February 13, 2021 Jenny Ha

5 tweaks: How to render faster in Cycles

We all know that Blender is not only an open-source 3D modeling and animation software often used by animation artists, product designers, game creators but it also has a strong community of artists and computer scientists behind it, constantly improving the code to deliver powerful software without the hefty price tag. Beyond its popularity, Blender still has one major drawback for users: It can take a really long time to render projects when finalizing an intensive project. Blender is able to use your computer’s central processing unit (CPU) or graphics card (GPU)—or both—for rendering.

In the words of Thomas Dinges (developer), “The Internal rendering engine was built for speed, but if you wanted realism you had to turn stuff on. Cycles is the other way round. It’s built for realism, and if you want it fast you have to turn stuff OFF.” (said during a conversation at the 2012 Blender Conference).

So for the article today by iRender, we will provide a list of 5 tweaks that help you speed up your Cycles.

1. Use Ubuntu operating system

Blender and Ubuntu have in common that they are both open source. Such compatibility helps a lot when you use the right software in the right environment for it. So with Ubuntu what are the advantages that you need to care about here to render Blender:

  • Ubuntu works well on most low to high configuration machines, consuming fewer hardware resources.
  • The terminal on Ubuntu is preeminent, serves well, increases productivity for data handling. You can easily render Blender with just simple commands, without much work on the interface.
  • Fast rendering speed.

Currently, iRender has launched a new service, connecting the remote computer to the Ubuntu operating system. We are proud to be one of a few render farms supporting Ubuntu operating system on the market now. If you are using Blender and want to render results quickly, do not hesitate to register and experience this.

2. Reduce Samples

What are Samples? Samples are the noise that appear as your scene is rendering. In the render panel you define the number of samples, and then blender stops once it reaches it. The more samples, the clearer, but longer your render is. While using as many samples as possible allows Blender to create clearer images and models, each new sample means another second to work on rendering it. By limiting the number of samples, you can greatly reduce your rendering time.

Keep in mind that obtaining fewer samples will affect the quality of the final product, so it’s best to use this method for web-only projects instead of those that require viewing on larger screens. Take these two examples:

2000 samples – 9 minutes

5000 samples – 21 minutes

Did you really need those extra 3000 samples? Unless you’re a pixel scientist, you probably wouldn’t have noticed much of a difference. And if you did, you could always put the render through photoshop to clear up any remaining noise. If you’re only rendering a still, an extra 12 minutes probably isn’t anything to stress over if it’s for the final render. But if you’re rendering an animation? Well those frames will add up very quickly.

3. Optimize the Tile Size

Tiles are small black boxes that appear on the screen when the blender renders the scene. Tile size is an important factor to minimize your rendering times. When you increase the number of tiles, the tile size will become small and it can focus on a smaller portion of your scene. And all cores work on the render until it’s finished without one core finishing before another. So, by optimizing the tile size your rendering time will minimize. Blender was always capable of increasing the number of tiles, but recently with the code update, you could also change the tile sizes. GPU can only render one tile at a time, while CPU renders multiple tiles at a time, so for optimizing tile size it needs CPU. We conducted some studies using this scene, and came to these results:

Yes… Tiles matters a whole lot more than you may have thought. Interestingly, the fastest render time for CPU is the slowest on the GPU. This due to the GPU only being able to render one tile at a time, so it doesn’t benefit from more tiles. In summary, the optimal tile size for GPU is 256 x 256. For CPU it’s 16 x 16. And if those don’t work for you, try to keep it in the power of 2s (eg. 128, 256, 512, 1024), as the processor handles these faster.

4. Reduce the amount of bounces

One of the biggest reasons that Cycles takes so long to render is because it calculates light bounces. What are light bounces? Light bounces are indirect light that bounces off walls and other objects. It’s what makes the scene look so good in comparison to the Internal renderer.

However, this realism comes at the price of render times. By default the maximum amount of Light Bounces is set to 8. Which is far too high in my opinion. I use Cycles a lot, and I rarely need more than 4 bounces for adequate realism.

To change the number of bounces, go to the render panel and under Light Paths, you’ll find Bounces (screenshot). Set the Min to 0 and Max to a low setting. Experiment with the setting till you find a value that achieves a good amount of realism, but without sacrificing too much in render times.

For even more fine tuning, you can adjust the amount of bounces for individual light path types like diffuse, transmission and glossy. In the example above, I would set the Transmission amount higher than others as it is the most noticeable when reduced.

5. Use CPU + GPU

Since Blender Version 2.8 you can use your GPU and CPU simultaneously. Which can give you a huge advantage especially if you own a good CPU like a Threadripper or a Xeon CPU. The entire machine of iRender is equipped with CPU Dual Intel Xeon E5 2678 v3 belonging to socket 2011-3 and owning 24 cores 48 threads thanks to Hyper Threading technology. The basic clock speed is from 2.4Ghz and Turbo Boost up is 3.3Ghz (clock speed of all cores is 3.0 Ghz). The L3 cache is 30Mb, combined with the QuickPath Interconnect (QPI) feature that allows operation on systems that support multi-socket with high bandwidth. Therefore, when running Dual CPU Xeon E5 2678 v3 on a main chip set, it will increase the maximum performance especially for those who specialize in rendering. 

If you have an Nvidia RTX GPU you can also switch from CUDA to OptiX which will also increase your render performance by 20%-30%. Let’s check how Cycle render with NVIDIA RTX 3090 at iRender:

Conclusion

We hope this overview will help you choose a suitable but high computing configuration for Blender with Cycles. At iRender, we try our best everyday to offer the best thing to our beloved customers. What you get is more than rendering to create the final product. You receive a new technology solution, a good service, high security, features and softwares, and other utilities to help you save costs and time, reduce stress while working and most importantly, it breaks the creative limits of many technology “artists” nowaday. If you have any questions, please do not hesitate to reach us via Whatsapp: +(84) 981-868-890. We will be ready to help you in any way!

Become a member of the iRender community today to stop wasting pointless hours of rendering. Always at the forefront of cutting-edge graphics technology, we do the rendering, the creativity is yours!

Thank you & Happy Rendering!

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Jenny Ha

Greeting everyone. I always hope to know more about 3D artists and share benefit information with them :)
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