Full text: XVIIIth Congress (Part B2)

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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 
  
 
	        
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