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Surface gradient characterization by light reflectance (SGCLR) is used for the first time for multiscale curvature calculations and discrimination of worn surfaces on six damaged ceramic–metal composites. Measurements are made using reflectance transformation imaging (RTI). Slope and curvature maps, generated from RTI, are analyzed instead of heigh...
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Context 1
... and directions of illumination are varied, while photographing the surface from a fixed position orthogonal to the surface to be measured. Images of the surface are captured, with different light directions (Figure 4). Unit vectors normal to the surface are obtained from this stereo-photometric data, providing slopes. ...
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... associated with 360 individual angular positions of the light were acquired for each measurement. The positions included 72 ϕ-positions (azimuth), from 0° to 360°, by 5° increments, each with five θ-positions (elevation) from 35° to 80° (Figures 4 and 7). Each image had a resolution of 1500 × 1400 pixels over a region of 5140 × 4797 μm, resulting in a pixel size about 3 × 3 μm. ...
Citations
... The reflectance method can therefore overcome these limits with the visual study (images in grayscale), and the slope/curvature study, based on reflectance images. parameter and possibly the multiscale filter with its cut-off length, which best discriminate surfaces, or highlight particular morphological signatures of a surface, making it possible to link its surface roughness to physics. Figure 1 presents a summary of the SGCLR methodology [9]. ...
... Hardware 2024, 2, FOR PEER REVIEW 3 al. [9], is proposed with the instrument for the characterization of surfaces. This analysis aims to determine the most relevant map(s) as well as the surface characterization parameter and possibly the multiscale filter with its cut-off length, which best discriminate surfaces, or highlight particular morphological signatures of a surface, making it possible to link its surface roughness to physics. Figure 1 presents a summary of the SGCLR methodology [9]. Figure 1. ...
... [9], is proposed with the instrument for the characterization of surfaces. This analysis aims to determine the most relevant map(s) as well as the surface characterization parameter and possibly the multiscale filter with its cut-off length, which best discriminate surfaces, or highlight particular morphological signatures of a surface, making it possible to link its surface roughness to physics. Figure 1 presents a summary of the SGCLR methodology [9]. Figure 1. ...
A new instrument using reflectance transformation imaging (RTI), named MorphoLight, has been developed for surface characterization. This instrument is designed to be adjustable to surfaces, ergonomic, and uses a combination of high-resolution imaging functions, i.e., focus stacking (FS) and high dynamic range (HDR), to improve the image quality. A topographical analysis method is proposed with the instrument. This method is an improvement of the surface gradient characterization by light reflectance (SGCLR) method. This aims to analyze slope/curvature maps, traditionally studied in RTI, but also to find the most relevant lighting position and 3D surface parameter which highlight morphological signatures on surfaces and/or discriminate surfaces. RTI measurements and analyses are performed on two zones, sky and sea, of a naval painting which have the same color palette but different painting strokes. From the statistical analysis using bootstrapping and analysis of variance (ANOVA), it is highlighted that the high-resolution images (stacked and tonemapped from HDR images) improve the image quality and make it possible to better see a difference between both painting zones. This difference is highlighted by the fractal dimension for a lighting position (θ, φ) = (30°, 225°); the fractal dimension of the sea part is higher because of the presence of larger brushstrokes and painting heaps.
... As a consequence, the computed gradient will be the gradient of the elementary facet. Lemesle et al. showed that computing the gradient on a facet allows for a better description of the physics of failure at very small scales [24]. ...
... Therefore, the idea is not to obtain a smooth gradient which be well able to characterize a surface [22], but a gradient which can capture the noise the noise has fractal characteristics, a method which characterizes it must be retained. gar et al. [23] showed that triangulation captures the fractal aspect with optical metho As a consequence, the computed gradient will be the gradient of the elementary fa Lemesle et al. showed that computing the gradient on a facet allows for a better desc tion of the physics of failure at very small scales [24]. ...
