Volume Rendering - Volume Rendering

Note注意

Please note that the effect described in this page refers to localized volumes such as clouds, smoke and fire. For the global, uniform fog, please refer to this page instead.

請注意，本頁中描述的效果是指局部的體積霧，如雲，煙和火。對於大氣，體積霧，請參閱此頁。

Introduction概述

Redshift can render non-homogeneous volume objects such as smoke and fire. A volume』s shape can be specified through an OpenVDB file. In the near future, Redshift will add support for other volume data containers (such as FumeFX) as well as support for 3d-app-native grids such as Maya fluids.

Redshift可以渲染非均勻體積對象，如煙霧和火。體積的形狀可以通過OpenVDB文件指定。在不久的將來，Redshift將增加對其他體積數據容器（如FumeFX）的支持，以及支持3D應用程序原生網格（如Maya流體）。

To define the volume』s shading, a Redshift Volume Shader needs to be assigned to

the volume. This is explained below.

要定義體積的陰影，需要將Redshift體積著色器分配給該體積。這將在下面解釋。

A cloud bunny in the Cornell box在箱子裏的體積雲兔子

OpenVDB files and channels OpenVDB文件和通道

OpenVDB files are to volumes what EXR files are to textures. While a texture stores pixels (also called texels), an OpenVDB file stores voxels which are 3D pixels. Each voxel stores information that describes the volume at a particular XYZ point. For example, it can store a density value which tells the renderer how opaque or transparent the volume is at that point. In some ways, this is similar to the alpha channel in a PNG or EXR file.

OpenVDB文件是指EXR文件對紋理的體積。當紋理存儲像素（也稱為紋素）時，OpenVDB文件存儲作為3D像素的體素。每個體素存儲描述特定XYZ點處的向量的信息。例如，它可以存儲一個密度值，告訴渲染器該體積在該點是不透明的還是透明的。在某些方面，這與PNG或EXR文件中的Alpha通道類似。

OpenVDB organizes its voxel data in channels. As mentioned above, a typical channel is 『density』. Another channel is『temperature』 which tells us how cold or hot a voxel is. As it will be shown later, the temperature channel can be used to render fire.

OpenVDB在通道中組織其體素數據。如上所述，典型的通道是「密度」。另一個通道是「溫度」，告訴我們體素是多麼冷或熱。如稍後將示出的，溫度通道可以用於火的渲染。

One thing to remember with OpenVDB channels is that they are named. In theory, a 3d app could be exporting VDB density information in a channel named 「bob」. Thankfully, though, most applications follow fairly standard naming conventions. In a later section of this document we』ll show how to use Redshift log files to find out the channel names within an OpenVDB file. Knowing the channel names of your OpenVDB file is essential when using the Redshift Volume Shader, as it will be shown below!

有一件事要記住OpenVDB通道是他們被命名。在理論上，3d應用程序可以導出為「bob」的通道中的VDB密度信息。幸運的是，大多數應用程序遵循相當標準的命名約定。在本文的後面部分，我們將演示如何使用Redshift日誌文件來查找OpenVDB文件中的通道名稱。在使用Redshift Volume Shader時，瞭解OpenVDB文件的通道名稱是必不可少的，如下所示！

Creating a volume grid創建體積網格

In Maya

To create a Redshift volume in Maya, through the Redshift menu, select Redshift->Volume->Create Redshift Volume Shape or CreateRedshift Volume Shape w/Material.

要在Maya中通過Redshift菜單創建Redshift Volume，請選擇Redshift->Volume-> Redshift->Volume->Create Redshift Volume Shape 或CreateRedshift Volume Shape w/Material.

As its name suggests, the second option creates a Redshift Volume Shader and automatically assigns it to the newly created Volume Shape. If this is the first volume shape in your scene, we recommend using the 「w/Material」 option.

