Light Source Model Research Articles

Multiple-image authentication method based on phase-only holograms and a logistic map

An interesting security method for a multiple-image authentication scheme is proposed based on computer-generated holograms and a logistic map. First, each original image is encoded as the complex-valued hologram under the point light source model. The resulting hologram is then converted to a phase-only hologram using the Floyd-Steinberg dithering algorithm. Second, each phase-only hologram is randomly sampled with the aid of a binary mask. Through the catenation of all selected pixels, a phase-only pixel sequence is formed. Finally, a non-periodic and non-converging sequence generated with the logistic map is used to scramble this sequence. After only preserving the phase data of the scrambled sequence, the real-valued ciphertext carrying the information of all original images is obtained. In the process of authentication, although no valid information can be discerned from noisy reconstructed images at a small sampling rate, the verification of original images can be efficiently accomplished using the nonlinear correlation maps. Besides binary masks, the parameters of the logistic map are served as secret keys. Due to their high sensitivity, the security of the proposed method is greatly enhanced. The proposed authentication mechanism has been demonstrated to be effective and robust through experiments. To our knowledge, it is the first time to implement multiple-image authentication using phase-only holograms, which can provide a new perspective for optical information security.

Image-based non-isotropic point light source calibration using digital fringe projection.

Accurate light source calibration is critical in numerous applications including physics-based computer vision and graphics. We propose an image-based method for calibrating non-isotropic point light sources, addressing challenges posed by their non-radially symmetric radiant intensity distribution and the non-Lambertian properties of the calibration target. We deduce an image formation model, and capture the intensity of the calibration target at multiple poses, coupled with accurate 3D geometry acquisition using the digital fringe projection technique. Finally, we design an iterative computational framework to optimize all the light source parameters simultaneously. The experiment demonstrated the high accuracy of the calibrated light source model and showcased its application by estimating the relative reflectance of diverse surfaces.

Research on ultraviolet-visible composite optical target simulation technology

This study proposes an ultraviolet-visible composite optical target simulation technique based on a liquid crystal display (LCD) spatial light modulation device to solve the problem of not being able to satisfy the demand for optical target simulation for both ultraviolet and visible light operating spectral ranges in a single system when composite simulation of multi-source spatial targets is performed. We establish a composite light source model of an ultraviolet light emitting diode (LED) and a xenon lamp to enhance the energy simulation of the ultraviolet portion, and the light is mixed and homogenized by an integrating sphere. We analyze the light transmission principle of LCD display devices and derive the equation for the relationship between its working band and transmittance. We design a transmission-type projection system with a wide spectral range and simulate the transmittance of the whole system, and demonstrate the optical target simulator can realize the simulation requirements of a wide working spectral range, high interstellar angular distance accuracy, and high magnitude accuracy.

FE-trans-net: Feature enhancement based single branch deep learning model for surface roughness detection

Real-time surface roughness measurement is crucial for modern manufacturing. Machine vision-based roughness measurement algorithms have the advantages of non-contact, high efficiency and adaptability. Light source is important for online machine vision-based roughness measurement. And different materials may need different light sources to extract more features. From the previous study, dual light sources are better than single light source for surface roughness prediction. However, it is inconvenient to assign two light sources for online detection equipment, and the two-branch model structure for dual light sources doubles the size of the model. To fully utilize the advantages of dual light sources, and avoid its disadvantages, a feature enhancement based single branch deep learning model FE-Trans-Net is proposed in this paper for surface roughness detection. Firstly, a dataset of different materials (Cu, Zn, Al, and Fe) shined with different light sources (white, red, green, red laser and green laser) is collected. Two most suitable light sources for different materials are chosen for dual light sources model as offline pre-training. In this model, lightweight cross-attention fusion (CAF-Trans) and graph convolutional channel attention (GCC-Atten) modules are designed to fuse the feature information of different light sources from the spatial and channel perspectives respectively, enabling the single-branch model to acquire the feature learning capability of different light sources. Then a single-branch network layer is remained as the online prediction. With the feature enhancement, it preserves the advantages of dual light source images, and has only half size of the dual light source model. Extensive experiments validate the effectiveness and generalization performance of the CAF-Trans and GCC-Atten modules, and the proposed FE-Trans-Net network achieves the best accuracy-efficiency tradeoff compared to other popular deep neural networks.

