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This paper studies the iris recognition under unconstrained conditions. In these circumstances iris recognition becomes challenging because of noisy factors such as the off-axis imaging, pose variation, image blurring, illumination change, occlusion, specular highlights and noise. A robust algorithm for localization of non-circular iris boundaries is proposed. It can localize the iris boundaries more accurately than the methods based on the Daugman algorithm. Operating on the filtered iris images, this method determines the outer iris boundaries. First we implemented Canny algorithm for edge detection in the segmented image. Then we ran the edge link algorithm on the edge map, achieving edge lists of connected edge points and selecting the longest one that has maximum number of points for outer iris boundary localization. Finally, we investigated how to extract highly distinctive features in the degraded iris images. We present a sequential forward selection method for seeking a sub-optimal subset of filters from a family of Gabor filters. The recognition performance is greatly improved with a very small number of filters selected. Experiments were conducted on the UBIRIS.v2 iris database and promising results were obtained.

In this paper, we propose a method for accurate 3D reconstruction based on Photometric Stereo. Instead of applying the global least square solution on the entire over-determined system, we randomly sample the images to form a set of overlapping groups and recover the surface normal for each group using the least square method. We then employ fourdimensional Tensor Robust Principal Component Analysis (TenRPCA) to obtain the accurate 3D reconstruction. Our method outperforms global least square in handling sparse noises such as shadows and specular highlights. Experiments demonstrate the reconstruction accuracy of our approach.

Providing the surgeon with the right assistance at the right time during minimally-invasive surgery requires computer-assisted surgery systems to perceive and understand the current surgical scene. This can be achieved by analyzing the endoscopic image stream. However, endoscopic images often contain artifacts, such as specular highlights, which can hinder further processing steps, e.g., stereo reconstruction, image segmentation, and visual instrument tracking. Hence, correcting them is a necessary preprocessing step. In this paper, we propose a machine learning approach for automatic specular highlight removal from a single endoscopic image. We train a residual convolutional neural network (CNN) to localize and remove specular highlights in endoscopic images using weakly labeled data. The labels merely indicate whether an image does or does not contain a specular highlight. To train the CNN, we employ a generative adversarial network (GAN), which introduces an adversary to judge the performance of the CNN during training. We extend this approach by (1) adding a self-regularization loss to reduce image modification in non-specular areas and by (2) including a further network to automatically generate paired training data from which the CNN can learn. A comparative evaluation shows that our approach outperforms model-based methods for specular highlight removal in endoscopic images.

Endoscopy imaging is utilized to provide a realistic view about the surfaces of organs inside the human body. Owing to the damp internal environment, these surfaces usually have a glossy appearance showing specular reflections. For many computer vision algorithms, the highlights created by specular reflections may become a significant source of error. In this paper, we present a novel method for restoration of the specular reflection regions from a single image. Specular restoration process starts with generating a substitute specular-free image with RPCA method. Then the specular removed image was obtained by taking the binary weighting template of highlight regions as the weighting for merging the original specular image and the substitute image. The modified template was furthermore discussed for the concealment of artificial effects in the edge of specular regions. Experimental results on the removal of the endoscopic image with specular reflections demonstrate the efficiency of the proposed method comparing to the existing methods.

This paper presents a new Phase Measuring Deflectometry (PMD) method to measure specular object having\ud discontinuous surfaces. A mathematical model is established to directly relate absolute phase and depth, instead of phase\ud and gradient. Based on the model, a hardware measuring system has been set up, which consists of a beam splitter to\ud change the optical path, and two LCD screens to display the same sinusoidal fringe patterns. By using model-based and\ud machine vision method, system calibration is accomplished to provide the required parameters and conditions. The\ud verification tests are given to evaluate the effectiveness of the developed system. The 3D shape of an artificial step\ud having multiple specular surfaces and a concave mirror has been measured. Initial experimental results show that the\ud proposed measurement method can obtain 3D shape of specular objects with discontinuous surface effectively.

Computer-assisted cardiac surgeries had major advances throughout the years and are gaining more popularity over conventional cardiac procedures as they offer many benefits to both patients and surgeons. One obvious advantage is that they enable surgeons to perform delicate tasks on the heart while it is still beating, avoiding the risks associated with cardiac arrest. Consequently, the surgical system needs to accurately compensate the physiological motion of the heart which is a very challenging task in medical robotics since there exist different sources of disturbances. One of which is the bright light reflections, known as specular highlights, that appear on the glossy surface of the heart and partially occlude the field of view. This work is focused on developing a robust approach that accurately detects and removes those highlights to reduce their disturbance to the surgeon and the motion compensation algorithm. As a first step, we exploit both color attributes and Fuzzy edge detector to identify specular regions in each acquired image frame. These two techniques together work as restricted thresholding and are able to accurately identify specular regions. Then, in order to eliminate the specularity artifact and give the surgeon a better perception of the heart, the second part of our solution is dedicated to correct the detected regions using inpainting to propagate and smooth the results. Our experimental results, which we carry out in realistic datasets, reveal how efficient and precise the proposed solution is, as well as demonstrate its robustness and real-time performance.

