Diffuse Reflection Components Research Articles

Inversion of Position for Low Speed Target in Near Space Using Non-resolved Photometric and Astrometric Data

A method for estimating the position parameters of a low speed target (LST) in near space was presented. The estimation method utilizes apparent magnitude, azimuthal angle, and angle of elevation to invert the position of a typical LST, such as a high altitude balloon (HAB). A photometric observation model composed of specular and diffuse reflection components for the LST was established. An astrometric observation model was discussed to deduce the azimuth and elevation of a ground-based opto-electronic detection system for the LST. An extended Kalman filter (EKF) was designed to invert the state parameters of the position and velocity of the LST from photometric and astrometric data. Two sets of simulations were carried out to validate this inversion method. The simulation results show that the simulation errors for the estimated parameters are small, the estimated positions agree with GPS very well, and the non-resolved photometric and angular data can be used to estimate the indirect observable position state parameters for a LST in near space.

Opaque construction materials solar loads calculation: Dependence on directional reflectance

Generally the solar reflectance associated to construction material surfaces is considered perfectly diffuse, namely they reflect in every direction the incident irradiance. Therefore reflectance and absorptance are assumed to be constant and independent on the incidence angles. This assumption, generally used in the most of energy analysis simulation tools, has to be considered not valid for materials characterized by a regular reflection, like glass or polished surfaces, where an angular dependence of their optical–radiative properties is observed. However, many opaque construction materials often show a mixed behavior, which includes regular and diffuse (or scattering) reflectance components. Moreover, the apparent roughness of the materials surface changes according to the angle of incidence of the solar irradiance. This issue is relevant for some cool materials, which are polished or treated with other methods to offer a very smooth surface, to increase the solar reflectance. In this work the dependence of opaque materials on the directional properties of their surfaces are investigated to assess the impact on solar loads and energy performances of the building envelope. The reflectance shape and the hemispherical values of two materials used for roofing are measured by means of a goniophotometer to characterize the directional reflectance. A numerical analysis was carried out to compute the differences in solar loads during cold and hot seasons between a reflectance angular dependent model and a constant reflectance model. Sensible discrepancies between the two models put in evidence that solar reflectance angular dependence should be included in the calculation tools to achieve more accurate results.

Specular Reflection Separation With Color-Lines Constraint.

According to dichromatic reflection model, the previous methods of specular reflection separation in image processing often separate specular reflection from a single image using patch-based priors. Due to lack of global information, these methods often cannot completely separate the specular component of an image and are incline to degrade image textures. In this paper, we derive a global color-lines constraint from dichromatic reflection model to effectively recover specular and diffuse reflection. Our key observation is from that each image pixel lies along a color line in normalized RGB space and the different color lines representing distinct diffuse chromaticities intersect at one point, namely, the illumination chromaticity. For pixels along the same color line, they spread over the entire image and their distances to the illumination chromaticity reflect the amount of specular reflection components. With global (non-local) information from these color lines, our method can effectively separate specular and diffuse reflection components in a pixelwise way for a single image, and it is suitable for real-time applications. Our experimental results on synthetic and real images show that our method performs better than the state-of-the-art methods to separate specular reflection.

Influences of Leaf-Specular Reflection on Canopy BRF Characteristics: A Case Study of Real Maize Canopies With a 3-D Scene BRDF Model