顧名思義，第二個選項創建一個Redshift Volume Shader，並自動將其分配給新創建的Volume Shape。如果這是場景中的第一個體積形狀，我們建議使用「W/Material」選項。

Once the Redshift volume shape is created,

you can click and see the follow options in the attribute editor:

創建Redshift體積形節點後，可以單擊並在屬性編輯器中查看以下選項：

You can use the filename box to point to an OpenVDB file. In this case we pointed to the bunny_cloud.vdb file which was downloaded from http://www.openvdb.org/download

您可以使用文件名框指向一個OpenVDB文件。在這種情況下，我們指向 http://www.openvdb.org/download下載的bunny_cloud.vdb文件

This is what』s shown in Maya when the Display Mode was set to 「Points」. 這是Maya顯示時顯示模式設置為「點」。

In 3dsMax

You can create a Redshift volume in 3dsMax through Create->Geometry->Redshift->Volume, as shown below:

您可以通過Create-> Geometry-> Redshift-> Volume在3dsMax中創建Redshift體積，如下所示：

You can use the filename box to point to an OpenVDB file. In this case we pointed to the bunny_cloud.vdb file which was downloaded from http://www.openvdb.org/download

您可以使用文件名框指向一個OpenVDB文件。在這種情況下，我們指向 http://www.openvdb.org/download下載的bunny_cloud.vdb文件

This is what』s shown in 3dsmax when the Display Mode was set to 「Points」. 這是3dsmax當顯示模式設置為「點」時顯示。

Note 注意

OpenVDB files might be in a different coordinate axis system compared to 3dsMax』s. In this case, we had to rotate the bunny by 90 degrees.

與3dsMax相比，OpenVDB文件可能位於不同的坐標軸系統中。在這種情況下，我們不得不將兔子旋轉90度。

The Volume Object Settings體積對像的設置

Use File Sequence/Frame Number/Frame Offset (Maya)

使用文件序列/幀編號/幀偏移（Maya）

The file sequence attributes work just like those found in the file node in Maya. When Use File Sequence is enabled, Frame Number and Frame Offset together define which frame will be loaded by the simple formula frame_to_load = frame_number +

frame_offset. By default, when you enable Use File Sequence, Frame Number is set to equal the current frame time by means of an expression. In other words, Frame Number will track the current frame. Arbitrary expressions can be used to drive thevalues of Frame Number and Frame Offset to perform more advanced numbering such as looping or ping-pong.

文件序列屬性與在Maya中的文件節點中找到的一樣。當啟用使用文件序列時，幀編號和幀偏移一起定義將通過簡單公式frame_to_load = frame_number + frame_offset載入哪個幀。默認情況下，啟用使用文件序列時，幀編號通過表達式設置為等於當前幀時間。換句話說，幀號將跟蹤當前幀。任意表達式可用於驅動幀號和幀偏移的值，以執行更高級的編號，例如循環或乒乓。

Use Sequence/Start Frame/End Frame/Frame Offset/End Condition (3dsMax)

使用序列/起始幀/結束幀/幀偏移/結束條件（3dsMax）

When enabled, Use Sequence instructs Redshift to detect and replace the frame number in the filename with a frame number calculated based on the Start Frame, End Frame, Frame Offset and End Condition parameters. The Start Frame and End

Frame parameters indicate the start and end of the frame sequence, while Frame Offset specifies an offset to apply to the current frame. The End Condition parameter specifies how the sequence should behave outside of the range Start Frame to EndFrame. Hide causes the volume to disappear when outside of the frame range, while Hold causes the Start Frame to be used for all frames before Start Frame and EndFrame to be used for all frames after End Frame. Loop wraps around to the Start Frame when End Frame is reached, while PingPong will run the through the sequence in reverse when End Frame is reached, then forward again when Start Frame is reached, and so on.