Design of a double lens freeform miniaturized antenna

The elliptical laser beam produced by a laser diode (LD) has asymmetrical divergence angle distribution and limits its application in long-distance space optical communication. In this paper, a double lens freeform miniaturized antenna design method is proposed to collimate, shape, and transmit elliptical beams from a LD. Based on the law of conservation of energy, refraction vector theory, equal optical path principle, and the three-dimensional point-by-point construction iterative method, two freeform surfaces on both lenses are constructed simultaneously. According to the simulation results, the maximum divergence angle of the output light is compressed to 4.92 µrad. The volume of the antenna is 1244.61cm3, which realizes the miniaturization of the antenna. In addition, the performance of the system is evaluated under different wavelength shifts, astigmatism based on the proposed improved line light source model, the offset of the light source, and the offset of both lenses. This paper provides a practical method for designing a simplified antenna that can collimate and shape laser beams and improve transmission efficiency. Furthermore, the proposed improved optimization method can provide a reference for the study of the initial parameters of lens freeform antennas.

MILO: Multi-Bounce Inverse Rendering for Indoor Scene With Light-Emitting Objects.

Recently, many advances in inverse rendering are achieved by high-dimensional lighting representations and differentiable rendering. However, multi-bounce lighting effects can hardly be handled correctly in scene editing using high-dimensional lighting representations, and light source model deviation and ambiguities exist in differentiable rendering methods. These problems limit the applications of inverse rendering. In this paper, we present a multi-bounce inverse rendering method based on Monte Carlo path tracing, to enable correct complex multi-bounce lighting effects rendering in scene editing. We propose a novel light source model that is more suitable for light source editing in indoor scenes, and design a specific neural network with corresponding disambiguation constraints to alleviate ambiguities during the inverse rendering. We evaluate our method on both synthetic and real indoor scenes through virtual object insertion, material editing, relighting tasks, and so on. The results demonstrate that our method achieves better photo-realistic quality.

Beam shaping for two-dimensional laser array by a computational model

The application of two-dimensional array laser source is more and more popular. Currently, many methods have been proposed for the collimation of laser beams; however, there is still a lack of research for the collimation of array laser sources so far. This paper presents a collimating method for array laser source. Through the calculation of the lens surfaces, the shape of the illumination spot on the target can be directly controlled, and the diameter of the lens can be directly constrained by setting the initial point coordinates. In this method, the edge-ray principle is used to simplify the extended light source model. The size and intensity distribution of the light spot irradiated by the light source to the target position were simulated by establishing a ray tracing model. The whole process was calculated using MATLAB software. The corresponding lens model can be obtained by fitting discrete coordinate points using Solid Works. Finally, the optical design software ZEMAX is used for simulation test. After shaping the laser light source with a luminous diameter of 1 mm, a circular and uniform spot is obtained at 100 m. For the point light source model, the divergence angle of 0.28° is achieved. Furthermore, an annular spot is also realized by setting the laser irradiation range, which provide a new solution for customized laser lighting.

Study of the differences among hyperspectral estimation models under different measurement light source conditions

ABSTRACT In hyperspectral remote sensing measurements, the spectral effective information extracted under different measurement light source conditions will produce differences, which in turn affects the robustness of the constructed models. Therefore, it is important to study the differences between hyperspectral estimation models under different measurement light source conditions to construct a general hyperspectral model of vegetation parameters under different light source conditions. In this paper, hyperspectral models are constructed from artificial and natural light sources, and the hyperspectral reflectance and the corresponding SPAD values of artificial and natural light sources under winter wheat, corn and tea tree were measured under the same time period and the same light measurement angle and height. The collected data were used to construct models for the four vegetation indices with better results after screening and to explore how to reduce model variability under different measured light source conditions. The results show that the difference between the artificial light source and natural light source models is significant (the coefficient of determination R2 is significantly different between the artificial light source and natural light source models), and the influence of different light sources on the construction of hyperspectral estimation models can be reduced by selecting vegetation indices. The linear regression equation model constructed by NDVI can effectively reduce the influence of different light sources on the construction of SPAD hyperspectral models and make the model more general. This study can provide new ideas and methods to investigate the differences in spectral models under different measurement light sources.

