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DSW 100 when the strategic alliance between Leica and
Helava began, improved its performance and reached its
peak in the early 1990s, after being ported to an 80486
PC. At that time PCs were becoming capable of large
image processing with their new virtual memory
hardware and operating systems. Unix workstations were
maturing as desktop power stations. The DSW 100
would ultimately produce 20 minute image scans at 25
um, but it no longer rectified the image, an operation the
photogrammetric workstations could now handle, and
image processing by the scanner was considered best
kept to a minimum. Image quality also became an issue
as the scanner output was increasingly being compared
to the original diapositive. About 30 units were sold
altogether, some of which were fitted with a housing
containing a software controlled colour filter wheel,
mounted in place of the familiar integrating sphere, and
a lively second user market continues.
2.2 DSW200
Soon it became clear that another increase in scanner
performance was needed to meet customer demand. The
introduction of the DSW200, based on Sun
SPARCstation 20 (Dam, 1994), at the end of 1994
increased scanner speed enormously over its predecessor
to provide high resolution, high quality scans with
resolutions in the 10-15 pm range in under 10 minutes,
using digital CCD technology. The DSW200 hardware
design was based on xenon light source (combined with
the colour filter wheel in a box removed from the xy
stage), liquid pipe optic, integrating sphere, single high
quality lens and Kodak MEGAPLUS 4.2 CCD camera
(later 4.2i). The software, too, increased significantly in
sophistication, with automated calibration and many
functions for optimising the radiometric parameters with
the help of the 24-bit Sun SX graphics. NITF JPEG
image compression was introduced in software and
became attractively fast when the Sun Ultra was
introduced as the host in the spring of 1996. Top
performance was now expected by customers. The
scanners became like the aerial cameras they augmented,
able to produce enough data to keep many digital
mapping workstations busy: customers could buy more
workstations without buying another scanner. Sales were
buoyant, with over 50 units sold.
This continuing scanner evolution depends
fundamentally on sensor technology. The sensor devices
have improved substantially in both cost and
performance in the last four years. Linear CCD arrays,
used in most desktop scanners, have tripled or
quadrupled in size (from 2k to 6k and 8k), quadrupled in
sensitivity (from 8-bit to 10-bit) and tripled in modality
(from monochromatic to trichromatic). Equally
impressive, the popular CCD area arrays in the industrial
measurement sector have increased in size (from 1k x 1k
to 1k x 1.5k), sensitivity (from 8-bit to 10-bit), modality
(from monochromatic to overlayed tricolor filter arrays)
and speed (from 10 frames/sec to 30 frames/sec). Large
area staring arrays, like those used in the DSW200, have
also grown in size (from 2k x 2k to 2k x 3k or more),
improved in accuracy (from .05 to .03 pixel) and yielded
to increasing electronic integration, resulting in more
robust camera packages that are half the size. Future
models of the DSW are being planned with the 2k x 3k
array and the newest 4k x 4k array camera from Kodak.
Large area arrays will one day dominate the scanning
market owing to their inherent efficiency and accuracy.
67
Shifts in computer technology have been critical too.
Scanners have established themselves in the mass market
place owing to increases in affordable disk storage, faster
computers, better software and public demand for digital
multimedia. Numerous models from dozens of vendors
are available. In photogrammetry, this digital revolution
has resulted in less expensive high resolution (10-30 pm)
film scanning for the aerial mapping market. The result
for the DSW200 was a wide range of developments by
Sun, for example dramatic increases in speed and hard
disk capacity. By the end of 1994, DSW200s were
typically supplied with 3 GB hard disk capacity and
offered black and white scanning of an aerial photograph
at 12.5 um in around 7 minutes. A year later, the
corresponding figures were 5-10 GB and 5 minutes.
Configurations with 60 GB RAID arrays were also
shipped, enabling many photographs to be stored
simultaneously with fast random access, though the
option of software compression is useful. These
capabilities are also factors in the success of digital
triangulation. Proliferation of models in the industry is a
sign of success and acceptance. The Sun Ultra 1 Creator
Model 170E selected for the DSW200 provides more
processor power, high performance 24-bit graphics, fast
and wide SCSI-2 hard disks and fast Ethernet (100-
BaseT) communications, ideal for correct set up and fast
storage and transfer of the rapidly acquired images.
2.3 DSW300
The real goal is not software and hardware per se, but
greater productivity. The customer wishes to install a
new scanner without adding a new employee and yet still
increase output. Automation is the key rather than speed:
faster scanning, which was a major productivity issue
two years ago, will still be improved, settling at perhaps
three minutes for a 12.5 um scan, but no longer
dominates. Simpler operation, quick set up, unattended
scanning and better quality control will share the
spotlight. Thus manufacturers are adding sheet and roll
film transports to automate the film loading process.
Helava will begin shipping the DSW300, a roll film
scanner model, in the fourth quarter of 1996. The
software to utilise this advanced hardware must be
increasingly powerful and support several fully
automatic functions that in the past were generally
interactive: frame search, measurement of fiducial
marks, tonal pre-scanning and data storage management.
In addition, new, sophisticated software for dodging is
required. The benefits of these developments, of course,
accrue to users of both roll film and single sheet film.
Similarly, the automated set up for roll film can be used
to achieve the simple, quick set up desired for scanning a
single diapositive.
The new DSW300 preserves as much of the DSW200
engineering design as possible. The main innovation is
the option of roll film scanning. The lighting, optics and
camera are kept stationary, like the DSW200, while the
film and transport move with the xy stage. The xenon
light source, integrating sphere, simple optical system
and Kodak camera are retained. Since it is imperative to
keep the camera to film distance constant with stage
travel, a stronger stage is needed to support the added
weight of a roll film transport and film media. To sense
and control the film roll position automatically, encoders
and motors have been added to the spooling mechanism,
requiring new electronics capable of four-axis control
since the DSW200 controller is limited to two-axis
International Archives of Photogrammetry and Remote Sensing. Vol. XXXI, Part B2. Vienna 1996