The Diachromoscope*
An Instrument for Increasing Contrast between
a Colored Object and a Different-Colored
Background on Color Photographst
PART III. INSTRUMENTAL AIDS IN PHOTO-INTERPRETATIONt
HUGH T. O'NEILL[[
and
WILLIAM
J.
NAGEL§
ABSTRACT: The diachromoscope is an instrument designed to increase
the visibility of a colored object in a background of a different color as
registered in any form of color photography. This is a accomplished by
using, instead of white light, colored light either passing through colored
transparent photographs or reflected from colored, opaque, photographic
prints. A n alternative is the combined use of both transmitted and reflected colored lights on color transparencies or on relatively thin color
prints. The diachromoscope provides for using the various available
common sources of colored light without or in conjunction with color
filters commonly obtainable, as well as with a number of newly invented
types of color filters.
"diachromoscope" is an instrument designed to increase the visibility of an object whose color (more precisely, whose hue) is appreciably or practically different from the hue of its background on color photographs, by the expedient of viewing the latter in colored
light instead of in white light. The name
"diachromoscope" which is suggested for
this instrument is newly coined.
An example of the use of this instrument
is the detection of a minute red object on a
green background on a color-transparency.
When such a transparency is viewed
over a source of white light, the ratio of the
intensity of the light transmitted by the
T
HE
red object (e.g. a leaf turned red by an infection to that of the light transmitted by
the green background (e.g. foliage in the
summer condition) is roughly 1 :1, varying to 2:1.
This ratio can be increased several to
many times (even 100 to 1 in some cases)
when such a transparency is viewed over a
neon-filled Geissler tube. This increases correspondingly the visiblity of the red object.
This increase in contrast and in visibility
is not due to increase in color (hue) contrast. It's cause is a great increase in the
intensity (brightness) of the light transmitted by the red object, and an even
* From the Greek Ola (dia) through; SKontv (skopein) to view and xpo/la (chroma) color. Note
that chromatoscope is used as a name for a reflecting and revolving telescope by which the observer
views a star as a ring of light instead of a mere point, and chromoscope is "a viewing-device for
obtaining superposed images of color separation positives. 2. A type of colorimeter using colors
produced by the rotary dispersion of quartz as standards." As defined by the Society of Motion
Picture Engineers, "Comparative list of color terms," Rep. Inter-Society Color Council, Jan. 1949,
page 13.
t Invented as part of a Research-contract for Wright Air Development Center.
t The first two papers of this series were published in PHOTOGRAMMETRIC ENGINEERING,
XVIII (1): 134-139, and (5): 699-701. 1952.
II Box 262A Annapolis, Md.
§ Of the Ansco Division of the General Ani,line and Film Corporation.
180
THE DIACHROMOSCOPE
greater decrease in the intensity of the
light transmitted by the green background.
By this means a red object so small as
to be invisible over ordinary light when
viewed over a neon light, may be made
visible even when the red object is so small
that the eye cannot recognize its hue. Such
a very small object appears as a mere dot
or point of light in the dark background.
There is obvious need for an instrument
that will enable the photo interpreter to
view color-transparencies of any size up
to 9"X9", over and/or under any convenient source of light of any color. For
this reason the "diachromoscope" was
constructed (Figure 1) and contains the
following features:
A) A viewing screen, inserted in the
table top, of a size su fficien t to accommodate a stereoscopic pair of any
size, not larger than the commonly
used 9"X9" photograph or colortransparency.
B) Three interchangeable drawers for
attaching three different types of illumination; viz,
Geissler Tubes, in the lower left
drawer eq~ipped only with two
handles (Figure 1) and shown in detail on Figure 2.
Fluorescent Tubular Lamps, in
the upper drawer equipped with two
handles and 10 toggle switches (Figure 1) and shown in detail on Figure
3.
181
Tungsten
Filament
Tubular
Lamps, in the right hand drawer
directly under the viewing screen,
equipped with 2 handles, 12 toggle
switches and 12 rheostat-knobs (Figure 1).