啟用時，使用序列指示Redshift檢測並替換文件名中的幀編號，其中幀編號基於起始幀，結束幀，幀偏移和結束條件參數計算。開始幀和結束幀參數指示幀序列的開始和結束，而幀偏移指定應用於當前幀的偏移。結束條件參數指定序列應如何超出範圍開始幀到結束幀的範圍。隱藏導致音量在幀範圍之外時消失，而保持使開始幀用於開始幀之前的所有幀，結束幀用於結束幀之後的所有幀。當到達結束幀時，循環到開始幀，而當到達結束幀時，PingPong將反向運行該序列，然後當到達開始幀時再次轉發，等等。

Display Mode 顯示模式

Selects how the volume data will be shown in the 3d app』s viewport. The choices are Bounding Box (where only the bounding box is shown), Points (where a number of representative points from the grid are shown) and Bounding Box & Points (where both the bounding box and points are shown). The number of points shown is controlled by the Max Points and Prune Threshold, explained below.

選擇如何在3d應用程序的視口中顯示體積數據。選擇是邊界框（其中僅顯示邊界框），點（其中示出了來自網格的多個代表點）和邊界框和點（其中示出了邊界框和點）。所示點的數量由最大點和修剪閾值控制，如下所述。

Keep Points In Memory保持點在內存中

Normally, when switching to a bounding box view, any allocated preview points are freed. Enabling this option keeps the preview points in memory so that the user can

quickly switch between bounding box and points without having to resample the OpenVDB file.

通常，當切換到邊界框視圖時，任何分配的預覽點都將被釋放。啟用此選項會將預覽點保留在內存中，以便用戶可以在邊界框和點之間快速切換，而無需重新對OpenVDB文件進行重新採樣。

Max Points最大點數

Specifies the maximum number of points that would be drawn if the OpenVDB file was completely filled.

指定在OpenVDB文件完全填充時將繪製的點的最大數目。

Prune Threshold修剪閾值

Any OpenVDB voxels that are lower or equal to this value won』t be drawn as points. This is useful to cut away empty space during volume data previewing.

任何低於或等於此值的OpenVDB體素將不會被繪製為點。這在體積數據預覽期間可用於刪除空白空間。

Creating A Redshift Volume Shader 創建Redshift體積著色器

To render a Redshift Volume, you have to assign a Redshift Volume Shader to it. Adjusting the settings of the Redshift Volume Shader defines the look of the volume object.

要渲染一個Redshift Volume，你必須為它指定一個Redshift Volume Shader。調整Redshift Volume Shader的設置可定義體積對象的外觀。

Creating a Redshift Volume Shader In Maya 在Maya中創建Redshift體積著色器

To create a Redshift Volume Shader in Maya, go to Get->Material->Redshift

Volume Material. The following options will appear in the attribute editor.

要在Maya中創建Redshift Volume Shader，請轉到Get-> Material-> Redshift Volume Material。以下選項將顯示在屬性編輯器中。

Creating a Redshift Volume Shader In 3dsMax 在3dsMax中創建Redshift體積著色器

To create a Redshift Volume Shader in 3dsMax, go to the material editor and in Redshift Renderer』s Materials section, choose Redshift Volume Material. The following options will appear:

要在3dsMax中創建Redshift Volume Shader，請轉到材質編輯器，在RedshiftRenderer的材質部分中，選擇Redshift Volume Material。將顯示以下選項：

Before You Proceed, Create A Volume-Affecting Light!

在之前創建影響體積的光

To be able to see your volume, you』ll need to place one or more volume-affecting lights in your scene. Simply create a Redshift light (any kind: physical, domelight, IES, etc) and ensure that its volume contribution scale is set to 1.0.

要能夠看到您的體積，您需要在場景中放置一個或多個影響體積的燈光。只需創建一個Redshfit燈光（任何種類：物理，domelight，IES等），並確保其體積貢獻刻度設置為1.0。

Important note! 重要的提示！ If the scene doesn』t contain any volume-affecting lights, the volume will render black!

如果場景不包含任何影響體積的燈光，則體積將呈現黑色！

Using The Redshift Volume Shader

使用Redshift體積著色器

The Scatter/Absorption/Emission Shading Components散射/吸收/發射遮光

As it can be seen, the Redshift Volume Shader is divided in three shading

components: scatter, absorption and emission.

