Rotoscoping alpha matte problem <Solved>

I have rotoscoped my film and saved all my alpha mattes to a png image sequence. Now for the effect I want to achieve I need to create a new alpha matte image sequence such that:

Frame 1 is the sane as the original frame 1.

Frame 2 is a stack of the original frames 1 and 2.

frame 3 is a stack of the original frames 1, 2 and 3.

etc. etc.

If played back as a movie the new sequence would look like a lengthening streak if you follow what I mean. I can’t figure out how to do this in the compositor nodes and would appreciate the help if someone knows how.

Thanks in advance,
GreyBeard

If you import all stills then, while all selected, navigate playhead to the start frame and press shift s-snap to. All strips will stack up at that frame. Then you need to nudge each frame right as you go up the stack. Labor intensive tho.

Oops I sugested a bad vse workflow.

In After Effects this is an echo effect, that repeats frames from a sequence over time. I don’t believe that Blender has such a function.

Image Node’s and offset each by one frame, then use the mix nodes to combine? Not tried it though. :slight_smile: Nah that won’t work.:frowning:

I thought I could solve Greybeard’s problem by making a single-vertex particle system emit stationary instances of a plane textured with a sequence of alpha masks. However I can’t get the alpha to stack up, ie I can’t see the previously emitted planes “behind” the current one. Am I missing something stupid with the alpha, or will this just not work?

CD38 what an interesting (semi)solution, if they occupy the same space then you could emit them toward an ortho camera. That way they would leave space between boards but not accrue perspective.

Thank you all for your suggestions which has lead me to a solution using the offset value in the image sequence nodes. If someone else need this I can send them a blend file with the node setup.

Thanks again,
GreyBeard

How did you get the images in the sequence to persist over time?

Hi,

Assume 100 original images in the directory called matte. Create a second directory called matte2 and copy the first two images from matte to matte2.

Add 2 image sequence nodes in the compositor loading the images from matte and matte2

The matte image sequence node should read:

frames: 100
start 2
offset 0

The matte2 image sequence node should read:

frames: 100
start 2
offset -1

Connect the two nodes to an alpha over node and the alpha over node to your composite node.
Render your image sequence (2 to 100) to matte2.
Done.

Hope this helps.
Greybeard

Hmmm, I did wonder about best uses for offset. I am unimaginative. Thank you.