纯粹翻译分享，原文来自photometrics如下
https://www.photometrics.com/learn/camera-basics/how-is-an-image-made

How Is An Image Made? --- 图像是如何制作的？

Introduction

Cameras are incredible tools that allow us to capture and make sense of the visible world around us. Most mobile phones made today come with a camera, meaning that more people than ever are becoming familiar with camera software and taking images. But one of the largest applications of cameras is for scientific imaging, in order to take images for scientific research. For these applications, we need carefully manufactured scientific cameras.

What Is Light?

The most important aspect of a scientific camera is the ability to be quantitative, measuring specific quantities of something. In this case, the camera is measuring light, and the most basic measurable unit of light is the photon.

科学相机最重要的方面是定量的能力，测量特定数量的某物。在这种情况下，相机正在测量光，光的最基本的可测量单位是光子。

Photons are particles that make up all types of electromagnetic radiation, including visible light and radio waves, as seen in Figure 1. One of the most important part of this spectrum for imaging is visible light, which ranges from 380-750 nanometers, as seen in the insert of Figure 1.

光子是构成所有类型电磁辐射的粒子，包括可见光和无线电波，如图 1 所示。成像光谱中最重要的部分之一是可见光，其范围为 380-750 纳米，如图 1 的插页所示。

What-is-light.png

Figure 1: The electromagnetic spectrum. This spectrum indicates what form of radiation is produced from photons at different wavelengths and frequencies, with photons of higher frequency having higher energy and lower wavelength, and vice versa. With increasing wavelength/decreasing frequency/decreasing energy, the spectrum includes gamma rays (Greek letter for gamma: γ), x-rays, ultraviolet (UV), visible light (more detailed spectrum shown in insert), infrared (IR), microwave, standard radio waves (including frequency modulation FM and amplitude modulation AM commercial radio frequencies) and long radio waves. Wavelength is shown in magnitudes of 10 in meters, frequency in magnitudes of 10 in Hz. For the visible spectrum, different wavelengths produce different colors, including violet (V, 380-450), blue (B, 450 495), green (G, 495-570), yellow (Y, 570 590), orange (O, 590-620), red (R, 620-750), all wavelengths in nanometers (nm). Image from Wikimedia Commons.

图 1：电磁频谱。该光谱表示不同波长和频率的光子产生哪种形式的辐射，频率较高的光子具有较高的能量和较低的波长，反之亦然。随着波长的增加/频率的降低/能量的降低，光谱包括伽马射线（伽马的希腊字母：γ）、X 射线、紫外线 （UV）、可见光（插页中显示的更详细光谱）、红外线 （IR）、微波、标准无线电波（包括调频 FM 和调幅 AM 商用无线电频率）和长无线电波。波长以 10 的幅度表示，以米为单位，频率以 10 的幅度表示，以赫兹为单位。对于可见光谱，不同的波长会产生不同的颜色，包括紫色（V，380-450），蓝色（B，450 495），绿色（G，495-570），黄色（Y，570 590），橙色（O，590-620），红色（R，620-750），所有波长均以纳米（nm）为单位。图片来自Wikimedia Commons。

As microscopes typically use visible, infrared (IR) or ultraviolet (UV) light in the form of a lamp or laser, a scientific camera is essentially a device that needs to detect and count photons using a sensor.

由于显微镜通常以灯或激光的形式使用可见光、红外线 （IR） 或紫外线 （UV），因此科学相机本质上是一种需要使用传感器检测和计数光子的设备。

Sensors

A sensor for a scientific camera needs to be able to detect and count photons, and then convert them into electrical signals. This involves multiple steps, the first of which involves detecting photons. Scientific cameras use photodetectors, where photons that hit the photodetector are converted into an equivalent amount of electrons. These photodetectors are typically made of a very thin layer of silicon. When photons from a light source hit this layer, they are converted into electrons. A layout of such a sensor can be seen in Figure 2.

科学相机的传感器需要能够检测和计数光子，然后将其转换为电信号。这涉及多个步骤，其中第一个步骤涉及检测光子。科学相机使用光电探测器，其中撞击光电探测器的光子被转换为等量的电子。这些光电探测器通常由非常薄的硅层制成。当来自光源的光子撞击该层时转化为电子。这种传感器的布局如图2所示。

Sensor.png

Figure 2: A cross-section of a camera sensor. Light first hits the microlens (top of image), which focuses the light onto the silicon pixel (at the bottom of the image). The sensor area outside of this light path is full of integrated electronics and wiring.

