I am having question about the HPF. In particular, it is having a high pass guassian filter which is applied to the original image below. High pass filter should only detect edge (lots of change in terms of intensity of the pixel). But how come the resulting image, still contains the two "white" things in the middle? Since they are not edge (no change in terms of intensity), should they be filtered out as well?

enter image description here

  • 1
    $\begingroup$ My guess is that the width of the filter is more than the width of the white object in the middle $\endgroup$
    – ThP
    Commented Oct 8, 2014 at 7:34
  • $\begingroup$ Does this have something to do with higher order terms? $\endgroup$
    – kuku
    Commented Oct 11, 2014 at 5:56
  • $\begingroup$ @kuku, Could you review my answer? $\endgroup$
    – Royi
    Commented Jul 11, 2023 at 16:41

1 Answer 1


When we say edge in context of the high pass filter we need to think of the size of the actual support of the filter.

If the support of the filter (Basically the support of the Gaussian Filter composing it) is large enough, those "two 'white' things in the middle" are think enough to be considered edges.


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