Lecture 12. Local Feature Detection. Matching with Invariant Features. Why extract features? Why extract features? Why extract features?
|
|
- Berniece Richards
- 6 years ago
- Views:
Transcription
1 Lecture 1 Why extract eatures? Motivation: panorama stitching We have two images how do we combine them? Local Feature Detection Guest lecturer: Alex Berg Reading: Harris and Stephens David Lowe IJCV We need to match (align) images Building a Panorama Matching with Invariant Features Darya Frolova, Denis Simakov he Weizmann Institute o Science March 004 M. Brown and D. G. Lowe. Recognising Panoramas. ICCV Why extract eatures? Motivation: panorama stitching We have two images how do we combine them? Why extract eatures? Motivation: panorama stitching We have two images how do we combine them? Step 1: Detect eature points in both images Step : Find corresponding pairs Step 1: Detect eature points in both images Step : Find corresponding pairs Step 3: Use these pairs to align images 1
2 Matching with Features Problem 1: Detect the same point independently in both images Matching with Features Problem : For each point correctly recognize the corresponding one? no chance to match! We need a repeatable detector We need a reliable and distinctive descriptor Selecting Good Features What s a good eature? Satisies brightness constancy Has suicient texture variation Does not have too much texture variation Corresponds to a real surace patch Does not deorm too much over time Applications Feature points are used or: Motion tracking Image alignment 3D reconstruction Object recognition Indexing and database retrieval Robot navigation Finding Corners Key property: in the region around a corner, image gradient has two or more dominant directions Corners are repeatable and distinctive C.Harris and M.Stephens. "A Combined Corner and Edge Detector. Proceedings o the 4th Alvey Vision Conerence: pages
3 he Basic Idea An introductory example: Harris corner detector We should easily recognize the point by looking through a small window Shiting a window in any direction should give a large change in intensity C.Harris, M.Stephens. A Combined Corner and Edge Detector Harris Detector: Basic Idea lat region: no change in all directions edge : no change along the edge direction corner : signiicant change in all directions Harris Detector: Mathematics Window-averaged change o intensity or the shit [u,v]: xy, [ ] E( uv, ) = wxy (, ) I( x+ uy, + v) I( xy, ) Harris Detector: Mathematics Change o intensity or the shit [u,v]: [ ] E( uv, ) = wxy (, ) I( x+ uy, + v) I( xy, ) xy, Window unction Shited intensity Intensity Second-order aylor expansion o E(u,v) about (0,0) (bilinear approximation or small shits): Window unction w(x,y) = or Eu (0,0) 1 Euu (0,0) E( u, v) E(0,0) + [ u v] + [ u v] Ev (0,0) Euv (0,0) Euv(0,0) u E vv(0,0) v 1 in window, 0 outside Gaussian 3
4 Harris Detector: Mathematics Expanding E(u,v) in a nd order aylor series expansion, we have,or small shits [u,v], a bilinear approximation: u Euv (, ) [ uv, ] M v Interpreting the second moment matrix First, consider an axis-aligned corner: where M is a matrix computed rom image derivatives: Ix IxI y M = w( x, y) xy, II x y Iy M Interpreting the second moment matrix First, consider an axis-aligned corner: M = I I x x I y I xi y λ1 = I y 0 0 λ his means dominant gradient directions align with x or y axis I either λ is close to 0, then this is not a corner, so look or locations where both are large. General Case Since M is symmetric, we have M = R 1 λ1 0 R 0 λ We can visualize M as an ellipse with axis lengths determined by the eigenvalues and orientation determined by R Ellipse E(u,v) = const u [ u v] M = const v direction o the astest change (λ max ) -1/ (λ min ) -1/ direction o the slowest change Slide credit: David Jacobs Harris Detector: Mathematics Harris Detector: Mathematics Classiication o image points using eigenvalues o M: λ 1 and λ are small; E is almost constant in all directions λ Edge λ >> λ 1 Flat region Corner λ 1 and λ are large, λ 1 ~ λ ; E increases in all directions Edge λ 1 >> λ Measure o corner response: ( trace ) R = det M k M det M = λ λ 1 trace M = λ + λ 1 (k empirical constant, k = ) λ 1 4
5 Harris Detector: Mathematics R = det( M ) k trace( M ) = λ1λ k( λ1 + λ), 0.04 k.06 R depends only on eigenvalues o M R is large or a corner R is negative with large magnitude or an edge R is small or a lat region λ Edge R < 0 Flat R small Corner R > 0 Edge R < 0 Harris Detector: Summary Average intensity change in direction [u,v] can be expressed as a bilinear orm: u Euv (, ) [ uv, ] M v Describe a point in terms o eigenvalues o M: measure o corner response R = λ ( ) 1λ k λ1+ λ A good (corner) point should have a large intensity change in all directions, i.e. R should be large positive λ 1 Harris Detector Harris Detector: Worklow Algorithm: 1. Compute Gaussian derivatives at each pixel. Compute second moment matrix M in a Gaussian window around each pixel 3. Compute corner response unction R 4. hreshold R 5. Find local maxima o response unction (nonmaximum suppression) Harris Detector: Worklow Compute corner response R Harris Detector: Worklow Find points with large corner response: R>threshold 5
6 Harris Detector: Worklow ake only the points o local maxima o R Harris Detector: Worklow Harris Detector: Some Properties Rotation invariance Ellipse rotates but its shape (i.e. eigenvalues) remains the same Corner response R is invariant to image rotation Harris Detector: Some Properties Invariance to image intensity change? Harris Detector: Some Properties Partial invariance to additive and multiplicative intensity changes Only derivatives are used => invariance to intensity shit I I + b Intensity scale: I a I R threshold R x (image coordinate) x (image coordinate) 6
