Autostereoscopy and Integral Photography UDC 778.39 + 778.4 Yu.A

422 V. A. KOMISSARUK

linear change in the path difference must be most If the wave surface is an assemblage of dif- obvious in the direction of the shift, while in the ferent aberrations, then its investigation is obvi- case of astigmatism it is in the perpendicular di- ously complicated. Nevertheless, if one distin- rection. For coma and spherical aberration we guishes the linear, quadratic and cubic terms of the should have, respectively, the highest quadratic and path difference in interpreting the interferogram, cubic terms in the path difference equation. In all one can distinguish the various types of aberrations cases other than astigmatism, the maximum change and investigate each of them separately. Thus, our in the pa th difference characteris tic of the given results are applicable also in this complex case. aberration at optimal shift is observed along that axis of symmetry ofthe interference field which is paral- References lel to the shift. Consequently, in these cases one should tune the instruments on bands parallel to the 1. M. Franpon, and M. Jordery: Revue d' Optique, shift. On the other hand, in investigating astigma- 32, 601 (1953) tism, it is more convenient to tune on bands per- 2. Õ:- Toraldo di Francia: in "Optical Image pendicular to the shift; for astigmatism, just as for Evaluation". NBS, Washington, 1954; Russian coma, one should first determine the meridional trans!., 1959. cross section of the wavefront (for example, by observing the type of interferogram obtained at various directions of the shift) and establish the optimal direction of the shift. Received July 14, 1969 =:i-=

OPTICAL TECHNOLOGY VOLUME 37, NUMBER 7 JULY 1970 Autostereoscopy and Integral Photography UDC 778.39 + 778.4 Yu.A. Dudnikov

A brief description of auto stereoscopic techniques for obtaining three-dimensional images is presented; the advantages and faults of integral photography are analyzed. A comparison is made between holography and integral photography, and the prospects of this latter method are indicated.

The viewing of stereo-photographs without the successful in their time, and in improved form aid of special optics (hence the term autostereo- are being used even today. scopy), is a long-sought goal. As of now, the The parallax stereogram is a replica from a recently developed holography technique produces normal stereoscopic pair, made optically through stereo images with the largest amount of informa- a line pattern, i. e. , through a screen of alternating tion presently possible. However, its practical vertical transparent and opaque lines. The lenses utiization is difficult since it requires coherent of the objective of the printing device superimpose ilumination. the images of the two stereoscopic negatives on The concept of holography, i. e., fixation of one another, but the screen subdivides them into an image by photographing the pattern of inter- narrow alternating strips. One must view the com- ference of waves incident on the subject and re- bined image through the same screen, set up in flected by it (1). derives from the color (non- such a way that the right eye sees the strips be- stereoscopic) photography of G. Lippmann (1894), longing to the left negative and the left eye those of in which interference nodes and antinodes of the the right negative (Fig. 1). The image thus pro- light waves incident on the photographic plate and duced is half as bright as that obtained with the reflected by its back mirror surface are fixed same illumination in a stereoscope, and contains within the light-sensitive layer. less visual information, since only half of the Autostereoscopic methods which do not re- area of each frame is viewed (and this without quire coherent ilumination, such as the parallax magnification). The stereoscopic effect is satis- stereogram of Berthier (1896) (2) and the parallax factory but in order not to lose it, both the photo- panoramogram of Kanolt (1915) (31, were graph and ones head must be perfectly stationary. AUTOSTEREOSCOPY AND INTEGRAL PHOTOGRAPHY 423

P.R

:~~~'" -_-_-;¡',__"'-:",'i 0 R, ~:~~~ ~L L'~JjP Li ~~'~A'~,;- ~ -. /. 0, ,~Ä ;'

