Hyperspectral Imaging Device Research Articles

Apple Bruise Grading Using Piecewise Nonlinear Curve Fitting for Hyperspectral Imaging Data

Apple fruits can be easily damaged, and bruises occur on peels during harvest, transportation and storage, which could decrease fruit quality. This paper proposed an apple bruise grading method based on hyperspectral imaging (HSI). The spectral information of sound apples (Yantai Fuji 8) was first captured using a hyperspectral reflectance imaging device (386-1016 nm). These apples were then mechanically damaged by the same impact forces, and the bruised regions were exposed to room temperature for at most 120 min. The spectral data of the bruised apples at four different exposure times (30 min, 60 min, 90 min and 120 min) were obtained. The spectral data were preprocessed using Procrustes analysis (PA) to enable a more diverse distribution of the spectra among different patterns. To both accurately maintain the spectral information of different patterns and reduce the dimensions of the spectra, piecewise nonlinear curve fitting (PWCF) was presented using the least squares algorithm, where the resultant fitting coefficients from different spectral intervals were catenated into a low-dimension feature descriptor. The feature descriptors were then fed to an error-correction output coding-based support vector machine (ECOC-SVM) to grade the bruised apples. To further evaluate the performance of the presented PWCF, conventional algorithms, including the successive projections algorithm (SPA), genetic algorithm (GA), principal component analysis (PCA) and kernel principal component analysis (KPCA), were introduced for comparison. Experimental results showed that the proposed method obtained the best grading accuracy (97.33%) compared to the other methods.

Study of temperature, apparent spectral emissivity, and soot loading of a single burning coal particle using hyper-spectral imaging technique

A hyper-spectral imaging device that can simultaneously capture three-dimensional data information of spectra, space, and time is employed to experimentally investigate the combustion behavior of a single coal particle. Three types of single pulverized coal particles are injected and burned on a Hencken flat-flame burner, and their flames are captured by a high-speed camera and the hyper-spectral imaging device. The camera observations demonstrate that the three single coal particles undergo particle heat-up, volatile release and combustion, and volatile and char oxidation during the combustion process. Furthermore, the image captured by the hyper-spectral imaging device records the spectral and spatial history of the single burning coal particles throughout the combustion process. Then, the time–space temperature and apparent spectral emissivity of the single burning char particles are calculated from the time–space spectra radiative intensity obtained by the hyper-spectral imaging device. The gray characteristic exhibited by the spectral emissivity of the three single burning char particles in the longer wavelength range demonstrates the feasibility of calculating the temperature using the two-color method. Finally, the soot temperature and volume fraction distribution in the volatile flames are obtained to investigate the formation of soot during the combustion of a single coal particle. The results show that an elongated tail-like soot cloud is formed around the two single bituminous coal particles during the combustion process, but a nearly spherical soot cloud is formed around the single lignite coal particle. Moreover, the range of soot volume fractions in the three envelope volatile flames is comparable to the order of magnitude of the values measured by other researchers.

Simultaneous Reconstruction of the Temperature and Inhomogeneous Radiative Properties of Soot in Atmospheric and Pressurized Ethylene/Air Flames

ABSTRACT An inverse method is proposed to retrieve soot temperature and radiative properties in co-flow laminar diffusion ethylene/air flames. The proposed inverse method is first verified as capable of the simultaneous reconstruction of soot temperature and inhomogeneous radiative properties with and without scattering. Thereafter, the soot temperature, absorption and scattering coefficients in atmospheric ethylene/air flames is experimentally inverted from the radiative intensity taken by a hyper-spectral imaging device by means of the inverse method. From the results, it is found that neglecting scattering has an insignificant influence on the retrieved flame radiative properties, due to the weak scattering ability of soot in the atmospheric flames. Furthermore, the simultaneous reconstruction of the soot temperature and inhomogeneous radiative properties is also numerically conducted in the pressurized flames, where scattering has comparable strengths with absorption. In general, neglecting scattering in pressurized flames leads to significant underestimation of the retrieved temperature and obvious deviation of the retrieved absorption coefficients. It follows that the effect of scattering from high levels of soot in these pressurized flames is significant and should generally be considered in the reconstruction (measurement) of soot properties.