A mathematical model of space target illumination characteristics is established based on the basic theory of radiation by considering geometry, background, and material characteristics of the space target. Using the model, the spatial distribution of scattering light intensity from the space target is calculated with the modeling and blanking technique of target when being illuminated by the sun. The relations of specular reflection with the position, geometry, materials and other attributes of the space target are analyzed. Furthermore, the effect of specular reflection on space target detecting is discussed. A method of characteristic simulation of space target is presented. The simulation result indicates that polyhedral structure, mirror surface, or solar sail is easy to cause specular reflection. It shows the effect of specular reflection is helpful for space target detection and identification.

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.

Photometric stereo is a technique for estimating the 3-D depth of a surface using multiple images taken under different illuminations from the same viewing angle. Most existing models make use of Lambertian reflection and an orthographic camera as underlying assumptions. However, real-world materials often exhibit non-Lambertian effects such as specular highlights and for many applications it is of interest to consider objects close to the camera. In our work, we aim at addressing these issues. Together with a perspective camera we employ a non-Lambertian reflectance model, namely the Blinn-Phong model which is capable to deal with specular reflection. Focusing on the effects of specular highlights, we perform a detailed study of one-dimensional test cases showing important aspects of our method.

Stray light in an endoscope largely contributes to whether a signal can be detected or not. This FRED analysis used a novel endoscope designed for the fallopian tubes to show how common endoscope elements cause stray light contamination, and to offer suggestions on how to mitigate it. Standard and advanced optical raytracing was performed. Raytrace reports determined which ray paths caused the highest power and irradiance distributions after reflecting one or more times from an element in the system. The analysis revealed that the cover plate introduced significantly more stray light into the system than other endoscope components. The imaging lenses and variable stop reflectivity had a negligible impact on the signal. To obtain acceptable signal-to- noise ratio, the source numerical aperture (NA) was lowered to 0.35 and 0.25 to keep the stray light within the same order of magnitude and an order of magnitude lower, respectively than the desired signal. There was a single specular reflection off of the cover plate distal surface. This illumination reflected back into the imaging fiber without first scattering off the tissue, which resulted in high stray power at the back of the imaging lenses. The specular light appeared brighter at higher source NAs and saturated the desired signal at the edge of the imaging fiber. An NA between 0.25 and 0.35 provides maximum illumination to image the tissue, with minimal stray light degrading the desired signal.

High quality video sequences are required for the evaluation of tone mapping operators and high dynamic range (HDR) displays. We provide scenic and documentary scenes with a dynamic range of up to 18 stops. The scenes are staged using professional film lighting, make-up and set design to enable the evaluation of image and material appearance. To address challenges for HDR-displays and temporal tone mapping operators, the sequences include highlights entering and leaving the image, brightness changing over time, high contrast skin tones, specular highlights and bright, saturated colors. HDR-capture is carried out using two cameras mounted on a mirror-rig. To achieve a cinematic depth of field, digital motion picture cameras with Super-35mm size sensors are used. We provide HDR-video sequences to serve as a common ground for the evaluation of temporal tone mapping operators and HDR-displays. They are available to the scientific community for further research.

Gloss is the second most relevant visual attribute of a surface beside its colour. While the colour originates from the wavelength repartition of the reflected light, gloss originates from its angular distribution. When an observer is asked to evaluate the gloss of a surface, he always first orientate his eyes along the specular direction before lightly tilting the examined sample. This means that gloss is located in and around the specular direction, in a peak that is called the specular peak. On the one hand, this peak is flat and broad on matte surfaces on the other hand, it is narrow and sharp on high gloss surfaces. For the late ones, the FWHM of the specular peak is less than 2° which can be quite difficult to measure. We developed a dedicated facility capable of measuring specular peak with a FWHM up to 0,1 °. We measured the evolution of the peak according to the angle of illumination and the specular gloss of the sample in the restricted field of very glossy surface. The facility and peaks measured are presented in the paper. The next step will be to identify the correlations between the peak and the roughness of the sample.

The geometric conditions of diffuse illumination, 8 degree observation, specular light include (SCI) and specular light exclude (SCE) often be employed to measure the surface color of material with different gloss value. The SCE condition is usually realized by setting light trap on the integrating sphere. However, the structure of light trap has its negative influence on the light intensity uniformity, and can led to the inaccuracy of the test results under SCE or SCI condition. Due to the different sizes of the light trap, structures of the measurement instrument will led to inter instrument agreement among the measurement of sample with different gloss. This paper designs a measuring structure to measure the SCE and SCI results simultaneously; proposes a method to calculate the 8 degree gloss value based on the SCE and SCI test result; proposes a computing modal to modify the SCI and SCE measure result based on the 8 degree gloss value, experimental verifying is also carried out. The experimental results demonstrate the structure and modified model effectively reduce the negative influence of light trap. The inter instrument disagreement caused by the geometric dimension of different light trap is significantly decreased.

