Satellite interior scene rendered with an Ai Area light
- Converting to Arnold Shaders
- Setting up an Environment
- Lighting the Scene
- Setting Sampling Values, Ray Depths, and Clamping
- Adding Atmosphere Volume
- Rendering the Final Image
We will also look at how to identify the source of noise when rendering an interior scene by using AOVs. Be aware that each interior scene is different and has its own unique lighting and rendering challenges. While this tutorial tries to use generally used techniques, they may not be appropriate for all interior scenes.
More information about sampling can be found here.
The original Maya scene files for this series of tutorials can be downloaded from Autodesk's Hyperspace Madness production.
- Open the satellite scene file. You will see that it comprises of an outer body, door and interior (selected below).
- Hide the rest of the objects so that you are left with just the satelliteInterior group.
- Replace the mental ray shader mia_material_x_passes called Interior with a Standard Surface shader.
- Create an Ai Area light. Change the Light Shape to Disk and position it so that it is pointing through the doorway as in the image below.
- Increase the Exposure to around 18.
- Render the scene with light Samples set to 1 and then with 3. You should notice that some of the noise is improved. However, in general, it is difficult to tell if the noise is coming from the light or from elsewhere.
Light Samples: 1 Light Samples: 3
If we set Diffuse and Specular samples to 0 (disabling them) we can isolate the direct lighting and better identify what effect increasing the number of Light samples has on the scene. Open the Render Settings window and under Sampling, set Diffuse and Specular samples to 0. Disabling Diffuse and Specular samples (0) helps to identify light any sampling issues. This is visible in the images below.
Light Samples: 1 Light Samples:3
This tutorial uses an Ai Area light with its Light Shape set to Disk. However, when rendering interiors with square windows you would be better off using a Quad light. The Quad light also has a Spread attribute that allows for focusing illumination along the light direction. This can be useful when rendering interior scenes. The images below show the difference in rendering this scene with different Spread values.
? Spread: 1 Spread: 0.5 Spread: 0.25?
The animation below shows the effect on the interior lighting when decreasing the lights Spread attribute.
Quad light 'Spread': 1 to 0.25
Even though we have increased the number of Light sample settings, we still have noise. We can try and resolve this by adjusting the Sampling values. Careful consideration must be taken when increasing these values as it can have a big effect on render times. A quick and easy way to identify where the noise is coming from and therefore which samples to increase is by rendering out AOVs.
More information about sampling and removing noise can be found here.
Render the scene with the Arnold Renderview window. You should see the Beauty render being rendered by default. You can change which AOV that you wish to see by clicking on the drop down menu or by going to View> AOVs.
On closer inspection of the AOVs we can isolate and identify more clearly where the noise is coming from in the scene. There is little noise visible in the direct_diffuse and direct_specular AOVs because we have already increased the number of direct Light samples. However, there is much more noise visible in the indirect_diffuse and indirect_specular AOVs. Therefore, we will need to increase the Diffuse and Specular samples respectively.
The images below show the AOVs visible in the Arnold Renderview window.
Camera (AA) Samples
We can try increasing the number of Camera (AA) samples to help resolve some of the noise in the scene, however there is still noise visible in the indirect diffuse and specular areas.
Camera (AA) Samples: 3 Camera (AA) Samples: 6
The images below show the difference when increasing the number of Diffuse Samples.
Diffuse Samples: 2 Diffuse Samples: 4
Remember that the Diffuse sampling is done for each AA sample, so high values for both AA Samples and Diffuse Samples will tend to result in slow renders.
Ray Depth allows you to configure settings that limit the ray recursion based on ray type. Higher values will increase render time.
Take care when increasing ray depth values. Increasing a ray depth value by one could effectively double your render time.
This defines the maximum ray diffuse depth bounces. Zero diffuse is equal to disabling Diffuse illumination. Increasing the depth will add more bounced light to the scene, which can be especially noticeable in interiors. You may notice subtle differences when increasing the diffuse bounces incrementally in the images below.
Diffuse Ray Depth: 0 (direct light only)
Diffuse Ray Depth: 1
Diffuse Ray Depth: 2
Diffuse Ray Depth: 3
To add some atmosphere to the scene, you could try adding some Atmosphere Volume to the scene.
- Go to the Environment tab of the Render Settings. Connect an Atmosphere Volume to the Atmosphere attribute.
- You will not see any result if you render the scene. That is because the Atmosphere Volume Density is 0 by default. Increase it to 1 and IPR render the scene.
Adding Atmosphere Volume has introduced some fireflies into the render. We can try to reduce them by increasing the number of Atmosphere Volume Samples.
More information on how to deal with fireflies can be found here.
However, even after increasing the number of Atmosphere Volume samples, there still remain some fireflies.
Atmosphere Volume Samples: 5 Atmosphere Volume Samples: 20
The images below show the effect on the fireflies when reducing the Max Value.
Max Value:10. Fireflies visible. Max Value: 1. No fireflies.
Rendering the Final Image
Open up Sampling in the Render Settings Window. For test rendering Camera (AA) samples at 3 is fine. However, for final frame rendering you will want to increase it to at least 5. In this case Diffuseand Specular were set to 6.
A simple guide to sampling can be found here.
When rendering scenes with MtoA it is a good idea to get familiar with the Arnold Log in the Diagnostics tab of the Render Settings window. This log file will show you any warnings and statistics which will help you diagnose your scene file.
Thats it. Congratulations, you have successfully converted a scene from mental ray to MtoA! Now go out there and explore new worlds of rendering!
More information about lighting an interior room scene can be found here.