98 PHOTO INTERPRETATION PICTURE, COLWELL
Figure 4. Consistent with the predictions, these tonal values are indeed obtained, as
indicated by the illustrations at the bottom of the figure, thereby permitting the four
surfaces to be differentiated from each other through simultaneous interpretation of the
two types of photography. Had a fifth surface been involved, an extension of this con-
cept, perhaps to the point of including a third film-filter combination, might have been
required. Eventually, so many film-filter combinations might be required that the main
problem of the photo interpreter would then be that of integrating what he sees for a
given surface or area on each of the many types of photographs with which he is con-
fronted. At this point the possibility of integrating two or more images into a single
composite color image should not be overlooked. In this regard it was thought until
recently that, to obtain a full color image, at least three black-and-white photos would
be required, each of which had been taken through the proper filter and later reconsti-
tuted through the proper filter to help compose the full-color image. However, Land
(1959ab) has recently demonstrated to the surprise of many that full color rendition can
be obtained from only two black-and-white photographs, properly combined. This capability
would seem to show great promise for those photo interpreters wishing to exploit the
concept of multiband spectral reconnaissance to the fullest. (See also Fig. 5).
8. Valuable means for enhancing the quality of photographic images have recently been
developed.
The previous section has discussed means for obtaining the most suitable tonal values
on photographic negatives through the proper choice of film and filter. Even the best of
aerial photographic negatives, however, often make unsatisfactory photographic prints
for use in making detailed interpretations.
At the time of our World Congress eight years ago, virtually all printing from aerial
negatives was done by direct contact printing, and the means of “dodging”, to improve
tonal values in the prints, were limited to flicking a few switches to turn on or off
certain of the light bulbs inside the printing box. Among the significant process that
have since been developed for enhancing the quality of photographic images at the time
of printing are the LogEtronics process (Craig, 1956) and the Fluoro-Dodge Process
(Watson, 1958). An example of the possibilities for image enhancement using the Log-
Etronics process is provided in Figure 6. This process has very recently been adapted
to permit electronic dodging to be employed even in the printing of aerial color photo-
graphy. At the time of this writing means are being developed for using electronic
image-enhancement techniques to accentuate photographic patterns, magnify photo-
graphic texture differences, and emphasize various other photo image characteristics
which, in a given situation, may constitute the subtle photo recognition features for
certain objects or conditions.
In conjunction with the above developmental work, means are being perfected for
enabling the photo interpreter to view photographic transparencies by transmitted light,
rather than opaque prints by reflected light, thereby permitting still greater enhancement
of the image.
9. There is an increased interest in the use of very low altitude, large scale photography
for making detailed interpretations.
Avery (1958) has found that vertical stereo-photography of timber volume plots,
taken from altitudes of 200 to 300 feet with a helicopter, is excellent for determining
average total tree heights and average tree crown diameters. The Japanese Ministry of
Agriculture and Forestry (1953) has obtained some excellent low altitude oblique photo-
graphy of coniferous plantations. Because of the very high density of trees in these
plantations (Fig. 7), such factors as heaviness of cone production, rate of height growth,
evidence of insect attack, and other features requiring study of the tops of the trees can