Polyp size quanti cation is currently the main variable for deciding the patient treatment during an endoscopic procedure. Nowadays, the polyp size is estimated by an expert, even when using devices that are provided with calibrated grids. As such estimation is highly subjective, automatic approaches have come to be appealing but also challenging because the polyp shape and appearance variability, the di erent types of motion present during the capture and the specular highlight noise. This work presents a novel approach to automatically estimate gastrointestinal polyp shapes in a video endoscopic sequence using spatiotemporal information. For doing so, a local spatio temporal descriptor is built up to obtain an initial segmentation since the polyp is the region with more movement. Then, an initial polyp manual segmentation outlines a region of interest (RoI) in the rst frame of the sequence and used as a reference for the polyp tracking during the sequence. Afterward, an exhaustive cross-correlation of the initial shape is carried out along the sequence and fused with the motion descriptor to re ne the original segmentation. The proposed approach was evaluated in 15 real video sequences achieving an average DSC score of 0:67% .

The three-dimensional (3D) metrology for specular reflecting surfaces attracted much attention due to their various applications in optics, electronics, or semiconductor industry. Fringe reflection technique is an effective tool to measure the specular surface slopes (gradient information), and then reconstruct the surface shape from gradient. However, most of the fringe reflection systems are built up for middle size (~10,000 mm 2 ) or larger size (~100,000 mm 2 ) objects by using the off-the-shelf desktop displays. In order to measure samples with smaller size (~200 mm 2 ) with higher measuring resolution, a compact fringe reflection system is proposed. The performance of the compact specular 3D shape measurement system is demonstrated with experiments.

Early detection and excision of melanoma skin cancer is crucial for a successful therapy. Dermoscopy in direct contact with the skin is routinely used for inspection, but screening is time consuming for high-risk patients with a large number of nevi. Features like symmetry, border, color and most importantly changes like growth or depigmentation of a nevus may indicate malignancy. We present a non-contact remote imaging system for human melanocytic nevi with homogenous illumination by an ultra-bright white LED. The advantage compared to established dermoscopy systems requiring direct skin contact is that deformation of raised nevi is avoided and full-body scans of the patients may timeefficiently be obtained while they are in a lying, comfortable position. This will ultimately allow for automated screening in the future. In addition, calibration of true color rendering, which is essential for distinguishing between benign and malignant lesions and to ensure reproducibility and comparison between individual check-ups in order to follow nevi evolution is implemented as well as suppression of specular highlights on the skin surface by integration of polarizing filters. Important features of the system which will be crucial for future integration into automated systems are the possibility to record images without artifacts in combination with short exposure times which both reduce image blurring caused by patient motion.

A subjective study was conducted to investigate the preferred maximum and minimum display luminances in order to determine the dy namic ranges for future displays. Two studies address the diffuse refle ctive regions, and a third study tested preferences of highlight regions. Preferences , as opposed to detection thresholds, were studied to provide results more directly relevant to the viewing of entertainment or art . Test images were specifically designed to test these limits without the perceptual conflicts that usually o ccur in these types of studies. For the diffuse range, w e found a display with a dynamic range having luminances between 0.1 and 650 cd/m 2 matches the average preferences. However, t o satisfy 90% of the population, a dynamic range from 0.005 and ~3,000 cd/m 2 is needed. Since a display should be able to produce values brighter than the diffuse white maximum, as in specular highlights and e missive sources, the highlight study concludes that even the average preferred maximum luminance f or highlight reproduction is ~4 ,000 cd/m

Novel techniques is proposed for rendering specular smooth surfaces in polygon-based computer holography that features reconstruction of fine 3D images accompanied with strong sensation of depth. The technique is an improvement of the conventional technique for rendering flat specular surfaces. In this technique, phase distribution that works as a diffuser is divided into small rectangular segments and the reflection direction is controlled for each segment. In addition, this new method increases freedom for lighting the object. Two high-definition CGHs are calculated by the proposed method. One of them is fabricated and demonstrated for verifying the technique.

We propose a technique to shade reconstructed images of electronic holography. Our technique modifies the zone plate technique, which represents a three-dimensional object as an aggregate of object points and zone plates, which generate object points, are summed to calculate a hologram. Our technique is based on the Phong reflection model developed for computer graphics, which assumes that light reflected from an object consists of three components: diffuse, specular, and ambient reflection light. Among these components, only the specular component depends on the position of the camera (or the eye). A holographic reconstructed image changes depending on the viewing direction. Therefore, the specular component changes for different viewing directions. Because light modulated by a zone plate converges to an object point, we assumed that light is redirected differently at each point on the zone plate. Therefore, two-dimensional amplitude modulation of the zone plate would generate an object point that emits light with different intensities in different directions. The proposed two-dimensional amplitude modulation comprises variable and constant modulations: the former one controls the specular component and the latter one controls the diffuse and ambient components. We experimentally verified the proposed technique.

