View source for Render Optimization

[[Category:Rendering]]
Render optimizations are methods and techniques that aim to improve render times, render quality, or sometimes a combination of both. These include modifying the behavior of the [[Render Engine|engine]] or modifying the scene itself.

== Optimizing Scenes ==

In many cases, optimizing the actual scene itself can improve render times or quality. Some of these include:

* Reducing geometry, or optimizing topology (e.g. using [[Quad|quads]] instead of [[N-gon|n-gons]])
* Reducing texture sizes (e.g. using 2K textures instead of 4K)
* Adequate routes for light paths (e.g. large gaps)
* Avoiding complex materials or adjusting materials to behave differently (e.g. [[Archviz Glass|archviz glass]])
* Reducing resolution of the final render
== Optimizing Engine Behavior ==

Often times optimizing an engine's behavior can also allow for reducing render times or scene quality. Some examples include:

* Limiting light bounces, or even approximating lighting through alternate means
* Adjusting sample count for [[Render Engine#Ray_Tracing|ray tracing]] engines, often in conjunction with [[Denoiser|denoising algorithms]]
* Adjusting shadow resolution for [[Render Engine#Rasterization|rasterized]] engines

== Software/Engine Specific Recommendations ==

The following are recommendations for specific programs or render engines. Depending on the scene, these may or may not need to be adjusted.

=== Cycles (Blender) ===

Although [[Cycles]] is one of the faster path tracing engines, there's some options that can be adjusted for performance.

==== Sampling ====

Beyond adjusting the sample count, there are alternate settings in Cycles specifically related to sampling. In particular, adjusting [[Adaptive Sampling|adaptive sampling]] settings to kick in earlier on can reduce render times, at the cost of more noise.<ref>https://docs.blender.org/manual/en/4.4/render/cycles/render_settings/sampling.html#adaptive-sampling</ref> Setting the noise threshold to <math>0.03</math> instead of <math>0.01</math> may be a good compromise of quality and render times.

Another sampling related setting in Cycles is [[Light Tree|light tree]], which reduces noise in scenes with a large amount of lights<ref>https://docs.blender.org/manual/en/4.4/render/cycles/render_settings/sampling.html#lights</ref>. Note that issues may result from overlapping area lights, though this may be a bug.<ref>https://projects.blender.org/blender/blender/issues/141576</ref>

==== Light Paths ====

Adjusting light path settings can also be another source of performance and/or quality improvement. This can be in the form of adjusting light bounces, volumetric stepping, or clamping bright pixels.

By default, Cycles sets its max light bounces to <math>12</math>, which may be excessive in many cases. Lowering to <math>8</math> often creates little to no difference, while reducing render times.

Some scenes may allow for reducing max light bounces further down to <math>4</math> or even <math>3</math>. However, it should be noted that adjustments the range of <math>1</math> to <math>5</math> typically introduce larger changes to the scene than higher ranges.<ref>[https://youtu.be/8gSyEpt4-60?t=307 Blender Guru: 18 Ways to Speed Up Cycles Rendering - Reduce Light Bounces]</ref>

<tabber>
|-|Forest Scene=
<gallery mode="packed" heights="400px">
File:Adaptive Sampling Example - Noisy Image.jpg|8 light bounces|alt=Noisy image of a forest scene
File:Adaptive Sampling Example - 4 Bounces.jpg|4 light bounces|alt=Noisy image of a forest scene
File:Adaptive Sampling Example - 3 Bounces.jpg|3 light bounces|alt=ENoisy image of a forest scene
File:Adaptive Sampling Example - 2 Bounces.jpg|2 light bounces|alt=Noisy image of a forest scene
File:Adaptive Sampling Example - 1 Bounce.jpg|1 light bounce|alt=Noisy image of a forest scene
File:Adaptive Sampling Example - 0 Bounces.jpg|0 bounces (direct light only, no global illumination)|alt=Noisy image of a forest scene
</gallery>

|-|Interior Scene=
<gallery mode="packed" heights="400px">
File:Interior Bounce Test - 8 Bounces.jpg|alt=Interior scene with 8 light bounces|8 light bounces
File:Interior Bounce Test - 4 Bounces.jpg|alt=Interior scene with 4 light bounces|4 light bounces
File:Interior Bounce Test - 3 Bounces.jpg|alt=Interior scene with 3 light bounces|3 light bounces
File:Interior Bounce Test - 2 Bounces.jpg|alt=Interior scene with 2 light bounces|2 light bounces
File:Interior Bounce Test - 1 Bounce.jpg|alt=Interior scene with 1 light bounce|1 light bounce
File:Interior Bounce Test - 0 Bounces.jpg|alt=Interior scene with 0 light bounces|0 light bounces
</gallery>
</tabber>

In addition to max light bounces, there is also stepping rate and max steps. Stepping rate defines how many "steps" is performed in a volumetric object, where lower values allow for more detail, at the cost of render time, and max steps defines how many steps Cycles will perform for volumes before giving up<ref>https://docs.blender.org/manual/en/4.4/render/cycles/render_settings/volumes.html</ref>. Depending on the scene, the default value of <math>1</math> may be excessively low, and increasing the rate may allow for performance improvements. In addition, decreasing max steps may also improve render times, at the cost of detail.

Like many path tracers, Cycles includes options to clamp the brightness of pixels caused by both direct and indirect bounces. When set to <math>0</math>, no clamping is done<ref>https://docs.blender.org/manual/en/4.4/render/cycles/render_settings/light_paths.html#clamping</ref>. While clamping direct lighting is usually not necessary, clamping indirect lighting may reduce the amount of [[Firefly|fireflies]] created when rendering. However, clamping indirect can often reduce the brightness of highlights on reflective objects.

