MXPA97007848A - Method and apparatus for presentation of stereoscope images - Google Patents

Abstract

Stereoscopic images are presented using the so-called "alternate eye" projection while the respective eyes of the observer are blocked alternately and in synchrony with the display so that the left eye of the observer sees only images of the left eye and the right eye images. of right eye. The blocking is effected using electro-optical liquid crystal shutters each of which has a linear polarizable front filter with a defined polarization axis. The respective abturators for the two eyes of the observer are oriented so that the defined polarization axes are at an angle with respect to each other. The projected images are linearly polarized so that the left eye images are polarized along an axis that is parallel to the defined axis of the electro-optic obturator for the observer's left eye and the right eye images are polarized throughout of a parallel axis the defined axis of the electro-optic obturator for the observer's right eye. The invention significantly reduces the perceptible phantom formation even when projecting high contrast images, such as dark figures against white background

Description

METHOD AND APPARATUS FOR PRESENTATION OF STEREOSCOPIC IMAGES FIELD OF THE INVENTION This invention relates to stereoscopic exhibitions in general and more particularly to the projection of stereoscopic cinematographic film.

BACKGROUND OF THE INVENTION Stereoscopic 3-D imaging requires the presentation of two slightly different sets of images for the observer; one set corresponds to a view of the left eye and the other corresponds to a view of the right eye. When the sets of images are presented in such a way that only the left eye of the observer can see the set of images of the left eye and the right eye can only see the set of images of the right eye, the observer will be able to perceive an image 3- D. Several different methods are known for separating the images of the left eye and the right eye. In the anaglyph method, different color filters are used. Typically, the left eye and right eye images are projected simultaneously though in different colors, say red and blue respectively, and the observers wear a pair of glasses equipped with red and blue filters placed to properly separate the images. A major disadvantage of this method is that the resulting 3-D images are deficient in the color information. Another method of image separation involves the use of polarizing filters of mutual extinction. The filters are placed in front of the left and right eye projectors with their polarization axes at 90 degrees from each other. The observers wear glasses with polarizing filters placed in the same orientation as the filters on the projectors. The left and right eye images appear on the screen at the same time, although only the polarized light of the left eye is transmitted through the left eye lens of the eyeglasses and only the polarized light of the right eye is transmitted through the lens of the eye. right eye. This method is not expensive and allows full-color 3-D images. However, it has limitations in that a substantial amount of undesirable transmission can occur and can result in the formation of objectionable ghost images. For example, the polarization characteristics of light can be significantly altered by reflection from a screen, although metallic screen coatings will reduce this effect. If linear polarizers are used (most of which are effective), the ghost images will also increase as observers tilt their heads to the left or to the right.

A third known method involves multiplexing the left eye and right eye images over time. The images of left eye and right eye are presented alternatively so that there is only one eye image on the screen at any time in time. Observers wear glasses that alternately block the view of an eye so that only the correct image will be observed by each eye. In other words, when a left eye image is projected on a screen, the lens of the left eye of the eyeglasses will be transparent and the lens of the right eye will be opaque. When the image on the screen changes to a right eye image, the left lens of the glasses becomes darker and the lens of the right eye becomes transparent. The glasses usually have electro-optical liquid crystal shutters and are energized by batteries. This method far exceeds the problems of undesirable transmission due to head tilt and does not require a special screen to maintain polarization. The liquid crystal shutters used in time-multiplexed stereoscopic imaging are usually blanks made of at least two linear polarizers on each side of a liquid crystal cell containing a thin layer of glass material liquid between two sheets of glass. The two polarizers are oriented with their generally orthogonal axes and the liquid crystal material acts as a variable polarizer influenced by an electric field.

