Simple tricks to reduce render times

Support Compositing and Post Processing
#1

Are there any tutorials for simple tricks to reduce render times? Or you can just tell me if it’s not too complicated.

My test renders right now consist of roughly 1000 highly reflective metal rods that need to be rendered as such along with a polished concrete floor, 40 area lights (representing a large area of overhead flourescent strip lighting) that must be clearly visible as such on the floor and a small number of metal columns with a glossy paint. Everything is reflective, the rods have a large number of faces, etc. Not only that but it’s being rendered at a high resolution.

What, if any, tricks can help reduce the time? Right now I’m only doing test renders of still shots and it’s taking upwards of 45 minutes to do a 60’x60’ floor area.

My computer is a dual core 2.66Mh with an nvidia geForce 5500 card and 2GB DDR2 ram. Yeah, I’m asking for a faster computer. 12 core, 8GB DDR3 dual video cards, cup holder, leather interior, etc.

#2

It all depends on your scene, what materials you are using, what you have ray depth set at, and a lot of other stuff, but one thing that will always reduce your render time, is to render from the command console. However, I don’t know what that command would be, so you may have to do a search.

#3

I’m not very skilled at blender, but should the render time decrease if you link relevant objects like the rods to each other?

#4

The rods on each section of wire shelf have already been merged into one single item but the number of faces for each section still is large due to the nature of the wire mesh. There is a rod every 2 inches for a total combined linear length of nearly 1400 feet in one room alone. Figure roughly 8,000 rods. It adds up in a hurry.

#5

what about using an array modifier? or dupliverts.

#6

I’ve been using Microstation for years now, I’ll stick to doing all my modeling in there. What might have to happen is to redo all of the wire rods and turn them into something like hexagonal extrusions instead of smooth round rods. They’re only 1/4" thick so it is unlikely anybody will ever notice anyway.

#7

There are several things I could think that might help:

  1. Bake the reflections of a nearby section of your wire mesh, then for all the distant sections, use this in place of the actual reflection. Close up you can tell that the reflections don’t match the things being reflected, but in the distance, it’s impossible to tell. Especially true if the object reflecting is small, glossy, or highly curved.
  2. Render sections separately and combine them together. Effectively what you want to do is build a ‘mock up’ of the rest of the room, for this section to reflect, and then render the section, and repeat for each section. Likewise for glossy reflections, - you cannot see the detail of the thing being reflected, so make a plane, draw or do a quick and dirty low res render to get an image, and reflect that, not the real room. Bake that reflection to the object, unless you need to do a fly-through, (in which case you need a render farm!)
  3. Remember that reflections don’t generally care about the lighting too much, so separate the reflection and lighting passes, and use a simpler lighting rig for the reflection pass. Also, reflective objects are not too sensitive to lighting themselves, as you don’t see shadows on them very much. Thus you can use fewer lights for the shadow pass on the reflective objects, and more for the less shiny objects.
  4. If you have shadows on the floor, think about making a low-poly stand-in for the thing throwing the shadow, and using that on a shadow pass for the floor only. This reduces the render time dramatically. For example, if you had a wire frame shelf standing on a floor lit by strip lights, you could model an object which is literally just the legs and a plane for each shelf. Make the planes semi-transparent, and the resulting shadow, once blurred by the area lights, will be indistinguishable from the shadow of the mesh shelf.

Obviously, if you have a reflective surface really close to the camera, you need to do a full reflection/lighting pass on it, once everything else is complete, so that you get all the detail in that section of the image, but for the more distant stuff, these things can easily drop your render time by 90% or more.

HTH.

Matt

#8

I have to build a gaming environment of the entire building in 7-8 weeks from now. That’s assuming 1-2 more weeks of getting to know Blender and 6 weeks of actual modeling and render time.

The good thing is the only animation will be doors opening. Depending on what’s decided in the Monday meeting I’m hoping to do only a fully lit building so I can bake all the shadows and reflections and not have to worry about that bogging things down.

#9

http://wiki.blender.org/index.php/Doc:Manual/Render/Performances

#10

Ah thank you very much. It looks like I’m going to be baking so much I should get a chef’s hat