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0answers
48 views

How to match a thumbnail to an area in the original image?

Suppose that you have a thumbnail and the original image from which it was generated. You need to match the thumbnail to an area in the original image that represents the original selection from which ...
0
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1answer
18 views

Should I use CV_HAAR_SCALE_IMAGE while using LBP CascadeClassifier?

I trained a cascade-LBP to detect Lollipops with 1000 images, now I'm trying to "adapt" the openCV HAAR-Cascade example to use my LBP trained .xml but I'm not sure about the "HAAR_SCALE_IMAGE" flag, I ...
4
votes
1answer
51 views

Structure Tensor vs. Hessian Matrix

Hello can someone explain the semantical meaning of the structure tensor and the Hessian matrix. I am aware of how it is calculated, but i find it difficult to comprehend what they describe in the ...
0
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0answers
68 views

Determinant of Hessian blob response

this question is about blob detection based on the determinant of Hessian as i am working with the SURF method. In the method SURF (speeded up robust features) by Bay et al. a local 3x3x3 ...
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2answers
32 views

What makes a feature stable?

Feature detection is an essential task in low-level vision. Good features are those that resist to different perturbations such as noise addition, blur, geometric transforms (3D rotation with ...
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0answers
7 views

Harris / Plessy Anisotropic response

Harris and Stephens states that they avoid the problem of anisotropic response: "all possible small shifts can be covered by performing an analytic expansion about the shift origin": Where the image ...
1
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1answer
30 views

Moravec, Harris noisy window

Harris and Stephens writes about the interest window of Moravec: "The response is noisy because the window is binary and rectangular", and suggests applying a Gaussian window. My Question: Why is the ...
0
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0answers
51 views

Question about SURF - speeded up robust features

I am trying to get my head around the SURF detection method (fast hessian), but I have run into some problems. I have only just begun to look at it, so I apologize for any "ill" asked questions. I am ...
1
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2answers
91 views

texture matching between patches of an image

I have an image A which I have divided into 4 x 4 subband images. For a given patch P1 in ...
0
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0answers
9 views

Redundant basis instead of PCA

I have an matrix of $M$ feature vectors with $N$ observations. Using PCA I can get an $N \times N$ orthonormal basis where each vector corresponds to the features of maximal variance. Is there an ...
0
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0answers
60 views

What's the optimal filter size for a 2D Gabor filter

I started to experiment with Gabor filters to extract various image features from usual camera snapshots (that's the image domain: everyday snapshots with a very diverse range of subjects). ...
3
votes
4answers
147 views

What kind of features can I extract from this signal

I want to monitor (automatic-)gearbox failures on some vehicles. For each vehicle I have a captured signal representing the selected gear at each one millisecond. An example of two signals are shown ...
1
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1answer
329 views

difference between feature detector and descriptor?

I am new to feature detection and tracking. can anybody please explain in detail the difference between detector and descriptors. which among these are detectors and which are descriptors : Harris, ...
0
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0answers
14 views

What is the relationship between the Harris corner detector and shape operator?

From my understanding, the Harris corner detector looks at the gradients in the principal directions of a small region. Why are the eigenvectors of the matrix the principal directions? More ...
0
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0answers
25 views

How to combine SURF and Harris points

As we know at Matlab, there is function to detect Harris or SURF feature individually. Then I need to combine these two list of features from both the Harris and SURF to make the matching more ...
1
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0answers
66 views

pre-processing to improve feature detector before tracking

I am trying to make tracking for soccer player, I need to detect features from this player and then estimate the distance difference of these pixels over number of frames. first I have to detect the ...
1
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0answers
17 views

what is in intuitive explanation of local derivative pattern (LDP)?

Zhang et al. proposed the LDPs for face recognition . They considered the LBP as the nondirectional first-order local pattern operator and extended it to higher orders ( th-order) called the LDP. is ...
0
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0answers
78 views

What is the difference between harris matrix and the hessian matrix?

What is the difference between the harris detector, and the one used in surf the hessian matrix. They look the same so I am a bit confused at that point?
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0answers
38 views

What does visual clue means ?

Given a keypoint p detected in an image I . What does visual clueof the keypoint p mean ? ...
0
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0answers
10 views

Good features/attributes for objects of which the location is already known

Suppose the object is outlined or in a bounding box already within the image. I want to know what kind of features is good to use, invariant to illumination and rotation. Obviously I aim to describe ...
0
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1answer
93 views

Haralick features, am I approaching this correcly?

I'm trying to personalise a custom CBIR by adding more features not only based on colour, but based on textures' features. What I don't know is if I'm approaching this well with Haralick's features. ...
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0answers
20 views

Algorithm to find similarities on a huge database querying one image [duplicate]

After days trying to look to some algorithms, I haven't found any good for my approach. My problem is the following one: I have a large dataset, for example of 2.000 images and I'm trying to query ...
0
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0answers
44 views

What exactly affine covariant features are?

I was reading about different blob detection algorithms. And I found an statement that determinant of Hessian is a affine covariant. What does it mean?
2
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0answers
141 views

Efficient Hessian-Laplace blob detector implementation

As it is mentioned in a paper for SURF, it is possible to approximate hessian determinant using integral images. If I want to implement Hessian-Laplace detector, is it feasible to also approximate ...
1
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3answers
127 views

Need critical help: How to detect and distinguish two very similar looking signals?

Hi guys I have a really tough signal processing question here. How do you detect and distinguish two very very similar looking waves? I need to distinguish between these two signals for an online ...
5
votes
1answer
338 views

Suggested Preprocessing methods for OCR on Circular Images

Hello this is my sample image I am going to do real time character detection on images like that. I've tried SURF, SIFT, MSER and template matching on original image without any preprocessing. I can ...
1
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2answers
55 views

LoG filter creating additional maxima in scale space

To create a scale space, I applied a Laplacian of Gaussian filter on the following image: After the scale space was created, I plotted circles around local maxima in scale space. However, instead ...
0
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2answers
1k views

Finding local brightness maximas with OpenCV

I want to find points (of a processed image) that are the brightest in their local region. Basically, I want all of the points whose 8 neighbors are all smaller but I want to have brighter maxima ...
2
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0answers
377 views

Why is LBP generaly faster than HAAR?

I am digging into Haar like and LBP features. More precisely its implementation in OpenCV. Every article or forum entry I found states, that LBP is faster than Haar. My local tests also confirm this ...
1
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0answers
241 views

Visual regression test - Extract elements of GUI-Screenshot - MSER OpenCV

For a visual regression test I need to compare screenshots of webpages (different release-versions). I started with pixel by pixel compare. Actually I split the screenshot in different parts (maybe ...
2
votes
1answer
1k views

Zernike Moments' implementation in OpenCV

The reason why Hu moments were implemented in OpenCV and why Zernike moments were not implemented is looking like their performance similar as stated in this paper. As stated in the paper Zernike ...
0
votes
2answers
167 views

Detecting sound inside a sound

I was searching on the Internet hopelessly about some materials regarding detecting a sound in another sound. Say, I've got a recorded short sound (which may be anything, fragment of speech, fragment ...
2
votes
0answers
577 views

MPEG-7 descriptors' implementation in OpenCV

I'm looking for implementation of MPEG-7 descriptors which are compatible with OpenCV's recent versions and containing "region-based shape descriptor ART(Angular Radial Transformation)". I ...
1
vote
1answer
94 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 ...
0
votes
1answer
52 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] ...
0
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1answer
141 views

Phase reference of a periodic signal

Assume an arbitrary (discrete) signal that is periodic and known over a whole period. I need a way to select a characteristic point along the signal such that I can always retrieve it even when the ...
0
votes
1answer
123 views

Feature for exact matching of images

I am trying to match images from a large dataset which exactly match the given input image.(images with deformations/transformations are treated as different) I have tried euclidean distance but it ...
3
votes
1answer
919 views

Feature extraction/reduction using DWT

For a given time series which is n timestamps in length, we can take Discrete Wavelet Transform (using 'Haar' wavelets), then we get (for an example, in Python) - ...
0
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0answers
338 views

CWT for filtering / feature extraction

I had asked a question last night in regards to how to process my data (Noise rejection / feature extraction) but I have a more specific question now that I hope someone can answer. As mentioned in ...
2
votes
1answer
67 views

What is localizability in Computer Vision?

Please consider the following excerpt (from Rodrigo R, Zouqi M, Chen Z, Samarabandu J.: Robust and efficient feature tracking for indoor navigation): Robust feature tracking is a requirement for ...
4
votes
1answer
345 views

Corner detection using Chris Harris & Mike Stephens [duplicate]

I am not able to understand the formula, What is $W$ (window) and intensity in the formula mean, I found this formula in opencv doc ...
4
votes
2answers
124 views

mean of wavelet for image processing

For many papers which talks about using wavelet transforms for feature detection in image processing, it is stated that it is advantageous for the wavelet to have zero mean? Why is this so? Thanks in ...
2
votes
2answers
516 views

Methods to quantify randomness (or complexity) in a signal

What are the methods through which we can quantify the randomness or complexity in a given signal. I know spectral flatness measure (geometric to arithmetic means) is one way to do it, but what are ...
3
votes
1answer
265 views

proving that a log gabor filter has 0 DC offset

I have read somewhere online that the log gabor filter has an advantage over the gabor filter, in the sense that it has 0 DC component. How do you prove this property mathematically? Thanks in ...
3
votes
1answer
2k views

difference between Gabor and log-Gabor function

I am reading a paper using log-gabor filters for feature detection. I was thinking about the difference between Gabor filters and log-gabor filters. Can anyone tell me the difference(s), and a way to ...
5
votes
3answers
1k views

Purpose of image feature detection and matching

I'm a new guy in image processing and computer vision, so this question might be stupid to you. I just learned some feature detection and description algorithms, such as Harris, Hessian, SIFT, SURF, ...
1
vote
2answers
2k views

normalized Laplacian of Gaussian

Laplacian of Gaussian formula for 2d case is $$\operatorname{LoG}(x,y) = \frac{1}{\pi\sigma^4}\left(\frac{x^2+y^2}{2\sigma^2} - 1\right)e^{-\frac{x^2+y^2}{2\sigma^2}},$$ in scale-space related ...
5
votes
1answer
5k views

How Hessian feature detector works?

I know about Harris corner detector, and I understand the basic idea of its second moment matrix, $$M = \left[ \begin{array}{cc} I_x^2 & I_xI_y \\ I_xI_y & I_y^2 \end{array} \right]$$, edges ...
0
votes
0answers
533 views

HOG descriptor algorithm

I would like to implement a HOG descriptor in C++. I found an implementation of this code here. An extract of the code follows: ...
2
votes
3answers
253 views

What are integration scale and differentiation scale?

In scale-adapted Harris detector, the scale adapted second moment matrix is defined by: $$\mu(x, \sigma_I, \sigma_D) = \sigma_D^2\ g(\sigma_I) *\left[ \begin{array}{cc} L_x^2(x, \sigma_D) ...