Topographic maps are composed of pixels associated with coordinates (x, y, z) on a surface. Each pixel location (x, y) is linked with fluctuations in a measured height sample (z). Fluctuations here are uncertainties in heights estimated from multiple topographic measurements at the same position. Height samples (z) are measured at individual locations (x, y) in topographic measurements and compared with gradients on topographies. Here, gradients are slopes on a surface calculated at the scale of the sampling interval from inclination angles of vectors that are normal to triangular facets formed by adjacent height samples (z = z(x, y)). Similarities between maps of gradients logs and height fluctuations are apparent. This shows that the fluctuations are exponentially dependent on local surface gradients. The highest fluctuations correspond to tool/material interactions for turned surfaces and to regions of maximum plastic deformation for sandblasted surfaces. Finally, for abraded, heterogeneous, multilayer surfaces, fluctuations are dependent on both abrasion and light/sub-layer interactions. It appears that the natures of irregular surface topographies govern fluctuation regimes, and that regions which are indicative of surface functionality, or integrity, can have the highest fluctuations.
... As topography is composed of multiple peaks of various scales, this light and dark interface pattern is always present when computing the reflectance map. Moreover, numerical gradient on reflectance maps has a lower sensitivity to discretization error compared to numerical gradient on topographic map [57], as most computer vision-based 3D topography stitching algorithms do during registration. Reflectance maps are then suited for computer vision-based registration algorithms. ...
... Scheme of reflectance principle-extracted from[57]. ...
Surface topography is an efficient tool for the understanding of physical phenomena, especially if multiscale roughness analysis is performed. However, the observable scale range in a topography measured with 3D optical profilometers is quite limited. Therefore, all scales linked to a physical phenomenon might not be measured, which impedes the correct analysis of the surface. Stitching of 3D topographies, a technique combining elementary topographic maps into a larger one, can be used to increase the scale range for an objective lens. A high resolution over a large field of measurement topography is then generated. A literature review of 3D topography stitching algorithm highlights the stitching procedure, and detailed explanations on in-plane registration algorithms are provided. However, some existing 3D topography stitching algorithms are not sufficiently accurate for the registration of surface, especially at smaller scales. This paper proposes a new reflectance-based multimap 3D stitching algorithm and three of its variants. These algorithm variants are compared to three existing 3D stitching algorithms (geometric, cross-correlation and global optimization of differences) on four test cases, containing measured elementary topographic maps obtained on four surfaces and with four 3D optical profilometers (two focus variation microscopes and two interferometers). Five qualitative and quantitative criteria and indicators are proposed for the comparison of 3D topography stitching algorithms: visual inspection, run time, memory usage, mean repositioning error and stitching error estimator. Lastly, two quantitative indicators and criteria are new indicators proposed in this article. Overall, the new 3D stitching algorithms based on reflectance and multimaps have a lower mean repositioning error and stitching error estimator compared to other existing algorithms. This highlights the relevance of multimap stitching algorithms in the case of 3D topographies. A new decision-helping tool, the stitching gain lift plot (SGL plot), is described for the selection of the best stitching algorithm for a given test case. The SGL plot especially highlights the higher performance of two of the variants of the novel algorithm compared to the three existing 3D stitching algorithms.
... RTI was originally developed at HP labs by Malzbender et al. [8,9] under a name, Polynomials Texture Mappings (PTM), that refers to the implemented modeling method. Other modeling methods have been developed, such as the HSH (Hemispherical Harmonics) model [10][11][12][13], the DMD (Discrete Modal Decomposition) method [14][15][16][17], and the approach based on RBF (Radial Basis Function) [18,19]. Particularly important development has occurred in the field of the digitization of historical and cultural heritage objects [20][21][22]. ...
... More recently, this technique has been implemented in the context of a wide variety of industrial applications. These applications have often been related to the challenge of mastering of surface appearance perception and the automation of inspection processes [23,24], although other applications have been found in biomedicine, forensics [25], materials mechanics [4,26], and the analysis of tribological properties [17]. The richness of the contribution of the RTI technique is linked to the quality and variety of surface information that it can estimate. ...
