The objective measurement of facial skin color and its variance is of great significance as much information can be obtained from it. In this paper, we developed a new skin color measurement procedure which includes following parts: first, a new skin tone color checker made of pantone Skin Tone Color Checker was designed for camera colorimetric characterization; second, the chromaticity of light source was estimated via a new scene illumination estimation method considering several previous algorithms; third, chromatic adaption was used to convert the input facial image into output facial image which appears taken under canonical light; finally the validity and accuracy of our method was verified by comparing the results obtained by our procedure with these by spectrophotometer.
Three dimensional Identification Card, with its three-dimensional personal image displayed and stored for personal identification, is supposed be the advanced version of the present two-dimensional identification card in the future . Three dimensional Identification Card means that there are three-dimensional optical techniques are used, the personal image on ID card is displayed to be three-dimensional, so we can see three dimensional personal face. The ID card also stores the three-dimensional face information in its inside electronics chip, which might be recorded by using two-channel cameras, and it can be displayed in computer as three-dimensional images for personal identification. Three-dimensional ID card might be one interesting direction to update the present two-dimensional card in the future. Three-dimension ID card might be widely used in airport custom, entrance of hotel, school, university, as passport for on-line banking, registration of on-line game, etc...
To provide accurate three-dimensional (3-D) data for production and processing, 3-D surface measurement is always an essential step to the production of glass. Profilometry and Interferometry are traditional measurement apparatus, referring to different procedures. Although more precise, Interferometry cannot be used in milling procedure, owing to the scattering property of rough glass. While as a widely used Profilometry, Coordinate Measuring Machine (CMM) employs a probe for measuring by contacting surface directly. It should be noted that such a time-consuming machine is not practical for measuring large-sized rough glass, so a novel designed method called temporal speckle is introduced to a non-contact binocular 3-D measurement system for measuring. Specifically, N band-limited binary patterns are sequentially projected to rough glass from a pattern generation device, such patterns have been proved to depress scattering properties of rough surface. The whole binocular 3-D measurement system can finish a single measurement in one second with a standard deviation less than 73.44um. This system performs fast and accurate 3-D surface measurement for large-sized rough glass block.
The achromatic diffractive optical element (DOE) was numerically studied. The light intensity distribution in the focal plane was studied by the vectorial diffraction theory, then the radially symmetric DOE to enable broadband achromatic focusing with low sidelobe intensity ratios and uniform central intensities were optimized by the simulated annealing (SA) algorithm. The plane wave with wavelength of 486nm, 588nm, and 656nm were used in our optimization and numerical research. Three DOEs with 60, 80, and 100 transition points were obtained. Numerical results shown that the sidelobe intensity suppression ratios of focal spots of these wavelengths are all less than 0.12, the principal peaks’ intensities differences and spots’ sizes differences of these focal spots are all less than 5% and 10%, respectively. The designed DOEs were polarization insensitive.
A Dammann grating coupling method and corresponding coupling condition are proposed. The different diffractive efficiency of the traditional 3x3 Dammann grating are analyzed by using both the scalar diffraction theory and the Fourier Modal Method (FMM). One new 3x3 Dammann grating is designed by using FMM in association with the simulated annealing optimization (SAO), and its diffraction efficiency and uniformity are about 40% and 15%, respectively. The new 3x3 grating and one traditional 64x64 Dammann grating are then coupled and analyzed numerically. The diffractive efficiency and the uniformity of the final 192x192 dense spots array are 30% and 18%, respectively. As the reference object, one 121x121 beam-splitting grating is designed, whose uniformity and overall diffractive efficiency are 50% and 85%, respectively. Numerical results show that the Dammann grating coupling method is more economical and applicable way to generate dense spots array.
In this paper, we develop a binocular three-dimensional measurement system using a Dammann grating. A laser diode and a Dammann grating are employed to generate a regular and square laser spot array. Dammann array illuminator is placed between two cameras and narrowband-pass filters are embedded in the project lens to eliminate the interference of background light. During the measurement, a series of laser spot arrays are projected toward the target object and captured by two cameras simultaneously. Similar to stereo vision of human eyes, stereo matching will be performed to search the homologous spot which is a pair of image points resulting from the same object point. At first, the sub-pixel coordinates of the laser spots are extracted from the stereo images. Then stereo matching is easily performed based on a fact that laser spots with the same diffraction order are homologous ones. Because the system has been calibrated before measurement, single frame three-dimensional point cloud can be obtained using the disparity of homologous points by triangulation methods. Finally, three-dimensional point clouds belong to different frame which represent different view of the object will be registered to build up an integral three-dimensional object using ICP algorithm. On one hand, this setup is small enough to meet the portable outdoor applications. On the other hand, measurement accuracy of this system is better than 0.3 mm which can meet the measurement accuracy requirements in most situations.
