Questions tagged [feature-detection]

Feature detection is a process in computer vision that aims to find visual features within the image with particular desirable properties. Detected features can be points, image regions or continuous curves in the image. Interesting properties can include invariance to noise, perspective transformations, or properties interesting for specific usages (e.g. tracking).

Feature detection is a process in computer vision that aims to find visual features within the image with particular desirable properties.

Detected features are some subsection of the image, and can be:

  • points (e.g. Harris corners)
  • connected image regions (e.g. DoG or MSER regions)
  • continuous curves in the image

Interesting properties can include invariance to noise, perspective transformations and viewpoint changes (camera translation and rotation), scaling (for use in visual feature matching), or properties interesting for specific usages (e.g. visual tracking).

Important information about visual features can include:

  • coordinates in the image
  • radius of the visual feature
  • scale (octave) of the image on which the feature has been extracted

After detecting the feature with some feature detection algorithm, it is usually described by a descriptor vector (several known descriptors are used today) for the purposes of visual feature matching, while the feature's position in the image can be used directly for application in tracking.

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SIFT keypoints in sift.detect

How are keypoints stored using the sift.detect method in opencv ? Are they in the form of an array ? How to extract the (x,y) coordinates of each keypoint? ( I am using opencv 2.4.11)
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OpenCV Error: Assertion failed using Bag of Words (BOW)

I'm trying to use SURF with Bag Of Words in c++ but OpenCV is throwing an exception that I don't know how to solve it. OpenCV Error: Assertion failed ((globalDescIdx>=0) && (globalDescIdx < size())) in getLocalIdx, file…
cecelia
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DIY check for browser support for TSL1.1 protocol?

I'm going to include GestPay Payment in my website. It has some browser requirements Buyer’s browsers must support TSL1.1 protocol or latest How can I programmatically check if the browser visiting my website achieves the requirement? In this…
nulll
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Feature Selection and Machine Learning for Merchant Names

I would like to classify/categorize/cluster/group together millions of rows of merchant names to their standardized merchant name. For example, 1. Walmart 2. Walmart NY 3. Walmart #12 AHN 4. Wal3mart 5. Sam's Club all belong to the standard name of…
msksantosh
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How to use opencv BOWKMeansTrainer in Java?

I am using opencv 3.2 for Java (build source with contrib modules), and trying to use SURF + BOWKMeansTrainer for detect, but it throws an error when I run it. My code: //read jpg to variable trainMats //... //train Mat allDesc = new Mat(); int…
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Installing Opencv Repository In Windows 10 for Python or Cmake

I want to know if someone can help me with install opencv repository files in Windows 10 system. I want to use xfeatures2d and i have been told from other peoples comments on other pages that the algorithm is patented and does not go with the open…
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OpenCV - How to match multi-instance of templates in image using C++

I need some help trying to match non-normal blood cell with original cell. After some searches I found SURF and SIFT feature extraction. I have this template; and this original image; This is my code: int main(int argc, char** argv) { Mat…
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What is the best way with opencv to select an object in the box?

I'm working on a school project made in python with opencv, and I have a question in two parts. I have 6 photos of an object (one of each side) and one of a box filled with the same object. The quality of the photos is terrible, but my next tests…
bachinblack
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OpenCV - cv2.perspectiveTransform() not working for all the images

I used PerspectiveTransform to draw an outline around the detected image. The cv2.perspectiveTransform() is able to draw a rectangle only for a few detected images but not for all the images. Some of the detected images are not showing up with an…
John
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Detecting all object in Image API .NET c#

I am working on a project C# and I have to write a code that detects all the objects inside an image (if not all as much as possible). is there any good API to do that in .NET? I tried Cognitive Services but they do not give me the detected…
Samy Sammour
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How to combine different sparse matrix in Python?

I am building Machine Learning model using sci-kit learn. My dataset is number of svm files. I've loaded that files using sklearn. It returns data as a sparse matrix and target as a numpy array. Now the problem is, different files have different…
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BoofCV (Android): How to use commercial-free alternatives to Surf

I recently came across the boofcv project and it is really amazing. I like it because it is very easy to use. I adjusted this example: http://boofcv.org/index.php?title=Example_Associate_Interest_Points to work on android. But this feature uses Surf…
fameman
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Matlab Hough transform for line detection

I am trying to detect the white straight lines on the image using the hough transform. Binary image with White = 1, Black= 0 - Lines detected in green and longest line detected in red The following code only detects sections of a curved line as…
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Auto Text Recognition (OCR) from Image

I want to recognize nutrient information from package labels Sample Nutrient label . This is one package image, different brands may style/layout their labels differently. But I know some things for sure, layout would be somewhat tabular with…
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how to recognise the squrae marker in matlab

In my project, it needs recognise the square marrker in the real time video input. In every frame,the square marker should be recoginzed stability.And the following codes was used to detected the square marker.however,it cause error in same…