7 Harris Detector: Some Properties Harris Detector: Some Properties Invariant to image scale? All points will be classiied as edges Corner! Not invariant to scaling Harris Detector: Some Properties Quality o Harris detector or dierent scale changes Repeatability rate: # correspondences # possible correspondences C.Schmid et.al. Evaluation o Interest Point Detectors. IJCV 000 We want to: detect the same interest points regardless o image changes Invariance We want eatures to be detected despite geometric or photometric changes in the image: i we have two transormed versions o the same image, eatures should be detected in corresponding locations Darya Frolova, Denis Simakov 7
8 Models o Image Change Geometric Rotation Scale Aine valid or: orthographic camera, locally planar object Photometric Aine intensity change (I a I + b) Rotation Invariant Detection C.Schmid et.al. Evaluation o Interest Point Detectors. IJCV 000 Scale Invariant Detection Scale Invariant Detection Consider regions (e.g. circles) o dierent sizes around a point Regions o corresponding sizes will look the same in both images he problem: how do we choose corresponding circles independently in each image? 8
9 Scale Invariant Detection Solution: Design a unction on the region (circle), which is scale invariant (the same or corresponding regions, even i they are at dierent scales) Example: average intensity. For corresponding regions (even o dierent sizes) it will be the same. For a point in one image, we can consider it as a unction o region size (circle radius) Scale Invariant Detection Common approach: ake a local maximum o this unction Observation: region size, or which the maximum is achieved, should be invariant to image scale. Important: this scale invariant region size is ound in each image independently! Image 1 scale = 1/ Image Image 1 scale = 1/ Image region size region size s 1 region size s region size Scale Invariant Detection Scale Invariant Detection A good unction or scale detection: has one stable sharp peak bad region size bad region size Good! region size For usual images: a good unction would be a one which responds to contrast (sharp local intensity change) Functions or determining scale Kernels: ( xx (,, ) yy (,, )) L= G x y + G x y σ σ σ (Laplacian) DoG = G( x, y, kσ ) G( x, y, σ ) (Dierence o Gaussians) where Gaussian x + y 1 πσ σ Gxy (,, σ ) = e = Kernel Image Note: both kernels are invariant to scale and rotation Scale Invariant Detectors Scale Invariant Detectors Harris-Laplacian 1 Find local maximum o: Harris corner detector in space (image coordinates) Laplacian in scale SIF (Lowe) Find local maximum o: Dierence o Gaussians in space and scale scale scale y y Harris x Laplacian DoG Experimental evaluation o detectors w.r.t. scale change Repeatability rate: # correspondences # possible correspondences DoG x 1 K.Mikolajczyk, C.Schmid. Indexing Based on Scale Invariant Interest Points. ICCV 001 D.Lowe. Distinctive Image Features rom Scale-Invariant Keypoints. Accepted to IJCV 004 K.Mikolajczyk, C.Schmid. Indexing Based on Scale Invariant Interest Points. ICCV 001 9
10 Scale Invariant Detection: Summary Given: two images o the same scene with a large scale dierence between them Goal: ind the same interest points independently in each image Solution: search or maxima o suitable unctions in scale and in space (over the image) Methods: 1. Harris-Laplacian [Mikolajczyk, Schmid]: maximize Laplacian over scale, Harris measure o corner response over the image. SIF [Lowe]: maximize Dierence o Gaussians over scale and space Aine Invariant Detection Above we considered: Similarity transorm (rotation + uniorm scale) Aine Invariant Detection ake a local intensity extremum as initial point Go along every ray starting rom this point and stop when extremum o unction is reached Now we go on to: Aine transorm (rotation + non-uniorm scale) points along the ray We will obtain approximately corresponding regions () t = 1 t t o It () I 0 I () t I dt 0 Remark: we search or scale in every direction.uytelaars, L.V.Gool. Wide Baseline Stereo Matching Based on Local, Ainely Invariant Regions. BMVC 000. Aine Invariant Detection Aine Invariant Detection Algorithm summary (detection o aine invariant region): Start rom a local intensity extremum point Go in every direction until the point o extremum o some unction Curve connecting the points is the region boundary Compute geometric moments o orders up to or this region Replace the region with ellipse.uytelaars, L.V.Gool. Wide Baseline Stereo Matching Based on Local, Ainely Invariant Regions. BMVC 000. he regions ound may not exactly correspond, so we approximate them with ellipses Geometric Moments: mpq p q = x y ( x, y) dxdy Fact: moments m pq uniquely determine the unction aking to be the characteristic unction o a region (1 inside, 0 outside), moments o orders up to allow to approximate the region by an ellipse his ellipse will have the same moments o orders up to as the original region 10
11 Aine Invariant Detection Covariance matrix o region points deines an ellipse: 1 p Σ = Σ = 1 1 p 1 pp region 1 ( p = [x, y] is relative to the center o mass) q= Ap Σ = AΣ A 1 q Σ = Ellipses, computed or corresponding regions, also correspond! Σ = 1 q 1 qq region Aine Invariant Detection : Summary Under aine transormation, we do not know in advance shapes o the corresponding regions Ellipse given by geometric covariance matrix o a region robustly approximates this region For corresponding regions ellipses also correspond. Methods: 1. Search or extremum along rays [uytelaars, Van Gool]:. Maximally Stable Extremal Regions [Matas et.al.] Point Descriptors We know how to detect points Next question: How to match them?? Point descriptor should be: 1. Invariant. Distinctive Descriptors Invariant to Rotation Harris corner response measure: depends only on the eigenvalues o the matrix M Ix IxI y M = w( x, y) xy, II x y Iy C.Harris, M.Stephens. A Combined Corner and Edge Detector
