Acquiring linear subspaces for face recognition under variable lighting

Previous work has demonstrated that the image variation of many objects (human faces in particular) under variable lighting can be effectively modeled by low-dimensional linear spaces, even when there are multiple light sources and shadowing. Basis images spanning this space are usually obtained in one of three ways: a large set of images of the object under different lighting conditions is acquired, and principal component analysis (PCA) is used to estimate a subspace. Alternatively, synthetic images are rendered from a 3D model (perhaps reconstructed from images) under point sources and, again, PCA is used to estimate a subspace. Finally, images rendered from a 3D model under diffuse lighting based on spherical harmonics are directly used as basis images. In this paper, we show how to arrange physical lighting so that the acquired images of each object can be directly used as the basis vectors of a low-dimensional linear space and that this subspace is close to those acquired by the other methods. More specifically, there exist configurations of k point light source directions, with k typically ranging from 5 to 9, such that, by taking k images of an object under these single sources, the resulting subspace is an effective representation for recognition under a wide range of lighting conditions. Since the subspace is generated directly from real images, potentially complex and/or brittle intermediate steps such as 3D reconstruction can be completely avoided; nor is it necessary to acquire large numbers of training images or to physically construct complex diffuse (harmonic) light fields. We validate the use of subspaces constructed in this fashion within the context of face recognition.     

Progressive Watermarking Techniques Using Genetic Algorithms

An innovative watermarking scheme based on progressive transmission with genetic algorithms (GAs) is proposed. We implement the watermarking embedding and extraction systems in the transform domain, and apply the JPEG spectral selection mode for scalable transmission of the watermarked image. By employing a GA with a proper fitness function into the watermarking system, both the watermark imperceptibility and watermark robustness requirements are considered and optimized. The number of embedded bits, or the watermark capacity, is much larger than that in other existing algorithms in the literature. Also, the watermark capacity in the proposed algorithm lies within the theoretical limit. In addition, the embedded watermark can be partly extracted at the receiver side even when the watermarked image is being transmitted. Simulation results show both the robustness and the effectiveness of progressive transmission under different attacking schemes and different bandwidth variations. The proposed scheme is directly applicable to scalable coding of multimedia, such as MPEG-4 scalable video coding.     

A Performance Study on Bounteous Transfer in Multiprocessor Sectored Caches

In a sectored cache, a cache line is divided into several subblocks. Each subblock is a basic coherence unit. In this way partial block invalidation can be done on the cache lines in order to eliminate false sharing on invalidate-based multiprocessors. Sectored caches often include a facility, called bounteous transfers, to supply extra subblocks after transferring the missed subblock on a read miss. Unfortunately, previous works on sectored caches concentrated mainly on solving the false sharing problem, while overlooked the prefetching effects of bounteous transfer. In this paper, we evaluate the performance impacts of bounteous based on a MESI-based sectored cache. Three different types of bounteous transfer are evaluated; bounteous transfer wuth valid subblocks (BT-V), bounteous transfer with clean subblocks (BT-C), and bounteous disabled (No-BT). We simulated the execution of typical benchmarksFFT, LU, Radix, SOR, on the MESI-based sectored cache. Two metrics U-rate and R-rate are proposed to help observe the sharing granularities and coherence overhead. Evaluation results show that different benchmarks work better with different kinds of bounteous transfer and using bounteous transfer carelessly may result in performance degradation.     

Strength and fracture toughness of heavy concrete with various iron aggregate inclusions

An extensive experimental study of the mechanical properties and fracture properties of heavy concrete used mostly in the construction of radiation shielding structures is presented. The mixtures considered herein are developed according to the one adapted in the Kuosheng nuclear power plant in Taiwan; tests of the basic mechanical characteristics properties conform to the ASTM and the fracture properties are determined by the method proposed by Karihaloo and Nallathambi [RILEM Report 5, Fracture Mechanics Test Methods for Concrete (1991) 1]. A crack analysis using pre-cracked specimens and a dye technique was also conducted to examine the crack fronts and the corresponding residual strengths of heavy concrete. Test results indicated that the elastic modulus of heavy concrete is higher than that of regular mortar and increase with iron ore content. The compressive strength of heavy concrete also increases with iron ore content, while the tensile strength declines. The concrete including 40% metallic aggregate content by volume performs higher compressive strength and fracture toughness in this study.