The diffuse and specular components of leaf reflection are both important to determine the leaf optical properties as well as to describe the leaf bidirectional reflectance distribution function (BRDF). However, the specular component is usually ignored in practice in numerous canopy reflectance models that describe the interaction between solar light and vegetated scene components. To evaluate the impact of leaf-specular reflection on canopy bidirectional reflectance factor (BRF) characteristics, we introduce a leaf BRDF model into the radiosity-graphics combined model (RGM; a 3-D scene model) to calculate canopy BRFs with nondiffuse leaves. The modified RGM is validated by comparing simulated BRFs against in situ measured BRFs over real maize canopies. The results show that ignorance of leaf-specular reflection can result in up to 50% of relative error in the blue band (435.8 nm). A series of maize canopies with different leaf angle distributions (LADs) is reconstructed to investigate the effect of five major biophysical/geometrical parameters such as leaf area index, LAD, leaf surface property, view direction, and solar zenith angle on leaf-specular reflection contributions to the canopy BRF. It is demonstrated that increasing the incident solar zenith angle and decreasing the mean leaf angle impact the angular distribution of the canopy BRF more significantly than other factors. The cumulative hemispherical relative and absolute errors of canopy BRF caused by the leaf-specular reflection are often too large to be ignored, even for canopies with rough surface leaves. Moreover, the relative error of BRF in visible waveband shows that, in general, leaf-specular reflection has a large impact than that in near-infrared waveband. However, such impact can be sufficiently accounted for by even just consideration of the first-order leaf-specular reflection in canopy reflectance calculation, leading to a substantial improvement in simulation accuracy for most vegetation canopies.

Directional and angular response of construction materials solar properties: Characterisation and assessment

Construction and building materials are generally considered Lambertian, namely they reflect as perfectly diffusive the radiation incident onto their surface. Thus, reflectance and absorptance are assumed to be constant and independent on the incidence and view angles. This assumption is not valid for specular materials, like glass or polished surfaces, where an angular dependence of their optical–radiative properties is observed. However, many opaque construction materials often show a mixed behaviour, which includes specular and diffuse (or scattering) reflectance components. Moreover, the apparent roughness of the materials surface changes according to the angle of incidence of the solar radiation. This issue is relevant for some cool materials, which are polished or treated with other methods to offer a very smooth surface, to increase the solar reflectance.Herein, the angular dependent solar reflectance of the opaque materials and the impact on the solar gains and energy balance of the building envelope is investigated. The off-normal solar spectral reflectance of four typical construction material for roofing and façade systems is measured with a spectrophotometer, equipped with a large integrating sphere, and with a goniophotometer to characterise the directional reflectance. The comparison between reflectance values in the visible band obtained with both devices shows relative variations lower than 2% for materials with prevalent diffusing behaviour. Discrepancies up to 6% are observed for the samples with a perceivable specular component. Solar reflectance angular dependent curves are calculated, starting from measurements, to compare different models to compute the solar gains. A building energy simulation tools is then used to compute the differences between heat fluxes and energy needs obtained with reflectance angular dependent models and with constant solar reflectance. Discrepancies of the thermal fluxes up 0.7kWh/m2 in summer and 0.5kWh/m2 in winter are calculated, with relative variations exceeding 7%. Discrepancies of 1.7kWh/m2 in winter and 1.2kWh/m2 in summer are calculated for the heating and cooling energy uses of a reference building.

Surface Selection Rule of Infrared Diffuse Reflection Spectrometry for Analysis of Molecular Adsorbates on a Rough Surface of a Nonabsorbing Medium

The surface selection rule (SSR) for discussing the molecular orientation in a thin film adsorbed on a rough surface is determined by analyzing a surface monolayer by defining the angle of incidence and polarizations. As the standard sample, a highly organized self-assembled monolayer (SAM) on a rough alumina surface is employed. By introducing crossed-Nicol polarizers in the incident and detection paths, the specular reflection and diffuse reflection components are readily separated. To fully understand the spectra of the SAM, a new idea is proposed that the incidental light can be excluded from the discussion when the angle of incidence is small, which is named the pseudotransmission (pd-Tr) model. Another important idea is that a part of a spectrum is degraded in the signal-to-noise ratio by the suppression of incidental light on the rough surface via a deconstructive interference, which can experimentally be revealed by the crossed-Nicol measurements of single-beam spectra depending on the angle of incidence. Through the experiments of all the combinations of polarizations and angles of incidence, the pd-Tr model and the light suppression are found to be an important base to fully understand the SSR of molecular adsorbates on a rough surface of a nonabsorbing medium.

