Uniform Reflectance Research Articles

Stereoscopic Face Reconstruction from a Single 2-Dimensional Face Image Using Orthogonality of Normal Surface and Y-Ratio

This paper modified the method of three-dimensional (3-dimensional) face reconstruction from a single two-dimensional (2-dimensional) image based on the Lambertian model consisting of height estimation, normal surface estimation, albedo calculation and image normalization, normal surface calculation, actual height calculation, and error correction. In height estimation, the facial height of each input image is estimated from the average facial height of face images in the training data set. The estimated height is used for estimating the normal surface by applying our proposed pattern morphing method (PMM). To calculate the actual normal surface, the albedo of the input face image is calculated to normalize the image first. Then, the actual normal surface is derived by using our proposed Y-ratio calculation with improved computational time. Finally, the actual height of input face image is computed afterwards to construct the 3-dimensional face. Two face databases of 110 human face images containing 10 real and 100 synthetic images were tested by our proposed method with uniform reflectance and high level of heterogeneous reflectance abilities. The experimental results were compared with the results obtained from other existing methods, such as the traditional minimization, shape propagation, local, and linear approaches. Our method can accurately reconstruct 3-dimensional face from a single 2-dimensional face image with the error less than 6%.

Automatic Segmentation Method for Segmenting PBGA Package and PWB Regions During Warpage Measurement of Unpainted PWB Assembly

Among the various warpage measurement techniques, digital fringe projection (DFP) technique is recent trend because of its noncontact, full-field, and high-resolution measurement capabilities for measuring the warpage of chip packages, printed wiring boards (PWBs), and PWB assemblies (PWBAs). When using the DFP technique, reflective painting is generally sprayed on a sample surface to ensure uniform surface reflectance and to obtain better image contrast for the measurement process. However, because painted samples may no longer be reused, and the spray-painting process is not suitable inline, warpage measurement of unpainted chip packages, PWBs, and PWBAs using the DFP technique is required. One of the important tasks for measuring the warpage of unpainted PWBAs is segmentation of the chip package and PWB regions in unpainted PWBA images so that separate warpage of the chip packages and the PWBs can be determined. This paper presents a novel automatic segmentation method, region-growing method (RGM), which segments plastic-ball grid array (PBGA) packages and PWB regions in unpainted PWBA images. The experimental results show that the RGM successfully segments the PBGA package and PWB regions in unpainted PWBA images. The results also show that the RGM can be used in a DFP system to measures the warpage of PBGA packages and PWBs in unpainted PWBAs.

Automatic Segmentation Method for Segmenting PBGA Package and PWB Regions during Warpage Measurement of Unpainted PWB Assembly

Among the various warpage measurement techniques, the digital fringe projection (DFP) technique is recent trend because of its noncontact, full-field, and high-resolution measurement capabilities for measuring the warpage of chip packages, printed wiring boards (PWBs), and PWB assemblies (PWBAs). When using the DFP technique, reflective painting is generally sprayed on a sample surface to ensure uniform surface reflectance and to obtain better image contrast for the measurement process. However, because painted samples may no longer be re-used, and the spray-painting process is not suitable inline, warpage measurement of unpainted chip packages, PWBs, and PWBAs using the DFP technique is required. One of the important tasks for measuring unpainted PWBAs is segmentation of the chip package and PWB regions in unpainted PWBA images so that separate warpage of the chip package(s) and the PWB can be determined. In this paper, an automatic image segmentation method that is used to segment plastic ball grid array (PBGA) package and PWB regions in unpainted PWBA images is presented. Because the patterns such as the copper patterns and traces, and inscriptions on a PWBA can cause measurement errors, the patterns and inscriptions are automatically masked out during the segmentation. The method is experimentally tested by segmenting the PBGA package and PWB regions in three different PWBA samples and measuring the warpage of the PBGA packages and the PWB in an unpainted PWBA.

First far-ultraviolet disk-integrated phase curve analysis of Mimas, Tethys and Dione from the Cassini-UVIS data sets

We perform an analysis of the photometric properties of the icy saturnian satellites at 180nm, based on the first far-UV disk-integrated phase curves of Mimas, Tethys and Dione. Their interactions with the environment (the E-ring and the magnetosphere) are investigated, leading to a better understanding of the effects of exogenic processes on the system of Saturn. We find that Tethys and Dione have a leading hemisphere brighter than their trailing hemisphere at far-UV wavelengths, while Mimas exhibits a quite uniform reflectance on its surface. No asymmetry is observed between the saturnian and anti-saturnian hemispheres of those satellites, indicating that exogenic processes are important primarily on the leading and trailing hemispheres. Tethys shows a narrower opposition effect, suggesting a more porous regolith on its surface than on Dione and Mimas. This could be the consequence of more significant bombardment by the E-ring grains at the orbit of Tethys. Dione’s photometric properties reveal a more absorbing surface, which could be explained by a lower amount of E-ring grain bombardment and/or by the deposit of a darkening agent mainly on its trailing side.

