# Tagged Questions

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11 views

### ASIFT does not appear to simulate all required possible views

ASIFT is an extension to SIFT to make it affine invariant. http://www.cmap.polytechnique.fr/~yu/publications/ASIFT_SIIMS_final.pdf According to the picture above, ASIFT algorithm is only sampling ...
23 views

### Finding SIFT keypoints on a plain surface

I am using SIFT for object recognition and tracking. The target object is metallic body which is painted with a single colour paint. There object is plain.(Consider something like a metallic plate ...
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### Analytical expression for salient Blob detection in scale space

I am working on exact mathematical expression which can be obtained in image processing tasks.(I do not know much about image processing but my work is more mathmatical) In Gaussian scale space, we ...
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I am a newbie about Computer vision. I am reading about the SIFT detector but I can not understand the step find subpixel maxima/minima and step eliminate edge and low contrast region. Can anyone give ...
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### Sift final key points

I am using a SIFT algorithm to extract invariant features from an image. After extracting the extrema from each octave,How to use all octaves to pick the final key points ?
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### Gaussian signal / image smoothing at sigma 0.5

I am currently reading up on Lowe's paper [1] on SIFT keypoint detection. On the page labeled 97 he mentions We assume that the original image has a blur of at ...
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### Hessian Matrix. Second partial derivative test

I have a question about the hessian matrix / determinant of the hessian matrix. For the Hessian matrix, one is able to determine the local curvature around a point. And with the Second partial ...
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### Counting percentage of fouling on a surface

I am completely new to image processing and python. I hope I can find some help here. I am trying out a project on detecting fouling% on a ship hull using raspberry pi. I am trying to learn how this ...
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1k 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 Ïƒ will apply as 2Ïƒ. 2) ...
161 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 ...
690 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 ...
2k 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 ...
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### 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 ...
691 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 ...
212 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 ...
128 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 ...
779 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 ...
483 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 ...
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### 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: ...
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### 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 ...
9k 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 ...
7k 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 multi-...
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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. ...
3k 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 ...