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From this study, certain facts emerge:
(1) Whereas conventional TV has an optical viewing distance of 7H (H =
screen height), a 940 interlaced system allows a viewing distance of
4H.
(2) If the scanning is non interlaced, 965 lines will support a viewing
distance of only 2.5H.
(3) A field frequency of 45 Hz is sufficient to give smoothness up to
the highest tracking speed of the human visual system, 20?/s.
The HDTV system is said to have a subjective quality comparable to that
of a 35 mm slide and superior to that of a 35 mm motion picture film; and
can also transfer an 8''x11" page of 10.5 point characters (2.6 mm x 2.6 mm).
This system is clearly more desirable than standard TV to replace the optics
on conventional stereo photogrammetric instruments. Meanwhile, standard TV
can be improved upon by using frame memories and a noninterlaced display of
1000 lines, Weber, 1985. A TV based image transfer system is more than a
substitute for an optical transfer system; it opens wide possibilities.
This concept allows portable instrument design of unconstrained physical
geometry, Real, 1979, capable of capturing and processing dynamic 3-D scenes
for in-situ, filmless analysis, measurement, manipulation, storage and
control.
3.1 Conversion; Video Memory
Flash video analog to digital converters to 13 bits resolution (and to
200 MHz for 8 bits) and low cost, high speed megapixel dynamic random access
frame memories are essential components in electronic imaging systems. When
preserving image fidelity is paramount, as it is in visual communications
(which includes photogrammetric instruments used by a human operator), there
are arguments for digitizing the photometric information to more than 8
bits, Frost, 1977, and having 12 bit wide video memory to permit digital
integration of low level data, Mengers, 1978. Since the least significant
bit of A/D conversion can almost be regarded as a noise bit, even 8 bit-wide
image data should be derived from 9 bit conversion.
The impact that electronic imaging and processing components have on the
inherent accuracy of a digitized image is important. Because studies on
this matter are incomplete, solid state camera calibration and error sources
in the digital image are subjects of concern at NRC, Havelock, 1984.
3.2 Image Display
There is no solid state substitute now for the electron beam CRT for high
resolution image display. State of the art in military solid state display
development is 10" 512x660 pixel black and white, 4" 320x240 color, Naegel,
1986. The analog nature of electron beam addressing in the CRT display may
compromise displayed metric fidelity. However, as is known from a history
of measurement experience on analytical plotters, some geometric distortion
is acceptable in the stereo viewing system provided the measuring marks are
properly positioned with respect to the images seen by the human operator.
It is known from experiments at NRC that once the marks are properly
aligned, relatively accurate measurement is possible, even from stereo TV
images which look significantly inferior to their optical counterpart.
CRT monochrome displays exist to 4000x4000 pixels and color to 2000x2000
pixels, Michaels, 1986. However, this latter device (Sony) is expensive
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