ROGER N. \iVELLER* University oj Arizona Tucson, Arizona 85721 Photo Enhancement By Film Sandwiches An enhanced photograph and the regular print may be studied separately, or they may be viewed as a stereopair. INTRODUCTION wichcs. The purpose of this article is to intro­ GREAT DEAL OF information is recorded by duce this technique and to present a detailed A modern films, but only a small portion of step-by-step procedure for enhancing photo­ it can be extracted through conventional graphs. methods of photoi nterpretation. Low-con­ FlU! SAXDWICHES trast, subtle features often escape detection due to the distracti ng presence of nearby Photo-enhancemen t il1\·oh·i ng film sand­ prominent features. At other times these sub­ wichcs is both mechanical and photographic tle features are simply left unrecorded be­ in nature. Tn one o[ the most useful tech­ cause their boundaries are too uncertain to niqucs, a high-contrast film, such as Kodalith map. This is quite unfortunate because thesc Ortho, is used to make negati\'e and positive subtle features may be of key importance. transparencies [rom the original negative ABSTRACT: .111 il1eXpellsil'e al1d simple step-by-step procedure can be used jor the enhancement of photographs. JIigh-col1trast negative and positive trans­ parencies formed by contact prillt'ing are superimposed to create a sandwich wliich is then slightly offset. COl1tact printil1g the sandwich on regular photo­ graphic paper produces the enhal1ced pril1t. A bas-relief e.ffect and the en­ hal1cement of linear features results from tile sliglit o./Tsellillg of the films. El1lwnced photographs of terrestrial lava flows al1d IUl1ar maria are il1cluded as examples. The technique is highly flexible and many useful variations are pos­ sible. Crop diseases and changes in lithology and by contact printing. The film sandwich is thcn soil chemistry are often indistinct. formcd by supcrimposing the negative trans­ One means of detecting these commonly parency over the posi tive and then offsetti ng missed featurcs is through photo-enhancc­ the films slightly. This displacement creates a ment. Although the recently devcloped elec­ thin, partial outlinc around features which tronic techniques of enhancemcnt yield cx­ allo\\'s light to pass through thc sandwich. cellcnt results, they still suffcr serious draw­ Contact prints arc thcn madc on regular backs [rom a practical standpoint. Bcsidcs photographic papcr using the sandwich as a being time consuming and complex, thesc ncgativc. techniques are often beyond thc fin<J.ncial One o[ the most noticcable cffects of off­ reach of most individuals and small firms. setting the films is the reduction of tonal There is another mcans of photo-enhance­ values. The blacks and grays vanish; only the ment, however, that not only produces finc contacts bctwccn areas o[ different tone re­ results but also is inexpensivc and simplc. main. The contrast betwecn dark shadows This method involvcs the use of film sand- and brilliant highlights disappears. Features of harsh contrast no longcr stand ou t; high­ * Geology Dept. Recent address: 8114 Stahclin, and low-contrasting features are simply out­ Detroit, :.vlichigan 48228. lined. Rock outcrops, roads, lakes, and 468 PHOTO E~II,\NCEMENT BY FILM S.\ND\\·ICIIES 469 changes in soil and \'egetalion are lraced by seconds of the aerial negati\'e, Develop the fine lines. As a result, the emphasis is re­ strips for 3 minules, stop, fix, and wash, moyed from tone and placed on shape, Examine the strips to estimate which expo­ Another in teresti ng resul t is the creation of sure is best. If the slrips are oYerexposed, cut shadows, The slight displacement of the nega­ dO\\'Il on the light source and run more test ti\'e causes the features to be hea\'ily outlined strips, on one side, This giYes a bas-relief or false POSITIVE THANSPARE:-ICY three-dimensional appearance to the contact lines, This shadow effect creates a textural \\'ith the red safe light on, place the aerial appearance and especially emphasizes linear photographic negative on top of the Kodalith featu res, film, emulsion to emulsion in order to prevent The following is a recommended step-by­ light diffusion, The dull side of the negative step procedure for making these enhanced should be in contact with the dull (light­ photographs usi ng sligh tly offset fd m sand­ colored) side of the unexposed Kodalith film. wiches, Place the glass sheet over the films and hold it down firmly during printing to insure tight MATERIALS contact (Figure 1). After printing, develop 3 • Contact printer or sheet of heavy duty minutes, stop, fix, wash, and dry carefully to glass with be\'eled edges and a light ayoid scratching the film, source (enlarger or lamp with 50 watt ",EGATIVE TRANSPARENCY bulb) • Aerial photographic negatiye After the positiye transiJarency has dried, • Package of S by 7-inch Kodalith Ortho use it just like the aerial photographic nega­ sheet film li\'e and make another contact pl'int on 1<0­ • Red safe light dalith film, emulsion to emulsion again. The • Paper de\'elopi ng trays dull surfaces of both films should again he in • Paper de\'eloper (Dektol), stop bath, and contact. Use an exposure of about the same fixer. period as the one used in maki ng the posi ti \'c transparency, De\'elop for 3 mi nutes, stop, TEST STRIPS fix, \\'ash, and dry, As in any photographic printing, there is a FILM SA!