C) Space for colored filters between the
viewing screen and the clear, plastic
shield above the tubes or lamps in
any of the three drawers as shown
in Figure 2.
. D) No special provision seems necessary
for sources of reflected colored illumination, since any of several
types of mountings for holding
colored bulbs or tubes qn be readily
adapted.
A list of parts and materials used in making this "diachromoscope" is given at the
end of this paper to assist anyone desiring
to make the apparatus.
Use of the "Diachromoscope" in Deciding
Which Color-Film is Best for Any Special
or Particular Purpose. Briefly, to obtain
the best results in the photo-interpretation
of color photographs for any particular
purpose, reliance should not be placed
upon the color film alone. Instead, this
film should be used in conjunction with
various sources of colored light and/or
color-filters. The "diachromoscope" permits, in a convenient way, estimating the
value of any color-film with such auxiliaires.
FIG. 1. The diachromoscope, front view.
182
PHOTOGRAMMETRIC ENGINEERING
FIG.
2. The interchangeabJe drawer with the neon tubular light, ready to slide in place beneath the viewing screen.
The Advantage of the Joint Use of Colored
Light and Colored Fitters in the Study of
Color Photography. Obviously, this joint
use enables the photo-interpreter to obtain conveniently a very considerable
variety of colored light not easily obtainable by the use of either lights or filters
alone. Further if the photo-interpreter has
spectrophotometric curves of both the object sought and its background* by superposing these curves, he can see in what
* As registered on the color film.
part of the spectrum, the two curves differ most. He can then choose the source of
light and the color filter whose spectrophotometric curves correspond most closely to this part of the spectrum.
The common disadvantage of the joint
use of colored lights and colored filters is
either that the available filters are too
densely colored, or the sources of light are
too weak, to send enough light through the
ordinary color transparency. Hence a
means of regulating the intensity of the
colored light is necessary.
FIG. 3. The interchangeable drawer showing the wiring of the 19 fluorescent tubular lamps.
THE DlACHROMOSCOPE
Thus, for a snow scene, a very small
amount of light is needed for best viewing.
On the other hand, for a photograph of a
spruce forest, a very intense illumination
is required. The "diachromoscope" offers
the following means of regulating the intensity of colored light:
By changing the intensity of the source
of colored light.
By varying the intensity of the source
of white light used with color-filters.
This needs no further explanation.
By using filters appropriate for use with
the sources of light provided by the
"diachromoscope," especially the variable color filters used with either
white or with colored light.
In the case of colored fluorescent lights,
the intensity can be varied by the number
of tubes switched on, i.e. any number from
1 to 19.
Likewise, in the case of the colored tungsten lights, the intensity can be varied by
the number of tubes switched on, i.e. any
number from 1 to 12. In addition, since
each of the tungsten lights has its own
rheostat, this additional means of varying
intensity is available. But the rheostat control alters the hue so that as the intensity
diminishes, tbe hue changes from yellowish
to finally a dull red glow.
The Geissler or the familiar Neon-lighttubes are of non-varying intensity in this
"diachromoscope." But in spite of this disadvantage, these lights yield very intense
colored light in some relatively narrow
areas of the visible spectru m, not obtainable by ordinary sources of light and color
filters.
It seems unnecessary to mention that a
considerable variety of colored phosphorescent and tungsten filament lamps are
readily obtainable. It should however be
mentioned that many more colors could be
readily made in the case of both types of
lamps.
Grateful acknowledgement is hereby
made to the General Electric Company for
the gift of twelve fluoresecnt tubes coated
with "green phosphor." These tubes are
extremely useful because they yield a
much more intense light than any other
lamp we have used. Further, these tubes
concentrate an intensity of light in the
green part of the spectrum, which is close
enough to the reflectance-spectrum of chlorophyll A and B in the living leaf, to have
183
a special value in the study of vegetation
on color photography.*
Filters Appropriate for Use with These
Sources of Light in the Diachromoscope. In
general, any colored transparent substance
obtainable in flat sheets, but especially
any commercially available filters can be
used provided the filter factor does not exceed four. In the case of many transparencies and most common sources of light, a
filter with a factor greater than two,
lowers the intensity of the light too much
for best results. Especially adapted for use
in the diachromoscope for covering the
entire viewing screen are the color printing
filters for use in making color positive
prints from color negatives. Thus, the set
of Ansco Color Printing Filters, made for
use in our viewing screen (cut to size 9!"