Since an imperfection can occur anywhere over the surface of a component of any size or even within an assembled system, measurement cannot take place until it has been found and located in the measurement area. Inspectors often prefer to retain inspection methods for locating imperfections that they themselves have developed. This is inevitable due to the subjective nature of visual inspection. This chapter describes the currently favored methods for the objective measurement of imperfections. Many different proposals have been made for the rapid inspection of optical elements for imperfections. A prime consideration is comfort for the observer, but with sufficiently high levels of illumination to permit detection of the smallest imperfections of interest. Clean laminar airflow over the specimen will minimize dust deposits. Dark-field viewing, with the aid of a magnifier if necessary, with the eye positioned to collect radiation scattered over low angles, is generally regarded as the preferred arrangement. A typical inspection station is shown in Fig. 6.1. The component under inspection, shown here, is being viewed in transmitted light by magnifier. A component to be inspected in reflected light is placed in the bottom corner of the box and tilted so that the specular light just misses the eye. Due to the directional effect of light scattered by a scratch, the component may need to be rotated in its plane so that the eye can receive as much scattered light as possible.

BATC has developed a new stray light test facility (SLTF) and performed initial tests demonstrating its capabilities. The facility interior is nearly all black and is a Class 5 cleanroom. Coupled with a double cylindrical chamber that reflects the specular light away from the instrument under test, the stray light control in the facility is excellent. The facility was designed to be able to test a wide variety of instruments at a range of source angles from in-field to large off-axis angles. Test results have demonstrated PST performance below 1E-9.

For over thirty years researchers have been trying to solve the shape from shading problem of determining 3D shape from a single image with a single light source. The basic problem of determining shape from shading is made more difficult due to challenges of light orientation, camera type, ambiguity, multiple materials, and specular highlights. This paper shows how some of these challenges can be overcome through the use of other techniques such as image segmentation and stereopsis. We present a new hybrid method of shape from shading that can be used to autonomously capture 3D information from two 2D images of single objects with multiple peaks and multiple materials with specular components.

This paper presents a novel technique for measuring the three-dimensional shapes of specular surfaces. Differing from the conventional techniques, the diffusive light source in our technique can be moved vertically to two different positions, and at each position the phase distribution of the deformed fringe pattern is measured, so that the orientation of incident light for each pixel is tracked through the corresponding phases. The 3-D coordinates of points on the specular surface are further determined. In so doing, the restrictions and limitations of the existing techniques in computational complexities, phase ambiguities and error accumulations are eliminated. The validity of this technique is demonstrated by experimental results.

When specular surface is imaged on a group of CCD cells, the image usually suffers from saturation and blooming problem. This problem is a serious obstacle to applying optical profiling methods based on structured light to specular objects. In this paper, a phase-based profiling system combined with a spatial light modulator in the imaging part is proposed to measure three dimensional shape of partially specular surfaces. The spatial light modulator prevents the image sensor from being saturated. In this way, projected fringes are well imaged and their phase information is correctly extracted. The system configuration and transmittance control scheme are explained in sequence. This idea is verified by experimental results, in which phase information is successfully extracted from the areas which are not normally measurable due to saturation.

LCD backlighting applications require diffuse illumination over an extended area of a display unit while maintaining high luminance levels. Since such applications involve multiple reflections within a reflective cavity, the efficiency of the cavity can be affected significantly by relatively small changes in the reflectance of the cavity material. Materials with diffuse rather than specular (or mirror-like) reflectance scatter light, averaging out hot spots and providing a uniform field of illumination. Reflectors with specular components tend to propagate non-uniformities in the illuminator system. The result is a spatial variation in brightness visible to the viewer of the display. While the undesirability of specular materials for such applications has been widely recognized, some diffuse materials in common use exhibit a significant specular component. This paper describes a method for measuring the specular component of such materials, and presents a simple approach to evaluating the effect of such secondary specular behavior on the performance of a backlight cavity. It is demonstrated that significant differences exist among available diffuse reflectance materials, and that these differences can lead to significant differences in the performance of the displays in which these materials are used.

We address the problem of re-rendering images to high dynamic range (HDR) displays, which were originally tone-mapped to standard displays. As these new HDR displays have a much larger dynamic range than standard displays, an image rendered to standard monitors is likely to look too bright when displayed on a HDR monitor. Moreover, because of the operations performed during capture and rendering to standard displays, the specular highlights are likely to have been clipped or compressed, which causes a loss of realism. We propose a tone scale function to re-render images first tone-mapped to standard displays, that focuses on the representation of specular highlights. The shape of the tone scale function depends on the segmentation of the input image into its diffuse and specular components. In this article, we describe a method to perform this segmentation automatically. Our method detects specular highlights by using two low-pass filters of different sizes combined with morphological operators. The results show that our method successfully detects small and middle sized specular highlights. The locations of specular highlights define a mask used for the construction of the tone scale function. We then propose two ways of applying the tone scale, the global version that applies the same curve to each pixel in the image and the local version that uses spatial information given by the mask to apply the tone scale differently to diffuse and to specular pixels.

