Estimating spectral reflectance from camera responses based on CIE XYZ tristimulus values under multi‐illuminants

A new spectral reflectance estimation method based on CIE XYZ values under multi‐illuminants was proposed to obtain multi‐spectral images accurately by using digital still cameras. CIE XYZ values under multi‐illuminants were initially predicted from raw RGB responses by using a polynomial model with local training samples. Then, spectral reflectance was constructed from the predicted CIE XYZ values via the pseudo‐inverse method. Experimental results indicated that the new spectral reflectance estimation method significantly outperformed the traditional colorimetric characterization method without requiring extra training samples or greatly increasing computational complexities. © 2016 Wiley Periodicals, Inc. Col Res Appl, 42, 68–77, 2017     

Estimation of CIE tristimulus values under various illuminants

In this work, a procedure is described to estimate the CIE tristimulus values of Munsell color chips under new illuminants from CIE tristimulus values under specific illuminant. The estimation was performed by multiple linear regression (MLR) and principal component analysis (PCA) techniques. In addition, the effects of illuminants combination and Munsell hue, value and chroma on reconstruction of CIE tristimulus values were evaluated in both methods. The results obtained indicate that the performance of principal component method is better than multiple regression method. The accuracy of estimation depends on the initial and target illuminants and hue, chroma and value of samples. © 2009 Wiley Periodicals, Inc. Col Res Appl, 34, 100–107, 2009     

Testing the accuracy of methods for the computation of CIE tristimulus values using weighting tables

The least squares method for computing colorimetric weighting tables is presented and its connection with the optimum weights method is investigated. Each requires solving three linear systems of equations with the same coefficient matrix but three different right hand side vectors. It is shown that the two methods have nearly the same performance when the wavelength interval of the data is large. The two methods however, will perform differently when Δλ is small. Comparisons are also made between the least squares method, the optimum weights method, the zero‐ and second‐order weighting tables, and the ASTM weighting tables, both the original 1985 tables and the new 2013 Tables V and VI. The results show that the least squares method is the best for measurement intervals equal to or lower than 10 nm, and is competitive with the optimum weights method for 20 nm steps. The results presented in this article will contribute to the work of CIE Technical Committee TC1‐71 Tristimulus Integration as it seeks to make recommendations for the calculation of tristimulus values. © 2015 Wiley Periodicals, Inc. Col Res Appl, 41, 125–142, 2016     

Interpolation,extrapolation, and truncation in computations of CIE tristimulus values

This article addresses some general practices for the computation of CIE tristimulus values (TSVs), including different methods used for the interpolation, extrapolation, and truncation of data in the visible wavelength range. In each case, a quantitative analysis is presented on the basis of a dataset with 2365 spectral reflectances covering a wide color gamut, assuming six CIE illuminants and the two CIE standard colorimetric observers. For interpolation, it is found that among five tested methods, the (cubic) spline method is the best one when the spectral reflectance factors are uniformly sampled over the visible wavelength range. For extrapolation, it is found that the second‐order extrapolation method gives better results than the use of nearest available data points or linear extrapolation methods. With respect to truncation, considering five different usual truncated ranges, it is found that the range from 360 to 780 nm provides more accurate results than the range from 380 to 780 nm currently recommended by CIE for nonfluorescent samples, and the use of the truncated range from 400 to 700 nm in place of the CIE‐recommended range of 360 to 830 nm leads to TSVs with considerably high color differences of up to 0.9 CIELAB units. © 2016 Wiley Periodicals, Inc. Col Res Appl, 42, 10–18, 2017     

Study of the reconstruction of reflectance curves based on tristimulus values: Comparison of methods of optimization

This article presents and compares different methods applied to the reconstruction of reflectance curves. These are optimization methods such as the simplex method, simulated annealing, genetic algorithms, neural networks, and Hawkyard's method, which is specific to colorimetry. Improvements have been made to these methods to maximize their application, notably to ensure a convergence toward the global optimum by avoiding being trapped in local optima and to obtain physically viable reflectance curves. Objective and subjective criteria were used to compare these methods; the study used textile samples (cotton fibers), with a panel of 15 samples covering the CIELAB L*a*b* space. © 2002 Wiley Periodicals, Inc. Col Res Appl, 27, 88–99, 2002; DOI 10.1002/col.10031     

