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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Android auto crop camera captured images

I am looking for some kind of auto trim/crop functionality in android. Which detects a object in captured image and creates a square box around object for cropping. I have found face detection apis in android, but my problem is captured images are…
Dory
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How to detect corner with specific angle degree

I have an image with a equilateral triangle and a rectangle: And I want to detect 3 corner of the triangle only. I follow the OpenCV Harris corner detector tutorial I see that all the corner-point of the triangle have the threshold = 80 (when all…
nvcnvn
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Find a good homography from different point of view of objects?

I am doing object detection using feature extraction (sift,orb). I want to extract ORB feature from different point of view of the object (train images) and then matching all of them with a query image. The problem I am facing is: how can I create a…
dynamic
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How to detect features and lazy-load only the needed polyfills with babel / core-js?

Polyfill services like polyfill.io seem to be delivering only small feature detects to the browser and then lazy-load only the polyfills that are actually needed. As I understand the babel documentation on polyfilling, babel always include the full…
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C# OpenCV FAST Feature Detection

I've been unable to find a tutorial on how to implement the FAST Feature detection algorithms with tracking using C# with openCV, and I can't figure it out from the documentation. How can I implement FAST feature detection and specifically feature…
Kleptine
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OpenCV Python Feature Detection: how to provide a mask? (SIFT)

I am building a simple project in Python3, using OpenCV3, trying to match jigsaw pieces to the "finished" jigsaw image. I have started my tests by using SIFT. I can extract the contour of the jigsaw piece and crop the image but since most of the…
Michał Gacka
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Implementation of ORB

I just used an open source implementation of an ORB. How can I implement ORB further by adding new modules? What can I do from my end in order to get better results than just using an ORB. Am thinking of to use RANSAC for eliminating the outliers…
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Difference between cv2.NORM_L2 and cv2.NORM_L1 in opencv python

I am using sift algorithm from python extra modules for some feature matching. Although one thing I did not understand is the concept behind the normType passed to the BFMatcher. i.e Which ones have to be used in what case? Any help will be…
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ORB is not detecting keyPoints in opencv 2.4.9

I'm trying to detect keypoints with ORB everything is fine until I switched to Opencv 2.4.9. Firts, it seems that the number of keys decresed, and for some images, no keypoints are detected : This is my code compiled with two version : (2.3.1 and…
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Manually make pairwise matching in OpenCV from features key points

Here's my problem. I manually extracted key points features with SURF on multiple images. But I also already know which pair of points are going to match. The thing is, I'm trying to create my matching pairs, but I don't understand how. I tried by…
widgg
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Responding to RAM availability in iOS

I have a texture-heavy OpenGL game that I'd like to tune based on how much RAM the device has. The highest resolution textures I have work fine on an iPhone 4 or iPad2, but earlier devices crash in the middle of loading the textures. I have low-res…
Marcelo Cantos
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DrawMatching between two images - image recognition

I was trying to show the matched keypoints between two Images (one that is captured from my camera and the other from the database) Can anyone help me out in writing DrawMatches function in my code in order to show the matched lines between 2…
WhoAmI
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Peak Detection in Python: How does the scipy.signal.find_peaks_cwt function work?

I'm looking to identify some peaks in some spectrograph data, and was trying to use the scipy.signal.find_peaks_cwt() function to do it. However, the official documentation I've found isn't too descriptive, and tends to pick up false peaks in noise…
NGXII
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Detect boundaries of a document in an image using opencv java

I want to detect the 4 corners of the document in android. Iam using opencv library. Iam using the following approach- (1) grayscale the image (2) Apply median blur (3) Apply adaptive threshold (4) Canny Edge detection (5) find contours (6) find the…
Ankit Aggarwal
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How to train a Support Vector Machine(svm) classifier with openCV with facial features?

I want to use the svm classifier for facial expression detection. I know opencv has a svm api, but I have no clue what should be the input to train the classifier. I have read many papers till now, all of them says after facial feature detection…
MMH
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