a rotating planar disc. The rotating disk provides the horizontal velocity component necessary to create the Pulfrich illusion. The subject application also discloses a system particularly adapted for use with video games capable of producing complex interactive stereoscopic images. In the video game devices presently on the market, the complexity of the images portrayed on the screen are limited by computing speed and memory size. Accordingly, it is difficult to produce complex stereographic images utilizing known video projection techniques. To overcome this problem, a system is disclosed which includes a means for actively generating stereoscopic images on the screen. These images may utilize the Pulfrich effect or may rely on other stereoscopic techniques, such as image selection by polarized light. In addition, a transparent overlay is mounted on the surface of the screen and includes passive stereoscopic images. These stereoscopic images may be formed from well known techniques, such as anaglyphs or vectographs. A combination viewing means is provided which permits the observance of both the active and passive stereoscopic images. By this arrangement, video games may be provided wherein moving objects interact with the stereoscopic overlay to produce complex stereoscopiceffects while utilizing limited active display techniques. Further objects and advantages of the subject invention will become apparent from the following detailed description taken in conjunction with the drawings in which:

Brief Description of the Drawings Figure 1 is a perspective view of the dual density filter spectacles of the subject invention.

Figure 2 is a perspective view of alternate embodiment of the spectacles formed in accordance with the subject invention. Figure 3 is a perspective view illustrating the use of a surround for reducing conflicting stereoscopic cues.

Figure 4 is a front elevational view of a combination system for generating Pulfrich effect images.

Figures 5A through 5C are illustrations of an alternate embodiment for generating stereoscopic images utilizing the Pulfrich effect.

Figure 6 is a perspective view of a combination system for generating complex stereoscopic images particularly adapted for video games.

Best Mode for Carrying Out the Invention

Referring now to Figures 1 and 2, there are illustrated two forms of viewing means for observing the Pulfrich illusion. As discussed above, in the prior art, the Pulfrich illusion was viewed by covering one eye of the observer with a neutral filter having a density in the range .9 to 1.0. The neutral density filter reduced the brightness of the object reaching the covered eye creating a time lag along the optic pathway. Where the object is moving, the time lagcreates a retinal disparity in the observed position of the object such that the brain assigns an apparent position different from the actual position. This illusion can be successfully created with a single filter element. However, it has been found that when an observer views Pulfrich images in this manner, eye strain, fatigue and headaches will occur after a relatively short period of time. These deleterious effects are attributed to the large brightness imbalance between the eyes of the observer.

In accordance with the subject invention, this difficulty can be overcome by viewing Pulfrich images through a pair of filters having different densities. This approach is illustrated in Figure 1 wherein a pair of neutral density filters 10 and 12 are mounted in a frame 14. Filters 10 and 12 are intended to be neutral density filters having a density difference sufficient to permit the stereoscopic viewing of

Pulfrich images. As discussed below, where two filters are used, the density imbalance may be reduced to relieve eye strain while still permitting the perception of the illusion. The density of the filters may be varied in accordance with the level of stereoscopic effect desired. However, the selection of the particular density levels should be governed by a few criteria. For example, since the brightness of the image reaching the eye is restricted by the filter, it would be desirable to use filters having the lowest effective density. More importantly, because of the undesirable effects of extreme density imbalance, it would be desirable to have the difference between the left and right filters 10 and 12 to be as small as possible.

Through experimentation, it was learned that the optimum density for the low density filter 10 was inthe range of .2 ND to .3 ND. A .3 ND is equivalent to one photographic stop, or a reduction in light intensity by one-half. The range in density values for the higher density filter 12 lies between .7 ND and 1.4 ND. As the difference in density between the two filters is reduced, problems such as eye strain will be minimized. However, as the density difference is reduced, the stereoscopic effect is also reduced. It has been found that a good balance between these factors can be achieved when the density difference between the filters is less than .9 ND but greater than .4 ND. In this range, the large imbalances used in the prior art are avoided such that eye fatigue and headaches can be reduced. This improvement is a great advantage. However, the use of a pair of filters has resulted in another surprising phenomenon. More particularly, when two filters are utilized, stereoscopic effects comparable to the prior art can be achieved even where the density difference between the filters is less than the overall difference used in the prior art provided a certain threshold density of between .2 ND and .3 ND is not exceeded for the less dense filter. Thus, good effects can be achieved while simultaneously reducing eye strain and headaches. As can be appreciated, when additional extra-stereoscopic or monocular cues are used, the density difference between the filters may be further reduced while maintaining good stereoscopic effects. For a discussion of the use of additional stereoscopic cues, see Foundations of tne Stereoscopic Cinema, Lenny Lipton (Van Nostrand Reinhold, 1982).

