http://www.cnr.it/ontology/cnr/individuo/prodotto/ID184153
An Active Vision System for 3D surface Colour Measurements (Contributo in atti di convegno)
- Type
- Label
- An Active Vision System for 3D surface Colour Measurements (Contributo in atti di convegno) (literal)
- Anno
- 2006-01-01T00:00:00+01:00 (literal)
- Alternative label
A. Balsamo (2), A. Chimienti(1), P. Grattoni(1), R. Nerino(1), G. Pettiti(1), M.L. Rastello(3), M. Spertino(1) (2006)
An Active Vision System for 3D surface Colour Measurements
in Proceedings of the ISCC/CIE Expert Symposium, Ottawa (Canada), May 2006
(literal)
- Http://www.cnr.it/ontology/cnr/pubblicazioni.owl#autori
- A. Balsamo (2), A. Chimienti(1), P. Grattoni(1), R. Nerino(1), G. Pettiti(1), M.L. Rastello(3), M. Spertino(1) (literal)
- Http://www.cnr.it/ontology/cnr/pubblicazioni.owl#affiliazioni
- (1) - IEIIT
(2) - IMGC
(3) - INRIM (literal)
- Titolo
- An Active Vision System for 3D surface Colour Measurements (literal)
- Http://www.cnr.it/ontology/cnr/pubblicazioni.owl#isbn
- 978 3 901906 51 0 (literal)
- Abstract
- Common surfaces have reflection characteristics that differ considerably from
those of a reference standard for colorimetry. They are neither totally diffusing nor
regularly reflecting, and their reflectance strongly depends on the viewing angle and
the illumination geometry. As a consequence, reliable measurements can be achieved
only if the measuring geometry is fixed or known. To solve this problem, the
Commission Internationale de l'Eclairage (CIE) recommended four standard
geometries, defining both irradiation and observation conditions. Unfortunately, when
dealing with 3D objects, with large dimensions in space, like for instance monuments
or automobiles, geometry can hardly controlled and new-concept instrumentation is
needed to obtain results reproducible in different times and/or locations.
Traditional instrumentation on the market rarely offers colorimetric and
geometric measurements combined in a single device and when it happens one function
is just a support to the other without any accuracy indication. In fact, accurate
geometric and colorimetric data permit detecting changes of surfaces at a given
resolution (e.g. erosion, mould growth, chemical alterations, ...) when these data are
strictly correlated for effective surveying analyses. Moreover, the assessment of the
measurement accuracy would allow establishing a possible correlation between the
geometric and colorimetric data of surfaces and the chemical-physical changes of the
surrounding environment with a number of possible implications of interest.
Concerning geometric measurements, devices and techniques for the acquisition
of three-dimensional structures can be grouped in three categories: topographic,
photogrammetric and laser-based techniques. Due to their physical working principle,
each of them has a specific range of operation within which it supplies its best
performances. In particular, all techniques merged together leave almost uncovered the
range from two - three meters to twelve-fifteen meters.
Concerning colorimetric measurements, techniques and devices on the market
can perform accurate measurements on single spots of at least some mm in size, or
more. Colorimeters can be roughly grouped in two categories based on their measuring
characteristics: in-contact and not in-contact. In-contact devices are equipped with an
internal calibrated source of light while the other ones need external sources of light,
possibly satisfying CIE recommendation on their spectral content. Even if all devices
require less than some seconds to carry out a single measurement, the dense sampling
of a surface can be very time-consuming because of the time needed for repositioning.
In addition, the color-to-geometry correlation is not immediate and can be difficult
establishing it.
In this context, there is a definite demand for a flexible, multifunctional
(geometric and colorimetric) instrumentation which should integrate the traditional
peculiar ones to easier the on-site data collection and promote its diffusion. The Active
Vision System (AVS) described in this paper has been designed and developed to
answer these needs. AVS works over a range from two to ten meters in depth and
carries out integrated colorimetric and geometric measurements with assessed
accuracies. Thanks to its computerized control for the automatic management of the
2
operations, it allows the in-field processing of the acquired data and their comparison
with databases for monitoring purposes.
The global functions of the SVA are essentially: the measurement of the 3D
position of a point in the scene of the imaged surface and the measurement of the
tristimulus values of this point. Then, the whole large scene is reconstructed with high
resolution by scene tessellation and image mosaicing, and the 3D surface is obtained
from sparse points or by dense reconstruction from the stereo TLs images. All these
functions are automatically performed under computer control and a man-machine
graphical interface has been developed for managing the whole system easily. The
acquisition and registration of accurate geometric and colorimetric parameters
concerning a given survey, such as the relative position between AVS and scene, the
spatial co-ordinates of the test points, and the spatial position of artificial light sources,
allow the system to carry out automatic and accurate repetition of that survey in
successive measuring campaigns.
AVS is composed of three B/W TV cameras aligned along a common axis ?
(see Fig.). Two of these cameras (TL1 and TL2) are equipped with long focal-length
lenses to frame only small portions of a scene at high resolution. They can be rotated by
known angles both around the parallel pan axes ?1and ?2 and the tilt axis ?, to perform
the fixation of some points of a scene. One TL is equipped with spectral filters,
allowing the acquisition of high accuracy colour images of the examined surface. The
third camera is equipped with a wide-angle lens (WA) to frame the whole region of
interest at a lower resolution.
When the field size framed by TL cameras is too small for analysis, a wider
field can be acquired as a sequence of partially overlapping tiles by automatically
scanning the Region Of Interest (ROI) with TLs. The ROI can be interactively selected
by an operator looking at the WA image on the computer display. In addition to texture
and colour information, the spatial position, orientation and gaze direction of each tile
are acquired at each step so that the entire framing geometry is completely controlled
by the system and can be saved for reliable repetitions of the measurements at different
times, i.e. for monitoring tasks. The reconstruction of the whole ROI information is
obtained by image mosaicing. The mosaicing procedure differs from the ones described
in literature mainly because the transformation of the acquired images is aimed at
compensating systematic acquisition errors and parallax effects independently of the
image contents, and not at minimizing the matching errors between adjacent images.
Therefore, this method is intrinsically non-iterative and offers the advantages of being
simple and fast, but accurate enough to satisfy the application requirements. (literal)
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