Structured light methods are triangulation-based methods for acquiring range data. Light sections are projected and encoded by sequences of light intensities. The association of sequences of intensities to light sections, called 'coding,' plays a major role in range data acquisition by structured light methods. The coding has an influence on the resolution, the speed and the robustness of the measurement. In this paper we present binary codes, used in structured light methods. Ideally we want codes, which combine high resolution with a short measuring time. Such a code would be called 'efficient.' We present important properties of binary codes for structured light and rules for the construction of efficient codes. By applying these rules of construction we have found new, highly efficient, binary codes. The efficiency of the new codes is compared to the efficiency of well-known codes and the maximum efficiency that can be achieved.

A new range sensing method based on depth from defocus is described. It uses illumination pattern projection to give texture to the object surface. Then the image of the scene is split into two images with different focus settings and sensed simultaneously. The contrast map of the two images are computed and compared pixel by pixel to produce a dense depth map. The illumination pattern and the focus operator to extract the contrast map are designed to achieve finest spatial resolution of the computed depth map and to maximize response of the focus operator. As the algorithm uses only local operations such as convolution and lookup table, the depth map can be computed rapidly on a data-flow image processing hardware. As this projects an illumination pattern and detects the two images with different focus setting from exactly the same direction, it does not share the problem of shadowing and occlusion with triangulation based method and stereo. Its speed and accuracy are demonstrated using a prototype system. The prototype generates 512 by 480 range maps at 30 frame/sec with a depth resolution of 0.3% relative to the object distance. The proposed sensor is composed of off-the-shelf components and outperforms commercial range sensors through its ability to produce complete three-dimensional shape information at video rate.

Micromechanics is placing new demands on surface metrology equipment due to the fragility and small size of the mechanical components being fabricated. For research and development purposes both static measurement of component dimensions and thickness and dynamic measurements of deflection and vibrational amplitude are essential. This paper describes a new laser based non-contacting surface measurement system which is finding increasing application for these tasks. The system employs the dynamic focusing principle and has a measurement range of 1000 micrometers and a vertical resolution of 6 nm. The lateral resolution of the system is 1 micrometer and measurements may be made at up to 10 KHz. A built in observation window allows simultaneous measurement and observation of the measurement spot and surrounding region.

Moire contouring techniques provide a rapid means of producing a full-field contour or depth map of a given surface. When used in combination with CCD cameras, digital image processing, and mathematical analysis, a powerful measurement tool emerges. The use of this technology allows rapid quantification of surface shapes, features, and geometry. Corrosion measurement is sorely lacking a suitable measurement tool. Current methods are highly qualitative and operator-dependent. Moire systems provide an excellent solution, producing quantifiable, operator-independent results.

The optical system proposed combines together the axial motion technique (where the camera remains motionless during the experiment measuring absolute range) with the triangulation technique giving relative range with respect to a reference point. The characteristics of this optical system, such as standoff distance and range resolution, are theoretically determined. Experimental results are shown for ranges varying from 50 cm to 1.50 m with a depth resolution increasing from 1 mm to approximately 10 mm.

A robust and accurate polarization phase-based technique for material classification is presented. The novelty of this technique is three-fold in (1) it theoretical development, (2) its application, and (3) its experimental implementation. The concept of phase of polarization of a light wave is introduced to computer vision for discrimination between materials according to their intrinsic electrical conductivity, such as distinguishing conducting metals, and poorly- conducting dielectrics. Previous work has used intensity, color and polarization component ratios. This new method is based on the physical principle that metals retard orthogonal components of light upon reflection while dielectrics do not. This method has significant complementary advantages with respect to existing techniques, is computationally efficient, and can be easily implemented with existing imaging technology. Experiments for real circuit board inspection, non-conductive and conductive glass, and outdoor object recognition have been performed to demonstrate its accuracy and potential capabilities.

The object distance is an important parameter for image recognition and robot 3D view. This paper presents a novel method of image pixel multidither passive ranging. Based on Fourier transform theory of lens imaging, we derive the mathematical model of ranging, obtain the ranging error equation using lens equation, and analyze the effect of spectrum width and the limit for demodulation. It shows that the performance of this method has high sensitivity and precise measurement.

