KEYWORDS: Skin, Calibration, Cameras, 3D modeling, 3D metrology, Imaging systems, Fringe analysis, 3D image processing, Dermatology, Profilometers, 3D acquisition, 3D imaging metrology, Medical diagnostic instruments
The skin prick test (SPT) is the standard method for the diagnosis of allergies. It consists in placing an array of allergen drops on the skin of a patient, typically the volar forearm, and pricking them with a lancet to provoke a specific dermal reaction described as a wheal. The diagnosis is performed by measuring the diameter of the skin wheals, although wheals are not usually circular which leads to measurement inconsistencies. Moreover, the conventional approach is to measure their size with a ruler. This method has been proven prone to inter- and intra-observer variations. We have developed a 3D imaging system for the 3D reconstruction of the SPT. Here, we describe the proposed method for the automatic measurements of the wheals based on 3D data processing to yield reliable results. The method is based on a robust parametric fitting to the 3D data for obtaining the diameter directly. We evaluate the repeatability of the system under 3D reconstructions for different object poses. Although the system provides higher accuracy in the measurement, we compare the results to those produced by a physician.
Accurate 3D imaging of human skin features with structured light methods is hindered by subsurface scattering, the presence of hairs and patient movement. In this work, we propose a wide-field 3D imaging system capable of reconstructing large areas, e.g. the whole surface of the forearm, with an axial accuracy in the order of 10 microns for measuring scattered skin features, like lesions. By pushing the limits of grating projection we obtain high-quality fringes within a limited depth of field. We use a second projector for accurate positioning of the object. With two or more cameras we achieve independent 3D reconstructions automatically merged in a global coordinate system. With the positioning strategy, we acquire two consecutive images for absolute phase retrieval using Fourier Transform Profilometry to ensure accurate phase-to-height mapping. Encouraging experimental results show that the system is able to measure precisely skin features scattered in a large area.
KEYWORDS: Calibration, Cameras, Projection systems, Imaging systems, Systems modeling, Fringe analysis, Digital cameras, 3D metrology, 3D modeling, 3D image processing
In order to get measures with a high accurate, three-dimensional reconstruction systems are implemented in
industrial, medical, and investigative fields. To obtain high accurate is necessary to carry out an appropriate
calibration procedure. In fringe projection profilometry, this procedure allows obtaining a relation between absolute
phase and three-dimensional (3D) information of the object in study; however, to execute such procedure a precise
movement stage is required. A fringe projection system is formed by a projector, a digital camera and a control unit,
called like a projection-acquisition unit in this paper. The calibration of the projection-acquisition unit consists in to
establish the parameters that are required to transform the phase of the projected fringes to metric coordinates of the
object surface. These parameters are a function of the intrinsic and extrinsic parameters of both camera and
projector, due to the projector is modeled as an inverse camera. For this purpose, in this paper a novel and flexible
calibration method that allows calibrating any device that works with fringe projection profilometry is proposed. In
this method is used a reference plane placed in random positions and the projection of an encoded pattern of control
points. The camera parameters are computed using Zhang’s calibration method; and the projector parameters are
computed from the camera parameters and the phase of the pattern of control points, which is determined by using
Fourier analysis. Experimental results are presented to demonstrate the performance of the calibration method.
Three-dimensional shape measurement is a subject that consistently produces high scientific interest and provides
information for medical, industrial and investigative applications, among others. In this paper, it is proposed to
implement a three-dimensional (3D) reconstruction system for applications in superficial inspection of non-metallic
pipes for the hydrocarbons transport. The system is formed by a CCD camera, a video-projector and a laptop and it
is based on fringe projection technique. System functionality is evidenced by evaluating the quality of three-dimensional
reconstructions obtained, which allow observing the failures and defects on the study object surface.
