Auto Exposure 自動曝光
本文檔主要是對Unity官方手冊的個人理解與總結（其實以翻譯記錄爲主：>）
僅作爲個人學習使用，不得作爲商業用途，歡迎轉載，並請註明出處。
文章中涉及到的操作都是基於Unity2018.4版本
參考鏈接：https://github.com/Unity-Technologies/PostProcessing/wiki/Auto-Exposure
In ocular physiology, adaptation is the ability of the eye to adjust to various levels of darkness and light. The human eye can function from very dark to very bright levels of light. However, in any given moment of time, the eye can only sense a contrast ratio of roughly one millionth of the total range. What enables the wider reach is that the eye adapts its definition of what is black.
在眼睛生理學中，適應性是指眼睛適應不同程度的黑暗和光亮的能力。人眼可以在非常暗到非常亮的光線下工作。然而，在任何給定的時刻，眼睛只能感知到大約百萬分之一的對比度。眼睛適應了黑色的定義範圍，這使得它的適應更廣。
This effect dynamically adjusts the exposure of the image according to the range of brightness levels it contains. The adjustment takes place gradually over a period of time, so the player can be briefly dazzled by bright outdoor light when, say, emerging from a dark tunnel. Equally, when moving from a bright scene to a dark one, the “eye” takes some time to adjust.
根據圖像所包含的亮度範圍可以動態調整圖像的曝光效果。這種調整是在一段時間內逐漸進行的，所以當玩家從黑暗的隧道中走出來時，他們可能會被室外明亮的燈光短暫地眼花繚亂。同樣，當從一個明亮的場景切換到一個黑暗的場景時，“眼睛”需要一些時間來調整。
Internally, this effect generates a histogram on every frame and filters it to find the average luminance value. This histogram, and as such the effect, requires Compute shader support.
在內部，這種效果在每一幀上生成一個直方圖（柱狀圖），並對其進行過濾，以找到平均亮度值。這個直方圖，以及它的效果，需要計算着色器的支持。
Properties
Exposure settings:
| Property | Function |
|---|---|
| Filtering | These values are the lower and upper percentages of the histogram that will be used to find a stable average luminance. Values outside of this range will be discarded and wont contribute to the average luminance. |
| 過濾 | 這些值是指低於或高於當前幀直方圖中用於找到穩定的平均亮度的百分比。超出此範圍的值將被丟棄，不會影響平均亮度。 |
| Minimum | Minimum average luminance to consider for auto exposure (in EV). |
| 最小值 | 自動曝光(曝光值)要考慮的最小平均亮度。 |
| Maximum | Maximum average luminance to consider for auto exposure (in EV). |
| 最大值 | 自動曝光(曝光值)要考慮的最大平均亮度。 |
| Exposure Compensation | Middle-grey value. Use this to compensate the global exposure of the scene. |
| 曝光補償 | 補償值。用這個來補償場景的總體曝光度。 |
Adaptation settings:
| Property | Function |
|---|---|
| Type | Use Progressive if you want the auto exposure to be animated. Use Fixed otherwise. |
| 類型 | 如果你想讓自動曝光動畫化，可以使用漸進方式。否則，使用固定方式 |
| Speed Up | Adaptation speed from a dark to a light environment. |
| 增加 | 從黑暗環境到光亮環境的適應速度。（僅Progressive ） |
| Speed Down | Adaptation speed from a light to a dark environment. |
| 減少 | 從光亮環境到黑暗環境的適應速度。（僅Progressive ） |
Details
Use the Filtering range to exclude the darkest and brightest part of the image. To compute an average luminance you generally don’t want very dark and very bright pixels to contribute too much to the result. Values are in percent.
使用過濾範圍來排除圖像中最暗和最亮的部分。要計算平均亮度，通常不希望非常暗和非常亮的像素對結果影響太多。值以百分比爲單位。
Minimum/Maximum values clamp the computed average luminance into a given range.
最小/最大值將計算出的平均亮度固定在給定的範圍內。
You can also set the Type to Fixed if you don’t need the eye adaptation effect and it will behave like an auto-exposure setting.
如果你不需要眼睛的適應效果，你也可以把類型設置爲Fixed，它的行爲像一個自動曝光設置。
It is recommended to use the Light Meter monitor when setting up this effect.
建議在設置此效果時使用光度計監視器。
Requirements
- Compute shader
- Shader model 5
See the Graphics Hardware Capabilities and Emulation page for further details and a list of compliant hardware.
有關詳細信息和兼容硬件列表，請參閱圖形硬件功能和仿真頁面。