STEREOSCOPIC PICTURES

Abstract: Method and arrangements for the viewing and formation of stereoscopic pictures including pictures from television screens. A method of viewing a stereoscopic pair of images in which the image for one eye (10) is viewed by reflection from a surface (17) of a prism (8) and the image for the other eye (9) is viewed directly through that surface (17) of the prism (8), the spacing between the eyes (9, 10) in relation to the prism (8) being such that the angle at which the said one eye (10) sees the first image is such that complete internal reflection occurs at the surface (17) but the angle at which the other eye (9) sees the image is such that substantial internal reflection does not occur. A pair of prisms (8, 115) abut one another along a common side (17, 117) so that for viewing an image directly and without reflection the light path through the prisms (8, 115) is approximately the same the whole way across that image thereby avoiding distortion as a result of the light from one part of the image seen by direct viewing having to pass through a greater thickness of prism material than the light from another part of that image.

Description: STEREOSCOPIC PICTURES This invention relates to the viewing and formation of stereoscopic pictures including pictures from television screens. Stereoscopic photography and the projection or viewing of the resulting stereoscopic image pairs is well known, both in respect of still pictures and moving pictures. To record a stereoscopic image pair, two images are recorded from positions spaced a small distance apart corresponding approximately to the spacing between the eyes of a person. The camera for recording these images can be an especially designed stereo camera having two lens systems, a single camera which is moved to take a second image from the side in the case of a still scene, or two spaced and synchronised cameras, e.g. in recording a moving . sequence of images. The resulting stereo image pairs can be viewed in a viewer with two lens systems, one for each eye, so that the left eye sees the left-hand image taken from the left side and the right eye sees the right-hand image taken from the right side. To see a good stereo picture the spectator must look very closely into the lens systems. The stereo image pairs can alternatively both be projected onto a screen and arrangements made so that the left eye of the observer sees only the left-hand image and the right eye only the right-hand image. This can be achieved by polarising the light for the left-hand image and right-hand image in opposite ways, and providing the observer with polarising spectacles which have polarising filters which allow the left eye to see the left-hand image but prevent it from seeing the right-hand image with the converse for the right eye. A similar effect can be achieved in black and white but not colour by using coloured lights and filters, e.g. red light for projecting the left image and a red filter in front of the left eye. and blue light for projecting the right image and a blue filter in front of the right eye. It is an object of this invention to provide a simple manner of viewing stereoscopic images. According to the invention in one aspect there is provided a method of viewing a stereoscopic pa r of images in which the image for one eye is viewed by reflection from a surface of a prism and the image for the other eye is viewed directly through that surface of the prism, the spacing between the eyes in relation to the prism being such that the angle at which the said one eye sees the first image is such that complete internal - 3 - reflection occurs at the surface but the angle at which the other eye sees the image is such that substantial internal reflection does not occur. Such an arrangement can be very simple and conveniently the prism will have presented adjacent two of its faces, the two images of the stereoscopic pair whilst the viewer looks at these images through the other face. It has been found that when a viewer sees the obverse side of a picture, a stereoscopic picture is not seen unless his eye is relaxed. Conversely, it has been found that if a viewer sees the reverse side of a picture, the stereoscopic effect is much clearer and his eye adjusts to the stereoscopic effect much more easily. Thus, in a first form of the invention, the viewer sees the obverse side of a picture but in a second, more preferred form of the invention the viewer sees the reverse side of a picture. According to a preferred embodiment of the invention there is provided a stereoscopic viewing device comprising a pair of prisms which abut one another along a common side so that for viewing an image directly and without reflection the light path through the prisms is approximately the same the whole way across that image, so avoiding distortion as a result of the light from one part of the image seen by direct viewing having to pass through a greater thickness of prism material than the light from another part of the image. O PI ^K WIPO The stereoscopic pair of images can be provided in a number of ways. Thus, for example, the two images can be images formed on the faces of two cathode ray tubes of two television screens and so in accordance with the invention, it is possible to provide stereoscopic television pictures provided of course that the picture presented on the television screens are themselves stereo¬ scopic images taken for example by two television cameras spaced a small distance apart. Because the image viewed by total internal reflection is reversed by the reflection it is necessary in the first aspect of the invention for that image itself to be a reversed image relative the other image and in the second aspect of the invention, the image viewed by total internal reflection is