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1answer
49 views

Using ROC curves for comparing the performance of SIFT and SURF

I want to compare the performance of SIFT and SURF against some standard image set. After a bit of research, I found that ROC curves are one of the best ways to do this task. In order to plot ROC ...
-1
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1answer
22 views

Is there two Types of Scale Space in SURF algorithm?

I couldn't figure out below paragraph on SURF paper and hope that someone can help me to understand it. Bay H., Ess A., Tuytelaars T. Van Gool L. - Speed-Up Robust Features (SURF), page 4, ...
1
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1answer
47 views

Can SIFT run in realtime?

What is the best possible runtime for extracting SIFT keypoints and Descriptors? I know it depends on #keypoints extracted. So, say for image of size 640x640, the code that I have been using requires ...
1
vote
1answer
44 views

Why does the odd multiple of $\frac{\pi}{4}$ on Gaussian cause loss in repeatability under image rotations?

I couldn't figure out below paragraph on SURF paper and hope that someone can help me to understand it. Why image rotations around odd multiples of $\frac{\pi}{4}$ lead to a loss of repeatability? ...
0
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1answer
35 views

need general resource about image matching

i'm working on image matching mainly SIFT and SURF for my thesis. i read Moravec's and harris corner detectors and understand them quiet well in my own opinion.A COMBINED CORNER AND EDGE DETECTOR[1] ...
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0answers
38 views

how to calculate feature points in SIFT?

i wanna know how to calculate key points? im doing it in matlab. when i select 3 DOG(differnce of gaussian) blured image and compared each pixels in the middle image with 26 neighbourhood(including 9 ...
0
votes
1answer
211 views

k-NN match for object recognition

The $\frac{d_1}{d_2}<0.6$ gives a large number of false matches and it assumes the nearest neighbour is a correct match. Anybody knows any good method to reduce number of false matches or filter ...
0
votes
1answer
49 views

Which is the best method for comparing the histogram obtained after BOW?

Euclidian distance Cosine similarity Histogram Intersection Or any other? Consider the importance of the method in case of images. Eg, Cosine Similarity matches angle of two vectors... What impact ...
1
vote
2answers
88 views

what is the output of BoW after an image has been trained with SIFT algorithm and k-means

SIFT algorithm provides a 128 dimensional feature vector that is used for image classification.When all the interest points(key points) are taken together and K-means clustering is applied,the image ...
1
vote
1answer
91 views

What steps come after finding the gradients of the SIFT key points?

I am using a SIFT algorithm to extract features from an image. I understand that the SIFT descriptor first finds the extrema and then finds the gradient and direction of each of these interest ...
0
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0answers
44 views

Distance-metric for SIFT descriptors matching

Will using Cosine-Similarity or Histogram Intersection as distance-metric, for matching SIFT descriptors, help to get better results? Anybody tried on that ever?
0
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2answers
81 views

Increasing Recall rate for SIFT

Is there a better way to increase Recall Rate when using SIFT features? I am thinking a way to replace the NN1/NN2 ratio to account for slightly distorted objects. Moving towards clustering and using ...
2
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3answers
139 views

Visualize visual words in bag of words model

I am implementing visual bag of words through these steps: Find interest points using SIFT Calculate SIFT descriptor Build codebook through kmeans clustering of SIFT descriptors. How can I ...
0
votes
1answer
77 views

Segmentation step when using feature descriptors

In my final year project, we are using a SIFT feature descriptor to classify and recognize objects, but I have never come across segmentation in the process of image classification/categorization. ...
0
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0answers
184 views

Training of SVM classifier in Matlab using SIFT features

Using SIFT extractor, I get keypoints of different sizes. How can I create a matrix for the classifier using these keypoints of different sizes? I would like to use an SVM for classification.
1
vote
1answer
443 views

SIFT - Taylor Expansion

I'm trying to implement SIFT algorithm. After I found the min/max points in DOG images I need to find the real min/max subpixels by taylor exapnsion: $$ \begin{equation} D(\mathbf{x}) = D + ...
3
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0answers
438 views

Creating a gaussian pyramid

I'm trying to recreate a gassuain pyramid using the following scales: There seems to be two concepts used here: 1) When an image is halved, applying a gaussian kernel of σ will apply as 2σ. 2) ...
3
votes
0answers
97 views

What is the story behind the story about SIFT descriptor?

