Diff of Sobel

• The added line is THIS COLOR.
• The deleted line is THIS COLOR.
• Go to Sobel.

[[Convolution]]

- https://docs.opencv.org/3.4/d2/d2c/tutorial_sobel_derivatives.html
- http://www.info.hiroshima-cu.ac.jp/~miyazaki/knowledge/tech0131.html
- Sobel Derivatives
--  https://docs.opencv.org/3.4/d2/d2c/tutorial_sobel_derivatives.html

- ソーベルフィルタのOpenCVによる実装
--  http://www.info.hiroshima-cu.ac.jp/~miyazaki/knowledge/tech0131.html