THE EFFECT OF THE EXTENT OF CORAL REEF AREA ON UNIFORM BOTTOM REFLECTANCE DETERMINATION FOR WATER COLUMN CORRECTION USING LANDSAT ETM

In one pixel of 30 meter spatial resolution of Landsat ETM multispectral sensor might consist of mixed bottom substrate types. The influence of a mixture of bottom substrate on the Landsat data can be a source of errors and together with the extent of coral reef area might contribute to affect the determination of uniform bottom reflectance. This study aimed to assess the effect of the extent of coral reef area on uniform bottom reflectance determination for water column correction. Lyzenga method was used for water column correction. This study carried out in two case studies using two sites with different size of coral reef ecosystems area i.e., Tidung island, in the Province of Jakarta and Maratua island, in the Province of East Kalimantan. Tidung island was selected to represent small area of coral reef ecosystem, while Maratua island was selected to represent relatively larger area of coral reef ecosystem. The results showed that the extent of coral reef influenced the determination of training sample areas for uniform bottom reflectance using Landsat ETM. The combination of moderate spatial resolution and the small area of coral reef ecosystem lead to the difficulties for uniform bottom substrate type determination at different depths.

Improved discrimination of volcanic complexes, tectonic features, and regolith properties in Mare Serenitatis from Earth-based radar mapping

Radar images at 70 cm wavelength show 4–5 dB variations in backscatter strength within regions of relatively uniform spectral reflectance properties in central and northern Mare Serenitatis, delineating features suggesting lava flow margins, channels, and superposition relationships. These backscatter differences are much less pronounced at 12.6 cm wavelength, consistent with a large component of the 70 cm echo arising from the rough or blocky transition zone between the mare regolith and the intact bedrock. Such deep probing is possible because the ilmenite content, which modulates microwave losses, of central Mare Serenitatis is generally low (2–3% by weight). Modeling of the radar returns from a buried interface shows that an average regolith thickness of 10 m could lead to the observed shifts in 70 cm echo power with a change in TiO2 content from 2% to 3%. This thickness is consistent with estimates of regolith depth (10–15 m) based on the smallest diameter for which fresh craters have obvious blocky ejecta. The 70 cm backscatter differences provide a view of mare flow-unit boundaries, channels, and lobes unseen by other remote sensing methods. A localized pyroclastic deposit associated with Rima Calippus is identified based on its low radar echo strength. Radar mapping also improves delineation of units for crater age dating and highlights a 250 km long, east-west trending feature in northern Mare Serenitatis that we suggest is a large graben flooded by late-stage mare flows.

Paper like cholesteric interferential mirror

A new type of flexible cholesteric liquid crystal mirror is presented. The simple and effective method for the deposition of a cholesteric mixture on a paper substrate and the particular design of the device give a homogeneous alignment of the cholesteric texture providing mirrors with an intense and uniform light reflectance. A desired polarization state for the reflected light, linear or circular, can be easily obtained varying the thickness and optical anisotropy of the polymer cover film. By using non-azobenzene based photosensitive materials a permanent array of RGB mirrors with high reflectivity can be obtained on the same device. Paper like reflective mirrors are versatile and they can find applications in reflective displays, adaptive optics, UV detectors and dosimeters, information recording, medicine and IR converters.

Land Surface Reflectance Retrieval from Hyperspectral Data Collected by an Unmanned Aerial Vehicle over the Baotou Test Site

To evaluate the in-flight performance of a new hyperspectral sensor onboard an unmanned aerial vehicle (UAV-HYPER), a comprehensive field campaign was conducted over the Baotou test site in China on 3 September 2011. Several portable reference reflectance targets were deployed across the test site. The radiometric performance of the UAV-HYPER sensor was assessed in terms of signal-to-noise ratio (SNR) and the calibration accuracy. The SNR of the different bands of the UAV-HYPER sensor was estimated to be between approximately 5 and 120 over the homogeneous targets, and the linear response of the apparent reflectance ranged from approximately 0.05 to 0.45. The uniform and non-uniform Lambertian land surface reflectance was retrieved and validated using in situ measurements, with root mean square error (RMSE) of approximately 0.01–0.07 and relative RMSE of approximately 5%–12%. There were small discrepancies between the retrieved uniform and non-uniform Lambertian land surface reflectance over the homogeneous targets and under low aerosol optical depth (AOD) conditions (AOD = 0.18). However, these discrepancies must be taken into account when adjacent pixels had large land surface reflectance contrast and under high AOD conditions (e.g. AOD = 1.0).

