Skin 皮肤

Introduction

引言

This shader simulates the scattering effect of skin. In real life, skin is made up of three distinct layers:

这个着色器模拟了皮肤的散射效果。在现实生活中，皮肤由三个不同的层组成:

• Epidermis - defines the skin tone and waterproof layer 表皮-界定皮肤色调和防水层
• Dermis - contains tough connective tissue 真皮-含有坚韧的结缔组织
• Subcutis (hypodermis) - made up of loose connective tissue, fat and blood vessels 皮下组织-由疏松结缔组织、脂肪和血管组成

To model this, the Redshift skin shader has three equivalent translucent, sub-surface scattering layers:

为了建立这个模型，红移皮肤着色器有三个等效的半透明的亚表面散射层:

• Shallow Scatter 浅层散布 - defines the pigment/skin tone of the skin - 决定皮肤的色素/肤色
• Mid Scatter 中期分散 - defines the dermis layer - 定义了真皮层
• Deep Scatter 深度散布 - defines the thick, subcutis layer 界定了厚，亚表皮层

Redshift also simulates the 'waterproof' oily property of the top-most epidermis layer by having a 'Primary Reflection' control. A 'Secondary Reflection' layer is also available for added sheen from, for example, oily cosmetic products, or for clear-coat effects.

红移也模拟了最上表皮层的“防水”油性特性，具有“主反射”控制。“二次反射”层也可用于增加光泽，例如，油性化妆品产品，或清洁外套的效果。

Free head model, courtesy of 3D Scan Store, with a textured skin shader material, illuminated by two area lights and a dome light

免费的头部模型，礼貌的3 d 扫描商店，质感的皮肤着色材料，照明两个区域灯和一个圆顶灯

You can see how sub-surface scattering of light affects thin parts of the model (the ear) versus the thick part of the model (the head).

你可以看到光的亚表面散射如何影响模型的薄部分(耳朵)和模型的厚部分(头部)。

Scattering Layers

散射层

Each layer uses sub-surface scattering to compute a diffuse lighting result and the results are blended together based on each layer's individual weight.

每一层使用次表面散射计算一个漫射照明结果和结果是混合在一起的基础上每一层的个别权重。

The Shallow Scatter layer is the thinnest, so it should have the smallest Radius, yielding an almost diffuse scattering response. The Deep Scatter layer is the thickest layer, so it should have the largest radius, adding the blood tone under the skin.

浅散射层是最薄的，所以它的半径应该最小，产生几乎漫散射的响应。深度散射层是最厚的一层，所以它应该有最大的半径，增加皮肤下的血液色调。

Common

常见问题

Radius Scale

半径比例尺

Allows you to adjust the strength of the scattering effect for all the layers. Lower values means scattered light is absorbed quicker, yielding a more diffuse look. Conversely, higher values yield a more translucent look.

允许你调整所有层的散射效果的强度。较低的数值意味着散射光吸收更快，产生更漫反射的外观。相反，较高的值会产生更透明的外观。

Overall Scale

整体比例

Allows you to adjust the overall brightness of all the scattering layers.

允许你调整所有散射层的整体亮度。

Diffuse Amount

扩散量

Controls how much of the SSS effect you get. A value of 0.0 means that you'll only get subsurface scattering. On the other hand, a value of 1.0 will make this surface behave as a perfectly diffuse surface without any SSS. This parameter is useful for materials that need a weaker SSS effect.

控制你获得多少 SSS 效果。值为0.0意味着你只能得到次表面散射。另一方面，值为1.0将使这个表面表现为一个完全漫反射表面没有任何 SSS。这个参数对于需要较弱 SSS 效应的材料是有用的。

Disable Diffuse Bump Mapping

禁用漫反射凹凸贴图

This option allows you to switch to using the default un-bumped surface normals for diffuse lighting calculations.

此选项允许您切换到使用默认的非颠簸表面法线漫射照明计算。

In the examples images below note how when this option is enabled the overall SSS effect is smoothed out since the geometry is much smoother than when the diffuse bump map is used when disabled.

在下面的例子图像中，注意当这个选项被启用时，整体的 SSS 效果是平滑的，因为几何形状比使用漫反射凹凸贴图时要平滑得多。

Normalize Diffuse Weights

标准化扩散权重

In order to be physically correct, by default Redshift shaders conserve energy by not emitting more light than they receive. When this parameter is checked, we apply physical correctness by ensuring the sum of the weights of each layer do not exceed 1.0.

为了在物理上正确，默认情况下，红移着色器通过不发出比接收到更多的光来保存能量。当这个参数被检查时，我们应用物理正确性通过确保每一层的权重之和不超过1.0。

When this option is un-checked we leave the weights alone, which can result in brighter, but not physically correct results.

