Why my plot comes out jaggy when it shouldn't

First of all, let me apologize in case, some of you, find my questions as duplicates. They are actually not. Sometimes, I start a question, but at the same time it gets broader by mixing with new information and lots of comments that make it very difficult for new users to follow the flow of the question. By adding new clues and new objectives the question loses its original focus, it gets saturated and that's why from a point and onwards I feel that a new question arrises.

On this question, I enclose a plot that is deriving by summing all pixels from a specific area of an image (I also enclose the image). This area is mainly inside the red mask contour. The graph should not have jaggy edges. It should be smooth. Can you please let me know why those jaggy edges?

[Jan]

@Stelios: Which "graph"? The line in the image "proof2.jpg"? What is "jaggy"? Why do you assume, that which "edge" is not "jaggy"? The result was obtained by a Matlab function, I guess. This function does, what you instruct it to do. So the only problem is, that you expect something else. Unfortunately you do neither mention, which function you have applied, nor which detail you expect to be different and why. Therefore I close this question, because it contains too few details to be answered.