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 detect rotated and quite deformed object

I have an A4 paper with some black stroked rectangle. I scan the image and try to use some basic OpenCV's function like template matching but I see the image I recive sometime rotated when I put it to the scanner or the paper somehow wrinkled so the…
nvcnvn
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Using FLANN with separate *double arrays

I'm working on a piece of code that performs feature matching with 128 dimensional descriptors. All descriptors for an image are stored in a std::vector, where InterestPoint contains a member *double desc, which is the descriptorvector. Now I want…
filipsch
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If I want to make my computer be able to 'see' itself, would examining the clipboard after a call to PrtSc be a wise method?

I have become increasingly interested in artifical intelligence, but I am still learning the basics of the windows API. My current goal is to create a c++ process which calls SendInput to simulate PrtSc being pressed (print screen button). This is…
Leonardo
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How to calculate Binary histogram of an image?

suppose a color image of size 256x256, how can I calculate the bianry histogram of the image? also which is the data structure suited to store the histogram if I want to cluster similar images? Please note that the histogram must be saved in the…
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Printing Keypoints Descriptors

I would print the descriptors of a feature keypoint. My method receive in input a vector of keypoint, and a mat descriptor for that point. Someone know a simply solution? Thanks
Mark
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iphone: Hands free gestures

In my iPhone app, I require to recognize the gesture or motion made by the user on the view without touching it. I want the hand free gestures to be recognized and perform a function on view. I need that the image should move with the gesture…
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How to detect if browser supports focus on disabled elements?

Can't move focus to the control because it is invisible, not enabled, or of a type that does not accept the focus jQuery threw the above error on IE8. I'd like to be able to detect if the browser supports focus on disabled elements (an input in…
Adam Lynch
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To use the second variant of FeatureDetector on an image set

I was able to successfully load a number of images into a vector, vector. The images once loaded in can be displayed with the imread function. The problem is that I want to apply SIFT on this set of images using the second variant, as…
ipunished
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Difference between SiftFeatureDetector() and Ptr

Whats the difference between SiftFeatureDetector() and Ptr. They both apparently have the same function. The opencv tutorial uses SiftFeatureDetector but when clicking on the official documentation they use Ptr and have no mention of…
StuckInPhDNoMore
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Code keeps breaking no matter what I try

Ive been trying to get my very simple code that I posted here: SiftFeatureDetector .detect function broken? to work. But it keeps breaking, it compiles fine but refuses to run. I have OpenCV 2.4.2, Windows XP. Here is what I have done: I first tried…
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Feature Detection Reliability

I have been trying to detect some features of an image and another image which is created by rotating the other image by 90 degrees. My aim was to confirm that OrbFeatureDetector with BriefFeatureExtractor is actually rotation invariant. However,…
Ozum Safa
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best features to extract for hand posture recognition?

I'm doing a project on hand posture recognition with OpenCV. I've done the segmentation using normalizedRGB and found the contours using cvFindContours. Now I need to find the features to be extracted. What are the best features to extract? What is…
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OpenCV cvFindContours finds only one contour

I'm continuing my work with openCV, my first adventures I described here. It goes on quite well, but I've stumbled upon another tricky thing. I want to find contours on the image I've applied adaptive threshold to: So the cvFindContours seems to…
Wojtek
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OpenCV Flann problems with AutotunedIndexParams

I have a problem with openCV 2.4.2 flann indexing with AutotunedIndexParams. If i use multiple images to create an index the program exits with the output: trees : 1 terminate called throwing an exception Thats a similar error I get for the equal…
Hans Sperker
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how to save lines storage in a matrix using a Hough transform?

i want to save detected lines using a probabilistic hough transform. Using a houghlines2 command there is a parameter called line_storage.line_storage is the place where this function stores its result. This can be either a CvMemoryStorage structure…
Nim4eng
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