| 1. |
- Chang, Lin, et al.
(författare)
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Multi-surface phase-shifting algorithm using the window function fitted by the nonlinear least squares method
- 2022
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Ingår i: Journal of Modern Optics. - : TAYLOR & FRANCIS LTD. - 0950-0340 .- 1362-3044. ; 69:3, s. 160-171
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Tidskriftsartikel (refereegranskat)abstract
- A multi-surface phase demodulation algorithm is proposed to measure surfaces of the transparent plate simultaneously. A non-linear least-squares method based on the trust region is utilized to fit the window function derived from the characteristic polynomials. The fitted window function requires fewer parameters and has a flexible form, which means the window length can be stretched freely and used flexibly. Then, a multi-surface phase demodulation technique combining the discrete Fourier principle and the fitted window function is investigated, allowing simultaneous reconstruction of the measured front surface, rear surface, and thickness variation. During the implementation of our algorithm, the processing time for the interferograms with 850x850 pixels is around 5.1s. Measurement errors caused by several factors are analyzed, including wavelength-tuning error, frequency order error, cavity length error, and average thickness error. The experimental result on a rectangular transparent plate further verifies the effectiveness of our algorithm.
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| 2. |
- Chang, Lin, et al.
(författare)
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Multisurface Interferometric Algorithm and Error Analysis With Adaptive Phase Shift Matching
- 2022
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Ingår i: IEEE Transactions on Instrumentation and Measurement. - : IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC. - 0018-9456 .- 1557-9662. ; 71
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Tidskriftsartikel (refereegranskat)abstract
- To simultaneously measure topographies of both surfaces of a transparent plate through wavelength-tuning interferometry at arbitrary cavity lengths, a flexible phase shift matching algorithm (FPSMA) is proposed. The FPSMA includes two parts: 1) taking the four-term third-order Nuttall window as an example, a phase demodulation approach is designed and analyzed for extracting the harmonic phases of the front surface, rear surface, and thickness variation of the measured plate and 2) based on the residual error analysis of the developed 5N-Nuttall algorithm for different cavity length coefficients M and the phase-shifting parameters N , a parameter-change technique that allows the developed phase demodulation approach is applied to arbitrary cavity lengths by adaptively changing the phase shifts and frames of the captured interferograms. By this technique, the algorithm failures due to the spectral aliasing of harmonics can be avoided effectively and conveniently, and then the correct phase demodulation can be ensured. Besides, using the developed method, when the values of N or M are chosen in advance, the corresponding available measurement ranges can be given. Besides, the relationship between the window length and the measurement limitation of the measurable thinnest optical thickness is investigated. Considering the common linear and nonlinear errors in the wavelength-shifting process, the error analysis of FPSMA is performed and discussed for situations close to reality. The comparative studies and the experimental results of two transparent parallel plates also support the performance of the developed FPSMA.
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| 3. |
- Chen, Dingfu, et al.
(författare)
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Bayesian uncertainty evaluation of stitching interferometry for cylindrical surface
- 2020
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Ingår i: Measurement. - : ELSEVIER SCI LTD. - 0263-2241 .- 1873-412X. ; 157
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Tidskriftsartikel (refereegranskat)abstract
- Uncertainty evaluation is one of the most important concepts in metrological characterizations. This paper proposes a method for uncertainty evaluation of measurements of cylindrical surfaces by means of stitching interferometry. The proposed method is based on the Bayesian statistical analysis. The prior deviation for a tested surface is determined by both calculation of standard deviation through multiple measurements of a single sub-aperture and calibration of the optical system error. The probability distribution functions (PDF) of the prior and real misalignment error and measured data of the aperture are derived according to the stitching model. Simulated observations are approximated with the Gibbs Sampler using the Markov Chain Monte Carlo (MCMC) method. Our proposed method is a promising alternative to the ordinary least square technique (LST) with the maximum likelihood estimation (MLE) for obtaining the uncertainty of the misalignment and measurement error in the stitching results. Moreover, it can take the inevitable environment errors into account. The prediction of the uncertainty interval makes our method more attractive in industrial applications. (C) 2020 Elsevier Ltd. All rights reserved.
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| 4. |
- Chen, Dingfu, et al.
