Answer:
I'dont really know the answer
It is a good programming practice to explain your functions by writing comments that describe what they do.
Adding a filter to a picture can change the whole effect of the picture. Say you wanted a more vintage theme for your picture, you could use a black and white theme to give it an old timey feel. Different filters can add effects to the picture, maybe the filter gives your picture a blueish cool toned tint, or maybe it adds more light to the filter.