What's the point of projecting images on cards?

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  08 August 2012
What's the point of projecting images on cards?


I was just wondering what is the point of using the Project3D node when placing images on cards into a 3d scene?

i know that the difference (from just connecting an image straight onto a card), is that when you go back to the 2D view, no matter how you move/rotate the card (when using the Project3D node), it will look exactly the same as how you placed the image in the first place in the 2D view.

so why doing it?

i hope i made myself clear.. if not, please tell me
  08 August 2012

You can use it for plate cleanup (removing unwanted items from the frame such as tracking markers, wires, actors, etc). You can project a couple of frames onto the cards in 3d space and bake those out as textures. This mean s you don't have to paint objects out on each and every frame. This demo might explain it better... http://www.youtube.com/watch?v=rckWPjnonjw although they're using geometry, the concept is still the same - for some things such as a wall or roof you might be able to get away with using a simple plane.

For applying a new camera move to a shot. You project from the original camera and then render it using a slightly different camera. This technique is sometimes used in converting 2d images into stereoscopic 3d images.
  08 August 2012
about your your first example:

ok, but in order to project a couple of frames to clean wires (for example), don't you need a baked camera animation (which you need to get by tracking your shot)?

if so, you can also do that by the Card node itself..
just set your shot on a card, your cleanup texture on another, place them "on top" of each other in the 3d space, and that's it, right?

i'm confused :/
  09 September 2012
Yes you do need a tracked (or aligned) camera in order for it to work. But if your adding a CG character or creature to a live-action plate you need a tracked camera anyway - so if you need to paint out the stand-in actor (like in the Transformers example) in the live-action plate you can do so by projecting the plate onto the card in order to create a clean plate. Nuke's matchmove node can also provide a point cloud based off the camera track, which allows you to place the cards (or geometry) in the correct 3d space.

I don't really understand what your trying to get at in your second paragraph - but it doesn't sound like it will work. In order for this to work you need to project the plate onto a card (or geometry) which is in the right 3d space.
  09 September 2012
that's right..

so if i manage to project the plate on a card which will be in the right 3d space (without using the Project3D node), will i get the same results?
  09 September 2012
Yes. But off the top of my head I can't think how you'd do that within Nuke without using a Project3d node.
  09 September 2012
with the Card node, i can just try to guess the position in the 3d space..

anyway, thanks for your answers!
  09 September 2012
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