可以看出，Redshift體積著色器分為三個陰影部分：散射，吸收和發射。

You can think of scatter as 「diffuse」. Absorption is 「transparency」. And emission

is 「incandescence」 or 「self-illumination」.

你可以認為分散是「漫反射」。吸收是「透明度」。而發射是「白熾」或「自照亮」。

Therefore, if you want to make your volume brighter or darker, you need to adjust the

scatter parameters. If you want to make your volume more solid or more transparent, you need to adjust the absorption parameters. And, finally, if your volume represents a self-illuminating effect like fire and want to make it brighter or dimmer, you need to adjust the emission parameters.

因此，如果要使您的體積更亮或更暗，您需要調整分散參數。如果你想讓你的體積更加堅實或更透明，你需要調整吸收參數。最後，如果你的體積表示像火的自照亮效果，並想要使它更亮或更暗，你需要調整發射參數。

Channel Names通道名

Important note! 重要的提示！ If you don』t set the scatter or emission channel names, Redshift won』t render the volume!

如果不設置散射或發射通道名稱，Redshift將不渲染體積！

All three shading components have a 「channel」 textbox. As mentioned earlier, each OpenVDB voxel can contain values that describe different properties of the volume. Typical examples include 『density』and 『temperature』. If your OpenVDB file was exported from SideFX Houdini, it will almost certainly contain a channel called 『density』. And if it』s a fire or explosion effect, it will also contain a channel called 『temperature』. The density channel name (in this case 『density』) should be typed in the scatter channel box. And the temperature channel name (in this case 『temperature』)should be typed in the emission channel box.

所有三個陰影部件都有一個「通道」文本框。如前所述，每個OpenVDB體素可以包含描述卷的不同屬性的值。典型的例子包括「密度」和「溫度」。如果您的OpenVDB文件從SideFX

Houdini導出，它幾乎肯定會包含一個名為「density」的通道。如果它是一個火或爆炸效應，它還將包含一個通道稱為「溫度」。密度通道名稱（在本例中為「density」）應在分散通道框中鍵入。並且溫度通道名稱（在這種情況下為「temperature」）應在發射通道框中鍵入。

But what if our OpenVDB doesn』t contain channels called 『density』 or 『emission』? What if they were called differently? You can use the Redshift Log File to find out which channels are contained in the OpenVDB file. When Redshift loads an OpenVDB file, it prints out the names of all the channels it contains. This is how this information looks like in the Redshift log file:

但是如果我們的OpenVDB不包含稱為density或emission的通道呢？如果他們被稱為不同？您可以使用Redshift日誌文件來找出OpenVDB文件中包含的通道。當Redshift載入OpenVDB文件時，它包含的所有通道的名稱。這是Redshift日誌文件中此信息的樣子：

Preparingvolume objects... Loading: c:MyVDBFilesunny_cloud.vdb Contained grids: density Done! Dim: (577, 572, 438). Num loaded grids: 1. Num voxelstotal: 26749120 Time to process 1 volume objects: 0ms

In this particular case, we can see that bunny_cloud . vdb contains one channel called 『density』, so we type 『density』(without the quotes) in the scatter』s channel box.

在這種特殊情況下，我們可以看到bunny_cloud . vdb 包含一個稱為「density」的通道，因此我們在scatter的通道框中鍵入density。

Scattering and absorption散射和吸收

Scattering and absorption are similar to「diffuse」 and 「transparency」 respectively. Redshift computes these using the OpenVDB file』s density channel. We』ll demonstrate how this happens through a series of examples.

