16-721: Advanced Machine Perception

1. 16-721: Advanced Machine Perception • Staff: • Instructor: Alexei (Alyosha) Efros (efros@cs), 4207 NSH • TA: David Bradley (dbradley@cs), 2216 NSH • Web Page: • http://www.cs.cmu.edu/~efros/courses/AP06/

2. Today • Introduction • Why Perception? • Administrative stuff • Overview of the course • Image Datasets

3. A bit about me • Alexei (Alyosha) Efros • Relatively new faculty (RI/CSD) • Ph.D 2003, from UC Berkeley (signed by Arnie!) • Research Fellow, University of Oxford, ’03-’04 • Teaching • I am still learning… • The plan is to have fun and learn cool things, both you and me! • Social warning: I don’t see well • Research • Vision, Graphics, Data-driven “stuff”

4. PhD Thesis on Texture and Action Synthesis Smart Erase button in Microsoft Digital Image Pro: Antonio Criminisi’s son cannot walk but he can fly

5. The story begins… • “All happy families are alike; each unhappy family is unhappy in its own way.” • -- Lev Tolstoy, Anna Karenina • “What does it mean, to see? The plain man's answer (and Aristotle's, too). would be, to know what is where by looking.” • -- David Marr, Vision (1982)

6. depth map Vision: a split personality • “What does it mean, to see? The plain man's answer (and Aristotle's, too). would be, to know what is where by looking. In other words, vision is the process of discovering from images what is present in the world, and where it is.” • Answer #1: pixel of brightness 243 at position (124,54) • …and depth .7 meters • Answer #2: looks like bottom edge of whiteboard showing at the top of the image • Is the difference just a matter of scale?

7. Measurement vs. Perception

8. Brightness: Measurement vs. Perception

9. Brightness: Measurement vs. Perception Proof!

10. Lengths: Measurement vs. Perception Müller-Lyer Illusion http://www.michaelbach.de/ot/sze_muelue/index.html

11. Vision as Measurement Device Real-time stereo on Mars Physics-based Vision Virtualized Reality Structure from Motion

12. …but why? • Reason #1: • Semester too short, can’t cover everything • Other great classes offered at CMU, e.g.: • Appearance Modeling (Srinivas Narasimhan, every fall) • Medical Vision (Yanxi Liu) • Structure from Motion (Martial Hebert, sometime?) • “But what if I don’t care about this wishy-washy human perception stuff? I just want to make my robot go!” • Reason #2: • For measurement, other sensors are often better (in DARPA Grand Challenge, vision was barely used!) • Reason #3: • The goals of computer vision (what + where) are in terms of what humans care about.

13. So what do humans care about? slide by Fei Fei, Fergus & Torralba

14. Verification: is that a bus? slide by Fei Fei, Fergus & Torralba

15. Detection: are there cars? slide by Fei Fei, Fergus & Torralba

16. Identification: is that a picture of Mao? slide by Fei Fei, Fergus & Torralba

17. Object categorization sky building flag face banner wall street lamp bus bus cars slide by Fei Fei, Fergus & Torralba

18. Scene and context categorization • outdoor • city • traffic • … slide by Fei Fei, Fergus & Torralba

19. Rough 3D layout, depth ordering

20. Challenges 1: view point variation Michelangelo 1475-1564

21. Challenges 2: illumination slide credit: S. Ullman

22. Challenges 3: occlusion Magritte, 1957

23. Challenges 4: scale slide by Fei Fei, Fergus & Torralba

24. Challenges 5: deformation Xu, Beihong 1943

25. Challenges 6: background clutter Klimt, 1913

26. Challenges 7: object intra-class variation slide by Fei-Fei, Fergus & Torralba

27. Challenges 8: local ambiguity slide by Fei-Fei, Fergus & Torralba

28. Challenges 9: the world behind the image

29. In this course, we will: Take a few baby steps…

30. Course Organization • Requirements: • Paper Presentations (50%) • Paper Advocate • Paper Demo Presenter • Paper Opponent • Class Participation (20%) • Keep annotated bibliography • Post questions / comments on Quick-topic • Ask questions / debate / flight / be involved! • Final Project (30%) • Do something with lots of data (at least 500 images) • Groups of 1, 2, or 3

31. Paper Advocate • Pick a paper from list • That you like and willing to defend • Sometimes I will make you do two papers, or background • Meet with me before starting to talk about how to present the paper(s) • Prepare a good, conference-quality presentation (20-45 min, depending on difficulty of material) • Meet with me again 2 days before class to go over the presentation • Office hours at end of each class • Present and defend the paper in front of class

32. Paper Demo Presenter • For some papers, we will have separate demo presentations • Sign up for a paper you find interesting • Get the code online (or implement if easy) • Run it on a toy problem, play with parameters • Run it on a new dataset • Prepare short 5-10 min presentation detailing results • Can cooperate with Paper Advocate

33. Paper Opponent • Sign up for a paper you don’t like / suspicious about • Prepare an argument (with or without slides) against the paper: • Paper weaknesses • Relevance to real problems • Existence of better alternative approaches • Etc. • Present in front of class (5-10 min)

34. Class Participation • Keep annotated bibliography of papers you read (always a good idea!). The format is up to you. At least, it needs to have: • Summary of key points • A few Interesting insights, “aha moments”, keen observations, etc. • Weaknesses of approach. Unanswered questions. Areas of further investigation, improvement. • Submit your thoughts for current paper(s) before each class (printout)

35. Class Participation • In addition, submit interesting observations or questions to QuickTopic before class for public discussion. • Be active in class. Voice your ideas, concerns. • You need to participate: either in class or in QuickTopic every week! • Dave will be watching and keeping track!

36. Final Project • Can grow out of paper presentation, or your own research • But it needs to use large amounts of data! • 1-3 people per project. • Project proposals in a few weeks. • Project presentations at the end of semester. • Results presented as a CVPR-format paper. • Hopefully, a few papers may be submitted to conferences.

37. End of Semester Awards • We will vote for: • Best Paper Presenter • Best Paper Opponent • Best Demo • Best Project • Prize: dinner in a nice restaurant

38. Course Outline • Physiology of Vision (1 lecture) • Overview of Human Visual Percetion (1 lecture) • Need presenter for Monday! • Part I: Low-level vision (images as texture) • Texture segmentation, image retrieval, scene models, “Bag of words” representations • Part II: Mid-level vision (segmentation) • Principles of grouping, Normalized Cuts, Mean-shift, DD-MCMC, Graph-cut, super-pixels • Part III: 2D Recognition • Window scanning (Schniderman+Kanade, Viola+Jones) • Correspondence Matching (schanfer matching, housedorf distance, shape contexts, invariant features, active appearance models) • Recognition with Segmentation (top-down + buttom-up) • Words and Pictures

39. Course Outline (cont.) • Part IV: Intrinsic Images • Shading vs. reflectance • Recovering surface orientations and depth • Style vs. content • Part V: Dealing with Data • Isomap, LLE, Non-negative Matrix Factorization • Part VI: Tracking and Motion Segmentation • Particle filtering, examplar-based, layers • Sign up to present one paper on Wed on QuickTopic

40. Datasets • See web page