A new manufacturable filter design approach for spectral reflectance estimation

Selection of the best possible filter set among a set of available filters is the obvious method of increasing dimension of camera signals for spectral reflectance reconstruction. There are also methods that are focusing on the filter design regardless of noticing to the constructability of the designed filters. This study shows that direct optimization of physical variables of filter manufacturing technique is more reliable than indirect approach of designing and then physical manufacturing of the designed filters. Direct optimization of the transmission‐controlling primaries in filter manufacturing process would guarantee having the designed filters in reality. Combination of some solvent dyes was used as the spectral transmission matching system for filter manufacturing. As a conventional technique, filters were designed and best possible dye concentrations that match the desired filters were calculated. As an alternative approach, filters were also designed using direct optimization of dyes concentrations. The results showed that direct optimization of dye concentrations exhibits better performance in comparison with the conventional technique. © 2016 Wiley Periodicals, Inc. Col Res Appl, 42, 316–326, 2017     

Noise segmentation for improving performance of Wiener filter method in spectral reflectance estimation

Noise is an indispensable part of an imaging system. For having acceptable performance of reflectance estimation from digital signals, noise effects should be controlled. In this study a new method based on segmentation of noise is presented. Simulation and real experiments on four reflectance data sets showed that noise segmentation improves Wiener filter estimation method. However, oversegmentation can have reverse effect on the reflectance estimation results.     

Representation and estimation of spectral reflectances using projection on PCA and wavelet bases

In this article, we deal with the problem of spectral reflectance function representation and estimation in the context of multispectral imaging. Because the reconstruction of such functions is an inverse problem, slight variations in input data completely skew the expected results. Therefore, stabilizing the reconstruction process is necessary. To do this, we propose to use wavelets as basis functions, and we compare those with Fourier and PCA bases. We present the idea and compare these three methods, which belong to the class of linear models. The PCA method is training‐set dependent and confirms its robustness when applied to reflectance estimation of the training sets. Fourier and wavelet bases allow good generalization; an advantage of wavelets is that they avoid boundary artifacts. The results are evaluated with the commonly used goodness‐of‐fit coefficient (GFC), and the reliability of the use of wavelets is proved. © 2008 Wiley Periodicals, Inc. Col Res Appl, 33, 485–493, 2008     

Artwork imaging from 370 to 1630 nm using a novel multispectral system based on light‐emitting diodes

The recent use of multispectral systems as a noncontact method for analysis of artworks has already shown promising results. This study explains the application of a novel portable multispectral system based on light‐emitting diodes (LEDs) for artwork imaging. This method provides spectral information in a spectral range from 370 to 1630 nm with a 25 cm × 25 cm field of view by using two different image sensors in synchrony with 23 bands of irradiation. The spectral information for each point is estimated and validated using the pseudo‐inverse and spline interpolation methods for spectral estimation and three different evaluation metrics. The results of the metrics obtained with both estimation methods show a general good performance of the system over the whole spectral range. The experiments also showed that the selection of the training set for the pseudo‐inverse estimation has a great influence in its performance, and thus, it defines whether or not the pseudo‐inverse outperforms the spline interpolation method. The system is applied in situ to the study of Catalan art masterpieces, and the results demonstrate the potential of a cost‐effective and versatile system using various off‐the‐shelf elements to reconstruct color information and to reveal features not previously identified. © 2014 Wiley Periodicals, Inc. Col Res Appl, 40, 398–407, 2015     

An integrated spectral imaging system for producing color images of static and moving objects

An integrated spectral imaging system constructed by synchronizing a programmable light source, a high‐speed monochrome camera, and a display device is proposed to produce tristimulus images of static and moving objects effectively in real time onto the display. This system is called the CIE‐XYZ display. Active spectral illuminants, containing both the device characteristics of camera and display, are projected onto object surfaces as time sequence. The images are captured synchronously by the camera and quickly transmitted to the display device in the RGB signal form so that the accurate tristimulus images are displayed. First, we describe the principle of the CIE‐XYZ tristimulus display. The theoretically optimal illuminants contain negative parts in the spectral curves. Second, we design practical illuminants with all positive spectral curves. The color images in our system are composed of the time sequence of RGB component images. Then, the synthesized color images on the display contain color artifacts when objects move fast. An image processing algorithm for correcting the motion color artifact is proposed based on optical flow estimation using a graphics processing unit. The comprehensive performance of the proposed system and algorithms is examined using both static and moving objects. © 2014 Wiley Periodicals, Inc. Col Res Appl, 40, 329–340, 2015     