E r

Fig. 1. Replacement of stereoscope by a line pattern screen: 01, Oz are projection lenses, Hi and HZ are the two stereoscopic negatives, PI and Pz are identical line pattern screens, E is a screen Fig. 2. Principles of a parallax panoramo- or a photographic fim, L and R are the eyes of the gram: Hi-H, are negatives photographed in the viewer, 1 and 2 are alternating strips of the left camera with several lenses arraned in a row: 0,- 03 are projection lenses; Pi. P, are iden- and right images. tical line pattern screens; E is a screen or a photographic plate; Li and Ri' L2 and R2 are the positions occupied by the eyes of the viewer while An attempt to overcome this latter disadvan- shifting perpendicularly to the line direction on the tage was the parallax panoramagram (3). The ;m" images are prepared just as in the parallax pattern; 1, 2, 3, are alternating image strips. ::il,lt stereogram method, but from a large number of "h i':,,'::~ negatives (rather than two) which are reprinted ,",. and the parallax panoramogram) was made by .,,tI' through a camera with several photographic nega- researchers at the Soviet Motion Picture and :,, tives arranged in a row (Fig. 2). The width of the Photography Research Institute (NIKFI), especially dark lines in the patterned screen is (n-l) times as S. P. Ivanov, who invented a stereoscopic motion large as the width of the transparent spaces (n is picture process (12). the number of photographic lenses or points from , The above auto stereoscopic techniques do not :J '!B which the photograph is taen). The image is n create a suffiCiently good ilusion of reality, since times darker than at the same ilumination in the they neglect certain characteristics of both the .'C'i, stereoscope; the amount of visual information also object space and of the stereoscopic viewing. For diminishes. However, the relief pattern is per- example, one of the great disadvantages of the ceived more naturally than in a stereoscope because parallax panoramogram is the break in the relation- of the ilusion of "scanin" the three-dimensional ship between accommodation and convergence (13). image by side-to-side movement of the head. It would seem that now it would be best to re- In the 1930's the line grating was replaced by turn to the so-called integral photography suggested embossed lens patterns, consisting of a number of by Lippmann at approximately the same time as his thin and long cylindrical lenses. Many specialists color photography technique (1908). Worked on improving the technology. There was An integral photographic plate is a surface com- the British "lenticulated screen" process, the posed of minute positive lens lets with blackened French method of Josse (5), the German "Diacor" side surfaces, adjoining each other in a honeycomb (6 J method and others (7 J. Considerable practical sUccess was attained in the 30's by H. E. Ives (8 J pattern (known as "fly's eye") (Fig. 3a). The back surfaces of the lens lets (which are also their who also devised the theory of the parallax panoram- back focal surfaces) carry a light-sensitve emul- ogram. Among present-day scientists who pro- sion. The subject is photographed, without the aid duced high-quality stereoscopic photographs with a of any auxilary optics, by the integrated plate screen containing an embossed cylindrical lens itself, which is then photographically developed. pattern one should mention the French investigator Then the viewer, stationed on the front side of the M. Bonnet (9 J. The screens, the photographic lens pattern, views the reconstituted integral image camera and other equipment developed by Kodak in obtained by iluminating the back (emulsion-covered) recent years have permitted many firms to mass- side of the plate with diffuse light (Fig. 3b). The produce stereoscopic photographs known as xographs subject appears restored to natural size in that (10), featuring an opaque backing and a screen of region of space where he was originally located. cYlmdrical lenses. A major contribution (11) to The term "integral photography" derives from the this type of stereoscopy (the parallax stereogram writings of Lippman, who stated that in iluminating --