(författare)
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Stitching interferometry of cylindrical surface
- 2022
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Ingår i: Optics and lasers in engineering. - : ELSEVIER SCI LTD. - 0143-8166 .- 1873-0302. ; 157
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Tidskriftsartikel (refereegranskat)abstract
- High resolution and high precision are advantages of measuring cylindrical objects employing stitching interferometry. However, due to errors in the cylinder position in a measurement procedure, it is difficult to ensure the accuracy of a macroscopic shape contour and surface waviness contour of the workpiece of the stitching results. To overcome this problem, we proposed a new strategy of stitching interferometry for cylindricity calibration. The measuring process is divided into two parts to measure the macroscopic shape and waviness contour, respectively. Finally, the two measurement results are merged to produce an accurate and complete 360 degrees form map. Besides, we build a two-dimensional Gaussian filter weighting function for a cylindrical profile according to its special shape characteristic. To express the stitching results more precisely, we provide the uncertainty map and power spectral density of the stitching results. An experiment is carried out by taking a ceramic plug gage as the workpiece. The results demonstrate the excellent performance of our method in analyzing the characteristic of the cylindrical profile and show good agreement with such by using cylindricity measuring instruments.
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| 5. |
- Fernandes, Rui D. V., et al.
(författare)
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Iridescence Mimicking in Fabrics: A Ultraviolet/Visible Spectroscopy Study
- 2024
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Ingår i: Biomimetics. - : MDPI. - 2313-7673. ; 9:2
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Tidskriftsartikel (refereegranskat)abstract
- Poly(styrene-methyl methacrylate-acrylic acid) photonic crystals (PCs), with five different sizes (170, 190, 210, 230 and 250 nm), were applied onto three plain fabrics, namely polyamide, polyester and cotton. The PC-coated fabrics were analyzed using scanning electronic microscopy and two UV/Vis reflectance spectrophotometric techniques (integrating sphere and scatterometry) to evaluate the PCs' self-assembly along with the obtained spectral and colors characteristics. Results showed that surface roughness of the fabrics had a major influence on the color produced by PCs. Polyamide-coated fabrics were the only samples having an iridescent effect, producing more vivid and brilliant colors than polyester and cotton samples. It was observed that as the angle of incident light increases, a hypsochromic shift in the reflection peak occurs along with the formation of new reflection peaks. Furthermore, color behavior simulations were performed with an illuminant A light source on polyamide samples. The illuminant A simulation showed greener and yellower structural colors than those illuminated with D50. The polyester and cotton samples were analyzed using scatterometry to check for iridescence, which was unseen upon ocular inspection and then proven to be present in these samples. This work allowed a better comprehension of how structural colors and their iridescence are affected by the textile substrate morphology and fiber type.
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| 6. |
- Kalustova, Daria, et al.
(författare)
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Color temperature tunable RGBW cluster with optimize color rendering and efficacy
- 2023
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Ingår i: Optical Engineering. - : SPIE-SOC PHOTO-OPTICAL INSTRUMENTATION ENGINEERS. - 0091-3286 .- 1560-2303. ; 62:4
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Tidskriftsartikel (refereegranskat)abstract
- Our work is devoted to the optimization of 4-component RGBW smart lighting systems that are able to obtain the resulting white light with a combination of high color rendering and luminous efficacy for a certain fixed correlated color temperature. Three approaches for the determination of the optimal brightness contributions of the light emitting diodes (LEDs) are studied. They are accordingly based on: (1) maximization of the color rendering, (2) prioritizing to reduce the color rendering maximum by 1 to 6 units to increase luminous efficacy, and (3) getting a constant value of RGB contribution and luminous efficacy while maintaining high color rendering. A comparison of the three systems with different base white LEDs is demonstrated. The obtained theoretical results are verified experimentally.
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| 7. |
- Kalustova, Darla, et al.
(författare)
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Color temperature tunable RGBW clusters with 3 control channels
- 2020
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Ingår i: Photonics Letters of Poland. - Warsaw, Poland : PHOTONICS SOC POLAND. - 2080-2242. ; 12:1, s. 10-12
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Tidskriftsartikel (refereegranskat)abstract
- The work is devoted to the development of a smart lighting system that is able to change correlated colour temperature and consists of tunable 4-components RGBW clusters controlled via three channels. It is shown that fixing a ratio between the intensities of white and red LEDs at a level of 100:9 enables obtaining high values of colour rendering in a wide range of correlated colour temperatures. The control of 3 from 4 channels simplifies the system. The influence of the red LED on CRI and luminous efficiency is analysed.