Custom Scanning Hyperspectral Imaging System for Biomedical Applications: Modeling, Benchmarking, and Specifications.

Prototyping hyperspectral imaging devices in current biomedical optics research requires taking into consideration various issues regarding optics, imaging, and instrumentation. In summary, an ideal imaging system should only be limited by exposure time, but there will be technological limitations (e.g., actuator delay and backlash, network delays, or embedded CPU speed) that should be considered, modeled, and optimized. This can be achieved by constructing a multiparametric model for the imaging system in question. The article describes a rotating-mirror scanning hyperspectral imaging device, its multiparametric model, as well as design and calibration protocols used to achieve its optimal performance. The main objective of the manuscript is to describe the device and review this imaging modality, while showcasing technical caveats, models and benchmarks, in an attempt to simplify and standardize specifications, as well as to incentivize prototyping similar future designs.

Measurement of the distribution of temperature and emissivity of a candle flame using hyperspectral imaging technique

A candle flame is experimentally studied using a hyperspectral imaging device in this paper. The distributions of temperature and wavelength-dependent emissivity are calculated using a Newton-type iterative method. The results show that the spectral radiation intensity increases from the outside to the inside in the candle flame, and at the same spatial point, the intensity increases as the wavelength increases. The highest temperature of the candle flame is about 1980 K, occurs close to the flame border, indicating the most vigorous reaction. Additionally, the radiation characteristics of the candle flame differ from a gray-body, and the emissivity of the flame decreases as the wavelength increases.

Changing channels

Researchers from New Mexico State University have put forward an experimental demonstration of a fluidic-based plasmonic device for use in spectral analysis which utilises the modification of surface plasmon resonance in periodically coupled metallic nanostructures. This work achieves precise control of the center wavelength of the surface plasmon resonance by changing the local environment of the nanostructures via microfluidic channels, offering an efficient way to acquire large spectral samples. To implement spectral analysis devices, two main components are required: dispersive optical elements, and photodetectors. The dispersive elements spatially separate frequency components of light and photodetectors convert spatially separated light into electrical signals for further data analysis. Prof. David Voelz (left), Mr. Charles Pelzman (middle), Prof. Sang-Yeon Cho (right). Mr. Charles Pelzman is a PhD candidate in Electrical and Computer Engineering at New Mexico State University, Las Cruces, NM, USA. Metallic nanostructures integrated with SU8-microfluidic channels. Right: Dark-field transmission photomicrograph showing optical transmission at different wavelengths through the nanostructures. One of the attractive features of spectral analysis devices is their capability to measure unique optical signatures of specific chemical elements. This detection capability is highly specific and quantitative in nature, which makes the spectral analysis devices useful for a variety of applications. In the teams Letter, they report the experimental demonstration of a fluidic-based plasmonic spectral analysis device. The demonstrated device consists of nanometer-scale metallic structures and polymer-based microfluidic channels. The metallic structures allow optical transmission within a pre-determined spectral band and reject other spectral components of light, acting as optical bandpass filters. The microfluidic channels were used to precisely control the center wavelength of each bandpass filter by changing the effective refractive index of the metallic nanostructures. Co-author Sang-Yeon Cho discusses the proposed system: “Compared to other dispersive-optical-element-based spectral analysis devices, this work used a combination of plasmonic spectral filtering and fluidic-based refractive-index control to measure spectral information. This approach does not rely on angular dispersion of light but utilises resonance-assisted enhanced optical transmission through nanostructures. Therefore, the entire spectral analysis system can be miniaturised into a chip-scale device.” This fluidic-based plasmonic spectral analysis device uses a novel approach to precisely control the location of the center wavelength. The microfluidic channels implemented on top of the plasmonic filters can alter the microscopic optical environment of the metallic nanostructures by delivering refractive-index calibrated fluids. In theory, this approach can provide an infinite number of transmission bands (sampling points) for spectral analysis, which was not possible in previous systems. A major fabrication challenge was the integration of polymer-based microfluidic channels and metallic nanostructures due to their incompatibility. During nanostructure patterning in a dual-beam lithography system, microfluidic channels accumulated electrons and ions on the surface, leading to significant reduction in imaging and patterning resolutions in the lithography system. This technical issue was resolved by depositing an optically thin conductive layer on the surface of the sample to provide a path for discharging electrons and ions around the polymer structures. This work is the first experimental demonstration of a fluidic-based spectral analysis device and this approach can greatly enhance spectral resolution by providing a very large number of sampling points for analysis. For short term uses, the demonstrated spectral analysis system can be used as a chip-scale optical spectrometer in the visible and near-infrared regions. For long-term developments, by making a 2D array of the demonstrated device, it can be used as a hyperspectral imaging device. Currently, the team is trying to reduce the spectral width of the optical transmission bands by creating a symmetric environment for the surface plasmon waves in the fabricated nanostructure. Professor Cho notes on the progress: “Chip-scale spectral analysis devices are enabling technology in many applications because of their compact size, lightweight, and low power consumption.” Over the next decade, this new technology can be integrated with personal mobile devices for various sensing applications. For instance, a smart phone equipped with a chip-scale spectrometer will be able to analyse air quality or detect hidden explosives from unknown packages by simply taking photos. To fully implement this mobile sensing technology, one of the remaining hurdles is the further reduction of the transmission bandwidth.

Experimental determination of distributions of soot particle diameter and number density by emission and scattering techniques**Project supported by the National Key Research and Development Program of China (Grant No. 2017YFB0601900), the National Natural Science Foundation of China (Grant Nos. 51827808, 51821004, and 51406095), the Fundamental Research Funds for the Central Universities, China (Grant Nos. 2018ZD03 and 2017ZZD005), and Science and

A diagnostics method was presented that uses emission and scattering techniques to simultaneously determine the distributions of soot particle diameter and number density in hydrocarbon flames. Two manta G-504C cameras were utilized for the scattering measurement, with consideration of the attenuation effect in the flames according to corresponding absorption coefficients. Distributions of soot particle diameter and number density were simultaneously determined using the measured scattering coefficients and absorption coefficients under multiple wavelengths already measured with a SOC701V hyper-spectral imaging device, according to the Mie scattering theory. A flame was produced using an axisymmetric laminar diffusion flame burner with 194 mL/min ethylene and 284 L/min air, and distributions of particle diameter and number density for the flame were presented. Consequently, the distributions of soot volume fraction were calculated using these two parameters as well, which were in good agreement with the results calculated according to the Rayleigh approximation, demonstrating that the proposed diagnostic method is capable of simultaneous determination of the distributions of soot particle diameter and number density.

Production of an innovative biowaste-derived fertilizer: Rapid monitoring of physical-chemical parameters by hyperspectral imaging

In this work the possibility to apply hyperspectral imaging as a fast and non-destructive technique for the monitoring of the production process at pilot plant scale of an innovative biowaste-derived fertilizer was explored. Different mixtures of urban organic waste, farm organic residues, biochar and vegetable active principles were selected and utilized in two different European countries, Italy and Spain, for the production of the innovative fertilizer. The biowaste-derived fertilizer samples were collected from the pilot plant piles at different curing time and acquired by the hyperspectral imaging device. Spectra have been collected in the near infrared wavelength range (1000–1700 nm). Conventional analyses were carried out on the same samples in order to find correlations between the physical-chemical parameters detected at laboratory scale, and the acquired reflectance spectra. The investigated parameters were: pH, electrical conductivity, soluble total organic carbon and soluble total nitrogen.Hyperspectral data were processed adopting chemometric strategies through the application of principal component analysis, for exploratory purposes, and partial least squares analysis to establish correlations between spectral features and measured physical-chemical parameters. Good correlations, with R2 ranging between 0.85 and 0.96, were obtained for all the investigated parameters. Results showed as the proposed approach, based on hyperspectral imaging, is suitable to be adopted for a rapid and non-destructive monitoring of waste-derived fertilizer production.

