The bidirectional reflectance distribution function (BRDF) data are essential for analyzing and modeling the material appearance of anisotropic surfaces. In order to acquire four-dimensional BRDF on the anisotropic material surfaces, a four-axis gonioreflectometer was designed and implemented. The instrument consists of a collimated, broadband light source, a four-axis rotation mechanism, a spectroradiometer, and a control system. The instrument is able to carry out spectral BRDF measurements over most of the incident and reflection hemispheres and the entire visible spectrum. One thousand twenty-four samples are obtained over the spectral range of 380 to 760 nm. The angular resolution of the BRDF measurement is <0.1 deg with good repeatability. A relative calibration method was adopted to obtain the absolute values of BRDFs. Various scanning schemes can be carried out by the instrument to scan the designated angular domains, enabling the instrument to capture material appearance with strong, distinctive anisotropic highlights and translucency. The obtained BRDF data of a textile sample demonstrate the instrument capability of capturing complex light scattering behaviors, including off-specular reflection peaks, off-plane reflection peaks, and backscattering.
This study attempted to solve the problem of conventional standard display devices encountering difficulties in displaying high dynamic range (HDR) images by proposing a modified tone-mapping operator (TMO) based on the image color appearance model (iCAM06). The proposed model, called iCAM06-m, combined iCAM06 and a multi-scale enhancement algorithm to correct the chroma of images by compensating for saturation and hue drift. Subsequently, a subjective evaluation experiment was conducted to assess iCAM06-m considering other three TMOs by rating the tone mapped images. Finally, the objective and subjective evaluation results were compared and analyzed. The results confirmed the better performance of the proposed iCAM06-m. Furthermore, the chroma compensation effectively alleviated the problem of saturation reduction and hue drift in iCAM06 for HDR image tone-mapping. In addition, the introduction of multi-scale decomposition enhanced the image details and sharpness. Thus, the proposed algorithm can overcome the shortcomings of other algorithms and is a good candidate for a general purpose TMO.
The sintering process is a crucial step for fabricating nickel hollow fiber membranes (NHFMs), which significantly affects hydrogen permeability of the membrane and the qualified rate of membrane manufacturing. Optimizing sintering conditions will accelerate the industrial applications of nickel hollow fiber membranes. In this work, the effects of the sintering conditions (temperatures, duration, and the atmosphere) on the membrane microstructure and hydrogen permeation performance of the resultant NHFMs are extensively investigated. Results show that small metal grain size results in large grain boundary density, leading to enhanced hydrogen permeability and decreased activation energy for hydrogen permeation. Sintering temperatures significantly affect the metal grain size, thereby affecting hydrogen permeation and activation energy. When the sintering temperature decreases from 1400 to 1100 °C, the hydrogen flux remarkably increases by a factor of 2 and the activation energy decreases from 57.47 to 48.89 kJ mol −1 . On the other hand, increasing the sintering time and hydrogen concentration in the sintering atmosphere only slightly affects the grain size and thus results in a minor change in hydrogen permeation. However, short sintering time and low hydrogen concentration in the sintering atmosphere may cause defects on the membrane and increase the difficulties on full removal of carbon residues in the membrane, which leads to the decrease in the qualified rate of produced membranes.
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