散射和吸收分別類似於「漫射」和「透明度」。Redshift使用OpenVDB文件的密度通道計算這些值。我們將通過一系列示例演示這是如何發生的。

The most basic adjustment of scattering and absorption can happen through the 「Scatter Coefficient」 and 「Absorption Coefficient」 parameters. Increasing the scatter coefficient makes the volume brighter. Increasing the absorption coefficient makes the volume more opaque. A thing to keep in mind is that, the more opaque the volume, the less light it will allow to travel through it. In other words, high absorption means the volume render darker. If you want to preserve the same approximate intensity, we recommend adjusting the scatter and absorption coefficients together. I.e. if you want to make your volume more opaque by doubling the absorption coefficient, also double the scatter coefficient. This is demonstrated in the following examples:

散射和吸收的最基本調整可以通過「散射係數」和「吸收係數」參數發生。增加散射係數使得體積更亮。增加吸收係數使得體積更不透明。要記住的一個事情是，體積越不透明，它將允許穿過它越少的光。換句話說，高吸收意味著體積變暗。如果要保持相同的近似強度，我們建議一起調整散射和吸收係數。也就是說如果你想通過雙倍的吸收係數使你的體積更加不透明，也是散射係數的兩倍。這在以下實施例中得到證明：

Default settings. Scatter Coefficient=1.0. Absorption Coefficient=1.0

默認設置。散射係數= 1.0。吸收係數= 1.0

Scatter Coefficient=3.0. Absorption Coefficient=3.0

散射係數= 3.0。吸收係數= 3.0

Scatter Coefficient=10.0. Absorption Coefficient=10.0

散射係數= 10.0。吸收係數= 10.0

If you want to make the volume brighter or darker, you can adjust the scatter coefficient without increasing the absorption one, as shown below:

如果要使體積更亮或更暗，您可以調整散射係數而不增加吸收係數，如下所示

Scatter Coefficient=5.0. Absorption Coefficient=5.0

散射係數= 5.0。吸收係數= 5.0

Scatter Coefficient=10.0. Absorption Coefficient=5.0

散射係數= 10.0。吸收係數= 5.0

You can also use the 「Scatter Tint」 to adjust the overall color of the volume, as shown below

您還可以使用「散點色調」調整體積的整體顏色，如下所示

White Tint(Scatter Coefficient=3.0. Absorption Coefficient=3.0)

白色（散射係數= 3.0，吸收係數=3.0）

Blue tint藍色色調

More advanced manipulation of scattering can happen vie the scatter color ramp. As mentioned above, scattering and absorption happen by remapping the density OpenVDB channel. The scatter color ramp allows us to map the density channel into different colors.

可以通過散射顏色漸變進行更高級的散射操作。如上所述，散射和吸收通過重新映射密度OpenVDB通道而發生。散射顏色漸變允許我們將密度通道映射到不同的顏色。

…and get the following psychedelic result!

...並得到以下迷幻的結果！

The absorption shading component also contains a ramp, except it』s a scalar ramp instead of a color ramp. Similar to the scatter component』s color ramp, the absorption ramp allows for finer control of the opacity of the OpenVDB.

吸收係數還包含漸變，除了它是標量漸變而不是顏色漸變。與散射分量的顏色類似，吸收係數漸變允許更好地控制OpenVDB的不透明度。

Say we wanted our volume』s low-density edges appear transparent while making the higher-density areas become suddenly opaque (i.e. a higher absorption). We could make a ramp that looks like this:

假設我們希望體積的低密度邊緣看起來是透明的，同時使更高密度的區域突然變得不透明（即更高的吸收）。我們可以做一個漸變，看起來像這樣：

Notice how the outer edges of the bunny (low density areas) are bright (lower absorption) while the deeper, denser parts are now darker because of the increased absorption.