Various kinds of laser radar systems have become widespread. But most of these systems are the systems with amplitude processing of information. The polarization processing of information is used considerably rarely. As a rule these systems are based on measurement of Stokes vector. Practically, there are not systems based on the measurement of Mueller matrix. Although it is known that the last one contained the maximum of information on physical properties of objects. The mostly full absence of processing methods of information contained in Mueller matrix makes such order of matter. The original method of Mueller matrix analysis and a laser radar system based on it are presented in the paper. The system created has got an accuracy of 0.05% for single measurements. It is reached due to use of a control electro- optical polarization converter in the probing and receiving channels of the system. This makes it possible to fully automate processes of measurement and calibration of the system. It also makes available operational elasticity of the system: choice of measurement parameters (whole Stokes vector, Mueller matrix or particularly some of their elements) only by software means. Measurement time reached a few microseconds. The exception of influence of the optical radiation background component on the measurement result without use of an interference filter is a distinction of this system. It considerably increases the level of interference suppression. It is possible due to the intensity modulation of optical radiation in the system probing channel with simultaneous modulation of polarization. Another distinction of this system is the concept of processing of received information. On the base of this concept the following statement is laid: an arbitrary Mueller matrix always may be presented on the basis of amplitude and phase anisotropy matrices. There are some very important consequences of this statement. Namely, it allows us to characterize suitably the physical behavior of the object with respect to polarization phenomena and to perform a general classification of objects based on the above mentioned approach. Furthermore it is possible on this base to synthesize the polarization systems with given characteristics.

This paper addresses the problems associated with the inspection of geometric features of machined objects using three-dimensional data provided from an active stereo vision system. The inspection strategies we are concerned with are mainly concerned with verifying geometric tolerances to typical engineering requirements, in other words, verifying the presence and the dimensions of features and measuring feature relationships. This paper discusses how three-dimensional data may be processed to produce relevant features, information and how these may be interrogated to perform inspection automatically using the described vision system. A key issue here is how best to acquire the data in the form of a series of images on which the inspection is performed. The main purpose of this paper is therefore to address problems of choosing appropriate inspection strategies so that an object can be accurately inspected using the minimum possible number of views. This is achieved by reasoning with geometric models in order that the inspection methods can be planned effectively. Consideration of the vision system configuration and the accessibility of viewpoints on the object provide other factors that need to be considered in the reasoning process.

Among basic design issues for laser-based triangulation systems are imaging geometry considerations which can seriously impact the 3-D measurement accuracy performance. Among these are numerical aperture, sensor orientation, telecentricity, and triangulation angle. While system designers specifying these parameters generally take into account certain first-order design objectives such as requirements for field-of-view and optoelectronic signal- to-noise, they may overlook other imaging error sources such as certain aberrations, defocus, multiple reflections, and measurement non-linearity which are equally integral to providing a high level of 3-D measurement accuracy. These errors are described here in relation to triangulation imaging geometry constraints, and corresponding design trade-offs to minimize the errors are discussed.

A three dimensional vision system that can instantly image stationary and moving objects and measure surface areas and volumes of complex unknown shapes is described. This system is based on the four dimensional imager (4DI), a technology developed for the measurement of 3D objects, that provides high speed and high accuracy measurements. The 4DI sensor uses several cameras and a structured light laser which can provide up to 50,000 data points per measurement. It has several advantages over existing systems and its applications to surface area and volume measurements is described. Applications of the 4DI to surface area and volume measurements have revealed it to be effective, accurate, and faster than most existing systems. This technology allows objects of different sizes, from several feet to fractions of an inch, to be quickly and easily imaged. The imaging system and the different algorithms used for surface area and volume measurements are described.

This paper describes continuing work with three-dimensional (3-D) rotating line-scan vision systems in robotics and measurement. Mathematical algorithms have been developed for use with the line-scan arrangement allowing the extraction of three-dimensional co-ordinate information from an observed object workspace. To determine the measurement capability of the stereoscopic system, comparison is made between the system output data (calculated from image space values) and a calibrated volume in object space containing a distribution of target points. This paper describes the mathematical model and results pertaining to the current research demonstrate the use of the rotating line-scan scenario to the solution of specific applications where conventional sensor modalities may not be appropriate.