Predicting macroalgal pigments (chlorophyll a, chlorophyll b, chlorophyll a + b, carotenoids) in various environmental conditions using high-resolution hyperspectral spectroradiometers

ABSTRACTPhotosynthetic pigments may indicate the health and productivity of vegetation and thereby are among the most important targets of the remote-sensing science. We studied the relationship between macroalgae pigment concentration measured in situ and spectral reflectance, to develop predictive remote-sensing methods for macroalgal pigments. The measurements of spectral reflectance of macroalgae were made using both a field portable spectrometer Ramses built by TriOS GmbH (Germany) and a laboratory hyperspectral imaging device HySpex built by Norsk Elektro Optikk (Norway). Our results showed that differences in total chlorophyll (Chl-a + b) concentrations resulted in the consistent change of spectral reflectance for studied brown (Fucus vesiculosus) and green (Cladophora glomerata, Ulva intestinalis) macroalgae species. Charophytes (Chara aspera, Chara horrida) were also studied, and the relationship was much weaker for this taxon. If spectral indices predicted relatively well the concentration of Chl-a + b (R2 = 0.64–0.73) and the carotenoid to total chlorophyll ratio (Car:Chl-a + b, R2 = 0.80) across the five studied macroalgae species, then the concentration of chlorophyll a (Chl-a), chlorophyll b (Chl-b), and carotenoids (Car) were more difficult to model (R2 = 0.004–0.51). The HySpex imaging system yielded systematically better results in predicting pigment concentrations compared to the Ramses spectroradiometer. By using traditional assessment of pigment concentration along with the Hyspex imaging device, we were able to build models with a capability to predict the spatial patterns of pigment concentration for Baltic Sea macroalgae.

SpectraCam® : A new polarized hyperspectral imaging system for repeatable and reproducible in vivo skin quantification of melanin, total hemoglobin, and oxygen saturation.

An accurate way to determine skin pigmentation is to acquire the spectral reflectance of a skin sample and to quantify chromophores by reverse calculation from physical models of light propagation. Therefore, we tested a new hyperspectral imaging device and software suite, the SpectraCam® system, and evaluated its accuracy to quantify skin chromophores. Validation of the SpectraCam® system was performed by, firstly, comparing the known and the acquired reflectance spectra of color phantoms. Repeatability and reproducibility were then evaluated by two operators who performed acquisitions at different time points and compared the acquired reflectance spectra. The specificity of the system was tested by quantitative analysis of single chromophore variation models: lentigo and pressure relief. Finally, we tested the ability of the SpectraCam® system to detect variations in chromophore in the eye region due to the daily application of a new anti-dark circle cosmetic product. The SpectraCam® system faithfully acquires the reflectance spectra of color phantoms (r2 >0.90). The skin reflectance spectra acquired by different operators at different times are highly repeatable (r2 >0.94) and reproducible (r2 >0.99). The SpectraCam® system can also produce qualitative maps that reveal local variations in skin chromophore or underlying structures such as blood vessels. The system is precise enough to detect melanin variation in lentigo or total hemoglobin and oxygen saturation variations upon pressure relief. It is also sensitive enough to detect a decrease in melanin in the eye region due to the application of an anti-dark circle cosmetic product. The SpectraCam® system proves to be rapid and produces high-resolution data encompassing a large field of view. It is a robust hyperspectral imaging system that quantifies melanin, total hemoglobin, and oxygen saturation and is well adapted to cosmetic research.

Evaluation of hyperspectral imaging technology in patients with peripheral vascular disease