12 Descriptors Invariant to Rotation Image moments in polar coordinates k iθ l m r e I(, r θ ) drdθ kl = Descriptors Invariant to Rotation Find local orientation Dominant direction o gradient Rotation in polar coordinates is translation o the angle: θ θ + θ 0 his transormation changes only the phase o the moments, but not its magnitude Rotation invariant descriptor consists o magnitudes o moments: m kl Compute image derivatives relative to this orientation Matching is done by comparing vectors [ m kl ] k,l J.Matas et.al. Rotational Invariants or Wide-baseline Stereo. Research Report o CMP, K.Mikolajczyk, C.Schmid. Indexing Based on Scale Invariant Interest Points. ICCV 001 D.Lowe. Distinctive Image Features rom Scale-Invariant Keypoints. Accepted to IJCV 004 Descriptors Invariant to Scale Use the scale determined by detector to compute descriptor in a normalized rame For example: moments integrated over an adapted window derivatives adapted to scale: si x Aine Invariant Descriptors Aine invariant color moments m abc p q a (, ) b (, ) c pq = x y R x y G x y B ( x, y) dxdy region Dierent combinations o these moments are ully aine invariant Also invariant to aine transormation o intensity I a I + b F.Mindru et.al. Recognizing Color Patterns Irrespective o Viewpoint and Illumination. CVPR99 1
13 Blur Subtract Aine Invariant Descriptors SIF Scale Invariant Feature ransorm 1 Find aine normalized rame Σ = 1 pp A Σ = qq Empirically ound to show very good perormance, invariant to image rotation, scale, intensity change, and to moderate aine transormations 1 1 Σ 1 = A1 A1 A 1 A Σ = A A Scale =.5 Rotation = 45 0 rotation Compute rotational invariant descriptor in this normalized rame J.Matas et.al. Rotational Invariants or Wide-baseline Stereo. Research Report o CMP, D.Lowe. Distinctive Image Features rom Scale-Invariant Keypoints. Accepted to IJCV 004 K.Mikolajczyk, C.Schmid. A Perormance Evaluation o Local Descriptors. CVPR 003 CVPR 003 utorial Recognition and Matching Based on Local Invariant Features Invariant Local Features Image content is transormed into local eature coordinates that are invariant to translation, rotation, scale, and other imaging parameters David Lowe Computer Science Department University o British Columbia SIF Features Advantages o invariant local eatures Locality: eatures are local, so robust to occlusion and clutter (no prior segmentation) Distinctiveness: individual eatures can be matched to a large database o objects Quantity: many eatures can be generated or even small objects Eiciency: close to real-time perormance Extensibility: can easily be extended to wide range o diering eature types, with each adding robustness Scale invariance Requires a method to repeatably select points in location and scale: he only reasonable scale-space kernel is a Gaussian (Koenderink, 1984; Lindeberg, 1994) An eicient choice is to detect peaks in the dierence o Gaussian pyramid (Burt & Adelson, 1983; Crowley & Parker, 1984 but examining more scales) Dierence-o-Gaussian with constant ratio o scales is a close approximation to Lindeberg s scale-normalized Laplacian (can be shown rom the heat diusion equation) 13
14 Blur Subtract Scale space processed one octave at a time Key point localization Detect maxima and minima o dierence-o-gaussian in scale space Fit a quadratic to surrounding values or sub-pixel and sub-scale interpolation (Brown & Lowe, 00) aylor expansion around point: Oset o extremum (use inite dierences or derivatives): Select canonical orientation Create histogram o local gradient directions computed at selected scale Assign canonical orientation at peak o smoothed histogram Each key speciies stable D coordinates (x, y, scale, orientation) Example o keypoint detection hreshold on value at DOG peak and on ratio o principle curvatures (Harris approach) (a) 33x189 image (b) 83 DOG extrema (c) 79 let ater peak value threshold (d) 536 let ater testing ratio o principle curvatures 0 π SIF vector ormation hresholded image gradients are sampled over 16x16 array o locations in scale space Create array o orientation histograms 8 orientations x 4x4 histogram array = 18 dimensions Feature stability to noise Match eatures ater random change in image scale & orientation, with diering levels o image noise Find nearest neighbor in database o 30,000 eatures 14
15 Feature stability to aine change Match eatures ater random change in image scale & orientation, with % image noise, and aine distortion Find nearest neighbor in database o 30,000 eatures Distinctiveness o eatures Vary size o database o eatures, with 30 degree aine change, % image noise Measure % correct or single nearest neighbor match A good SIF eatures tutorial By Estrada, Jepson, and Fleet. 15
Local Features (contd.)
Motivation Local Features (contd.) Readings: Mikolajczyk and Schmid; F&P Ch 10 Feature points are used also or: Image alignment (homography, undamental matrix) 3D reconstruction Motion tracking Object
More informationAdvances in Computer Vision. Prof. Bill Freeman. Image and shape descriptors. Readings: Mikolajczyk and Schmid; Belongie et al.
6.869 Advances in Computer Vision Prof. Bill Freeman March 3, 2005 Image and shape descriptors Affine invariant features Comparison of feature descriptors Shape context Readings: Mikolajczyk and Schmid;
More informationInvariant local features. Invariant Local Features. Classes of transformations. (Good) invariant local features. Case study: panorama stitching
Invariant local eatures Invariant Local Features Tuesday, February 6 Subset o local eature types designed to be invariant to Scale Translation Rotation Aine transormations Illumination 1) Detect distinctive
More informationCorners, Blobs & Descriptors. With slides from S. Lazebnik & S. Seitz, D. Lowe, A. Efros
Corners, Blobs & Descriptors With slides from S. Lazebnik & S. Seitz, D. Lowe, A. Efros Motivation: Build a Panorama M. Brown and D. G. Lowe. Recognising Panoramas. ICCV 2003 How do we build panorama?