Comparison of real colour gamuts using a new reflectance database

A large set of data, comprising the spectral reflectances of real surface colours, has been accumulated. The data comprise 16 groups with different materials and include 85,879 measured spectra. From these data, CIELAB colorimetric coordinates were calculated under CIE illuminant D50 and the CIE 1931 standard colorimetric (2°) observer. Several published colour gamuts including those developed by Pointer and ISO reference colour gamut [ISO Graphic Technology Standard 12640‐3:2007] were compared using the present data set. It was found that the Pointer gamut is smaller than the new real data in most of the colour regions. The results also showed that the ISO reference colour gamut is larger than the new real accumulated data in most regions. The present finding indicates that there is a need to derive a new colour gamut based on the newly accumulated data for common applications. © 2013 Wiley Periodicals, Inc. Col Res Appl, 39, 442–451, 2014     

Reconstruction of reflectance spectra using weighted principal component analysis

The weighted principal component analysis technique is employed for reconstruction of reflectance spectra of surface colors from the related tristimulus values. A dynamic eigenvector subspace based on applying certain weights to reflectance data of Munsell color chips has been formed for each particular sample and the color difference value between the target, and Munsell dataset is chosen as a criterion for determination of weighting factors. Implementation of this method enables one to increase the influence of samples which are closer to target on extracted principal eigenvectors and subsequently diminish the effect of those samples which benefit from higher amount of color difference. The performance of the suggested method is evaluated in spectral reflectance reconstruction of three different collections of colored samples by the use of the first three Munsell bases. The resulting spectra show considerable improvements in terms of root mean square error between the actual and reconstructed reflectance curves as well as CIELAB color difference under illuminant A in comparison to those obtained from the standard PCA method. © 2008 Wiley Periodicals, Inc. Col Res Appl, 33, 360–371, 2008     

Recovery of potash values from feldspar

ABSTRACT

India does not possess any soluble potassium (K) sources but an abundant resource of alumino-silicate rock such as feldspar is available. In the present work, an attempt has been made to unlock the potassium values from feldspar sample by mechanical milling, roasting and leaching and delineating the underlying mineral phase changes. CaCl₂ was found to be effective flux for K release with valuable by-products such as quartz and anorthite. The roasting kinetics follows the product layer diffusion model with an activation energy of 49.50 kJ/mol. It is found that the planetary ball milling has a significant effect on enhancing K-dissolution. With the combination of different treatments, it is possible to recover more than 95% K from feldspar.     

Recovery of unburned carbon from lime calcination process using statistical technique

In this study, unburned carbon recovery from lime calcination plant tailings was investigated using diesel oil, kerosene, MIBC and pine oil. A series of laboratory experiments using 2³ full factorial designs was conducted to determine the types and dosages of collector and frother. For these tests, data were analyzed by the paired t-test. The main and interaction effects on combustible recovery were evaluated using Yates' analysis. By optimizing the flotation parameters at slurry concentration of 34% solids, flotation time of 2.5 min, pH of 7.5, collector diesel oil dosage of 2780 g/t, and frother pine oil dosage of 2620 g/t, unburned carbon (UC) has been successfully recovered with 93.07% combustible recovery (CR) and 6030 kcal/kg calorifical value.     

Measuring the particle size of a known distribution using the focused beam reflectance measurement technique

The accuracy of the focused beam reflectance measurement (FBRM) probe, which measures a chord length distribution, from Mettler-Toledo Lasentec^® has been explored. A particle video microscope (PVM) probe, which provides in situ digital images, was used as a direct visual method to test the reliability of the FBRM results. These probes can provide in situ particle characterization at high pressures. The FBRM has been used to study emulsions and ice and clathrate hydrate formation. The ability of the FBRM to accurately characterize unimodal and bimodal distributions of particles and droplets and to measure agglomeration events was investigated. It was found that while the FBRM can successfully identify system changes, certain inaccuracies exist in the chord length distributions. Particularly, the FBRM was found to oversize unimodal distributions of glass beads, but undersize droplets in an emulsion and was unable to measure full agglomerate sizes. The onset of ice and hydrate nucleation and growth were successfully detected by the FBRM, but quantitative analysis of the particle and agglomerate sizes required simultaneous PVM measurements to be performed.     