In the preferred embodiment, filters 10 and 12 are neutral density filters. A neutral density filter functions only to reduce light intensity and does not effect the color spectrum. It is to be understood, that similar effects can be achieved using colored .filters where the color filters also reduce light intensity to an equivalent degree. In the illustrated embodiment, the left filter 12 (as worn by the user) is shown having greater density than the right filter 10. This arrangement is consistent with standard conventions, adopted in most prior art references. However, it is to be understood that the subject invention is not to be limited thereby. For example, if the density of the lenses is reversed, an object which had appeared farther away than it actually was, would now appear to be closer. The apparent location of a moving object is also a function of the direction in which it travels. For the remainder of the application, objects which have a horizontal velocity component moving from left to right, when seen with the denser filter on the left eye, appear to be farther away than they actually are and thus have a positive effective parallax.

Objects moving from right to left will appear closer to the observer and thus have a negative effective parallax.

The dual filter spectacles illustrated in Figure 1 satisfy the requirements necessary for viewing the Pulfrich illusion by creating a difference in the illumination received in the eyes of the observer. While the spectacles illustrated in Figure 1 can be produced at relatively low cost, if it was desired to distribute them to a very large number of people, the overall cost could be significant. Accordingly, it is another object of the subject invention to provide an alternate viewing means for observing the Pulfrich illusion which may be manufactured at extremely low cost. The alternate viewing means is illustrated more particularly in Figure 2.

Figure 2 shows a pair of spectacles 20 having a first slit 22 and a second slit 24 formed therein. Preferably, slits 22 and 24 are elongated and rectangular in shape, with their longer dimension being in the horizontal orientation. In the illustrated embodiment, only slit 24 is intended to serve as a light attenuator, while slit 22 is provided for the comfort of the wearer. In order to provide the necessary light attenuation, the height "H" of slit 24 should be in the range of .3 mm to 1.0 mm. If the height is less than .3 mm, horizontal bands may be observed due to diffraction effects. Where the slit height is greater than 1.0 mm, there is insufficient light attenuation to observe the Pulfrich illusion. Optimal stereoscopic effects have been achieved with a slit height "H" of .5 mm, which provides sufficient light attenuation without distracting diffraction bands. Preferably, the surface of the spectacles facing towards the observer are darkened to reduce reflections.

In order to observe the Pulfrich illusion, the opening 24 should be defined to achieve a reduction in light intensity in the range of seventy-five to ninetyseven per cent. Optimum effects are achieved where light intensity is reduced approximately ninety percent. As long as these parameters are satisfied, aperture 24 can be configured in shapes other than rectangular, such as a circular opening. However, because the aperture has to be aligned directly with the eye, the rectangular configuration is preferred.

Since aperture 22 is provided for aesthetic and comfort reasons, the subject invention should be construed to include a shield covering only one eye of the observer and having a single aperture formed therein. Because of the extremely low cost of manufacture of the subject spectacles 20, they could be widely distributed for promotional purposes as, for example, an insert to a magazine for viewing television images.

As discussed above, when viewing stereoscopic images, the presence of any conflicting visual cues greatly attenuates the stereoscopic effects. One of the more significant conflicting cues is that of interposition. Simply stated, when an object crosses over a vertical side edge of the screen it will be occluded. However, if the object has a negative effective parallax, and appears in front of the screen, the observer expects the object to obscure the side edge. of the screen. Since the latter situation is physically impossible, a conflict arises which attenuates the stereoscopic effect. This conflict arises with any objects having negative generated parallax which results in the images appearing in front of the plane of the screen. As discussed below, in order to add realism to Pulfrich effect displays, it is quite desirable to have objects with negative generated parallax. This can best be understood by recognizing that in normal viewing situations, distant objects appear to move more slowly than close objects. Since one method of generating more depth in a Pulfrich illusion is to increase the speed of the object, distant clouds can be made to appear farther away by increasing their speed relative to closer trees or houses. This arrangement will produce good stereoscopic images even though there are some logical conflicts. However, the latter arrangement is not consistent with reality where objects at a distance generally appear to move slower.

