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
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. 3. Regular (A) and enhanced (B) contact prints frolll an aerial photo~raphic negative of the Journada del :Yluerto lava flow, Soccorro and Sierra Counties, New Mexico. so these lineations are not patterns created of photo-enhanccment. I nstead of making the accidentally by the shifting of the films. positive transparcncy a a contact print, a Comparison with the regular print reveals 3S-mm. negati\'c was placed in an enlarger that these features exist there also, although and projcctcd onto the Kodalith film. Figure more highly subdued. 4 is a closeup \'iew of a large Lunar Orbiter Figures 4, 5, and 6 show some of the flexi photograph whcreas Figures 5 and 6 were bility inherent in the film sandwich tcchnique taken from a screened print in the Rectified
A FIG. 4. Regular (A) and enhanced (B) prints of the western limb region of the Moon taken from a small portion of a medium resolution Lunar Orbiter IV photograph (frame 188). The area shown is on the western shore of Oceanus Procellarum which appears as the dark, smooth material at the right. North is up. 472 I'II{)TOGR.\~BIETRIC ENGINI,IWING
A B
FI(;. 5. Regular (A) and enhanced (B) prints of a high sun angle, earth-based photograph of the central area of the front side of the Moon. The dark area is :\rare Vaporulll and the streaked light areas to the lower right are the Haelllus Illountains. North is to the right. The regular print is frol1l the Reclified Lunar . It/as, edited by G. P. Kuiper.
Lunar . Ii/as. In spite of the high degree of Figure 6b is a highly blO\I"Il up portion of enlargement and the screening dot pattern, i\[are Vaporum displaying the screening dot many subtle features were uncovered. pattern used to print the picture. ]n spite of Three of the major lunar lineament systems this granular texture it is still possible to de can be seen in Figure 4. The Ii neamen ts of the tect two major lineament systems on the northeast and northwest systems are numer mare which are not related to the grid pattern ous on the left hand portion of the photograph of dots. This is a particularly good example of but are short and broken up. The north-south an instance where the subtle features would lineaments, on the other hand, are relatively have remained undiscovered without photo few in number, fairly long, and intact. The en hancemen t. most pronounced one dissects a largc domed structure in the upper right hand corner. VARIATJOKS Several other north-south lineamcnts are The great potcn tial of photo-enhancemen t located near the northern rim of the large, film sandwiches lies in its extensive Aexibility. mare-Aooded crater to the far right. One of Many controllablc variables exist which can the most widely accepted explanations [or be altercd to control enhancement in thc final these particular lineaments is that they are print. Figurcs Sb and 6b demonstratc this great fault systems resulting from planctary principle for both werc derived from the same wide stresses that acted on thc Moon in the ncgati\'e with only the cxposures used in mak past. ing the positivc transparencies different. The Figures 5b and 6b also display lincament sharp change in character between the two systems. In Figure Sb the Hyginus and Ari prints can bc attributed to the high contrast adeus rilles appear as long gougcs on the left of thc film being used. hand sidc o[ the print. Thc light crater rays Varying thc contrast of the film will also that extcnd across the marc differ in tcxture alter thc final print. In the step-by-step pro from the fine darker lineaments. The polyg cedure just given, it was rccommended that onal nature of the Haemus mountains is also Dektol or another paper de\'eloper be used emphasized, suggesting block faulting. The because this sligh tly lowers the extremely most noticeable enhancemcnt, howevcr, is high contrast of Kodalith film and allows that of the darkest areas o[ marc material; more rea tures to be cn ha nced. The lower con these areas are now quite distinctivc and may trast, howcver, has the undesired effect of even be classified as prominent. softening thc boundaries of the enhanced PHOTO ENIIANCI<:M" '1' BY FILM S.\ND\\'ICHES 473
A B FIG. 6. Regular (A) and enhauced (B) priuls of a closer view of :\Iare \·ap0rllll1. Both Figures 5 and 6 were made from the same 35-mm. negalive hut the cxposures werc varied. \Torth is to the right. featurcs. If more contrast is dcsircd, thcn of the ol'iginal tonal \'alues will be seen in the Kodali th .1 and B devclopcrs should be used. final print. For I("ss contrast, other films such as Kodak X egati\'e and posi ti\'c transparencies of Plus-X or Panatomic-X should be tric-d. different exposure may also be combined, Transparencies of differen t can trast may Using Kodalith film, an underexposed posi also be combined. A Panatomic-X positi\'e ti\'e may be combincd with a negati\'e ob may be combined with a Kodalith negatiye tai ned from a ligh tly overexposed posi tive to add detail to an otherwise simple print. (Figure 7), ~o offset of the films is necessary Another useful suggestion is to pri n t the nega because the outlines arc created by the shift tive transparency sligh tty darkcr than the ing of borders that accompanies a change in positive one. The denser negatiye will be more exposure on high contrast film, The maximum effective than the positive one and some hint shifting occurs \\'here the tonal change is most
UNDEREX POSED POSITIVE FILM ORIGINAL SANDWICH NEGATIVE \
OVEREXPOSED CONTACT POSITIVE NEGATIVE FJG. 7. Basic procedure for the creation of a sandwich in which difTerenl exposures are used. Final outline around feature is creatcd by shifl in borders that accompanies a changc in exposure. 474 PHOTOGRAMMETRIC ENGINEER! G gradual on the negative, and so the borders of negati\'es and positives might be mixed and sharp features of high con trast show Ii ttle then combined to enhance color differences. displacemen t. Therefore, the thickness of any The careful selection of particular combina outline on the final print is a measure of the tions of fil ters, con trast, and exposures migh t contrast of that feature. Subtle, low-contrast even lead to the developmen t of an ore detec features will have the thickest and most no tion tech niq ue involving the color charac ticeable outlines. teristics of specific ores. One variable which will not be discussed It is recommended that the reader attempt in detail here, but which is ne\'ertheless quite at least a few deviations from the prescribed promising, is color. By adding color to the step-by-step procedure offered, in order to variables of contrast and exposure, a number appreciate more fully the flexibility and of new enhancement types could be devised. variety of this technique. Quite often, even a For example, by printing a color negative on slight change alters the print and emphasizes panchromatic Kodalith film with the aid of different details. To enhance a specific type filters, an entit'e spectrum of offset film sand of detail often requires only a little experimen wiches could be created. Furthermore. these tation.
PHOTOGRAMMETRIC ENGINEERING Staff EDITOR G. C. Tewinkel* ASSOCIATE EDITOR Robert C. Eller NEWSLETTER EDITOR William D. Lynn COVER EDITOR James R. Shepard ENGIKEERIKG REPORTS EDITOR Lawrence W. Fritz REVIEW BOARD l\alervo N. llIaki, Chairman Leon J. KosofsllY Bernard H. Colner ADVERTISING i\'IA:\'AGER AIrs. Barbara N. JlJuirt * 11612 Michale Ct., Silver Spring, Md. 20904. Tel. (301) 496-8140. t 2618 Spencer Road, Chevy Cha.e, Md. 20015. Tel. (301) 587-6107.
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