Reflectance Transformation Imaging (RTI) is a non-contact technique which consists in acquiring a set of multi-light images by varying the direction of the illumination source on a scene or a surface. This technique provides access to a wide variety of local surface attributes which describe the angular reflectance of surfaces as well as their local microgeometry (stereo photometric approach). In the context of the inspection of the visual quality of surfaces, an essential issue is to be able to estimate the local visual saliency of the inspected surfaces from the often-voluminous acquired RTI data in order to quantitatively evaluate the local appearance properties of a surface. In this work, a multi-scale and multi-level methodology is proposed and the approach is extended to allow for the global comparison of different surface roughnesses in terms of their visual properties. The methodology is applied on different industrial surfaces, and the results show that the visual saliency maps thus obtained allow an objective quantitative evaluation of the local and global visual properties on the inspected surfaces.
... The method requires that both the surface and the camera are in fixed positions, and only the light changes its position [29,30] (3). The resulting image stack can be exploited in different ways [26,27,[31][32][33][34][35]. In this paper, statistical analysis is based on calculating or comparing the mean per-pixel angular reflectance response deriving from the raw RTI data in the following ways: (fig. ...
... Furrows maps ( Figure 4B,E) are generated and from them, parameters, such as the maximum depth of furrow (Fd max ), mean depth of furrow (Fd mean ) and mean density of furrows (Fρ mean ), are calculated and their values are placed in Table 3. These parameters are estimated in topography according to Lemesle et al. [40] as the number of deep lines or scratches detected by patterns in curvature per unit area. The detection and characterization of the furrows from all over the surface indicated that Fd max , Fd mean and also Fρ mean are influenced by the surface roughness, being higher for the rough unmodified sample with higher flexibility (EPI-pBAPS). ...
The efficiency of photovoltaics (PVs) is related to cover material properties and light management in upper layers of the device. This article investigates new polyimide (PI) covers for PVs that enable light trapping through their induced surface texture. The latter is attained via a novel strategy that involves multi-directional rubbing followed by plasma exposure. Atomic force microscopy (AFM) is utilized to clarify the outcome of the proposed light-trapping approach. Since a deep clarification of either random or periodic surface morphology is responsible for the desired light capturing in solar cells, the elaborated texturing procedure generates a balance among both discussed aspects. Multidirectional surface abrasion with sand paper on pre-defined directions of the PI films reveals some relevant modifications regarding both surface morphology and the resulted degree of anisotropy. The illuminance experiments are performed to examine if the created surface texture is suitable for proper light propagation through the studied PI covers. The adhesion among the upper layers of the PV, namely the PI and transparent electrode, is evaluated. The correlation between the results of these analyses helps to identify not only adequate polymer shielding materials, but also to understand the chemical structure response to new design routes for light-trapping, which might significantly contribute to an enhanced conversion efficiency of the PV devices.
... The acquired data obtained with the RTI technique enable building a local experimental model of the angular reflectance at each point of the inspected surface, which characterizes the appearance [25]. It is then possible to estimate the maps of local characteristics of surfaces, which are linked to the distribution of measured luminances or to the local micro-geometry [26,27], and to reconstruct the visual rendering of the surfaces under a virtual lighting. ...
This work investigates the use of Reflectance Transformation Imaging (RTI) rendering for visual inspection. This imaging technique is being used more and more often for the inspection of the visual quality of manufactured surfaces. It allows reconstructing a dynamic virtual rendering of a surface from the acquisition of a sequence of images where only the illumination direction varies. We investigate, through psychometric experimentation, the influence of different essential parameters in the RTI approach, including modeling methods, the number of lighting positions and the measurement scale. In addition, to include the dynamic aspect of perception mechanisms in the methodology, the psychometric experiments are based on a design of experiments approach and conducted on reconstructed visual rendering videos. The proposed methodology is applied to different industrial surfaces. The results show that the RTI approach can be a relevant tool for computer-aided visual inspection. The proposed methodology makes it possible to objectively quantify the influence of RTI acquisition and processing factors on the perception of visual properties, and the results obtained show that their impact in terms of visual perception can be significant.
