Corona Renderer for 3ds Max – How to Render Faster (Part 3)

In parts 1 and 2 of this article series, we explored how to properly handle materials and lighting. In part 3, we’ll focus on the final essential factor: settings. Corona’s settings are relatively minimal, mainly located within the Performance section of the Render Setup panel. The default settings work well in most cases, and it’s generally best to leave them unchanged if everything is running smoothly.

However, there are instances where adjusting settings can yield significantly better results, which we’ll discuss in this section. As in previous parts, we can also check noise sources by rendering without materials. When you feel that, despite having well-configured lighting and materials, the render still has excessive noise and takes a long time, it’s time to start fine-tuning the settings.

It’s important to understand that adjusting settings in Corona always involves trade-offs: gaining in one area often means compromising in another. Therefore, when customizing settings, it’s essential to know exactly what you’re doing and what you need; otherwise, you may even end up reducing render speed.

Corona Renderer for 3ds Max – How to Render Faster (Part 3)

Max Sample Intensity (MSI)

Max Sample Intensity (MSI) is a parameter that defines the maximum brightness of secondary GI samples. Apologies for the somewhat complex introduction, but I couldn’t find a clearer way to express it.

This parameter affects the balance between render speed and the physical accuracy of the image. A lower MSI value will produce less noise and faster renders, but the rendered image will appear darker, with lower reflection intensity and weaker caustic effects.

On the other hand, a higher MSI value will result in a brighter render, slower render times, and stronger reflection and caustic effects, but it may also introduce more noise to the image.

The default value of 20 works well in almost all cases. However, in some situations, we can trade accuracy for performance by lowering the MSI to increase render speed, especially in scenes with many glass, mirrors, or similar reflective materials.

I usually set MSI to 5 or 10 for scenes that feel “dry,” meaning those with few reflective objects. Note: do not set MSI to 0.

Light Samples Multiplier (LSM)

The Light Samples Multiplier (LSM) parameter controls the number of direct light samples for each GI sample. Essentially, LSM is a unitless parameter closely related to the GI vs. AA balance setting, which we’ll cover in the next section.

This setting affects the balance between render speed and the quality of direct lighting.

• A lower LSM value renders faster but results in more noise in direct lighting. I usually set this parameter to 1 for quick test renders.
• A higher LSM value renders more slowly but improves the quality of direct lighting. However, it’s generally best not to set this value higher than 4, as it significantly increases render time without much quality improvement.

To check the quality of direct and indirect lighting, we can add two channels, CESSENTIAL_Direct and CESSENTIAL_Indirect, in the Render Setup > Elements panel. If the CESSENTIAL_Direct channel exhibits more noise, increase the Light Samples Multiplier, and vice versa.

Like other parameters, the default LSM value of 2 works well in most cases. However, in certain situations, we can adjust this value up or down (trading quality for speed) to achieve faster or better renders.

GI vs. AA Balance

The GI vs. AA balance (Global Illumination versus Anti-Aliasing balance), often abbreviated as GIvsAA, is a parameter that balances GI and AA. A higher value means more emphasis on GI (global illumination), while a lower value gives more priority to AA (anti-aliasing). Essentially, it dictates the number of GI samples within each anti-aliasing sample.

When GIvsAA is higher, the lighting will have noise reduced more quickly (more GI). Conversely, when GIvsAA is lower, effects such as Motion Blur, Depth of Field, and Anti-Aliasing will have their noise reduced more quickly (more AA).

Like other parameters, the default setting of GI vs. AA = 16 works well in most cases. We can adjust this parameter up or down (trading off GI and AA) to achieve faster or higher-quality renders. If indirect lighting in the scene produces excessive noise, increase GIvsAA. If the render shows aliasing or has strong effects from Motion Blur or Depth of Field, decrease GIvsAA.

To check the quality of direct and indirect lighting, we can add two channels, CESSENTIAL_Direct and CESSENTIAL_Indirect. If the CESSENTIAL_Indirect channel has more noise, increase the GI vs. AA balance, and vice versa.

Note that you should never lower GIvsAA below 2 (which results in poor quality) and should not increase it beyond 64 (as it will lead to excessively long render times). I typically set this parameter to 8, as I rarely use camera effects.

Max Ray Depth

Max Ray Depth is a parameter that indicates the number of times light can bounce. Reducing this value will improve render performance at the expense of image realism. For example, when two mirrors are placed opposite each other, Max Ray Depth refers to the number of reflections before the light becomes black.

I typically set this parameter to 15, as it slightly reduces render time without significantly affecting image quality.

Balancing GI vs. AA Balance and Light Samples Multiplier

The total number of samples per pixel for each pass in a render depends on LSM (Light Samples Multiplier) and GIvsAA (GI vs. AA balance). The more samples you have, the less noise will appear, but the render time will increase significantly. Therefore, to improve quality without increasing render time, we need to balance the total number of samples to avoid excessive increases and decide whether to prioritize GI samples or direct light samples in the render view.

The number of direct light samples is calculated as follows:

Number of direct light samples = Number of GI samples (GIvsAA) x LSM:

• If LSM = 1 and GIvsAA = 16, there will be 16 GI samples and 16 x (LSM) 1 = 16 direct light samples.
• If LSM = 2 and GIvsAA = 16, there will be 16 GI samples and 16 x (LSM) 2 = 32 direct light samples (default).
• If LSM = 2 and GIvsAA = 32, there will be 32 GI samples and 32 x (LSM) 1 = 64 direct light samples.

For example, in a scene where LSM = 1 and GIvsAA = 16, if the direct light is very noisy while the indirect light is not, we can increase LSM to 2 and reduce GIvsAA to 10. This will result in 20 direct light samples + 10 GI samples (instead of 16 direct light samples + 16 GI samples), improving overall speed and quality of direct light at the cost of global illumination quality.

Using Highlight Clamping to Reduce Noise

Highlight Clamping is a feature that limits the intensity of pixels within a certain range before they are sent to the frame buffer. This can help reduce both benign noise and fireflies, as well as minimize aliasing around the edges of bright areas, at the cost of some image realism.

Set up Highlight Clamping in Render Setup > System > Frame Buffer > Image Filter. The default value is 0 (disabled). Refer to example images to understand how Highlight Clamping works. Note that Highlight Clamping should not be confused with Highlight Compression.

Resetting Corona Settings to Default

It can be great to have control over the parameters in Corona; however, after a period of experimentation that does not yield satisfactory results and may even slow down render times, resetting the settings to default might be the best and safest option at this point.

To reset a parameter in Corona, right-click on the increment/decrement arrows next to the parameter. Instead of resetting to 0 like in 3ds Max, the parameter in Corona will reset to its default value. If you want to reset all parameters, go to the Render Setup, select the Scene tab, and click Reset Settings.

Written by Dang Tien Dung

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