umma08

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.

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…

revealing-sections-expanding-circles-of-a-jpeg

Jitter Tutorial 29: Using the Alpha Channel

that has helped so much, thankyou Christopher, and god bless these forums ;-)

Revealing sections (expanding circles) of a jpeg