光程

参考

面板:渲染 ‣ 光程

Max Bounces

光线反弹的最大次数可以手动控制。尽管这一数值理论上没有限制，然而在实际中，一个较小的数值即可满足需要，或者屏蔽某些光线交互来加快收敛控制。此外，漫反射次数、光泽反射次数以及透射反弹次数也可以分别进行控制。

当指定了一个低于最大值的最小数值时，光程将会遵循盖然性而终止。这种情况下，当光程按照预想中那样降低对图像的光照作用时，长于最小数值的光程会随机停止。这仍然会让渲染收敛到相同的最终图像结果，在产生较多噪点时会让渲染速度会更快。

Total

Maximum number of light bounces. For best quality, this should be set to the maximum. However, in practice, it may be good to set it to lower values for faster rendering. A value of 0 bounces results in direct lighting only.

Diffuse

Maximum number of diffuse bounces.

Glossy

Maximum number of glossy bounces.

透明度

Maximum number of transparency bounces.

透明反弹次数上限是通过其它的反弹来单独控制的。也可以使用概率性透明反弹终止机制，这会有助于渲染多个透明度层。

Transmission

Maximum number of transmission bounces.

Volume

Maximum number of volume scattering bounces.

Clamp

Clamp Direct

This option limits the maximum intensity a sample from rays which have not yet bounced can contribute to a pixel. It reduces noise at the cost of accuracy. Setting this option to 0.0 disables clamping altogether. Lower have a greater affect (dimmer samples) on the resulting image than higher values.

Note

A common issue encountered with Path Tracing is the occurrence of "fireflies": improbable samples that contribute very high values to pixels. This option provides a way to limit that. However, note that as you clamp out such values, other bright lights/reflections will be dimmed as well.

Care must be taken when using this setting to find a balance between mitigating fireflies and losing intentionally bright parts. It is often useful to clamp indirect bounces separately, as they tend to cause more fireflies than direct bounces. See the Clamp Indirect setting.

Clamp Indirect

The same as Clamp Direct, but for rays which have bounced multiple times.

Caustics

A common source of noise is caustics.

Reflective Caustics

While in principle path tracing supports rendering of caustics with a sufficient number of samples, in practice it may be inefficient to the point that there is just too much noise. This option can be unchecked, to disable reflective caustics.

Refractive Caustics

The same as above, but for refractive caustics.

Filter Glossy

When using a value higher than 0.0, this will blur glossy reflections after blurry bounces, to reduce noise at the cost of accuracy. 1.0 is a good starting value to tweak.

Some light paths have a low probability of being found while contributing much light to the pixel. As a result these light paths will be found in some pixels and not in others, causing fireflies. An example of such a difficult path might be a small light that is causing a small specular highlight on a sharp glossy material, which is observed through a rough glossy material. In fact in such a case there practically occurs a caustic.

With path tracing it is difficult to find the specular highlight, but if you increase the roughness on the material, the highlight gets bigger and softer, and so easier to find. Often this blurring will hardly be noticeable, because it is blurred by the material anyway, but there are also cases where this will lead to a loss of detail in lighting.

See also

See Reducing Noise for examples of the clamp settings in use.