Such shutters block a significant proportion of the light when they are in an opaque state although they have limited transmission when they are in the transparent state, typically around 25-30% incident light. It has also been found that liquid crystal shutters exhibit low extinction when used to view high-contrast scenes such as dark figures against a white background. Also, the low extinction in corner areas of "wide" screens such as those used by Imax Corporation is notorious. When determining the quality of the film images in 3-D two figures of value are used, mainly the maximum transmission and the extinction relation. The maximum transmission is the percentage of light generated by the projectors that actually reaches the eyes of an observer. The extinction ratio is defined as a ratio of the brightness of a corrected or desired image to the brightness of an uncorrected or undesirable image that is filtered through the system. In a 3-D film projection system, the extinction ratio gives an indication of how much phantom formation an observer will perceive. It is an object of the invention to provide an improved stereoscopic image separation method in which phantom formation is reduced or eliminated BRIEF DESCRIPTION OF THE INVENTION According to the invention there is provided a method of presenting stereoscopic images comprising the steps of: alternately displaying the corresponding images of left eye and right eye in succession; alternately and in synchrony with the alternate display of images, block the right eye of the observer when the left eye images are displayed, and block the left eye of the observer when the right eye images are displayed, using electro-optical liquid crystal shutters respective, each including a front linear polarizing filter having a first polarization axis and a subsequent linear polarizing filter having a second polarization axis at an angle with respect to the first axis; wherein the respective liquid crystal shutters are oriented so that the first polarization axes of the front linear polarizing filters are at an angle with respect to each other.; and wherein the images are displayed by projecting the images onto a screen and linearly polarizing the projected light so that the left eye images are polarized along an axis that is parallel to the first axis of the elctro-optic shutter for the images of the left eye and the right eye of the observer are polarized along an axis parallel to the first electro-optic obturator axis for the observer's right eye. It should be noted that the term "parallel" is to be interpreted broadly in the preceding paragraph and in the claims. Therefore, while parallelism may represent an ideal condition, acceptable results can be achieved with a deviation of a few degrees. The invention also seeks to improve the quality of presentation of stereoscopic images and reduces or eliminates the "phantom formation". By offsetting the polarization axes of the front polarizers of the respective liquid crystal shutters of 3-D "alternate eye" spectacles, and alternately displaying the left eye and right eye images that are polarized to "couple" , the so-called "crosstalk" interference between the images and the formation of phantoms is minimized. The practical limitations of currently available electro-optical shutters for mutually extinguishing undesirable images inevitably results in some "leakage" of undesirable image information. The present invention seeks to eliminate the undesirable image by the use of coupled polarizers as previously described. It has been found that it is possible to surprisingly improve the extinction ratio of the system while retaining high levels of maximum light transmission and acceptable background contrast.

It should be noted that the corresponding images of the left eye and right eye may overlap with time. This improves the level of maximum light transmission although at the cost of some phantom training. Therefore, the references herein for the alternating display of images does not indicate that the images should be presented separately (as is the case with the time multiplexing systems of the prior art). In a practical example of the invention as applied to the film projection system, the linear polarizing filters are placed in front of the projection lenses of a stereoscopic film projector with the polarization axes of the polarized projector aligned so that they are parallel to the axes of the linear polarizers in front of each liquid crystal telescope lens. For example, the left-hand liquid crystal shutter has a first linear polarizer oriented with the polarization axis at 45 ° deworming relative to the vertical. The linear polarizer placed in front of the left eye lens of the stereoscopic film projector has an identical orientation; at 45 ° dextrógiros from the vertical. Similarly, the right liquid crystal telescope shutter has a first linear polarizer oriented with the polarization axis at 45 ° clockwise with respect to the vertical and the linear polarizer positioned opposite the right eye lens of the stereoscopic film projector is oriented at 45 ° levorotatory from the vertical.

The above arrangement significantly reduces the perceptible phantom formation at the expense of a slight reduction in overall brilliance. The loss of brightness is due to the extra polarizer in the optical path and is approximately 10%. Usually a loss of brightness of this magnitude is too great to observe, especially in a large-format 3-D widescreen cinema where obtaining bright images is typically difficult. The invention also provides the corresponding apparatus for presenting stereoscopic images and glasses for use in this invention.

