KERNELS: DIRECT LIGHTING

The Direct Lighting Kernel is generally used for faster preview rendering. It's not unbiased and will not yield photorealistic results, however because of its speed it can be the ideal choice for rendering animations or stills depending on your purpose. The following picture shows the Directlighting settings. Some of these settings are shared with the other kernel types. Now let's see what these options are:



Max. Samples:  

Sets the maximum number of samples per pixel before the rendering process stops. The higher the number of samples per pixel, the cleaner the render. There is no rule as to how many samples per pixel are required for a good render, it is subjective and may vary depending on the content and complexity of the scene being rendered. For example, since Directlighting is a fast kernel, 500-1000 samples for static images and animations will suffice. If you have more than one direct and indirect light source in your scene and you are also using mesh light, you can increase a few hundred samples. But we can not say the same thing for Pathtracing kernel mode, for instance. As we've just mentioned, there is no magic number for it.



GI Mode:  

From here you can choose GI Mode for Directlighting. This mode also has 3 sub options:

GI_NONE

Only direct lighting from the sun or area lights is included. Shadowed areas receive no contribution and will be black.

GI_AMBIENT OCCLUSION

Standard ambient occlusion. This mode can often provide realistic images but offers no color bleeding.

GI_DIFFUSE

Provides GI quality that is in between Ambient Occlusion and Pathtracing. In this mode, the indirect light sources also taken into account and affects the diffuse mode. This increases the level of realism of your render. However the caustics does not appear in this mode, but the realism level of your render is often sufficient. At least you get better results than Ambient Occlusion mode. Since it is a fast mode, you can quickly get a final render; for both static images and animations.



Specular Depth:  

Controls how many times a ray is refracted after hit the surface without losing its energy. A zero number means that the ray does not hit the surface and can not continue on the path (reflect or refract). if it is greater than zero, it continues on its way through the surface and refracts until it loses its energy. Higher numbers mean higher render times but more color bleeding and more details in transparent materials. Low numbers can introduce artifacts or turn some refractions into pure black. You can see different specular depth results from the picture below.



Glossy Depth:  

Controls how many times a ray is reflected after hit the surface. A zero number means that the ray does not hit the surface and can not continue on its path (reflect or refract). When it is greater than zero, it hits the surface and continues to be the same as the angle of incidence, so the reflection occurs. Higher numbers mean higher render time. Low numbers (under 4) can introduce artifacts, or turn some reflections into pure black. You can see different glossy depth results from the picture below.



Diffuse Depth:  

Gives the maximum number of diffuse reflections if GI Mode is set to Diffuse. 3-5 is enough for the most scenarios.



Ray Epsilon: 

The distance between the geometry and the light ray when calculating ray intersections for lighting and shadowing. Larger values push rays away from the geometry surface. Lower values are more accurate, but can cause artifacts on large or distant objects. Ray Epsilon is similar to raytracing bias in other rendering engines. Adjust Ray Epsilon to reduce artifacts in large scale scenes. Look at the picture below.



Filter Size:  

Sets the filter size in terms of pixels. This can improve aliasing artifacts in the render. However, if the filter is set too high, the image can become blurry.



AO Distance:  

Controls the distance of the ambient occlusion shadowing spread. This setting should be adjusted in order to achieve realistic results depending on the scale of the objects in the scene. For example a small value is more appropriate for small objects such as toys and larger values for an object such as a house.



Alpha Shadows:  

Allows any object with transparency (specular materials, materials with opacity settings, and alpha channels) to cast a shadow accordingly instead of behaving as a solid object. As you can see in the picture below, we have a plane object in the scene and we only put an image in the opacity channel with an alpha. Shadows look correct when turned on.



irradiance mode  

This setting works similar to clay mode, but is only applied to the first bounce, disables bump and makes samples that are blocked by back faces transparent. (In case you are wondering: This is required for baking in Unity).


Alpha Channel:  

This option removes the background (for example daylight or any sky background) and renders it as transparent (zero alpha). This can be useful if you want to composite the render over another image and does not want the background to be present.



Keep Environment:  

This option is used in conjunction with the Alpha Channel setting. It allows the background to be rendered with zero alpha but it's still visible in the final render. This allows even further flexibility in compositing software.



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Path term. power:  

This parameter provides a system where users can tweak samples/second vs. convergence (how fast noise vanishes). Increasing this value will cause the kernels to keep paths shorter and spend less time on dark areas (which means they stay noisy longer) but may increase samples/second. Reducing this value will cause kernels to trace longer paths on average and spend more time on dark areas. In short, high values increases the render speed but may lead to higher noise in dark areas.


Coherent Ratio:  

When the coherent mode is turned on, the picture is quickly noise-free, but the negative side of the feature is that you see a flickering blotch effect in the animation output. It's just like the effect you used to see when you did Light Cache in old days (now these techniques are out of date since the unbiased render engines are available). Just use it if you want to get the test animation quickly. Do not use it in Final Production.



Static Noise:  

Keeps noise patterns static between rendered frames in a sequence when enabled. Note that the noise is fully static as long as the same GPU architecture is being used for rendering. Different architectures will produce slightly different numerical errors which manifest as small differences in the noise pattern.


Parallel Samples:  

Controls how many samples are calculated in parallel. Smaller values require less memory to store the samples state but may cause the render to be a bit slower. High values require more memory but can reduce render time. The change in performance depends on the scene and the GPU architecture. As you can see in the picture below, more Vram usage is shortening the render time. If you have a lot of Vram, be sure to use this option.



Max. Tile Samples:  

This controls the number of samples per pixel that Octane will render until it takes the result and stores it in the film buffer. A higher number means that results arrive less often at the film buffer, but reduce the CPU overhead during rendering and as a consequence can improve performance, too.


Minimize Net Traffic:  

Distributes only the same tile to the net render slaves until the max samples/pixel has been reached for that tile and only then will the next tile is distributed to slaves when enabled. Work done by local GPUs is not affected by this option. This way a slave can merge all its results into the same cached tile until the master switches to a different tile.


Adaptive Sampling:

A method of sampling that determines if areas of a rendering require more sampling than other areas instead of sampling the entire rendering equally. In Octane, Adaptive Sampling disables sampling for pixels that have reached a specified noise level. With adaptive sampling, Octane is able to stop rendering on areas which no longer need to be rendered thus, freeing more gpu power to render on pixels that still need to be rendered. This allows you to bump up the maximum samples quite high (even more than 30,000) and then rely on the adaptive sampling to figure out which pixels actually need that many samples and which don't.



Adaptive sampling

Enables adaptive sampling.


Noise threshold

Specifies the smallest relative noise level. When the noise estimate of a pixel becomes less than this value, sampling will be switched off for this pixel. Good values are in the range of 0.01 - 0.03. The default is 0.02, which is pretty clean. This is the most important part of Adaptive Sampling process. The effective processing of the adaptive sample depends on the structure of your scene settings. So you should pay attention to the Noise Mask part during the render. If there are dark places in your scene and all the areas are green, then there is a problem. In this case, you may need to adjust the noise threshold setting. The following picture shows the correct and incorrect Noise mask.



Min. adaptive samples

Specifies the minimum samples that must have been calculated before adaptive sampling kicks in. The reason for this option is the fact that the noise estimate of a pixel is just an estimate with a fairly large initial error. The higher you set the noise threshold, the higher you should also set min. samples, to avoid artifacts.


Pixel grouping

Specifies the number of pixels that are handled together. Only if all pixels of a group have reached the noise level, sampling will stop for all of these pixels.


Expected Exposure

The expected exposure should be approximately the same value as the exposure in the image or 0 to ignore these settings. The default value is 0. This parameter is used by Adaptive Sampling to determine the pixels that are bright and those that are dark - which depends on the exposure setting in the Octane Imager. If the value is not 0, Adaptive Sampling will tweak/reduce the noise estimate of very dark areas of the image. It also will also increase the minimum adaptive samples limit for very dark areas, because very dark areas tend to find paths to light sources irregularly resulting to an otherwise overly optimistic noise estimate.


toon shadow ambient

This is used for the setting default toon ambient light color.