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 can I use OpenCV to find an arbitrarily transformed rectangle in a depth image?

I'm attempting to work with a depth sensor to add positional tracking to the Oculus Rift dev kit. However, I'm having trouble with the sequence of operations producing a usable result. I'm starting with a 16 bit depth image, where the values sort…
Jherico
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how to find local maxima in image

The question is about feature detection concept. I'm stuck after I finding the corner of image and I want to know how to finding the feature point within the computed corners. Suppose I have grayscale image that have data like this A = [ 1 1 1 1 1 1…
someone
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How to black out everything outside a circle in Open CV

I am currently trying to black out everything outside a circle. I am drawing the circle using the following lines of code: cv::Point center(cvRound(circles[i][0]), cvRound(circles[i][1])); // CVRound converts floating numbers to integer int radius =…
Sebastian Boldt
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Facial expression recognition from webcam

I am currently working on a project where I have to extract the facial expression of a user (only one user at a time from a webcam) like sad or happy. There are a lot of programs/APIs to do face detection but I did not find any one to do automatic…
TIBOU
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knnMatch with k = 2 returns 0 nearest-neighbour even with images trained

I am basically extracting many keypoints with SURF from similar images and adding them to the BFMatcher(NORM_L2) In runtime It can happen that I add new keypoints to my matcher with matcher->add(myNewDescriptors); Now when I have added an image with…
dynamic
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Can't get clean output in my MATLAB implementation of Canny-Deriche

My code so far is: function imgg = derichefilter1(x, k, a, b, c) osize = size(x); x = double(x); a = double(a); b = double(b); c = double(c); k = double(k); y1 = zeros(osize(1),osize(2)); y2 = zeros(osize(1),osize(2)); y1(:,1) = a(1)*x(:,1); y1(:,2)…
Hameer Abbasi
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OpenCV line detection in general

I am new to opencv (in c++) and I am trying to implement line detection. I have a picture with a couple of lines and I am trying to determine the distance between the lines. I know there is Hough, Canny and so on but how can I get the coordinates of…
marc
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How to decide if a device can login with Webauthn's fingerprint in Javascript?

I created a Webauthn authentication for my website. Now I'm trying to create a good interface for the best user experience. My users are not techies. I'm interested in the fingerprint authentication as option. The webauthn via Yubico 2 or Google…
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opencv-python : drawMatchesKnn() always return NULL

I want to make a simple project about logo detecting. So I tried to follow OpenCV-Python tutorial about feature detection. OpenCV: Feature Matching I wrote my code like below. ratio = 0.8 logo = cv.imread("T01/CocaCola_logo2.png",…
HS. Choi
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How to feature detect Input Events Level 1 or 2 support?

Browser input events have been around long enough to be categorised into at least three different levels of support beside "no support", by now (recent history about the W3C specs on github): InputEvents Level 0? (no inputType, nor beforeinput,…
ecmanaut
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Query to identify if current SQL Server version supports columnstore indexes

I have a stored procedure that creates some dynamic tables. If columnstore indexes are supported on the host version of SQL Server then I want to create a columnstore index, otherwise fallback to creating just a normal row store index. I have found…
Mark Robinson
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Angular Universal and browser feature checks

When developing a web app with jQuery or normal JavaScript, it is commonplace to check for feature availability first. So for example, if I want to use the document.oncopy event, I should first have something like this to ensure my code doesn't…
Cobus Kruger
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How to feature detect for CSS custom properties?

Is there any way to detect whether a browser supports CSS custom properties (eg. color: var(--primary))? I need to write a script that behaves slightly differently in browsers that don't support custom properties, but I can't find any documented…
Nick F
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OpenCV evaluateFeatureDetector for Python?

I am working with Python and OpenCV 3.0 and I am trying to evaluate the SIFT descriptor for two images. More specifically I am interested in the repeatability rate. In C++ there is this function that is used to perform the evaluation: …
GStav
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OpenCV / Image Processing techniques to find the centers of bright spots in an image

I'm currently doing a project based on the methodology described in this paper: Camera calibration from a single night sky image As a beginner in computer vision, I do not quite understand how I can implement the method used in the paper to find…
LawrenceH
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