Therefore, a more desirable arrangement for generating depth is to speed up the foreground images in a manner to generate negative parallax. By this arrangement, the distant clouds will move more slowly than the nearer trees and houses. Thus, the use of negative parallax has advantages in that the images of the objects conform to everyday expectations. However, where negative parallax is used, problems with conflicting visual cues, such as interposition can arise.

In accordance with the subject invention, two systems are disclosed for attenuating the conflicting cue of interposition. The first of those systems is illustrated in Figure 3 and consists of a border means or surround 30 which is mounted in front of the viewing screen 32. The surround 30 has a central opening 34 which is aligned with the screen 32. The surround is spaced from the front of the screen in an amount sufficient to create a false border, behind which all objects will appear. Thus, in operation, objects having a negative effective parallax will appear to be in front of the screen 32 and behind the border means 30. Since the viewer will not expect the object to obscure the border means 30, the conflicting cue of interposition is eliminated and stereoscopic effects are enhanced.

The distance which the border means 30 is spaced in front of the screen 32 will vary based upon the size of the screen and the distance of the audience from the screen. In a typical television display, the border means may be spaced in front of the screen several inches. For motion picture or large screen displays, the distance from the border means to the screen will be measured in feet. The best distance can be determined empirically and will depend upon the effective parallax values created by the Pulfrich effect. Preferably, a fairly rigid, dark material is used to form the border means 30. The border means 30 can be utilized not only with Pulfrich images but any other conventionally projected stereo pairs wherein objects are generated with negative effective parallax.

A border means which is continuous, as illustrated in Figure 3, may be preferred for a number of reasons including ease of mounting or aethestic considerations. However, since the primary conflict relates to the vertical side edges of the screen, an effective border means can be defined by a pair of vertical border members 36 and 38 disposed adjacent the vertical side edges of the screen. As with the continuous border means, the vertical border members 36 and 38 are mounted in front of and in spaced relationship to the screen, an amount such that objects which would appear to an observer to be in front of the screen appear behind the border members. The use of border means 30 represents one way of reducing conflicting stereoscopic cues. In accordance with the subject invention, conflicting cues arising in Pulfrich effect images can also be attenuated by controlling the motion of the moving objects on the screen. As discussed above, the degree of retinal disparity or generated parallax is, in part, a function of the horizontal velocity component of the moving object. Thus, when the horizontal velocity component of an object is increased, the generated parallax is increased. In accordance with the subject invention, conflicting visual cues can be overcome by reducing the horizontal velocity component of the object when it is adjacent a vertical side edge of the screen. By this arrangement, the generated parallax is reduced such that the observed location of the object will appear to move smoothly back towards the surface of the screen at the side edges thereof.

In the prior art, such as exemplified in the above cited patent to Dudley, the Pulfrich effect was utilized in cell animation techniques. Because of limits in these techniques, the images moved at a constantvelocity. Therefore, the concept of altering the velocity of the moving object has not been explored. However, with today's technology of computer animation and computer generated graphics, one skilled in the art can readily perceive methods for varying the velocity of moving images displayed on a screen.

In operation, the speed of an object is accelerated after it enters the screen area and is reduced when it approaches the opposite border prior to exiting the screen. This approach is particularly useful where the object has a negative parallax and appears in front of the screen. In this situation the observer will expect the object to obscure the vertical side edges of the screen. However, if the velocity of the object is reduced, it will appear to move smoothly back towards the screen surface such that the sharp contrary cue of interposition will be attenuated. Having described various improvements for viewing stereoscopic images, some new and improved techniques will be discussed for creating Pulfrich images,. utilizing photography of live subjects with or without combined computer generated graphics. Referring to Figure 4, there is illustrated one proposed arrangement for creating stereoscopic images utilizing the Pulfrich effect wherein an image field is rotated relative to a camera. More particularly, models 40 and 41 are supported by a turntable 42. Turntable 42 is rotatable about a vertical axis 44 in a direction as illustrated by arrows A. The plane of rotation of the turntable is intended to be substantially perpendicular to the image which will be projected on the screen. As discussed below, by rotating the models about the turntable, relatively true to life stereoscopic effects can be generated.

