Signal Processing Stack Exchange
Signal Processing Stack Exchange

Questions tagged [sift]

57 questions
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4 answers

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…
Andrey Rubshtein
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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 multi-class classifier. So far I have been looking at SIFT…
Jono Brogan
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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 to detect potential interest points. These points…
water
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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 to go through before applying SIFT to my image so…
KT Harris
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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 feature vectors for an image, and have implemented a…
Jono Brogan
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10
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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 it. Let me show you the pictures and then describe…
user1916182
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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 scale, and to match these using a normalized…
jakeoung
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What Is "Description Vector" in Image Processing?

When we want to use classifiers like SVM, we first should extract descriptors using algorithms like SIFT. But I have a question which might call a silly one: Let's assume $$ \begin {equation} D_a=\{d_{a,1},d_{a,2},d_{a,3},...,d_{a,M}\} \end…
David
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6
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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 you need to compute s+3 levels. Why there are 3 and not 2 additional levels required.…
who9vy
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Laplacian of Gaussian Approximation and Gaussian Blur as the Solution of Heat Equation

While I was reading SIFT paper(Lowe, 2004), I came across the method that he apply "heat diffusion equation" to Gaussian function to derive that $$ \frac{∂G}{∂σ} = σ∇^2G $$ I searched Wikipedia and found that original heat equation is $$…
alryosha
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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? Bay H., Ess A., Tuytelaars T. Van Gool L. -…
Alireza
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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 scale space means the sigma of gaussian…
jakeoung
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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. Is it 6 times the detector "scale"? 3? 1? …
wallet
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Why optical flow ? why not tracking

I have a question that might be stupide ! Supposing that I try to detect object moving in a video or human action. Many works are based on optical flow computation. My question is why using OF is the best for motion detection. A tracking of pixels…
Video retrieval
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Would the locations of SIFT features generally agree with features detected by Shi-Tomasi method?

I am having a comparison of different feature detection methods. So if we compare the SIFT (Scale-invariant feature transform) and Shi-Tomasi method, will their feature locations agree and why? Are they comparable? Thanks in advance.
i_a_n
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