not a - reversed image but rather the other image is a reversed . image. In the case of a television screen in either case this can readily be achieved electronically simply by reversing the direction of scanning for the television receiver which presents that image. According therefore to an aspect of this invention there is provided a stereoscopic television set comprising a pair of screens which are capable of presenting stereoscopic pairs of images one on each screen, one of those pairs being reversed in the sense of the other image and a double prism, preferably each of right-angled shape, with the hypotenuse face of each prism positioned in abutting relationship such that when viewed through another face of one prism in the first form of the invention, the image on one screen can be seen through the abutting face whilst the reversed image can be seen by total internal reflection on the abutting face whereas in the second form of the invention, the reversed image on one screen can be seen through the abutting face whilst the image can be seen by total internal reflection on the abutting face. A multiplexing method using conventional television equipment such as a television broadcast, a * video tape cassette or a video tape recorder can provide a two picture source for the device of the present invention. Therefore, in another aspect, the present invention provides a stereoscopic viewing arrangement comprising a pair of television cameras, a pair of television screens, a multiplexing device whereby the signals from the two television cameras are combined for transmission such that the signal from one camera occupies the first half of each raster scan and the signal from the other camera occupies the second half of each raster scan, the first television screen being switched to receive the first half of the raster scan and the second television screen being switched to receive the second half of the raster scan, and a double prism with the hypotenuse face of each prism positioned in abutting relationship, so that when viewed through another face of the prism the image on one screen can be seen through the abutting face whilst the image on the other screen can be seen by total internal reflection on the abutting face. The invention is not only applicable to television screens but can also be used to view in a stereoscopic fashion other images such as, for example, those on photographic transparencies or prints. Thus, such images can be substituted for the television screens. This embodiment of the invention can be useful in providing a stereoscopic advertising or like display. The device of the present invention gives a stereoscopic effect over a region roughly equivalent to the distance between the viewer's eyes [generally 2% to 3 inches (6.35 to 7.62cm)] when the viewer is one to two feet (30.48 to 60.96 cm) in front of the device. This region can be doubled if a cylindrical lens is placed in front of the device. However, if this is done, it is to be noted that the region over which the stereoscopic image can be observed is reduced if the viewer is located more than two feet (60.96 cm) from such a lens. These embodiments of the invention will now be described, by way of example, with reference to the accom¬ panying drawings, in which: Figure 1 is a perspective view of a first form of stereoscopic display unit according to the invention; Figure la is a plan,view of that display unit; Figure 2 is a perspective view of a second form of stereoscopic display unit according to the invention; Figure 2a_ is a plan view of that display unit; 5 Figure 3 is a view similar to Figure 2a_ showing a modified display; Figure 4 is a view similar to Figure 2 of the modified display; Figure 5 is a diagram showing a television set 10 arranged to show stereoscopic images; Figure 6 is a diagrammatic representation showing how two aspects of the present invention are achieved; Figure 7 shows the width of the stereoscopic 15 region presented to the viewer by use of the device of the present invention; Figure 8 shows the height of the stereoscopic region presented to the viewer by use of the device of the present invention; 20 Figures 9 and 10 show a further embodiment of the device of the present invention in perspective and plan view; Figure 11 shows diagrammatically equipment for producing a picture on a television tube; 25 Figure 12 shows diagrammatically equipment for producing a pair of stereo pictures on two television tubes; and O PI Figure 13 shows diagrammatically in greater detail switching equipment of Figure 12. Referring to Figures 1 and la_, these show a right-angled isosceles triangle shaped prism 8 made of glass, transparent plastics or o her suitable material. This prism has two shorter faces 15 and 16 of equal size and a larger hypotenuse -face 17. The angle 25 between the faces 15 and 16 is a right angle whilst the angles 33 at o the other corners are each 45 . A stereoscopic pair of images 13 and 14 are provided and the image 13 is reversed relative the image 14. This reversed image 13 is placed against the face 15 whilst the image 14 is placed behind the face 17 but parallel with the front face 16. When a person looks at these images through the front face 16, he can see with his left eye 9 the image 14 which is the left-hand image directly through the face 17 because the angle 39 of the light 38 from the image 14 to the eye 9 and the reflective index of the material of the prism is such that there is substantially no internal reflection at the face 17. However, he sees the' right-hand image 13 with his right eye 10 by total internal reflection at the face 17 because the angle 36 of the light 35 from the vertical image 32 of the image 13 is less than the critical angle at which total internal reflection occurs. As a result the observer can