I'm trying to calculate the normal direction in a grayscale image using a pixel neighborhood like this.
Suppose I have a matrix
| 148 141 145 | | 144 140 148 | | 146 147 148 |
The normal direction I want to calculate is the difference in gray scale from the central pixel. if the difference in grayscale is greater than a value, the final normal direction of this plurality is a sum of the normal direction.
How to implement this method effectively in MATLAB?