More informationEdges and Scale. Image Features. Detecting edges. Origin of Edges. Solution: smooth first. Effects of noise
Edges and Scale Image Features From Sandlot Science Slides revised from S. Seitz, R. Szeliski, S. Lazebnik, etc. Origin of Edges surface normal discontinuity depth discontinuity surface color discontinuity
More informationFeature extraction: Corners and blobs
Feature extraction: Corners and blobs Review: Linear filtering and edge detection Name two different kinds of image noise Name a non-linear smoothing filter What advantages does median filtering have over
More informationFeature detectors and descriptors. Fei-Fei Li
Feature detectors and descriptors Fei-Fei Li Feature Detection e.g. DoG detected points (~300) coordinates, neighbourhoods Feature Description e.g. SIFT local descriptors (invariant) vectors database of
More informationFeature detectors and descriptors. Fei-Fei Li
Feature detectors and descriptors Fei-Fei Li Feature Detection e.g. DoG detected points (~300) coordinates, neighbourhoods Feature Description e.g. SIFT local descriptors (invariant) vectors database of
More informationLecture 8: Interest Point Detection. Saad J Bedros
#1 Lecture 8: Interest Point Detection Saad J Bedros sbedros@umn.edu Review of Edge Detectors #2 Today s Lecture Interest Points Detection What do we mean with Interest Point Detection in an Image Goal:
More informationINTEREST POINTS AT DIFFERENT SCALES
INTEREST POINTS AT DIFFERENT SCALES Thank you for the slides. They come mostly from the following sources. Dan Huttenlocher Cornell U David Lowe U. of British Columbia Martial Hebert CMU Intuitively, junctions
More informationLecture 8: Interest Point Detection. Saad J Bedros
#1 Lecture 8: Interest Point Detection Saad J Bedros sbedros@umn.edu Last Lecture : Edge Detection Preprocessing of image is desired to eliminate or at least minimize noise effects There is always tradeoff
More informationImage Analysis. Feature extraction: corners and blobs
Image Analysis Feature extraction: corners and blobs Christophoros Nikou cnikou@cs.uoi.gr Images taken from: Computer Vision course by Svetlana Lazebnik, University of North Carolina at Chapel Hill (http://www.cs.unc.edu/~lazebnik/spring10/).
More informationRecap: edge detection. Source: D. Lowe, L. Fei-Fei
Recap: edge detection Source: D. Lowe, L. Fei-Fei Canny edge detector 1. Filter image with x, y derivatives of Gaussian 2. Find magnitude and orientation of gradient 3. Non-maximum suppression: Thin multi-pixel
More informationLecture 7: Finding Features (part 2/2)
Lecture 7: Finding Features (part 2/2) Professor Fei- Fei Li Stanford Vision Lab Lecture 7 -! 1 What we will learn today? Local invariant features MoHvaHon Requirements, invariances Keypoint localizahon
More informationLecture 7: Finding Features (part 2/2)
Lecture 7: Finding Features (part 2/2) Dr. Juan Carlos Niebles Stanford AI Lab Professor Fei- Fei Li Stanford Vision Lab 1 What we will learn today? Local invariant features MoPvaPon Requirements, invariances
More informationBlobs & Scale Invariance
Blobs & Scale Invariance Prof. Didier Stricker Doz. Gabriele Bleser Computer Vision: Object and People Tracking With slides from Bebis, S. Lazebnik & S. Seitz, D. Lowe, A. Efros 1 Apertizer: some videos
More informationCSE 473/573 Computer Vision and Image Processing (CVIP)
CSE 473/573 Computer Vision and Image Processing (CVIP) Ifeoma Nwogu inwogu@buffalo.edu Lecture 11 Local Features 1 Schedule Last class We started local features Today More on local features Readings for
More informationCS 3710: Visual Recognition Describing Images with Features. Adriana Kovashka Department of Computer Science January 8, 2015
CS 3710: Visual Recognition Describing Images with Features Adriana Kovashka Department of Computer Science January 8, 2015 Plan for Today Presentation assignments + schedule changes Image filtering Feature
More informationDetectors part II Descriptors
EECS 442 Computer vision Detectors part II Descriptors Blob detectors Invariance Descriptors Some slides of this lectures are courtesy of prof F. Li, prof S. Lazebnik, and various other lecturers Goal:
More informationKeypoint extraction: Corners Harris Corners Pkwy, Charlotte, NC
Kepoint etraction: Corners 9300 Harris Corners Pkw Charlotte NC Wh etract kepoints? Motivation: panorama stitching We have two images how do we combine them? Wh etract kepoints? Motivation: panorama stitching
More informationLecture 6: Finding Features (part 1/2)
Lecture 6: Finding Features (part 1/2) Professor Fei- Fei Li Stanford Vision Lab Lecture 6 -! 1 What we will learn today? Local invariant features MoHvaHon Requirements, invariances Keypoint localizahon
More informationLoG Blob Finding and Scale. Scale Selection. Blobs (and scale selection) Achieving scale covariance. Blob detection in 2D. Blob detection in 2D
Achieving scale covariance Blobs (and scale selection) Goal: independently detect corresponding regions in scaled versions of the same image Need scale selection mechanism for finding characteristic region
More informationVlad Estivill-Castro (2016) Robots for People --- A project for intelligent integrated systems
1 Vlad Estivill-Castro (2016) Robots for People --- A project for intelligent integrated systems V. Estivill-Castro 2 Perception Concepts Vision Chapter 4 (textbook) Sections 4.3 to 4.5 What is the course
More informationAchieving scale covariance
Achieving scale covariance Goal: independently detect corresponding regions in scaled versions of the same image Need scale selection mechanism for finding characteristic region size that is covariant
More informationSIFT keypoint detection. D. Lowe, Distinctive image features from scale-invariant keypoints, IJCV 60 (2), pp , 2004.