Distribution and origin of minerals in high-rank coals of the South Walker Creek area, Bowen Basin, Australia

The coals of the South Walker Creek area in the northern Bowen Basin, with a vitrinite reflectance (Rvmax) of 1.7 to 1.95%, are among the highest rank coals currently mined in Australia. X-ray diffraction studies have identified an unusual mineral variation through the vertical sequence, with kaolinite-rich assemblages typical of other Australian coals at the top and bottom of the seam section and an illite–chlorite assemblage resembling a metamorphic association in the middle. Calcite and ankerite are also abundant in parts of the vertical sequence. Diaspore is abundant in the middle section of the seam in some areas, and paragonite, dickite or nacrite occurs in some locations as well.The distribution of the non-carbonate mineral assemblages cross-cuts the seam stratigraphy, and appears to be primarily controlled by faults and other structural features. Integration of the mineral distribution with optical and electron microscope data on the coal and non-coal bands, chemical data from coal ash analysis, and information from X-ray micro-tomography, suggests that the illite–chlorite and diaspore-bearing assemblages resulted from hydrothermal effects associated with fluid migration through the middle part of the coal seam. This is further confirmed by the development of metamorphic textures in a tonstein band, also altered to illite and chlorite, in the illite-rich part of the seam section, in contrast to a tonstein with more normal sedimentary textures and a kaolinite composition in the kaolinite-rich upper part of the seam.Detailed studies of cleat mineralisation suggest that fluids rich in Ca, Mg and Al were introduced relatively early in the seam's post-depositional history, associated with heat flow sufficient to alter the minerals in the coal and tonstein in the affected part of the seam section. The relatively uniform vitrinite reflectance profile observed through the seam section may indicate that the coal was already of high rank before the fluids were introduced, or that any localised heat effects on the organic matter associated with the changes in clay mineralogy were overprinted by subsequent wider-ranging rank advance processes.

Carbon dioxide exchange of a pepperweed (Lepidium latifoliumL.) infestation: How do flowering and mowing affect canopy photosynthesis and autotrophic respiration?

[1] The net ecosystem carbon dioxide (CO2) exchange of invasive plant infestations, such as perennial pepperweed (Lepidium latifolium L.), is not well understood. A characteristic feature of pepperweed's phenological cycle is its small white flowers during secondary inflorescence. Pepperweed flowering causes uniform reflectance over the visible range of the electromagnetic spectrum, thus decreasing the amount of energy absorbed by the canopy and available for photosynthesis. Little is known about how pepperweed flowering and control measures such as mowing affect canopy photosynthesis and autotrophic respiration (FAR) and thus ecosystem respiration. To examine this question, we analyzed CO2 flux measurements made with eddy covariance over a pepperweed infestation in California, covering three growing seasons. Unmowed pepperweed caused the site to be almost CO2 neutral (2007: −28 g C m−2 period−1) or a net source (2009: 129 g C m−2 period−1), mostly because of reduced maximum photosynthetic capacity by 13 (2007) and 17 μmol m−2 s−1 (2009) due to flowering during the plant's prime photosynthetic period. Reference FAR at 10°C was reduced by 2 μmol m−2 s−1 in 2007 and 2009. Mowing during early flowering reversed the attenuating effects of pepperweed flowering, causing the site to act as a net CO2 sink (2008: −174 g C m−2 period−1) mainly due to prolonged photosynthetic CO2 uptake over the plant's early vegetative growth phase. Our results highlight the tight link between pepperweed's prominent key phenological phase and applied control measures, which together exert dominant control over the infestation's CO2 source-sink strength.

