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Shipping Terms: Orders usually ship within 2 business days. It is known to those versed in the art that this is a result of the Law of Malus, which tells us that even a small rotation of one of a pair of crossed polarizers away from the orthogonal axes condition will produce substantial transmission. Therefore, the extinction of the unwanted image cannot be guaranteed, unless the audience members' heads are held in a fixed position.
However, the use of circularly polarized light, as described by Land in U. However, commercially available circularly polarizing filters, of a type including sheet quarter wave retarder and sheet linear polarizer, have not had the same good extinction ratio of their linearly polarized counterparts. Hence, a further improvement of the present invention is to produce circularly polarized light which is of superior quality to that which may be produced by commercially available circular polarizers built of plastic sheet quarter wave retarders and sheet polarizers.
The stereoscopic projection system of the invention has one or more electro-optical light modulators preferably surface mode liquid crystal modulators positioned in the optical path of the stereoscopic projection optics. The modulators control the polarization characteristic of the subframe image forming light, to cause the subframes to remain tagged with the polarization characteristics necessary for projection of proper stereoscopic rather than pseudostereoscopic images.
A preferred embodiment of the invention includes an electro-optical light modulator of the type known as a push-pull modulator, which comprises a pair of surface mode liquid crystal panels such as panels 14 and 15 shown in FIG. Every other subframe of the motion picture print to be projected is indexed with a mark such as one of marks shown in FIG.
The presence or absence of each index mark is detected by a light sensor, and the sensor output is used to control the retardation state of the push-pull modulator to suitably alter the characteristics of the polarized light to match the requirements of each subframe's perspective view. Each of FIGS. This has become the accepted approach in the film industry for projection of stereoscopic motion pictures.
Table 1 of FIG. Table 2 of FIG. The symmetrical version of the format is the format which is of interest to us, since for the symmetrical format, if subframe A and B are interchanged in other words, if A is the lower subframe and B is the upper subframe , there will be no introduction of vertical parallax in projection. It will be seen by reading the rest of this disclosure that use of film having the symmetrical format is a key element in making the invention work.
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It is necessary for the symmetrical format to be employed, and it is assumed that the symmetrical format is used throughout this disclosure. In FIG. One of dots 92a and 92b is projected as image on surface By observing the color of the projected image , the projectionist is informed whether the film is being correctly projected in true stereo, or incorrectly projected in pseudo stereo.see url
ISBN 13: 9780442247249
As has been mentioned, if the projectionist mis-threads the projector or misassembles the reels and upsets the sequence of subframes, the result will be a pseudoscopic rather than a stereoscopic projected image. A key ingredient in the successful projection of stereoscopic images is for the left image to be projected through its assigned polarizer and the right image to be projected through its assigned polarizer. When linearly polarized light is used for encoding the images the only difference between the image codings is that their polarization axes are at 90 degrees to each other.
Nevertheless, if the relationship between the perspective viewpoint and the polarizer is inverted, the stereoscopic image will be pseudoscopic, since the right eye will see the left eye's image and vice versa. Kent et al, in U. To accomplish this, Kent et al. Signals from the sensor would be used to control the framing device via an electrical circuit and electromechanical actuator. The present invention improves on this suggestion by Kent et al. Kent, et al.
'18 Lenny Lipton
This is an inelegant and time consuming procedure, which would be visible to audience members, and subject to concerns with regard to accurate positioning of the subframes. Those familiar with 35 mm motion picture projectors would undoubtedly agree that it would be a difficult task to retrofit a motor to the framing knob in a manner that would allow it to rapidly and accurately reposition the subframes with respect to the aperture.
The instant invention on the other hand, acts virtually instantly and in a manner that would be impossible to detect, since it would not require reframing of the film. Use of the index marks as suggested by Kent, et al. If the projectionist keeps an eye on projected index mark shown in FIG. The problem with this approach is that there is usually no projectionist in attendance in the projection booth.
Today projection is automated, and the projector is remotely started. There is, in all likelihood, no one in the projection booth.
