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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How to get pixel coordinates from Feature Matching in OpenCV Python

I need to get the list of the x and y coordinates of the pixels that the feature matcher selects in the code provided. I'm using Python and OpenCV. Can anyone help…
kotopanda
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What is difference between features and keypoints in computer vision?

I am studying something about some possibilities of OpenCV object detection and this is confusing to me. I just don't see the difference between these two.
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Detect browser support for CSS-animated SVG

I am playing around with CSS-animated SVG elements and came across the problem that even though all technologies, which are used, are supported by some browsers the combination is not, i.e. CSS-animated DIVs work but SVG elements don't. I am…
F Lekschas
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OpenCV image comparison in Android

[EDIT] I have devised some code for image comparison. The matching part is still a bit flawed and I would love some assitance. The project can be found at - GitHub. I have these two images Img1 and Img2: When I use the following command in…
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What does size and response exactly represent in a SURF keypoint?

I'm using OpenCV 2.3 for keypoints detection and matching. But I am a bit confused with the size and response parameters given by the detection algorithm. What do they exactly mean? Based on the OpenCV manual, I can't figure it out: float size:…
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OpenCV ORB detector finds very few keypoints

I'm trying to use the ORB keypoint detector and it seems to be returning much fewer points than the SIFT detector and the FAST detector. This image shows the keypoints found by the ORB detector: and this image shows the keypoints found by the SIFT…
coderunner
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What is `query` and `train` in openCV features2D

Everywhere in features2D classes I see terms query and train. For example matches have trainIdx and queryIdx, and Matchers have train() method. I know the definition of words train and query in English, but I can't understand the meaning of this…
Larry Foobar
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OpenCV - find bounding box of largest blob in binary image

What is the most efficient way to find the bounding box of the largest blob in a binary image using OpenCV? Unfortunately, OpenCV does not have specific functionality for blob detection. Should I just use findContours() and search for the largest…
1''
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HOG features visualisation with OpenCV, HOGDescriptor in C++

I use the HOGDescriptor of the OpenCV C++ Lib to compute the feature vectors of an images. I would like to visualize the features in the source image. Can anyone help me?
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HTML 5 input type=“date” not working in Firefox

I am using HTML5 , which works fine in Chrome and I get the calendar popup to select the date. But in firefox it acts like a text box and no calendar pops up. After doing few research I see few solutions using webshims,…
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The pro and con of BRIEF and ORB compared to SIFT

I am doing some research in Local Feature representation, so SIFT, SURF and such. Now, has anybody here ever tried BRIEF and ORB? If so, can you discuss what are some of the pro and con with respective to SIFT?
Karl
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Feature detect opening in a new window/tab(target=_blank) with JavaScript

According to my research: "WebView" can disable "opening links in new windows/tabs". WebView is used by native app developers to display webpages within their app(see Twitter's app). Detecting WebView via user agent doesn't work consistently and…
Brian Petro
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Is Center-Surround mechanism implemented in opencv?

I am new to the concept of Biologically Salient Regions Detector, and I read some papers and they always use the mechanism of Center-Surrond to computer features intensity, color and orientation. I googled that mechanism but i did not find…
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How to check the existence of NEON on arm?

How to determine whether NEON engine exists on given ARM processor? Any status/flag register can be queried for such purpose?
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FREAK Descriptor with Opencv Python

I was trying to implement the FREAK Descriptor in Python using Opencv. Here is the code i'm using: def surf_freak_detect(image,hessianThreshold): surfDetector = cv2.SURF(hessianThreshold) …
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