The underwater photic environment of Cape Maclear, Lake Malawi: comparison between rock- and sand-bottom habitats and implications for cichlid fish vision

Lake Malawi boasts the highest diversity of freshwater fishes in the world. Nearshore sites are categorized according to their bottom substrate, rock or sand, and these habitats host divergent assemblages of cichlid fishes. Sexual selection driven by mate choice in cichlids led to spectacular diversification in male nuptial coloration. This suggests that the spectral radiance contrast of fish, the main determinant of visibility under water, plays a crucial role in cichlid visual communication. This study provides the first detailed description of underwater irradiance, radiance and beam attenuation at selected sites representing two major habitats in Lake Malawi. These quantities are essential for estimating radiance contrast and, thus, the constraints imposed on fish body coloration. Irradiance spectra in the sand habitat were shifted to longer wavelengths compared with those in the rock habitat. Beam attenuation in the sand habitat was higher than in the rock habitat. The effects of water depth, bottom depth and proximity to the lake bottom on radiometric quantities are discussed. The radiance contrast of targets exhibiting diffused and spectrally uniform reflectance depended on habitat type in deep water but not in shallow water. In deep water, radiance contrast of such targets was maximal at long wavelengths in the sand habitat and at short wavelengths in the rock habitat. Thus, to achieve conspicuousness, color patterns of rock- and sand-dwelling cichlids would be restricted to short and long wavelengths, respectively. This study provides a useful platform for the examination of cichlid visual communication.

컬러 매칭에 의한 폴리에스테르 직물의 심색효과

The deep black coloration of polyester fabrics was obtained by the physical properties of color and color mixing system. In this experiment, we have measured the absorbance and the reflectance of various disperse dyes for accomplishing the lowest lightness value and uniform reflectance, and new matching algorithm and computer color matching was made. The matching used both isomeric and metameric matching. The color matching of deep black color represented low lightness. Though actual reflectance of dyed polyester fabrics using these matching results was as high as theoretical one, low lightness value(<TEX>$L^*$</TEX>) and uniform appearance were achieved.

Do colored highlights look like highlights?

Case IV: When a colored specular component was combined with a white diffuse component (e.g., red on white), the surface images looked somewhat strange. They looked less glossy, and more importantly, did not appear to have a uniform reflectance. Colored highlight regions appeared to be spatially segregated from the surrounding white-body regions, as if pieces of colored foil were attached to a white matte surface.

Model and analysis of spectropolarimetric BRDF of painted target based on GA-LM method

Models based on microfacet were used to describe spectropolarimetric BRDF (short for bidirectional reflectance distribution function) with experimental data. And the spectropolarimetric BRDF values of targets were measured with the comparison to the standard whiteboard, which was considered as Lambert and had a uniform reflectance rate up to 98% at arbitrary angle of view. And then the relationships between measured spectropolarimetric BRDF values and the angles of view, as well as wavelengths which were in a range of 400-720 nm were analyzed in details. The initial value needed to be input to the LM optimization method was difficult to get and greatly impacted the results. Therefore, optimization approach which combines genetic algorithm and Levenberg-Marquardt (LM) was utilized aiming to retrieve parameters of nonlinear models, and the initial values were obtained using GA approach. Simulated experiments were used to test the efficiency of the adopted optimization method. And the simulated experiment ensures the optimization method to have a good performance and be able to retrieve the parameters of nonlinear model efficiently. The correctness of the models was validated by real outdoor sampled data. The parameters of DoP model retrieved are the refraction index of measured targets. The refraction index of the same color painted target but with different materials was also obtained. Conclusion has been drawn that the refraction index from these two targets are very near and this slight difference could be understood by the difference in the conditions of paint targets' surface, not the material of the targets.

Analysis of colour channel coupling from a physics-based viewpoint: Application to colour edge detection

The Dichromatic Reflection Model (DRM) introduced by Shafer in 1985 is surely the most referenced physics-based model of image formation. A preliminary analysis of this model derives in the conclusion that colour channels remain coupled by the reflectance of objects surface material. Taking this observation as a basis, this paper shows that this coupling manifests itself at the signal level in the form of a set of properties only satisfied in uniform reflectance areas. Such properties are deeply analysed and formalized throughout the paper, and, eventually, they are stated geometrically. As will be seen, a compatibility relationship stems from this geometric interpretation, which allows checking at a very low cost whether two pixels correspond to the same scene reflectance or not. Finally, an edge detector based on the use of the previous relationship is presented as an example of application. This edge detector inherits all the properties of the compatibility relationship: simplicity, low computational power requirements, sensor noise adaptivity and insensitivity to image intensity changes due to scene objects curvature.

