We describe one setup employed for the recording of two types of holographic screens that can be used in white-light applications. We show how to obtain holographic screens with areas up to 1370 cm2 and diffraction efficiency of 17%. We analyze the holographic screens in their relevant aspects as to focal lengths, theoretical approach, sizes, and diffraction efficiencies, specifying when each type is appropriate for particular applications.
Diffracted images with inverted depth were first reported by the authors where a lens or slit intermediated the white-light double diffraction process. The diffracting elements were simple straight line diffraction gratings and the image could be seen but not projected due to its strong astigmatism. The generalization of the symmetry properties to bi-dimensionally defined diffracting elements allows to produce projected images with circular gratings intermediated by a pinhole. Acting as a focusing element, the possibility of enlargement is reported here with experimental results.
Diffracted images with inverted depth were first reported by the authors where a lens or slit intermediated the white-light double diffraction process. The appearance of an image with orthoscopic relief was reported, generated with the same system consisting of simple straight line diffraction gratings. We report now that the generalization of the symmetry properties to bi-dimensionally defined diffracting elements eliminates the vertical astigmatism of the images.
Display systems relying on computer graphics techniques usually create 2.5D image display on a 2D screen. To obtain 3D image display, most system uses auxiliary devices or viewing tricks, such as polarized glasses, virtual reality helmet, detection of observer's location, divergent viewing, etc. We call these systems stereoscopic. A system that can display 3D images in a natural way is called a self- stereoscopic system. We know that stereoscopic system do not have horizontal parallax such as seen in holograms, which display continuum parallax. In this paper, we introduce a new technique based on shell rendering to discretize horizontal parallax by coding several views of the object forming a holographic-like stereogram and a new self- stereoscopic 3D display system to visualize holographic stereograms on a holographic screen. We also demonstrate the new system using medical image data.
Very few possibilities are referred to give a solution to the problem of holographic television. We mean here holographic being any system capable of bringing images in continuous horizontal parallax. Occlusion is a necessary property for representing objects with realm, as opaque elements instead oftransparent ones. The only system we know that satisfies this requirements is being developed by Benton since 1989. It consists in processing the object information by Fourier transformation by very powerful parallel computing processing introducing this information in one crystal electrooptical modulator by means of acoustic waves while reading it by means of a laser. Color can be obtained by making a three-chromatic RGB system. The computer simulated images are, to our knowledge, well defmed in continuous horizontal parallax . It was recently reported 2 to have reached the size 8.5cm (V) x 13cm (H) x 20 cm3. We proposed a white light system capable of generating a vectorially addressed holo-like image This system was further developed recently to generate a sequence of TV planes where reach TV frame is seen oblique to a holographic screen, traversing it from its front to his back. A controlled mirror makes this plane to fill a volume by scanning along the screen, so that if we project a sequence of contour lines of an object it can be seen in continuous horizontal parallax, to a size of 1m3, up to now. First results using computer generated models will be described. The system has the possibility of occiussion by control of the spectral distribution when encoding each point, a development to reach in future work.
We report the enlargement of holograms by illuminating with a halogen lamp from the small format of 3 5mm. A special configuration is employed to concentrate the luminous energy on the projection lens. An enlargement factor of 20 was obtained in a 75cm x 114cm holographic screen.
Archaeological mirrors from the Olmec civilization were analyzed in the context of a bibliography produced in the last two decades. Photographs of its images are shown as a proof of its good quality. Some suggestions are made on its probable utilization.
Holographic screens were previously reported by one of the authors (J. J. L.) as a means of keeping parallax when projecting images of objects and holophotographs. The images formed in that way offer stereoscopic vision to the audience, without the help of glasses, but in addition to that they offer color encoded continuous parallax effects when the onlooker changes position along a horizontal track. First, we report on the manufacture and use of diffractive screens of dimensions up to 1.14 m X 0.75 m that show all of the previous reported abilities. They were made by means of a ruby laser. In the next section a number of possible uses of those screens are presented, going from diffraction encoded projection of photographs, over real object projection, to transmission and reflection holograms. Magnifications by a factor of 20 were possible.
It could be said that holography in Brazil took its roots from Argentina. since the first hologram made in Latin America is to mv knowledge. the one made by myself in July 1969 in La Plata University at the Laboratory for Spectroscopv. Optics and Laser directed by Dr. Mario Garavaglia. Although the single box of Kodak 649-F plates we imported was opened at the customs. the part that was in shadow during the inspection remained useful. That hologram was shown at the Latin American School for Physics that happened at La Plata City in 1970 and generated a general interest on the subject. Some of the participants that saw it later developed holography in Venezuela and Argentina.
Directionality in a holographic screen may be useful for projecting images to be seen in complete horizontal parallax. The continuous sequence of views from an object may be transferred from the object and enlarged at the screen, giving the same appearance of a holographic image. Due to the actual movement of the object, images in four dimensions may now be produced with a projector whose spatial dimensions are much smaller than those of the screen. One technique that allows for this result is the chromatic encoding of views by means of holographic optical elements. This is demonstrated to be a complete reproduction of the original light distribution, although its spectral continuous distribution of colors makes each view monochromatic, not allowing for good color reproduction. The resulting system may substitute conventional holography in some visual applications if registering is not necessary but only the effect of the phantasmagoric image. Furthermore, it allows for the enlarging of holographic images, performing also the direct conversion of the image of a conventional off- axis hologram to a white-light image.
Color encoding of depth is shown to occur naturally in images of objects observed through diffraction gratings under common white light illumination. A synthetic image is then obtained from a single point of view, a phenomenon that can be applied to stereophotography. The image can be recorded in a common color photograph, providing a simple method of visual decoding by means of ordinary colored 3-D spectacles. The fundamental equations and the photographic procedure for maximum fidelity in three dimensional reproduction are described. The result is a photograph that has the capability of registering all of the views of an object in a continuous sequence, which is called holophotography and was previously obtained by means of a hologram. By eliminating the need for a laser and holographic film, a new technique for holography in white light is foreseen.
Colorencoding of depth is shown to occur naturally in holograms that are reconstructed under white light illumination. It can be registered in a common color photograph, allowing a simple method of visual decoding by means of ordinary colored 3-D spectacles. The fundamental holographic equations and the photographic procedure required for maximum fidelity in threedimensional reproduction are described. The result is a new kind of photograph that shows all of the views of the object in a continuous sequence. It permits an animated photographic representation and also makes it possible to adjust the degree of depth visualization when observed as a stereoscopic representation.
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