如果取消选中此选项，我们将不使用权重，这可能导致更明亮的结果，但不能从物理上纠正结果。

Mode

模式

• Point-Based 基于点的
• Point-Based (Legacy) 基于点的(遗留)
• Ray-Traced 射线追踪

You can use either point-based or ray-traced multiple sub-surface scattering in Redshift and both have their own advantages and disadvantages. In quite a few cases the techniques should look similar to each other but there are situations where the differences will be readily apparent, this is primarily due to the normalization of light that occurs when using point-based mode. Ray-traced mode does not normalize the light which can lead to differences that are most notable on thin objects or objects with more surface detail.

在红移中，可以使用基于点的多次子表面散射或者光线跟踪的多次子表面散射，这两种方法各有优缺点。在相当多的情况下，这些技术应该看起来彼此相似，但是在有些情况下，差异会很明显，这主要是由于在使用基于点的模式时发生的光的正常化。光线追踪模式并不能使光正常化，这会导致在薄物体或表面细节更多的物体上最显著的差异。

Point-Based

基于点的

• Faster and smoother

  更快更流畅

• Less detailed / accurate

  不够详细/准确

• Does not work in progressive mode

  不在渐进模式下工作

• Requires a “prepass” stage

  需要一个“准备阶段”

• Higher chance of flickering in difficult lighting situations.

  在光线困难的情况下闪烁的几率更高。

• Not possible to isolate SSS effect on a particular object which can result in unnecessary “light bleeding” artifacts.

  不可能隔离 SSS 效应的一个特定的对象，可能会导致不必要的“光出血”伪影。

Ray-Traced

射线追踪

• Slower and noisier

  更慢更吵

• More detailed / accurate

  更详细/更准确

• Works in progressive mode

  以渐进模式工作

• The higher the scatter radius the more samples are needed for clean results.

  散射半径越大，清洁结果需要的样本就越多。

• Possible to isolate SSS effect between objects or have it affect all objects. Please see here for more info.

  可能隔离 SSS 效果之间的对象或有它影响所有的对象。请看这里的更多信息。

Samples

样本

This controls the number of samples cast for Multiple Sub-Surface Scattering rays. Higher numbers will reduce noise issues but will take longer to render.

这控制了多次亚表面散射射线的采样数量。更高的数字会减少噪音问题，但渲染时间会更长。

In the images below the sample difference is most noticable in the ear.

在下面的图片中，样品的差异在耳朵中是最明显的。

Include Mode 包含模式

• All Objects : All other objects participate in the SSS effect. 所有对象: 所有其他对象都参与 SSS 效应
• Only Self : Contain the SSS effect in the same object only.  只有自我: 只在同一个物体中包含 SSS 效果

Notice the difference between the different methods around the collar and neck in the images below. To make the difference more prominent a Redshift Skin shader is applied to the jacket part of the model and the Radius Scale for both the head and jacket shaders has been increased to 10.

请注意下面图片中围绕衣领和脖子的不同方法之间的区别。为了使差异更加突出，红移皮肤着色器应用到模型的夹克部分，头部和夹克着色器的半径缩放已经增加到10。

Shallow / Mid / Deep Scatter Layers

浅层/中层/深层散射层

Color

颜色

This is the color of the scatter layer.

这是分散层的颜色。

Weight

重量

This is a multiplier of the scatter layer color and can be used to adjust the brightness / strength of the layer.

这是一个分散层颜色的倍增器，可以用来调整图层的亮度/强度。

This value is multiplied by the 'Overall Scale' parameter.

这个值乘以“总体规模”参数。

Radius

半径

This parameter is scene-scale related. It controls how deep light can travel within this surface. If the value is high, light can go deeper which creates a softer effect. Smaller values, on the other hand, mean that the light reaches extinction early which creates a harder more diffuse effect.

这个参数与场景尺度有关。它控制着光在这个表面的传播深度。如果数值很高，光线可以变得更深，从而产生更柔和的效果。另一方面，较小的数值意味着光线很早就会消失，从而产生更难扩散的效果。

This value is multiplied by the 'Radius Scale' parameter.

此值乘以“半径缩放”参数。

Single Scattering

单次散射

Transmittance 透射率

Describes the sub-surface attenuation color. A color of black means full light absorption, yielding a solid material, while a color of white means light rays will pass right through without being absorbed. Dark colors can be used to describe denser materials.

描述了次表面的衰减颜色。黑色意味着充分的光吸收，产生固体材料，而白色意味着光线会直接穿过而不被吸收。深色可以用来描述密度更大的材料。

Thickness 厚度

This acts as a scale of the absorption effect, with a value of 0.0 meaning no absorption and larger values meaning stronger absorption and thus denser-looking materials.