We propose a new technique to reproduce faithfully both the color and the gloss of an object on a computer, using multispectral images. An imaging spectrograph equipped with a monochrome charge-coupled device (CCD) camera is fixed in front of the target object. Multispectral images of a linear portion of the object's surface are captured at suitable intervals by a measuring system which comprises a light source orbiting the target object. To obtain spectral images for the whole surface, the target object is also rotated. The reflection is separated into diffuse and specular components, according to the dichromatic reflection model, and the diffuse parameters are estimated at 5-nm intervals between 380nm and 780nm for each pixel. Since the CCD camera used to capture images has a limited dynamic range, we suppose that the specular reflection is independent of wavelength for the dielectrics, and that the specular reflections are saturated, although some of them can be non-saturated. We adopt the Torrance-Sparrow reflectance model for the specular reflection, and estimate the specular parameters using the least squares method for each pixel. Our experimental results reveal that the diffuse parameters for the color and the specular parameters for the gloss of the target object are satisfactorily estimated.

One of the biggest clues in specularity detection algorithms is the color of the specular highlights. There is a prevalentassumption that the color of specularities for materials like plastics and ceramics can be approximated by the color of theincident light. We show that such an assumption is not generally appropriate because of the effects of the Fresnel reflec-tance coefficient and its dependence on wavelength. Our theoretical analysis establishes that the sensitivity of the Fresnelterm to the wavelength variations of the refractive index can be at least as large as 15%. Our experiments demonstratethat, even with traditional RGB color cameras, the recorded color of specular highlights is distinct from the color of theincident light. Furthermore, by computing the spectral gradients (i.e. the partial derivatives of the image with respect towavelength) at specular regions we can isolate the Fresnel term up to an additive illumination constant. Our theory is sup-ported by experiments performed on multispectral images of different colored plastic tiles. The refractive indices of theopaque plastics were measured using a specialized spectroscopic ellipsometer. The computed spectral gradients of the tilespecularities exhibited a less than 2.5% deviation from the predicted theoretical values.Keywords : specular highlights, plastics, Fresnel term, index of refraction, spectral gradients.

Lighting plays an important role in many applications of computer vision, machine vision and computer graphics. Often, an object needs to be photographed multiple times, in each of which lighting comes from a different direction. Lighting which uses a single source per image is prone to dynamic range problems, especially in dark areas and in specular highlights. In addition, it becomes a practical problem to use an increasingly larger number of discrete sources (say, hundreds). To counter these problems we develop a novel illumination strategy. In each image, multiple light sources irradiate the scene simultaneously. The set of light sources is different in each image, but not mutually exclusive. Then, the contribution of each individual source is extracted in computational post-processing. The number of acquired images using this approach is the same as the number used in single-source images. However, thanks to the multiplexing of light in the raw images, more light is used from a variety of directions, diminishing problems of dynamic range. We derive the optimal illumination multiplexing scheme, which increases the SNR of the images by (√n}/2, where {n} is the number of sources. This lighting strategy is complemented by a novel illumination setup. The setup is easily built and scaled to a huge number of sources, and is controllable by the computer. These advantages are obtained since the apparatus is based on indirect lighting originating from an LCD projector.

This white paper reviews the method for making bearer printed information indistinguishable on a non-copyable substrate when a copied attempt is made on either an analog or digital electrostatic photocopier device. In 1995 we received patent number 5,704,651 for a non-copyable technology trademarked MetallicSafe. In this patent the abstract describes the usage of a reflective layer, formed on a complex pattern region and having graphic or font size shapes and type coordinating to particular patterns in the complex pattern region. The technology used in this patent has now been improved and evolved to new methods of creating a non-copyable substrate trademarked CopySafe+. CopySafe+ is formed of a metallic specular light reflector, a white camouflaged diffused light reflector, and the content information 'light absorption' layer. The synthesizing of these layers on a substrate creates dynamic camouflaged interference patterns and the phenomena of image chaos on a copy. In short, the orientation of a plurality of spectral and diffused light reflection camouflaged layers, mixed and coordinated with light absorption printed information, inhibits the copying device from reproducing the printed content.

A method is proposed for estimating various parameters of a reflection model using both the image data and the range data of an object surface. A unified measuring system, combining a laser range and a multi-band camera system, is made for acquiring the 3D shape data and the spectral reflectance data of the object surface. First, the diffuse reflection component and the specular reflection component at every pixel are obtained using the observed images at two illumination directions and the surface normal vectors calculated from the range data. The spectral reflectance is then estimated from the diffuse reflection component. Next, the extracted specular reflection component is fitted to the specular function of the Torrance-Sparrow model. The performance of the proposed method is examined on an experiment using a painted object in details. We show the estimation results for (1) spectral reflectance, (2) surface roughness, and (3) diffuse and specular intensities. The overall feasibility of the proposed method is confirmed based on computer graphics images created by using the estimated parameters.