see with his eyes 9 and 10 a stereoscopic image. OMPI Referring to Figures 2 and 2a_, these show the same right-angled isosceles triangle shaped prism 8 of Figures 1 and la_. However, in this case the reversed image 13 is placed against the face 17 whilst the image 14 is placed behind the face 15 but parallel with the front face 16. So in this case when a person looks at these images through the front face 16, he can see with his left eye 9 the image 13 which is the left-hand image directly through the face 17 because the angle 39 of the light 38 from the image 13 to the eye 9 and the reflective index of the material of the prism is such that there is substantially no internal reflection at the face 17 and the right-hand image 14 with his right eye 10 by total internal reflection at the face 17 because the angle 36 of the light 35 from the vertical image 32 of the image 13 is less than the critical angle at which total internal reflection occurs. By this arrangement, the viewer sees a much clearer stereoscopic effect since his eyes, which are viewing the reverse side of the picture, adjust to the stereoscopic effect more easily than with the arrangement shown in Figures 1 and la_ where, unless the viewer's eyes are relaxed, he would not see a stereoscopic picture. A disadvantage of the simple embodiment shown in Figures 2 and 2<a is that there will be some distortion of the image 13 because the light from the left-hand side of that image passes through a much greater thickness of ' prism material to reach the left eye 9 than that from the right- hand side of that image. To overcome this the modified device 108 shown in Figures 3 and 4 can be used where a second prism 115 is provided. This prism is in all respects identical to the prism 8 except that as seen in plan view it is reversed so that its longest or hypotenuse face 117 is placed in face to face abutting relationship with the face 17. The left-hand image 13 is placed against the rear face 116 and in this way the light from all parts of the image 13 travel through approximately the same thickness of prism material before reaching the left eye 9. The stereoscopic images 13 and 14 can be provided by projecting images from projectors or in a simple embodiment can be in the form of a photographic or like transparencies illuminated from the rear by suitable bulbs 37 (see Figure 4) . It will be seen that an advantage of this aspect of the invention is that although the angle over which the stereoscopic image is visible may be fairly restricted, •the person does not need to wear any special glasses. Turning now to Figure 5 this shows how the system of the invention can be applied to view stereoscopic television pictures. The two prisms 8 and 115 of the device 108 as described in connection with Figures 3 and 4 are provided but instead of the images 13 and 14 these are replaced respectively by television tubes OMP - 11 - 48 and 49. The latter are supplied with stereoscopic images seen by two cameras 46 and 45, respectively, which observe a scene 30 but are spaced by a small distance approximating the spacing between a typical human being's 5 eyes although in some circumstances it may be desirable to increase or decrease this spacing so as to alter the stereoscopic effect " . The television tubes 48 and 49 are operated in a conventional manner by electronics 47 with the one exception that the picture 490 on the tube 49 is 10 reversed from left and right so as to compensate for the subsequent reversal which occurs upon reflection on the surface 17. This can readily be achieved by causing the electronics 47 associated with it to form the picture on the screen 48 by scanning in the opposite direction from 15 normal. The picture 480 on tube 48 is non-reversed. Figure 6 shows the two aspects of the invention in diagrammatic form. In the first aspect 14 is a picture taken by a left-side camera 46 of subject 30; Picture 14 is treated as the left eye picture and is seen by the 20 viewer's left eye 99. Similarly, the right eye picture 13 of subject 30 taken by right-side camera 45 is seen by the right eye 1010 so producing a stereo picture. In the second aspect, the viewer is able to see a reversed stereo picture as follows. 25 The viewer's left eye 9 sees the reverse side of the picture 13 which is taken by right side camera 45 and O the viewer's right eye 10 sees the reverse side of picture 14 which is taken from left side camera 46. Thus, in this aspect, the reverse side (the left side of the subject becomes the right side of the picture and the right side of the subject becomes the left side of the picture) of picture 13 which is taken from the right side camera 45 will be treated as the left eye picture and the picture 14 which is taken by left side camera 46 will be treated as the right eye picture. As shown in Figures 7 and 8, when a viewer looks into the prism of the device of the present invention, the width of the stereoscopic region "d" is about the same as the distance between eyes 9 and 10 [generally 2% inches to 3 inches (6.35 to 7.62 cm)]. The height of the stereoscopic region is a vertical strip 500. As shown in Figures 9 and 10, to widen the stereoscopic region "d w , a cylindrical lens 200 is placed in front of the prism device. The refraction of the cylindrical lens widens the stereoscopic region "d" [Preferably, the radius of cylindrical lens 200 is eight inches (20.32cm). When the viewer is one to two feet (30.48 to 60.96 cm) in front of the lens 200, the width of the stereoscopic region "d" is expanded to approximately six inches (15.24 cm). If the viewer is more than two feet (60.96 cm) in front of the lens, the stereoscopic region "d" is reduced] . _ r i OMPI Since the cylindrical lens will magnify the width of both pictures 13 and 14, to maintain the space width, the width of