SIFT keypoint detection D. Lowe, Distinctive image features from scale-invariant keypoints, IJCV 60 (), pp. 91-110, 004. Keypoint detection with scale selection We want to extract keypoints with characteristic
More informationBlob Detection CSC 767
Blob Detection CSC 767 Blob detection Slides: S. Lazebnik Feature detection with scale selection We want to extract features with characteristic scale that is covariant with the image transformation Blob
More informationCS5670: Computer Vision
CS5670: Computer Vision Noah Snavely Lecture 5: Feature descriptors and matching Szeliski: 4.1 Reading Announcements Project 1 Artifacts due tomorrow, Friday 2/17, at 11:59pm Project 2 will be released
More informationCorner detection: the basic idea
Corner detection: the basic idea At a corner, shifting a window in any direction should give a large change in intensity flat region: no change in all directions edge : no change along the edge direction
More information6.869 Advances in Computer Vision. Prof. Bill Freeman March 1, 2005
6.869 Advances in Computer Vision Prof. Bill Freeman March 1 2005 1 2 Local Features Matching points across images important for: object identification instance recognition object class recognition pose
More informationEE 6882 Visual Search Engine
EE 6882 Visual Search Engine Prof. Shih Fu Chang, Feb. 13 th 2012 Lecture #4 Local Feature Matching Bag of Word image representation: coding and pooling (Many slides from A. Efors, W. Freeman, C. Kambhamettu,
More informationSIFT: Scale Invariant Feature Transform
1 SIFT: Scale Invariant Feature Transform With slides from Sebastian Thrun Stanford CS223B Computer Vision, Winter 2006 3 Pattern Recognition Want to find in here SIFT Invariances: Scaling Rotation Illumination
More informationOverview. Introduction to local features. Harris interest points + SSD, ZNCC, SIFT. Evaluation and comparison of different detectors
Overview Introduction to local features Harris interest points + SSD, ZNCC, SIFT Scale & affine invariant interest point detectors Evaluation and comparison of different detectors Region descriptors and
More informationCS4670: Computer Vision Kavita Bala. Lecture 7: Harris Corner Detec=on
CS4670: Computer Vision Kavita Bala Lecture 7: Harris Corner Detec=on Announcements HW 1 will be out soon Sign up for demo slots for PA 1 Remember that both partners have to be there We will ask you to
More informationExtract useful building blocks: blobs. the same image like for the corners
Extract useful building blocks: blobs the same image like for the corners Here were the corners... Blob detection in 2D Laplacian of Gaussian: Circularly symmetric operator for blob detection in 2D 2 g=
More informationHarris Corner Detector
Multimedia Computing: Algorithms, Systems, and Applications: Feature Extraction By Dr. Yu Cao Department of Computer Science The University of Massachusetts Lowell Lowell, MA 01854, USA Part of the slides
More informationImage matching. by Diva Sian. by swashford
Image matching by Diva Sian by swashford Harder case by Diva Sian by scgbt Invariant local features Find features that are invariant to transformations geometric invariance: translation, rotation, scale
More informationSURF Features. Jacky Baltes Dept. of Computer Science University of Manitoba WWW:
SURF Features Jacky Baltes Dept. of Computer Science University of Manitoba Email: jacky@cs.umanitoba.ca WWW: http://www.cs.umanitoba.ca/~jacky Salient Spatial Features Trying to find interest points Points
More informationInstance-level recognition: Local invariant features. Cordelia Schmid INRIA, Grenoble
nstance-level recognition: ocal invariant features Cordelia Schmid NRA Grenoble Overview ntroduction to local features Harris interest points + SSD ZNCC SFT Scale & affine invariant interest point detectors
More informationProperties of detectors Edge detectors Harris DoG Properties of descriptors SIFT HOG Shape context
Lecture 10 Detectors and descriptors Properties of detectors Edge detectors Harris DoG Properties of descriptors SIFT HOG Shape context Silvio Savarese Lecture 10-16-Feb-15 From the 3D to 2D & vice versa
More informationOverview. Harris interest points. Comparing interest points (SSD, ZNCC, SIFT) Scale & affine invariant interest points
Overview Harris interest points Comparing interest points (SSD, ZNCC, SIFT) Scale & affine invariant interest points Evaluation and comparison of different detectors Region descriptors and their performance
More informationSIFT: SCALE INVARIANT FEATURE TRANSFORM BY DAVID LOWE
SIFT: SCALE INVARIANT FEATURE TRANSFORM BY DAVID LOWE Overview Motivation of Work Overview of Algorithm Scale Space and Difference of Gaussian Keypoint Localization Orientation Assignment Descriptor Building
More informationSIFT, GLOH, SURF descriptors. Dipartimento di Sistemi e Informatica
SIFT, GLOH, SURF descriptors Dipartimento di Sistemi e Informatica Invariant local descriptor: Useful for Object RecogniAon and Tracking. Robot LocalizaAon and Mapping. Image RegistraAon and SAtching.