... Lemesle [25] states how a wide range of physical properties such as erosion, diffusion, decay and wear can be explained by appropriately characterized surface topographies. Lemesle [25] studied metal-ceramic composites that had been worn under industrial conditions. ...
... Lemesle [25] states how a wide range of physical properties such as erosion, diffusion, decay and wear can be explained by appropriately characterized surface topographies. Lemesle [25] studied metal-ceramic composites that had been worn under industrial conditions. For instance, surface slope is a characteristic that can define the stick-slip phenomenon. ...
The study of MEMS devices is highly dependent on the information that imaging techniques can provide. There are two main approaches to observe MEMS devices: Optical and non-optical imaging techniques. Although each of the techniques has its own advantages and disadvantages, optical microscopy is of great interest due to its low-cost, accessibility, resolution and the colored images it provides. A critical shortcoming of optical microscopy is the strict viewing direction and lighting angle that result in flat images with no visual representation of MEMS 3D structure that may lead to some confusion in terms of interpreting the topography of MEMS surfaces and their out-of-plane displacements. This thesis aims at enhancing the 2D representation of MEMS devices by capturing a sequence of images at different illumination angles and highlighting the lateral facets, based on the RTI imaging technique, and then creating a sequence of post-processed images. The proposed algorithm offers a rapid, non-invasive, cost-effective and non-contact imaging technique that aims at minimizing the necessity of using other imaging approaches by revealing the 3D aspects of MEMS devices in terms of 2D visualization.
... In the latter field, two objectives are pursued through this kind of analysis. The first objective is a better understanding of how the surface was fabricated in order to better control the process and manufacturing aspects [7,8]. The second relies on better understanding and mastering of how surfaces are perceived, which has become 10 a potent lever of value creation for many industries [9]. ...
Reflectance Transformation Imaging (RTI) is a technique for estimating surface local angular reflectance from a set of stereo-photometric images captured with variable lighting directions. The digitization of this information fully fits into the industry 4.0 approach and makes it possible to characterize the visual properties of a surface. The proposed method, namely HD-RTI, is based on the coupling of RTI and HDR imaging techniques. This coupling is carried out adaptively according to the response at each angle of illumination. The proposed method is applied to five industrial samples which have high local variations of reflectivity because of their heterogeneity of geometric texture and/or material. Results show that coupling HDR and RTI improves the relighting quality compared to RTI, and makes the proposed approach particularly relevant for glossy and heterogeneous surfaces. Moreover, HD-RTI enhances significantly the characterization of the local angular reflectance, which leads to more discriminating visual saliency maps, and more generally to an increase in robustness for visual quality assessment tasks.
... The RTI provides access to multidimensional information (dynamic image relighting, luminance, slopes, curvatures, 3D mappings, visual saliency cartographies, etc.). These data are very valuable for evaluating and describing the visual quality of a surface, [4][5][6][7][8][9] especially in the case of manufactured products. [10][11][12][13][14][15] The principle of RTI acquisition is to vary the direction of the light source (azimuth and elevation angles) while keeping the sensor fixed orthogonally to the inspected surface for each light position. ...
Reflectance Transformation Imaging (RTI) is a technique for estimating the surface local angular reflectance and characterizing the visual properties by varying lighting directions and capturing a set of stereo-photometric images. The proposed method, namely HD-RTI, is based on the coupling of RTI and HDR imaging techniques. The HD-RTI automatically optimizes the necessary exposure times for each angle of illumination by using the response of the scene. Our method is applied to industrial surfaces with micro-scratches from which we will estimate saliency information. Results show that coupling HDR and RTI enhance the characterization and therefore the discrimination on the surfaces visual saliency maps. It leads to an increase in robustness for visual quality assessment tasks.
