采样

Reference

Panel:Render ‣ Sampling

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。

Rays are traced from the camera into the scene,bouncing around until they find a light source such as a light, an object emitting light,or the world background. To find lights and surfaces emitting light,both indirect light sampling (letting the ray follow the surface BSDF)and direct light sampling (picking a light source and tracing a ray towards it) are used.

  • Integrator

  • There are two sample methods that can be used: Path Tracing and Branched Path Tracing.

    • 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.
    • 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 fordifferent 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.

  • Render
  • 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。

When using Branched Path Tracing, this changes the _AA Samples_which are multiplied by the Sub Samples and improve anti-aliasing.

  • Viewport
  • 这是视窗渲染时的采样次数。

Sub Samples

The panel is visible only when using Branched Path Tracing.

  • Diffuse
  • 每个抗锯齿采样中的漫射反弹采样数
  • Glossy
  • 每个抗锯齿采样中的光泽反弹采样数
  • Transmission
  • 每个抗锯齿采样中的漫射传递采样数
  • AO
  • 每个抗锯齿采样中的环境遮罩采样数
  • Mesh Light
  • 每个抗锯齿采样中的网格照明采样数
  • Subsurface
  • 每个抗锯齿采样中的次表面散射采样数
  • Volume
  • Number of volume scattering samples to take for each AA sample.

Advanced

  • 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 thiswhen making animation because in the real world each frame has a different noise pattern.
  • 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 paperfor more information.
  • 二次方采样
  • Square the amount of samples.
  • Min Light Bounces
  • 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.
  • Min Transparent Bounces
  • Minimum number of transparent bounces. Setting this higher reduces noise in the first bounces,but can also be less efficient for more complex geometry like hair and volumes.
  • Light Threshold
  • Probabilistically terminates light samples when the light contributionis 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 calculatethe rays which in the end have very little affect on the image.
  • Sample All Direct Lights
  • When enabled, Cycles will sample all lights in the scene for direct bounces, instead of randomly picking one.Disabling this can improve the performance, but will need a lot of Samples, to clear up the render.

Visible only when using Branched Path Tracing.

  • Sample All Indirect Lights
  • Similar to direct light, but for indirect lights. This can reduce noise in scenes with many lights.

Visible only when using Branched Path Tracing.

  • 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.