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I have a scene of an office. It has chairs, tables, computers, and so on.

I would like to know how I can render this scene faster as I am planning to make animation inside the office and don't want the render to take forever.

I know of sampling, resolution and most things in render settings. I have also heard of render passes or rendering using layers.

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You can't just "render faster" for the most part, there are really no shortcuts or magical tricks. You can optimize your scene, tweak settings, and adjust parameters. While these can under certain situations make a significant difference, they will most often lead to marginal speedups compared to the total duration of the process. These can add up frame upon frame when rendering long animations, yielding more significant benefits though, but don't expect miracles.

Rendering is by definition slow. It takes time, a lot of time and resources, rendering animations even more so; so be prepared to wait.

As a wise man once said

match your expectations to your hardware, or match your hardware to your expectations.

Time is money, if your are serious about rendering, if work depends on it, if you are making money out of it, or you are interested enough in your hobby invest in better hardware, or if you can't front the cash or prefer not to own it, rent computing power (a render farm, web services etc.).

Rendering speed is mostly a sum of variables like the performance capabilities of the infrastructure (computer, farm, available devices, among others), available resources, desired level of quality and scene complexity. Faster renders always come at a cost of sacrificing either render quality, money, or complexity of the scene.

That being said, for Cycles (and path tracing in general), there are a few setups that are slightly faster to calculate, and additionally there are numerous ways you can optimize your scene so it generates less noise. With less noise you could require less samples to achieve the same level of quality, hence taking less time to calculate, which results in faster rendering.

Generally speaking Cycles likes big and easy to find light sources. Path tracing is sort of like target practice, smaller or harder to reach or hidden lamps produce noisier output that needs more samples and takes longer to render. Things to avoid:

  • Lights
    • Very small light sources (spots, point lights or area lights with small size or radius property)
    • Lamps hidden behind objects, in crevices or contributing indirect light to a scene
    • Lights behind or inside glass objects or refractive surfaces
  • Geometry
    • Very highly subdivided meshes
    • Mesh with Subdiv modifiers with adequate subdivisions for the viewport but very high rendering subdivisions value
    • Hidden or secondary objects with unnecessarily high quality meshes (generally speaking keep subdivisions and mesh density to the absolute minimum required for the desired quality and proportional to the objects importance in the overall scene)
    • Very dense meshes resulting from sculpting, 3D scans or importing from other CAD software
  • Shaders and materials
    • Very complex shaders trees or materials
    • Unnecessarily large image textures sizes
    • Lots of glossy materials and reflections (which cause fireflies)
    • Abusing bump maps
    • Small objects with emission shaders or illumination

Try searching the internet for "Reduce Cycles noise" or "Optimize Cycles render" and you will find plenty of tips about it like the ones bellow as an example:

Modern versions of Blender now have multiple built-in options for denoising renders, which can cause blurry images and splotches when used incorrectly, but if used properly can help reduce the needed amount of samples save some rendering time. See:

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  • $\begingroup$ How about moving some objects/mesh toa different layer, and rendering each one separately and thrn compositing them together with a node later? Will that not make things faster or is it the same? $\endgroup$ – TheRageMachine May 14 '16 at 10:10
  • $\begingroup$ Never tried that myself, but as far as I know each layer will render faster but overall both together would take longer than just a single render, I think. Plus composting time on top of that. Separating layers is generally done for the purpose of composting or memory management, since each layer could potentially require less memory than the full scene, not for increased speed $\endgroup$ – Duarte Farrajota Ramos May 14 '16 at 12:52
  • $\begingroup$ Hi :). Since this answer doesn't mention denoising, it might be useful to link this one: Type of Denoiser built into Blender $\endgroup$ – Jachym Michal May 16 at 11:21
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    $\begingroup$ @JachymMichal Good point, added. Thanks $\endgroup$ – Duarte Farrajota Ramos May 16 at 14:17
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You could try baking your textures. By baking your textures you get cycles to render one high quality texture and use it with one sample in the final animation. One limit is you will want to use a static light source. See the results of this blenderguru tutorial.

Depending on how you want to animate, you could render one static image (or several from different angles) of the office, then render an animation of just the characters moving and composite them onto the static image/s. The render of only the characters will be very fast in the transparent areas around the characters - 70-80% of the image?

You can even combine the two ideas. Use the baked scene to quickly render a fly through animation of the office and then use it like a live video and composite the character animation over the top. Rendering the two separately allows you to render shadows with the characters and composite them onto the background. You can find several questions here about shadow only rendering and compositing.

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First off, BlenderGuru has some good tips in his 4 Easy Ways to Speed Up Blender Cycles article. The tile size mod is especially effective. In addition, if you make the edits in 7 Ways to Get Rid of Fireflies In a Blender Render, you will be able to drastically reduce the render samples (speeds up render).

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Turning up exposure can help along with lowering light passes but it will depend on what results you are after

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