Efficient FMT reconstruction based on L1-αL2 regularization via half-quadratic splitting and a two-probe separation light source strategy.

Fluorescence molecular tomography (FMT) can achieve noninvasive, high-contrast, high-sensitivity three-dimensional imaging in vivo by relying on a variety of fluorescent molecular probes, and has excellent clinical transformation prospects in the detection of tumors in vivo. However, the limited surface fluorescence makes the FMT reconstruction have some ill-posedness, and it is difficult to obtain the ideal reconstruction effect. In this paper, two different emission fluorescent probes and L 1-L 2 regularization are combined to improve the temporal and spatial resolution of FMT visual reconstruction by introducing the weighting factor α and a half-quadratic splitting alternating optimization (HQSAO) iterative algorithm. By introducing an auxiliary variable, the HQSAO method breaks the sparse FMT reconstruction task into two subproblems that can be solved in turn: simple reconstruction and image denoising. The weight factor α (α>1) can increase the weight of nonconvex terms to further promote the sparsity of the algorithm. Importantly, this paper combines two different dominant fluorescent probes to achieve high-quality reconstruction of dual light sources. The performance of the proposed reconstruction strategy was evaluated by digital mouse and nude mouse single/dual light source models. The simulation results show that the HQSAO iterative algorithm can achieve more excellent positioning accuracy and morphology distribution in a shorter time. In vivo experiments also further prove that the HQSAO algorithm has advantages in light source information preservation and artifact suppression. In particular, the introduction of two main emission fluorescent probes makes it easy to separate and reconstruct the dual light sources. When it comes to localization and three-dimensional morphology, the results of the reconstruction are much better than those using a fluorescent probe, which further facilitates the clinical transformation of FMT.

Increasing beam stability zone in synchrotron light sources using polynomial quasi-invariants

The objective of this article is to propose a scheme to increase the stability zone of a charged particles beam in synchrotrons using a suitable objective function that, when optimized, inhibits the resonances onset in phase space and the dynamic aperture of electrons in storage rings can be improved. The proposed technique is implemented by constructing a quasi-invariant in a neighborhood of the origin of the phase space, then, by using symbolic computation software, sets of coupled differential equations for functions involved in nonlinear dynamics are obtained and solved numerically with periodic boundary conditions. The objective function is constructed by proposing that the innermost momentum solution branch of the polynomial quasi-invariant approaches to the corresponding ellipse of the linear dynamics. The objective function is optimized using a genetic algorithm, allowing the dynamic aperture to be increased. The quality of results obtained with this scheme are compared with particle tracking simulations performed with available software in the field, showing good agreement. The scheme is applied to a synchrotron light source model that can be classified as third generation due to its emittance.

Multi-Modal Non-Isotropic Light Source Modelling for Reflectance Estimation in Hyperspectral Imaging

Estimating reflectance is key when working with hyperspectral cameras. The modelling of light sources can aid reflectance estimation, however, it is commonly overlooked. The key contribution of this letter is a physics-based, data-driven model formed by a Gaussian Process (GP) with a unique mean function capable of modelling a light source with an asymmetric radiant intensity distribution (RID) and a configurable attenuation function. This is referred to as the light-source-mean model. Moreover, we argue that by utilising multi-modal sensing information, we can achieve improved reflectance estimation using the proposed light source model with shape information obtained by depth cameras. An existing reflectance estimation method, that solves the dichromatic reflectance model (DRM) via quadratic programming optimisation, is augmented with terms that allow input of shape information. Experiments in simulation show that the light-source-mean GP model had less error when compared to a parametric model. The improved reflectance estimation outperforms existing methods in simulation by reducing the error by 96.8% on average when compared to existing works. We further validate the improved reflectance estimation method through a multi-modal classification application.