这就像一个吸收效应的尺度，0.0的值意味着没有吸收，更大的值意味着更强的吸收，因此密度更大的材料。

Scatter Amount 分散数量

Acts as a scale of the scattering effect, with a value of 0.0 meaning no scattering and larger values meaning more scattering and thus denser-looking materials.

作为散射效应的一个尺度，0.0的值意味着没有散射，更大的值意味着更多的散射，因此更密集的材料。

Samples

样本

This is the maximum number of samples shot for single scattering rays. More samples will mean less noisy looking single scattering, but can affect rendering performance.

这是单次散射射线的最大采样数。更多的样本将意味着更少的噪声看起来单一散射，但会影响渲染性能。

Phase

第二阶段

This describes the anisotropy of the scattering effect, for forward and back scattering. Forward scattering requires values between 0 and 1, which means rays will scatter away from the light source. Back scattering requires values between -1 and 0 which means rays will scatter back towards the light source.

这描述了前向和后向散射的散射效应的各向异性。前向散射要求值在0到1之间，这意味着光线会从光源散射开来。后向散射要求值在 -1和0之间，这意味着光线会向后散射到光源。

Scattering Options in Detail

详细的散射选项

The 'Overall Scale' allows you to adjust the brightness of all the layers together, so you can quickly fine tune the intensity your diffuse lighting for the overall material.

“整体比例”可以让你调整所有层的亮度在一起，所以你可以快速调整整体材质的漫射照明的强度。

The 'Radius Scale' allows you to adjust the strength of the scattering effect for all the layers. Since sub-surface scattering is heavily dependent on the scale of the object, you can use this option to quickly adjust the scattering effect until it is visually pleasing. Smaller values mean quicker absorption of light, resulting in less scattering effect and a more diffuse look. With larger values you get a more translucent look.

“半径比例尺”允许你调整所有层的散射效果的强度。由于子表面散射是严重依赖于规模的对象，您可以使用这个选项，以迅速调整散射效果，直到它是视觉赏心悦目。较小的数值意味着更快的光吸收，导致较少的散射效果和更漫反射的外观。使用较大的值，可以得到更透明的外观。

For physical correctness, the 'Normalize Diffuse Weights' should be left enabled. This will ensure the material does not reflect more light than it receives. However, if you want better control over the overall layers brightness or want your material to be more emissive than physically correct, you can disable this option.

对于物理正确性，应该启用“标准化分散权重”。这将确保材料不会反射比接收到更多的光线。然而，如果你想更好地控制整个图层的亮度，或者想要你的材质更加发射而不是物理上正确，你可以禁用这个选项。

Below is a side-by-side example showing the difference in lighting with the 'Normalize' option disabled, using the default layer weights of the material.

下面是一个并排的例子，显示了禁用“标准化”选项后照明的差异，使用材料的默认层权重。

The 'Diffuse Amount' lets you control how much of the overall sub-surface scatter effect you want, versus pure diffuse lighting. When the 'Diffuse Amount' is set to 1.0, there will be no sub-surface scattering. Equally, when set to 0.0, there will be only sub-surface scattering.

“漫反射量”可以让你控制多少整体亚表面散射效果，你想要的，而不是纯粹的漫反射照明。当“漫射量”设置为1.0，将不会有次表面散射。同样，当设置为0.0时，将只有亚表面散射。

Now let's take a look at how each layer can contribute to the scattering effect. While the differences can be subtle at times, they are noticeable.

现在让我们来看看每一层是如何对散射效果做出贡献的。虽然这些差异有时是微妙的，但是是显而易见的。

Reflections

反思

Primary / Secondary Reflection

主/次级反射

Color

颜色

This defines the color of the reflection.

这定义了反射的颜色。

Weight

重量

This scales the overall amount of the reflection.

这可以缩放反射的总量。

BRDF

Allows you to choose the technique for simulating physically correct rough reflections. Beckmann is generally considered the standard for a good range of materials, but GGX has a wide specular tail, which is good for chrome materials.

允许您选择模拟物理上正确的粗糙反射的技术。贝克曼通常被认为是一个很好的材料范围的标准，但 GGX 有一个广泛的镜面尾巴，这是很好的铬材料。

• Beckmann (Cook-Torrance) 贝克曼(库克-托伦斯)
• GGX
• Ashikhmin-Shirley

Glossiness

光泽度

This controls the glossiness, or roughness, of the reflection. A glossiness of 1 means almost mirror reflection, while a glossiness of 0 means very rough, almost diffuse reflection.

这控制了反射的光泽度或粗糙度。光泽度为1意味着几乎是镜面反射，而光泽度为0意味着非常粗糙，几乎是漫反射。

Samples

样本

This defines the number of samples to use for the reflection. More samples means less noise.