Modeling light reflection from rough surfaces is an essential problem in computer graphics, computational vision, and multispectral imaging. Existing methods commonly separate the total reflection into diffuse and specular components, but this leads to the nonphysical arbitrariness in choosing the relative weights for the two components. There also lacks a sufficient model for the self-shadowing effect, which is important for rough surfaces. To eliminate these drawbacks, we propose a new reflection model entirely using physical parameters. The surfaces are assumed homogeneous, isotropic, and microscopically smooth, and their height probability densities are assumed Gaussian. Thus we derive the one-bounce reflection through Fresnel coefficient, self-shadowing factor, and probability function for surface orientation. The shadowing factor is calculated analytically from the statistical properties of a rough surface, including the height probability density and correlation function, and it agrees well with numerical simulation. Since all involved parameters in this model are physical, it can be easily verified with measurement. Besides, as a single term, this model generates a sharp specular highlight when a surface is smooth and shows diffuse behavior when the surface is rough. This advantage will be shown through rendered images.

An integral part of computer graphics, machine vision and human vision understanding is modeling how a surface reflects light. There is a substantial body of work on models describing surface reflectance ranging from purely matte to purely specular. One of the advantages of diffuse reflectance is that the color and the intensity of the reflected light are separable for most materials. Color is determined by the chromophores of the material, while intensity depends on the scene geometry. In specular highlights the color and the intensity of a specularity depend on both the geometry and the index of refraction of the material, which in turn is a function of wavelength. The graphics and vision communities often employ the following simplifying assumption when modeling specular highlights: For non-conductive materials the color of the specularity is the color of the light source. We will show that in most cases this assumption is violated. Theoretical analysis demonstrates that even for non-metallic surfaces the reflectivity ratio at specularities varies with both wavelength and angle of incidence. Furthermore, our experiments with a multispectral sensor clearly show that the deviation of the color of the specularities from the color of the incident light can be consistently measured.

A texture image has often been used to reproduce real objects in computer graphics (CG). However, the appearance of the object is not reproduced appropriately when lighting conditions of real and CG environments are not consistent. To overcome the problem, we propose a new method for estimating non-uniform reflectance properties which consist of diffuse reflectance, specular reflectance, and surface roughness parameters with convex and concave surface. Such a surface reflectance estimation requires object surface normal, light source position, camera position, and surface color under different illumination conditions for each surface point (pixel). Therefore, we use a laser rangefinder which takes accurately registered range and color images of an object. It is difficult to estimate a specular reflectance parameter, since the specular reflection is observed only within a fixed range of angles among the camera, light source, and viewing position. In our method, an algorithm is proposed to determine light source positions with which the specular reflection component is strongly observed over the surface. We also consider a self shadow and make calculation stable by separating two reflection components. The Torrance-Sparrow model, which accurately represents object reflectance properties, is employed to estimate reflectance parameters by using color images under multiple illumination conditions. In our experiments, a measured object has partially different specular reflection and surface roughness parameters. Experiments show the usefulness of the proposed method.

During the design and manufacturing processes of specular surfaces, waviness and shape defects may occur, reducing the quality of the surface regarding its visual appearance and/or its technical performance. Typically, these defects are only a few micrometers deep and a few centimeters wide. Beside the plain defect recognition, the reconstruction of the surface topography is of great interest, because it allows to characterize defects quantitatively. To reconstruct specular surfaces, a reflection technique based on structured-lighting is used. The specular object is considered as a part of the optical system. This technique is sensitive to changes of the slope of the surface. A series of patterns produced by an illumination system and reflected at the specular surface is observed by a camera. The distortions of the patterns in the acquired images contain information on the shape of the surface. This information is recovered through a model of the imaging function of the optical system. In contrast to previous approaches, with the proposed method it is possible to reconstruct the topography of the specular surface without an iterative approximation. This is achieved by applying a smoothness constraint to the surface data and directly calculating the surface topography from the imaging function.