P‐3.7: An Improved Dehazing Algorithm for Fog Image at Night

In order to solve the problem of lack of detail information and serious damage to the texture of the light source area when the dark channel prior dehazing algorithm processes fog images at night, this paper proposes a dehazing algorithm for nighttime fog images using the dark‐state point light source model. By introducing the dark state point light source model, the dark channel credibility weight factor and the pseudo dehazing image, combined with the nighttime image imaging model, the improved transmittance distribution is obtained, and the fog image at night is dehazed. The experimental results show that the image processed by the algorithm in this paper has little loss of texture details, high image definition, and the contrast between the light and dark of the image is better stretched, which can effectively dehaze the fog image at night.

Design of off-axis double reflection freeform miniaturized antenna

The asymmetrical divergence angle distribution of elliptical laser beam produced by a laser diode (LD) severely limits the application. In this paper, an off-axis double reflection freeform miniaturized antenna design method is proposed to collimate, shape, and transmit elliptical beams from LD. Based on the law of conservation of energy, reflection vector theory, and equal optical path principle, two freeform mirrors are constructed simultaneously by using the three-dimensional point-by-point construction iterative method. The simulation results show that the maximum divergence angle of the output light is compressed to 3.42 μrad, and the ratio of beam waist (RBW) of the output beam is reduced from 3.0000 to 1.0668 at the target plane (L=1 km). The volume of the antenna is 3229.99 cm 3 and the design realizes the miniaturization of the antenna. In addition, the effects of wavelength shift, astigmatism, and the offset of the light source on the collimation effect are analyzed. These research results will provide a practical method to collimate and shape the laser beam and increase the transmission efficiency of the optical communication system. Meanwhile, the proposed optimization method to obtain optimal parameters can be applied to design the initial structure of the freeform surface, and the method of constructing a line light source model in the design process can also provide a reference for the study of astigmatism of LD.

Development of a virtual teaching environment with Algodoo: ‘eye’ and ‘cactus type light source’ models

It is often necessary to enrich the teaching environment in order for students to learn optics in depth and to interpret the real optical situations with the information they have learned. In this study, a virtual teaching environment was developed using by Algodoo, a 2D simulation software. An eye model was created in order to explain the formation of the image in the eye in the teaching environment. Also, a cactus type light source model has also been developed to demonstrate that the image can be created in optics by using rays other than special rays. In order to show the success of the virtual teaching environment in modelling, previously known situations that the students had difficulty in understanding were simulated. Finally, some suggestions were made about the use of the virtual teaching environment.

A consistency method of discharge detection results at solar‐blind ultraviolet based on a radiation transmission model

Solar-blind ultraviolet (UV) discharge detection based on UV signals in the solar-blind band from 240 to 280 nm is an effective non-contact discharge detection method for electrical equipment, but there is still a problem that the detection results of different types of UV imagers are not comparable. To this end, by using standard light source and MODTRAN model, the relationship between the facular area and the radiant flux received by UV imagers was investigated by establishing a radiation transmission model for UV detection under different environmental conditions. Through analysis, it was found that the influence of humidity on the transmittance of the solar-blind band in atmosphere can be neglected, and the transmittance is slightly affected by atmospheric pressure, temperature, and detection distance under conditions suitable for UV detection. Moreover, a consistency formula for UV detection results was proposed, thus forming a consistency method for detection results suitable for various types of UV imager. Finally, the feasibility of the consistency method was verified by UV discharge detection tests with a rod-plate model and the absolute irradiance at discharge points of the rod-plate model measured by a grating spectrometer. The consistency method is conducive to the promotion of UV discharge detection technology.

