Calibration method to improve the accuracy of THz imaging and spectroscopy in reflection geometry

We introduce a novel method to accurately extract the optical parameters in terahertz reflection imaging. Our method builds on standard self-referencing methods using the reflected signal from the bottom of the imaging window material to further compensate for time-dependent system fluctuations and position-dependent variation in the window thickness. Our proposed method not only improves the accuracy, but also simplifies the imaging procedure and reduces measurement times.

Watermarking through image geometry change tracking

Most of the digital image watermarking techniques are susceptible to geometric attacks such as cropping,rotation and scaling.These attacks are the easiest yet most successful in rendering the survival of watermark difficult.Such geometric operations alter the pixel orientation in the cover thereby rendering the watermark difficult to locate and extract.However,if the alterations produced by the geometric attacks such as scaling,cropping and rotation can be modeled in terms of the change in the image geometry,it is possible to relocate the watermark even after the original cover has suffered an attack.This paper contributes to the state of the art by proposing an image watermarking technique that attempts to model the attacks like cropping,scaling and rotation in terms of the image geometry.The proposed scheme is acceptably resistant to common geometric attacks and common image processing attacks.The watermark embedding is also done efficiently to offer resistance to image processing attacks.The watermark detection procedure is blind and key based,also not requiring the original cover work for watermark extraction.Efforts have been given to ensure that the proposed scheme conforms to robustness against attacks and exhibits high visual fidelity of the watermarked cover.

The Number of Independent Kruppa Constraints from N Images

It is well known that without any priori knowledge on the scene, camera motion and camera intrinsic parameters, the only constraint between a pair of images is the so-called epipolar constraint, or equivalently its fundamental matrix. For each fundamental matrix, at most two independent constraints on the cameras＇ intrinsic parameters are available via the Kruppa equations. Given N images, N（N- 1）/2 fundamental matrices appear, and N（N- 1） Kruppa constraints are available. However, to our knowledge, a formal proof of how many independent Kruppa constraints exist out of these N（N - 1） ones is unavailable in the literature. In this paper, we prove that given N images captured by a pinhole camera with varying parameters and under general motion, the number of independent Kruppa constraints is （5N - 9） （N 〉 2）, and it is less than that of independent constraints from the absolute quadric by only one. This one-constraint-less property of the Kruppa equations is their inherent deficiency and is independent of camera motion. This deficiency is due to their failure of automatic enforcement of the rank-three-ness on the absolute quadric.

MCGIM-Based Model Streaming for Realtime Progressive Rendering

While most mesh streaming techniques focus on optimizing the transmission order of the polygon data, few approaches have addressed the streaming problems by using geometry images （GIM）. In this paper, we present a new approach which firstly partitions a mesh into several surface patches, then converts these patches into multi-chart geometry images （MCGIM）. After resampling the MCGIM and normal map atlas are obtained, we hierarchically construct the regular geometry image representation by adopting the quadtree structure. In this way, the encoded nodes can be transmitted in arbitrary order with high transmission flexibility. Also, the rendering quality of the partially transmitted models can be greatly improved by using the normal texture atlas. Meanwhile only the geometry on the silhouette to the current viewpoint are required to be refined and transmitted, therefore the amount of data is minimized for transferring each frame. In particular, our approach also allows users to encode and transmit the mesh data via JPEG2000 technique. Therefore, our mesh streaming method is suitable for transmitting 3D animation models with use of Motion JPEG2000 videos. Experimental results have demonstrated the effectiveness of our approach, which enables one server to stream the MCGIM texture atlas to the clients. Also, the transmitted model can be rendered in a multiresolution manner by GPU acceleration on the client side, due to the regular geometry structure of MCGIM.

A hybrid rendering algorithm for textile objects

Although realistic textile rendering has been widely used in virtual garment and try-on systems, a robust method to simulate textile with a realistic appearance and high fidelity is yet to be established. We propose to use a novel hybrid geometric- and image-based rendering （GIBR） method to achieve photo realistic representation of textile products. The image-based technique, with its radiance synthesis algorithm, enables us to recover the reflectance properties of textile in an environment photo, and thus can render the appearance of textile material. The geometry-based technique, with its traditional illumination model of assigning illumination parameters extracted from the original scene （such as radiance and chroma dispatch）, makes it possible to interactively manipulate 3D virtual objects in the ＂real＂ environment. Our realistic textile rendering method has advantages over the traditional ones in its easiness to implement and its wide range of applications.