Detect Corners Using cornerHarris ?

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Hi, all:

Sorry to ask such a naive question, but it does keep me annoying I'm trying to see the Harris Corner effect using the modified code here https://code.ros.org/trac/opencv/browser/trunk/opencv/samples/cpp/tutorial_code/TrackingMotion/cornerHarris_Demo.cpp?rev=5982 with my Logitech USB camera. However, from time to time, the code in the above linkage looks on all the pixels inside the captured image as corners ---- namely, a picture full of corners. Does anybody meet the same situation? How can we avoid such "all pixels are corners" situation?

Best Regards Pei