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A Fast Local Descriptor for Dense Matching
Engin Tola, Vincent Lepetit, Pascal FuaComputer Vision Laboratory, EPFL
Reporter: Jheng-You Lin
• Introduction• DAISY Computation• Results• Conclusion
Outline
• Wide-base line matching propose : SIFT、 GLOH、 SURF… (histogram based descriptor)– Good performance and robustness to image
transformations.– High computational cost and sensitivity to occlusions.
• Purpose– Design a descriptor that is as robust as SIFT or GLOH but
can be computed much more effectively and handle occlusions.
Introduction
• Novelty– introduces DAISY local image descriptor
Introduction (cont.)
• Novelty– introduces DAISY local image descriptor
Introduction (cont.)
* S. Winder and M. Brown. Learning Local Image Descriptors in CVPR’07
Improved performance : + Precise localization+ Rotational Robustness
• Novelty– introduces DAISY local image descriptor
Introduction (cont.)
Replacing weighted sums by convolutions
DAISY Computation
DAISY Computation
First compute gradient magnitude layers in different orientations
DAISY ComputationThen, apply convolution with a Gaussian kernel to pre-compute the histograms for every point
DAISY Computation
DAISY Computation
DAISY Computation
DAISY Computation
The computation mostly involves 1D convolutions, which is fast.
DAISY Computation
Rotating the descriptor only involves reordering the histograms.
…
DAISY Computation
Rotating the descriptor only involves reordering the histograms.
…
DAISY Computation
Computation Time Comparison(in seconds)
DAISY Computation
The full DAISY descriptor D(u, v) :
The descriptor of the same point that is close to an occlusion would be very different.
Normalize to unit norm
Results
Laser scan DAISY SIFT
SURF Pixel DifferenceNCC
Results
baseline increaseblock
Error threshold :
Top : 10%Middle : 5%Bottom : 1%
DAISY SIFT SURF
NCC
SURF Pixel Difference
Results
Using low-resolution of the Brussels images[24]
768x510 (2048x1360 origin)
[24] Combined Depth and Outlier Estimation in Multi-View Stereo, CVPR’06
Results
Using low-resolution of the Rathaus images[25]
768x512 (3072x2048 origin)
The holes are caused by the fact that a lot of the texture is not visible.
[25] Dense Matching of Multiple Wide-Baseline Views, ICCV’03
ResultsInput images Virtual view Synthesized
ResultsVirtual view Synthesized DAISY NCC
• Efficient descriptor and produces good reconstructions.
• Can handle low quality imagery
Conclusion