Research on filter selection method for broadband spectral imaging system based on ancient murals

Digitization of cultural heritage protection has received considerable attention in heritage studies and spectral imaging technology has been playing an important role in this research. This article aims to study the technique of selecting optimal filter set to obtain ancient murals spectral image with high spectral and colorimetric accuracy based on the broadband spectral imaging system. The 330 Dunhuang murals mineral pigment color patches and the GretagMacbeth ColorChecker (CC) as well as 27 pieces of optical filters chosen as samples were examined. For each piece of filter, the three‐channel image was captured by the spectral imaging system. Then, 351 groups of six‐channel digital count images were acquired by arbitrary combinations of two among the 27 three‐channel digital count images. The pseudo‐inverse, principal component analysis, and R‐matrix methods were used to reconstruct the spectral reflectance from the six‐channel digital counts for each sample. Finally, this study identified the optimal filter set by evaluating the integrated error (TOTAL ERROR), which was calculated by normalizing the mean spectral root‐mean‐square error (RMS), mean spectral goodness‐of‐fit error (1‐GFC), and mean CIEDE2000 color difference (ΔE₀₀) and by multiplying them together. After the optimal optic filter set was selected, it was applied to the Dunhuang murals spectral imaging and was evaluated. The results showed that the optimal optic filter set could result in promising improvement both in spectral and color accuracy when compared with the production camera. In addition, it can be used for the construction of Dunhuang murals spectral image database. © 2015 Wiley Periodicals, Inc. Col Res Appl, 41, 585–595, 2016     

Assessing color performance of whole‐slide imaging scanners for digital pathology

The color performance of two commercial whole‐slide imaging (WSI) scanners was compared against the ground truth and a hypothetical monochrome scanner. Three biological tissue slides were used to test the WSI scanners. A multispectral imaging system was developed to obtain the color truth of the biological tissue slides at the pixel level. The hypothetical monochrome scanner was derived from the color truth as a lower bound for comparison. The CIEDE2000 formula was used to measure color errors. Results show that color errors generated by the modern commercial WSI scanner, the legacy commercial WSI scanner, and the monochrome WSI scanner are in the range of [8.4, 13.0], [18.0, 26.33], and [17.4, 17.6] ΔE₀₀, respectively. The legacy commercial WSI scanner was outperformed by not only the modern commercial WSI scanner but also by the hypothetical monochrome scanner.     

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     

Bernstein polynomial estimation of a spectral density

Abstract. We consider an application of Bernstein polynomials for estimating a spectral density of a stationary process. The resulting estimator can be interpreted as a convex combination of the (Daniell) kernel spectral density estimators at m points, the coefficients of which are probabilities of the binomial distribution bin(m ? 1, |λ|/π), λ ∈ Π ≡ [?π, π] being the frequency where the spectral density estimation is made. Several asymptotic properties are investigated under conditions of the degree m. We also discuss methods of data‐driven choice of the degree m. For a comparison with the ordinary kernel method, a Monte Carlo simulation illustrates our methodology and examines its performance in small sample.     

Dictionary‐based estimation of spectra for wide‐gamut color imaging

With the widespread use of commercialized wide‐gamut displays, the demand for wide‐gamut image content is increasing. To acquire wide‐gamut image content using camera systems, color information should be accurately reconstructed from recorded image signals for a wide range of colors. However, it is difficult to obtain color information accurately, especially for saturated colors, if conventional color cameras are used. Spectrum‐based color image reproduction can solve this problem; however, bulky spectral imaging systems are required for this purpose. To acquire spectral images more conveniently, a new spectral imaging scheme has been proposed that uses two types of data: high spatial‐resolution red, green, and blue (RGB) images and low spatial‐resolution spectral data measured from the same scene. Although this method estimates spectral images with high overall accuracy, the error becomes relatively large when multiple different colors, especially those with high saturation, are arranged in a small region. The main reason for this error is that the spectral data are utilized as low‐order spectral statistics of local spectra in this method. To solve this problem, in this study, a nonlinear estimation method based on sparse and redundant dictionaries was used for spectral image estimation—where the dictionary contains a number of spectra—without loss of information from the low spatial‐resolution spectral data. The estimated spectra are represented by a mixture of a few spectra included in the dictionary. Therefore, the respective feature of every spectrum is expected to be preserved in the estimation, and the color saturation is also preserved for any region. Experiments performed using the simulated data showed that the dictionary‐based estimation can be used to obtain saturated colors accurately, even when multiple colors are arranged in a small region. © 2011 Wiley Periodicals, Inc. Col Res Appl, 2013     

Signal modelling and algorithms for parameter estimation in pneumatic conveying

Capacitive measurement principles offer a non-invasive approach to determine particle velocity as well as particle concentration in pneumatic conveying. In order to assess the quality of a reconstruction method, it is mandatory to know the prevailing velocity and concentration profiles. For particulate bulk solids transportation, accurate reference systems are either not available or very expensive. Based on measurement data, a signal model of the particle flow is developed for dilute phase and dense phase conveying. These models are used to demonstrate the applicability of proposed algorithms for parameter determination — a cross-correlation technique for dilute phase and a two-step approach using the Fourier transform for dense phase.     

The theoretical estimation of effective spectral dimension for polymer melts

The theoretical technique of an effective spectral dimension estimation for polymer melts is offered. The comparison of experimental and theoretical values of this parameter has shown their good correspondence. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 94: 1353–1356, 2004     

Numerical simulation of particulate processes for control and estimation by spectral methods

Results of application of pseudospectral methods, also known as spectral collocation methods, to practical particulate processes including growth, nucleation, aggregation, and breakage are presented. For growth‐dominated processes, a considerable reduction in model dimension can be achieved; for pure aggregation and breakage they form a viable option. To handle problems that include aggregation, breakage, and growth phenomena simultaneously, we introduce a hybrid algorithm combining the advantages of spectral methods and cell average or fixed pivot methods for aggregation and breakage. Results are shown for analytical examples as well as real processes taken from the fields of granulation and crystallization. © 2011 American Institute of Chemical Engineers AIChE J, 58: 2309–2319, 2012     

Dynamic parameter estimation and optimization for batch distillation

This work reviews a well-known methodology for batch distillation modeling, estimation, and optimization but adds a new case study with experimental validation. Use of nonlinear statistics and a sensitivity analysis provides valuable insight for model validation and optimization verification for batch columns. The application is a simple, batch column with a binary methanol–ethanol mixture. Dynamic parameter estimation with an ℓ₁-norm error, nonlinear confidence intervals, ranking of observable parameters, and efficient sensitivity analysis are used to refine the model and find the best parameter estimates for dynamic optimization implementation. The statistical and sensitivity analyses indicated there are only a subset of parameters that are observable. For the batch column, the optimized production rate increases by 14% while maintaining product purity requirements.     

感温变色建筑涂料的制备及光谱反射性能实验研究

感温变色建筑涂料在降低建筑冷热负荷、改善城市热环境方面具有很大的应用潜力。为了探究感温变色材料光学性能的影响因素,优化材料配方,首先制备了12种不同配方,变色温度为31℃的感温变色涂料,并分析了金红石型TiO₂质量百分含量对涂料光谱反射率和太阳光反射比的影响,研究表明涂料光谱反射率均随着TiO₂含量的增加而提高,感温变色粉最佳质量分数5%,TiO₂的最佳质量分数应在5%~10%之间,此时浅色态的反射比比深色态高0.2以上。同时探究了TiO₂粒径对涂料在不同波段反射率的影响,结果表明,在紫外和除红光外的可见光波段,感温变色涂料的反射率基本上随TiO₂粒径的增大而减小;在红光和近红外波段,感温变色涂料反射率基本上随TiO₂粒径的增大而增大。     

