image and the existing maps. During this operation the congruent bundles of rays 
are projected in the form of a mixed image of greenish yellow color onto the map 
tracing table. Filter spectacles are not needed, generally, for map revision ef 
forts. For contour plotting a special plotting table is provided and viewing is done 
with conventional red and green filter spectacles. Illumination consists of two 
lamps and Fresnel condenser with anaglyphic filters mounted between the lenses. 
CBS LABORATORIES. 
The CBS Laboratories, Stamford, Connecticut, USA, has produced several 
items of interest in photogrammetry during the period 1964-68, including a 
’’Superimposition Viewer” and a "Double Image Enhancement Viewer. 
a. Superimposition Viewer. A unique and versatile device utilizes electro- 
optical techniques to satisfy three major photogrammetric services: change de 
tection, screening, and super imposition. This device will electronically rectify 
any two of several photographic, radar, or infrared formats and superimpose them 
on a third format to facilitate change detection, map revision, and image inter 
pretation. Its characteristics are: 
(1) The film inputs may be either positives or negatives of variable 
widths. Images are displayed on a cathode ray tube monitor with a high resolu 
tion. Electronic reversal is possible to change from positive to negative or from 
negative to positive. Magnification, either optical or electronic, is possible 
through a large range. Rotation of the image of 180° is possible, as well. 
(2) Electronic image correction for tilts, cylindrical distortion, and 
warpage is possible. Optical image correction is used for differential scale changes. 
(3) A common joystick is used for X-Y positioning. 
(4) Changes in planimetric detail are detected by use of a variable 
rate of flicker (from one to 12 times per second) for each image being presented 
on the screen. 
(5) Optional capabilities include remote display, image enhancement, 
and display of remote compatible inputs. 
b. Double Image Enhancement Viewer. This device provides real time, 
electronically sc an-gene rated color enhancement of pairs of aerial photographic 
negatives. Its characteristics are: 
(1) A near ultraviolet high resolution microspot scanner (using 
suitable split optics) provides the necessary scanning capability. Differences in 
image intensity are extracted by an enhancer electronic processor (driven by 
photomultipliers); the extracted data are written onto another flying spot scanner 
(having an orange overlay output) after which the data are imaged back onto the 
film plane by the same optics. 
(2) A special zoom stereomicroscope is used to view directly the