Leica DSW700 User Manual

DSW700 System Description

DSW700 Technical Details

Overview

Softcopy photogrammetry work, stereo-compilation, and ultimately, orthophotos can
only be as accurate as the source imagery. Working in a digital photogrammetry environment requires
that the scanned aerial photographs are not only as accurate as possible but that the appearance of
the film is reproduced faithfully and that the raw air photos are scanned quickly so that production can
begin rapidly.

The Leica DSW700 Digital Scanning Workstation is a photogrammetric scanner,
designed for maximum throughput. It is capable of scanning aerial film, cut sheets or roll, black and
white, color or false color, positive or negative, at a very high speed. The geometric and radiometric
performances meet all photogrammetric requirements. The DSW700 includes several innovations,
not only to achieve maximum speed but also to optimize radiometric performance by virtually
eliminating Newton rings.

The DSW700 is built on the successful design of the earlier DSW200/300/500/600 models, based on
a heavy, precise mechanical construction with moving stage plate, and stationary digital camera with
state-of-the-art CCD sensor. The principal improvements over current scanner design include a novel
ring light with LEDs of various colors, a high quality 11-megapixel sensor, and anti-reflective coatings
on the stage and cover plates to combat Newton rings. A further innovation is the use of next
generation optical encoders to position the stage, resulting in increased geometric accuracy.

Key Features

The Leica DSW700 Digital Scanning Workstation performs precision scanning of black and white,
color or false color, cut or roll film negatives and diapositives at a very high speed, to provide the
highest quality digital imagery for use in softcopy photogrammetric workstations.

The system consists of the following principal components:

• Heavy mechanical construction, with stage plate mechanism, to support the motorized roll-film

transport, moving in the X and Y directions below the stationary illumination source and above the
lens and sensor

• Dome light source consisting of LEDs of different colors

• 12-bit CCD large-array sensor to capture the image patchwise

• Convenient change of optical pixel size throughout the full 3µm to 20µm continuous resolution

range, so that scanning takes place at the pixel size required by the user, without any image
resampling

• High performance PC host computer running Windows® XP Professional

• Comprehensive, flexible software to control all aspects of the scanning operation, facilitated by an

easy-to-use graphical user interface.

The XY stage is built to very high mechanical standards, taking into account that both cut and roll film
must be accommodated. The stage is exceptionally sturdy and provides independent positioning with
respect to the X and Y sensor axes. Mounted on the base are the optics and 12-bit digital sensor
used to digitize the transparencies. The optical path has been minimized for optimal performance: no
beam splitters or folding mirrors are used and the light path is straight. The stage and optical path are
mounted inside a specially designed enclosure, which prevents dust and dirt from accumulating on
the film or extraneous light from entering the system during scanning. Illumination is provided directly
by an LED dome light supported above the stage. This cool light source is located 125 mm above the
platen, so does not subject the film, stage or optical path to unwanted heat. The dome consists of
LEDs of different colors to allow for color as well as black and white images to be scanned.

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DSW700 System Description

Hardware characteristics

1. Basic design The DSW700 has at its center an extremely rigid base plate, manufactured as
a precision casting. This is supported on a frame, furnished with casters and stabilizers
(leveling screws). On the base plate are mounted precision steel rails, which derive their
flatness from the base surface together with a jack screw approach, which ensures
straightness before the rails are screwed tight in their final positions. Both X and Y stages are
milled from aluminum. A back-lit panel mounted on the lower stage enables the operator to
view a section of the film, for example to select a particular exposure for scanning. An
automated motor and cam arrangement raises and lowers the glass cover plate automatically,
under software control, to permit roll film to be transported. For cut film, the operator raises
and lowers this plate manually, at which point it behaves like a hinged lid.

2. Input media The stage accepts film transparencies, as roll film or cut film, or glass plates of
any thickness. The scanning format accepts images more than 260 mm square (10.2 x 10.2
inches). Input transparencies can be color or black and white and can be positive or
negative.

