QUANTITATIVE PHOTOGRAPHY—A GEOLOGIC RESEARCH TOOL
F1G. 9. Part of a conventional aerial photograph
showing several rock types and surficial materials
of contrasting colors.
COLORIMETRY
A potential value of color aerial photo-
graphs in geologic research lies in the use of
color transparencies as an intermediate prod-
uct in providing black-and-white photo-
graphs from which data may be collected
readily. Color aerial photographs are little
used because adequate viewing and plotting
systems in which they can be accommodated
do not exist. However, color photographs can
be used to provide black-and-white photo-
graphs that can be accommodated in existing
instruments. An expensive alternative is to
devise instruments primarily for color aerial
photography.
As an intermediate product in obtaining
geologic data the color aerial photograph can
be scanned with a colorimeter to provide in-
formation that would permit selection of
film-filter combinations which in turn would
emphasize specific terrain features. That is,
the color photograph would be re-photograph-
ed through selected filters and on selected film
in order to emphasize certain features. Fig-
ures 9 and 10 contrast the appearance of dif-
ferent geologic formations on a conventional
aerial photograph and on a photograph of an
FrG. 10. Part of an ecktachrome transparency
photographed through a No. 47 Wratten filter
showing same area as Figure 9. Tonal contrasts
between different rock types or surficial materials
may be accentuated, as at 4.
ektachrome transparency re-photographed
through a No. 47 Wratten filter on panchro-
matic film. Note the increased tonal contrast
at locality 4, for example, in Figure 10. Fil-
ter selection in re-photographing the color
transparency was based on spectral trans-
mission measurements made on a McBeth-
Ansco Model 12A densitometer.
If the requirement for differentiating sev-
eral terrain features exists, then multiple
black-and-white photographs of a color trans-
parency could be obtained using different
film-filter combination. Photographing an
area with different photographic systems
thus is reduced to a laboratory procedure,
once the initial color photography has been
accomplished.
The common products of black-and-white
photographs would be obtained by using
color photographs as an intermediate step in
making paper prints, Kelsh diapositives and
other plates, and in addition a powerful
photo interpretation research tool would be
gained. It may besuggested that color photog-
raphy should be taken instead of much of the
current black-and-white photography. Alti-
tude restrictions in successful color aerial
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