424 YD. A. DUDNIKOV

the plate one no longer sees individual microscopic a I.P. c images; they are replaced by a single (integral) image, which is seen under the same anle as the original subject" (14). The resulting images change t'4Em~~:~:" form, just like the object itself, depending on the position of the viewer, and also change their angu- lar dimensions with distance. A 3600 panorama can be fixed on an integral cylindrical plate, and a ~~~~:c dd-n~~ spherical one can even accommodate all surround- -i ing space. Unlike other methods, integral photography .~EI ~2:::/llll'¡- ~~'EZ,D,,,- - a creates a three-dimensional optical model of the ~-il2 subject which can be examined and photographed in the usual maner. The three-dimensionality of the image produced by this method is due to the fact Fig. 3. Lippman's integral photography: 0 is that integral photography can reproduce very ac- the subject; 0' is the reconstituted integral image curately the wavefront emanating from the subject of the subject; IP is the integral plate; A is a glow- (151. This is, in turn, due to the abilty of the lens- ingpoint, 01 and 02are the centers of projection of lets of the integrated plate to "remember" both the images of two elements (lenslets) of the integral directions of the incident beams of light and the plate; ai and a2 are the images of point A fixed in parallax of the microimage fixed by each such lens- the emulsion; A' is the reconstituted image of point let. Figure 3c, d shows how the lenslet "remem- A, which exhibits strict localization in space due bers" each individual pointon the subject. Every to the strictly determinable position of the points subject which can be represented as a set of such points is "remembered" in the same maner. The 01' ai, and 02, a2. above-mentioned features make the integral image approach the qualities of the holographic image of three-dimensional objects. Practical realization of integral photography immediately encountered considerable technical Another technique of integral photography of problems. Lippmann was able only to verify his small objects was realized by Gramont and Plan- concept theoretically. With the aid of 12 stanope overn (Fig. 4; (21). An array of flat mirrors were magnifying glasses * (14) he proved the existence placed in such a way that each gave an image of of an optical three-dimensional image in which new the subject from a slightly different point of view. parts could be seen by shiftin the position of the Byprojecting the overall photographed image eye. through the same system of camera and mirrors A detailed mathematical and experimental one produces a three-dimensional image of the proof of Lippman's concept was produced in 1911 by subject which gives an ilusion of the natural sub- Professor P. P. Sokolov of Moscow State Univer- ject. The original integral photography technique sity (16-17), who first computed the shape of the back surface of the lens element of the integral had several faults which impeded further develop- plate and established that integrated photographs ment. Its main fault was that the reconstituted "being taken without an objective lens, give upon image was pseudoscopic, i. e., geometrically direct examination an impression of relief char- similar, but with an inverted relief (22). It is acteristic of stereoscopic photography, the photo- interesting that this was fully eliminated by copy- graphs exhibiting not only a complete relief, but ing from an expsed integral plate onto an identical a perspective varyin depending on the angle at unexpsed one. (This practical technique, the which one views the plate, that is, an approxima- basis of which was given by Lippmann in his earli- tion of reality which unti now has been unattainable est work (23-24), was apparently forgotten by him, in any other instrument". since he mentions nothing about it in any of his Estanve (18-20) made a further contribution later papers.) The exposed integrated plate with to integral photography; he worked with units of 56 the image of the object imprinted on it and an iden- and 95 Stanhope glasses, and then later used a tical unexposed plate are arranged with their block of 1250 stenopic cameras**. convex surfaces facing each other. The reconstituted integral image, produced by iluminating the expsed integral plate from the side of the emulsion, is recorded on the unexposed one. Copies of the integral photographs thus generated exhibit less contrast than the originals as well as lower resO- * A Stanhope magnifying glass is a column of lution of fine details; this substantially reduces glass of, for example, square cross section, their value. spherical at one end and flat at the other. In 1967-1968, other methods of reversing the ** A stenopic camera is a small opening which relief were proposed (25-26 j, but they too are gives a diffraction image of the object. fairly primitive. AUTOSTEREOSCOPY AND INTEGRAL PHOTOGRAPHY 425

