2016年7月15日（light field 光场技术, magic leap使用原理之一）

Light Field Imaging: The Future of VR-AR-MR- Part 4: Jon Karafin (youtube, Lytro CEOpresentation)
Gordon Wetzstein: "Why should we care about light field displays?" (youtube,advanced knowledge)
The Lytro Light-Field Camera: How It Works (article)
Light-Field technology is here! Smart phone focusing after taking the shot (article)
两则视频，两篇报道，了解光场技术！

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Lytro相机可在拍摄后自由选取聚焦点

光线穿过透镜阵列示意图

Adobe和Nvidia的微型透镜阵列原型

翻译一下article里对原理通俗的描述：

The technology is based on the idea of a light field, or "the amount of light traveling in every direction in every point in space," Ng says. While a conventional camera captures just a two-dimensional image of the light as it enters the camera, a light-field camera also captures the direction that the light was coming from.
这项技术（Lytro光场相机）是基于光场这个概念的，用Wu（创始人）的话来说就是：“从所有方向，穿过空间中所有的点，的光，的多少”（呵呵）。一个传统相机记录的是光进入摄像机的二维图像，一个光场相机更能做到捕捉光进入的方向（天顶角、方位角）。

A normal camera has a lens, a sensor for recording the image, an aperture to allow a certain amount of light into the camera and a shutter to time how long the sensor is exposed to that light. All those working in concert create (hopefully) a well-lit single image. But in a light-field camera, there's an extra layer called a microlens array, which is placed between the sensor and the lens. This layer is composed of multiple smaller lenses, which allow the sensor to record more information about the incoming rays of light, including the light coming from different distances away from the camera.
传统（数码）相机有许多透镜、感光元件、光圈（调节多少光进入）和快门（调节曝光时间）组成。他们足够拍一张好照片了。但是在光场相机的摄像头和感光元件之间，多了一层叫“微型透镜阵列”的东西。这东西不得了，它能帮助记录物体离相机的距离（这样就可后期加工景深了aka聚焦在不同位置。利用的是光场的额外信息，而不是仅仅靠算法，虽然还是加工出来的）

That extra information is the key to Lytro's trick. "In order to be able to focus after the fact, you have to collect the light field," Ng says. The additional recorded information allows software to manipulate the image, translating the stored information into what Lytro calls living pictures that can be refocused interactively, or even into three-dimensional pictures. The software essentially does the work of a physical camera, performing algorithms on the information collected by the light-field camera to mimic the physics used to focus a traditional camera.

数码相机|光场相机对比

更通俗的版本！：

Basically the idea of the so called **light-field **technology is that depth of field information is stored by taking a picture with arrays of pixels instead of single pixels.The resulting directional information can help a computer (or smart phone for that matter) calculate depth of field information after the shot has been taken.
光场技术，基本上就是用像素阵列而不是单个像素，来记录方向数据。在拍摄照片之后，我们可以用记录下的方向数据来计算景深（从而调焦距）。

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关于magic leap是如何利用光场的， 非技术人员，无责任猜测：

magic leap原型，注意背景里的“人眼光学解构”墙报

淘宝上的光纤灯

不出意料的话，magic leap是对光场相机技术的逆运用！

如上图的光纤灯，如果把光纤末端对准墙壁，你一定会看到一个五彩斑斓的投影。小时候家里也有一个这样的光纤灯，宜家出品。把玩的时候（经常玩坏就是了），我就在想，有没有可能用光纤投影出一整副照片呢？

答案是肯定的：华盛顿大学的Eric Seibel一直致力于完成这样的研究。（老实说在看到他的研究之前我早已忘记自己提过这样的疑问-.-） Scanning Fiber Endoscope （youtube）（这是对光纤内窥镜的逆运用）

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继续往下想，如果我们投影的不是二维图片，而是经过编程的四维光场（四维就是有四个变量来描述这个场），包含RGB、光强度和景深信息，是不是就能投影出一具3D物体了呢？

就像光场相机记录的图片可以合成3D图片，反过来，电脑里的3D模型也可以经过光场化，再投影在现实世界里。当然，可能要经过特殊的微型透镜阵列！

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即使是这样，分辨率、压缩和计算机感知（知道使用者相对3D模型的位置）仍然是让人担忧的问题，不过就magic leap的实力来说不在话下。估计今年(2016)年底会有大动作，明年(2017)年底就可以当年货卖了:)。

这篇文章对光场投影提供了依据：
A Compressive Light Field Projection System——MIT
知乎上也有牛人提点：
Magic Leap 和微软的 HoloLens 相比有哪些异同点？