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Keypoint response and size, what are they?

asked 2015-01-30 09:33:47 -0500

Doombot gravatar image

updated 2015-01-30 10:05:44 -0500

What exactly are the keypoint.response and keypoint.size field of a keypoint (in my case, BRISK)?

I found an answer for SURF, but I would like to know what is the meaning for binary keypoint such as BRISK (which is based on AGAST if I remember correctly).

As a reminder, here is the definition that is shown by IntelliSense when typing:

Size: diameter of the meaningful keypoint neighborhood; Response: the response by which the most strong keypoints have been selected. Can be used for further sorting or subsampling

Knowing that, I would be able to assess their use as a way to filter the keypoints.

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Be aware that not all keypoint detectors fill those fields. It might be that e.g. AGAST only gives a keypoint size of 1 and a response of 0. Check the code to see if these fields are set up. I only know of ORB,SIFT and SURF for sure that they use these fields (however the meaning in SIFT is differentl afaik since they pack these values somehow if I remember correctly).

Guanta gravatar imageGuanta ( 2015-01-31 06:51:11 -0500 )edit

Thanks! In the case of BRISK, I get values ranging between 11.2 and 16 for the size and about 31 to 310 for the response.

Doombot gravatar imageDoombot ( 2015-02-02 13:04:51 -0500 )edit

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answered 2015-01-30 14:49:52 -0500

updated 2015-01-30 14:50:09 -0500

Size is the region around a point of interest that is used to form the description of the keypoint. The larger it is the more regional information is used to describe your featurepoint. As to the response, this defines how strong a keypoint is according to the formulae described by the technique. The higher the value, the more likely the feature will be recognized among several instances of an object.

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Do you know what is highest value the response may take? My guess would be 512, but if you know... I have personally seen values from 31 to 310 for BRISK.

Doombot gravatar imageDoombot ( 2015-02-02 15:09:37 -0500 )edit

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Asked: 2015-01-30 09:33:47 -0500

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Last updated: Jan 30 '15