Where movement is achieved through rotation, points in the field have a rotational velocity which is proportional to the distance from the axis of rotation. Assuming a constant rate of rotation, points further from the axis of rotation 44 will generate the greatest retinal disparity and the parallax will be the greatest. Maximum parallax is achieved as points in the field cross over the midline 44. This result occurs because even though rotational velocity of any point remains constant, its horizontal velocity component will follow a sine function, similar to the acceleration of a pendulum bob.

The effects of this arrangement can best be understood by looking at models 40 and 41 separately. Model 40 is located such that the central axis 44 of rotation passes through the center of the model 40. Assuming a clockwise rotation, as viewed from the top of model 40, a point on the midline 44 at the front of the model will have a maximum horizontal velocity moving from right to the left. As the point moves towards the far left, its horizontal velocity component, as viewed by the observer, will decrease to zero. The point will then accelerate from left to right towards the midline (and maximum positive parallax). The horizontal velocity component will then return to. zero as it approaches the right-hand side of the model. Finally, to complete the cycle, the point will accelerate to maximum horizontal velocity (and maximum negative parallax), when it reaches the midline 44. The latter relationships result in the production of highly pleasing stereoscopic images. As can be appreciated, points on model 40 which are either the nearest or farthest from the observer will be located on midline 44 and thus have the largest horizontal velocity component and the greatest effective parallax. Thus, a relatively true to life stereoscopic image of model 40 is generated.

The overall image field will also have good stereoscopic qualities. For example, model 41 which is displaced from the center of rotation, will have a greater rotational velocity than model 40. This rotational velocity is maximized as it crosses midline 44. Because model 41 is displaced farther from the center than model 40, its horizontal velocity component as it passes the midline 44 will be greater than the velocity component of any points on the model 40. Thus, model 41 will appear to the observer to be either in front of or behind model 40, depending on the direction of the horizontal velocity component. Any objects which are placed on the turntable, in the field of the camera, will appear to assume their actual relative locations in the stereoscopic composite image. In the preferred embodiment, the most pleasing stereoscopic effects are obtained by rotating turntable 42 between 4 and 15 revolutions per minute. Figure 4 also illustrates a means for generating a stereoscopic background image utilizing the Pulfrich effect. As discussed below, there are other methods to provide this background. However, common to all of systems disclosed herein, the background image is made to appear to be stereoscopically behind the foreground image. To achieve this result, a means must be provided for supplying the background image with a horizontal velocity component relative to the horizontal velocity component of the foreground image in a manner to create this illusion.

In accordance with the subject invention, one means for providing this effect is through the use of a rotatable disc 46, having the background images formed thereon. In the illustrated embodiment, the plane of disc 46 is parallel with the plane of the two-dimensional screen upon which the image will be projected. However, the angle of inclination can be .adjusted to produce various stereoscopic effects. The disc may be rotated about its central axis, as illustrated by arrows B.

Similar to the rotation by the turntable 42, the rotational speed of the images on the disc will be proportional to their distance from the rotational axis. Accordingly, in the illustrated example, the images formed on the disc, towards the outer periphery thereof, will have the highest velocity component and therefore appear to be farthest in the background behind the model 40.

In order to insure that a pleasing stereoscopic effect is produced, the rotational axis of the disc 46 should be arranged relative to the field of the camera such that all the recorded images have a horizontal velocity component in the same direction. As illustrated in Figure 4, the field of the camera is depicted by a rectangle 48. If the disc is rotated in a clockwise manner, all of the images within the field 48 will have a horizontal velocity component moving from left to right and a positive generated parallax. Of course, in certain situations, it may be desirable to expand the camera field to include objects moving in both directions. The latter effect may be pleasing in some abstract image generation.

Referring to Figure 5, an alternate arrangement is shown for providing stereoscopic background and foreground images which exhibit the Pulfrich effect. In this instance, the moving images defined by the rotatable disc in Figure 4 are replaced with means capable of generating moving images. For example, in Figure 5A, a subject 50 is photographed by a camera 52 in front of a screen 54. Using prior art matting techniques an image of the subject 50 can be created. Foreground or background images can then be generated separately.