Droplet spectra measurements of fan and cone atomisers using a laser diffraction technique

The droplet spectra of cone (D2/D4/D6 with 25 and 45 swirl plates) and single orifice fan (SS65015. SS6503 and SS6504) pressure atomisers were assessed at selected pressures (500, 700, 1000 and 1 500 kPa) using a laser diffraction technique. Care must be exercised when aligning the spray cloud with the laser beam when droplet spectra are measured using this technique. Because the cone was filled with small droplets (VMD 56.4 ± 1.8 μm) measurements taken at increasing distances between the laser and atomiser orifice resulted in decreasing VMDs, i.e. they reflected the higher volume of small droplets sampled, so the laser beam should penetrate the diameter of the cone as close to the break-up of the sheet as possible. With fan atomisers, consistent results were obtained if the spectra were measured with the spray cloud horizontal and the laser beam passing through the long axis of the spray cloud at right angles to the axis of the atomiser. Comparisons of this droplet spectra sampling technique with previous work show it to be more sensitive to the small droplet component of the spray.     

Bitumen content estimation of Athabasca oil sand from broad band infrared reflectance spectra

Oil sand is a mixture of quartz grains, clay minerals, bitumen, water, and minor accessory minerals. There is a need in oil sands mining operations for a robust method to estimate total bitumen content in real time; and so modelling of the total bitumen content (TBC) in Athabasca oil sands of Western Canada was undertaken on the basis of hyperspectral reflectance spectra. A selection of different bitumen, water, and clay mineral spectral features (3.0–30.0 µm) was used to develop broad‐band TBC predictive models that have good accuracy, with less than 1.5% error with respect to laboratory methods of bitumen assay. These models are also robust, in that they are independent of mine location. Simple broad band models, based upon previously identified Gaussian features or wavelet features, provide an incremental improvement over the currently deployed industry two‐band ratio model. An improved two‐band model was also developed, which makes use of a combination of the same two bands but normalised to their mean. A wavelet‐based, broad‐band model comprised of indices and five bands, where the bands are normalised to the mean of the bands, adequately addresses the influence of water, clay, and textural variation on selected bitumen features. This five‐band model appears to produce the most robust estimator of TBC, with a dispersion of ∼1.1–1.5%, which can be applied to different sites within a mine and to different mines without additional tuning or calibration, as evidenced by regression slopes of 0.99–1.0 for modelling, validation, and blind data sets.     

Remote bitumen content estimation of Athabasca oil sand from hyperspectral infrared reflectance spectra using Gaussian singlets and derivative of Gaussian wavelets

Modeling of the total bitumen content, TBC, in Athabasca oil sands was undertaken on the basis of its hyperspectral reflectance spectra. Spectra (8 cm⁻¹ resolution) were obtained that covered both the short-wave infrared and thermal infrared (TIR: 3.00-30.00 μm). Two methods, Gaussian fitting and wavelet analyses, were investigated to identify useful bitumen features as well as the best removal of the baseline. We aim to obtain the best determination of the TBC for a suitable suite of test and validation oil sands samples. The Gaussian model relied explicitly on features at 2.282 and 2.532 μm though these were only two of 10 features simultaneously fit with a quadratic baseline to the range of 2.230-2.603 μm of the spectra. The wavelet model relied on bitumen features selected at 2.274, 2.396 and 3.725 μm that could be isolated from the baseline and noise. Both models yielded similar dispersion in their estimates of TBC (±∼1-2%) while the wavelet model proved to be more robust when applied to the validation and blind data suites. We also considered the effects of using the L2 optimization (classical least-squares) and L1 optimization (minimization of largest outlier) schemes for both models. Both schemes produced similar results for the model suite of samples for TBC but the L1 was superior when applied to the validation and blind data suites. The wavelet model using the L1 optimization appeared to be quite robust producing estimates of TBC (±∼1.0-1.7%).     