y Several authors (28) see the explanation of this remarkable similarity between the two tech- 0.; niques in the presence of the three-dimensional a'8 , 0., moiré effect, which is obtained in reconstitution 0.'5 a' of the integral image. , j Let us point out also several substantial ad- 0.+ vantages of integral photography over holography: , 0.'J 1. Coherent ilumination is not needed at any EmulsionC 0, stage of production of the integral image. 0.'f 2. One can photograph specifc objects which y cannot be recorded holographically. More than that one can reconstruct models of three-dimensional surfaces described by mathematical equa- Fig. 4. Gramont and Planovern integral tions, these models having no analogy in nature photographs: C is the camera; 0 is the subject; (26 j. 1-9 are fIat mirrors located on the curve XX in 3. It is easy to work with live subjects and such a way that the subject images 01' - 09' are easy to produce color images. located on the straight line YY, perpendicular to To sum up, we conclude that holography and the axis of the camera C. The optical model is integral photography are not mutually exclusive, but supplement one another. There are areas of reconstituted at the site of the subject by project- science and technology in which integral photog- in the positive through the same system of camera raphy is more applicable (for example, optical and mirrors. methods of information readout, three-dimensional television, landscape imaging), advertising, etc. ). Furthermore, combinations of integral Another fault of integral photography is (15) photography and holography are possible and have that for a maximum accuracy reproduction of the already been used (29, 30). ;,;ji subject one requires infinitely small lenslets in In the USSR and abroad there is a practical "I the fly's eye pattern, but then the resolving power interest in three-dimensional color optical images i~!lØ of each lens let and the resolution of the reconsti- and in the theory of integral photography (13, 31). .~ tuted image as a whole becomes zero. This can be The latestdevelopments in screens with em- ""~ overcome by a compromise as to the dimens ions bossed spherical lens lets should help in intensifying ;, of the fly's eye lenslet. However, at larger lens- theoretical and practical research. :)' lets the discrete structure of the plate itself inter- Thus, integral photography is a promising feres wi th viewing and, what is more, the integral technique, in many respects alternative to holog- ~ image itself acquires a similar structure. Correc- raphy. It now has certain faults which appear , tion of this fault, as well as the development of a surmountable, at which point it may become wide- , way of reconstituting a normal, noninverted relief spread in professional and amateur photographic II is a dificult, but important problem. practice. -, Comparison of holography and integral photog- I wish to acknowledge the great help of 1. A. .~ raphy shows a certain similarity between them, Cherniy in working on this problem and to express as well as several substantial advantages of appreciation to A. A. Vorozhbit for valuable integral photography (27). criticism of the manuscript. Let us cite the similarities of the two techniques: References 1. Both holography and integral photography are autostereoscopic techniques, i. e., no viewing 1. Yu. N. Denisyuk, Opt. Spektrosk., xiv, No.5, equipment is required for observing the image. 721 (1963). 2. Both techniques require fims of very high 2. A. Berthier, Cosmos, 34, 2 (1896);cited in resolution. Comptes Rendus, 139, 920 (1961). 3. Both techniques permit multiple expsure 3. C. W. Kanolt, US Pat. No.1, 260, 682 a~d recording of different images on the same plate, (1915/1918 ). with subsequent simultaneous reconstitution of all 4. Cited from K. Symons and M. Hande, stereo- the recorded images. This was done recently by photography, London, 1957. American researchers (26). 5. M. Bonnet, La photographie en relief, Paris, 4. The viewing images are virtually identical to 1942. that of viewing the real objects because all the Psychophysiological laws and geometric conditions corresponding to the natural stereoscopic viewing . The three-dimensional moiré effect appears are satisfied. in diffuse-light ilumination of a system of two . 5. Defects in the plates do not destroy the plates having a honeycomb structure. To achieve lmage. a three-dimensional moiré pattern the repetition 6. When part of the plate is covered, the interval of lenslets of one plate must differ only entire image stil remains visible. insignificantly from the interval of the other plate. -