BackgroundHyperspectral imaging technology is a novel method of using transcutaneous measurement of oxyhemoglobin (HT-Oxy) and deoxyhemoglobin (HT-Deoxy) concentrations to create a two-dimensional, color-coded “oxygen map.” The aims of this study were to compare the use of a hyperspectral imaging device with the transcutaneous oxygen measurement (TCOM), ankle-brachial index (ABI), and severity of peripheral vascular disease (PVD) and to assess their correlations. MethodsThis prospective study recruited 294 participants divided into three distinct groups composed of healthy volunteers and patients with PVD. Patients underwent measurements of lower limbs at a standardized point over the head of the first metatarsal on the plantar aspect using the hyperspectral imaging device, generating four outputs including HT-Oxy, HT-Deoxy, oxygen saturation (HT-Sat), and skin temperature, and the TCOM system, generating transcutaneous partial pressure of oxygen (TcpO2) and carbon dioxide (TcpCO2). Demographic data, severity of PVD, ABI, and other pertinent information were obtained from both the participants and medical records. ResultsInteroperator reliability ranged from 86% to 94% across the four hyperspectral imaging device outputs, whereas intraoperator reliability ranged from 92% to 94%. The HT-Oxy, HT-Sat, TcpCO2, and ABI of the diseased limb correlated significantly with the severity of PVD. HT-Sat significantly correlated with TcpO2 (R = 0.19), TcpCO2 (R = −0.26), ABI (R = 0.42), and skin temperature (R = 0.56). HT-Deoxy also correlated with TcpCO2 (R = 0.27). ConclusionsThis study demonstrates the reliability of hyperspectral imaging in comparison to TCOM, ABI, skin temperature, and severity of PVD in a series of patients. Its correlation to other established modalities and low interoperator and intraoperator variability could enable this modality to be a useful screening tool in PVD.

Measurement of Soot Temperature and Volume Fraction of Axisymmetric Ethylene Laminar Flames Using Hyperspectral Tomography

Three kinds of atmospheres, namely, air, oxygen-enriched air, and oxygen/carbon dioxide atmospheres, and a total of ten axisymmetric coflow ethylene laminar flames are experimentally studied using a hyperspectral imaging device. 2-D distributions of the local emission source term in the visible and near-infrared ranges are reconstructed using the least-squares method. Then the distributions of temperature and absorption coefficient are calculated using the Newton-type iterative method, while the wavelength dependence of the absorption coefficient is fitted by polynomials. For the nonoptically thin flame, an iterative algorithm is adopted by substituting the absorption coefficients back into the reconstruction. The experimental results show that there exists a local temperature peak near the flame edge and the flame root. Additionally, for an oxygen-enriched atmosphere, there also exists another local temperature peak in upper center part of the flame in an air/oxygen atmosphere or in the upper edge part in an oxygen/carbon dioxide atmosphere. The results also reveal that the reduction in the flow of ethylene will result in the decrease in the highest soot volume fraction, and a higher oxygen content will generate a higher temperature peak and a lower soot volume fraction peak in an oxygen-enriched air atmosphere, but a higher soot volume fraction peak in an oxygen-enriched oxygen/carbon dioxide atmosphere. In addition, in an air atmosphere or an atmosphere with a large quantity of carbon dioxide, there will be another local peak of the soot volume fraction in the upper center part of the flame, which may be aggravated by the reduction in the amount of ethylene.

Digital restoration of damaged color documents based on hyperspectral imaging and lattice associative memories

This paper introduces an autonomous hybrid technique designed for the digital restoration of the missing parts and occluding artifacts in damaged historical or artistic color documents. For this purpose, a hyperspectral imaging device is used to acquire sets of images in the visible and near infrared ranges. Assuming the presence of linearly mixed pixels registered from the spectral images, our technique uses two lattice auto-associative memories to extract the set of pure pigments spectra. Fractional abundance maps indicating the distributions of each pigment along the image are obtained by spectral linear unmixing. These maps are then used to locate holes and cracks in the document under study. The restoration process is performed by the application of a modified morphological region filling algorithm, followed by a vectorial linear interpolation scheme to restore the original color appearance of the filled areas. For illustration purposes, our procedure has been applied successfully to the restoration of superimposed scripts and an art painting.

Field identification and spatial determination of hazardous chemicals by Fourier transform infrared imaging

ABSTRACTA hyperspectral imaging device is reported for the remote sensing of hazardous chemical clouds. The device, which is based on Fourier transform spectrometry, displays two-dimensional images of spatially resolved spectral information delivered from a focal-plane-array detector. An algorithm for chemical-cloud detection using the spectrum obtained by the hyperspectral imaging device was also developed. In order to promptly extract results from the large quantity of spectral information, the detection algorithm included approximate and precise detection steps. The performance of the hyperspectral imaging device was characterized in the lab and in the field using the detection algorithm. The real-time distribution of a chemical cloud was successfully observed.

