# KeyPoint size

Hello, i'm using OpenCV for some objectrecognition application. When i calculate KeyPoints with a method like SIFT the KeyPoints have a parameter size. In the documentation it says that this is the diameter of KeyPoint. My question is how this is calculateted? Or is the parameter depending on the scale where a KeyPoint is found? And if yes, how?

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Keypoints are detected by Scale-Space extrema detection using Difference of Gaussian images. So the size is basically at what scale those points are detected.

This is somewhat incorrect: The size of the patch being described is linear dependent on the keypoint scale, i.e. size = scale * magnifier. How you choose the magnification factor depends on the application.

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Keypoints are detected by Scale-Space extrema detection using Difference of Gaussian images. So the size is basically at what scale those points are detected.

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