A telecentric flying spot scanner consisting of a rotating multifaceted mirror and a 500 mm diameter parabolic mirror for the inspection of large flat and embossed surfaces up to 400 mm wide is described. Real time high resolution 2-D images at three different angles are obtained providing various types of intensity profiles of the surface. These channels are linearly combined to form pseudo-color images. The image size per channel is limited to about 4 Mbytes by the maximum direct memory access buffer area used by the image grabber card. Images with variable resolutions (for example, 2048 X 2048 pixel or 10000 X 400 pixel) are therefore feasible. Photomultiplier tubes are used for light detection to offer good signal-to-noise ratio and to cover a wide dynamic signal detection range varying from scattered to specular light. Composite images for ceramic tiles with different textures, colors and surface features are presented. These images show some interesting features of the surface profile and texture which otherwise could not be observed using a CCD camera or a single channel scanner. Subtle flaws such as fine scratches and finger marks on the surface and the surface texture variations can be easily identified.© (1999) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Effective computer graphic applications should accurately convey 3D shape. Previously, we investigated the contributions of shading and contour, specular highlights, and light source direction to 3D shape perception. Our experiments use displays of convex solid objects based on the superquadric parameterization, permitting continuous variation in their cross-sectional shapes. Our present work concerns the impact of surface markings. Rotating wireframe or uniformly shaded objects may produce perceptually distorting shapes. We investigate the idea that such distortions interfere with shape judgements, and that surface markings may either enhance perceptual accuracy by encouraging stability, or impair it by interfering with global shading patterns. Our displays include rotating objects with no surface markings, stripes, latitudinal or longitudinal stripes, each with two different scene illuminations. Observers view pairs of objects, a target shape and a second object whose shape they adjust, using mouse clicks, to match that of the target. Our principal result is that these surface patterns do not enhance performance, even though the chosen stripe intensities minimize interference with global shading, and the stripe patterns may actually encode surface curvature. We are now investigating alternatives for applying surface patterns to modelled objects, including hardware supported texture mapping. Our long term goal remains the identification of a comprehensive set of conditions for optimizing shape understanding of graphic objects.© (1998) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

An analytical solution to the two-flow equations developed by Bostater, et al. is modified, and a sensitivity analysis is performed on the remote sensing model which contains both diffuse and specular light components. The resulting model simulates the solution to two different cases of the two- flow equations. The Case I model uses the two-flow irradiance equations where sub-surface collimated or specular irradiance is evaluated implicitly. All of the irradiance is assumed to become completely diffuse when it enters the water column. The Case II model uses equations that explicitly include collimated irradiance in the water column. Both models are simulated in three different ways in this paper based on the vertical distribution of the constituents in the water column. The concentrations of the water quality parameters can be assumed (a) constant with depth, (b) divided into three distinct layers with different concentrations in each layer, or (c) divided into n layers of differing concentrations. The solutions to the two-flow equations with and without the specular, collimated irradiance and assuming a uniform water column, are given by Bostater et. a. This paper focuses on the derivation of the layered Case I and II models, a sensitivity analysis performed on the Case II model coefficients, and comparisons of the output from the differing model assumptions are presented.

A new shading model for linear light source is presented. It accounts for both diffuse reflection and specular reflection of the illuminated surface. By regarding a linear light source as a directional rectangular light source with infinitesimal width, a simple formula is derived for calculating the diffuse reflection component. The specular reflection component is represented by an integration taking Phong's specular model as the kernel and evaluated by a linear approximation. Finally, an efficient shadow detection algorithm for linear light source is proposed. The images rendered with the shading model are very photo realistic.© (1996) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

The radiative properties of cirrus clouds are of wide interest because of the visually striking effects they produce, the significant global coverage of cirrus and thin cirrus, and their intrinsic complexity. Within a limited class of crystal shape and size, hydrodynamic forces tend to orient the crystals with their long axis nearly horizontal, which can produce a narrow, intense specular reflection. First-principles scattering calculations are especially difficult because the scatterers are diverse in shape, size and tilt distributions. However, a geometric optics approximation to the single-crystal BRDF combined with plausible distributions of flutter-angle can be used to both simulate the appearance of the specular radiance feature, and extract microphysical cloud information from imagery of the specular point. This paper will review an empirical approach to radiative-transfer in the specular layer and integrate two different models for the specular BRDF into a cloud radiance simulation code. This will then be used to illustrate the appearance of the subsun and Bottlinger's ring for various spectral bands. The extraction of microphysical information on the specular layer from vis - near-ir cloud imagery will then be discussed.© (1995) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Graphic displays for virtual environments and telerobotics require effective communication of the details of 3-D object shape. This paper presents empirical evidence on the relation between human perception and several properties of graphic shape depiction. A series of experiments examined a 3-D shape discrimination task requiring judgments of superquadric volume primitives varying in shape within different rendering and display conditions. The displays were dynamic, with constant rotational motion. Over the series of experiments, the contributions of diffuse and specular shading, occluding contour, aspect ratio, and covarying size were evaluated. The results revealed a consistent sensitivity to differences in superquadric shape parameters, that was surprisingly robust over rendering variations. One major finding was that the presence of specular highlights did not enhance shape discrimination performance beyond that observed for purely diffuse reflectance. The results suggest strategies for optimizing interface properties where 3-D shape is a primary component of the display. They also support the use of superquadric primitives in situations where humans interact with shape display systems.

