Zero average in image processing ( Pascal transformation )

I am doing pascal transformation on 4x4 block of image.Anyway i am having some problems at specific placeses.I know how to reduce effect of noice. 1.One point of text i don't understand and that is : Shifting the data values to zero average first will improve this effect. 2.How can i detect all bump in image, every value that's not same as one before is behaving as bump.Maybe some treshhold, but what value should it have ?

Discrete Pascal transformation: Basicaly it is used to detect bumps and edges.For example when i do transformation on starting matrix z resulting matrix Z will be as : 0 0 0 0 0 0 0 0 z= 0 0.5 0 0 => Z= 0 0.5 1 1.5 0 0 0 0 0 2 2.5 3 0 0 0 0 0 3.5 4 4.5