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| 8. |
- Kalustova, D. O., et al.
(författare)
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RGBW lighting systems : Influence of the white LED
- 2022
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Ingår i: Semiconductor Physics, Quantum Electronics & Optoelectronics. - : National Academy of Sciences Ukraine ; Institute of Semiconductor Physics. - 1560-8034 .- 1605-6582. ; 25:1, s. 76-82
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Tidskriftsartikel (refereegranskat)abstract
- People spend most of the time under artificial light sources, so it is important to create a comfortable lighting environment for work and rest. Four-component RGBW systems are the most effective for this. It is needed to create methods for obtaining white light with the specified parameters and choose the most optimal LED components. In this work, the influence of the white LEDs parameters on the resulting white light of the RGBW systems is studied. Two different methods proposed by us earlier for obtaining white light are applied for three RGBW systems with different warm white LEDs. It is shown that the use of white LEDs with a colour rendering index close to 80 is more optimal for most applications. In this case, they provide the resulting white light with the colour rendering index above 90 and luminous efficacy above 130 lm/W.
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| 9. |
- Kalustova, Daria, et al.
(författare)
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Red, green, blue, and white clusters for daylight reproduction
- 2020
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Ingår i: Optical Engineering. - : SPIE-SOC PHOTO-OPTICAL INSTRUMENTATION ENGINEERS. - 0091-3286 .- 1560-2303. ; 59:5
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Tidskriftsartikel (refereegranskat)abstract
- Daylight is an inherent attribute of a sustainable building. Artificial reproduction of natural illumination under varying needs and environmental conditions has been made possible after the appearance of the new wave of solid-state light sources. Our work is devoted to the development of white light-emitting diode (LED) clusters consisting of red, green, blue, and white (RGBW) LEDs for implementation in a smart lighting system that is able to reproduce light with correlated color temperature (CCT) similar to daylight, high values of color rendering index, and luminous efficacy. A method for determination of the optimal contribution of each of the four LEDs is demonstrated and discussed. We show that only three LEDs-green, blue, and white (no red) can be used in many cases for reproducing daylight. Both luminous efficacy of radiation and actual luminous efficacy of the considered RGBW clusters as functions of the CCT are analyzed. (C) 2020 Society of Photo-Optical Instrumentation Engineers (SPIE).
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| 10. |
- Pranovich, Alina, 1993-, et al.
(författare)
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Angular dependent reflectance spectroscopy of RGBW pigments
- 2022
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Traditional printing relies primarily on subtractive color mixing techniques. In this case, optical color mixing is achieved by one of the established halftoning methods that use Cyan, Magenta, Yellow and Black (CMYK) primaries on a reflective white substrate. The reason behind the subtractive color mixing in printing is the high absorbance of available pigments used in inks. A new type of mica-based pigments that exhibit high reflectivity at Red, Green, Blue and White (RGBW) spectral bands was recently introduced by Merck (SpectravalTM). Printing with RGBW primaries on black background allows additive color mixing in prints. While offering excellent color depth, the reflected spectra of such pigments vary with the angles of incidence and observation. As a result, new approaches in modelling the appearance of prints as well as strategies for color separation and halftoning are needed. The prior optical characterization of the reflective inks is an essential first step. For this purpose, we have used SpectravalTM pigments to prepare acrylic based inks, which we applied on glass slides by screen printing. In this work, we measured the relative spectral bidirectional reflection distribution of Red, Green, Blue and White reflective inks. The measurements were conducted on an experimental set up consisting of a goniometer, spectrometer, and a xenon light source. Based on the measurements, we simulate the reflectance spectra under diffuse illumination and demonstrate ratios of red, green, and blue spectral components for different observation angles of individual inks and their combinations.
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| 11. |
- Pranovich, Alina, 1993-, et al.
