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Recognising Panoramas
M. Brown and D. Lowe, University of British Columbia
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Introduction
• Are you getting the whole picture?– Compact Camera FOV = 50 x 35°
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Introduction
• Are you getting the whole picture?– Compact Camera FOV = 50 x 35°– Human FOV = 200 x 135°
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Introduction
• Are you getting the whole picture?– Compact Camera FOV = 50 x 35°– Human FOV = 200 x 135°– Panoramic Mosaic = 360 x 180°
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Why “Recognising Panoramas”?
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Why “Recognising Panoramas”?
• 1D Rotations ()– Ordering matching images
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Why “Recognising Panoramas”?
• 1D Rotations ()– Ordering matching images
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Why “Recognising Panoramas”?
• 1D Rotations ()– Ordering matching images
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Why “Recognising Panoramas”?
• 2D Rotations (, )– Ordering matching images
• 1D Rotations ()– Ordering matching images
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Why “Recognising Panoramas”?
• 1D Rotations ()– Ordering matching images
• 2D Rotations (, )– Ordering matching images
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Why “Recognising Panoramas”?
• 1D Rotations ()– Ordering matching images
• 2D Rotations (, )– Ordering matching images
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Why “Recognising Panoramas”?
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Overview
• Feature Matching• Image Matching• Bundle Adjustment• Multi-band Blending• Results• Conclusions
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Overview
• Feature Matching• Image Matching• Bundle Adjustment• Multi-band Blending• Results• Conclusions
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Overview
• Feature Matching– SIFT Features– Nearest Neighbour Matching
• Image Matching• Bundle Adjustment• Multi-band Blending• Results• Conclusions
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Overview
• Feature Matching– SIFT Features– Nearest Neighbour Matching
• Image Matching• Bundle Adjustment• Multi-band Blending• Results• Conclusions
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Invariant Features
• Schmid & Mohr 1997, Lowe 1999, Baumberg 2000, Tuytelaars & Van Gool 2000, Mikolajczyk & Schmid 2001, Brown & Lowe 2002, Matas et. al. 2002, Schaffalitzky & Zisserman 2002
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SIFT Features
• Invariant Features– Establish invariant frame
• Maxima/minima of scale-space DOG x, y, s• Maximum of distribution of local gradients
– Form descriptor vector• Histogram of smoothed local gradients• 128 dimensions
• SIFT features are…– Geometrically invariant to similarity transforms,
• some robustness to affine change
– Photometrically invariant to affine changes in intensity
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Overview
• Feature Matching– SIFT Features– Nearest Neighbour Matching
• Image Matching• Bundle Adjustment• Multi-band Blending• Results• Conclusions
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Nearest Neighbour Matching
• Find k-NN for each feature– k number of overlapping images (we use k = 4)
• Use k-d tree– k-d tree recursively bi-partitions data at mean in the
dimension of maximum variance– Approximate nearest neighbours found in O(nlogn)
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Overview
• Feature Matching– SIFT Features– Nearest Neighbour Matching
• Image Matching• Bundle Adjustment• Multi-band Blending• Results• Conclusions
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Overview
• Feature Matching• Image Matching• Bundle Adjustment• Multi-band Blending• Results• Conclusions
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Overview
• Feature Matching• Image Matching• Bundle Adjustment• Multi-band Blending• Results• Conclusions
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Overview
• Feature Matching• Image Matching
– RANSAC for Homography– Probabilistic model for verification
• Bundle Adjustment• Multi-band Blending• Results• Conclusions
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Overview
• Feature Matching• Image Matching
– RANSAC for Homography– Probabilistic model for verification
• Bundle Adjustment• Multi-band Blending• Results• Conclusions
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RANSAC for Homography
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RANSAC for Homography
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RANSAC for Homography
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Overview
• Feature Matching• Image Matching
– RANSAC for Homography– Probabilistic model for verification
• Bundle Adjustment• Multi-band Blending• Results• Conclusions
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Probabilistic model for verification
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Probabilistic model for verification
• Compare probability that this set of RANSAC inliers/outliers was generated by a correct/false image match
– ni = #inliers, nf = #features
– p1 = p(inlier | match), p0 = p(inlier | ~match)
– pmin = acceptance probability
• Choosing values for p1, p0 and pmin
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Finding the panoramas
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Finding the panoramas
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Finding the panoramas
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Finding the panoramas
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Overview
• Feature Matching• Image Matching
– RANSAC for Homography– Probabilistic model for verification
• Bundle Adjustment• Multi-band Blending• Results• Conclusions
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Overview
• Feature Matching• Image Matching• Bundle Adjustment• Multi-band Blending• Results• Conclusions
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Overview
• Feature Matching• Image Matching• Bundle Adjustment• Multi-band Blending• Results• Conclusions
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Overview
• Feature Matching• Image Matching• Bundle Adjustment
– Error function
• Multi-band Blending• Results• Conclusions
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Overview
• Feature Matching• Image Matching• Bundle Adjustment
– Error function
• Multi-band Blending• Results• Conclusions
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Error function
• Sum of squared projection errors
– n = #images– I(i) = set of image matches to image i– F(i, j) = set of feature matches between images i,j
– rijk = residual of kth feature match between images i,j
• Robust error function
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• Parameterise each camera by rotation and focal length
• This gives pairwise homographies
Homography for Rotation
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Bundle Adjustment
• New images initialised with rotation, focal length of best matching image
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Bundle Adjustment
• New images initialised with rotation, focal length of best matching image
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Overview
• Feature Matching• Image Matching• Bundle Adjustment
– Error function
• Multi-band Blending• Results• Conclusions
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Overview
• Feature Matching• Image Matching• Bundle Adjustment• Multi-band Blending• Results• Conclusions
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Overview
• Feature Matching• Image Matching• Bundle Adjustment• Multi-band Blending• Results• Conclusions
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Multi-band Blending
• Burt & Adelson 1983– Blend frequency bands over range
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Low frequency ( > 2 pixels)
High frequency ( < 2 pixels)
2-band Blending
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Linear Blending
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2-band Blending
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Overview
• Feature Matching• Image Matching• Bundle Adjustment• Multi-band Blending• Results• Conclusions
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Overview
• Feature Matching• Image Matching• Bundle Adjustment• Multi-band Blending• Results• Conclusions
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Results
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Results
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Overview
• Feature Matching• Image Matching• Bundle Adjustment• Multi-band Blending• Results• Conclusions
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Overview
• Feature Matching• Image Matching• Bundle Adjustment• Multi-band Blending• Results• Conclusions
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Conclusions
• Fully automatic panoramas– A recognition problem…
• Invariant feature based method– SIFT features, RANSAC, Bundle Adjustment, Multi-
band Blending– O(nlogn)
• Future Work– Advanced camera modelling
• radial distortion, camera motion, scene motion, vignetting, exposure, high dynamic range, flash …
– Full 3D case – recognising 3D objects/scenes in unordered datasets
http://www.cs.ubc.ca/~mbrown/panorama/panorama.htmlhttp://www.cs.ubc.ca/~mbrown/panorama/panorama.html
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Questions?
http://www.cs.ubc.ca/~mbrown/panorama/panorama.htmlhttp://www.cs.ubc.ca/~mbrown/panorama/panorama.html
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Analytical computation of derivatives
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Levenberg-Marquardt
• Iteration step of form