블로그 이미지
Leeway is... the freedom that someone has to take the action they want to or to change their plans.
maetel

Notice

Recent Post

Recent Comment

Recent Trackback

Archive

calendar

1 2 3 4
5 6 7 8 9 10 11
12 13 14 15 16 17 18
19 20 21 22 23 24 25
26 27 28 29 30 31
  • total
  • today
  • yesterday

Category

2010. 9. 24. 23:16 Computer Vision
Janne Heikkila, Olli Silven, "A Four-step Camera Calibration Procedure with Implicit Image Correction," cvpr, pp.1106, 1997 IEEE Computer Society Conference on Computer Vision and Pattern Recognition (CVPR'97), 1997


Matlab toolbox: http://www.ee.oulu.fi/~jth/calibr/

JanneHeikkilä - Machine Vision Group, Computer Science and Engineering Laboratory, University of Oulu
Olli Silven - Information Processing Laboratory, University of Oulu

cf.
http://www.vision.caltech.edu/bouguetj/calib_doc/htmls/parameters.html


1. Introduction

4-step
1) DLT (direct linear transformation) for initial parameter values [Tsai 1987, Abdel-Aziz 1971, Melen 1994]
2) Nonlinear parameter estimation for final parameter values [Slama 1980]
3) Correcting errors sourced from feature extraction
4) image correction: new implicit model to interpolate the correct image points


2. Explicit camera calibration

The pinhole camera model is based on the principle of collinearity, where each point in the object space is projected by a straight line through the projection center into the image plane.

http://en.wikipedia.org/wiki/Euler_angle











posted by maetel
2010. 7. 29. 17:08 Computer Vision
Seitz, S. M., Curless, B., Diebel, J., Scharstein, D., and Szeliski, R. 2006. A Comparison and Evaluation of Multi-View Stereo Reconstruction Algorithms. In Proceedings of the 2006 IEEE Computer Society Conference on Computer Vision and Pattern Recognition - Volume 1 (June 17 - 22, 2006). CVPR. IEEE Computer Society, Washington, DC, 519-528. DOI= http://dx.doi.org/10.1109/CVPR.2006.19


S. Seitz et al. Multi-view stereo evaluation web page
http://vision.middlebury.edu/mview/
posted by maetel
2010. 7. 18. 17:05 Computer Vision
Accurate Camera Calibration from Multi-View Stereo and Bundle Adjustment
Yasutaka Furukawa & Jean Ponce, CVPR 2008

Yasutaka Furukawa
http://www.cs.washington.edu/homes/furukawa/

Jean Ponce
http://www.di.ens.fr/~ponce/
http://www-cvr.ai.uiuc.edu/ponce_grp/

DxO Labs (렌즈 왜곡 교정 소프트웨어)
http://www.dxo.com/

PMVS (Patch-based Multi-view Stereo Software) version 2
http://grail.cs.washington.edu/software/pmvs/

CMVS (Clustering Views for Multi-view Stereo)
http://grail.cs.washington.edu/software/cmvs/

sba : A Generic Sparse Bundle Adjustment C/C++ Package Based on the Levenberg-Marquardt Algorithm (Manolis Lourakis)
http://www.ics.forth.gr/~lourakis/sba/


image-based modeling

multi-view stereovision (MVS)

> two main approach camera calibration problem
1) chart-based calibration (CBC)
2) structure from motion (SFM) + auto-calibration + bundle adjustment (BA)

* selection of feature correspondences (SFC)
eg. RANSAC


Standard BA algorithms optimize both the scene point and camera parameters by minimizing the sum of squared reprojection errors.

Unlike BA algorithms, multi-view stereo algorithms are aimed at recovering scene information alone given fixed camera parameters.

DxO Optics Pro - Lens Distortion


In practice, we have found PMVS to be robust to errors in camera parameters as long as the image resolution matches the corresponding reprojection errors - that is, when features to be matched are roughly within two pixels of the corresponding 3D points.


> Algorithm

1) initializing feature correspondences
1-1) building image pyramids
1-2) for the given camera parameters, obtaining a conservative estimate of the expected reprojection error
1-3) sub-sampling

2) refining feature correspondences
2-1) determining a patch and the local image texture inside
2-2) optimizing the reference camera with the conjugate gradient method
2-3) removing outliers and updating the corresponding visibility information

3) updating the camera parameters with the SBA bundle adjustment software

4) repeat 1)-3) 4 times with the updated expected reprojection error and the fixed pyramid level







posted by maetel
2009. 11. 8. 16:31 Computer Vision
Branislav Kisačanin & Vladimir Pavlović & Thomas S. Huang
Real-Time Vision for Human-Computer Interaction
(RTV4HCI)
Springer, 2005
(google book's overview)

2004 IEEE CVPR Workshop on RTV4HCI - Papers
http://rtv4hci.rutgers.edu/04/


Computer vision and pattern recognition continue to play a dominant role in the HCI realm. However, computer vision methods often fail to become pervasive in the field due to the lack of real-time, robust algorithms, and novel and convincing applications.