这定义了用于反射的样本数量。更多的样本意味着更少的噪声。

IOR

返回抑制

The index of refraction which is used to compute the view-dependent Fresnel reflectivity effect. Reflections with an IOR value closer to 1.0 will have less facing reflectivity. The recommended default value is 1.44.

用于计算视场相关菲涅耳反射效应的折射率。返回抑制值接近1.0的反射面反射率较低。推荐的默认值是1.44。

General

将军

Disable Reflection Bump Mapping

禁用反射凹凸映射

This option allows you to switch to using the default un-bumped surface normals for direct and indirect reflection rays.

此选项允许您切换到使用直接和间接反射射线的默认非碰撞表面法线。

Optimization

优化

Specular Highlights Only

镜面高光

This optimization option will disable indirect reflection ray tracing of the environment and just capture specular reflections of lights.

这个优化选项将禁用间接反射射线追踪的环境，只是捕捉镜面反射光。

Enable Trace Depth Overrides

启用跟踪深度重写

This enables the Max Reflection Trace Depth parameter. When not enabled, the global trace depth will be used.

这启用了最大反射跟踪深度参数。当没有启用时，将使用全局跟踪深度。

Max Trace Depth

最大追踪深度

This parameter controls the trace depth for reflection rays shot from this material. If the reflections of a material are not very defined (meaning: they are blurry because of the glossiness parameter or have a low weight), then multiple reflection bounces can be a waste of rendering time. This parameter allows the user to reduce the trace depth and speed up rendering.

这个参数控制从这种材料射出的反射光的跟踪深度。如果一个材质的反射没有很好的定义(意思是: 它们因为光泽度参数而变得模糊或者重量很轻) ，那么多次反射反射就会浪费渲染时间。此参数允许用户减少跟踪深度并加快呈现速度。

Cut-off Override Enable

切断重写启用

This parameter allows you to override the global cut-off setting for reflections.

此参数允许您覆盖反射的全局截止设置。

Cut-off Override Threshold

截止覆盖阈值

When the reflections of a material are very dark (because of low "Weight" or "Color" values) they contribute very little to the final image. This parameter defines what is considered "very dark" at which point no more reflection rays will be shot - which will speed up rendering. Scenes containing very strong lights might need this parameter set to very low values such as 0.0001 in order to avoid early termination of tracing which can produce a grain-like effect.

当一个材质的反射非常暗(因为低的“重量”或“颜色”值) ，它们对最终图像的贡献很小。这个参数定义了什么被认为是“非常黑暗”，在这一点上没有更多的反射射线将被拍摄-这将加速渲染。包含非常强光的场景可能需要将这个参数设置为非常低的值，如0.0001，以避免过早终止跟踪，因为跟踪会产生类似颗粒的效果。

Reflection Settings in Detail

反射设置的细节

Below are some examples of how different reflection settings can affect the look of the material.

下面是一些不同的反射设置如何影响材质外观的例子。

Bump Mapping

凹凸贴图

Add Bump Input To Material Bump

添加凹凸输入到材质凹凸

Skin Example

皮肤例子

There are various tutorials on the web for different renderers that describe how to use texture maps for the sub-surface scattering layers. The tutorials that describe how to map three sub-surface layers also apply reasonably well to the Redshift skin material.

在网上有各种各样的教程，为不同的渲染器，描述如何使用纹理地图的次表面散射层。描述如何映射三个子表面层的教程也适用于红移皮肤材质。

Although the best results can be gotten using dedicated textures for the layers and reflections, here we show a simplified example, using a single diffuse texture that can be manipulated to add color detail to the shader, while still maintaining the sub-surface effect.

虽然最好的效果可以通过使用层和反射的专用纹理得到，这里我们给出一个简化的例子，使用一个单一的漫反射纹理，可以添加颜色细节到着色器，同时仍然保持亚表面效果。

The first step is to de-saturate the texture, then adjust its contrast to darken the dark details (such as facial hair). Once you have that texture you apply a red tint for the deep scatter color, a green-ish tint for the mid scatter color (so the sum of which becomes a deep orange) and simply use the diffuse texture for the shallow scatter layer. You can also use the de-saturated texture for the reflection color.

第一步是去掉纹理的饱和度，然后调整它的对比度，使黑色的细节变暗(比如面部毛发)。一旦你有了这个纹理，你就可以为深度散射颜色应用一个红色的色调，为中度散射颜色应用一个绿色的色调(所以它的总和变成了深橙色) ，然后简单地为浅度散射层使用漫射纹理。你也可以使用去饱和纹理作为反射颜色。

Below is an example showing the different layers, with its appropriate weight, and the other layers having a weight of 0.0.

下面是一个示例，显示了不同的层，其适当的重量，和其他层的重量为0.0。

Below now shows the layers successively summed together, by setting the layer weights to their appropriate values.

现在，下面显示层依次总结在一起，通过设置层权重到它们的适当值。