Papers by Keyword: Specular Reflection

Abstract: The paper proves the possibility to control the surface microprofile with due regard to the optical characteristics of a rough surface; proposes an installation diagram for studying the optical characteristics of a rough surface; introduces an experimental procedure for evaluating the surface roughness via a contactless method; and substantiates a correlation relationship between the optical characteristics of the surface and the height parameters of the microprofile.

Abstract: Non-line-of-sight optical imaging technology is a novel application of imaging technology developed recently, achieving the effective imaging of the corner, basements and other scenes which are difficult to be directly observed by traditional vision with intermediate reflective surface. Smooth building walls, such as tiles and marbles, are typical intermediate reflective surfaces. Because reflecting surface is neither ideal specular reflective nor Lambertian reflective, the reflection characteristics of the intermediate reflective surface have a significant impact on the non-line-of-sight imaging. Based on the test data of the spectral bidirectional reflectance distribution function (BRDF) of common smooth tiles, the surface transfer function and angle spread function of smooth tiles are established according to the Harvey-Shack surface scatter theory in the paper. And the descriptions of the characteristics of specular reflection and forward scattering are implemented. Furthermore, according to the measured BRDF data at a certain wavelength for a certain angle of incidence, we can predict the reflection and scattering distribution at any other wavelengths or for other incident angles. The simulation results indicate that the curves fitted by the model basically are in agreement with the measured data, so that the simulation of the specular reflection and the forward scattering in the model is valid.

Abstract: The paper proposes a novel method of improving the traditional composite grating in 3-D measurement of the specular objects. The traditional composite grating is improved by altering the intensity of the center stripe in one of the fringes. The improved composite grating not only includes the primary phase information, which is modulated by the object's surface, but also includes the code information, which is necessary for the phase unwrapping. The paper introduces the formation of the improved composite grating, demodulating the composite grating and computing the unwrapped phase based on the altered fringe. Simulated and actual experiments prove that this method is valid. Because of projecting a single composite grating, the method is suitable for dynamical measurement.

Abstract: Per-Pixel lighting can greatly improve the computational efficiency because of the model has been completed the hidden and visibility judge processing. However, each pixel brightness values need to recalculate when the viewpoint changes. And per-pixel lighting will still be constrained computational efficiency in the case of greater pixel number. In this paper, a fast calculation method for view-dependent per-pixel lighting under a fixed light source is proposed, and a symmetric relationship between pixel brightness value and specular reflection was given. Finally, the brightness under the current viewpoint can calculate fastly. Experimental results show that this method has an efficient lighting calculation than the method of per-pixel lighting and hardware-accelerated lighting calculation.

Abstract: Photometric stereo is a widely-used non-contact optical technology for surface shape measurement in industry. However, it is subject two limitations: (1) all light directions used should be known; (2) reflection on the surface to be measured should obey the Lambertian model. In this paper, an extended photometric stereo is proposed to overcome these limitations. Firstly, initial light directions are estimated in terms of normals of those points on the silhouette; secondly, an iterative process is established to refine alternately both the normals and all light directions, with specular pixels removed; at last, the final surface shape is worked out by integrating the normals. Experimental results show the considerable feasibility of this algorithm.