注意兔子（低密度區域）的外邊緣是明亮的（較低的吸收），而較深，較緻密的部分現在更暗，因為增加的吸收。

Without the ramp (Scatter Coefficient=3.0. Absorption Coefficient=3.0)

沒有漸變（散射係數= 3.0，吸收係數=3.0）

With the ramp (Scatter Coefficient=1.5, Absorption Coefficient=3.0)

Emission發射

The emission component is useful when creating effects such as fire and explosions. For this section, we』ll use the fire.vdb file which was downloaded from http://www.openvdb.org/download

當產生諸如火災和爆炸的效果時，發射分量是有用的。在本節中，我們將使用從http://www.openvdb.org/download下載的fire.vdb文件

This file contains both a density and a temperature channel, as it can be seen in the Redshift log file:

此文件包含密度和溫度通道，如可在Redshift日誌文件中看到的：

We, therefore, type 『density』 (without the quotes) in the scatter channel textbox and 『temperature』 (without the quotes) in the emission channel textbox.

因此，我們在散射通道文本框中鍵入「density」，在發射通道文本框中鍵入「temperature」。

This is how the fire vdb file looks like without and with emission

這是火vdb文件看起來像沒有和發射

Without emission, we can only see the smoke (density) part

沒有發射，我們只能看到煙霧（密度）部分

With emission we can see the fire effect

隨著發射我們可以看到火效果

Achieving the effect shown above involves adjusting the emission color ramp. The reason for that is that the temperature channel that is stored in the OpenVDB file is simply a number per voxel which tells us how hot a voxel is. It doesn』t describe how red or yellow the fire is. It』s up to the user to adjust the emission color ramp to 『translate』 the temperature value into emissive colors.

實現上述效果涉及調整發射顏色斜坡。其原因是存儲在OpenVDB文件中的溫度通道僅僅是每個體素的數字，其告訴我們體素是多熱。它不描述火是紅色還是黃色。由用戶調整發射顏色斜坡以將溫度值「轉換」成發射顏色。

For the above example, we used a ramp that looks like this:

對於上面的例子，我們使用了一個漸變，看起來像這樣：

One way to read the above ramp is this: 一種讀取上述漸變的方法是：

For low temperatures, use black/gray對於低溫，請使用黑色/灰色
For medium temperatures use red對於中溫使用紅色
For higher temperatures use yellow/white對於較高的溫度使用黃色/白色

Achieving the expected look for emission can sometimes be challenging for two reasons:

實現預期的發射量有時是具有挑戰性的原因有兩個：

Emission works in conjunction with scattering and absorption. As it can be seen in the above example, there』s also a density (smoke) channel in the OpenVDB file which can be seen in the left picture.Smoke (scatter/absorption) naturally obstructs fire (emission) so it reduces its effect. Therefore, care has to be taken to ensure thatscattering/absorption (smoke) is adjusted properly and doesn』t interfere too much or too little with the emission (fire).

發射和散射和吸收一起工作。它可以在上面的例子中看到的，還有一個密度（煙）在openvdb文件，可以在左邊的圖片看到通道。煙霧（散射/吸收）自然阻礙火（排放），從而降低其效果。因此，必須注意，以確保散射/吸收（煙）適當調整，不能幹擾太多或過少的發射（火）。

The emission ramp is driven by the temperature OpenVDB channel. Depending on the 3d app used to author the OpenVDB file, the ranges can be pretty dramatic. In certain cases, a range remapping might have to happen (see relevant section below).

發射漸變是由溫度openvdb通道驅動。取決於使用作者的openvdb文件的3D應用程序，範圍可以非常戲劇性。在某些情況下，一系列映射可能發生（見相關章節）。

Advanced Topics高級選項

Shadow Density Scale 陰影的密度大小

In the advanced tab of the Redshift Volume Shader, you can find a parameter called 「shadow density scale」. This parameter allows a volume to appear more transparent or more opaque to shadow rays. It is, in essence, a「trick」 that can help emulate multiple scattering, i.e. the effect of light bouncing around a volume. This can be achieved by setting the shadow density scale below 1.0.

在Redshift Volume Shader的高級選項卡中，可以找到一個名為「陰影密度標度」的參數。此參數允許卷顯示為更加透明或對陰影光線更不透明。它本質上是可以幫助模擬多個散射的「技巧」，即光圍繞體積彈動的效果。這可以通過將陰影密度標度設置為低於1.0來實現。

The other way for allowing more light to pass through the volume would have been to reduce its absorption. However, this would make the volume appear more 『puffy』 and transparent. The shadow density scale, on the other hand, allows the volume to retain its 「tightness」 while allowing more light to pass through it, as shown below.

