Given a Horizontal Derivative Kernel What Would Be the Output Image? Hi, im solving this problem and everything went well until i went and solved the position p(5,3) and i got the  answer of 0. However, the solution guide  lists the solution  as 150 which is pointed at in blue. I don't understand this since the pixel at the location is 0, meaning we don't have to calculate the solution however the solution says otherwise. Thanks for your time.
The solution provided is correct. Here is why. 

To compute the derivative at index(3,5)

d(3,5) = value_at(4,5) - value_at(2,5)
d(3,5) = 150 - 0 
d(3,5) = 150


Hence the solution provided there is correct. Hope this helps :)