Antibunching and superbunching photon correlations in pseudo-natural light

Since Hanbury Brown and Twiss revealed the photon bunching effect of a thermal light source in 1956, almost all studies in correlation optics have been based on light’s intensity fluctuation, regardless of fact that the polarization fluctuation is a basic attribute of natural light. In this work, we uncover the veil of the polarization fluctuation and corresponding photon correlations by proposing a new light source model, termed pseudo-natural light, embodying both intensity and polarization fluctuations. Unexpectedly, the strong antibunching and superbunching effects can be simultaneously realized in such a new source, whose second-order correlation coefficient g ( 2 ) can be continuously modulated across 1. For the symmetric Bernoulli distribution of the polarization fluctuation, particularly, g ( 2 ) can be in principle from 0 to unlimitedly large. In pseudo-natural light, while the bunching effects of both intensity and polarization fluctuations enhance the bunching to superbunching photon correlation, the antibunching correlation of the polarization fluctuation can also be extracted through the procedure of division operation in the experiment. The antibunching effect and the combination with the bunching one will arouse new applications in quantum imaging. As heuristic examples, we carry out high-quality positive or negative ghost imaging, and devise high-efficiency polarization-sensitive and edge-enhanced imaging. This work, therefore, sheds light on the development of multiple and broad correlation functions for natural light.

Thermodynamically revealing the effect mechanism of Cu on the interfacial metallurgical reaction for Al/steel welding-brazing joint

Developing excellent mechanical properties of Al/steel welding-brazing joint adding alloy elements for vehicle structure lightweight is in immediate need to reveal the effect mechanism of alloy elements on the interfacial metallurgical reaction. Here, the Al/steel welding-brazing joints with different Cu-coating thicknesses were designed to determine the effect rule of Cu on mechanical properties and interfacial microstructure evolution. More importantly, the action mechanism of Cu element on diffusion behavior of interfacial elements was clarified by synchrotron radiation light source and thermodynamic models. The results showed that appropriate Cu could improve the tensile strength of joints. And the Cu could efficiently inhibit the growth of interfacial brittle intermetallic compounds (IMCs) and the Fe diffusion into molten pool. Because the chemical potential of Fe in the molten pool increased with an increasing Cu content, which weakened the driving force of Fe diffusion. Besides, Cu and Al would react with each other to form Al 2 Cu with a lower Gibbs free energy under higher Cu content, which deteriorated the tensile strength of joints. Unambiguously, this work will deepen the understanding of the effect mechanism of Cu on the interfacial metallurgical reaction, which will be beneficial to the development and application of excellent properties of Al/Cu-coating/steel welding joints.

Single-scatter path loss model of LED-based non-line-of-sight ultraviolet communications.

Light-emitting diodes (LEDs) are popularly used as light sources in non-line-of-sight (NLOS) ultraviolet communications (UVC). However, currently reported single-scatter path loss (PL) models of NLOS UVC links assume that the radiant intensity of the light source is uniformly distributed within the beam divergence angle, which cannot well characterize the light emission pattern of LEDs. In this Letter, we propose a single-scatter PL model for LED-based NLOS UVC systems, and the corresponding analytical expression is derived by modeling the LED emission pattern as a Lambertian distribution. Monte Carlo simulations and experimental results are provided to verify the effectiveness of the proposed PL model. Results show that the proposed model can accurately predict PL results in actual situations. The root-mean-square error of the proposed PL model is only about 1 dB in typical scenarios with experimental results as benchmarks. Also, the proposed model is much easier to implement than the currently reported PL model with the light source model of a uniformly distributed emission pattern.

Design of defect detection system for semiconductor plastic packaging based on machine vision

At present, the ability of defect detection system to detect the position of semiconductor plastic packaging defects is poor, so a defect detection system of semiconductor plastic packaging based on machine vision is designed. In terms of hardware, based on machine vision technology, the system framework is determined, the camera, lens and light source models are selected, and the detection target image acquisition parameters are determined. In terms of software, according to the target image obtained by machine vision technology, the image is preprocessed, segmented and feature extracted to identify and detect the target image and detect the semiconductor plastic packaging defects. Experimental results: compared with the system selected in this experiment, the design system can accurately detect the defects in the semiconductor plastic packaging and the location of the defects.

The linearization of the relationship between scene luminance and digital camera output levels

The linearization of the relationship between scene luminance and digital camera output levels