X 18!") is available in 7 degrees of density for each of three colors, viz, Cyan,
Magenta and Yellow; none of these
colors is too dense for transparencies of ordinary density. However the disadvantage
of all such ready-made filters is that their
density is fixed. Obviously, most useful in
this connection would be sources of light
whose intensity can be varied for joint use
with colored filters and where the intensity
of the filters can also be varied. Accordingly the authors contrived a number of
different types of liquid filters for this purpose.
Variable Colored Liquid Filters. Flat
cells of plastic or glass, filled with colored
liquids, can be placed either on top of the
viewing screen or underneath this screen,
in any of the three drawers. Such cells can
be placed on the clear plastic cover or
shield immediately above the tubular
lamps. The density of such colored solutions can be changed by varying the concentration of the liquids.
A much more convenient form of such a
variable colored filter is shown on Figure 4,
* The senior author has accumulated evidence that the reflectance-spectrum of nearly
all, if not all land vegetation, varies within narrow limits and is virtually constant for our purposes. He gratefully acknowledges the numerous
spectrophotogrammetric curves of green leaves
determined at the National Bureau of Standards, by Messrs. Harry Keegan and John
Schleter in a contract-research for Wright Air
Development Center. Certain marine algae living at considerable depths, contain chlorophyll
of a different structure and r:eflectance than
chlorophyll A and B, the only kinds present in
land vegetation so far as the author knows.
184
PHOTOGRAMMETRIC ENGINEERING
FIG. 4. (Top) showing the two double-wedgetype liquid filters on the left side of the viewing
screen, a third darker filter of the same type at
righ t angles to these, across the top of the
screen. A fourth wedge-filter is shown leaning
against the storage bottle of colored liquid.
(Middle) showing the liquid filter covering the
viewing screen and how the thickness of the
liquid is controlled by running in or drawing
off any desired volume of the colored liquid.
(Bottom) showing a stereo pair color transparencies in place on top of the cell which completely covers the viewing screen.
where the colored solution is held in a gallon bottle. Near the base of the bottle a
rubber tubing connection is made to the
side tube in a plastic cell that covers the
entire screen. By lowering or raising the
storage bottle, and the use of a common
pinch-cock on the rubber tubing, the depth
of the colored liquid in the plastic filtercell can be accurately controlled and read
on the calibration 111 millimeters on the
side of the plastic cell (shown in place on
top of the viewing screen. It is filled with
9 mm. of blue liquid, (Figure 4, middle
photograph) and has a pair of stereo transparencies on top of the filter cell (Figure
4, lowest photograph) illuminated by the
special high intensity green fluorescent
lights supplied by the General Electric Co.
Since the depth of the colored liquid can
be varied from 1 to 50 mm. and the intensity of the source light underneath also
varied over a wide range, this combination
offers a very wide range of intensity of
colored light of constant hue.
Mutually Variable Two-color Filters.
Certain problems of photo interpretation
could be solved by the joint simultaneous
use of two colored filters. Here again, the
use of commercially available filters is a
serious hindrance. Accordingly the authors
contrived a plastic cell with a diagonal partition which divides the cell into two wedgeshaped cells (Figure 4, top photograph)
thus affording every possible combination
of the two liquid filters. By moving this
filter across the transparency or vice versa,
the effect of every possible combination of
the two colors of light transmitted, can be
observed. Such a two-color, mutuallyvariable filter has further implications in
the study of the practical results of the
"tristimulus" color theory in that the two
cells can be filled with a "duet" of colored
liquids, thus obtaining all possible combinations, while the third of such a trio is
lacking. Further, by merely using one of
these cells, a wedge-shaped filter of only
one color, is obtained, varying from 0 to
any practical density. A large number of
colored substances, inorganic salts, dyes,
etc. yielding colored ions in solution can
be used in various solvents or suspensions
in making such liquid filters. Dr. F. W. H.
