Filtering an Image

Question

Hi all, I am a beginner in C# but somehow it is required of me to use C# to create a presentable GUI that will place a movable filter on to an image. What I wish to do is load an image to a picturebox. Then place black plane with a circular hole of a specified radius. So the final picture will be only viewable via this little hole and everything else will be black. Now this hole needs to traverse line by line such that at the end the whole image would have been presented to the user. The time it takes to traverse to the end should be made variable. I thought of doing the above task by drawing a circle with a pen that has a very large width. And then refreshing the picturebox before the next circle is drawn. However, this caused too much flickering and since I am truly a beginner in both GDI+ as well as C#, I thought there would a much better way of doing this task. I also tried to pre-sample all the required images, however, as the radius gets smaller there were too many images to store in advance and the time for it process was extremely long. I also tried to create an array of pixels that will be ANDed with the image but I could not get too far with it, for I am currently lost in regards to where to start from. Any kind of help will be greatly appreciated. Thank you all for reading this, and also thanks in advance.