\DWICH need to determine the correct exposure time, Kodalith fdm may be treated as a fast photo­ After the negatiye transparency is dry, tri m graphic paper, hu t the de\'elopmen t and ex­ a half-inch wide strip oR' both ends of the posure times are much more critical due to the film, making it shorter than the positi\'e high contrast of the film, Fix the deYelopment transparcncy. Also cut se\'eral one-inch long time at 3 minutes at 68°F to simplify matlers, pieces of masking tape and keep them handy. \\'ith the red safe light on, cut se\'eral one­ Place the positive transparency with the dull inch wide stri ps of Kodali th fi 1m and make side (emulsion side) up on a light box or clean contact prints with (;xposures of 1, 2,4, and 8 sheet of glass with a light source below. Now ENLARGER OR) ( !lO WATT BULB /GLASS SHEET / /NEGATIVE FILM 2::S;:;;;:::::S==dit;;~~~;:::>~ KODA LITH --- BASE 1'1(., I, Hasic set-up for contact prinling, 470 PHOTOGRAMMETRIC ENGINEERING NEGATIVE TRANSPARENCY / FILM SANDWICH WITH SLIGHT OFFSET POSITIVE TRANSPARENCY FIG. 2. The combination of high-contrast negative and positive transparencies into a film sandwich of slight offset. place the negative transparency directly over DISPLAY it so that all of the features match up and no light comes through the sandwich. Carefully A regular contact print should also be made shift the negative transparency one tenth to from the original negative to provide a basis one-half millimeter in the direction of the for comparison. The enhanced photograph length of the film, making sure no rotation of and regular print may be studied separately, the fil m occurs. Any rotation can be easily or they may be combined as a stereo pair or stereogram (Figures 3,4,5, and 6). spite of detected, however, because it prod uces a con­ In centric pattern of light and dark bands. Make both prints originating from the same neg­ a tive, a false three-dimensional effect is sure that the displacement is uniform across the film by checking the maximum width of created if the prints are viewed stereoscopi­ the lines created. VVith one hand hold the film cally. This false three-di mensional effect causes the fine features to become even more in place and use the other to tape the negative noticeable. transparency to the posi tive one at the ends of the film (Figure 2). Obtaining uniform dis­ EXAMPLES placement may be difficult at first, but with Before going on to the variations and modi­ practice few difficulties are encountered. fications of this technique, a few examples of FINAL PHINT enhancement will be presented. Figure 3b was created by specifically fol­ Carefully clean the fingerprints and dust lowing the step-by-step proced ure i ust ou t­ off the film sandwich and then use it as a lined. The area consists of several super­ regular negative to make contact prints on imposed lava flows and small collapse de­ photographic paper. After making as many pressions which are still quite fresh and show prints as needed, disassemble the sandwich, little weathering. In fact, surface cooling return it to the light box, and reassemble it cracks can be observed on the larger smooth there wi th displacemen t in the direction of the flows in the enhanced print. Also emphasized width of the fil m. This is done to insure the are at least four systems of lineations which enhancement of linear features in all direc­ not only dissect flows but also appear to have tions. Afterwards, the sandwich may be dis­ the original growth of the flows. One inter­ assembled and reassembled any number of pretation for these lineations is that they are times to vary the amount and direction of dis­ expressions of rei uvenated faul t systems in placement. A small displacement emphasizes the older underlying rocks. The existence of fine features, whereas a slightly larger dis­ these linear features has been verified by other placemen t en hances the more massive ones. smaller-scale photographs of this same area. PHOTO I,NIL\NCE~IENT BY FILM S.\NIJ\\"Il'IIES 471 A B FIG.