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Transactions of the Symposium on Photo Interpretation

1. The colour film could reveal more detail and more definite interpretation criteria than
black und white.
2. This increase in interpretive ability was however frequently only slightly better than black
and white film and was either not needed in the majority of studies proceeding at that time,
or was offset by the difficulty in obtaining good colour photography and the high cost of
colour photography.
3. That the cost of processing colour film, particularly if prints were desired, was very high -
and precluded the use of colour film exept in those instances where the criteria of colour
was the only identification method that could be used.
4. That the use of colour transparencies was relatively inconvenient compared with paper
black and white prints - particularly if field work was envisaged.
With these conclusions the interest in colour photography waned, and on a commercial scale,
little aerial colour photography was completed. Since that time the status of both photo
interpretation and colour film has changed, and perhaps it is time for a re-examination of the
use of colour film in interpretation procedures. We are now demanding a much greater
amount of photo interpretive detail from air photographs, in a much wider range of subject
matter than ever before. The essential purpose of the main body of present photo interpretation
seems to be the elimination of more and more fieldwork, while keeping the reliability and
type-accuracy high. Into this present day climate of photo interpretation comes a relatively
new instrument - the 70 mm aerial camera, and widely available 70 mm colour film. This
camera-film combination allows excellent quality photography to be obtained in a format
that is able to be stereoscopically examined with a hand stereoscope without cutting the film
roll — and, most important, is relatively inexpensive.
Perhaps it can best be used as a key to smaller scale black and white photography of the same
area. Certainly it has proved itself in this regard in initial attempts to use it in forest photo
interpretation. The 70 mm colour strip is inmediately at a larger scale (with the lens used)
and presents a greater tonal range than the black and white prints. The special tree identifica
tion, height and age and density of stand are immediately measurable with far greater accuracy
than on the conventional photography. It is almost as if a cruised strip were available at
regular intervals through the forested areas. It may be that use of this type of photography
will limit that amount of subsequent ground research necessary to produce present forest
inventory maps prepared by photo interpretation of black and white photographs. Further
it may add to the data which can be obtained from the air photographs. The colour may
allow a preventage estimate of disease of trees if such disease shows as a change in foliage
colour. The addition of colour film strip may also allow easy preventive recognition of subtle
changes in tree species composition which can then be traced outwards on the black and
white photography - but which would possibly have been overlooked if black and white
photography had been used alone. Applications of this sampling technique may well be
thought of in other fields. Those of land use with crop identification, and detailed soil analysis
may lend themselves most readily to examination.
With regard to large (9" X 9”) format it can be said, that colour photography remains expen
sive, though the remarks emphasizing the present day demands of photo interpretation
definitely apply. Survey problems certainly exist where continuous colour coverage is needed,
and where the criteria of colour is the only possible way to isolate the data required (certain
underwater studies). In these cases the expense of colour photography in large format is no
longer a factor of choice. It is however considered that the smaller scale techniques can be
applied most economically to present photo interpretation and may yield measurable reduc
tion in field work checking procedures, and/or additional photo interpretative detail.
Certainly further use and examination of these colour techniques is indicated.