[Ioannis mentioned another edge detector](http://www.parallelpoints.com/node/46#comment-132) he’s fond of using – so here’s a comparison.
To summarise, his method involves shifting the image 1 pixel to the right, and subtracting it from the original image. And then doing the same but shifting one pixel down instead.
This is equivalent to convolving with
[1 -1]
rather than
[1 0 -1]
[2 0 -2]
[1 0 -1]
There’s two differences that are worth commenting on: