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16-721: Advanced Machine Perception Staff: Instructor: Alexei (Alyosha) Efros ( efros @cs ), 4207 NSH TA: David Bradley ( [email protected] ), 2216 NSH Web Page: http://www.cs.cmu.edu/~efros/courses/AP06/ Today Introduction Why Perception ? Administrative stuff Overview of the course

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16 721 advanced machine perception l.jpg
16-721: Advanced Machine Perception

Today l.jpg

  • Introduction

  • Why Perception?

  • Administrative stuff

  • Overview of the course

  • Image Datasets

A bit about me l.jpg
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”

Phd thesis on texture and action synthesis l.jpg
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

The story begins l.jpg
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)

Vision a split personality l.jpg

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?

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Lengths: Measurement vs. Perception

Müller-Lyer Illusion


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Vision as Measurement Device

Real-time stereo on Mars

Physics-based Vision

Virtualized Reality

Structure from Motion

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…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.

Slide13 l.jpg

So what do humans care about?

slide by Fei Fei, Fergus & Torralba

Slide14 l.jpg

Verification: is that a bus?

slide by Fei Fei, Fergus & Torralba

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Detection: are there cars?

slide by Fei Fei, Fergus & Torralba

Slide16 l.jpg

Identification: is that a picture of Mao?

slide by Fei Fei, Fergus & Torralba

Slide17 l.jpg

Object categorization







street lamp




slide by Fei Fei, Fergus & Torralba

Slide18 l.jpg

Scene and context categorization

  • outdoor

  • city

  • traffic

slide by Fei Fei, Fergus & Torralba

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Challenges 1: view point variation

Michelangelo 1475-1564

Slide21 l.jpg

Challenges 2: illumination

slide credit: S. Ullman

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Challenges 3: occlusion

Magritte, 1957

Slide23 l.jpg

Challenges 4: scale

slide by Fei Fei, Fergus & Torralba

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Challenges 5: deformation

Xu, Beihong 1943

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Challenges 7: object intra-class variation

slide by Fei-Fei, Fergus & Torralba

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Challenges 8: local ambiguity

slide by Fei-Fei, Fergus & Torralba

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In this course, we will:

Take a few baby steps…

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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

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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

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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

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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)

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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)

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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!

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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.

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End of Semester Awards

  • We will vote for:

    • Best Paper Presenter

    • Best Paper Opponent

    • Best Demo

    • Best Project

  • Prize: dinner in a nice restaurant

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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

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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

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  • See web page