Background
Hyperspectral imaging for in vivo human skin study has shown great potential by providing non‐invasive measurement from which information usually invisible to the human eye can be ...revealed. In particular, maps of skin parameters including oxygen rate, blood volume fraction, and melanin concentration can be estimated from a hyperspectral image by using an optical model and an optimization algorithm. These applications, relying on hyperspectral images acquired with a high‐resolution camera especially dedicated to skin measurement, have yielded promising results. However, the data analysis process is relatively expensive in terms of computation cost, with calculation of full‐face skin property maps requiring up to 5 hours for 3‐megapixels hyperspectral images. Such a computation time prevents punctual previewing and quality assessment of the maps immediately after acquisition.
Methods
To address this issue, we have implemented a neural network that models the optimization‐based analysis algorithm. This neural network has been trained on a set of hyperspectral images, acquired from 204 patients and their corresponding skin parameter maps, which were calculated by optimization.
Results
The neural network is able to generate skin parameter maps that are visually very faithful to the reference maps much more quickly than the optimization‐based algorithm, with computation times as short as 2 seconds for a 3‐megapixel image representing a full face and 0.5 seconds for a 1‐megapixel image representing a smaller area of skin. The average deviation calculated on selected areas shows the network's promising generalization ability, even on wide‐field full‐face images.
Conclusion
Currently, the network is adequate for preview purposes, providing relatively accurate results in a few seconds.
Abstract
The bidirectional scattering-surface reflectance distribution function (BSSRDF) describes the radiance originated by the volume scattering and the surface reflectance of any position on the ...surface of a sample, when it is directionally irradiated at any other position. The present state of the technology for appearance rendering requires a more detailed physical description of translucent objects by traceable measurements of the BSSRDF. This work presents two primary facilities developed for traceable BSSRDF measurements by different measuring approaches. Their results on the same translucent samples have been compared and the achieved BSSRDF scale has been transferred to a commercial measuring system. This study highlights the problems of the different measuring instrument designs and provides the scientific community with more knowledge on the measurement of the BSSRDF, which will be crucial for future works on material appearance.
Hyperspectral imaging has shown great potential for optical skin analysis by providing noninvasive, pixel-by-pixel surface measurements from which, applying an optical model, information such as ...melanin concentration and total blood volume fraction can be mapped. Such applications have been successfully performed on small flat skin areas, but existing methods are not suited to large areas such as an organ or a face, due to the difficulty of ensuring homogeneous illumination on complex three-dimensional (3-D) objects, which leads to errors in the maps. We investigate two methods to account for these irradiance variations on a face. The first one relies on a radiometric correction of the irradiance, using 3-D information on the face's shape acquired by combining the hyperspectral camera with a 3-D scanner; the second relies on an optimization metric used in the map computation, which is invariant to irradiance. We discuss the advantages and drawbacks of the two methods, after having presented in detail the whole acquisition setup, which has been designed to provide high-resolution images with a short acquisition time, as required for live surface measurements of complex 3-D objects such as the face.
Abstract In recent years, a growing demand for the capability of performing accurate measurements of the bidirectional transmittance distribution function (BTDF) has been observed in industry, ...research and development, and aerospace applications. However, there exists no calibration and measurement capabilities-entry for BTDF in the database of the Bureau International des Poids et Mesures and to date no BTDF comparison has been conducted between different national metrology institutes (NMIs) or designated institutes (DIs). As a first step to a possible future key comparison and to test the existing capabilities of determining this measurand, two interlaboratory comparisons were performed. In comparison one, five samples of three different types of optical transmissive diffusers were measured by five NMIs and one DI. By specific sample choice, the focus for this study lay more on orientation-dependent scatter properties. In comparison two, where one NMI, one DI, one university, and three industrial partners investigated their measurement capabilities, the dependence on the orientation was not assessed, but two additional samples of the same material and different thickness were measured. Results of the two comparisons are presented, giving a good overview of existing experimental solutions, and showing specific sample-related problems to be solved for improved future BTDF measurements.
Hyperspectral imaging is an emerging non-invasive method for the optical characterization of human skin, allowing detailed surface measurement over a large area. By providing the spectral reflectance ...in each pixel, it enables not only color simulation under various lighting conditions,
but also the estimation of skin structure and composition. These parameters, which can be correlated to a person's health, are deduced from the spectral reflectance in each pixel thanks to optical models inversion. Such techniques are already available in 2D images for flat skin areas, but
extending them to 3D is crucial to address large scale and complex shapes as in the human face. The requirements for accurate acquisition are a short acquisition time for in vivo applications and uniform lighting conditions to avoid shadowing. The proposed method combines wide field hyperspectral
imaging and 3D surface acquisition, using a single camera, with an acquisition time of less than 5 seconds. Complete color consistency can be achieved by computationally correcting irradiance non-uniformities using 3D shape information.
PDF
