Why do I must use Sobel Operator?

Monday, May 5, 2014

As I've recently read some journals and pdfs about Neural Network. And i anchored my mind to an article about "Handwriting Recognition Using Neural Network". For addition, I'm studying Backpropagation. And my question is "Why do the author recommend the reader to use Sobel Operator as a Preprocessing Technique instead of plainly process the handwriting to the neural network ?