Comparison of certain MINLP algorithms when applied to a model structure determination and parameter estimation problem

The maximum likelihood method is frequently used in parameter estimation. If the structure of the model is unknown, the maximization of the likelihood function can be replaced by minimizing an information criterion. One criterion that allows this to be done is Akaike’s information criterion (AIC). Minimizing the AIC is a mixed integer non-linear programming (MINLP) problem. In this paper, three different MINLP algorithms are compared in the solution of a simultaneous model structure determination and parameter estimation problem by minimizing the AIC criterion. The problem considered appears in quantitative Fourier transformed infra red (FTIR) spectroscopy where concentration estimates of certain gas components are to be obtained from measured absorbances at different wave numbers. The resulting problem is a large MINLP problem containing several hundreds, or even thousands, of variables including a huge number of possible model structures. It is, however, found that the studied algorithms solve the considered problem in quite a small number of iterations and a reasonable CPU-time.     

Ultraviolet and infrared spectral analysis of irradiated polyethylene films: Correlation and possible application for large-dose radiation dosimetry

A detailed study was performed to develop the dosimetric characteristics of commercial low-density polyethylene film (LDPE), which is, by far, the most commonly used plastic for food and for many other-purpose packaging film, to be used as a film dosimeter for large-dose γ-radiation dosimetry. The useful dose range extends up to 880 kGy. Correlations were established between the absorbed dose of γ-radiation and the radiation-induced changes in LDPE measured using Fourier transform infrared (FTIR) and ultraviolet (UV) spectrophotometry. The results showed a significant dependence of the response on the selected readout tool of measurements whether FTIR (at 1716 cm⁻¹) or UV (at 220 and 270 nm) as well as on the quantity used for calculation. The radiation-chemical yield of the ketonic carbonyl group produced in irradiated LDPE film was found to be 0.7 μmol/J. The assessment of the random uncertainty associated with the measurement of the dose response and the effect of relative humidity during irradiation on the dosimeter performance as well as the postirradiation stability at different storage conditions are discussed. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 67:1837–1851, 1998     

低温多效蒸发海水淡化系统性能估算方法及公式

Low temperature multi-effect evaporation (LT-MEE) seawater desalination systems with top brine temperature lower than 70℃ have attracted attention in recent years.A method for performance estimation of LT-MEE is proposed, and a formula is built for a typical LT-MEE configuration.Excluding complex properties of working fluids and details of heat and mass transfer processes, this formula involves only simple algebraic operations, thus provides a convenient way to evaluate the water production of LT-MEE for different motive heat source conditions and design parameters.Comparing the formula prediction with the data from both rigorous models and references, it indicates that the formula can give good results in wide parameter ranges.Although this method is proposed based on a typical LT-MEE configuration, it is also applicable to other LT-MEE configurations and thermal desalination systems.     

Sequential experimental design for estimation and analysis of thermal parameters in a fixed bed

The analysis of the effective radial thermal conductivity and the film heat transfer coefficient were carried out in a fixed bed. The temperature profiles were described by two‐dimensional pseudo‐homogeneous model. The thermal parameters were estimated using a sequential experimental design technique. The minimum volume criterion was used to design the next point for temperature measurement in the bed. The utilization of T = T₀ (constant) as the boundary condition at the bed inlet resulted in an axial variation of thermal parameters, which was the factor responsible for the inadequacy of the model in fitting experimental data of different bed heights simultaneously. Using T = T(r) as the boundary condition makes the thermal parameters independent of the axial position and the model statiscally adequate to describe the axial and radial temperature profiles throughout the bed.     

Comparative study of estimation methods for continuous time stochastic processes

In this paper we investigate the finite sample performances of five estimation methods for a continuous-time stochastic process from discrete observations. Applying these methods to two examples of stochastic differential equations, one with linear drift and state-dependent diffusion coefficients and the other with nonlinear drift and constant diffusion coefficients, Monte Carlo experiments are carried out to evaluate the finite sample performance of each method. The Monte Carlo results indicate that the differences between the methods are large when the discrete- time interval is large. In addition, these differences are noticeable in estimations of the diffusion coefficients.