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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Detecting IE version using CSS Capability/Feature Detection

IE10+ no longer supports browser detection tags to identify a browser. For detecting IE10 I am using JavaScript and a capability-testing technique to detect certain ms prefixed styles are defined such as msTouchAction and msWrapFlow. I want to do…
dano
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Classification of detectors, extractors and matchers

I am new to opencv and trying to implement image matching between two images. For this purpose, I'm trying to understand the difference between feature descriptors, descriptor extractors and descriptor matchers. I came across a lot of terms and…
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What is the difference between feature detection and descriptor extraction?

Does anyone know the difference between feature detection and descriptor extraction in OpenCV 2.3? I understand that the latter is required for matching using DescriptorMatcher. If that's the case, what is FeatureDetection used for?
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What is a feature descriptor in image processing (algorithm or description)?

I get often confused with the meaning of the term descriptor in the context of image features. Is a descriptor the description of the local neighborhood of a point (e.g. a float vector), or is a descriptor the algorithm that outputs the description?…
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Detecting a cross in an image with OpenCV

I'm trying to detect a shape (a cross) in my input video stream with the help of OpenCV. Currently I'm thresholding to get a binary image of my cross which works pretty good. Unfortunately my algorithm to decide whether the extracted blob is a cross…
Tobi
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Extracting HoG Features using OpenCV

I am trying to extract features using OpenCV's HoG API, however I can't seem to find the API that allow me to do that. What I am trying to do is to extract features using HoG from all my dataset (a set number of positive and negative images), then…
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How to determine if an Android device has a touchscreen?

I'm spending considerable time in making my UI to work with keyboard input only. But in the end I'm not sure whether I can rely on the assumption that Android devices all have touch screens. Is there a way to determine if an Android device has a…
Hidden Android
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How to check if a CSS property or value is supported by a browser?

My div that uses vh is not working in some browsers, so I want to check if it is supported. I found this article by Lea Verou on the subject, but I'm really not sure how to use it with a CSS value: Here is the code given as a shortcut for…
Guillaume Palm
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A good approach for detecting lines in an image?

I've written some code that uses OpenCV libraries to detect white lines painted on grass. I need someone's opinion on the approach I used (as I'm sure there's a much better way than mine). Also, the results I'm getting are not as good as I expected…
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Are there any fast alternatives to SURF and SIFT for scale-invariant feature extraction?

SURF is patented, as is SIFT. ORB and BRIEF are not patented, but their features are not scale-invariant, seriously limiting their usefulness in complex scenarios. Are there any feature extractors that can extract scale-invariant features as fast as…
Diego
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General approach to developing an image classification algorithm for Dilbert cartoons

As a self-development exercise, I want to develop a simple classification algorithm that, given a particular cell of a Dilbert cartoon, is able to identify which characters are present in the cartoon (Dilbert, PHB, Ratbert etc.). I assume the best…
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Improve matching of feature points with OpenCV

I want to match feature points in stereo images. I've already found and extracted the feature points with different algorithms and now I need a good matching. In this case I'm using the FAST algorithms for detection and extraction and the…
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Nesting CSS @supports and @media queries

I have been trying to figure out whether it's possible to nest CSS feature queries (also known as “CSS @supports”) and regular media queries, and what would be the correct way to do it. Example A shows the feature query inside the media…
oelna
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What does the distance attribute in DMatches mean?

I have a short question: When I do feature-matching in OpenCV, what does the distance attribute mean of DMatches in MatOfMatches? I know that I have to filter matches with bigger distance because they aren't as good as them with lower distance. But…
stetro
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Detect touching/overlapping circles/ellipses with OpenCV and Python

i want to measure the circularity of circles (difference of the "circles" height and width or ellipse parameters). The circles are given in pictures as shown here: After doing usual stuff like color2gray, thresholding and border detection, I get…
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