Revealing sections (expanding circles) of a jpeg

    Feb 26 2014 | 2:06 pm
    Hi all,
    i am trying to reveal a certain section of a jpeg (an expanding circle).
    A jpeg will remain black until a point in time that i want to reveal a shape within the window, thus slowly revealing the section of the jpeg behind, while keeping the rest of the jpeg hidden.
    Does anybody know how i could do this?
    I have got as far as to getting a jpeg into a matrix, and then unpacking it, and then altering the alpha channels so that i start from a black image and then move to reveal the picture, but how would i go about revealing certain sections of the picture?
    Any help would be much appreciated. File attached as far as i have got so far…
    thankyou in advance!