Questions tagged [local-features]
The local-features tag has no usage guidance.
-1
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0answers
6 views
Can anybody explain the difference between SIFT and GLOH image descriptors
There are very few resources on GLOH (Gradient Location and Orientation Histogram), Can anyone explain how is it different from SIFT?
0
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1answer
85 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 ...
1
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0answers
27 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 ...
1
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0answers
207 views
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 ...
1
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0answers
21 views
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 ...
1
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0answers
485 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 ...
0
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3answers
1k views
Principal component analysis (PCA) on convolutional network features
Please, I have a question regarding PCA and features which are extracted from a convolutional layer. link
if we have a test dataset , and we extract all conv features of all images at test dataset ...
1
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1answer
42 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 ...
1
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1answer
115 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?
1
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3answers
148 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 ...
1
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2answers
185 views
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,.....
2
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1answer
106 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 ...
3
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2answers
114 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 ...
1
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1answer
570 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
$$
\...
1
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0answers
38 views
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. ...
1
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0answers
230 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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2answers
3k 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
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1answer
799 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 ...
5
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2answers
103 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 ...
1
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1answer
70 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 ...
1
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2answers
701 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 ...
3
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4answers
838 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 ...
8
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1answer
11k 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, ...
1
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0answers
148 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
106 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 ...
1
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1answer
233 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.
...
2
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0answers
399 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
187 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 ...
7
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1answer
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 ...
1
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2answers
90 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 $...
0
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2answers
5k 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
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 ...
1
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0answers
674 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
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1answer
4k 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 ...
2
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2answers
199 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
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0answers
1k 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
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1answer
209 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
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1answer
73 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
228 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 ...
1
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1answer
469 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 ...
6
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1answer
9k 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
859 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
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1answer
89 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
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1answer
964 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 http://docs.opencv.org/trunk/doc/py_tutorials/py_feature2d/...
4
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2answers
162 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
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2answers
2k 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
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1answer
558 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 advance....
5
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1answer
3k 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 ...
6
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3answers
3k 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
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2answers
6k 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 ...
