Questions tagged [local-features]
The local-features tag has no usage guidance.
77
questions
0
votes
0answers
7 views
BRIEF feature vector random point sampling 3rd method
When using the BRIEF algorithm to generate a feature vector, 5 methods are provided for selecting 2 random points inside a feature point patch. The 3rd method is described as follows:
Let consider ...
0
votes
1answer
22 views
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 ...
1
vote
1answer
170 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:
...
1
vote
2answers
176 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 ...
0
votes
0answers
26 views
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 ...
0
votes
1answer
259 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
vote
0answers
38 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
vote
0answers
244 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
vote
0answers
23 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
vote
0answers
732 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
votes
3answers
2k 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. link
if we have a test dataset , and we extract all conv features of all images at test dataset ...
1
vote
1answer
52 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
vote
1answer
132 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
vote
3answers
179 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
vote
2answers
194 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
votes
1answer
113 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
votes
2answers
116 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
vote
1answer
772 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
vote
0answers
44 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
vote
0answers
265 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
votes
2answers
4k 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 ...
3
votes
1answer
986 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
votes
2answers
104 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
vote
1answer
80 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
vote
2answers
894 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 ...
5
votes
4answers
2k 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 ...
10
votes
1answer
14k 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
vote
0answers
171 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
vote
0answers
114 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
vote
1answer
266 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
votes
0answers
434 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
vote
3answers
194 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 ...
asked Feb 1 '15 at 7:37
Carlos - the Mongoose - Danger
5512 gold badges7 silver badges22 bronze badges
7
votes
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
vote
2answers
99 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
votes
2answers
7k 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
votes
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
vote
0answers
757 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
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
votes
2answers
225 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
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 ...
2
votes
1answer
221 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
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]
...
0
votes
1answer
257 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
vote
1answer
559 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 ...
7
votes
1answer
12k 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
votes
0answers
937 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
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
votes
1answer
1k 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
votes
2answers
166 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 ...
3
votes
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 ...
