积分器

积分器是一种用于计算光照的渲染算法。目前,Cycles引擎支持一种积分器,一种带直接光照采样的路径追踪积分器。它可以很好地适用于各种照明设定,但不适用于焦散以及其它一些复杂的光照情形。

光线从摄像机出发射到场景中,并来回反弹,直到它们找到一个光源,例如一个灯光物体,一个发光物体,或是环境背景光。为了找到灯光或发光的表面,间接照明采样(让光线跟随表面BSDF)与直接照明采样(选取一个光源并追踪射向它的光线)都将会用到。

采样

Reference

Panel:Render ‣ Sampling
采样方法
There are two integrator modes that can be used: Path Tracing and Branched Path Tracing.
二次方采样
Square the amount samples.
采样种

Seed value for integrator to get different noise patterns.

Animate Seed (clock icon)
This button which can be found on the right side of the Seed value can be used to give different seed values. It is a good idea to enable this when making animation because in the real world each frame has a different noise pattern.
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.
Light Sampling Threshold
Probabilistically terminates light samples when the light contribution is below this threshold (more noise but faster rendering). Zero disables the test and never ignores lights. This is useful because in large scenes with many light sources, some might only contribute a small amount to the final image, and increase render times. Using this setting can decrease the render times needed to calculate the rays which in the end have very little affect on the image.
Pattern

Random sampling pattern used by the integrator.

Sobol
Uses a Sobol pattern to decide the random sampling pattern used by the integrator. See Sobol sequence on Wikipedia for more information.
Correlated Multi-Jitter
Uses a Correlated Multi-Jitter pattern to decide the random sampling pattern used by the integrator. See this Pixar paper for more information.
Layer Samples

When render layers have per layer number of samples set, this option specifies how to use them.

Use
The render layer samples will override the set scene samples.
Bounded
Bound render layer samples by scene samples.
Ignore
Ignore render layer sample settings.

Path Tracing

The Path Tracing integrator is a pure path tracer; at each hit it will bounce light in one direction and pick one light to receive lighting from. This makes each individual sample faster to compute, but will typically require more samples to clean up the noise.

渲染采样
这是最终渲染中单像素的光程追踪次数。采样次数越多,结果中的噪点就会越少,也会更加精确。
预览采样
这是视窗渲染时的采样次数。

Branched Path Tracing

The non-progressive Branched Path Tracing integrator offers finer control over sampling. It is similar to Path Tracing, but at the first hit it will split the path for different surface components and will take all lights into account for shading instead of just one.

This makes each sample slower, but will reduce noise, especially in scenes dominated by direct or one-bounce lighting. To get the same number of diffuse samples as in the path tracing integrator, note that e.g. 250 path tracing samples = 10 AA samples x 25 diffuse samples. The Sampling panel shows this total number of samples.

抗锯齿采样
Number of samples to take for each pixel in the final render. More samples will improve anti-aliasing.
抗锯齿采预览样
这是视窗渲染时的采样次数。
漫射色采样
每个抗锯齿采样中的漫射反弹采样数
光泽采样
每个抗锯齿采样中的光泽反弹采样数
传递采样
每个抗锯齿采样中的漫射传递采样数
环境光遮罩采样
每个抗锯齿采样中的环境遮罩采样数
网格照明采样
每个抗锯齿采样中的网格照明采样数
次表面采样
每个抗锯齿采样中的次表面散射采样数
Volume Samples
Number of volume scattering samples to take for each AA sample.
Sample All Direct Lights
When enabled, Cycles will samples all lights in the scene for direct bounces, instead of randomly picking one. Disabling this can improve performance, when using a lot of AA Samples anyway, to clear up the render.
Sample All Indirect Lights
Similar to direct light, but for indirects lights. This can reduce noise in scenes with many lights.

Light Paths

Reference

Panel:Render ‣ Light Paths

反弹

最大反弹次数
光线反弹最大数值。要最好的质量的话,可以将该数值设到最大。但从实践来说,较小的数值会渲染得快一些。只能在直接光线下把最大值设置为零。
最低反弹次数
Minimum number of light bounces for each path, after which the integrator uses Russian Roulette to terminate paths that contribute less to the image. Setting this higher gives less noise, but may also increase render time considerably. For a low number of bounces, it is strongly recommended to set this equal to the maximum number of bounces.
漫射反弹
漫射反弹的最大次数
光泽反弹
光泽反弹的最大次数
传递反弹
传递反弹的最大次数
Volume Bounces
Maximum number of volume scattering bounces.

透射

透射最大值
透射反弹的最大次数
透射最小值
透射反弹的最小值,决定选用哪种罗斯轮盘。
透明阴影
对于直射光采样,用在阴影面和光源之间的表面的透明度来生成受表面透明度影响的阴影。

Caustics & Filter Glossy

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.
滤除光泽

设置一个高于 0.0的值的话,会在模糊反弹后将光泽反射模糊掉,通过降低精度来达到减少噪点的目的。1.0是用来调优的最好的起始值。

在光线要对某个像素点贡献很大光亮的时候这些光路被寻找到的概率是非常低的。正因为如此,这样的光路可能会在某些像素点上找到,在另外的像素点又找不到,这就引起了亮点问题。一般引起这样问题的原因比如:非常锐利的光泽材质上的很小的一个高光反光点产生的反射光。

路径追踪是很难找到反射高光的,但是如果我们把材质的粗糙度提高,高光会更大和柔和,也更容易找到。通常这种模糊很难被发觉,因为我们是在模糊的材质上看到的,不过也会损失掉一些光线的细节。

See also

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