文档

Unity Engine

User Manual

Script Reference

Unity Engine

HDR Output in URP

Understand how HDR Output works in URP.
阅读时间6 分钟最后更新于 1 个月前
High Dynamic Range content has a wider color gamut and greater luminosity range than standard definition content.
URP can output HDR content for displays which support that functionality.
注意
You can only use HDR Output with a linear color space. For more information on color spaces in Unity, refer to Color space.

Understand HDR Output implementation

Unity's HDR Output is split into the following steps which always occur in this order:
  1. Tone mapping
  2. Transfer Function

Tone mapping

Tone mapping is the first step in the HDR Output process. In this step, Unity balances the exposure and hue of the scene according to the target display's dynamic range. Dynamic range is determined by the following properties:
  • Minimum brightness
  • Maximum brightness
  • Paper white brightness
For more information on these properties, refer to Important tone mapping values.
At the same time, Unity performs the color space conversion. Unity converts the colors from the default Rec. 709 color space to the target display's color space. This maps the colors in the scene to the wider gamut of colors of the target display and ensures Unity utilizes the full color gamut available on the display.
For more information, refer to HDR tone mapping in URP and configure HDR tone mapping settings.

Transfer function

The second step of HDR Output is the transfer function. The transfer function converts the output of the rendering process to levels of brightness of a given display. Unity determines the correct transfer function for the display and uses it to encode the output according to the standard the display expects. This enables Unity to use the correct level of precision for the gamma and create accurate exposure levels on the target display.

HDR tone mapping in URP

After you enable Allow HDR Display Output, you must configure tone mapping settings for your HDR input.
In order to configure these settings effectively, you need to understand how certain values related to tone mapping determine the visual characteristics of your HDR output.

Important tone mapping values

To properly make use of the capabilities of HDR displays, your
Tonemapping

?

configuration must take into account the capabilities of the target display, specifically these three values (in nits):
  • Minimum supported brightness.
  • Maximum supported brightness.
  • Paper White value: This value represents the brightness of a paper-white surface represented on the display, which determines the display's brightness overall.
注意
Low Dynamic Range (LDR) and High Dynamic Range (HDR) content do not appear equally bright on displays with the same Paper White value. This is because displays apply extra processing to low dynamic range content that bumps its brightness levels up. For this reason, it is best practice to implement a calibration menu for your application.

Usable user interfaces depend on accurate Paper White values

Unlit materials do not respond to lighting changes, so it is standard practice to use an Unlit material for user interfaces. Calculations for Unlit material rendering define brightness with values between 0 and 1 when you are not specifically targeting HDR displays. In this context, a value of 1 corresponds to white, and a value of 0 corresponds to black.
However, in HDR mode, URP uses Paper White values to determine the brightness of Unlit materials. This is because HDR values can exceed the 0 to 1 range.
As a result, Paper White values determine the brightness of UI elements in HDR mode, especially white elements, whose brightness matches Paper White values.

Configure HDR tone mapping settings

You can select and adjust tone mapping modes in the Tonemapping Volume component settings. You can also adjust some aspects of your HDR tone mapping configuration with a script. For more information on this, refer to the HDROutputSettings API.
After you enable Allow HDR Display Output, HDR tone mapping options become visible in the Volume component.

Tonemapping

URP provides two Tonemapping modes: Neutral and ACES. Each tone mapping mode has some unique properties.
  • Neutral mode is especially suitable for situations where you do not want the tone mapper to color grade your content.
  • ACES mode uses the ACES reference color space for feature films. It produces a cinematic, contrasty result.
For more information on these modes, refer to the HDR Output section of Tonemapping Volume Override reference.

The HDROutputSettings API

The HDROutputSettings API makes it possible to enable and disable HDR mode, as well as query certain values (such as Paper White).
These values are also listed on the HDR output display table on the Rendering Debugger. To access the table, navigate to Window > Analysis > Render Pipeline Debugger > Rendering > HDR Output.

Use Offscreen Rendering with HDR Output

When you use offscreen rendering techniques, not all cameras in a scene output directly to the display, for example, when Unity renders the output to a Render Texture. In these situations, use the output of the camera before rendering post-processing.
Unity does not apply HDR Output processing to the output of cameras which use offscreen rendering techniques. This prevents HDR Output processing from being applied twice to the camera's output.

Use Standard Dynamic Range (SDR) Rendering with HDR Output enabled

HDR Output relies on HDR Rendering to provide pixel values in the correct format for tone mapping and color encoding. The values after HDR tone mapping are in nits and exceed 1. This differs from SDR Rendering where the pixel values are between 0 and 1. As a result of this, the use of SDR Rendering with HDR Output can cause the rendered image to look underexposed or oversaturated.
You can use SDR Rendering on a per-camera basis when you have HDR Output enabled, this can be useful for cameras that only render unlit materials, for example, for mini-map rendering. However, the use of SDR Rendering with HDR Output imposes some limitations.
To ensure correct rendering when you use SDR Rendering with HDR Output, you must avoid any render passes that occur after post-processing. This includes URP's built-in effects which insert render passes after post-processing. As a result, SDR Rendering with HDR Output is incompatible with the following features:

2D Renderer

To use SDR Rendering with HDR Output on the 2D Renderer, you must ensure post-processing is turned off.

Platform Compatibility

URP only supports HDR Output on the following platforms:
  • Windows with DirectX 11, DirectX 12 or Vulkan
  • macOS devices that use Metal
  • iOS 16+ devices
  • Consoles
  • XR devices with HDR support
  • Android devices that use Vulkan and GLES
Notes: