March 29, 2023 Maddie Quach

Houdini Render Optimization Tips

With its generative node-based workflow, Houdini FX offers a potent and approachable 3D experience and includes tools for simulating fluids, destructive effects, and many more. In this article, let’s learn some useful render optimization tips for Houdini render.

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Disable the Use Max Processors

Houdini uses all of the processors by default to speed up rendering. You can disable the Use Max Processors checkbox on the Render sub-tab of the Rendering tab of the render node if you do not want to use all processors. If you disable this option, you may choose how many processors to utilize by setting the Thread Count.

By speeding up rendering, lowering the Volume Step Rate on the Rendering => Sampling sub-tab mantra render node reduces mantra’s capacity to discern fine information in volumes.

Altering the Motion Factor value

Try adjusting the Motion Factor value, which is found on the Dicing sub-tab of the Rendering tab of the mantra output node, if you are using either depth of field or motion blur. This setting dynamically regulates the shading quality. You can alter the depth of field and/or motion blur levels by lowering the shading quality, which will consume less memory and shorten render times.

Limiting the number of lights

Limiting the amount of lights to look up will correspondingly lower render times since, with micropolygon rendering, each shader call will loop through all the lights illuminating the current micropolygon in the volume.

Rendering times will also be sped up by employing deep shadow maps and using less lights. You might just want one or two lights with this option switched on and the other lights not using shadows because deep shadows offer you depth. Your volume rendering will take longer if you utilize the Environment Light from the shelf with your volume objects since each shaded micropolygon will generate a disproportionately large number of rays as a result of the raytraced ambient occlusion.

Enabling the Active Radius parameter

Enabling the Active Radius parameter on the light object and setting it to the maximum radius of effect for that light will speed up renders for lights that only affect a portion of the displayed scene. Shaders will completely disregard a light source when they are executed outside of the active radius, speeding up rendering. This option is especially helpful in situations when there are plenty of little light sources, like in a scenario with lots of external street lights.

Use Opacity Limit effectively

The opacity limit can be used to stop the current ray if the required level of transparency is reached when rendering geometry. On the Rendering tab of the mantra output node’s Limits sub-tab is where you’ll find the Opacity Limit setting.

When utilized too aggressively, if the camera moves or the smoke changes, you will notice flickering and odd banding in your volume across a series of renders. This is the fluctuating opacity thresholds in the volume, which is more noticeable if your volumes are more transparent and wispy. Changes to the Opacity Limit will only result in a 1%–5% reduction in render time. Be careful to avoid introducing unnecessary artifacts because the default value is already rather aggressive.

Opaque shaders 

When shaders that it is aware are entirely opaque, Mantra especially enhances the rendering performance (both ray tracing and micropolygon rendering). Make sure that opaque shaders either deactivate all shader/material settings that would make the shader transparent or set the opacity (Of) VEX variable to a constant of “1,1,1” to enhance rendering performance.

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Maddie Quach

Hi everyone. Being an Customer Support from iRender, I always hope to share new things with 3D artists, data scientists from all over the world and learn from them as well.


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