2.2. Ray Tracing Options

Determines the maximum number of steps in the ray path from the camera. A value of 1 corresponds to direct illumination without secondary illumination (global illumination off). Values ​​over 5 do not contribute much in diffuse interior scenes, values ​​over 25 do not make a visible difference. But in some cases, such as specular scattering on water droplets or scattering in dense fogs, larger values ​​may be required.

Use Russian Roulette with high Ray Depth values.

 

The ray depth at which the Russian Roulette is turned on. It randomly breaks rendering on long paths and trades the render time for noise.

 

In some scenes, the ray can bounce off a diffuse surface and pass through a specular surface (a surface with little or no roughness). In this case, its intensity will greatly increase. If it then collides with a light source, it will result in a bright firefly (the bright point in the picture). Since the probability of such an event is low after a diffuse surface, the noise will remain in the picture. Diffuse Cutout allows you to disable these rare events. A value of 0 prevents any collisions with light sources after the SDS path (Specular-Diffuse-Specular). A value of 1 only allows one after SDS, etc.

Diffuse Cutout automatically becomes at least 1 if the REDS algorithm is enabled, otherwise there would be no caustic.

 

Enables REDS algorithm. REDS is an algorithm for detecting and investigating rare events such as caustics, caustics in volume, blurring of reflections at wide camera apertures. It allows you to render caustics at the bottom of the pool, rays of light in the ocean, physically correct refraction of light in the eyes of the character. For its work, it requires orders of magnitude more computing resources than the usual Path Tracing, but for an equivalent time it gives a qualitatively better picture. Can you get caustics in a few minutes? No, just a preview. But overnight you can get the final image, which in the usual way can be obtained only in a month of rendering. The REDS algorithm produces an unbiased picture without any simplifications.

It is highly recommended to use REDS in conjunction with Path guiding.

 

REDS currently has the following limitations:

- It does not know how to work well with volumetric caustics in volumes with variable density. That is, you cannot get silent caustics in the cloud using REDS. But in a homogeneous water column or fog - you can.

- It does not work well with smooth monotonic caustics, for example, the refraction of light from an ideal sphere. REDS likes challenging surfaces like water waves.

- To activate the analysis of potential caustics, the REDS must be able to "catch" on the illumination source. If direct hits to illumination sources are too rare, then REDS will not be able to complete in a reasonable amount of time. REDS will help when caustics could be obtained in classic Path Tracing, but are very noisy. In this case, REDS will make them virtually clean.

- REDS does not work with point emitters as it does not use photon maps.

 

Scene with the eyes of the character. The scene is lit by a single Sun + Sky, the brightness of the sky is 25% of normal. The eyes are a complex optical system with several layers of dielectrics (lenses).

Path Tracing cannot illuminate a diffuse surface deep in the eye with light from the Sun. Illumination is there only from the sky.

Special mode when dielectrics do not block Shadow Rays:

no refraction, no caustics, bump mapping is too strong.

Path guiding + REDS was able to properly illuminate the iris of the eye. That rare case when Path guiding sped up rendering.

 

Determines the sharpness of caustics on the surface. Values ​​from 0 to 2, where 0 is blurry caustics, 2 is sharp.

Allows REDS to work with volumetric caustics. Sometimes volumetric caustics (not on surfaces) are not needed. But calculating them requires resources. When you turn off the volumetric caustics, they would be replaced by a rare intense noise, which can be easily removed by post-processing using the Fireflies removal option.

 

Allows REDS to work with blurry flares at wide camera apertures.

 

Those pixels for which the REDS operation was detected will receive several times more samples than the usual ones.

 

When set to 0, the REDS result is completely physically unbiased. At values ​​greater than 0, it is darker and differs from the reference values, but rendering is faster. The rendering speed increases as the number of passes made increases.

 

Determines how many bounces on a reflective surface, without going inward, the ray should make for REDS to become interested in it.

 

Determines how many times the ray has to go inside the material for REDS to become interested in it.

 

Determines how much the intensity of the ray should be attenuated to stop further tracing. A value of 0.01 means that it should weaken 100 times.

 

When animating, it can be useful to lock the seed values ​​of the random number generator frame by frame. This will not reduce the noise, but it will make it immobile and less noticeable.

 

Reserved for future versions.

 

Sets the sampling quality for textures:

Linear: Bilinear anisotropic filtering, the fastest and easiest. Recommended for preview.

Cubic: Spline anisotropic filtering, slow and not as good as elliptical. Not recommended for use. Most likely will be removed in future versions.

Elliptical: Elliptical anisotropic, highest quality. 1.5 times slower than bilinear, but faster than cubic. Recommended for final renders.

Additional settings on the tab System Options.

 

For bump mapping, filtering will be used better than bilinear.