Effect of classification by competitive neural network on reconstruction of reflectance spectra using principal component analysis

The best way to describe a color is to study its reflectance spectrum, which provide the most useful information. Different methods were purposed for reflectance spectra reconstruction from CIE tristimulus values such as principal components analysis. In this study, the training samples were first divided into 3, 6, 9, and 12 subgroups by creating a competitive neural network. To do that, L*a*b*, L*C*h or L*a*b*C*h were introduced to neural network as input elements. In order to investigate the performance of reflectance spectra reconstruction, the color difference and RMS between actual and reconstructed data were obtained. The reconstruction of reflectance spectra were improved by using a six or nine‐neuron layer with L*a*b* input elements. © 2016 Wiley Periodicals, Inc. Col Res Appl, 42, 182–188, 2017     

Recovery of copper values from bio-heap leaching of low grade Malanjkhand chalcopyrite ore

M/S Hindustan Copper Limited (HCL), India generates large amounts of lean sulfide ores of copper. The current production of lean copper ores in India is 0.55 million tons with ∼0.3% average copper content. Heap-bioleaching of the lean copper ores in 15 and 30 ton scales was undertaken at IMMT, Bhubaneswar. The leaching study showed 0.09% dissolution of copper from the ore body per day. The leach liquor was processed through solvent extraction and electrowinning. Extraction of copper from the actual leach liquor was carried out with 1.5% LIX 622N in kerosene with zero co-extraction of iron. The copper-free raffinate was fed back to the leaching unit. Stripping of copper from the loaded organic was carried out with 180 kg/m³ H₂SO₄. The copper pregnant electrolyte was passed through a carbon column to make it free from entrained organic and was fed to the electrowinning unit. The increase in current efficiency was due to the increase in the concentration of electrolyte. The energy consumption was 1.7 kWh/kg at a flow rate of 4.5 L/h. Smooth and bright sheets of copper of 99.99% purity were obtained.     

Effect of a standard colorimetric observer on the reconstruction of reflectance spectra of coloured fabrics

Principal component analysis is a statistical and mathematical method in colour science, which can be used in compression and reconstruction of reflectance spectra. The goal of this work is to study the effect of standard colorimetric observers and illuminant source combinations on the reconstruction of reflectance spectra of textile fabrics. Several computational approaches were introduced by using different combinations of D65, A and D75 illuminant sources and 2° and 10° standard colorimetric observers in reconstruction reflectance spectra from corresponding tristimulus values. The obtained results indicate that the accuracy of the estimation depends on the type of illuminant sources, standard observers and number of principal components. The best result was achieved by a 2° standard observer with more than four principal components. The optimal numbers of principal components for achieving the imperceptible colorimetric accuracy are 4 and 6 for 2° and 10° standard observers, respectively.     

Recovery of chromium from tannery effluents using a redox–adsorption approach

Adsorption isotherms for sodium and trivalent chromium uptake from aqueous solutions onto Amberlite resin were prepared at 18°C. Adsorption of each cation followed the Langmuir model. The rate of uptake of each cation was found to be film diffusion controlled with sodium showing the most rapid uptake. In aqueous solutions containing both chromium and sodium as the only cationic species, it was found that with increasing initial concentration of sodium, the trivalent chromium uptake on the resin decreased substantially. To overcome this difficulty a four step redox–adsorption system has been developed for the removal of Cr³⁺ from tannery effluents. The first step comprises the oxidation of trivalent chromium to the hexavalent form using selected common oxidising agents. The liquid effluent is then passed through an Amberlite cation-exchange resin in step 2 where the sodium in the waste stream is completely removed. The anionic hexavalent form of chromium (Cr₂O) passes unaltered through the resin along with the waste stream. In the third stage the dichromate is reduced back to the trivalent cationic form which is subsequently removed from the waste stream by a second Amberlite ion-exchange bed in stage 4. Each step in this process is assessed in batch and flow mode using simulated and real tannery effluents.     