BRIEF DESCRIPTION OF THE DRAWINGS The invention will be better understood with reference to the drawings that illustrate a particular preferred embodiment of the invention, in comparison with the prior art. In the drawings: Figure 1 is a schematic illustration of an "alternate eye" 3-D film projection system; Figure 2 is a view similar to Fig. 1 illustrating the method and apparatus of the invention; and Figure 3 is a graph illustrating the temporal multiplexing of the left eye and right eye images according to the invention.

DESCRIPTION OF THE PREFERRED MODALITIES Referring first to Fig. 1, a film projection screen is indicated at 20 and a pair of film projectors for projecting respective series of images on the screen 20 are diagrammatically represented at 22 and 24 respectively. Two projectors have been shown although it must be understood of course that a single stereoscopic film projector can be used. An example of such a projector is described in U.S. Patent No. 4,966,454 (Toporkiewicz), the disclosure of which is incorporated herein by reference. In any case, as shown in Fig. 1, two projectors are used and alternately project respective images of left eye and right eye onto the screen 20 through respective projection lenses 22a and 24a. A pair of 3-D "alternate eye" glasses such as would be used by an observer of images projected on a screen 20 is represented at 26 and has respective left and right lenses 28 and 30 in the form of liquid crystal shutters. The shutters are actuated alternately in synchronization with the projection of images on the screen 20 so that the right lens 30 is opaque (and the observer's right eye is locked) when the images appear on the screen andconversely, the lens of the left eye is opaque and the left eye of the observer is blocked when the right eye images appear on the screen. Seals of that type are well known in the art and are described for example in Patent No. 4,424,529 (Roose et al), the description of which is incorporated herein by reference. The lenses 28 and 30 will now be described in greater detail in connection with Fig. 2. For present purposes, it is sufficient to note that, while shutters of this type are reasonably efficient in blocking light, some leakage may occur. light and can result in an unacceptable ghost formation. Particularly when glasses are used to see high contrast scenes such as dark figures against a white background. Also, the low extinction is notorious in corner areas of "wide" screens such as those used by Imax Corporation. As seen in Figure 1, a left eye image is being projected onto the screen 20 from the projector 22. The left lens 28 of the eyeglasses 26 is in its transmitting state while the right lens 30 is opaque. The image 32 on the screen 20 is clearly visible through the left lens 28 of the glasses. However, a ghost image 32a is filtered through the right opaque lens 30 of the glasses, providing an objectionable perception to the observer. The reverse situation arises of course when projecting the right eye images and the left lens of the glasses is opaque; that is to say, the objectionable ghosts of the image of the right eye are filtered through the left opaque lens 28.

Fig. 2 shows the same components as in Fig. 1, except that the linear polarizing filters 34 and 36 have been placed in front of the respective projection lenses of the projectors 22 and 24. Also in Fig. 2, the two lenses 28 and 30 of the lenses 26 have been shown in greater detail. Referring to the lens 28 by way of example, the lens includes a front polarizing filter 38 having a polarization axis indicated at 40, and a rear biasing filter 42 having a polarization axis 44 at an angle (eg, 90). °) with respect to the axis 40 of the front polarization filter. Similarly, the lens 30 has a front polarization filter 46 with a bias axis 48 and a rear bias filter 50 with a bias axis 52 at an angle to the axis 48. Located between the two polarizers in each lens is a cell comprising a thin layer of liquid crystal material between the two sheets of glass. The two cells are indicated at 54 and 56 respectively. As is well known in the art, the liquid crystal material acts as a variable polarizer influenced by an electric field. Therefore, in the transmitting state, the liquid crystal material actually "rotates" the light as it moves between the front and rear polarizers, so that the light is transmitted through the lens. In the "off" state, this spin effect does not occur and the light is not transmitted since the polarization axes of the two polarizers are not in line.