Figure 5B illustrates one way of generating the moving background wherein images are formed on a scroll 56 that is moved relative to the camera. As can be appreciated, the speed of movement of the scroll will affect the depth of the Pulfrich images formed thereon. Moving background images can also be computer generated.

The image of the subject 50 in Figure 5A can then be superimposed on the images generated in Figure 5B to arrive at a composite picture illustrated in Figure 5C. The composite stereoscopic image can be further enhanced if the foreground subject 50 were photographed on a turntable as illustrated in Figure 4. In the alternative, subject 50 could be given a horizontal velocity component simply by moving the subject relative to the camera. The above described techniques are equally applicable for generating stereoscopic foreground images. For example, in an underwater scene, images of fish on the scroll can be superimposed in front of subject 50. In the latter case, the direction of the horizontal velocity component of the scroll is merely reversed. As can be appreciated, a wide variety of effects can be achieved by properly controlling the relative horizontal velocity of the foreground and background images. All of the above described techniques can be used in a variety of systems capable of generating stereoscopic images for projection on a two-dimensional screen such as movies and television. Another environment which is particularly suited for applying these techniques is in the field of video games.

In video game technology, electronic images are produced through the use of computer generated displays. With proper programming, images having horizontal velocity components necessary for creating the Pulfrich illusion can readily be created. The complexity of the images, however, is restricted by the game hardware. The earliest versions of video games were extremely limited in the amount of graphics that could be generated. As improvements are made in the technology, increasing levels of sophistication are possible, however, active display techniques are still fairly restricted. In accordance with the subject invention, a unique arrangement is provided to substantially enhance the stereoscopic effects associated with a video game, while utilizing limited display technology. Referring to Figure 6, there is illustrated a television monitor 60 that includes a standard cathode ray tube screen 62 or other display device such. as a liquid crystal display. In accordance with the subject invention, the active display on the screen 62 is intended to include stereoscopic images. In the illustrated embodiment, stereoscopic images are generated utilizing the Pulfrich illusion. The Pulfrich images may be computer generated or produced from live models as described earlier in conjunction with Figures 4 and 5.

In accordance with the subject invention, a transparent overlay 64 is mounted on the front of the screen 62. The transparent overlay 64 is provided with passive stereoscopic images. Methods for forming passive stereoscopic images are known in the art and include anaglyphs and vectographs. Briefly, an anaglyph overlay is formed in two colors and can be observed stereoscopically with the use of coordinated color filters. In a vectograph, dichroic dyes are used to create a polarized stereo pair that can be printed as a single photograph transparency. A vectograph is viewed stereoscopically utilizing polarized lenses.

In accordance with the subject invention, a viewing means is provided for stereoscopically observing both the active and passive systems. The exact nature of the viewing means will, of course, be dependent upon the particular active and passive stereoscopic techniques used. For example, if the active images on the screen 62 are adapted to exhibit the Pulfrich illusion, spectacles 66 would be designed to permit the viewing of the illusion. More particularly, spectacles 66 are provided with a pair of filters wherein the left filter 68 is of a greater optical density than the right filter 70. As discussed above with regard to Figure 1, this density difference will allow the viewing of the Pulfrich illusion.

In accordance with the subject invention, the spectacles 66 also include a means for simultaneously viewing the passive stereoscopic image formed on the overlay 64. For example, where the overlay is formed with an anaglyph, filters 68 and 70 can also be tinted with the appropriate colors. In contrast, if the passive means is defined by a vectograph, lenses 68 and 70 will not only have a density difference but will also be polarized in opposite directions. Each filter element 68 and 70 may be formed from a dual layered sheet defined by both a neutral density filter and a colored or polarizing filter. In the alternative, a composite filter of a single sheet can be used to create each lens.

Various other combinations of stereographic techniques can be used in the subject system. However, in all cases, the unique display of active and passive stereoscopic images in combination with a single composite viewing means, permits relatively complex stereoscopic images to be formed using limited active display techniques. It is envisioned for example, that the overlay may include a stereoscopic playing field through which moving objects of a video game will pass. The interaction between the active images and the passive images can be designed to provide pleasing and commercially acceptable video game systems.