A method for recognizing closed containers based on features extracted from their circular tops is presented. The approach developed consists of obtaining images from two spatially separated cameras that utilize both diffuse and specular light sources. The images thus obtained are used to segment target objects from the background and to extract representative features. The features utilized consist of container height as computed using stereopsis as well as the mean, variance, and second central moments of the intensities of the segmented caps. The recognition procedure is based on a minimum distance Mahalanobis classifier which takes feature covariance into account. The discussion that follows details the algorithmic approach for the entire system including image acquisition, object segmentation, feature extraction, and pattern classification. Result of test runs involving sets of several hundred training samples and untrained samples are presented.© (1992) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

We present a simple method for determining the 3-D orientation of a flat surface from the specular reflection of light, exploiting the polarizing properties of materials. Existing methods which compute surface orientation from specular reflection are purely intensity based and need to rely upon precise knowledge of how specularly reflecting light rays are initially incident upon the material surface. These methods require elaborate structured lighting environments which involve much preliminary calibration. The method presented here computes surface orientation independent of any a priori knowledge of the geometry of specular reflection, as long as specular reflection occurs into the camera sensor from points of interest at which orientation is to be constrained. This obviates the need for any structured lighting. By observing how the transmitted intensity of specularly reflected light through a polarizing filter is varied by rotating the filter, one can determine the specular plane of incidence in which the path of specular reflection must lie. Under the assumption that the surface normal is contained in the specular plane of incidence, a determination of two nonparallel specular planes of incidence from a stereo pair of cameras yields a computation of the surface normal from their planar intersection. For flat surfaces the correspondence of points between the stereo pair of cameras need not be precise, only that the intersecting specular planes of incidence correspond to two points that lie on the same flat surface, or on two flat surfaces with equivalent orientation. This is a much weaker correspondence requirement than for conventional parallax stereo.

The purpose of the lighting in an industrial machine vision application is to produce an image that is well matched to the camera and vision system. The brightest areas of the scene should cause a sensor illuminance that is just below the camera's saturation level and the video signal from the darkest significant areas of the scene should lie just above the vision system's noise level. This paper describes the fundamental principles and the techniques used to design lighting that meets these requirements. The camera's transfer function, the vision system's noise level, and the relative lens aperture are used to calculate optimal luminances for the brightest and darkest areas in the scene. The necessary reflectivity coefficients for the objects in the scene are measured and lighting is designed which produces the correct object luminances in both the specular highlights and the diffuse background areas of the scene. We show how to specify the light sources required to produce the lighting and present an example of printed circuit board inspection. The burden that this design method places on the vision algorithms is also discussed.

Universal acceptance of a proposed standard measurement method can depend not only upon how soundly it is based in scientific theory but on its cost and technical implementation as well. A total integrated scatterometer for the optical shop is described with emphasis on economy, rapid measurement, repeatability, and ergonomic packaging as controlling design criteria. The advent of low-cost microvolt resolution in digital multimeters allows the use of large-area silicon photovoltaic cells for detection of the scatter and specular light from the sample. The thin cell profile permits placement of the scatter detector closer to the sample port for minimal scatter obscuration. The large cell area accepts the blur circle from an inexpensive molded acrylic dome for scatter collection. A dedicated pocket computer and printer calculates, displays and prints sample RMS roughness, average, and standard de-viation for multiple measurements; it also controls laser user-access, prints a tutorial, and identifies sample, operator and date/time. The laser is a 2mW HeNe (633 nm); safety issues are addressed. The specular beam reflects off the specular detector and onto an alignment target screen, ensuring sample alignment and measurement repeatability. The inverted design provides a gravity-loading sample stage that is completely accessible; custom sample mounts are readily added. Component sources are provided. Performance and correlation to other scatterometer and roughness measurement techniques such as optical and mechanical profilers are presented.

Recently there has been interest, in computer vision research, in the segmentation of images based upon the actual material makeup of the objects or object parts that constitute image regions. The idea is to identify image characteristics which can be used to predict the material properties of objects that are being imaged. A majority of object surfaces can be simply classified according to their basic electrical properties; metal objects (e.g. Aluminum, Copper) conduct electricity rather well while dielectric objects (e.g. Rubber, Plastic, Ceramic) conduct electricity poorly. Distinguishing image regions according to whether they correspond to metal or dielectric material can provide important information for scene understanding especially in industrial machine vision. One such major application is circuit board inspection where the presence of dielectric or metal material in the wrong place can cause trouble. A previous approach to the problem of identifying metal or dielectric material in images is based upon careful spectral (i.e. color) analysis of reflected light from material objects. This paper presents a technique for identifying the material properties of objects in an image using a polarizing lens (i.e. Polaroid filter). Two images of the same scene are taken with a polarizing lens placed in front of a camera in two different respective orientations. Effectively these two images represent two linearly independent polarization components of the reflected light. It is shown that when the linearly independent components of polarization are taken parallel and perpendicular with respect to the plane in which specular rays travel that dielectric objects can be distinguished from metallic objects when specular highlights are present. In particular the two polarization components are very similar at specular highlights on metals while the two polarization components for specular highlights on dielectrics are very different, the perpendicular component having much larger magnitude than the parallel component. This is shown to hold regardless of whether the surface is polished or rough. Results for coated surfaces will be presented at a future date.