Victoria University of Wellington 3D Film Project
This being the case, the projectionist-operated means suggested by Kent, et al. Although the electrooptical means of the invention described below with reference to FIGS. Electro-optical modulators 14 and 15 are used in front of the projection lens 8. Lens 8, in this case, is made up of two projection lenses 6 and 7, mounted in a single barrel.
Mounted in front of projection lenses 6 and 7, or as part of the projection lenses, is linear polarizing filter ensemble 9. Polarizing filter ensemble 9 is made up of two sheet polarizers, 10 and Axis 12 of polarizer 10 is orthogonal to axis 13 of polarizer This type of projection lens is one which was offered for sale in the early 's by Bolex of Switzerland and in the last two decades by Stereovision International of Burbank, Calif.
A lens of the type shown is also manufactured by Isco of Germany. Although for illustrative purposes FIGS. Various other projection lenses and attachments, although of different designs, perform the identical function, and the invention described herein will work in conjunction with any of them. With reference to FIGS. Film 1 is made up of subframes comprising stereopairs such as the stereopair consisting of subframes 3 and 4.
A preferred embodiment of the index marks of the invention are index marks shown in FIG. For completeness the sound track and perforations are also shown. Subframes and of FIG.
Notes by Dr. Optoglass: Stereoscopy – Challenges in Reproducing Stereopsis in Cameras and Displays
It will be seen that every other subframe has attached to it, adjacent to it, or in association with it, an index mark which is a clear area printed against a black or dark background. The reader will realize that black index marks against a clear background would work as well, and that any combination of colors or densities for the index marks and background may be employed as long as a photosensor is able to distinguish between the two.
Furthermore, the index marks may be otherwise optically distinguishable from the background film region, or from each other, or from both the background region and each other. Throughout this specification, including in the claims, the phrase "index mark" is used in a broad sense, to denote any optically distinguishable mark or code. Although the index marks in FIG. The index marks can alternatively be punched into the film, rather than printed on the film as part of the print stock's image carrying surface. We will return to the subject of how the index marks of the invention can be produced and other aspects of their format.
With reference again to FIG. Information about the light intensity detected by sensor 5 is supplied by part 5A to electronic control circuit 20 "controller" The sensor 5 may be a photo cell or it may be an optical system consisting of lenses and a light pipe or fiber optics cable. In the case that sensor 5 is a photo cell, part 5A consists of a set of electrical wires which transmit changes in voltage to controller If sensor 5 takes the form of an optical system, then part 5A is a light pipe or fiber optics assembly, and a photo cell may be located within controller The important concept is that a light sensor of some type is mounted so as to observe index marks 1A and report on their presence or absence to controller In response to data received from sensor 5, controller 20 appropriately powers the push-pull modulator consisting of liquid crystal panels 14 and Panels 14 and 15 are mounted parallel to each other, with their axes, respectively identified as 16 and 17, rubbed orthogonally.
The planes of panels 14 and 15 are substantially perpendicular to the lens axes of lens 8. The push-pull modulator is preferably constructed in accordance with the teaching of U. Lines 18 and 19 provide electrical power from controller 20 to cells 14 and Although each of lines 18 and 19 is shown as a single line in FIG.
The light modulator formed by panels 14 and 15 can be mounted outboard of polarizer unit 9 and lens 8 which can be any existing projection lens of the type described herein , or it can be an integral part of optic 8,9. This disclosure is not meant to be limited to the embodiment shown, in which the modulator is an attachment to unit 9 and lens 8.
Although shutter is three-bladed, two-bladed shutters of the type shown in FIG. Aperture plate is mounted in the film trap plate , and, as is typical with 35 mm projectors, it is interchangeable.
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Notch is cut into aperture plate This notch provides sensor which corresponds to sensor 5 with a view of the index marks which are printed on the film. Cable of FIG. If sensor is a photo cell, then cable should be an electrical connection for conveying the sensor's electrical output signal. If, on the other hand, sensor is an optical system including a remotely mounted photo cell, such as a photo cell mounted within controller 20 of FIG. In either case, variations in illumination which are associated with the index mark's presence or absence are reported to the controller.
Related Foundations of the Stereoscopic Cinema
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