Questions tagged [local-features]

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Is there a way to measure an image SNR blindly?

Are there known techniques to estimate the SNR of an image in small neighborhoods (say like 11x11) without any knowledge of the clean image, with arbitrary content ? Denoising is not required. Update:...
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1 vote
1 answer
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Invariances of FFT-based Image-Registration vs. SIFT-Features

TL;DR: I don't understand how invariant FFT-based image-registration techniques are to object alterations (scratches, marks etc.) in comparison to SIFT-features. I want to build kind of a feature-...
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1 answer
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Are location in BRIEF feature descriptor reused?

In the BRIEF feature descriptor ("BRIEF: Binary Robust IndependentElementary Features", Calonder et al., 2011) they investigate five different methods of choosing point pairs to compute the ...
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1 answer
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Corner detector vs feature detector

In the literature, I see "corner detector" and "feature detector" are interchangeably used for these methods e.g. Harris, Shi-Tomasi, FAST, etc. What is the difference between a ...
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5 votes
1 answer
402 views

What Is an Oriented Gaussian Second Derivative Filter

In the paper: Detecting and Localizing Edges Composed of Steps, Peaks and Roofs, the authors refer to an image filter as an oriented second-derivative Gaussian filter. I'm trying to figure out what ...
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131 views

Use sparse optical tracking to track a Bounding Box object

I need some help on solving this issue. Any tips are appreciated. The goal of the project is to try to track a Bounding Box object, chosen arbitrarily in an image, throughout many frames of a ...
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1 answer
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What are the ranges of values for each audio feature/descriptor?

I need to normalize some audio feature measurements I've done with the software Wolfram Mathematica. Coming from a non signal processing background, I have some difficulties understanding what ...
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2 votes
1 answer
493 views

Sum of Squared Intensity Difference for block matching with ORB features, c++

I am trying to implement feature matching algorithm between image reference and image current. The pipeline is as follows: ...
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1 vote
2 answers
334 views

Understanding of Histogram-of-Oriented-Gradients

I am learning about HOG and I understand it from here. A well-explained page with an example. I am not understanding this concept that how it works A 16×16 block has 4 histograms which can be ...
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Finding Local mean value of pixels of window

I want to solve the equation (2) in the attached picture which tells the local mean value. But i don't have any idea about how to evaluate this equation using matlab code. could only guess w indicates ...
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1 vote
1 answer
699 views

How can I extract information about timbre from a .wav file. In which form can I study those features?

To study the frequencies of a piece of audio, we can generate a spectrogram from that audio file. I'm wondering how the features of timbre are saved in such tiny wave files, and how we can extract ...
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41 views

zernik moments and Local binary pattern

Both of zernik moments and Local binary pattern (LBP) are feature detectors and can achieve rotation invarient. How can they achieve rotation invarient over an image? What are the advantages of ...
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VLFEat: How to extract the SIFT descriptor without SIFT feature detection?

I am using the MATLAB interface to the VLFeat toolbox in order to calculate a SIFT descriptor for image patches extracted around key points. Due to the greater framework of what I'm doing, I cannot ...
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Classification test by embedding true positives in high frequency recordings

I'm evaluating a cyclostationary approach to signal classification. My first step in doing so was generating signals and embedding them into a few specified parameter sets of the Watterson channel ...
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2 votes
0 answers
1k views

Relationship between Wavelet transform and Fourier Power Spectral Density

Is there anyway to obtain the Fourier Power Spectral Density from a wavelet transform of a time series? I am particularly interested in this problem because I was wondering if there is any ...
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6 votes
3 answers
6k views

Principal Component Analysis (PCA) on Convolutional Neural Network (CNN) Features

Please, I have a question regarding PCA and features which are extracted from a convolutional layer based on Faster R-CNN features for Instance Search if we have a test dataset , and we extract all ...
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  • 171
1 vote
1 answer
65 views

How to recognise different symbols from their slope ? like (<,>,^) etc

i am trying to build a program in which user input a symbol with mouse and program recognise the symbol by saving mouse coordinates in array ,for this i have followed following steps: Firstly check ...
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1 vote
1 answer
171 views

Using Local Binary Pattern for finding Homography between two Image

Can LBP be used to find the homography between two images with similar field of view for Image Registration?
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2 votes
3 answers
251 views

Can I use standard computer vision techniques for images taken in the NIR spectral range?

I'm relatively new in Computer Vision and I need some advice with respect to the general possibilities and shortcomings of images taken in the near infrared (NIR) range. I passed a great deal of time ...
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2 answers
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Measure similarity between quantized grayscale images

I want to measure the similarity between quantized grayscale images (8 levels) that mostly depict organic patterns found in nature, say pigmentation patterns in animals (zebra pattern, leopard spots,.....
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2 votes
1 answer
130 views

Feature matching of images without corners

I am trying to stitch aerial images using feature-based registration. Most image pairs are matched well, such as this: Others are not matched due to lack of common features: As you can see, the ...
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5 votes
2 answers
130 views

Useful natural "Hilbert-like" $n$-uples and $n$-fold "analytic signals

If $\mathcal{H}$ denotes the Hilbert transform, the analytic signal of a signal $x(t)$ is $$x_a(t) = x(t) +\imath \mathcal{H}(x(t))\,.$$ The real and imaginary parts form Hilbert pairs. Are there ...
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2 votes
1 answer
1k views

Determinant of Hessian approximation (SURF)

I have a question regarding formula in SURF article by Bay et al. Theory Given a point $p=(x,y)$ in an image $I$, the Hessian matrix $\mathcal{H}$ in $x$ at scale $\sigma$ is defined as follows $$ \...
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1 vote
0 answers
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Get level of wellness in a cascade classifier using LBP

I'm currently working in a Lolipop LBP cascade detector using OpenCV. The training is correctly done and the cascade classifier detects the sticks of the Lolipops correctly but with some minor errors. ...
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0 answers
357 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 ...
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2 answers
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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 ...
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4 votes
1 answer
1k 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 ...
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5 votes
2 answers
107 views

What makes an image 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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1 vote
1 answer
101 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: ...
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1 vote
2 answers
997 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 ...
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11 votes
4 answers
3k views

What Kind of Features Can I Extract from a 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 ...
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15 votes
1 answer
19k views

What is the difference between feature detectors and feature descriptors?

What is the difference between feature detectors and feature descriptors? Which among these are detectors and which are descriptors: Harris, SURF, Min Eigen, FAST, SIFT, BRISK
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1 vote
0 answers
182 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 ...
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2 votes
0 answers
121 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 ...
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2 votes
1 answer
319 views

Haralick features, am I approaching this correctly?

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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2 votes
0 answers
468 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 ...
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1 vote
3 answers
261 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 ...
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8 votes
1 answer
1k 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 ...
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1 vote
2 answers
152 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 of $...
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0 votes
2 answers
9k 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 ...
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2 votes
0 answers
3k 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 ...
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1 vote
0 answers
848 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 ...
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  • 111
2 votes
1 answer
5k 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 ...
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2 votes
2 answers
362 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 ...
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2 votes
0 answers
2k 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 ...
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2 votes
1 answer
237 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 ...
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0 votes
1 answer
77 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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  • 161
0 votes
1 answer
351 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 ...
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1 vote
1 answer
684 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 ...
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8 votes
1 answer
15k 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) - ...
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