More informationInstance-level recognition: Local invariant features. Cordelia Schmid INRIA, Grenoble
nstance-level recognition: ocal invariant features Cordelia Schmid NRA Grenoble Overview ntroduction to local features Harris interest points + SSD ZNCC SFT Scale & affine invariant interest point detectors
More informationAdvanced Features. Advanced Features: Topics. Jana Kosecka. Slides from: S. Thurn, D. Lowe, Forsyth and Ponce. Advanced features and feature matching
Advanced Features Jana Kosecka Slides from: S. Thurn, D. Lowe, Forsyth and Ponce Advanced Features: Topics Advanced features and feature matching Template matching SIFT features Haar features 2 1 Features
More informationInstance-level l recognition. Cordelia Schmid INRIA
nstance-level l recognition Cordelia Schmid NRA nstance-level recognition Particular objects and scenes large databases Application Search photos on the web for particular places Find these landmars...in
More informationScale & Affine Invariant Interest Point Detectors
Scale & Affine Invariant Interest Point Detectors Krystian Mikolajczyk and Cordelia Schmid Presented by Hunter Brown & Gaurav Pandey, February 19, 2009 Roadmap: Motivation Scale Invariant Detector Affine
More informationScale-space image processing
Scale-space image processing Corresponding image features can appear at different scales Like shift-invariance, scale-invariance of image processing algorithms is often desirable. Scale-space representation
More informationGiven a feature in I 1, how to find the best match in I 2?
Feature Matching 1 Feature matching Given a feature in I 1, how to find the best match in I 2? 1. Define distance function that compares two descriptors 2. Test all the features in I 2, find the one with
More informationInstance-level recognition: Local invariant features. Cordelia Schmid INRIA, Grenoble
nstance-level recognition: ocal invariant features Cordelia Schmid NRA Grenoble Overview ntroduction to local features Harris interest t points + SSD ZNCC SFT Scale & affine invariant interest point detectors
More informationFeature detection.
Feature detection Kim Steenstrup Pedersen kimstp@itu.dk The IT University of Copenhagen Feature detection, The IT University of Copenhagen p.1/20 What is a feature? Features can be thought of as symbolic
More informationMaximally Stable Local Description for Scale Selection
Maximally Stable Local Description for Scale Selection Gyuri Dorkó and Cordelia Schmid INRIA Rhône-Alpes, 655 Avenue de l Europe, 38334 Montbonnot, France {gyuri.dorko,cordelia.schmid}@inrialpes.fr Abstract.
More informationOverview. Introduction to local features. Harris interest points + SSD, ZNCC, SIFT. Evaluation and comparison of different detectors
Overview Introduction to local features Harris interest points + SSD, ZNCC, SIFT Scale & affine invariant interest point detectors Evaluation and comparison of different detectors Region descriptors and
More informationScale & Affine Invariant Interest Point Detectors
Scale & Affine Invariant Interest Point Detectors KRYSTIAN MIKOLAJCZYK AND CORDELIA SCHMID [2004] Shreyas Saxena Gurkirit Singh 23/11/2012 Introduction We are interested in finding interest points. What
More informationCEE598 - Visual Sensing for Civil Infrastructure Eng. & Mgmt.
CEE598 - Visual Sensing for Civil nfrastructure Eng. & Mgmt. Session 9- mage Detectors, Part Mani Golparvar-Fard Department of Civil and Environmental Engineering 3129D, Newmark Civil Engineering Lab e-mail:
More informationAffine Adaptation of Local Image Features Using the Hessian Matrix
29 Advanced Video and Signal Based Surveillance Affine Adaptation of Local Image Features Using the Hessian Matrix Ruan Lakemond, Clinton Fookes, Sridha Sridharan Image and Video Research Laboratory Queensland
More informationProbabilistic Model of Error in Fixed-Point Arithmetic Gaussian Pyramid
Probabilistic Model o Error in Fixed-Point Arithmetic Gaussian Pyramid Antoine Méler John A. Ruiz-Hernandez James L. Crowley INRIA Grenoble - Rhône-Alpes 655 avenue de l Europe 38 334 Saint Ismier Cedex
More informationEECS150 - Digital Design Lecture 15 SIFT2 + FSM. Recap and Outline
EECS150 - Digital Design Lecture 15 SIFT2 + FSM Oct. 15, 2013 Prof. Ronald Fearing Electrical Engineering and Computer Sciences University of California, Berkeley (slides courtesy of Prof. John Wawrzynek)
More informationFeature extraction: Corners and blobs
Featre etraction: Corners and blobs Wh etract featres? Motiation: panorama stitching We hae two images how do we combine them? Wh etract featres? Motiation: panorama stitching We hae two images how do
More informationInstance-level l recognition. Cordelia Schmid & Josef Sivic INRIA
nstance-level l recognition Cordelia Schmid & Josef Sivic NRA nstance-level recognition Particular objects and scenes large databases Application Search photos on the web for particular places Find these
More informationWavelet-based Salient Points with Scale Information for Classification
Wavelet-based Salient Points with Scale Information for Classification Alexandra Teynor and Hans Burkhardt Department of Computer Science, Albert-Ludwigs-Universität Freiburg, Germany {teynor, Hans.Burkhardt}@informatik.uni-freiburg.de
More informationEdge Detection. CS 650: Computer Vision
CS 650: Computer Vision Edges and Gradients Edge: local indication of an object transition Edge detection: local operators that find edges (usually involves convolution) Local intensity transitions are