A comprehensive characterization of a surface can only be effected through a combination of visualization techniques and numerical descriptors -- no one technique suffices. In addition, for this analysis to bear a useful relation to function, the three-dimensional (3-D) nature of the surface must be taken into consideration. The latter consideration has meant that over the last decade, 3-D surface measurement techniques have become more prevalent and a large number of visualization techniques have emerged -- but there is as yet, no standard for measuring surfaces in 3-D. Recent work carried out by the University of Birmingham and Ecole Centrale de Lyon and sponsored by the Commission of the European Communities has sought to develop an integrated approach to three-dimensional micro-topography analysis. The long term objective of the work was the emergence of standardization in the area. The main aspect of this work relates to the definition of a clutch of fourteen parameters for surface topography analysis as a means of easing communication in the topography community as well as limiting the unnecessary proliferation of parameters whose functional implications are dubious. This paper sets out to describe the use of visualization techniques to assess 3-D surfaces as well as to present a detailed summary of the parameters developed at the University of Birmingham. These have now been incorporated into many commercial instruments and there is every likelihood that they will form the basis of a future international standard in 3-D topography.

This paper deals with the in-line three-dimensional measurement of circuit boards with mounted electronic components. The surface for inspection is scanned by a laser beam, and three-dimensional data are obtained by triangulation from the position of the reflected light measured with a position-sensitive detector (PSD). The location of reflected light is measured from a direction at an angle to the axis of the incident laser beam. The light from the target is reflected by the mirror which is positioned between the f (theta) lens and the target to increase the angle and the measuring sensitivity. The position of the image plane of the reflected beam varies according to the scanning position, which produces a similar effect to the variation of height. The measured value is corrected by a ROM set for three-dimensional space in data processing. The error in height measurement is 0.06 to 0.08 mm, and 0.025 mm accuracy is obtained in the neighboring area of the electronic component targets in practical inspection.

A new industrial 3D laser scanner is presented for measurement of solder paste screening quality in an automated PCB assembly line. Its unique scan optics provide telecentric illumination and imaging on a long scan line of 305 mm (12') at a maximum rate of more than 1000 scans per second. Synchronized height measurement is performed using a double triangulation scheme at large angles and wide aperture by means of a confocal like design based on elliptical mirrors. Using a spot size of 20 micrometers multiplied by 30 micrometers (FWHM), lateral resolution can be set electronically down to 10 micrometers pixel size. Depth resolution is 10 micrometers over a 2.5 mm measuring range. Combined with accurate and fast processing and control electronics this 3D sensor enables full 100% inspection at production speed.

This paper describes the machine concept and electronics of a new industrial 3D laser scanner for 100% measurement of solder paste deposits in an automated PCB assembly line. The throughput of the system can be optimized for the product type by the flexibility of scan speed (more than 1000 scans/sec), resolution (up to 20,000 pixels/scan line) and data rate (up to 10 multiplied by 10⁶ samples/sec). Sensor electronics involve customized position sensing detectors and low noise high speed amplifiers. Analogue preprocessing of the PSD signals guarantees a large dynamic range. The vision module simultaneously processes height and intensity data. The control electronics realize a precision synchronization of the PCB transport and an extremely stable but fast pullable pixel clock to the rotating polygon mirror. Modular parallel image processing is performed to produce data of the solder deposits such as volume, area, height, registration and bridging.

Three-dimensional imaging systems may be configured to provide a high figure of merit based upon speed, accuracy, and cost. Typically the object is imaged with a line scan arrangement which, depending upon the application, may have disadvantages of lack of symmetry and associated constraints imposed by directional illumination and viewing. Furthermore, a potential compromise often exists between scan efficiency and accuracy caused by unnecessary data acquisition in regions not containing information of interest. This paper illustrates a method for 3D scanning in a non-orthogonal system, particularly applicable for inspection of micro-electronic circuits and patterns, which mitigates the above mentioned tradeoffs. The use of optimized scanning patterns with high speed, addressable beam deflectors is discussed. Improvements associated with the imaging system are quantified with respect to standard line scan configurations at similar pixel rates.