In summary, there has been provided a variety of new techniques for viewing and generating stereoscopic images. More particularly, two improved means are disclosed for viewing the Pulfrich illusion. In addition, a system is disclosed for enhancing stereoscopic effects by reducing conflicting visual cues. A system is also disclosed for generating stereoscopic images of live models and for creating stereoscopic background and foreground images. Finally, a system is disclosed for combining active and passive stereoscopic techniques in a video game environment in a manner to produce complex stereo images with limited active display capabilities. While the subject invention has been explained with reference to preferred embodiments, it is to be understood that various other changes and modifications could be made therein, by one skilled in the art, without varying from the scope and spirit of the subject invention as defined by the appended claims.

Claims

Claims:

1. In combination with a video system wherein images are projected on a two-dimensional screen, said images designed to exhibit the Pulfrich effect, an improved means for reducing the intensity of the illumination reaching the eyes of the observer, said means comprising: a first filter element adapted to be aligned with one eye of the observer; and a second filter element adapted to be aligned with the remaining eye of the observer and having a density greater than said first element.

2. A combination as recited in claim 1 wherein said first filter element has a light reducing capacity equivalent to at least .2 ND filter and said second filter element has a light reducing capacity equivalent to at least .7 ND filter.

3. A combination as recited in claim 1 wherein said first filter element has an equivalent density in the range of .2 ND to .3 ND and said second filter element has an equivalent density in the range of .7 ND to 1.4 ND.

4. A combination as recited in claim 1 wherein the difference in density between said filters is equivalent to at least .4 ND and less than .9 ND.

5. In combination with a system for projecting images on a two-dimensional screen, said images designed to exhibit the Pulfrich effect, an improved means for reducing the intensity of illumination reaching the eyes of the observer, said means comprising: a first filter element adapted to be aligned with one eye of the observer; and a second filter element adapted to be aligned with the remaining eye of the observer and having a density greater than said first element.

6. A combination as recited in claim 5 wherein said first filter element has a light reducing capacity equivalent to at least .2 ND filter and said second filter element has a light reducing capacity equivalent to at least .7 ND filter.

7. A combination as recited in claim 5 wherein said first filter element has an equivalent density in the range of .2 ND to .3 ND and said second filter element has an equivalent density in the range of .7 ND to 1.4 ND.

8. A combination as recited in claim 5 wherein the difference in density between said filters is equivalent to at least .4 ND, and less than .9 ND.

9. A combination as recited in claim 5 wherein said screen is a video screen.

10. An improved method of viewing Pulfrich effect images by an observer comprising the step of: covering one eye of the observer with a first light-diminishing filter element and the remaining eye of the observer with a second filter element, wherein said second filter element has a density greater than said first filter element.

11. A method as recited in claim 10 wherein said first filter element has a light reducing capacity equivalent to at least . 2 ND and said second filter element has a light reducing capacity equivalent to at least .7 ND.

12. A method as recited in claim 10 wherein said first filter element has an equivalent density in the range of .2 ND to .3 ND and said second filter element has an equivalent density in the range of .7 ND to 1.4 ND.

13. A method as recited in claim 10 wherein the difference in density between said filters isequivalent to at least .4 ND and less than .9 ND.

14. In a system for projecting stereoscopic images on a two-dimensional screen, an improved means for enhancing stereoscopic effects by reducing conflicting visual cues comprising: a pair of vertical border members disposed adjacent the vertical side edges of the screen, said border members being mounted in front of and in spaced relationship to the plane of the screen in a manner such that said objects which appear to an observer to be in front of the screen appear behind said border members, thereby reducing the conflicting visual cue of interposition.

15. A system as recited in claim 14 wherein said border members are formed from a dark material.

16. In a system for projecting stereoscopic images on a two-dimensional screen, an improved means for enhancing stereoscopic effects by reducing conflicting visual cues, comprising: border means having a central opening aligned with said screen, said border means being mounted in front of and in spaced relationship to the screen in a manner such that objects which appear to an observer to be in front of the screen appear behind said border means, thereby reducing the conflicting visual cue of interposition.

17. A system as recited in claim 16 wherein said border means is formed from a dark material.

18. In a system for projecting moving objects on a two-dimensional screen, said objects intended to exhibit the Pulfrich illusion, an improved means for enhancing stereoscopic effects of objects byreducing conflicting visual cues, said improvement comprising: means for reducing the horizontal velocity component of the moving object when it is near a vertical edge of the screen such that the apparent distance of the object from the screen is attenuated near the vertical side edges thereof.