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I was wondering how to blur a video background (a person is talking and you wish to remove the background)? Should the compositor be used?

Example video that you can use for testing: http://www.youtube.com/watch?v=zncqb-n3zMo

Example of blurred background image:

enter image description here

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  • $\begingroup$ If you are rendering the video from a 3D scene (so you have Z pass depth information) you can use the Defocus node. $\endgroup$ – gandalf3 Jan 11 '14 at 1:48
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Expanding on Matt's answer, to blur based on a mask in the compositor:

  1. Create a new mask in the UV image editor by selecting Mask mode and clicking new:

    enter image description here

  2. Add a mask primitive (ShiftA) and edit it to match your the part of your image you don't want to blur (or the other way around, do whatever is easier to mask because you can always invert it later) using CtrlLMB to add more points.

    enter image description here

  3. Once you have your mask, add it in the compositor with a Mask node (ShiftA> Input > Mask and pick your mask from the drop down):

    enter image description here

    You should be able to view it by connecting it to the viewer node:

    enter image description here

Here are two methods for bluring based on this mask:

Method 1

Using a Gaussian blur node with a variable size:

enter image description here

Method 2

Using a Fast Gaussian blur (which doesn't support variable sizes):

enter image description here

I believe method 2 is a little faster (in computation speed) for large blurs, however it's a little more complex and artifact prone than method 1.

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  • $\begingroup$ Very detailed answer! $\endgroup$ – Turbo Jan 11 '14 at 8:24
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Yes, the compositor should be used. The most straightforward approach would probably be to animate a mask which you use to selectively blur (or remove) parts of the video.

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