In assuring the quality of aircraft, the skin quality must be free of surface imperfections. Surface imperfections such as scratches are unacceptable for cosmetic and structural reasons. Scratches beyond a certain depth are not repairable, resulting in costly replacement of an aircraft's part. Measurements of aircraft exterior surfaces require a ladder or cherry picker for positioning the inspector. Commercially-available computer vision systems are not portable, easy to use, or ergonomic. The machine vision system must be designed with these criteria in mind. The scratch measurement system (SMS) uses computer vision, digital signal processing, and automated inspection methods. The system is portable and battery powered. It is certified for measuring the depth and width of the anomaly. The SMS provides a comprehensive, analytical, and accurate reading. A hardcopy output provides a permanent record of the analysis. The graphical data shows the surface profile and provides substantial information of the surface anomaly. The factory and flight line use the SMS at different stages of aircraft production. Six systems have been built for use within Boeing. A patent was issued for the SMS in February 1994.

Scattering techniques are mostly used to investigate rough surfaces with rms values less than lambda 'the wavelength of the illumination beam.' An investigation was made on the scattering of laser light from rough surfaces having amplitudes larger than the wavelength of the illumination beam. A numerical solution of the Beckmann's scattering model, based on the facet model approach, was applied for the assessment of surface roughness. The proposed model was used to calculate the amplitude and wavelength of a number of periodic rough surfaces. A special scattering geometry was adopted in which the illumination beam was parallel to the roughness lay and the grazing angle was small. The numerical investigation included a number of periodic rough surfaces with a wide range of roughness amplitudes. The facet model was also used to calculate the characteristics of the investigated surfaces using their digitized profile coordinates. Numerical results were compared with the results obtained experimentally from real periodically rough surfaces. The facet model approach makes it possible to study wider range of rough surfaces with profiles that do not follow a defined mathematical form. Experimental results show a very good agreement with those obtained from the numerical solution using the facet model approach.

Laser based scanning methods have proven to be a valuable tool for a variety of 3D measurement applications. However, just as touch probes do not measure soft or flexible parts well, laser based methods have encountered problems with surfaces which are very rough or translucent. Either type of surface tends to spread the laser light out over an extended region, creating an uncertainty blob which can lead to false measurements. This paper discusses the types of errors associated with these light scattering surfaces, and efforts to minimize these effects through tight control of the viewing optics. Specific data is presented from tests performed with a laser based measurement probe on a variety of surfaces from smooth metal to translucent plastics.

An optical microscope has been adapted for 3-D inspection of small capillaries in thread spinnerets by placing a diffraction grating between the microscope objective and the specimen. We show how a grating was specified using a quantitative analysis of groove spacing and geometry. An illumination system was specified based on incident angle and light wavelength. Specimens are placed on a robotic stage for positioning, and repositioning affords multiple perspective views of the target depending upon the diffraction order visible to the objective.

This paper introduces and describes the concept of intelligent acquisition routines (IAR) and its relevance in surface microtopography data acquisition. In essence, IAR is a computer system that automatically computes and utilizes optimum sampling variables in surface micro- topography instrumentation. The functional specification of the proposed system is presented together with a complete system design of a prototypal system. It is argued that such a system would lead to an objective and reliable system of selecting sampling conditions for surface data acquisition. Such a system would ensure that maximum information is obtained from the surface and at minimum cost and would be a partial answer to the need for more intelligent topography instrumentation.

Holographic interferometric technique for measurement of laser diode crystal thermoelastic deformations is presented. Using this technique allows us to estimate thermoelastic stresses in laser crystal, active layer temperature and dynamics of heat transfer from laser crystal to heatsink.

This paper describes a laser scanning range finder that may produce a real time space encoding pattern. Laser diode is modulated by a programmable controller. So a space encoding sequential constructive laser beam is employed as an active illuminating source. Using less frames of space encoding patterns to produce a range image with high resolution is the main goal of this study. The calculation of 3D coordinates of each point on the measured object is explained briefly.

The past decade has seen the development of multispectral and hyperspectral imaging spectrometers for use in remote sensing applications in the aerospace business. Correspondingly, advanced electronic imaging techniques have been exploited for use in industrial inspection and manufacturing process control. TRW has been involved in hyperspectral imaging since 1989 for use in remote sensing of earth resources and has developed many instruments and related technologies which can easily be re-applied to unique industrial inspection applications. These instruments operate in the visible, near-infrared and short-wave infrared wavebands covering the range from 0.4 microns to 2.5 microns depending on the application. The exploitation of hyperspectral imagers for remote sensing has shown the power of spectral imaging for typing and discrimination tasks, which can be readily applied to industrial applications. In this paper we explain the relevant fundamentals of hyperspectral imaging and how it can be exploited for industrial inspection and process control tasks, particularly those that require color or spectral typing and discrimination. The associated technologies used to perform measurements and reduce the data also are described.

