[Bf-vfx] Feature request - 'overscan' rendering option for better distortion compositing

[Sean Kennedy]

I'm not in front of my computer at the moment, but I have an idea about this.

I'm thinking the trick to getting the overscan is in the compositor. For the sake of discussion, let's say the footage tracked and undistorted is 1920x1080, and undistorted, its size is 2100x1160.

You would set your render size to be 2100x1160, so the 3d elements are the overscan size. In the compositor, you would also work at the 2100x1160 size, which you could do by scaling up the footage to that absolute pixel size, then putting the original footage at 1920x1080 over it. This essentially sets the canvas size to 2100x1160, but you're still working with your original size footage. Then add your undistort node, alpha over your oversized 3d render, then reapply the distortion. This will crop in your 3d, like it normally does, but your working at the overscan size, so you may be ok once you crop it down to 1920x1080. You could add a crop node and an output node to save out the correct 1920x1080 file. The default render will have to be the oversized one, but just don't use that one.

Again, there could be something I'm overlooking in this workflow, but that's what I would try.

And of course this is just a workaround, not a real solution.

Sean

Sent from my iPad

On Feb 24, 2016, at 6:11 PM, "Stephen Hamacek" <s.hamacek at gmail.com<mailto:s.hamacek at gmail.com>> wrote:

Hi all, first post here so forgive me if I'm in the wrong place :)

An issue that came up recently was the compositing situation where a CG element needs to be placed over a footage plate, where the plate has been undistorted for matchmoving etc. but then the original ('distorted') footage is desired for the composite.

The CG element can be distorted effectively with the distort node, but if it ran off the edge of the rendered frame, that edge would then impinge on the composite, cutting off the edges of the CG element.

I'm wondering if there is some way of creating an 'overscan' option somehow, maybe in the render settings, that could be linked to the distortion settings, so that the CG is rendered slightly larger, so that when it is distorted this issue does not arise.

Here is a thread where this was discussed somewhat:

http://blenderartists.org/forum/showthread.php?390200-The-composition-of-distortion

Would love to know your thoughts on this. It seems to be a common enough issue with compositing which other software (e.g. Syntheyes) knows about, but maybe I'm missing something in my understanding. Thanks!

Stephen Hamacek (Hammers)
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