FURTHER DEVELOPMENTS IN HIGH PERFORMANCE SCANNING
Alex Dam?, Andrew Calarco and A. Stewart Walker? '
* Leica Geosystems GIS & Mapping, LLC, 10840 Thornmint Road, Suite 100
San Diego, CA 92127, USA
? Leica Geosystems GIS & Mapping, LLC, 61 Inverness Drive East, Suite 200
Englewood, CO 80112, USA
(alex.dam, andrew.calarco, stewart.walker)@gis.lerca-geosystems.com
Commission I, WG 1/2
KEY WORDS: Scanner, Scanning, Digital, Film, Photogrammetry, Workflow
ABSTRACT:
High performance scanning is a routine part of the digital photogrammetric production workflow. Modern scanners offer geometric
precision similar to analytical plotters and high quality CCD sensors capable of faithfully capturing the information in the aerial
photograph at 12 bits per channel to provide excellent dynamic range and tonal set-up. Modern practice is typically based on
scanning positive or negative roll films. One of the critical requirements of the best scanners is high optical resolution at very high
speed, motivated by the desire to complete roll-film scans overnight. Currently this can be done on the Leica DSW600 Digital
Scanning Workstation for black and white photography owing to its industry fastest scan times of 2 minutes per 23 x 23 cm frame.
No scanner can yet do this for a 500 foot colour roll. Recent improvements attempt to extend this performance on the DSW to
colour, while at the same time improving image quality and control. Leica Geosystems has undertaken a number of innovations
aimed at these goals, including: large format 12-bit sensor; novel LED illumination system, to increase amount and uniformity of
light, enlarge the illuminated area to maximize scanning speed, reduce cost and improve reliability; coatings on stage plate and cover
glass to eliminate Newton Rings; higher performance linear encoders to optimise geometric integrity; software refinements,
including ease-of-use features and JPEG2000. These advances are incorporated in a new model, the DSW700, but most are available
to users of existing scanners by means of a well defined upgrade program.
1 INTRODUCTION respond to customers’ increasing demands for scanning
performance, in terms of geometry, radiometry, speed and ease-
Scanning is an accepted, proven phase of the digital of-use. A summary of the various models introduced is given in
photogrammetric workflow. Since the late 1980s, Leica Table 1.
Geosystems and its predecessor companies have striven to
Model First CCD Bits | Pixel size Scanning times | Host Main innovations
shipment | (mega- range (um) | (minutes)
pixels) (b/w, color,
12.5 pm)
HAI-100/ | 1989 2%0.25 8 12.5, 25 60, 180 MicroVAX, | Scanned whole image, not patches;
DSW 100 Unix PC two sensors for different
resolutions
DSW200 | 1994 4.2 10 5-15 10, 30 Sun High speed via large format sensor
SPARC-
station
DSW300 | 1997 1.6, 4.2 10 4-20 5, 14 Sun Ultra Roll film
DSW500 1999 16,4 2.6.3 | 10 4-20 3,7 Sun Ultra, Xenon strobe illumination, PC host
PC
DSW600 2002 8.0 12 3-22 2.8 PG 12-bit sensor, easy pixel size
change
Table 1. Main features of Leica DSW scanners
included an innovative stroboscopic illumination source
under software control, a 6.3 megapixel sensor and a PC
host, all providing yet more performance. The DSW600
followed in 2002, the primary innovation being a high
performance 12-bit sensor. Throughout all this hardware
development, the software kept pace, moving through a
range of platforms and continuously adding functionality,
The 4.2 megapixel sensor in the DSW200 gave the DSW line
the market lead in speed, to which Leica Geosystems has
held ever since. The exhibition of the DSW300 model at the
XVII Congress in Vienna (Dam and Walker, 1996) enabled
customers to exploit not only higher performance than the
previous DSW200 model, but, importantly, was capable of
accommodating roll film. The DSW500 (Dam er al. 2000)
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