Recovery and representation of spectral bidirectional reflectance distribution function from an image‐based measurement system

A spectral‐based method can acquire and represent the surface appearance of a given material physically correctly. But, it has drawbacks due to its high measurement cost and a long computation time in measuring, modeling, and rendering. In this article, we present spectral recovery and representation of spectral bidirectional reflectance distribution function (BRDF) from multispectral reflectance measurements in which we can render real appearance materials over a 3D model with accuracy and efficiency. First of all, an accurate spectral BRDF recovery algorithm, which transforms multispectral high dynamic range images into highly dense BRDFs in both a spectral and an angular domain, is proposed. Second, an efficient representation method is developed representing spectral BRDFs compactly using a factorization method and an adaptive spectral sampling method that uses a given error bound. The results show that the proposed method can compress the spectral BRDF data down by several hundred times while maintaining the given accuracy in colorimetric and spectral domains under a specific illuminant. © 2015 Wiley Periodicals, Inc. Col Res Appl, 41, 358–371, 2016     

Recovery of silicon from silicon sludge using supercritical water

In this paper, we propose a new methodology for recovering silicon from silicon sludge using supercritical water in a semi-batch reactor. Silicon sludge is the waste discharged from the silicon ingot cutting process and consists of cutting oil, cooling water, and silicon particles. The oil contained in silicon sludge was removed completely within several minutes by supercritical water elutriation at 400 or 500 °C and 25 MPa. The recovery percentage of silicon was only 70% at 400 °C owing to silicon dissolution. However, the recovery percentage was greater at a higher temperature (95% at 500 °C) because silicon dissolution was suppressed owing to the low ion product of water at higher temperatures. The silicon recovered at 500 °C and 25 MPa was approximately 99.2% pure. Contamination by oxidation was negligible because an oxide film did not grow on the silicon surface during the supercritical water treatment. We conclude that high-purity silicon can be recovered efficiently by supercritical water elutriation using a semi-batch reactor and that the methodology is promising for recovery of silicon from silicon sludge.     

Recovery of fluoride values from spent pot-lining: Precipitation of an aluminium hydroxyfluoride hydrate product

Treatment of spent pot-lining (SPL) from aluminium smelting cells by a two-stage leaching scheme comprising a water wash and an Al³⁺ leach and fluoride recovery as an aluminium hydroxyfluoride product has been studied for extraction of fluoride and then recovery as smelter grade AlF₃. The NaF content of a −1.18 mm size fraction was removed by the water wash, while the more refractory Na₃AlF₆ and CaF₂ were removed by treatment with 0.34 M Al³⁺ solution at 25 °C for 24 h, which yielded an overall fluoride extraction of 76–86 mol%. Mathematical modelling using experimental stability constant data was carried out to predict the effect of combining solutions and identify ways to manipulate the solution equilibria to maximise fluoride precipitation yields. The predictions were then tested experimentally. In the 4.5–5.5 pH range, selective precipitation of fluoride as an aluminium hydroxyfluoride hydrate product was achieved by neutralisation of the combined solutions with addition of 2 M NaOH solution. Higher pH values lead to the co-precipitation of hydrolysed sodium fluoroaluminates. Characterisation of precipitates using X-ray diffraction, scanning electron microscopy coupled with energy-dispersive spectroscopy, thermogravimetric analysis, differential thermal analysis, aluminium and fluoride determination have pointed out both the AlF₂(OH)·1.4H₂O stoichiometry and possible thermal decomposition pathways to yield a dehydrated aluminium hydroxyfluoride product, AlF₂(OH), that could be used for smelter grade AlF₃ production. The kinetics of hydrolysis are such that nucleation dominates while particle growth is restricted. Techniques to allow slow hydrolysis are necessary to form smelter grade AlF₃.