Keywords:
head and face modeling
map building
pervasive computing
real-time detection

Contents:
RTV4HCI: A Historical Overview.
- Real-Time Algorithms: From Signal Processing to Computer Vision.
- Recognition of Isolated Fingerspelling Gestures Using Depth Edges.
- Appearance-Based Real-Time Understanding of Gestures Using Projected Euler Angles.
- Flocks of Features for Tracking Articulated Objects.
- Static Hand Posture Recognition Based on Okapi-Chamfer Matching.
- Visual Modeling of Dynamic Gestures Using 3D Appearance and Motion Features.
- Head and Facial Animation Tracking Using Appearance-Adaptive Models and Particle Filters.
- A Real-Time Vision Interface Based on Gaze Detection -- EyeKeys.
- Map Building from Human-Computer Interactions.
- Real-Time Inference of Complex Mental States from Facial Expressions and Head Gestures.
- Epipolar Constrained User Pushbutton Selection in Projected Interfaces.
- Vision-Based HCI Applications.
- The Office of the Past.
- MPEG-4 Face and Body Animation Coding Applied to HCI.
- Multimodal Human-Computer Interaction.
- Smart Camera Systems Technology Roadmap.
- Index.




RTV4HCI: A Historical Overview
Matthew Turk (mturk@cs.ucsb.edu)
University of California, Santa Barbara
http://www.stanford.edu/~mturk/
http://www.cs.ucsb.edu/~mturk/

The goal of research in real-time vision for human-computer interaction is to develop algorithms and systems that sense and perceive humans and human activity, in order to enable more natural, powerful, and effective computer interfaces.

Computers in the Human Interaction Loop (CHIL)

perceptual interfaces
multimodal interfaces
post-WIMP(windows, icons, menus, pointer) interfaces

implicit user awareness or explicit user control

The user interface
- the software and devices that implement a particular model (or set of models) of HCI

Computer vision technologies must ultimately deliver a better "user experience".

B Shneiderman, Designing the User Interface: Strategies for Effective Human-Computer Interaction, Third Edition, Addison-Wesley, 1998.
: 1) time to learn 2) speed of performance 3) user error rates 4) retention over time 5) subjective satisfaction

- Presence and location (Face and body detection, head and body tracking)
- Identity (Face recognition, gait recognition)
- Expression (Facial feature tracking, expression modeling and analysis)
- Focus of attention (Head/face tracking, eye gaze tracking)
- Body posture and movement (Body modeling and tracking)
- Gesture (Gesture recognition, hand tracking)
- Activity (Analysis of body movement)

eg.
VIDEOPLACE (M W Krueger, Artificial Reality II, Addison-Wesley, 1991)
Magic Morphin Mirror / Mass Hallucinations (T Darrell et al., SIGGRAPH Visual Proc, 1997)

Principal Component Analysis (PCA)
Linear Discriminant Analysis (LDA)
Gabor Wavelet Networks (GWNs)
Active Appearance Models (AAMs)
Hidden Markov Models (HMMs)

Identix Inc.
Viisage Technology Inc.
Cognitec Systems


- MIT Medial Lab
ALIVE system (P Maes et al., The ALIVE system: wireless, full-body interaction with autonomous agents, ACM Multimedia Systems, 1996)
PFinder system (C R Wren et al., Pfinder: Real-time tracking of the human body, IEEE Trans PAMI, pp 780-785, 1997)
KidsRoom project (A Bobick et al., The KidsRoom: A perceptually-based interactive and immersive story environment, PRESENCE: Teleoperators and Virtual Environments, pp 367-391, 1999)




Flocks of Features for Tracking Articulated Objects
Mathias Kolsch (kolsch@nps.edu
Computer Science Department, Naval Postgraduate School, Monterey
Matthew Turk (mturk@cs.ucsb.edu)
Computer Science Department, University of California, Santa Barbara




Visual Modeling of Dynamic Gestures Using 3D Appearance and Motion Features
Guangqi Ye (grant@cs.jhu.edu), Jason J. Corso, Gregory D. Hager
Computational Interaction and Robotics Laboratory
The Johns Hopkins University



Map Building from Human-Computer Interactions
http://groups.csail.mit.edu/lbr/mars/pubs/pubs.html#publications
Artur M. Arsenio (arsenio@csail.mit.edu)
Computer Science and Artificial Intelligence Laboratory
Massachusetts Institute of Technology



Vision-Based HCI Applications
Eric Petajan (eric@f2f-inc.com)
face2face animation, inc.
eric@f2f-inc.com



The Office of the Past
Jiwon Kim (jwkim@cs.washington.edu), Steven M. Seitz (seitz@cs.washington.edu)
University of Washington
Maneesh Agrawala (maneesh@microsoft.com)
Microsoft Research
Proceedings of the 2004 Conference on Computer Vision and Pattern Recognition Workshop (CVPRW'04) Volume 10 - Volume 10  Page: 157   Year of Publication: 2004
http://desktop.google.com
http://grail.cs.washington.edu/projects/office/
http://www.realvnc.com/



Smart Camera Systems Technology Roadmap
Bruce Flinchbaugh (b-flinchbaugh@ti.com)
Texas Instruments

posted by maetel