More informationarxiv: v1 [cs.cv] 10 Feb 2016
GABOR WAVELETS IN IMAGE PROCESSING David Bařina Doctoral Degree Programme (2), FIT BUT E-mail: xbarin2@stud.fit.vutbr.cz Supervised by: Pavel Zemčík E-mail: zemcik@fit.vutbr.cz arxiv:162.338v1 [cs.cv]
More informationCOMP 408/508. Computer Vision Fall 2017 PCA for Recognition
COMP 408/508 Computer Vision Fall 07 PCA or Recognition Recall: Color Gradient by PCA v λ ( G G, ) x x x R R v, v : eigenvectors o D D with v ^v (, ) x x λ, λ : eigenvalues o D D with λ >λ v λ ( B B, )
More informationThe state of the art and beyond
Feature Detectors and Descriptors The state of the art and beyond Local covariant detectors and descriptors have been successful in many applications Registration Stereo vision Motion estimation Matching
More informationMachine vision. Summary # 4. The mask for Laplacian is given
1 Machine vision Summary # 4 The mask for Laplacian is given L = 0 1 0 1 4 1 (6) 0 1 0 Another Laplacian mask that gives more importance to the center element is L = 1 1 1 1 8 1 (7) 1 1 1 Note that the
More informationVIDEO SYNCHRONIZATION VIA SPACE-TIME INTEREST POINT DISTRIBUTION. Jingyu Yan and Marc Pollefeys
VIDEO SYNCHRONIZATION VIA SPACE-TIME INTEREST POINT DISTRIBUTION Jingyu Yan and Marc Pollefeys {yan,marc}@cs.unc.edu The University of North Carolina at Chapel Hill Department of Computer Science Chapel
More informationVisual Object Recognition
Visual Object Recognition Lecture 2: Image Formation Per-Erik Forssén, docent Computer Vision Laboratory Department of Electrical Engineering Linköping University Lecture 2: Image Formation Pin-hole, and
More informationComputer Vision I. Announcements
Announcements Motion II No class Wednesda (Happ Thanksgiving) HW4 will be due Frida 1/8 Comment on Non-maximal supression CSE5A Lecture 15 Shi-Tomasi Corner Detector Filter image with a Gaussian. Compute
More informationPerception III: Filtering, Edges, and Point-features
Perception : Filtering, Edges, and Point-features Davide Scaramuzza Universit of Zurich Margarita Chli, Paul Furgale, Marco Hutter, Roland Siegwart 1 Toda s outline mage filtering Smoothing Edge detection
More informationHilbert-Huang Transform-based Local Regions Descriptors
Hilbert-Huang Transform-based Local Regions Descriptors Dongfeng Han, Wenhui Li, Wu Guo Computer Science and Technology, Key Laboratory of Symbol Computation and Knowledge Engineering of the Ministry of
More informationMachine vision, spring 2018 Summary 4
Machine vision Summary # 4 The mask for Laplacian is given L = 4 (6) Another Laplacian mask that gives more importance to the center element is given by L = 8 (7) Note that the sum of the elements in the
More informationSURVEY OF APPEARANCE-BASED METHODS FOR OBJECT RECOGNITION
SURVEY OF APPEARANCE-BASED METHODS FOR OBJECT RECOGNITION Peter M. Roth and Martin Winter Inst. for Computer Graphics and Vision Graz University of Technology, Austria Technical Report ICG TR 01/08 Graz,
More informationImage Processing 1 (IP1) Bildverarbeitung 1
MIN-Fakultät Fachbereich Informatik Arbeitsbereich SAV/BV KOGS Image Processing 1 IP1 Bildverarbeitung 1 Lecture : Object Recognition Winter Semester 015/16 Slides: Prof. Bernd Neumann Slightly revised
More informationRotational Invariants for Wide-baseline Stereo
Rotational Invariants for Wide-baseline Stereo Jiří Matas, Petr Bílek, Ondřej Chum Centre for Machine Perception Czech Technical University, Department of Cybernetics Karlovo namesti 13, Prague, Czech
More informationOptical Flow, Motion Segmentation, Feature Tracking
BIL 719 - Computer Vision May 21, 2014 Optical Flow, Motion Segmentation, Feature Tracking Aykut Erdem Dept. of Computer Engineering Hacettepe University Motion Optical Flow Motion Segmentation Feature
More information* h + = Lec 05: Interesting Points Detection. Image Analysis & Retrieval. Outline. Image Filtering. Recap of Lec 04 Image Filtering Edge Features
age Analsis & Retrieval Outline CS/EE 5590 Special Topics (Class ds: 44873, 44874) Fall 06, M/W 4-5:5p@Bloch 00 Lec 05: nteresting Points Detection Recap of Lec 04 age Filtering Edge Features Hoework Harris
More informationLecture 05 Point Feature Detection and Matching
nstitute of nformatics nstitute of Neuroinformatics Lecture 05 Point Feature Detection and Matching Davide Scaramuzza 1 Lab Eercise 3 - Toda afternoon Room ETH HG E 1.1 from 13:15 to 15:00 Wor description:
More informationObject Recognition Using Local Characterisation and Zernike Moments
Object Recognition Using Local Characterisation and Zernike Moments A. Choksuriwong, H. Laurent, C. Rosenberger, and C. Maaoui Laboratoire Vision et Robotique - UPRES EA 2078, ENSI de Bourges - Université
More informationImage Stitching II. Linda Shapiro CSE 455
Image Stitching II Linda Shapiro CSE 455 RANSAC for Homography Initial Matched Points RANSAC for Homography Final Matched Points RANSAC for Homography Image Blending What s wrong? Feathering + 1 0 1 0
More informationFiltering and Edge Detection
Filtering and Edge Detection Local Neighborhoods Hard to tell anything from a single pixel Example: you see a reddish pixel. Is this the object s color? Illumination? Noise? The next step in order of complexity
More informationInterest Operators. All lectures are from posted research papers. Harris Corner Detector: the first and most basic interest operator
