MAXtoA provides some automatic, optimized, image-based lighting (IBL) from the Environment map you provide in the Environment & Effects dialog box (Rendering -> Environments or press 8), along with manual control of the Environment and Background.
The environment options can operate in two modes:
This mode sets the scene up in an optimal way for standard usage scenarios. The scene environment is used to provide illumination and reflections to the scene and the background color/map provides a backplate to the camera. In this mode, MAXtoA automatically places a hidden Skydome in the scene to provide improved and faster IBL rendering.
This mode enables full customization for the behavior of both the environment and background. In this mode, you have access to the parameters of the automatically-created Skydome and can adjust or even disable that feature. It still uses the Environment map defined in the Environment/Effects dialog box. In Advanced mode, if the Background is set to Scene Environment, you can control how the Background is visible to the camera and other scene elements.
You can view more information about these parameters on the Skydome light page.
Controls the quality of the noise in the soft shadows and direct specular highlight. The higher the number of samples, the lower the noise, and the longer it takes to render. The exact number of shadow rays sent to the light is the square of this value multiplied by the AA samples.
A schematic of how light noise occurs in Arnold
Note that setting light samples to 0 disables the light.
Noise from lights can sometimes be difficult to diagnose, particularly if the light source is broad in comparison to the scene and the shadows have an extremely wide penumbra. In these cases, it can sometimes be mistaken for indirect diffuse noise. It highlights the necessity for testing noise ray type. This diagram shows how light is traced in Arnold.
The example below shows specular highlights from area light sources. There are four spherical mesh light sources of varying sizes and color temperatures. Underneath are four cubes with Standard shaders assigned to them with varying degrees of specular roughness. Note that more noise is apparent with smaller light sources. Increasing the number of light samples resolves the noise.
Specular roughness from top to bottom: 0, 0.1, 0.2, 0.3
If the issue is noise in a specular highlight, you will need to confirm that the source is the direct light and not a secondary ray type (such as specular). This is easy to achieve by turning off global illumination; set the Diffuse Depth and Specular Depth to zero (this essentially turns off all global illumination). If the noise is still there, we know it is the specular component of the illumination model. If the issue is shadow noise, then we can simply toggle ignore shadows in the Arnold render settings, and the noise will completely resolve.
The key, again, is to modify the sampling and observe the changes. Increasing the number of light samples should have an immediate and quantitive effect on the smoothness of the specular highlight and the shadow. If there is no change, light samples are not responsible for the noise.
Multiple importance sampling (MIS) is enabled by default in Arnold. The images below show the difference when rendering with and without multiple importance sampling.
Background is considered deprecated and will be removed in a future release.
The Background image can be the same as the Environment (default), or you can choose to use a solid color or a custom Map/shader that you can control through the Material Editor by dragging it into the Slate editor.
The background is visible to the camera and through transparent objects. You can select the source for the background color using the following options:
- Scene Environment uses the settings from the scene environment panel.
- Custom Color provides a custom color that is different from the environment settings.
- Custom Map provides a custom texture map that is different from the environment settings.
- Custom Arnold Shader gives the option to add a custom Arnold shader (such as the ray_switch shader).
Choose which rays you want to make the background visible to.
This light is designed for outdoor scenes and is represented by a spherical dome in the background. Multiple importance light sampling will trace rays to specific directions of this dome. However, in an interior scene, most of these rays will hit an object, getting no contribution from the light at all and thus creating noise. In this situation, adding light portals to the windows will help to reduce noise in an interior scene when using Skydome lighting.
There are two types of atmosphere in Arnold, fog, and atmosphere_volume. Fog simulates the effect of light scattering, which causes more distant objects to appear lower in contrast, especially in outdoor environments. Atmosphere_volume simulates light scattered by a thin, uniform atmosphere. It produces shafts of light and volumetric shadows cast from geometric objects.
It is not possible to render both fog and atmosphere_volume in the same scene.
More information about atmosphere shaders can be found here.