Combining electro-optic tunable bandpass filters with solid state cameras for multispectral imaging in remote-sensing applications is appealing to say the least, and has been attempted on a prototype level by a number of organizations. Several system design issues must be carefully considered for a commercial or military system that is both quantitative and versatile. This paper addresses selected electro-optical design issues for an imaging spectrometer based on a tunable filter. They include selection of filter parameters, selection of the imaging sensor, optical configuration, and calibration.

The acousto-optic tunable filter (AOTF) is a compact, rugged, solid-state spectrometer well suited to high frequency amplitude control and wavelength selection. The AOTF utilizes radio frequency (rf) acoustic disturbances in transparent materials to establish an electronically controllable diffraction grating. By launching the combination of several rf signals into the AOTF, multiple wavelengths of light can be diffracted simultaneously and light can be adaptively filtered to match the spectral profile of the sample. In addition, Hadamard transform (HT) spectroscopy can be performed with an AOTF serving as the polychromator. The integrated intensity on the detector is the combination of the encoded transmission or reflectance wavelengths. Hadamard transformation mathematics govern the multiplexed sequence allowing the efficient recovery of the spectrum. We describe the multiplexed AOTF spectrometer design as well as the design of a maskless HT imaging system.

Remote measurement of temperature requires thorough knowledge of the surface emissivity characteristics. Emissivity can be thought of as a figure of merit to how closely a material follows a blackbody radiator. The emissivity behavior often has a wavelength dependence and with accurate emissivity prediction, the temperature of a surface can be determined using a passive IR camera. It is both important to create precise emissivity models as well as develop instrumentation that can acquire the data accurately. To develop a model for materials such as metals, it can be observed that the primary contribution to the absorption characteristics can be attributed to the free electron plasma. It can be shown that the emissivity for heated metals in thermal equilibrium can be modeled as a second order polynomial. Consequently, a four color optical pyrometer can be used to accurately determine emissivity profile so that the true temperature can be determined.

Airborne optical remote sensing has recently seen an evolution from limited spectral discrimination into high spectral resolution imagery. Hyperspectral imagers now have the ability to sample a scene at both high spatial and high spectral resolution, permitting optimal selection from the available information to meet specific applications. Techniques have been developed which provide for high speed acquisition, radiometric calibration, conversion to spectral reflectances, geometric correction and interpretation of airborne hyperspectral data. The same technology currently in use for discrimination of subtle features in airborne scenes is available for industrial inspection applications which can benefit from combined spectral reflectance and imaging information.

Surface mount devices (SMDs), a dominant component type on printed circuit boards these days, are becoming smaller and growing more leads. This is in response to the shrinking of electronic components that is necessary for smaller electronic tools. The trend toward ever smaller components makes component leads more fragile and makes packages harder to handle. As a result, lead inspection has become more crucial than ever before. This paper includes a description of the object-oriented visual inspection tool (OOVIT) development for fine-pitch SMD components and its final structure.

Automatic reconstruction of occlusal surfaces of teeth is an application which might become more and more urgent due to the toxicity of amalgam. Modern dental chairside equipment is currently restricted to the production of inlays. The automatic reconstruction of the occlusal surface is presently not possible. For manufacturing an occlusal surface it is required to extract features from which it is possible to reconstruct destroyed teeth. In this paper, we demonstrate how intact upper molars can be automatically extracted in dental range and intensity images. After normalization of the 3D location, the sizes of the cusps are detected and the distances between them are calculated. In the presented approach, the detection of the upper molar is based on a knowledge-based segmentation which includes anatomic knowledge. After the segmentation of the interesting tooth the central fossa is calculated. The normalization of the spatial location is archieved by aligning the detected fossa with a reference axis. After searching the cusp tips in the range image the image is resized. The methods have been successfully tested on 60 images. The results have been compared with the results of a dentist's evaluation on a sample of 20 images. The results will be further used for automatic production of tooth inlays.

It is now well known and well accepted that stochastic algorithms are very powerful in the case of degraded image reconstruction. One of the classes of such an approach is simulated annealing based algorithms. However, the reconstruction of a degraded image using iterative stochastic process requires a large number of operations. We are investigating massively parallel implementation of image processing dedicated simulated annealing based algorithms. In this paper, we discuss a massively parallel implementation of Carnevali's algorithm. We debate the elementary processor's structure of such implementation.