(författare)
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Dot Off Dot Screen Printing with RGBW Reflective Inks
- 2023
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Ingår i: Journal of Imaging Science and Technology. - : The Society for Imaging Science and Technology. - 1062-3701 .- 1943-3522. ; 67:3
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Tidskriftsartikel (refereegranskat)abstract
- Recent advances in pigment production resulted in the possibility to print with RGBW primaries instead of CMYK and performing additive color mixing in printing. The RGBW pigments studied in this work have the properties of structural colors, as the primary colors are a result of interference in a thin film coating of mica pigments. In this work, we investigate the angle-dependent gamut of RGBW primaries. We have elucidated optimal angles of illumination and observation for each primary ink and found the optimal angle of observation under diffuse illumination. We investigated dot off dot halftoned screen printing with RGBW inks on black paper and in terms of angle-dependent dot gain. Based on our observations, optimal viewing condition for the given RGBW inks is in a direction of around 30◦ to the surface normal. Here, the appearance of the resulting halftoned prints can be estimated well by Neugebauer formula (weighted averaging of the individual reflected spectra). Despite the negative physical dot gain during the dot off dot printing, we observe angularly dependent positive optical dot gain for halftoned prints. Application of interference RGBW pigments in 2.5D and 3D printing is not fully explored due to the technological limitations. In this work, we provide colorimetric data for efficient application of the angle-dependent properties of such pigments in practical applications.
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| 12. |
- Pranovich, Alina, 1993-, et al.
(författare)
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Empirical BRDF model for goniochromatic materials and soft proofing with reflective inks.
- 2024
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Ingår i: IEEE Computer Graphics and Applications. - 0272-1716 .- 1558-1756.
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Tidskriftsartikel (refereegranskat)abstract
- The commonly used analytic bidirectional reflectance distribution functions (BRDFs) do not model goniochromatism, that is, angle-dependent material color. The material color is usually defined by a diffuse reflectance spectrum or RGB vector and a specular part based on a spectral complex index of refraction. Extension of the commonly used BRDFs based on wave theory can help model goniochromatism, but this comes at the cost of significant added model complexity. We measured the goniochromatism of structual color pigments used for additive color printing and found that we can fit the observed spectral angular dependence of the bidirectional reflectance using a simple modification of the standard microfacet BRDF model. All we need to describe the goniochromatism is an empirically-based spectral parameter, which we use in our model together with a specular reflectance spectrum instead of the spectral complex index of refraction. We demonstrate the ability of our model to fit the measured reflectance of red, green, and blue commercial structural color pigments. Our BRDF model enables straightforward implementation of a shader for interactive preview of 3D objects with printed spatially and angularly varying texture.
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| 13. |
- Pranovich, Alina, 1993-
(författare)
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Modelling appearance printing : Acquisition and digital reproduction of translucent and goniochromatic materials
- 2024
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Colour perception is fundamental to our everyday experiences, allowing us to communicate and interpret visual information effectively. Yet, replicating these experiences accurately poses a significant challenge, particularly in the context of full-colour 3D printing. Advances in this field have revolutionised the fabrication of customised prosthetic body parts, such as eyes, teeth, and skin features, with profound implications for medical and aesthetic applications.The key to successful 3D printing lies in the digital preview of objects before fabrication, enabling users to assess colour reproduction and quality. However, accurately representing colour in a digital environment is complex, as it depends on numerous factors, including illumination, object shape, surface properties, scene context, and observer characteristics. Traditional methods of previewing conventional 2D prints overlook this complexity.This thesis addresses this challenge by focusing on two types of materials: semitransparent polymers commonly used in 3D printing, and goniochromatic colorants employed in printing to introduce unique effects unattainable with conventional inks for 2D printing. For semitransparent materials, we developed an empirical function to represent colour based on sample thickness, enabling efficient digital representation. Additionally, we adapted a colour measuring device to identify two key material parameters, absorption and scattering coefficients, essential for accurate colour reproduction.Goniochromatic materials, such as thin film-coated mica particles, are slightly more complicated and less predictive in terms of their final colour appearance. Although not yet used in 3D printing, these particles used in conventional printing introduce colour variation while rotating the print. We found that goniochromatic properties can be expressed with an empirically found function after collecting angle-dependent light reflecting properties of the sample. We used this function and showed how prints with goniochromatic materials can be efficiently previewed on a computer monitor.
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