Interest Operators All lectures are from posted research papers. Harris Corner Detector: the first and most basic interest operator SIFT interest point detector and region descriptor Kadir Entrop Detector
More informationImage Stitching II. Linda Shapiro EE/CSE 576
Image Stitching II Linda Shapiro EE/CSE 576 RANSAC for Homography Initial Matched Points RANSAC for Homography Final Matched Points RANSAC for Homography Image Blending What s wrong? Feathering + 1 0 ramp
More informationAnnouncements. Tracking. Comptuer Vision I. The Motion Field. = ω. Pure Translation. Motion Field Equation. Rigid Motion: General Case
Announcements Tracking Computer Vision I CSE5A Lecture 17 HW 3 due toda HW 4 will be on web site tomorrow: Face recognition using 3 techniques Toda: Tracking Reading: Sections 17.1-17.3 The Motion Field
More informationLecture 7: Edge Detection
#1 Lecture 7: Edge Detection Saad J Bedros sbedros@umn.edu Review From Last Lecture Definition of an Edge First Order Derivative Approximation as Edge Detector #2 This Lecture Examples of Edge Detection
More informationEdge Detection. Introduction to Computer Vision. Useful Mathematics Funcs. The bad news
Edge Detection Introduction to Computer Vision CS / ECE 8B Thursday, April, 004 Edge detection (HO #5) Edge detection is a local area operator that seeks to find significant, meaningful changes in image
More informationInterest Point Detection. Lecture-4
nterest Point Detection Lectre-4 Contents Harris Corner Detector Sm o Sqares Dierences (SSD Corrleation Talor Series Eigen Vectors and Eigen Vales nariance and co-ariance What is an interest point Epressie
More informationLecture 6: Edge Detection. CAP 5415: Computer Vision Fall 2008
Lecture 6: Edge Detection CAP 5415: Computer Vision Fall 2008 Announcements PS 2 is available Please read it by Thursday During Thursday lecture, I will be going over it in some detail Monday - Computer
More informationSlide a window along the input arc sequence S. Least-squares estimate. σ 2. σ Estimate 1. Statistically test the difference between θ 1 and θ 2
Corner Detection 2D Image Features Corners are important two dimensional features. Two dimensional image features are interesting local structures. They include junctions of dierent types Slide 3 They
More informationImage Alignment and Mosaicing
Image Alignment and Mosaicing Image Alignment Applications Local alignment: Tracking Stereo Global alignment: Camera jitter elimination Image enhancement Panoramic mosaicing Image Enhancement Original
More informationVideo and Motion Analysis Computer Vision Carnegie Mellon University (Kris Kitani)
Video and Motion Analysis 16-385 Computer Vision Carnegie Mellon University (Kris Kitani) Optical flow used for feature tracking on a drone Interpolated optical flow used for super slow-mo optical flow
More informationLucas-Kanade Optical Flow. Computer Vision Carnegie Mellon University (Kris Kitani)
Lucas-Kanade Optical Flow Computer Vision 16-385 Carnegie Mellon University (Kris Kitani) I x u + I y v + I t =0 I x = @I @x I y = @I u = dx v = dy I @y t = @I dt dt @t spatial derivative optical flow
More informationRapid Object Recognition from Discriminative Regions of Interest
Rapid Object Recognition from Discriminative Regions of Interest Gerald Fritz, Christin Seifert, Lucas Paletta JOANNEUM RESEARCH Institute of Digital Image Processing Wastiangasse 6, A-81 Graz, Austria
More informationFeature Vector Similarity Based on Local Structure
Feature Vector Similarity Based on Local Structure Evgeniya Balmachnova, Luc Florack, and Bart ter Haar Romeny Eindhoven University of Technology, P.O. Box 53, 5600 MB Eindhoven, The Netherlands {E.Balmachnova,L.M.J.Florack,B.M.terHaarRomeny}@tue.nl
More informationLecture 8 Optimization
4/9/015 Lecture 8 Optimization EE 4386/5301 Computational Methods in EE Spring 015 Optimization 1 Outline Introduction 1D Optimization Parabolic interpolation Golden section search Newton s method Multidimensional
More informationOptical flow. Subhransu Maji. CMPSCI 670: Computer Vision. October 20, 2016
Optical flow Subhransu Maji CMPSC 670: Computer Vision October 20, 2016 Visual motion Man slides adapted from S. Seitz, R. Szeliski, M. Pollefes CMPSC 670 2 Motion and perceptual organization Sometimes,
More informationGalilean-diagonalized spatio-temporal interest operators
Galilean-diagonalized spatio-temporal interest operators Tony Lindeberg, Amir Akbarzadeh and Ivan Laptev Computational Vision and Active Perception Laboratory (CVAP) Department of Numerical Analysis and
More informationImage Filtering. Slides, adapted from. Steve Seitz and Rick Szeliski, U.Washington
Image Filtering Slides, adapted from Steve Seitz and Rick Szeliski, U.Washington The power of blur All is Vanity by Charles Allen Gillbert (1873-1929) Harmon LD & JuleszB (1973) The recognition of faces.
More informationTemplates, Image Pyramids, and Filter Banks
Templates, Image Pyramids, and Filter Banks 09/9/ Computer Vision James Hays, Brown Slides: Hoiem and others Review. Match the spatial domain image to the Fourier magnitude image 2 3 4 5 B A C D E Slide:
More informationTRACKING and DETECTION in COMPUTER VISION Filtering and edge detection
Technischen Universität München Winter Semester 0/0 TRACKING and DETECTION in COMPUTER VISION Filtering and edge detection Slobodan Ilić Overview Image formation Convolution Non-liner filtering: Median
More information