允許更多的光通過該體積的另一種方式將是減少其吸收。然而，這將使體積看起來更加「膨脹」和透明。另一方面，陰影密度標度允許體積保持其「緊密度」，同時允許更多的光通過它，如下所示。

Shadow density scale=1.0 (Scatter Coefficient=3.0. Absorption Coefficient=3.0)

陰影密度大小= 1.0（散射係數= 3.0，吸收係數= 3.0）

Shadow density scale=0.5 (Scatter Coefficient=3.0, Absorption Coefficient=3.0)

陰影密度大小= 0.5（散射係數= 3.0，吸收係數= 3.0）

Range Remapping範圍映射

The values stored in OpenVDB channels can vary wildly depending on the 3d app that

was used to author them. This can be true for both density and emissionchannels.

存儲在OpenVDB通道中的值可能會有很大變化，具體取決於用來創作它們的3d應用程序。這對於密度和發射通道都是正確的。

The range remapping controls found in the advanced tab of the Redshift Volume

Shader, allow the adjustment of these values just before Redshift uses them. The old min/max range is remapped to the new min/max range.

在Redshift Volume Shader的高級選項卡中找到的範圍重新映射控制項允許在Redshift使用它們之前調整這些值。舊的最小/最大範圍被重新映射到新的最小/最大範圍。

For example, a temperature channel might contains values that range between 0 and

100 but the emission color ramp only accepts inputs ranging between 0 and 1. Inthis case, the user should use old min=0, old max=100 and leave new min and newmax at their default 0 and 1 respectively. In essence, this would 『squash』 the0->100 range into a 0->1 range.

例如，溫度通道可以包含範圍在0和100之間的值，但是發射顏色斜坡僅接受範圍在0和1之間的輸入。在這種情況下，用戶應該使用舊的min= 0，old max =100並且保留new min和new max分別為默認值0和1。實質上，這將「擠壓」0-> 100範圍到0-> 1範圍。

Noise噪點

As mentioned above, a volume-affecting light is required in the scene in order to

be able to see our volumes. Each light has a 「volume samples」 parameter whichdefines the quality of lighting on the volume. If a volume is rendering noisy/grainy, it』s likely that it』s being lit by a light that doesn』t have enough samples. The following picturesdemonstrate the effect of the lights volume num samples. Notice how the right image is cleaner.

如上所述，在場景中需要影響體積的光，以便能夠看到我們的體積。每個燈光具有定義該體積上的照明質量的「體積樣本」參數。如果一個體積正在渲染噪點/顆粒，它可能是由一個沒有足夠的樣品的燈照亮。以下圖片展示了燈光體積採樣的效果。注意圖像如何變得更乾淨。

Tip提示

The more transparent the volume, the more samples it will need to render cleanly.

Relatively opaque volumes can render cleanly with fewer samples.

體積越透明，需要更乾淨地渲染的樣本越多。相對不透明的體積可以用更少的採樣得到乾淨的圖像。

Domelight』s Volume Num Samples set to 1

Domelight體積採樣數值設置為1

Domelight』s Volume Num Samples set to 512

Domelight體積採樣設置為512

When using global illumination (GI), volume noise can appear because of brute-force GI rays, too.

當使用全局照明（GI）時，體積的出現噪點是由於Brute-Force GI射線。

In the scene below we disabled our domelight, made the ground plane emissive and enabled brute-force GI. The effect is GI lighting coming from below the bunny.

在下面的場景中，我們禁用了Domelight，使地平面發射並啟用了Brute-Force。照明從兔子下面來。

Notice how the image using more GI rays is cleaner.

注意使用越多GI射線圖像變得更乾淨。

Brute-force GI with 16 rays

Brute-Force GI射線為16