Color Signal Estimation of Surrounding Scenes from Human Corneal Surface Images

A method is proposed for estimation of the wide-area color signals of the surrounding scene in the image reflected on the corneal surface. A digital color camera and the human eyeball are used to develop a simple imaging system without the need for any specialized devices. First, the authors introduce the corneal imaging system. Second, they correct the geometric distortion of the reflected image using gnomonic projection. Third, the color signals in the surrounding scene are estimated from the RGB image data according to the Wiener estimator. The corneal image consists of a combination of specular and diffuse reflections from the cornea and the iris. The desired color signals are recovered only from the specular reflection component after removing the diffuse reflection component. Finally, experiments are performed in several different conditions. The results demonstrate that the proposed corneal imaging method can estimate reliable color signals over a wide area.

An optimisation approach to the recovery of reflection parameters from a single hyperspectral image

In this paper, we present a method to recover the parameters governing the reflection of light from a surface making use of a single hyperspectral image. To do this, we view the image radiance as a combination of specular and diffuse reflection components and present a cost functional which can be used for purposes of iterative least squares optimisation. This optimisation process is quite general in nature and can be applied to a number of reflectance models widely used in the computer vision and graphics communities. We elaborate on the use of these models in our optimisation process and provide a variant of the Beckmann–Kirchhoff model which incorporates the Fresnel reflection term. We show results on synthetic images and illustrate how the recovered photometric parameters can be employed for skin recognition in real world imagery, where our estimated albedo yields a classification rate of 95.09±4.26% as compared to an alternative, whose classification rate is of 90.94±6.12%. We also show quantitative results on the estimation of the index of refraction, where our method delivers an average per-pixel angular error of 0.15°. This is a considerable improvement with respect to an alternative, which yields an error of 9.9°.

Real-time highlight removal using intensity ratio

In this paper, we propose an efficient method to separate the diffuse and specular reflection components from a single image. The method is built on the observation that, for diffuse pixels, the intensity ratios between the maximum values and range values (maximums minus minimums) are independent of surface geometry. The specular fractions of the image pixels can then be computed by using the intensity ratio. For textured surfaces, image pixels are classified into clusters by constructing a pseudo-chromaticity space, and the intensity ratio of each cluster is robustly estimated. Unlike existing techniques, the proposed method works in a pixel-wise manner, without specular pixel identification and any local interaction. Experimental results show that the proposed method runs 4× faster than the state of the art and produces improved accuracy in specular highlight removal.

Specular-based illumination estimation using blind signal separation techniques

Illumination estimation is important in many approaches to colour constancy, where object colour is measured without the effect of the spectral distribution of the illumination. Many illumination estimation methods for achieving colour constancy, particularly those based on the dichromatic reflection model, have performance limitations because they operate on images composed of blended specular and diffuse reflection components, and they may require image segmentation into regions; segmentation is a well-known image-processing challenge. This study proposes an illumination estimation method, which uses constrained blind signal separation anchored on the dichromatic reflection model, connected to a linear model of the illumination spectrum. Unlike conventional methods that use mixed-image components, the proposed method uses a specular image component extracted explicitly by blind signal separation. This can yield better illumination estimates, and blind signal separation can avoid image segmentation problems. Results of experiments show that the proposed method can recover the illumination spectral distribution, and that the extracted specular component yields better illumination estimation than mixed components. Similar results were observed for the two blind signal separation techniques assessed in this study; namely, the spatially constrained FastICA and independent component analysis based on mutual information.

Specularity removal based on reflection component separation and joint bilateral filtering

We propose a novel specularity removal method based on reflection component separation and joint bilateral filtering. In general, specularities in images are represented as the linear combination of diffuse and specular reflection components in homogeneous objects. Although diffuse and specular components are correctly classified by reflection component separation, some illumination effects still remain in diffuse images due to the inaccurate illumination chromaticity estimation. Therefore, we refine the separated diffuse components using a joint bilateral filter. We test our method on both synthetic and real images, and the experimental results demonstrate that the proposed method outperforms the state-of-the-art ones in specularity removal.

