Patrick Chenard

Faster rendering for white background?

Quick question, I have a simple scene, an object, a plane (used as shadow catcher), camera and lights. 

I want to render an animation, when I see the rendering process, I notice that the tiles which are white (background color) seems to take a lot more time than I'd expect a tile with nothing on it, not even shadows, to render.


Is there a setting that might aleviate this process? Or a way to setup my scene?

  • Quick question: from the picture you attached it seems that the whole plane is on the camera field, right? Cycles will render it as diffuse (or whatever shader you applied), and hence take more time. Tiles with background (plane white, alpha...) are indeed very fast: if it's these one your talking about it's indeed unusual.

  • tbrbn Oh I get it, and it makes sense. I'll scale the ground plane to only the action zone.


    Thanks for the help!

  • patnard  no problem !
    I actually got a bit curious and did some tests, with an extremely basic scene as below:

    The plane is a shadow catcher, and none of the object have a specific shader. The plane is in another layer (#2).

    The first render is using two sub-renders: one of the object, one of the shadow catcher. I set a very low amount of sample for the shadow (25 samples) compared to the object (125), see below:

    The in the compositor, I combined them with an Alpha Over node. Total render time: 7 seconds (left)


    The second test is rendering both layers at once, with 125 samples. Total render time: 16 seconds (right)

    Render results:

    What obviously makes the difference is the significnatly lower amount of samples used for the shadow, which is noticeable along the edges. In your case, the scene is more complex and you will probably want to have better quality results, but there's maybe possibility for you to drop down the amount of sample if you isolate the shadow catcher.

    Good luck!