Color imaging depends strongly on the illumination conditions. Semi-specular surfaces impose ambiguity in colorimetric analysis and the specular reflection component has to be treated differently depending on the material. To exclude the specular component, special configuration of photometric devices is required. Such conditions cannot easily be met for images of irregular surfaces. I propose a simple method of structured light illumination for separating the specular and diffuse components of semi-specular surfaces using color camera and a calibrated flat-screen monitor.
Estimation of geometry and reflectance of 3D objects requires that surface geometry is registered together with
photometric data. We present a method which combines geometrical camera calibration and photometric calibration into
a single procedure utilizing only one calibration target. Using structured light projection and directional illumination, the
surface of a 3D object can be registered with an integrated measuring device. To estimate spatial distribution of
reflectance parameters, a Spatially Varying Bidirectional Reflectance Distribution Function (SVBRDF) model is used.
We also show a 3D image processing method to estimate SVBRDF parameters using an arbitrary defined array of
illuminators and algorithms to reconstruct this surface using specialized visualization software. This approach allows for
effective measurement of geometry and visual properties of 3D objects represented by a dense point cloud model. It can
become a valuable tool for documentation of digital heritage and in industrial computer vision applications.
To create faithful reproduction of a cultural heritage object, it is crucial to gather information on intrinsic optical properties of the object's surface, as well as its geometry. An integrated device has been developed that performs a three-dimensional measurement using structured light projection, followed by multispectral imaging for precise color retrieval and directional illumination for estimating bidirectional reflectance distribution function (BRDF) parameters. The main advantage shown in this work is the use of only one detector during the whole acquisition process to assure ideal correspondence of multimodal surface data in the image space. A method is shown for performing the measurement using an integrated device. Methods of data organization and processing are described facilitating robust operation of the developed software. A prototype setup for the integrated system is presented together with measurement parameters and sample measurement.
KEYWORDS: 3D printing, 3D metrology, Reflectivity, Cultural heritage, System integration, 3D modeling, Current controlled current source, Digital Light Processing, Projection systems, Structured light
In this paper a new 3D measurement system along with the study on 3D printing technology is presented from the perspective of quality of reproduction. In the first part of the paper the 3DMADMAC SPECTRAL system which integrates 3D shape with additional color and angular reflectance measurement capabilities is presented. The shape measurement system is based on structured light projection with the use of a DLP projector. The 3D shape measurement method is based on sinusoidal fringes and Gray codes projection. Color is being measured using multispectral images with a set of interference filters to separate spectral channels. Additionally the set up includes an array of compact light sources for measuring angular reflectance based on image analysis and 3D data processing. All three components of the integrated system use the same grayscale camera as a detector. The purpose of the system is to obtain complete information about shape, color and reflectance characteristic of measured surface, especially for cultural heritage objects - in order to use their models in 3D copying application. In the second part of the paper the 3D printing technology will be tested on artificial objects as well as on real measured cultural heritage ones. Testing on artificial objects allows to assess measurement and color accuracy of reproduction by selected 3D printing technology. Testing on real objects sheds some light on how current 3D printing technology can be applied into cultural heritage.
KEYWORDS: Clouds, Data modeling, 3D modeling, Data processing, 3D metrology, Reflectivity, Bidirectional reflectance transmission function, RGB color model, Calibration, Visualization
A set of calculation methods has been developed and tested to provide means of creating virtual copies of three
dimensional (3D) historical objects with minimal user input. We present a step by step data processing path
along with algorithm description required to reconstruct a realistic 3D model of a culturally significant object.
The important feature for archiving historical objects is the ability to include both information about its shape
and texture, allowing visualization using arbitrary conditions of illumination. Data samples used as input for the
processing method chain were collected using an integrated device consisting of shape, multispectral color and
simplified BRDF measurements. To confirm the usability of presented methods, it has been tested by example
of real life object - statue of an ancient Greek goddess Kybele. Additional visualization methods have also been
examined to render a realistic virtual representation satisfying intrinsic surface properties of the investigated
specimen.
In this paper a 3D shape measurement system with additional color and angular reflectance measurement capabilities
is presented. The shape measurement system is based on structured light projection with the use
of DLP projector. 3D shape measurement method is based on sinusoidal fringes and Gray codes projection.
The color measurement system uses multispectral methods with a set of interference filters to separate spectral
channels. Additionally the setup includes an array of compact light sources for measuring angular reflectance
based on image analysis and 3D data processing. All three components of the integrated system use the same
grayscale camera as a detector. The purpose of the system is to obtain complete information about shape,
color and reflectance characteristic of measured surface, especially for cultural heritage objects in order to use in
documentation, visualization, copying and storing. Some measurement results of real objects with a discussion
of accuracy are presented along with future development plans.
In this paper a distributed intelligent system for civil engineering structures on-line measurement, remote monitoring,
and data archiving is presented. The system consists of a set of optical, full-field displacement sensors connected to a
controlling server. The server conducts measurements according to a list of scheduled tasks and stores the primary data
or initial results in a remote centralized database. Simultaneously the server performs checks, ordered by the operator,
which may in turn result with an alert or a specific action.
The structure of whole system is analyzed along with the discussion on possible fields of application and the ways to
provide a relevant security during data transport. Finally, a working implementation consisting of a fringe projection,
geometrical moiré, digital image correlation and grating interferometry sensors and Oracle XE database is presented.
The results from database utilized for on-line monitoring of a threshold value of strain for an exemplary area of interest
at the engineering structure are presented and discussed.
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