According to the invention, the front linear polarizing filters 38 and 40 of the respective spectacle lenses are deliberately placed with their polarization axes (40 and 48 respectively) at an angle one with respect to the other, preferably 90 ° (orthogonal) . The two polarizing lenses 34 and 36 which are placed in front of the lenses of the respective projectors 22 and 24 are "coupled" to the front polarizing filters 38 and 40 of the respective left and right lenses of the glasses. In other words, the filter 34 in front of the projector 22 (the left eye image projector) is positioned with its polarization axis (denoted 58) parallel to the polarization axis 40 of the front polarizer 38 of the left eyeglass lens 28. Similarly, the filter 36 that is placed in front of the right eye image projector 24 is positioned with its polarization axis (60) parallel to the bias axis 48 of the front polarizer 46 of the right eye lens 30. At the instant shown in Fig. 2, a left eye image is being projected onto the screen 20 and is polarized, say, 45 ° dextrorotative from the vertical as indicated by the 58th axis of the filter 34. In contrast to the situation in Fig. 1 in which this image light is not polarized, there can be no filtering through the right eye lens lens 30 of the eyeglasses 26. In the embodiment of Fig. 2, any of this left eye image light which impacts the right lens 30 will first find the front polarizer 46 which is orthogonally polarized (at 45 ° left-handed from the vertical) so that there will be no filtering of the left eye image light within the right eye lens. The reverse situation will be obtained of course when the right eye images are projected and the left eye lens 28 is in its opaque state This placement significantly reduces the perceptible phantom formation at the expense of a slight reduction in overall brightness The loss of brightness is due to the linear polapzador extra in the optical path compared to the mode in Fig. 1 and will typically add up to around 10% Usually, a loss of brightness of this magnitude is too large to be seen, especially in a 3-D widescreen cinema and format large where obtaining bright images is typically difficult however, it has been found in practice that this loss of brightness is acceptable and does not represent a practical obstacle. For clarification purposes, Fig 3 illustrates the alternate projection of the left eye and right eye images of the inventive method. Right eye are alternately displayed and the glasses are operated in the opposite way with the same temporal frequency. The left eye and right eye images are alternately displayed in a repetitive on / off cycle in which the "on" and "off" portions of the cycle they are of equal length (a complete work cycle of '50 / 50 '), so that there are never images of left eye and right eye on the screen at the same time (although this is not essential) .When a left image is projected, the The left lens of a pair of 3-D glasses is transparent (period of time T), considering that the right eye lens is opaque (period of time O). when a right eye image is projected the left lens is opaque. The alternate projection of the left eye and right eye images can be achieved, for example, by projecting the images from two film strips using two projectors that are synchronized with one another. Alternatively, a single rolling cycle projector capable of so-called "alternating image" projection can be used from two separate film strips. In any case, provision must be made so that the images are polarized differently. The electro-optic shutters incorporated in the glasses used by the observer must be activated in synchrony with the projection of the images. This can be achieved in a variety of ways, for example by means of suitable electrical circuits for actuating the shutters in synchronization with the projectors (s). U.S. Patent No. 5,002,387 (Baljet et al.) Discloses a projection synchronization system in which infrared signals are used to synchronize block shutters of the prior art in a stereoscopic system with time multiplexing. The description of this patent is hereby incorporated by reference. The following discussion will further illustrate the advantages of the invention, compared to the prior art. The valuable elements of the inventive method can be calculated by comparison including the effects of adding aligned polarizers to the projection lenses. The following table illustrates the advantages of the invention. The first column contains three valued image quality elements of the prior art method of 3-D film projection using linear polarizers in front of the projection lenses and in the glasses used by audience members. The second column contains the two value elements of the 3-D inventive method. The extinction ratio of the inventive shutters increased dramatically (over 10,000%). The maximum transmission when the inventive method is used is decreased only marginally. In general, the quality of a 3-D presentation is greatly improved when the inventive method is used. Table of Value Elements Shutter LC Invention Transmission 30% 30 x 9 = 27% Extinction Ratio 150 1 15000 1 (on the axis) Extinction Ratio 10 1 1000 1 (off-axis) The invention addresses several limitations and disadvantages of the prior art systems. It provides a 3-D image separation method that has a maximum extinction ratio especially in high contrast scenes and is not susceptible to phantom formation caused by tilting the head. The above description should not be considered as limiting the scope of the invention but only as the axis of the preferred embodiments of this invention. For example, although polarizing filters are described, other optical quench filters such as color or wavelength bandpass filters may be used.

