control. A further development is possible for motorised
camera and lens movement to change pixel size. In two
important respects, however, the DSW300 departs from
the DSW200: the appearance is modernized (Figure 1)
and the time to produce the units will be reduced.
Figure 1. DSW300 Digital Scanning Workstation
Specifications for the DSW300 are similar to the
DSW200. Stage size and travel are optimized for 23 cm
(9 inch) film but will allow smaller formats as well. With
the film transport option, the DSW300 can use rolls up
to 152 m (500 feet) long by supporting a reel diameter of
-up to 194 mm (7 5/8 inches). The transport has a set of
motorized operator controls for frame search, much as a
light table would. The operator uses the controls to load,
search through and rewind the film. After positioning
the roll to the first frame to be scanned, the operator
moves to the host computer console, a Sun Ultra 1
Creator Model 170E, to set up the scanning process. This
involves identifying the aerial film camera and interior
orientation choices, the tonal preferences and finally the
number and type of images desired. Multiple images
with no operator intervention are allowed in the case of
roll film scanning. Fully automatic interior orientation
makes this possible once the camera has been
characterized, which takes place once and can be used
for both single sheets and roll film. The benefits of
automatic interior orientation are really seen with roll
film: efficient data capture and significantly less operator
intervention. Once a new frame is in the stage window,
the program's ability to measure the fiducials allows the
film area to be exactly known on the stage. By also
allowing software to control the roll film advance, the
scanner can automatically drive to the next frame,
measure fiducials and scan the precise, predefined
footprint on the film. Theoretically, successive frames
can then be captured unattended for up to the entire roll.
Density range may vary from frame to frame, and that
range is typically larger for original negatives as opposed
to the copied diapositives made for analytical plotters.
The 10-bit CCDs perform well in capturing this larger
range but unfortunately there is not a well understood
method of compressing the 10-bit range into the standard
8-bit image format that works satisfactorily for all image
types. Simple log or gamma processing to compress the
range to 8 bits is often unacceptable since tonally flat
images result. Therefore there is a need for research into
more complex tonal adaptive methods that can be set up
either by the operator based on visual inspection or
automatically by the scanner using prescan statistical
methods. Although the latter may not be as visually
optimal as an expert operator on a per frame basis, they
may provide greater consistency and reduce the costly
scanning errors of too bright or too dark regions. The
goal in an automated roll film set up is to increase the
number of frames that can be automatically collected.
Finally, the last and perhaps most difficult issue in
scanning raw film is to correct for vignetting and hot
spots, traditionally the province of film dodging, This
has an even less known set of procedures, since a
desirable result may not always be precisely described.
Our current approach is to normalize the image to a
more or less uniform and acceptable contrast, a task
which can be accomplished automatically after scanning,
This more aesthetic processing is one job that may best
be handled by the operator on an "as needed" basis. But
perhaps the next generation scanners will be able to
make aesthetic judgements too!
3.0 WORKSTATIONS
The evolution of the Digital Photogrammetric
Workstations has been no less active and the account
begins with a chronology of the development of the
DPW770 and its SOCET SET software (Table 2).
SOCET SET is based on software developed for custom
workstations developed for the Defense Mapping Agency
with expertise from Dr Uki Helava and has been offered
as a commercial product for about seven years.
Host Graphics sub- Dates
systems for stereo
80386/80486 PC Parallax VIPER 1989-93
Sun 4/670, 4/470 VITec-30, 1990-92
VITec-50,
Sun VX
Peritek 1993-94
Sun SPARCstation 2 | VITec-30, 1991-93
VITec-50
Sun SPARCstation VITec-30, 1992-94
10 VITec-50,
Du Pont/3Dlabs
Pixel PX15
Sun SPARCstation 3Dlabs Pixel PX15, 1994-
20 Sun ZX
HP 9000 family VITec-30, 1994-
VITec-50
SGI Indigo? SGI XL 24-bit, 1994-
SGI High Impact,
SGI Solid Impact
Sun SPARCstation 5 | Sun ZX 1995-
Sun Ultra 1 Sun Creator 3D 1996-
SGI Indy SGI Indy 24-bit 1996-
Table 2. Evolution of DPW770
International Archives of Photogrammetry and Remote Sensing. Vol. XXXI, Part B2. Vienna 1996
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