# Which frequency filter is it?

To which frequency filter the following operator is equivalent?

-1 0 -1
0 4 0
-1 0 -1


In the image domain, it is a laplacian rotated by 45 degrees. In the frequency domain a combination of negative and positive values can not be a low pass filter, so it must be high pass filter?

moreover, if we take the unit impulse function and subtract the low pass filter from it, we will always get the low pass filter?

1 0 1
0 5 0
1 0 1