Traditionally, ultrasonic ranging sensors emit pulse trains. The distance traveled by the received signal is calculated from
its delay with respect to the emitted signal. There are different strategies to encode the signal in order to determine the
delay. In this paper we present a method for encoding amplitude that encodes the amplitude of a signal formed by
rectangular pulse trains whose frequency is 40 kHz. The pulse amplitude is encoded in a binary manner according to a
pseudorandom sequence. Owing to that the emitted signal is formed by pulse trains whose amplitude is modulated, the
impulse response of the designed system generates sinusoidal pulse trains whose amplitude is variable. The proposed
strategy uses the phase of signal to position temporally each pulse trains. This positioning has higher precision than the
sampling time of the signal.
In the podiatry field, many of the foot dysfunctions are mainly generated due to: Congenital malformations, accidents or
misuse of footwear. For the treatment or prevention of foot disorders, the podiatrist diagnoses prosthesis or specific
adapted footwear, according to the real dimension of foot. Therefore, it is necessary to acquire 3D information of foot
with 360 degrees of observation. As alternative solution, it was developed and implemented an optical system of threedimensional
reconstruction based in the principle of laser triangulation. The system is constituted by an illumination unit
that project a laser plane into the foot surface, an acquisition unit with 4 CCD cameras placed around of axial foot axis,
an axial moving unit that displaces the illumination and acquisition units in the axial axis direction and a processing and
exploration unit. The exploration software allows the extraction of distances on three-dimensional image, taking into
account the topography of foot. The optical system was tested and their metrological performances were evaluated in
experimental conditions. The optical system was developed to acquire 3D information in order to design and make more
appropriate footwear.
An analysis of the axial resolution of a chromatic dispersion confocal microscopy is presented. The system is based on the principle of focus multiplexing by wavelength encoding due to a phase Fresnel lens. The axial resolution is related with the measure of the FWHM value of every spectral response.
Taking into account the need to characterize the foot in its dimensions with the objective to prevent and correct deformities, an optical system that allows its 3D reconstruction using the laser triangulation principle was created. Parameters are measured on the digitalized 3D image that is obtained of the foot.
In the industrial application field, the presence of blisters in coated steel is an important quality factor of the protection coating applied on the surface. In this work, an optical system of three-dimensional reconstruction for the detection quantitative evaluation of blisters in polymer coated steel was implemented. The implemented optical system explores a region of 4 x 3 mm with a resolution of 10 μm, using the fringe projection method. The experimental evaluation was realized using six test samples of different protection coating. The test samples were continually exposed to controlled saline atmospheres and they were periodically measured. The presence of first blisters on the surface was determined. Also, the quantitative parameters were measured as maximum height and mean width of blisters, after 566 hours of exposition.
In this work the Gray code method for numerical 3D reconstruction of complicated objects was implemented. Based on structured projection, the Gray code method projects in different binary patterns. Grouping this sequence, this sequence of patterns allow to describe 2n different directions of projection, where each direction corresponds to a word in binary code. Thus, each point in the observation field corresponds to a unique binary code that can be identified in the digitized image. The surface object introduces a lateral shift of each binary word in relation to the reference plane. A digital procedure that identifies each code, allows calculating the lateral shift and the corresponding height. The technique of gray code is easy to implement, it is flexible to the size of the object and it can resolve discontinuity objects. The system was designed to reconstruct human faces and was evaluated using objects of well-known form. Experimental results are presented and discussed.
The chromatic confocal method to measure the refractive index and thickness of membranes is developed. The method is based on the longitudinal chromatic aberration produced by a diffractive element. The identification of the maximal spectral components coming from the membranes are used for measuring its thickness or its refractive index.
A method for the verification of handwritten signatures based on the three-dimensional correlation is proposed. The input images to the algorithms of 3D correlation are those range images obtained from the 3D information formed by the signature path. An optic system based on the laser triangulation method, allows the extracting of 3D information. The method takes into account local characteristics that set shape and pressure of signatures together, discrimining characteristics for verification that have been traditionally used separately.
This communication introduces the Optics and Signal Processing Group from Universidad Industrial de Santander at Bucaramanga, Colombia. First, a brief description of how the group was formed, its strategic importance and also some of its more important achievements are presented. Then, the main scientific domains where the group carries out its research are described and finally, some guidelines about future research work in the group are given.
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