both pictures 13 and 14 will have to be reduced in accordance with the magnification of the lens. In the case of television pictures, the width of the pictures can be reduced by reducing the horizontal sweep voltages. Figure 11 shows standard studio equipment using two cameras 45 and 46. Switching equipment 44 is provided to combine and transmit simultaneously the pictures from cameras 45 and 46 to television receiver 480 so that picture 14 from camera 46 will appear on the left half of the screen and picture 13 from camera 45 will appear on the right half of the screen. Thus, if camera 46 is to be used to give the left eye picture 14 and camera 45 is to be used to give the right eye picture 13, these stereo pictures 13, 14 can be transmitted and recorded by standard equipment as shown in Figure 12. As shown in Figure 12 the two pictures transmitted by the switching equipment 44 have to be separated so that one picture will appear on television receiver 481 and one will appear on television receiver 482. In receiver 481, the right-hand video signal is gated and in receiver 482 the left-hand video signal is gated, thus the left eye picture 14 from camera 46 and the right eye picture 13 from camera 45 will appear separately on two television tubes. In Figure 13 the switching equipment 44 is shown in greater detail. An electronic circuit 441 combines the video signals from cameras 45 and 46. The normal sync signal 79 ensures that the cameras 45 and 46 work synchronously and the gating circuit 440 alternately enables the left and right-hand eye cameras 46 and 45 respectively to send signals along the transmission line 200 over the first half and second half respectively of each raster scan. At the receiver end, the circuit 470 provides a synchronising signal to a gate circuit 472. This in turn gives two signals 80' and 81' to enable the receivers 48 and 49. Signal 80* sent to the left eye television tube. 49 enables the receiver over the first half of each raster scan and signal 81' sent to the right eye television tube 48 enables the receiver over the second.half of each raster scan to synchronise signals from cameras 46 and 45 so that the left eye picture appears only on screen 49 and the right eye picture appears only on screen 48 with the right-hand side of the left eye picture blank and the left-hand side of the right eye picture blank.

Claims: WHAT I CLAIM IS : 1. A method of viewing a stereoscopic pair of images in which the image for one eye is viewed by reflection from a surface of a prism and the image for the other eye is viewed directly through that surface of the prism, the spacing between the eyes in relation * to the prism being such that the angle at which the said one eye sees the first image is such that complete internal reflection occurs at the surface but the angle at which the other eye sees the image is such that substantial internal reflection does not occur. 2. A method as claimed in Claim 1 wherein the image viewed by reflection through the prism is the reverse side of the image and the image viewed directly through the prism is the obverse side of the image. 3. A method as claimed in Claim 1 wherein the image viewed by reflection through the prism is the obverse side of the image and the image viewed directly through the prism is the reverse side of the image. 4. A stereoscopic viewing device comprising a pair of prisms which abut one another along a common side so that for viewing an image directly and without reflection the light path through the prisms is approximately the same whole way across that image thereby avoiding distortion as a result of the light from one part of the image seen by direct viewing having to pass through a greater thickness of prism material than the light from another part of that image. 5. A device as claimed in Claim 4 wherein each prism is of right-angled shape with the hypotenuse face of one abutting the hypotenuse face of the other. 6. A device as claimed in Claim 4 or 5 which is a stereoscopic viewer for photographic transparencies or prints. 7. A stereoscopic television set comprising a pair of screens capable of presenting stereoscopic pairs of images one on each screen, one of the pairs being reversed in the sense of the other image and a double prism with the hypotenuse face of each prism positioned in abutting relationship, so that when viewed through another face of the prism the image on the screen can be seen through the abutting face whilst the image on the other screen can be seen by total internal reflection on the abutting face. 8.. A stereoscopic viewing arrangement comprising a pair of television cameras, a pair of television screens, a multiplexing device whereby for transmission the signals from the two television cameras are combined such that the signal from one camera occupies the first half of each raster scan and the signal from the other camera occupies the second half of each raster scan, the first television screen being switched to receive the first half of the raster scan and the second television screen being switched to receive the second half of the raster scan and OMPI WIPO a double prism with the hypotenuse face of each prism positioned in abutting relationship, so that when viewed through another face of the prism the image on one screen can be seen through the abutting face whilst the image on the other screen can be seen by total internal reflection on the abutting face. 9.' -A device as claimed in any of claims 4 to 7 which additionally comprises a cylindrical lens located in front of the prism to widen the stereoscopic region presented to a viewer.

Inventors: LIKITANUPAK CHALERM, LIKITANUPAK, CHALERM
Applicants: RACKHAM ANTHONY CHARLES, RACKHAM, ANTHONY, CHARLES
Application year: 1982
Main classification: G02B27
IPC codes: G02B27, G03C9, H04N13