Miiller, Director of Research at "Ansco,"
kindly furnished us with twelve dyes for
use in making some of these solutions.
LIST OF PARTS AND MATERIAL USED
IN MAltING THE DIACHROMOSCOPE*
The construction and the frame of the
table is evident on the photdgraph and is
not described here. The three drawers,
each of which can be placed directly under
the viewing screen, were fitted as follows:
* The list was prepared by William]. Nagel.
THE DIACHROMOSCOPE
THE NEON LIGHT DRAWER
Neon grill to fit the bottom of the drawer
Acme Cold Cathode Fluorescent Lighting
Transformer. Pri. Volts 115; Sec. Volts
7,500. Secondary Midpoint grounded to
case. Volt. Amp. Capacity 450
1 Piece Plexiglass i" X Bi" X20 X ~"
8 Glass receptacles for neon grill
1 Plexiglass safety rod 20f' X t" diameter
2 Plexiglass safety guards for receptacles under floor of this drawer to prevent static
discharge to operator.
2 Cable connectors
High voltage wire for hook-up and from
transformer to receptacles
2 male Amphenol plugs 61 M
4 Ventilation guards
THE FLUORESCENT DRAWER
38 General Electric 95 X432 Lampholders
19 General Electric 95X299 Starter sockets
19 General Electric 89G435 Ballasts
19 General Electric F8 T5/cw Lamps
19 General Electric FS-5 Starters
19 S.P. ST. Switches (Heavy duty)
9 Ventilator guards
1 male Amphenol plug 61-M
1 piece of Plexiglass i" X 13i" X 20f'
THE TUNGSTEN LAMP DRA WER
24 General Electric 49 X698 Lumiline receptacles
24
12
12
12
4
1
1
185
General Electric 49 X805 Lumiline sockets
General Electric L 40/1 F Lumiline lamps
IRC 500 ohm 50 watt rheostats
S.P.S.T. switches
Ventilator guards
male Amphenol plug 61 M
piece of Plexiglass i" X 12i" X20~"
ELECTRIC EQUIPMENT FOR THE TABLE PROPER
1 TN 5321 Herbach and Rademan Blower
5 Amphenol receptacles 61 F
2 Pilot lights, one-inch, one red, the other
green
2 S.P.S.T. switches
16 feet of 18 gage rubber cord with 2, 20-amprec
fuses
HARDWARE
3 pair Grant Drawer-slides No. 306
3 pair 1til chrome drawer knobs
i-piece of chromium-plated pipe 56" X 1" outer
diameter (to serve as base bar)
2 pieces of chromium-plated pipe 29" X ~"
outer diameter (the standards or uprights)
piece of Flash opal glass 10" X 19"
WOOD FOR THE TABLE PROPER
1 piece of oak plywood i"X4 feetX8 feet
3 pieces solid oak 2" X 4" X 28"
8 sq. ft. ~" and til gum plywood.
A Study of the Private Photogrammetric
Mapping Activity in the United States*
C. L. MILLER,
Assistant Professor of Surveying,
Director, Photogrammetry Laboratory,
Department of Civil and Sanitary Engineering,
Massachusetts Institute of Technology
INTRODUCTION
mapping is an imP HOTOGRAMMETRIC
portant technical and professional activity in the United States. Although
many engineers are aware of the large
federal mapping agencies and their extensive use of photogrammetry, very little
information has been available on the extent of the private practice in this field.
This report presents the results of a
survey of the private firms engaged in
aerial photography and stereophotogram-
metric mapping. It is hoped that the
results of this study will increase respect
for photogrammetry and encourage even
greater use of its professional and technical
services.
THE SURVEY
During the early part of 1956, questionnaires were sent to approximately one
hundred firms throughout the United
States. Approximately one half of these
firms were excluded from the final study
because, although they were engaged in
* The material reported in this publication is from an unsponsored study conducted as a professional service, Publication 102, August 1956.-THE AUTHOR.