The render engine analysis series: Arnold

09.10.2017 Home >Blog >The render engine analysis series: Arnold

In this series, we take you through some of the different render engines on the market. There are plenty of them, all with their perks and downsides. This series explores Arnold, V-Ray, mental ray, and Redshift – all for Maya 2017. The lighting set up will be the same, and we’ll see if it’s possible to get the same results.

In this scene, our Render Wrangler Iris will use a HDRI for the overall lighting, four lights at the doors to mimic strong light falling through the door openings, and some extra small lights to highlight details or to light up the overall scene

Arnold was created by Solid Angle (now owned by Autodesk) and kindly named after Arnold Schwarzenegger; this render engine likes to keep things simple, like the lines in his movies. Because the system is based on the Monte Carlo algorithm, it relies on repeated random sampling to obtain numerical results. By using randomness, it solves issues that might be affected by external influences. What this means for us using the Arnold renderer is that light behaves with a certain randomness. It bounces at ever so slightly different angles, and drops off more naturally.

Monte Carlo ray tracing, or path tracing, renders a 3D scene by randomly tracing samples of possible light paths. Repeated sampling of any given pixel will eventually cause the average of the samples to converge on the correct solution of the rendering equation, making it one of the most physically accurate 3D graphics rendering methods in existence.

So let’s give it a go! I have taken an image of the barn I have modelled and I want to try to recreate this lighting set up.
3D Barn model

For this anlysis, I’m using Arnold We will start off with some global lighting. I like to start and recreate the natural light outside and see how far that gets us.

We start off with making an AiSky and an AiSkydome light. I do both, so that you immediately get a background for your renders, but it is a personal preference. You can also only create a AiSkydome light. Attach the HDRI to the colour channel. Make sure the format is set correct, as usually it is a latlong image. This setup will give you nice colours in your light, and a very decent result for one light source.

I have raised the resolution to 3000 and in my scene raised the exposure to 2.0. Raising the exposure with one stop will give you double the amount of light. So, if I go from one to two, I get double the light. If I then go from 2 to 3 it will double the light from 2 again so basically you get 4 times the light from stop 1. I am not going to worry about grain or anything. We will work from big to small, global lights and then detailed lights. After that we will have a look at the render settings.

I am keeping one of my doors in the checker texture so I can see the colours of the light and such. Later on, I will change the texture on the door when I am happy with how the light looks.

Time for a first render.

As you can see, it is a fairly decent result. Still quite dark.

Let’s add some more light. I think we can use some more light from the door opening, so I will add 4 AiArealights. I have made them as big as the doors to make it as natural as possible. As my Aiskydome is at exposure 2.0 I will raise these a bit more to 4.0.


Not a huge change but enough to cast some light on the walls and have some bounce light on the ceiling.

I am going to raise the Aisky with one stop to 3.0.

I am quite happy with this result for now. I see that in the original barn there are a few small windows that allow light to come in. These are not in my model, but I will cheat a bit and put in some small area lights.


Looking at the original image, a flash has been used and it is quite strong. I have added a light above my camera but the difference is hardly noticeable. I have also given my small lights a bit of colour so they look a bit warmer.

At this point, I’m quite happy with the render but it is still pretty dark. When using Arnold, you will often see people adjust the gamma to 2,2. I am going to do this as well to see what difference that makes.

This now makes an enormous difference and all of a sudden, the warm sunlight from the left is nice and bright, the bounces reveal a bit more of the roof. There is only the bit in the middle that I find too dark. I have added a couple of lights, just 3 AiArealights on 0.5 exposure, with a mild brown/yellow tint to the light. This creates that bit of extra light in the tip of the roof but leaves enough shadow.

I have also played a bit with some rubble and my wall texture. Did you spot that?

Now we are going to have a look at the render settings as we can reduce the noise for quite a bit here. Keep in mind that changing these settings will up the render time a lot. My average render time was about 2-3 minutes, but we are going to go increase that dramatically.

In the render settings, go to the Arnold tab and look at the AA sampling. By increasing the samples, the light get calculated more accurately. Arnold collects information from the scene geometry, shaders, lights, etc., and traces a number of random light transport paths that connect the objects. It then calculates the result per pixel. The quality of the image largely depends on the number of samples, generated for each pixel. Autodesk has a great explanation on this subject which you can read here.

I have raised my samples to 8 and my diffuse to 4. All the other channels I have put down to 0 as I am not using glossy materials: no refraction, subsurface scattering, or indirect volume. If you are using these things in your scene, I would recommend testing them individually to see how much difference they make, and how much they increase your render time. Try to find a balance between the result and your render times.

I have rendered my one frame on a HD_540 res (970*540), and with the increased sampling my render took 97 minutes on an 8 core machine. It gives me a very crisp look, and I would even consider going down a bit just to get a more efficient render time.

I am lowering my settings to 6 samples and 3 diffuse. 90+ minutes for me is really too long for just one still frame. I have also toned my lights down a bit in the front as I don’t like the brightness of the floor and then the dark shadows in the middle.

I think the result is ok-ish but I am not completely happy with it. I think I will stick to the 8 samples as it is overall just crisper.

What do you think of the way that we lit and rendered this still? Do you find Arnold easy to use? Hate using Arnold to render but learnt something new that should help you? Make sure you read our results to see which render engine is best for you!



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