Presto/IR Settings

The settings for the Presto/Interactive Rendering engine.

Note: Presto GPU support for macOS 10.14 (Mojave) and above is unavailable due to driver incompatibility. In this case, CPU is used.
Select this option if you plan to create multiple renderings of an animation or lighting study. Options to change the emitter power and color will be available during post-processing.
Tip: We recommend turning off Relight when only a single rendering is needed because of its high demand on memory. During initialization, multiple buffers—one for each light group—are allocated for blended results in the animation sequence. Since each of these light buffers must converge, the overall convergence is slower than when rendering into a single buffer (where a bright emitter may quickly hide noise from a dim one).
Important: Relight is only available with the Render in Darkroom tool. It's not available with the Render tool, even if you select Continue rendering in Darkroom.
Reduce the amount of noise/grains in the final rendered image.
  • None (default)
  • Optix: To use Optix, you need a NVIDIA GPU with a computing capability of 3.0 or higher and a driver version of 450.00 or higher.
    Note: For RTX graphics cards, the NVIDIA drivers need to be higher than 418.81.
  • Intel: This open denoiser uses CPU and works with all graphic cards.
Note: To turn off the denoiser for interactive rendering, deselect Denoise Interactive Render.
There are noise/grains around the bottom of the car, as indicated by the red arrows.
After applying a denoiser, noise/grains have been removed.


Tracing Depth
Define the maximum number of bounces a ray will have (diffuse, reflection, etc.).
Increase the value for a more accurate visualization, or decrease it to reduce rendering time.
Transparency Depth
Calculate how many rays can pass through a transparent object. The Transparency Depth value is added to the Tracing Depth value.
Increase the value to minimize black artifacts on transparent objects.
Internal Reflections
Control the amount of reflection inside transparent objects. The Internal Reflections value is added to the Tracing Depth value.
Increase the value to minimize black artifacts on transparent objects.
SSS Depth
Calculate the subsurface scattering effect. When light enters the surface of a translucent object, it interacts with the material and becomes scattered, exiting the surface at a different point. Subsurface scattering is important when you render materials like wax, skin, leaves, and milk. The SSS Depth value is added to the Tracing Depth value.
Increase the value to increase the accuracy of the subsurface scattering effect.
Ambient Light
Observe the uniform non-directional illumination created in the environment by ambient light.
Shadow Radius: Define the maximum distance that the sample may be evaluated as an intermediate (gray) color. After that distance, the sample is evaluated as a white color.
Intensity: Define the intensity of the ambient occlusion used.
Full Caustics (CPU Only)
Select this option to achieve a more accurate visualization of refraction and reflection. For example, you can use this option to render the shimmering waves of light at the bottom of a swimming pool.
Adaptive BIAS (%): By increasing this value, difficult-to-evaluate light paths are given lower weight, resulting in less noise on the image and faster overall convergence. Nevertheless, due to this lower weighting, the image may lack some lighting and appear having a smaller dynamic range.
Adaptive Tracing
Select this option to solve difficult lighting situations to reduce noise, such as fireflies, indirect lighting, and caustic lighting. Typical use cases include an interior scene that is lit from the sun coming through small windows or scenes with lots of glass that generates caustics or pool caustics.
Clamp Firefly: Adaptive Tracing should remove most fireflies. Use this clamping option with care, as it tends to make the scene look less realistic. Enter a Value to limit the brightness in the scene to remove fireflies. Fireflies are ultra bright pixels that appear as isolated noise as a result of sparsely generated light paths. They are more prominent when both Sharpness and Burn filtering effets are turned off in the Darkroom display settings.

Figure 1. Fireflies appear around the sphere's edge

Figure 2. Most fireflies are removed using Adaptive Tracing
Diffuse Interreflection
Select this option to increase the accuracy of global illumination when using Progressive AO.
Diffuse Depth: Control the maximum number of diffuse bounces.
In general, use a value of 1 or 2 to minimize rendering time while achieving an accurate global illumination. Higher values increase the rendering time.
Note: The maximum Diffuse Depth value is equal to the Tracing Depth value. Any number larger than that will have no effect on the final image.
Super Sampling
This feature determines how each pixel of the image is subdivided in order to calculate its real color. Selecting a higher setting will increase the quality of the rendering details, but it will also increase the rendering time and the amount of memory used during the rendering.
  • Auto (default): Automatically set Supersampling to None for interactive rendering and to Normal for final rendering.
  • None: No super sampling.
  • Normal: Render the image at a higher resolution (2x2).
  • High: Render the image at a higher resolution (3x3).
Bucket Rendering
The image will be rendered in small square parts rather than all together. This option is useful when rendering very large images that would require a huge quantity of memory using the normal rendering.
Note: Only use bucket rendering for final rendering.
Time Limit (min)
Enter 0 for no limit.
Max Samples
Control how many times each pixel will be calculated and refined. This is useful for producing an animation because you can make sure each frame that is rendered has the same quality.
Enter 0 for no limit.
Select which of the available graphics cards and CPUs you'd like to use for rendering.
If selected, CPU will be used in the Interactive rendering calculation.
Restore Default
Click this button to restore the default settings for the Presto/Interactive Rendering engine.


Create an opaqueness grayscale image with respect to the background. A black color corresponds to no opaqueness (background is fully visible) while a gray color corresponds to partial opaqueness.
Ambient Occlusion
This feature calculates how much light hits a point of the object. For example, enabling this option will cause objects to appear closer and corners in the wall to appear darker.
Depth Channel gives the depth (distance along camera Z-axis) of the first hit objects in the scene. The depth values will be mapped afterwards to a gray-scale image according to Min/Max Z.
Display direct lighting.
Global Illumination (GI)
Display global illumination.
Invert Mask
Display indexed objects in black and other objects in white.
This channel, shows the Irradiance, computed by photon mapping and final gathering and interpolated using the Irradiance Cache (if used). This channel is used in conjunction with illuminance photometric analysis (see next table).
Mask selected objects/groups and create masks for post-processing processes.
Material ID
Display each material in a distinct color.
Stores the normals of the first hit objects in the scene. Black is assigned to vector (-1,-1,-1), while white is assigned to vector (1,1,1). Due to the normalization of surface normals, these values are never reached; instead we get intermediate colors.
Object ID
Display each object in a distinct color.
Display the position of each point of the scene regarding the global frame; useful for post-processing purposes.
Raw Diffuse Color
Display raw diffuse color (all materials diffuse color).
Raw Diffuse GI
Display raw diffuse global illumination (not multiplied by the diffuse color).
Raw Diffuse Lighting
Display raw diffuse lighting (not multiplied with the diffuse color of the scene).
Display reflections.
Display refractions.
Display self-illumination.
Render shadows separately. When used in conjunction with other channels like Mask or Object ID, Shadow can produce effects like objects with shadow in .png format at the post-processing stage.
Subsurface Scattering (SSS)
Display subsurface scattering.
Display transparency (thin film like glass, alpha mapping transparency).
Display the UV coordinates of objects in the scene.