3. Servo drives The drive mechanism is a friction drive that provides excellent performance and
requires little maintenance. This design has been successful on all DSW models for the past
fifteen years. Modern precision positioning encoders with non-contact reading heads have
been selected for improved performance.

4. Stage accuracy The resolution of stage positioning at any point is 0.5 µm. The accuracy
threshold is a maximum 1.5 µm (0.00006 inch) root mean square error (RMSE) or better on
each axis, based on computer calibration and compensation. Stage calibration is provided
via automated grid plate measurement and is required infrequently.

5. Light source and optics The illumination system provides uniform overhead illumination
over the field of view of the CCD array sensor. The DSW700 uses an LED dome light,
supported in a stationary position above the stage plate. The dome consists of an array of
red, green, and blue LEDs, arranged in two concentric rings.

The new LED source is more economical, with a life expectancy of more than 10 years under
constant use. Most importantly, the use of LEDs in the DSW700 allows for a much more
efficient, substantially faster implementation of sequential color capture than in the past.

Flat bed scanners sometimes produce a phenomenon called Newton rings when the film is
not held perfectly flat between the pressure plates. Typically, they become visible in a color
scanned image as a rainbow series of light and dark rings around nondescript points in
homogeneous areas. 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. The solution
in the DSW700 is to reduce significantly the formation of ring patterns by controlling one of
the contributing physical factors – the reflection coefficient of the surfaces. By suitably
reducing the amount of reflection between the glass pressure plates, it is possible to reduce
the ring amplitude until it is virtually invisible.

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DSW700 System Description

6. Digital sensor and lens A large-format, 12-bit, CCD array sensor is fitted on the DSW700. It
provides better performance than any previous model in terms of the area of the film that can
be captured. Faster and larger sensors that are also lower in noise translate directly into
speed and quality improvements. The new sensor also creates a cleaner, more consistent
scan and allows future efforts to be redirected away from perfecting raw capture towards
higher level image processing, such as dodging or automatic light balancing in roll-film
scanning. A 120 mm color-corrected lens has been selected to image the film on to the
sensor. This lens provides greater light throughput and low distortion. An 80 mm lens is
available as an option to facilitate even higher resolution for special applications. By varying
the vertical positions of the CCD sensor and lens, both of which are mounted on a rail
mechanism with clamps and slow motion screws, the physical pixel size at the film plane is
adjustable in the range 4.5-22 µm (0.00018-0.00087 inch). With the optional 80 mm lens,
pixel sizes as small as 3 µm are possible. Raw imagery is captured and may be output at any
pixel size selected by the user, up to 256x the raw pixel size at the film plane. The precise
CCD image geometry and low distortion optics provide an almost distortion-free image.

7. User control panel The user control panel is mounted inside the upper casing of the
DSW700. It has two rows of 16 buttons and a small LCD panel with four rows of characters.
The panel is used to input user commands, run diagnostics, etc. It contains a small computer
circuit to control the LCD display, read the push button switches and communicate with a
DOS-based communications computer card. The panel may also be used for manual
movement of the stage and roll-film transport.

8. Power supplies and electronics There are four DC power supplies: one gives 5V and 12V,
one gives 40V for the motors, one gives 12-24V for the CCD sensor, and the fourth gives 24V
for the LED dome light. The DSW700 runs at 3.2 amps on 110V (1.6 amps at 220V) and the
peak load with a 500 foot (152 m) film roll is calculated to be 6 amps.

9. Outer housing The stylish skins of the DSW700 consist of two main parts. The pedestal
around the base structure is made from pressure formed plastic and the top housing of
fiberglass. The pedestal is dark gray, the top housing silver gray and the colored inserts
Leica red. The product name is in black and the Leica logo in red on white. There is a single
LED to indicate power and the top housing has a large lid for loading and unloading cut or roll
film or for viewing the position of a film roll.

10. Tools and accessories Standard system delivery provides all special tools and accessories
required for routine maintenance, lubrication and calibration, including a precision glass grid
plate for checking stage accuracy, and special filters for calibration of sensor radiometric
response.

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