426 YU. A. DUDNIKOV

19. E. Estanave, Comptes Rendus, CXC, 584, 6. R. Mandler, German Pat. No.1, 139, 731 (1930). (1958/1963 ). 20. E. Estanave, Comptes Rendus, CXC, 1405, 7. A. H. J.. de Lassus St. Geniè's,German Pat. No. 959, 078 (1957). (1930). 21. N. A. Valyus, Stereoskopiya (stereoscopy), 8. H. E. Ives, J. Opt. Soc. Am. , 20, 585 (1930). 9. M. Bonnet, W. German Pat. No. 899, 499 Press of Acad. Sci., USSR, 1962. 22. H. E. Ives, J. Opt. Soc. Am., 21, No.3, 171 (1947). 10. K, Bartusch, Papier und Druck, 1964, No.9, (1931 ). 132. 23. G. Lippman, Comptes Rendus, CXLVI, 446, 11. N. A. Valyus and G. V. AviIov¡ Trudy NIKFI (1908). 1948, No.9, 94. 24. G. Lippmann, J. Phys. Theor. Appl., Ser. 4, VI, 821 (1908), 12. S. P. Ivanov and L. V. Akimakina: Sovt. Pat. No. 138, 141, Byull. lzobret., 1961, No.9, 25. C:B. Burckhardt, R. D. Coller and E. T. 61. Doherty, Appl. Optics, '! No.4, 627 (1968). 13. O. F, Grebennikov and V. P. Gusev, Tezisy 26. A. Chutjian and R. J. Coller, Appl. Optics, dokladov na konferentsii, posvyashchennoy 7, No.1, 99 (1968). 50-letiyu LIKI (Transactions of the Confer- 27. R. Coller, Physics Today, 1968, No.7, 54. ence on the 50-Year of the Leninrad Institute 28. W. Hesse, Kino-techn. (W. Germany) 22, of Motion-Picture Engineers), Leninrad, No. I, 1 (1968). .- 1968, p. 33. 29. R. V. Pole, AppL. Phys. Lett., 10, No.1, 20 14. G. Lippman, J. Soc. franc. phys., 1912, 69, (1967). - 15. Yu. N. Denisyuk, Opt. -Mekh. Prom., 1968, 30. W. E. Kock, Proc. IEEE, 55, No.6, 1103 No. 11, 18 (Sov. J. Opt. Tech., 35, No.6, (1967). - 695 (1968)). 31. C. B. Burckhardt, J. Opt. Soc. Am. 58, 16. P. P. Sokolov, Zh. Obshch. Lyubiteley Yes- No.1, 71 (1968). testvoznaniya, 123, 23, (1911). 17. P. P. Sokolov,Vestnik Fotografi, 1908,113. 18. E. Estaave, Comptes Rendus, CLX, 1255 Received January 27, 1969 (1925), =:i-=

JULY 1970 OPTICAL TECHNOLOGY VOLUME 37, NUMBER 7

Attenuation of Monochromatic Radiation by the Near-Ground Atmosphere UDC 551. 593. 5: 621. 378. 9 V.A. Borisov

We measured molecular absorptance of monochromatic radiation of wavelengths of 0.488, O. 633, O. 694, 0.844, 1. 06, 1. 15, 3.51 and 10. 6 in horizontal paths in near-ground air. We showed that in certain cases (0.694 and 1. 15 ¡.) molecular absorption is the basic factor governing the power loss in the beam during travel in the atmosphere.

of the degree of monochromatization of the radiation. Interest in data on the transmittance of the atmo- Therefore, in studying the transmittance of the sphere for monochromatic radiation has grown con- siderably in recent years, particularly with the ad- atmosphere for monochromatic radiation. one should first measure the specific transmittance funC- vent of various lasers operating in the visible, the ul- traviolet and the infrared. Within anyone partof the tion of a given layer, which is governed by selective spectrum, aerosol and molecular scattering, as well absorption in the narrow lines of the vibrational as fluctuations in the intensity and angle of approach rotational spectra of atmospheric gases. Such mea-, in a turbulent atmosphere are virtually independent surements should yield the "reduced" absorptanCe