Thermal wave imaging typically refers to a number of techniques in which a sample to be nondestructively tested is actively heated with either a pulsed or stepped source, and the time dependence of either the heating or cooling of the sample is monitored with an IR camera. Although these techniques have been used in manufacturing applications, the methods used for data analysis have been either too computation intensive for real time implementation, or too qualitative and subjective to be used reliably. Dynamic histogram analysis offers an alternative method for data interpretation that is computationally simple, yet quantitative and repeatable. Features which may be weak or ambiguous in the actual image can be easily identified using a data volume based on the time evolution of the histogram.

Requirements for automotive head lamp luminous intensity tests are introduced. The rationale for developing a non-goniometric photometric test system is discussed. The design of the Ford photometric vision system (FPVS) is presented, including hardware, software, calibration, and system use. Directional intensity plots and regulatory test results obtained from the system are compared to corresponding results obtained from a Ford goniometric test system. Sources of error for the vision system and goniometer are discussed. Directions for new work are identified.

Abstract not available.

We analyze material properties underlying visual appearance, such as surface bidirectional reflection distribution function (BRDF) and texture. We perform gonioradiometric measurements on bricks and fit the data to sets of models of specular and diffuse reflectance on rough surfaces in order to describe the composite reflection mechanisms, of the surfaces under study. We also acquire images and perform image texture statistical discrimination techniques to determine the textural differences in the surface appearance, resulting from the variation of illumination and viewing.

The quality of the image is crucial for the performance of a visual surface inspection system. The final image quality is affected by the properties of the illumination and imaging units. In order to evaluate the quality of these units a designer should be able to characterize their performance using quantitative figures of merit. In this paper the suitability of the modulation transfer function (MTF) for the figure of merit in visual web inspection is considered. An uncomplicated test set-up for measuring the system MTF of an imaging unit is presented and MTFs of typical web inspection imaging arrangements are introduced as a function of the f- number of the imaging lens. An appropriate set of defective samples from a paper manufacturing process is collected and imaged using the same arrangements as in the MTF measurements. Defect contrasts and signal-to-noise ratios are determined from the images and the results are compared to the corresponding MTF values. The objective of the study is to demonstrate the relationship between the MTF and the capability of inspection system to detect certain kinds of surface defects. The existence of this relationship is a necessity when MTF is considered as a figure of merit. Based on the experimental results surface defects are classified in two categories: (1) Defects whose detectivity is critically dependent on the MTF, and (2) defects whose detectivity is practically independent of the MTF. As a conclusion, examples are introduced on how the MTF measurement can be used as an imaging system evaluation and design tool.

Theoretical background of the multichannel (multifrequency and multipolarization) approach to radar remote sensing soil moisture and erosion state estimation is presented. Possible variants of radar data acquisition and their processing are discussed, they are based on preliminary experimental investigation results. The necessary operations of image-to-image and image-to-topology map superimposing as well as radar data preliminary filtering are considered. The results of remote sensing soil characteristic estimation using a multichannel airborne radar system are compared with in situ measurements, rather good accuracy of remote sensing estimates is proved.

An instrument for fine-machined pipe (longer than 10 m) inspection and measurement is introduced in this paper. The non-contact interior wall roughness measurement system based on light reflecting and scattering theory has a wide range (Ra from 0.012 micrometer to 4 micrometer) and is suitable for different types of machined surface measurements. The interior diameter is measured by a pair of gratings which produce Moire fringes. The accuracy of which is better than 5 micrometer for a pipe diameter greater than 100 mm. A CCD video camera inspection system is also installed on the measuring head to check the interior wall quality.

We report a polarization-based peak detection method for use in laser triangulation range sensors. Such sensors depend critically on the accurate detection of a pattern of laser light projected onto a scene, usually a point or line. Problems arise with highly specularly reflective surfaces, which can generate visible reflections of the light in various parts of the image. These can confuse intensity-based detection algorithms and lead to incorrect range measurements. This paper demonstrates the failure of intensity-based methods by reference to an existing triangulation scanner and sample depth data. A polarization-based method is proposed and we demonstrate experimentally the feasibility of polarization-based vision for disambiguating multiple specular inter-reflections of the laser light.