TIME-MOTION DIAL " EXPOSURE DIAL LATITUDE ZONE MAP n.. __fII"' __~~ ......~_. ___"'-"'-_'-"-to __fII __ to __ "-.__.. __.......... _ • ....-....... fII_-.. ==-..r-.trIotlfN.-'-....:t:a. __........ ... ...... ~~_(.-"'to__ If ...,-.-...........,,__ -'»fII_ ......._ ti"_ ~ol... _ _""'""'*" _ ....... " _ Ot~ .. " 11 .. h· ' ...lO . FRONTISPIECE. The Kodak Aerial Exposure Computer. ALLAN L. SORE]\{* Eastman Kodak Company Rochester, N. Y. 14650 Principles of Aerial Color Photography Aerial photographers may have many new questions about exposure, filters, processing, and quality. r:-iTRODUCTION photographs in color could be used to locate bodies of ore, and Herness,2 in 1955, con­ AERIAL PHOTOGRAPHY IN COLOR is still a 11.. relatively new and untried technique to cluded that such photographs, in conjunction many aerial photographers despite the fact wi th geological maps, represen ted the most that the requisite materials and processes effective and economical approach to mineral 3 have been available for a long time. One exploration. Ray and Fischer provided explanation for this is the belief that the further support for these conclusions in an adyantages are not commensurate with the article in Science dealing with applications of increased cost, complexity, and uncertainty aerial photography in geological studies. 4 of using color materials. In the past two Fischer reported further studies of the decades, howeYer, a number of specialists in geological uses of color aerial photography different fields who thought that the possible which indicated that many features were benefi ts of color should be explored, have pro­ delineated with greater continuity and clarity duced some com'incing demonstrations that in full-color photographs, and latera he dis­ color does offer worthwhile ad\'antages oyer cussed techniques by which abridged spectral black-and-white photography. They haye reAectance characteristics can be estimated also shown that color information can be re­ from color photographs. The detection of corded even at high al ti tudes. underground glacial deposits of water through In 1952, Laylanderl determined that aerial the use of infrared-sensitive false-color film was reported in Science News Letter6 in July, 1959. Further geologic mapping applications * Presented at the Annual Convention of the American Society of Photogrammetry in Washing­ were described by Minard7 in 1960. In his ton, D. c., March 1967. studies, in terpretation of color aerial photo- 1008 PRI 'CIPLES OF AERIAL COLOR PHOTOGRAPHY 1009 graphs particularly facilitated the mapping of tion." Both this and the preceding article two formational contacts which were ex­ have full-color illustrations. tremely difficult to locate other than by exten­ Aid richu experi men ted wi th large-scale, sive boring. 70-mm. aerial color photographs for obtaining Haack8 inYestigated the performance of forest il1\'entories, appraising insect damage, photointerpreters in land- and forest-class and recording the effects of fire and disease. recognition, from photographs taken on pan­ He suggested further applications in range, chromatic, infrared, and color films. Although wildlife, and watershed management. The a com plete study of the color fi Ims was not results of similar studies are reported by made because of the cost of the film and view- Heller, Doverspike, and Aldrich12 in Agricul- ABSTRACT: The addition and snbtraction of the three primary colors are basic concepts in the design and use of color photographic materials. A reprodnction need 110t, (tnd almost never does, have the same spectral characteristics as the original scene. Color-negative materials may offer significant advantages of flexibility over color-reversal types. Color diapositive plates are used successfully in stereoscopic mapping. A 11. exposure computer is available to aid the aerial photographer, and the proper use of filters may -require difficult decisious, whereas color processing may impose no real di.Oic'lllty, The color characteristic of the viewil1g light may limit the amount of il1formatiou retrievable from a system., ing equipment and the difficulty of obtaining ture Handbook No. 261, and a quotation correct exposures, which Haack did not think from their conclusions is appropriate here: could be justified on the basis of preliminary "Color film is superior to panchromatic film results, he concluded that color would be for use in identifying individual tree species, desirable in regions containing a greater \Vhy? First, people are accustomed to seeing and identifying objects not only by shape and form \'ariety of tree species than the one studied, but also by color. A ripe tomato is picked from and that color transparencies best bri ng ou t the vine by its color rather than its shape, and minute tonal details. cotton can be graded by the ligh tness and yellow­ Smith 9 presented an excellent survey of the ness of the fiber. A forester trained to recognize trees