Why do 3D animations take so long to render?

Rendering is a vital component in creating any animation. It’s part of the process that turns a 3D image into a video you can play on any device. Rendering for 3D animations can take a longer amount of time in comparison to 2D animation. When creating production timelines and schedules with clients we are regularly asked “why does rendering take so long?”. So, in today’s Quacking Tip we’re going to share our knowledge on what rendering is and why it takes time.

A brief introduction to 3D rendering

3D rendering is the process of taking a computer-generated 3D scene and producing a 2D image.

There are multiple programs that offer the ability to create a 3D scene, such as Autodesk Maya, Cinema 4D, Blender etc. These programs work with a render engine to calculate the final image.

3D Software Logos
3D Software Logos

At Colonel Duck, we mainly use V-Ray as our render engine. This uses ray tracing technology, which generates an image by tracing rays and simulates how the light interacts with the 3D assets within a scene.

It is much like how light works in the real word. If you shined a torch in a dark room, imagine rays of light coming from the torch, then bouncing off surfaces in different directions depending on the surface’s material/texture/colour. The effect is increased when interacting with translucent materials such as glass or water.

When the render engine runs, it first sends Primary Rays from the camera. These rays gather information such as lighting, shadows, reflection, refraction etc. They then react with objects they touch and Secondary Rays will them bounce out. This process is run for every frame within the animation. The more details and objects there are in a frame, the more information that the render engine has to process.

Ray Tracing Example

Let’s have a cooking lesson.

To understand where the render time comes from, we must first understand the process.

A 3D scene is built using some core elements – Polygons, Materials, and Lighting. The Polygons are the models themselves, the Materials are what give the models texture and colour and the lighting is what illuminates the scene.

Once these are in place, and any animation has been applied, we can start a render queue. Each frame will take a certain amount of time to render and once all images have been rendered they can be composited together to produce the final animation.

The time we have to wait for a render to complete depends on two factors.

1. How many ingredients were used.

– How many polygons are in the scene?
– What quality are the texture files?
– How many reflective and refractive materials are in the scene?
– How many lights are in the scene?

2. What temperature the oven is on.

– What quality do the final images need to be?


Let’s do a little maths

The time needed to render an animation can be misleading. Rendering a single frame may seem quite fast at first, but when you have a lot of frames to process, the time quickly adds up. There are usually 25 frames in one second of animation. It’s important to carry out some test renders not to be misled – one scene may take 1 minute to render, where another may have lots of reflective materials and take around 5 minutes to process, so be sure to work out the average.

With that in mind, let’s use an example average time of 1 minute to render a single frame.
The animation is 3 minutes in length (180 seconds) and we’re using 25 frames per second (fps).

180 (seconds) x 25 (fps) = 4500. That’s the total number of frames that are required for the animation.
4500 (total frames) x 60 (seconds it takes to render each frame) = 270,000 total seconds.

That’s 4500 Minutes / 75 Hours / 3.125 Days to render a 3 minute animation.

A one-minute render has quickly turned into over 3 days, this is why it’s paramount that calculations are done before submitting the render queue, especially when having set completion dates in mind.

You can always reduce the render time, but you do compromise on the quality of the final rendered image.

If you’re an animator, here are some ways to reduce your render time:


Removing unwanted models and materials

Compress your textures

Delete your history

Reducing your poly count

Use proxy models

Reduce your Global Illumination Primary and Secondary bounces

Tweak your Image Sampler and DMS sampler to best suit your scene

Rendering is a relatively long process, but it is easily manageable.

No one wants to be forced into a situation where you have to reduce the quality of your final animation, that’s why when working to a set completion date we make sure to be mindful of how long the animation is and leave plenty of time within the production process to render all of the required frames. We also leave any additional time within the production process for last-minute tweaks and changes that may require us to re-render.

If you’re interested in using animation in your marketing and communications and would like professional creative support, contact Colonel Duck below.

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