Cycles also includes options to disable caustics.<ref>https://docs.blender.org/manual/en/4.4/render/cycles/render_settings/light_paths.html#caustics</ref> However, disabling these will drastically change lighting if a scene contains many reflective objects, and should be considered a last resort in most cases.<ref>[https://youtu.be/8gSyEpt4-60?t=1331 Blender Guru: 18 Ways to Speed Up Cycles Rendering - Clamp it]</ref>

Fast GI approximation can also improve render times<ref>https://docs.blender.org/manual/en/4.4/render/cycles/render_settings/light_paths.html#fast-gi-approximation</ref>, though it can also drastically change how a scene looks.

<tabber>
|-|Forest Scene=
<gallery mode="packed" heights="400px">
File:Adaptive Sampling Example - Noisy Image.jpg|Without Fast GI|alt=Noisy image of a forest scene
File:Adaptive Sampling Example - Fast GI after 1 bounce.jpg|Fast GI approximation after 1 light bounce|alt=Noisy image of a forest scene
File:Adaptive Sampling Example - Fast GI after 2 bounces.jpg|Fast GI approximation after 2 light bounces|alt=Noisy image of a forest scene
</gallery>
|-|Interior Scene=
<gallery mode="packed" heights="400px">
File:Interior Bounce Test - 4 Bounces.jpg|alt=Noisy image of an interior scene|Without Fast GI
File:Interior Bounce Test - Fast GI after 1 bounce.jpg|alt=Noisy image of an interior scene|Fast GI approximation after 1 light bounce
File:Interior Bounce Test - Fast GI after 2 bounces.jpg|alt=Noisy image of an interior scene|Fast GI approximation after 2 light bounces
</gallery>
</tabber>

==== Shaders ====

In Cycles, certain shaders often create additional noise in a given scene. For example, a glass shader may create additional noise due to the calculation of caustics, leading some to create workarounds (such as archviz glass).

Like glass, the emission shader is often linked to increased noise.

Alpha transparency may introduce slow down when rendering as Cycles has to execute an object's shader trace a ray when hitting a transparent portion.<ref>https://docs.blender.org/manual/en/latest/render/cycles/render_settings/light_paths.html#transparency</ref> In cases where many objects with alpha transparency overlap, such as leaves or grass, it may be beneficial to remove the transparent portions. <ref>[https://youtu.be/8gSyEpt4-60?si=yKZp6k1iYtFfiVPH Blender Guru: 18 Ways to Speed Up Cycles Rendering - Remove Alpha Transparency]</ref> However, it's possible that any performance improvement is negated by the cost any additional geometry needed to remove alpha transparent faces.

Volumetric shaders may introduce additional noise and render time.<ref>[https://youtu.be/8gSyEpt4-60?t=1931 Blender Guru: 18 Ways to Speed Up Cycles Rendering - Remove Volumetrics]</ref> In cases where volumetric shaders are used for god-rays, 2D emissive plans can make a suitable substitute.

==== Lights ====

Smaller lights (and by extension smaller beam spread values for area lights) can make it harder for samples to converge in a scene, leading to additional noise.

For a long time, light portals were a suggested method of decreasing noise in interior scenes.<ref>https://docs.blender.org/manual/en/latest/render/cycles/light_settings.html#render-cycles-lights-area-portals</ref><ref>[https://youtu.be/8gSyEpt4-60?t=458 Blender Guru: 18 Ways to Speed Up Cycles Rendering - Use Portals]</ref> However, in practice, light portals do not seem to make any difference in noise quality, both with large exterior gaps and small exterior gaps, while also slightly increasing render times. For this reason, light portals '''are not recommended''' as of Blender 3.0+. Cycles Legacy (Blender 2.61 to 2.93) may see benefits from portals, but more tests are needed.

<tabber>
|-|Large Gap=
<gallery mode="packed" heights="400px" caption="4096 samples, 0.03 noise threshold">
File:Portals Test- Nishita - No Portals.jpg|alt=Heatmap of sample count in a scene without portals|Heatmap of sample count in a scene without portals
File:Portals Test- Nishita - With Portals.jpg|alt=Heatmap of sample count in a scene with portals|Heatmap of sample count in a scene with portals. Note the lack of any major difference to the heatmap without portals
</gallery>

|-|Small Gap=
<gallery mode="packed" heights="400px" caption="4096 samples, 0.03 noise threshold">
File:Portals Test- Nishita - No Portals Small Gap.jpg|alt=Heatmap of sample count in a scene without portals and small gap|Heatmap of sample count in a scene without portals
File:Portals Test- Nishita - With Portals Small Gap.jpg|alt=Heatmap of sample count in a scene with portals and small gap|Heatmap of sample count in a scene with portals. Note the lack of any major difference to the heatmap without portals
</gallery>
</tabber>

In theory, path guiding is a more viable alternative, though only CPU rendering is supported.<ref>https://docs.blender.org/manual/en/latest/render/cycles/render_settings/sampling.html#path-guiding</ref>

==== Objects ====

To reduce memory usage, using object instancing and/or duplicating objects with shared data may reduce memory usage when rendering.<ref>[https://youtu.be/8gSyEpt4-60?t=1503 Blender Guru: 18 Ways to Speed Up Cycles Rendering - Object Instancing]</ref> This mainly benefits scenes with multiple objects that look the same/similar, such as trees in a forest, where each object doesn't have many unique features.

Adaptive subdivision and/or [[Level of Detail|LOD]] may also introduce memory savings for terrain.<ref>[https://youtu.be/8gSyEpt4-60?t=1670 Blender Guru: 18 Ways to Speed Up Cycles Rendering - Adaptive Subdivision]</ref>