Derek Bradley

Derek Bradley
Department of Computer Science
University of British Columbia

PhD, University of British Columbia, 2010
MCS, Carleton University, 2005
BCS, Carleton University, 2003

bradleyd (at) cs.ubc.ca

This website is a portfolio of my research and publications, plus access to my resume and a few other things. I recently completed my PhD in Computer Science (Computer Graphics) at the University of British Columbia. My supervisor was Dr. Wolfgang Heidrich. I am interested in various capture projects, including multiview stereo, facial performance capture, and space-time reconstruction of other deforming objects.

Globally Consistent Space Time Reconstruction        PDF    MOV

T. Popa, I. South-Dickinson, D. Bradley, A. Sheffer, W. Heidrich

Computer Graphics Forum (Proceedings of Eurographics Symposium on Geometry Processing). 2010. (Lyon, France).

Most objects deform gradually over time, without abrupt changes in geometry or topology, such as changes in genus. Correct space-time reconstruction of such objects should satisfy this gradual change prior. We introduce a new method for globally consistent space-time geometry and motion reconstruction from video capture. We use the gradual change prior to resolve inconsistencies and faithfully reconstruct the geometry and motion of the scanned objects. In contrast to most previous methods our algorithm doesn’t require a strong shape prior such as a template and provides better results than other template-free approaches.

High Resolution Passive Facial Performance Capture        PDF    MP4

D. Bradley, W. Heidrich, T. Popa, A. Sheffer

ACM Transactions on Graphics (Proceedings of SIGGRAPH). 2010. (Los Angeles, USA).

We introduce a purely passive facial capture approach that uses only an array of video cameras, but requires no template facial geometry, no special makeup or markers, and no active lighting. We obtain initial geometry using multi-view stereo, and then use a novel approach for automatically tracking texture detail across the frames. As a result, we obtain a high-resolution sequence of compatibly triangulated and parameterized meshes. The resulting sequence can be rendered with dynamically captured textures, while also consistently applying texture changes such as virtual makeup.

Binocular Camera Calibration Using Rectification Error        PDF

D. Bradley, W. Heidrich

Proceedings of Canadian Conference on Computer and Robot Vision. 2010. (Ottawa, Canada).

Reprojection error is a commonly used measure for comparing the quality of different camera calibrations, for example when choosing the best calibration from a set. While this measure is suitable for single cameras, we show that we can improve calibrations in a binocular or multi-camera setup by calibrating the cameras in pairs using a rectification error. The rectification error determines the mismatch in epipolar constraints between a pair of cameras, and it can be used to calibrate binocular camera setups more accurately than using the reprojection error.

Synchronization and Rolling Shutter Compensation for Consumer Video Camera Arrays    PDF

D. Bradley, B. Atcheson, I. Ihrke, W. Heidrich

Proceedings of International Workshop on Projector-Camera Systems (PROCAMS). 2009. (Miami, USA).

Two major obstacles to the use of consumer camcorders in computer vision applications are the lack of synchronization hardware, and the use of a "rolling" shutter, which introduces a temporal shear in the video volume. We present two simple approaches for solving both the rolling shutter shear and the synchronization problem at the same time. The first approach is based on strobe illumination, while the second employs a subframe warp along optical flow vectors. In our experiments we have used the proposed methods to effectively remove temporal shear, and synchronize up to 16 consumer-grade camcorders in multiple geometric configurations.

Wrinkling Captured Garments Using Space-Time Data-Driven Deformation        PDF    AVI

T. Popa, Q. Zhou, D. Bradley, V. Kraevoy, H. Fu, A. Sheffer, W. Heidrich

Proceedings of Eurographics. 2009. (Munich, Germany).

In this work we propose a method for reintroducing fine folds into captured garment models using data- driven dynamic wrinkling. We first estimate the shape and position of folds based on the original video footage used for capture and then wrinkle the surface based on those estimates using space-time deformation. Both steps utilize the unique geometric characteristics of garments in general, and garment folds specifically, to facilitate the modeling of believable folds. We demonstrate the effectiveness of our wrinkling method on a variety of garments that have been captured using several recent techniques.

Augmented Reality on Cloth with Realistic Illumination

D. Bradley, G. Roth, P. Bose

Machine Vision and Applications. 2009. Vol. 20, No. 2, pp 85-92. [Submitted Sept. 2005]

Augmented reality (AR) is the concept of inserting virtual objects into real scenes. Often, augmentations are aligned with rigid planar objects in the scene. However, a more difficult task is to align non-rigid augmentations with flexible objects like cloth. To address this problem, we present a method to perform real-time flexible augmentations on cloth. Our method involves sparse cloth-tracking in video images using a new vision-based marker system with temporal coherence. We include an image-based method to automatically acquire real world illumination and shadows from the input frame.

Time-resolved 3D Capture of Non-stationary Gas Flows        PDF    AVI

B. Atcheson, I. Ihrke, W. Heidrich, A. Tevs, D. Bradley, M. Magnor, H.-P. Seidel

ACM Transactions on Graphics (Proceedings of SIGGRAPH Asia). 2008. (Singapore).

Fluid simulation is one of the most active research areas in computer graphics. However, it remains difficult to obtain measurements of real fluid flows for validation of the simulated data. In this paper, we take a step in the direction of capturing flow data for such purposes. Specifically, we present the first time-resolved Schlieren tomography system for capturing full 3D, non-stationary gas flows on a dense volumetric grid.

Markerless Garment Capture        PDF     AVI

D. Bradley, T. Popa, A. Sheffer, W. Heidrich, T. Boubekeur

ACM Transactions on Graphics (Proceedings of SIGGRAPH). 2008. (Los Angeles, USA).

In this paper, we describe a marker-free approach to capturing garment motion. We establish temporally coherent parameterizations between incomplete geometries that we extract at each timestep with a multiview stereo algorithm. We then fill holes in the geometry using a template. This approach, for the first time, allows us to capture the geometry and motion of unpatterned, off-the-shelf garments made from a range of different fabrics.

Accurate Multi-View Reconstruction Using Robust Binocular Stereo and Surface Meshing      PDF

D. Bradley, T. Boubekeur, W. Heidrich

IEEE Computer Vision and Pattern Recognition (CVPR) 2008. (Anchorage, USA).

This paper presents a new algorithm for multi-view reconstruction that demonstrates both accuracy and efficiency. Our method is based on robust binocular stereo matching, followed by adaptive point-based filtering of the merged point clouds, and efficient, high-quality mesh generation. All aspects of our method are designed to be highly scalable with the number of views. Our technique produces the most accurate results among current algorithms for a sparse number of viewpoints according to the Middlebury datasets. Additionally, we prove to be the most efficient method among non-GPU algorithms for the same datasets.