The International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences. Vol. XXXVII. Part B7. Beijing 2008 
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2.1 The electronically tunable narrow-band optical filter. 
The use of liquid crystal filters is based on the 
phenomenon of wave polarization. In the part of the filter called 
the polarizer, any wave without a given direction is polarized, 
meaning, it is given a direction. When light is polarized, its 
vibration plane can be rotated in a process called involution by 
the angle A<p. The aim of this process is being able to control the 
angle by which the wave is rotated with the use of electrical 
current. 
One of the greatest disadvantages of using a tunable filter is the 
fall in the amount of transmitted waves when the wavelength is 
lowered. The transmission of the filter varies from 4% to 50%. 
The fall in transmission can be compensated by extending the 
time of exposure. This however can lead to an increase in the 
amount of noise on the resulting image. 
Test data: filter 51237a 
400 450 500 550 600 650 700 
Wavelength (nm) 
Fig no2. The filter transmission in relation to the light 
wavelength 
2.2 The monochromatic digital camera. 
The Qimaging QICAM is a digital camera which has 
been especially designed for high resolution experimental and 
industrial tasks. It is equipped with a monochromatic 
progressive CCD matrix ( Sony ICX205 Progressive Scan 
Interline CCD Monochrome ), which means that the image is 
registered on the matrix line by line, not every second line, as is 
the often the case. In contrast to traditional digital cameras, the 
matrix in this camera is monochromatic and does not contain 
elements of the Bayer filter, by means of which colour images 
are created. According to the specification, the camera has a 
12bit grayscale, although analysis of the dynamic range of the 
matrix has shown that the proportion of the potential well 
(lOOOOe) to the noise (12e') is 834, so technically the image 
will have a 9.70bit grayscale. The attached software makes it 
possible to register an 8bit image. The camera uses a 
thermoelectric Peltier cooling system, which allows for the 
cooling of up to 25 °C below the surrounding temperature. The 
cooling system guarantees a constant level of noise on the 
matrix, which is essential for the repeatability of results. 
The QICAM video camera has an electronic shutter. This means 
that it contains no mechanical parts, and that its „opening” and 
„closing” takes place by applying a certain current into the 
matrix. Use of the electronic shutter allows for the integration of 
the exposure time with the software and additional hardware 
(for example with filters and lamps). The exposure times on the 
given camera can be from 12Dm to 17.9 minutes and can be 
freely changed, according to the needs, with the given software. 
It is possible to automatically adjust the exposure time to a 
given part of the image. 
2.3 Software used to operate the hyperspectral acquisition 
of images. 
The specialized software - „Wiano” - created for 
these tests is used to capture hyperspectral images. The software 
controls the functioning of the monochromatic camera coupled 
with the liquid crystal tunable filter. The main functions of the 
program are: 
a. The interactive control of the camera 
b. The interactive control of the filter 
c. A constant preview of the camera image on the 
computer screen 
d. The acquisition of an image from the camera into the 
computers memory, with the possibility of an 
automatic adjustment of the exposure time for an area 
chosen by the user 
e. Saving the image to file (the filename should 
automatically contain the range in which the image 
was creates, the date, etc.) 
f. The automated registration of a sequence of n images 
with the tuning of the mid wavelength by a certain 
interval for each successive image 
g. Compatibility with the Windows 2000 and XP 
operating systems 
3. TESTING THE SET 
3.1 Lens selection. 
The camera equipment does not include a lens. The 
user can choose a lens for the camera depending on the 
photographed scene. For the purpose of this research, lenses 
with a focal length of 12.5mm, 25mm and 50mm were tested in 
order to examine the cameras capabilities. Because of the focal 
length of the tunable filter (20mm) the lens with a focal length 
of 50mm was used in further studies. The remaining lenses 
caused too much vignietting, which had a direct affect on the 
acquiring of image information. 
3.2 Acquiring image information. 
Research has shown that it is possible to automate the 
selection of the time of exposure on the basis of a chosen ROI 
area. It is also possible to select the exposure time manually, 
however this requires the user to take into account the way in 
which the objects are illuminated and with what type of 
lighting. Using the automatic method of exposure time selection 
for the entire scene, the exposure measurement is set based on a 
weighted average for the scene and is equal to 18% of its value. 
When setting the ROI area onto a white reference standard, the 
camera automatically sets the ROI do 91% of the maximum 
value in each spectral band. Therefore bright areas on the 
images will not be overexposed. 
Test plates of different shades of grey were used in the research.