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Hello guys iv got a sphere that has particles (stars) and im putting some blur on them how do i set that image as a background? and keep the ship in front of it ?

the particle system is connected to the sphere the ship is inside of it and the camera is too. the particle system is on another layer. im rendering them separately and in the compositor view adding blur to the stars. the ship is not a single object. id like the stars not to be visible in front of the ship. as seen in the render view (bottom left)

And my plans are going around the ship with the camera.

Image

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  • $\begingroup$ is there a reason you didn't position the spaceship in front of the sphere? $\endgroup$
    – bstnhnsl
    Apr 6, 2018 at 8:30
  • $\begingroup$ or make your sphere bigger so both the ship and camera are inside it. $\endgroup$
    – David
    Apr 6, 2018 at 12:02
  • $\begingroup$ possible duplicate of: blender.stackexchange.com/questions/49049/… $\endgroup$
    – user1853
    Apr 6, 2018 at 15:03

2 Answers 2

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Assuming your rendered image has an Alpha channel then simply change the last Add node in the chain to ‘Mix’ and use the Alpha as the Fac. This will mix between your shapceship and the stars based on the alpha.

Note that if you don’t have an alpha (if you haven’t rendered with transparancy enabled) then you can use the Depth as a filter instead as it will be very high for points on the background behind your spaceship (1000000000 or similar - effectively ‘infinity’) and much lower for points on it - pass the Depth through a Greater Than maths node to compare it with, say, 10000000 and the output of that can be used effectively as an alpha.

This resulted in a final solution (from @IvanVujacic) as follows :

did it

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  • $\begingroup$ Thx the alpha tip helped. i noticed after adding the alpha to the factor in the add node the stars were visible only on the ship so i used a invert node and in the end the stars were only visible around the ship. i needed them on separate layers because i was adding blur to the stars and making thme + shape. a mod deleted my old msg... $\endgroup$
    – Ivan Vujacic
    Apr 11, 2018 at 20:18
  • $\begingroup$ Thanks for the feedback - glad to help. I’ve edited the question to include your image. $\endgroup$
    – Rich Sedman
    Apr 11, 2018 at 21:02
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A simple way is to create a very large sphere and place your camera inside the sphere.

You could put the star field on a plane and place that behind your main scene. This implies you have made an image out of your particle system.

You could also consider setting a star field as a world background. This also implies that you have made an image out of your particle system, but you should also be able to find suitable images (check the licence for allowable uses) on the internet. There are some HDR images out there for star fields.

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  • $\begingroup$ the particle system is connected to the sphere the ship is inside of it and the camera is too. i should add that to the question. $\endgroup$
    – Ivan Vujacic
    Apr 6, 2018 at 8:16

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