OSPRay renderer pro

OSPRay is a software-based ray-tracing engine, which can generate high-fidelity scene renderings including global illumination effects, shadows and depth of field (focal blur). The OSPRay renderer has a smaller memory footprint than the Tachyon renderer. It is thus suitable for rendering very large datasets with higher visual quality than the Standard renderer.

For more information on the capabilities of the OSPRay engine and its technical background, please visit the website https://www.ospray.org. The OSPRay documentation contains more in-depth information on this rendering engine’s various parameters.

The “More Options” (vertical ellipsis) button next to each numerical parameter opens a context menu with the option to reset each parameter to its default value.

The depth of field effect and the direction of the direct light source are specified on the Effects tab of the rendering page, because they apply to all rendering engines alike.

Quality settings

Refinement passes: OSPRay uses a progressive rendering method, which further refines the generated image during each rendering pass. This parameter controls the number of refinement iterations to compute (default value: 4).
Samples per pixel: The number of ray-tracing samples computed per pixel (default value: 8). Larger values can help reduce aliasing artifacts and will yield better results, especially if the depth of field effect is turned on.
Ray recursion depth: The maximum number of recursion steps taken during ray-tracing (default value: 10). Normally, 1 or 2 is enough, but when rendering many overlapping semi-transparent objects, a larger recursion depth may be needed.
Roulette depth: Ray recursion depth at which to start Russian roulette termination (default value: 5).
Denoising filter: Applies a denoising filter to the rendered image to reduce Monte Carlo noise inherent to stochastic methods such as path tracing.

Light sources

Direct light: Enables a directional light source positioned behind the camera and pointing roughly along the viewing direction. Its exact direction is set on the Effects tab of the rendering page. The angular diameter specifies the apparent size (angle in degrees) of the light source. Setting the angular diameter to a value greater than zero yields soft shadows. For instance, the apparent size of the sun is about 0.53°.
Ambient light: The ambient light surrounds the entire scene and illuminates it from infinity with constant radiance.
Sun-sky light: The sun-sky light produces the light typically coming from the sky and the sun in an outdoor scene. The radiance values are calculated using the Hošek-Wilkie sky model and solar radiance function. The zenith of the sky as well as the sun are positioned along the positive Z axis of the scene and are independent of the camera orientation.

Materials

The surface appearance of the rendered objects is determined by the materials assigned to them, which are managed on the Materials tab of the rendering page and are independent of the rendering engine. The OSPRay renderer translates the shading model of a material as follows: the Diffuse and Glossy shading models are rendered using OSPRay’s OBJ material, and the Physically based shading model is rendered using OSPRay’s Principled material, whose parameters (roughness, metalness, specular, index of refraction) map directly to the parameters of the OVITO material (see the documentation of OSPRay).

The table below shows how the Physically based shading model looks for different parameter settings. The Blender wiki also offers a good visual overview of the various parameters of this material model and how they affect the appearance.


Roughness: 10%	Roughness: 30%	Roughness: 50%
Metalness: 100%	Metalness: 10%	Metalness: 30%
Specular brightness 80%	Specular brightness 80%	Specular brightness 80%
Index of refraction: 1.0	Index of refraction: 1.0	Index of refraction: 0.1

Roughness: Controls the variation of microfacets and thus how polished the metal looks (default value: 30%). A value of 0% gives a perfectly polished mirror surface, while a value of 100% gives a completely rough surface.
Metalness: Gradually switches from a dielectric/diffuse material to a metallic material (default value: 10%).
Specular brightness: Controls the specular reflectivity of the dielectric/diffuse component of the material (default value: 80%).
Index of refraction: Controls the index of refraction (IoR) for specular reflection. For most materials, the IoR is between 1.0 (air) and 4.0 (germanium). Default value: 1.0