geometric 
the aerial 
based on 
very high 
)0 Digital 
em frame. 
: DSW to 
novations 
ormity of 
and cover 
1nements, 
available 
scanning 
and ease- 
s given in 
t patches; 
at sensor 
, PC host 
ize 
n source 
nd a PC 
DSW600 
> a high 
hardware 
hrough a 
tionality, 
  
speed and ease-of-use. Standardization on Windows XP in 
2003 simplified maintenance and support. 
1.1 Upgrades 
Meanwhile, in addition to introducing new models, Leica 
Geosystems had built up a base of several hundred customers 
who required support and wished to benefit from the 
innovations. The focus had shifted slightly from raw 
performance towards greater reliability, further ease-of-use, 
which was addressed through software, and the desire to 
upgrade earlier models. Leica Geosystems responded, as 
early as 1999, to customers' requirements with upgrades to 
enable earlier scanners to benefit from technical refinements. 
In 2001, it became possible to upgrade DSW300 models to 
DSW500 status. After the introduction of the DSW600, this 
program was extended considerably. Customers could 
upgrade DSW300 and DSW500 models to DSW600, 
including sensor, lens, integrating sphere and related 
electronics. A roll film upgrade was available also for 
DSW300 and early DSW500 models to raise their 
performance and reliability to DSW600 standards. Similarly, 
earlier models could be upgraded with the DSW600 wiring 
harness, including modern cable technology capable of 
operating for years without problems despite the millions of 
X and Y movements of the stage plate. Finally, a newly 
designed colour wheel arrangement was developed to replace 
the existing sub-assembly in the DSW300, in order to 
increase reliability. 
2 RECENT REQUIREMENTS 
Though the DSW600 was the fastest scanner in the market- 
place and reliability had increased beyond earlier models, 
there was still scope for development and innovation. Early 
in 2004, a major release of the software included significant 
improvements, for example tonal enhancement of the fiducial 
marks without disturbing the rest of the image. Customers 
requested further performance improvements, however. 
Spurred by the increasing competence of photogrammetric 
service companies, with their growing attention to smooth 
workflows, and by the letting of large government contracts, 
especially in the US, projects grew extremely fast and firms 
or consortia undertook mapping tasks involving huge 
numbers of rolls of film. A good example is the project 
managed by Surdex of St. Louis, Missouri to produce digital 
orthorectified imagery of 574,119 square miles of Missouri, 
Oklahoma and Kansas, requiring 31,522 exposures 
(Molander, 2003). The project required eight aircraft and 
four scanners — two DSW500s and two DSW600s, working 
round the clock. With such enormous projects, customers 
wish to proceed from image acquisition to triangulation as 
fast as possible. The critical limitation is the time taken to 
scan a roll of color or false color film. At the same time, 
radiometric quality assumes additional importance, because 
time saved in radiometric manipulations to produce attractive 
deliverables is extremely valuable. Naturally, when capacity 
is fully utilized in these enormous projects, reliability is of 
the essence. 
Once the DSW600 had successfully entered the market- 
place, Leica Geosystems turned its attention to further 
development. One direction was the continuing search for 
higher performance, cost effective sensors. Another was 
examination of new technologies capable of brighter, more 
International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences, Vol XXXV, Part Bl. Istanbul 2004 
uniform illumination of larger areas, so that the whole field 
of the sensor could be used to maximize speed and the tonal 
range could be extended to make use of the 12 bit sensor. A 
possible source of increased robustness might be replacement 
of the mechanical color wheel assembly whereby a filter 
wheel was rotated in front of the light source, assuming three 
positions to capture a patch of color or false color imagery. 
Finally, new approaches became available to reduce Newton 
rings, one of the biggest remaining image quality issues. 
3 RECENT DEVELOPMENTS 
Key technologies in a product guide its evolution. Three of 
those, the illumination system, optical and sensor 
components, have been responsible for many of the 
performance and quality improvements over the 15 years 
comprising the six DSW models. In the latest model, the 
DSW700, the illumination system is being upgraded from 
traditional blackbody to solid state. The sensor is being 
changed for a higher performance version. Finally, the 
optical system is being treated to eliminate the old problem 
of Newton rings. 
3.1 Treatment of Newton rings 
Newton rings are one of the oldest artifacts in film printing 
and scanning. They are artifacts that flat bed scanners 
produce when the film is not held perfectly flat between the 
pressure plates. Typically, they become visible in a colour 
scanned image as a rainbow series of light and dark rings 
around non-descript points in homogeneous areas (Figure 1). 
  
Figure 1. Typical Newton ring pattern 
They are, however, not related to the image itself, but to the 
film surface in contact with the glass plates. Unless a special 
optical fluid is used to eliminate the air gaps and therefore 
the index change between two media, Newton rings will 
usually form. Physically, they are formed from the re- 
combination of reflected light waves bouncing between two 
semi-transparent surfaces that are smooth and whose distance 
varies slowly. When the distance variation is small compared 
to the wavelength of light, then the reflections can create 
visible interference fringes on re-combination. Spectral 
coherency and columniation of the light will affect their