Detecting Zero Crossing in Image Filtered by Laplacian Operator
It was my mistake. 
My PY script was thresholded to output 1 if pixel value was above 0.5, and 0 if otherwise.
Removing the threshold, I got the following result

`

[[ 0.  0.  0.  0.  0.  0.  0.  1.  0.  0.],
 [ 0.  0.  0.  0.  0.  0.  2. -3.  1.  0.],
 [ 0.  0.  0.  0.  0.  2. -2. -1.  1.  0.],
 [ 0.  0.  0.  0.  2. -2.  0. -1.  1.  0.],
 [ 0.  0.  0.  2. -2.  0.  0. -1.  1.  0.],
 [ 0.  0.  2. -2.  0.  0.  0. -1.  1.  0.],
 [ 0.  2. -2.  0.  0.  0.  0. -1.  1.  0.],
 [ 1. -3. -1. -1. -1. -1. -1. -2.  1.  0.],
 [ 0.  1.  1.  1.  1.  1.  1.  1.  0.  0.],
 [ 0.  0.  0.  0.  0.  0.  0.  0.  0.  0.]]


`

Here I can find the transition between negative and positive pixels easily.

Damn you coding...