Today my question might be a bit complex, but I hope that Blender has an easy solution for this. So, let's say I have a scene with several objects in it and I have a background. The background is image/video which has some objects on it. Some of them are supposed to be closer to camera than my 3D models. I have a representative 3D model made for those objects, but texturing it would be real complex. Instead what I inted to do is to use it as a culler - wherever the object is, render the background(cull the other objects). Is this possible to do? Also, a solution for both - Blender Internal and Blender Cycles is needed.
Thanks! ;)

  • $\begingroup$ I guess it is something like object mask. Basically what I am trying to do is to use one object to cull others. Or, in other words, wherever that object is directly visible to camera, it must render the background instead of any objects). $\endgroup$ Feb 18 '17 at 17:20
  • $\begingroup$ Can you use the edit link and clarify your question? $\endgroup$
    – user1853
    Feb 18 '17 at 17:21
  • $\begingroup$ In cycles you can use a holdout material. But there are a few options. Read: related?;blender.stackexchange.com/questions/48122/… $\endgroup$
    – user1853
    Feb 18 '17 at 17:22
  • $\begingroup$ UV Project modifier... maybe. But could you post some images to have a better understanding? $\endgroup$
    – lemon
    Feb 18 '17 at 17:29
  • $\begingroup$ You might also want to have a look at this. Instead of fashioning a 3D model you just shape a 2D plane in the shape of the object that's in the bkd film. Set it's transparency to .008. That works in Blender's 3D window and using OpenGL rendering. I'm not into Cycles but I imagine if a model can be used for a mask, a 2D plane could be also. (No transparency though) The Question - drop to the bottom answer. blender.stackexchange.com/questions/69832/… $\endgroup$
    – Edgel3D
    Feb 18 '17 at 22:13

Using Renderlayers

Position your masking objects on a separate layer. (In my case layer 2.)

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Go to the Properties > Renderlayers Tab. Set the Mask Layer to the layer, which contains the mask objects. Note that you have to have the layers switched on in the scene for them to be included in the render.

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Rendering this setup results in the following. The mask object renders as transparent.

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If you do not wish the object to have a shadow, set it to a transparent material or turn off cast shadows.

Using the Material Setup


Set the material to holdout.

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Check Transparent, use Mask mode and set Alpha to 0.0. Disable Cast Shadows.

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