by morphological features also associates a reasons why the U. S. Coast and Geodetic color with that tree. \\'hen he is trained to Survey has come to rely increa ingly on recognize the tree on aerial color photographs, he color photography, and the historical back­ has one more factor on which to base his deter- ground of its work with color. He also ga\'c many yaluable tcchnical hints based on his experience. Thc techniques of using aerial color photo­ graphs in the U. S. Coast and Geodetic Sur­ \'ey were described in considerable detail by Swanson lO in 1964, He presented many ex­ amples of the yalue of color photographs, par­ ticularly in the mapping of coastal and shallow-water areas. Using color diapositi\'e plates in plotting instruments, he found that "A distinctive advantagc has bcen expe­ rienced in color for acrotriangulation: the superior interpretative qualities enable one to make more accurate readings on the pass points used for connecting models, rcsulting in more accurate aerotriangulation. Color photography also permits the operator to see better into shadows, and is advantageous in finding those exact points identified by the field parties for control of the aerotriangula- ALLAN L. SOREM 1010 PHOTOGRAMMETRIC ENGINEERING mination. Thus, it requires more training for an jectively perceived and the degree of objec­ interpreter to be able to recognize objects by tive similarity between the picture and the tones of gray than by the normal colors with which he associates the object...." original scene. As an intermediary between the original A recent paper by Mottl3 contains ma­ scene and the eyes of the viewer, a picture terial which the reader will find helpful. does not literally record the scene, but rather In the next few years we shall undoubtedly captures clues that we have learned to de­ see many further experiments with aerial cipher. ext to shapes and relative sizes, color photography, and, in some applications, colors are the most important of these clues. a shift to the rou tine use of color materials. As we are concerned here with a picture as a A new generation of photo interpreters will source of information rather than for its learn to utilize, and then to take for granted, emotional content or artistic qualities, we the information that is available in increased assume that the more accurately it conveys q uan ti ty and wi th increased ease of in terpre­ the same sense impressions as the original, tation in color photographs compared with the better. But these impressions are evoked that of black-and-white photographs. by pictorial clues which are not like the The purpose of this paper is nei ther to original in any exactly measurable sense. This present new data from experimental work, is an obvious, yet subtle, point. Failure to nor to describe color materials and processes understand it has been responsible for overly in detail, but rather to bring together for optimistic hopes for automated photointer­ aerial color photography some general infor­ pretation. Failure to understand it also leads mation and observations which may be help­ some photographers to expect to be able to ful in practical aerial work. Good amateur measure such things as the per cen t reflec­ color pictures can be taken wi th Ii ttle or no tance, or the spectral reflectance charac­ understanding of color vision or the principles teristics of objects in photographs of them. of color photography, by following a few The fact is that a black-and-white photo­ simple instructions on a data sheet. However, graph tells us nothing about the proportion the aerial photographer who wan ts to, and of the incident light reflected by an object in should, get consistently good results will find the scene, except what we can infer from prior it easier to de\'elop his judgment and tech­ knowledge of the object and its surroundings. nique if he does understand some of the prin­ Likewise, a color photograph tells us nothing ciples of color vision and color photography, about the proportion of the light of various and the complex interplay between scene wavelengths reflected by an object in the characteristics, the degree of haziness, the scene except, again, what we can infer from sun angle, the choice of filters, and the selec­ our knowledge of the object. To see why this tion of the required camera exposures. Al­ is so, we turn to a consideration of the visual though only a superficial review of the taking perception of colors, and the way in which of color pictures is possible here, it is hoped color photographs are produced. this will be sufficient to help some readers The characteristic of human vision that is achieve a degree of success which will stimu­ of basic importance in understanding color late further interest. photography is that a match for the color of practically any natural object can be pro­ PRINCIPLES OF PHOTOGRAPHIC duced by mixing lights of three properly COLOR REPRODUCTION chosen colors.