Edge Detection Convolution Intuition I was learning about convolution and how filtering helps us to detect an edge in an image;however I still cannot not understand how the convolution process in the image below does this. 
I understand how the last 4x4 matrix is created(the math operations);however I do not understand why the resultant matrix indicates that there is an edge in the image. In the resource it basically says : "If we interpret the matrix on the right as an image, there will be a lighter region (white) in the middle, that corresponds to the vertical edge detected in the center of an original 6×6 image." but it makes no sense for me why lighter region in the middle indicates vertical edge.

I think it seems that white region of the 4x4 array is difficult to understand because there is only one edge in the 6x6 array.
It will be easier to understand if you expand this a bit and draw it.

The two white lines shown in the left 16x16 matrix have two edges each compared to the black background.
So if you look at the 14x14 result matrix on the right, you will see 4 edges.
Here are some things to note:

*

*Among the white lines on the left, the thick line is displayed in black between the red and yellow lines. In other words, the thickness of the line depends on the distance between the edges.

*Even if the area is not displayed because the white line is thin, the value is different to distinguish the two edges.

If you look at this broadly and think about various cases, you can see how the edge is found.