Mt. Etna aerosol optical thickness from MIVIS images

This work focuses on the evaluation of Aerosol Optical Thickness (AOT) in Mt. Etna volcano area starting from the analysis of MIVIS VIS images. MIVIS images and ancillary data (atmospheric profiles, photometric measurements, atmospheric infrared radiances, surface temperatures, ground reflectances, SO2 abundances) were collected during the «Sicily ’97» campaign. Data elaboration was performed with extensive use of 6S radiative transfer model, determining optical thickness with an inversion algorithm that uses atmospheric vertical profile, ground reflectance data and radiance measured by the first MIVIS spectrometer (channels 1-20; range 0.44-0.82 n). Ground reflectance is the most problematic parameter for the algorithm. In order to have a low and ‘uniform’ surface reflectance, only pixels located at an altitude between 2000-3000 m a.s.l. were analysed. At this altitude,AOT is very low during non-eruptive periods: at Torre del Filosofo (2920 m a.s.l.) on June 16th 1997, during one MIVIS flight, AOT at 0.55 n was 0.19. The uncertainty about ground reflectance produces significant errors on volcanic background AOT, and in some cases the error is up to 100%. The developed algorithm worked well on volcanic plume, allowing us to determine the plume related pixels’AOT. High plume AOT values minimize the problems deriving from reflectance uncertainty. Plume optical thickness shows values included in a range from 0.5 to 1.0. The plume AOT map of Mt. Etna volcano, derived from a MIVIS image of June 16th 1997, is presented.

McCART: Monte Carlo Code for Atmospheric Radiative Transfer

McCART is a numerical procedure to solve the radiative transfer equation for light propagation through the atmosphere from visible to near-infrared wavelengths. The procedure has been developed to study the effect of the atmosphere in the remote sensing of the Earth, using aerospace imaging spectrometers. The simulation is run for a reference layered plane nonabsorbing atmosphere and a plane ground with uniform reflectance. For a given distribution of ground reflectance and for a specific profile of scattering and absorption properties of the atmosphere, the spectral response of the sensor is obtained in a short time from the results of the Monte Carlo simulation by using scaling relationships and symmetry properties. The procedure also includes an accurate analysis of the adjacency and trapping effects due to multiple scattering of photons coming from neighboring pixels. McCART can generate synthetic images of the Earth's surface for arbitrary viewing conditions. The results can be used to establish the limits of applicability of approximate algorithms for the processing and analysis of hyperspectral images acquired by imaging spectrometers. In addition, the algorithm can be used to develop procedures for atmospheric correction for the accurate retrieval of the spectral ground reflectance.

Applications of real-world gas detection: Airborne Natural Gas Emission Lidar (ANGEL) system

An airborne DIfferential Absorption Lidar (DIAL) system was used to detect methane, propane, and light crude gas vapors during real-world collections. A series of overflights were conducted at two separate test locations (Kingsville/Corpus Christi, TX and Spencerport, NY). DIAL, digital orthophotography, and video data were collected, processed and analyzed at both sites. A new Hydrocarbon Detection Algorithm (HHDA) was developed to detect gasses other than methane. The HHDA shows promise for detecting multiple species in a local area with uniform surface reflectance or known variability.

Dichromatic illumination estimation without pre-segmentation

An illumination estimation method based on the dichromatic reflection model is proposed. Unlike most previous dichromatic methods, no explicit image segmentation into regions of uniform surface reflectance or highlight areas is required. An estimate is obtained by optimizing a cost function on the color of the illuminating light.

Daylighting in atria: The effect of atrium geometry and reflectance distribution

The aim of this research was to examine the influence of atrium geometry and surface reflectance distributions on daylight factor (DF) at the base of the atrium. Ecotect and Radiance programmes were used to simulate square, four-sided, top-lit atria under overcast sky conditions. To achieve the variability in reflection distribution, surfaces were assigned alternating horizontal bands of white and black. For each of the experiments the widths of these bands were altered but the overall split between white and black bands was always maintained at 50% white and 50% black. Models were built for atriums with a well index of 0.5, 1 and 2. Results of the banded models were compared with models with a uniform reflectance of 0.43%; an average of the black and white bands to understand the influence of reflectance distribution patterns. It was concluded that the reflectance distributions had limited influence on daylight distribution on the atrium floor in the medium and shallow/wide atriums but had practically no effect in the tall atrium. The distribution of well reflectances had almost no influence on the average daylight factor (ADF) values in atria. Besides, the effect of reflectance distribution patterns on the DF reduced as the number of bands increased.