The following is from Lowe 2004 paper ( http://www.cs.ubc.ca/~lowe/papers/ijcv04.pdf ). One obvious approach would be to sample the local image intensities around the keypoint at the appropriate ...
2
votes
2answers
278 views

SIFT - why s+3 scales per octave?

I have a problem with SIFT that I do not understand. Lowe [1] proposed in his work the s=3 levels of scale are enough for one octave. Afterwards, he mentioned that ...
1
vote
1answer
518 views

Why is it necessary to implement octaves in sift

I've been studying sift very hard for two weeks. I found much materials about scale space. It is very hard to understand scale space depthly. What I've found and confusing things are that 'scale' in ...
1
vote
1answer
74 views

I have a question on SIFT

I am reading a paper on SIFT by Lowe. In it, gradient magnitudes and orientations are calculated using these formulae: $$$$ I don't know why m(x,y) is calculated above. I heard that gradient ...
0
votes
1answer
237 views

taylor expansion of scale space function

I see the following expression from http://en.wikipedia.org/wiki/Scale-invariant_feature_transform The quadratic Taylor expansion of the Difference-of-Gaussian scale-space function, with the ...
0
votes
1answer
132 views

Keypoint position and scale in SIFT

If I understood it right, a keypoint is a tuple $$(x,y,\sigma, r),$$ where $x,y$ define the position of the keypoint and $r$ an orientation (given by the most domiant gradiant vector around the ...
2
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0answers
87 views

Affine detector + SIFT descriptor

I am approaching to the Oxford Buildings dataset which contains already computed SIFT descriptors from affine detected keypoint locations. Usually SIFT detector provides to its detected keypoints ...
9
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2answers
359 views

Detecting a filled glass object

I've been sent here from this question in stackoverflow, please excuse me if the question comes too specific and it's not in the manners in here:) The task is to find a glass with specific liquid in ...
0
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0answers
167 views

How to proceed for BOW creation From sift features

I extracted sift feature to construct a bag-of-words model. I did the following to extract the feature vector: Extracted features from the key frames. After the feature extraction I tried using ...
1
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0answers
57 views

Geometric models to discard image features

I am working on the implementation of a location recognition pipeline as detailed in the section 5.4 of the paper Leveraging 3D City Models for Rotation Invariant Place-of-Interest Recognition: ...
2
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2answers
437 views

Object-Recognition using SIFT: Switching the order of images creates two different results

I've developed a large test-system which can use every interest-point-detector and -descriptor. I use it for evaluation of the given algorithms with the standford-image-collection of cd-covers. This ...
8
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1answer
4k views

Image classification using SIFT features and SVM

I am hoping someone can explain how to use the bag of words model to perform image classification using SIFT/SURF/ORB features and a support vector machine? At the moment I can compute the SIFT ...
7
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3answers
3k views

Scale and Rotation invariant feature descriptors

Can you list some scale and rotational invariant feature descriptors for use in feature detection. The application is for the detection of cars and humans in video captured by a UAV, using a ...
3
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1answer
117 views

What scale should a detected SIFT point be extracted at?

I've heard this from a few different researchers but I can't find a definitive value. Given the "scale" extracted by David Lowe's SIFT detector, we need to extract a descriptor at a specific scale. ...
11
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3answers
1k views

Is sift a good way to extract features from an image?

I am trying to extract features from an image, but I have failed to get the points that I want to extract, and hence my image fails to match with the template. Are there any checkpoints that I have ...
33
votes
3answers
10k views

What are some free alternatives to SIFT/ SURF that can be used in commercial applications?

As far as I understand, both SURF and SIFT are patent protected. Are there any alternative methods that can be used in a commercial application freely? For more info on the patent check out: ...
11
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2answers
2k views

Why is the difference of gaussians scale space scale invariant?

I'll use the Scale-invariant feature transform algorithm as an example here. SIFT creates a scale space based on scaled gaussian filtering of an image, and then computes the difference of gaussians ...