Dynamic Multipath Model of Low Angle Passive Radar Tracking with Experimental Evaluation

The problem of multipath propagation encountered in radar tracking of low elevation targets in the presence of reflections from the sea is addressed. A detailed model of the multipath propagation considering both the specular and the diffuse reflection components in target tracking using passive radars is established. Based on the geometry of the specular and the diffuse reflections, expressions for the reflection coefficient and the scattering field are derived. Experiments in the outfield indicate that the model proposed agrees with the test data well, which can provide an accurate prediction of the angle measurement errors in the presence of multipath effects. Defence Science Journal, 2012, 62(5), pp.331-337 , DOI:http://dx.doi.org/10.14429/dsj.62.1000

Application of infrared spectroscopic imaging in specular reflection mode for determination of distribution of chemical components in urinary stones

Distribution of chemical components in the mixed oxalatic, phosphatic and uratic urinary stones was analysed by means of infrared microspectroscopy. The specular reflection from the surface of the cross-sectioned stones was used for the infrared spectroscopic imaging. It was found that the reflection spectra consist from specular and diffuse reflection components and the former one exhibit Reststrahlen bands which resemble first derivative of the spectral bands in the absorption spectrum. In order to use the measured spectra for the chemical imaging they were corrected for asymmetry by subtracting the diffuse reflection component and applying Kramers–Kronig transform to the specular reflection component. The Kramers–Kronig transformed spectrum was then combined with the diffuse reflection component. Spectra corrected in this manner were used to create false-colour images of the stones. It was found that the images obtained after applying the correction procedure to the spectra differ substantially from the ones obtained from the raw spectra. They are in good agreement with the stones’ images obtained from the FT-Raman spectra.

Effects of diffuse and specular reflections on the perceived age of facial skin

Age perception is a better biomarker of skin aging than chronological age. However, the optical cues that determine the perception of human skin age are difficult to assess given the complex interactions between light and the multi layered structure of the skin. The aim of the present study is to clarify the independent contribution of both diffuse and specular reflection components to the skin age perception. First, according to our results, subjects were able to estimate the age of skin only by using the diffuse reflection component. Moreover, we showed that inclusion of the specular reflection component added on average 5 years to their age estimation. Second, by artificially manipulating the specular component, we concluded that the luminance distribution affects the perceived age of the skin.

Reflection infrared spectroscopy for the non-invasive in situ study of artists’ pigments

The potential of fibre optic reflection infrared spectroscopy for the non-invasive identification of artists’ pigments is presented. Sixteen different carbonate, sulphate and silicate-based pigments are taken into account considering their wide use during the history of art and their infrared optical properties. The infrared distortions mainly generated by the specular reflection are discussed on the basis of experimental measurements carried out on reference samples. The study on pure materials permitted the definition of marker bands, mainly combination and overtone modes, enhanced by the diffuse reflection component of the light, functional for the non-invasive pigment identification in real artworks. Several case studies are reported, including wall, easel, canvas paintings and manuscripts from ancient to modern art demonstrating the strengths of the technique on the identification of pigments even in the presence of complex mixtures of both organic (binders, varnishes) and inorganic (supports, fillers and other pigments) compounds.

An introduction to image-based 3D surface reconstruction and a survey of photometric stereo methods

This paper provides an introduction to photometric methods for image-based 3D shape reconstruction and a survey of photometric stereo techniques. We begin with taxonomy of active and passive shape acquisition techniques. Then we describe the methodical background of photometric 3D reconstruction, define the canonical setting of photometric stereo (Lambertian surface reflectance, parallel incident light, known illumination direction, known surface albedo, absence of cast shadows), discuss the 3D reconstruction of surfaces from local gradients, summarize the concept of the bidirectional reflectance distribution function (BRDF), and outline several important empirically and physically motivated reflectance models. We provide a detailed treatment of several generalizations of the canonical setting of photometric stereo, namely non-distant light sources, unknown illumination directions, and, in some detail, non-Lambertian surface reflectance functions. An important special case is purely specular reflections, where an extended light source allows capturing a surface that consists of perfectly specular surface patches. Linear combinations of purely Lambertian and purely specular reflectance components are favorably used for reconstructing smooth surfaces and also human skin. Nonuniform surface reflectance properties are estimated based on a simultaneous 3D reconstruction and determination of the locally variable parameters of the reflectance function based on a multitude of images. Assuming faceted surfaces, the effective resolution of the 3D reconstruction result can be increased to some extent beyond that of the underlying images. Other approaches separate specular and diffuse reflectance components based on polarization data or color information. The specular reflections can be used additionally to estimate the direction from which the surface is illuminated. Finally, we describe methods to combine photometric 3D reconstruction techniques with active and passive triangulation-based approaches.

