because of its 100 pixel/inch pitch and 300 MHz video bandwidth to support a 
60 Hz noninterlaced display. The 1024x1024 pixel color display however is 
now a mature technology, because of the demand for color graphics in 
computer engineering design and other applications. The human eye is 
sensitive to relatively few shades of grey (50 as a round figure), 
but thousands of colors, therefore a color display has the potential 
of conveying more information more clearly. Complete color electronic image 
transfer systems are not cost effective unless preserving original color in 
a scene is essential, because the system bandwidth is increased threefold 
(i.e., 24 bits per pixel for photometric information as opposed to 8). On 
the other hand, color display of black and white imagery by tinting, false 
color emphasis of otherwise obscure detail and highly contrasting 
graphics/text overlays can convey information to the human in a much more 
appealing manner than otherwise. The stationary dot structure of color CRT 
screens however imposes limits to sub pixel image positioning which may 
require additional neighborhood processing to simulate, Mord, 1985. Color 
stereo display is more bulky because commercially available high resolution 
monitors have a 13 inch (diagonal) lower bound to screen size, resulting in 
larger viewing optics than would be the case for the miniature CRT used in 
fighter aircraft displays. 
3.3 Mass Storage 
Digital storage of image data bases is an overwhelming issue in photo- 
grammetry. With a gigabyte of information resident in each aerial photo- 
graph, the photographic data base is not about to be converted to digital 
archives. Nor are large format aerial cameras about to be replaced by 
arrays of solid state imagers, although this is technically possible and 
solid state imagers are performing complementary functions within aerial 
cameras. As digital technology beomes faster and cheaper, electron and 
chemical based image systems will coexist for a lengthy period with the 
electronic component increasing. 
Digital imaging in photogrammetry is of three classes: 
(1) Images already in digital form, as from spacecraft and satellites. 
(2) Images in close-range applications which are digitized, processed, 
and analysed, then discarded after some process decision is made and 
control executed. 
(3) Images digitized from photo archives for processing. These will 
form an input, along with other information, to create new data and 
images for a variety of purposes: 
(3.1) Generate reduced digital data for use with other data in 
computer banks, 
(3.2) For new computer processed optical images, 
(3.3) All or parts, in combination with other data, stored 
digitally as retrievable images. This application is of 
immediate interest in this paper. 
An example of digital archiving of an existing photo base has been the 
storing of existing x-rays onto digital optical disk of medical records. A 
small scale close-range application requiring the storage of image data 
digitally is given by Real, 1984a. Storing significant portions of aerial 
photography in digital form requires state of the art (and beyond) multi 
gigabyte memory systems. For the last two decades optical storage in one 
form or another (volume holograms, laser disks) has been on the verge of a 
breakthrough. It finally seems to be happening with the design of a 
suitable optical disk, Laub, 1985 and magneto-optic storage, Ohr, 1985. 
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