Claims (7)

1. CLAIMS A method of presenting stereoscopic images comprising the steps of alternately displaying the corresponding images of left eye and right eye in succession, alternately and in synchrony with the alternate display of images, blocking the view of the observer's right eye when they are being displayed the left eye images and, blocking the left eye of the observer when the right eye images are being displayed, using respective electro-optical liquid crystal shutters, each including a front linear polapper filter having a first polarization axis and a rear linear polarization filter having a second polarization axis at an angle with respect to the first axis, wherein the respective liquid crystal shutters are oriented so that the first polarization axes of the respective front linear polarizing filters are at an angle one with respect to the other, and wherein said images are displayed by projecting the images onto a screen and, linearly polarizing the projected light so that the left eye images are polarized along an axis that is parallel to the first axis of the electrode shutter. optical for the observer's left eye images and the observer's right eye images are polarized along an axis parallel to the first axis of the electro-optic obturator for the observer's right eye.
2. A method as claimed in claim 1, wherein the respective liquid crystal shutters are oriented so that the first polarization axes of the linear polarizing filters are at an angle one with respect to the other.
3. 3. A method as claimed in claim 1, wherein the right eye and left eye images are projected through separate projection lenses and are linearly polarized providing respective polarization filters in front of the lenses.
4. 4. An apparatus for presenting stereoscopic images comprising the steps of: means for alternately displaying the corresponding images of left eye and right eye in succession; means for blocking alternately and in synchrony with the alternate display of images, the view of the observer's right eye when the left eye images are being displayed, and blocking the observer's left eye when the right eye images are being displayed, said means comprising respective electro-optical liquid crystal shutters, each including a front linear polarizing filter having a first polarization axis and a subsequent linear polarization filter having a second polarization axis at an angle with respect to the first axis, wherein the liquid crystal shutters are oriented so that the first polarization axes of the respective front linear polarizing filters are at an angle one with respect to the other; and wherein the means for alternately displaying the images the corresponding left eye and right eye images comprise means for projecting the images onto a screen and, means for linearly polarizing the projected light so that the left eye images are polarized to along an axis that is parallel to the first axis of the electro-optic obturator for the left eye images of the observer and the right eye images of the observer are polarized along an axis parallel to the first axis of the electro-optic obturator for the observer's right eye.
5. An apparatus as claimed in claim 4, wherein the respective liquid crystal shutters are oriented such that the first polarization axes of the respective front linear polarizing filters are orthogonal to each other, wherein the images of Left eye and projected right eye are also polarized along axes that are orthogonal to each other.
6. 6. An apparatus as claimed in claim 4, wherein the left eye and right eye images are projected through separate projection lenses and are linearly polarized by providing respective polarizing filters in front of said lenses.
7. 7. Spectacles for viewing respective stereoscopic images comprising the corresponding left eye and right eye images exhibited in succession, the spectacles having respective left eye and right eye lenses each comprising an electro-optical liquid crystal shutter including a linear forward polarizing filter having a first axis for polarization and a subsequent linear polarizing filter having a second polarization axis with respect to an angle with respect to the first axis, wherein the respective liquid crystal shutters are oriented so that the first polarization axes of the respective front linear polarizing filters are at an angle one with respect to the other.