Is Reverse Projection possible?

I'm not too sure if this is possible with Projector, or it's a 'write only' Effect.

Is it possible to look at what Projector projects onto a polygon as a flat texture, so I can save it as an image? I'd then want to be able to reapply it as a normal polygon instead of the original plane that it was projected on.

So, as in Simon's example here, I'd want to be able to save the plane with the grass projection on, extend the grass to fill the whole plane by cloning it in 2D outside Hitfilm, then putting that plane back in the scene and turning off Projector, to allow for more sideways movement without running out of grass.

That's not actually what I want to use it for, but it's the simplest explanation I can think of for what I want to be able to do.



  • Triem23Triem23 Moderator

    Set up your projection in a high res comp then create a second camera, put it way up high pointed down at the projected image and export the frame? Hitfilm's camera doesn't barrel distort so screen shots of the projected image should be as good as an ortho. 

  • edited March 2016

    @Triem23, thanks. I thought of trying something like that, but it seemed like a bit of a cludge, so I was hoping there was a way to export the actual projected image from the plane directly? :)

    What I actually want to do is use it for removing items in a shot that's not a simple pan/tilt/zoom. Track the section in mocha, slap a Projector in there to get the image on the plane that's superimposed over the problem section, then export that, fix it up in Photoshop etc., then have it put back into the scene, following the original plane, only now it's overlaying it with the corrected version. A bit of feathered masking around the edge to blend it in if required - single image won't be able to change geometry perspective, but OK for short sections - and Bob's your Dad's brother.

    I've seen variations of this in several AE tutorials, where it seemed like it was trivial to do with its Projection, but I'll have to watch more closely and see if they're actually doing a semi-cludge too.

  • edited March 2016

    @Triem23, Ok, I managed to get a reasonable result actually, but I'm sure I could have done it in a neater way.

    As I'm still learning how many tools work, I got out my trusty hammer and used that to beat things into an approximation of what I wanted. Nail? Hammer. Screw? Hammer. Bolt? Bigger Hammer.

    So... I duplicated the whole comp for luck, then added a Static camera, then set the view for that to Front and turned off everything else in the second comp.

    As I played through the video the projection was shown as more or less staying the same as it tracked through the footage using the original camera projection onto the plane. So far, so good.

    Thing is, I could not for the life of me get a way to look at that projection 'face on' to export as a frame.

    Moving the original camera changed what it was tracking. Moving the new one just moved the projection around the screen. I tried everything I could think of to copy, reset, inverse the values from camera 1 to camera 2 etc. but could only get it more or less forwards and at a slight angle. That was only because the start frame from the video looked like that.

    So I gave up, dropped a Quad Warp on it, stretched out out to fill the screen and saved that as an image.

    Then, as the original plane I'd projected on was 400x200 (2:1)and had then been stretched about a bit to cover the projection area, I resized the saved image from 1920x1080 to 1920x960 (2:1), scribbled on it (as a test), then saved it out.

    I imported the image, dropped it on the timeline, parented to the same point as the projected plane, and copied all the Transform properties from that plane to the new image.

    It was the right angle, orientation, shape etc, just too large (400x200 > 1920x960), so I just scaled it down a bit and...Bingo! :D

    The newly scribbled on section (or in the future, the 'fixed up' version) tracked and looked just like the original texture, just a bit softer due to scaling and possibly the size of the original plane, but pretty close. Some minor drift from the original mocha track was fixed by dropping a mask on it and feathering the edges.

    But, at least one thing I'm sure I did wrong: having to use Quad Warp to extract the flat texture. There has to be a better way. How can I get the projected plane to face forwards properly without it changing what it's projecting? Maybe @SimonKJones has a suggestion?

    You can see the change when I do a wipe in the video, but if I hadn't done that, it would have been acceptable.

    Actually, playing some more. What I think I need is the ability to freeze a frame in the projection, then it doesn't need to go out and come back in again, as I can probably do the clean up with masking and cloning inside Hitfilm on the freeze frame.


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