Integrated Polarization Analyzing CMOS Image Sensor for Material Classification

Material classification is an important application in computer vision. The inherent property of materials to partially polarize the reflected light can serve as a tool to classify them. In this paper, a real-time polarization sensing CMOS image sensor using a wire grid polarizer is proposed. The image sensor consist of an array of 128 <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$\, \times \,$</tex></formula> 128 pixels, occupies an area of 5 <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex Notation="TeX">$\, \times \,$</tex></formula> 4 mm <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex Notation="TeX">$^{2}$</tex></formula> and it has been designed and fabricated in a 180-nm CMOS process. We show that this image sensor can be used to differentiate between metal and dielectric surfaces in real-time due to the different nature in partially polarizing the specular and diffuse reflection components of the reflected light. This is achieved by calculating the Fresnel reflection coefficients, the degree of polarization and the variations in the maximum and minimum transmitted intensities for varying specular angle of incidence. Differences in the physical parameters for various metal surfaces result in different surface reflection behavior, influencing the Fresnel reflection coefficients. It is also shown that the image sensor can differentiate among various metals by sensing the change in the polarization Fresnel ratio.

Robust low-angle estimation by an array radar

One of the origins of error in the angle of arrival estimation of a signal is the response of the ground to the reflected waves from the target. In low-height target situations, this phenomenon can be so harrowing that it may result in much more error than thermal noise. In this article, two methods of fixed beam and double null are used as preliminary techniques to overcome the problem of low-altitude target angle estimation, and the optimum weights for beam-forming array radar are proposed. These beam-forming methods enable the radar to estimate the target angle precisely without the exact knowledge of the surface slope, whereas they are robust against diffuse and specular ground reflection components.

Perceived glossiness and lightness under real-world illumination

Color, lightness, and glossiness are perceptual attributes associated with object reflectance. For these perceptual representations to be useful, they must correlate with physical reflectance properties of objects and not be overly affected by changes in illumination or viewing context. We employed a matching paradigm to investigate the perception of lightness and glossiness under geometric changes in illumination. Stimuli were computer simulations of spheres presented on a high-dynamic-range display. Observers adjusted the diffuse and specular reflectance components of a test sphere so that its appearance matched that of a reference sphere simulated under a different light field. Diffuse component matches were close to veridical across geometric changes in light field. In contrast, specular component matches were affected by geometric changes in light field. We tested several independence principles and found (i) that the effect of changing light field geometry on the diffuse component matches was independent of the reference sphere specular component; (ii) that the effect of changing light field geometry on the specular component matches was independent of the reference sphere diffuse component; and (iii) that diffuse and specular components of the match depended only slightly on the roughness of the specular component. Finally, we found that equating simple statistics (i.e., standard deviation, skewness, and kurtosis) computed from the luminance histograms of the spheres did not predict the matches: these statistics differed substantially between spheres that matched in appearance across geometric changes in the light field.

Reliefs as images

We describe how to create relief surfaces whose diffuse reflection approximates given images under known directional illumination. This allows using any surface with a significant diffuse reflection component as an image display. We propose a discrete model for the area in the relief surface that corresponds to a pixel in the desired image. This model introduces the necessary degrees of freedom to overcome theoretical limitations in shape from shading and practical requirements such as stability of the image under changes in viewing condition and limited overall variation in depth. The discrete surface is determined using an iterative least squares optimization. We show several resulting relief surfaces conveying one image for varying lighting directions as well as two images for two specific lighting directions.