Measurement of distributions of temperature and wavelength-dependent emissivity of a laminar diffusion flame using hyper-spectral imaging technique

A generalized method to estimate a two-dimensional (2D) distribution of temperature and wavelength-dependent emissivity in a sooty flame with spectroscopic radiation intensities is proposed in this paper. The method adopts a Newton-type iterative method to solve the unknown coefficients in the polynomial relationship between the emissivity and the wavelength, as well as the unknown temperature. Polynomial functions with increasing order are examined, and final results are determined as the result converges. Numerical simulation on a fictitious flame with wavelength-dependent absorption coefficients shows a good performance with relative errors less than 0.5% in the average temperature. What’s more, a hyper-spectral imaging device is introduced to measure an ethylene/air laminar diffusion flame with the proposed method. The proper order for the polynomial function is selected to be 2, because every one order increase in the polynomial function will only bring in a temperature variation smaller than 20 K. For the ethylene laminar diffusion flame with 194 ml min−1 C2H4 and 284 L min−1 air studied in this paper, the 2D distribution of average temperature estimated along the line of sight is similar to, but smoother than that of the local temperature given in references, and the 2D distribution of emissivity shows a cumulative effect of the absorption coefficient along the line of sight. It also shows that emissivity of the flame decreases as the wavelength increases. The emissivity under wavelength 400 nm is about 2.5 times as much as that under wavelength 1000 nm for a typical line-of-sight in the flame, with the same trend for the absorption coefficient of soot varied with the wavelength.

Hyperspectral Imaging as an Early Biomarker for Radiation Exposure and Microcirculatory Damage.

Radiation exposure can lead to detrimental effects in skin microcirculation. The precise relationship between radiation dose received and its effect on cutaneous perfusion still remains controversial. Previously, we have shown that hyperspectral imaging (HSI) is able to demonstrate long-term reductions in cutaneous perfusion secondary to chronic microvascular injury. This study characterizes the changes in skin microcirculation in response to varying doses of ionizing radiation and investigates these microcirculatory changes as a possible early non-invasive biomarker that may correlate with the extent of long-term microvascular damage. Immunocompetent hairless mice (n = 66) were exposed to single fractions of superficial beta-irradiation in doses of 0, 5, 10, 20, 35, or 50 Gy. A HSI device was utilized to measure deoxygenated hemoglobin levels in irradiated and control areas. HSI measurements were performed at baseline before radiation exposure and for the first 3 days post-irradiation. Maximum macroscopic skin reactions were graded, and histological assessment of cutaneous microvascular densities at 4 weeks post-irradiation was performed in harvested tissue by CD31 immunohistochemistry. CD31 immunohistochemistry demonstrated a significant correlation (r = 0.90, p < 0.0001) between dose and vessel density reduction at 4 weeks. Using HSI analysis, early changes in deoxygenated hemoglobin levels were observed during the first 3 days post-irradiation in all groups. These deoxygenated hemoglobin changes varied proportionally with dose (r = 0.98, p < 0.0001) and skin reactions (r = 0.98, p < 0.0001). There was a highly significant correlation (r = 0.91, p < 0.0001) between these early changes in deoxygenated hemoglobin and late vascular injury severity assessed at the end of 4 weeks. Radiation dose is directly correlated with cutaneous microvascular injury severity at 4 weeks in our model. Early post-exposure measurement of cutaneous deoxygenated hemoglobin levels may be a useful biomarker for radiation dose reconstruction and predictor for chronic microvascular injury.