This paper summarized our work on three-dimensional optical technologies using Dammann gratings, e.g., threedimnensional Dammann gratings, three dimensional imaging using a Dammann grating, etc.. We developed threedimensional Dammann grating which can produce three-dimensional array with equal distance and equal intensity with a high-numerical-aperture lens. As we know, a lens usually has a single focal point. Fresnel zone plate can generate several axial focal points, but the intensity between them is unequal. By introducing the concept of Dammann grating into the circular phase plate, we invented Dammann zone plate(DZP) which can produce a series of axial focal points with equal intensity. Combining DZP with a Dammann grating, three-dimensional Dammann array will be generated, which is highly interesting for various applications. We also built a three–dimensional measuring system using a Dammann grating, with two cameras as the right eye and right eye, respectively. We used a 64×64 Dammann grating for generation of a square array of light spots for parallel capturing the three-dimensional profile of an object. The two cameras and the illuminating part are packaged together. After scanning the object, its three-dimensional profile will be obtained. Experimental results demonstrated the effectiveness of this technique.
In this paper we propose a 3D measurement system based on a structured light with a special pattern. The structured light is projected on an object by a projector. Two calibrated digital cameras are used to capture the images of projected area on the object separately. Artificial corner points generated by the structured light are detected. We defined a simple but effective feature parameter of the corner points. The corner points are clustered into several groups by adopting k-means cluster to analyze the feature parameter of corner points. We propose a stereo matching method using the cluster result and geometric constraint. A sequence of images is captured to enhance the measuring resolution. According to triangulation, the 3D point clouds are obtained from the pair of images. Experiment result demonstrated the feasibility of this 3D measuring system. The system with the advantages of high measuring precision and good robustness is highly attractive for applications in 3D measurement, 3D display and so on.
Although there are several well -known methods such as RCWA, FMM, for analyzing the diffraction properties of
gratings, design of these optical elements with specified spectral properties is commonly a challenging problem. It is
relatively not easy for the researchers to design narrow line-with diffraction filters based on guided mode resonance
phenomenon with common diffraction algorithm.
Simulated Annealing (SA) method is evolutionary, robust technique that has been widely utilized to design optical
diffraction components. This method is inspired by the physical process of heating and controlled cooling of metal
material to increase the size of its crystals and reduce their defects. The most distinctive features of this method lie in its
powerful ability of convergence towards the global minimum in a reasonable computation time and the independence of
the initial parameter values.
In this paper, first, the physical basis of SA and its mathematical realization are introduced. Then, a Guided-Mode
Resonant Grating (GMRG) filters with single layer is designed by using SA algorithm. The central wavelength of
GMRG filter is locked at 532nm and its line-width is fixed at 1nm. The plane wave light radiates the grating from air
cover with normal incidence.
The optimized parameters are refractive indices and thicknesses of high and low material of grating, other parameters are
grating period and fill factor of the grating. It is shown from our calculation that an excellent reflection spectrum with
narrow line-width, high peak and low sideband can be obtained after optimizing the grating parameters. Next, a double
layered GMRG filter with line-width of 4nm, which is relatively easy fabrication in experiment, is designed at central
wavelength of 1064nm. The optimized parameters are grating period, groove depth, refractive index of waveguide layer
and fill factor respectively. The grating substrate and waveguide layer are Sio2 and Hfo2 respectively, the grating
structure is directly etched on the waveguide layer. The above grating values should be included in reasonable ranges in
consideration of grating fabrication in our experiment condition.
It is demonstrated from the calculations with the parameters obtained from SA optimization algorithm that the peak
diffraction efficiency is more than 99% at central wavelength 1064nm and the sideband reflection is depressed at the
level bellow 5% in a large wavelength range. Moreover, the parameters of a triple layer GMRG filter structure are also
provided with this powerful method. Meanwhile, the results found by SA method are compared with RCWA theory.
A novel approach of optically exciting and detecting the vibration of a microresonator by a sinusoidally driven
semiconductor laser subject to optical feedback is proposed. A theoretical model for the approach is established, and the
working parameters are optimized. In our experiments, an Al-coated microcantilever is designed with optimized working
parameters, and the microcantilever is optically excited by a sinusoidally driven semiconductor laser. We have
demonstrated that there exist periodic dips of the optical power of semiconductor laser, which is caused by the resonant
vibration of microcantilever. The optical power of semiconductor laser is also analyzed theoretically by using L-K
equations. The experimental result is consistent with the result of theoretical analysis.