What’s learning? • Example problem: face recognition
Prof. K
Prof. F
Prof. P
Prof. V
Chenyi
• Training data: a collection of images and labels (names)
Who is this guy?
• Evaluation criterion: correct labeling of new images
What’s learning? • Example problem: scene classification
road
road
sea
mountain
city
• a few labeled training images
What’s the label of this image?
• goal to label yet unseen image
Why learning? • The world is very complicated • We don’t know the exact model/mechanism between input and output • Find an approximate (usually simplified) model between input and output through learning • Principles of learning are “universal” – society (e.g., scientific community) – animal (e.g., human) – machine
A Taste of Machine Learning
True label
Estimated label We want to minimize the difference between them!
Artificial Neural Network
Fundamentals of Computer Vision
Chenyi Chen
What is Computer Vision? • Input: images • Output: information about the world
What is Computer Vision? Example: • What is in this image? • Who is in this image? • Where are they? • What are they doing?
What is Computer Vision? Other questions: • What camera settings were used? • Which pixels go with which objects? • What is the scene description in 3D?
Camera Projection
Camera Projection
Camera Projection
Dimensionality Reduction Machine (3D to 2D) 3D world
Two important coordinate systems: 1. World coordinate system z 2. Camera coordinate system
x
o “The World”
Geometric Transformations
What is the geometric relationship between these two images?
?
Image alignment
Why don’t these image line up exactly?
What is the geometric relationship between these two images?
Very important for creating mosaics!
2D image transformations
These transformations are a nested set of groups • Closed under composition and inverse is a member
Projective Transformations / Homographies
Called a homography (or planar perspective map)
Image warping with homographies
image plane in front
image plane below black area where no pixel maps to
Homographies
A Quick Application: Lane Detection
Lane Detection
Lane Detection
Stereo Vision
A Taste of Stereo Vision
Visual Odometry, Structure-from-Motion, 3D Street Scene Reconstruction
KITTI Datasets • • • • • •
Stereo images Grayscale Color Rectified 1382*512 10 FPS
Visual Odometry • Visual odometry computes the trajectory of the vehicle only based on image sequences (LIBVISO2)
Depth Map • Disparity map is computed from grayscale stereo image pairs (LIBELAS) • Depth map can be derived from disparity map and camera model
Lane Detection • Projecting lane markers on the road (Caltech Lane Detector)
3D Street Scene Reconstruction
+ +
3D Street Scene Reconstruction • Dense reconstruction on run_70
Reconstruction with Non-Stereo Images/Structure-from-Motion • Triangulation: tracking a same point in three (or more) frames, its spatial position can be determined
Figure courtesy of Jianxiong Xiao
Sparse Reconstruction with Non-Stereo Images • Sparse reconstruction on run_70
Sparse Reconstruction with Non-Stereo Images • run_1
Sparse Reconstruction with Non-Stereo Images • run_9
Other Demos for Structure-from-Motion • https://www.youtube.com/watch?v=i7ierVkXY a8 • https://www.youtube.com/watch?v=vpTEobp YoTg
Vision Based Self-driving Car - Princeton University
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