Spectral Imaging Technologies for Food Safety and Quality Evaluations

ARS researchers in Beltsville, Maryland, pioneered the online implementation of hyperspectral/multispectral line-scan imaging technologies in a commercial food processing environment such as wholesomeness inspection of broiler chickens on poultry processing lines. The research and development effort for the use of hyperspectral line-scan imaging as a multispectral platform has been expanded to online produce safety and quality inspection. To achieve comprehensive online quality and safety inspection of fruits and vegetables, whole-surface sample presentation and imaging regimes must be considered. Because of the morphological shape differences between relatively round fruits and flat leafy greens, two independent methods are in development to achieve effective whole-surface sample evaluation based on the use of a single hyperspectral line-scan imaging device on a processing line. The whole-surface fruit and vegetable spectral imaging methods that allow simultaneous safety and quality inspection online are presented.

Screening of anthocyanins in single red grapes using a non-destructive method based on the near infrared hyperspectral technology and chemometrics.

Anthocyanins are the main compounds responsible for the colour of red wines and therefore it may be important to evaluate the content of the aforesaid secondary metabolites during grape ripening due to the crucial importance to determine wine colour. Nowadays, there is a growing demand of rapid and non-destructive analytical tools for analysing grapes, such as the emerging hyperspectral analysis. The hyperspectral images of intact grapes (Vitis vinifera L. cv. Tempranillo, Graciano, Garnacha and Mazuelo red grape from vineyards located in the D.O.Ca. Rioja at two different developmental stages) were recorded using a near infrared hyperspectral imaging device (900-1700 nm). Reference values of anthocyanins were obtained by HPLC-DAD. Calibrations were performed by modified partial least squares regression and present a good potential (coefficient of determination of 0.72 and standard error of cross-validation values of 0.78 and 0.70 mg per grape for total and non-acylated anthocyanins respectively). The procedure reported here presents a good potential for a fast and reasonably inexpensive screening of these compounds in intact single berries. Moreover, the heterogeneity of anthocyanins within the same ripeness stage could be evaluated using this non-detructive tool.

Outdoor scene reflectance measurements using a Bragg-grating-based hyperspectral imager

The acquisition of spectral reflectance factor image data in an outdoor environment is a challenging task, mostly due to nonstatic scene content and illumination. In this work, we propose a work-flow for this task using a commercial Bragg-grating-based hyperspectral imager that can capture the visible and near-infrared part of the light spectrum. To our knowledge, we are the first who use this technology for outdoor spectral reflectance factor imaging. The work-flow involves focus position and exposure time estimation, illumination scaling, and image registration, among other procedures. Most of them generally apply to hyperspectral imaging, while some are specific to a Bragg-grating-based hyperspectral imaging device when dealing with specific challenges in outdoor environments. We have conducted some experiments to evaluate the quality of the acquired image data and discussed some limitations of the technology for spectral imaging of outdoor scenes. Fourteen urban scene spectral images acquired using the proposed approach are already publicly available to the scientific community under a Creative Commons license.

Application of Visible and Near-Infrared Hyperspectral Imaging for Detection of Defective Features in Loquat

The intent of present work was to develop a valid method for detection of defective features in loquat fruits based on hyperspectral imaging. A laboratorial hyperspectral imaging device covering the visible and near-infrared region of 380–1,030 nm was utilized to acquire the loquat hyperspectral images. The corresponding spectral data were extracted from the region of interests of loquat hyperspectral images. The dummy grades were assigned to the defective and normal group of loquats, separately. Competitive adaptive reweighted sampling (CARS) was conducted to elect optimal sensitive wavelengths (SWs) which carried the most important spectral information on identifying defective and normal samples. As a result, 12 SWs at 433, 469, 519, 555, 575, 619, 899, 912, 938, 945, 970, and 998 nm were selected, respectively. Then, the partial least squares discriminant analysis (PLS-DA) model was established using the selected SWs. The results demonstrated that the CARS-PLS-DA model with the discrimination accuracy of 98.51 % had a capability of classifying two groups of loquats. Based on the characteristics of image information, minimum noise fraction (MNF) rotation was implemented on the hyperspectral images at SWs. Finally, an effective approach for detecting the defective features was exploited based on the images of MNF bands with “region growing” algorithm. For all investigated loquat samples, the developed program led to an overall detection accuracy of 92.3 %. The research revealed that the hyperspectral imaging technique is a promising tool for detecting defective features in loquat, which could provide a theoretical reference and basis for designing classification system of fruits in further work.