图 2：相机传感器的横截面。光线首先照射到微透镜（图像顶部），微透镜将光线聚焦到硅像素（在图像底部）。该光路之外的传感器区域充满了集成的电子设备和布线。

Sensor Pixels

However, having just one block of silicon would mean detection was possible, but not localization. By separating the silicon layer into a grid of many tiny squares, photons can be both detected and localized. These tiny squares are referred to as pixels, and technology has developed to the point where you can fit millions of them onto a sensor. When a camera advertises as having 1 megapixel, this means the sensor is an array of one million pixels, a 1000×1000 grid.

然而，只有一块硅意味着可以进行检测，但不能进行定位。通过将硅层分离成许多小方块的网格，可以检测和定位光子。这些微小的方块被称为像素，技术已经发展到可以将数百万个正方形安装到传感器上的地步。当相机宣传为具有 100 万像素时，这意味着传感器是一个 100 万像素的阵列，即 1000×1000 网格。

In order to fit more pixels onto sensors, pixels have become very small, but as there are millions of pixels the sensors are still quite large in comparison. The Prime BSI camera has 6.5 µm square pixels (42.25 µm2 area) arranged in an array of 2048 x 2048 pixels (4.2 million pixels), resulting in a sensor size of 13.3 x 13.3 mm and a diagonal of 18.8 mm. Meanwhile, the Prime 95B has the same 18.8 mm diagonal sensor, but with 11 µm square pixels (area of 121 µm2) in a 1200 x 1200 array (1.4 million pixels). The Prime 95B, therefore, has fewer sensor pixels (decreasing the maximum imaging resolution), but each pixel is 3x larger in the area (increasing the sensitivity).

为了在传感器上安装更多的像素，像素变得非常小，但由于有数百万像素【像素就是像元pictureelement】，相比之下，传感器仍然相当大。 PrimeBSI相机具有6.5μm方形像素(42.25μm2区域)，排列成2048x2048像素(420万像素)的阵列，传感器尺寸为13.3x13.3mm，对角线为18.8mm。 Prime95B相机具有11μm方形像素(面积为121μm2)，排列成1200x1200阵列(140万像素)的阵列，传感器尺寸为13.3x13.3mm，对角线为18.8mm。 后肢传感器像素较少(降低了最大成像分辨率)，但每个像素的面积增加了3倍(提高了灵敏度)。

Making sensor pixels smaller allows for more to fit on a sensor, but if pixels become too small they won’t be able to detect as many photons, which introduces the concept of compromise in camera design between resolution and sensitivity. One option to consider is binning, which is discussed in a separate article. Due to these reasons the overall sensor size, pixel size, and the number of pixels are carefully optimized in camera design. When deciding which scientific camera to get, pixel size is a vital metric that is important to consider.

传感器像素变小可容纳更多像素，但如果像素变得太小将无法检测到尽可能多的光子，这在相机设计中引入了分辨率和灵敏度之间折衷的概念。可以考虑的一个选项是binning分箱，这将在另一篇文章中讨论。由于这些原因，在相机设计中，传感器的整体尺寸、像素尺寸和像素数量都经过了精心优化。在决定购买哪种科学相机时，像素大小是一个重要的指标，需要考虑。

Generating An Image

When exposed to light, each pixel of the sensor detects how many photons come into contact with it. This gives a map of values, where each pixel has detected a certain number of photons. This array of measurements is known as a bitmap and is the basis of all scientific images taken with cameras, dependant on the signal level of the experiment and application. The bitmap is accompanied by the metadata, which contains all the other information about the image, such as the time it was taken, camera settings, imaging software settings, and microscope hardware information.

当暴露在光线下时，传感器的每个像素都会检测到有多少光子与之接触。这给出了一个值图，其中每个像素都检测到一定数量的光子。这种测量数组被称为位图，是相机拍摄的所有科学图像的基础，取决于实验和应用的信号电平。位图附带元数据，其中包含有关图像的所有其他信息，例如拍摄时间、相机设置、成像软件设置和显微镜硬件信息。

The following are the processes involved in generating an image from light using a scientific camera:

1. Photons hit the sensor are converted into electrons (called photoelectrons). 撞击传感器的光子被转化为电子（称为光电子）。
   • The rate of this conversion is known as quantum efficiency (QE). With a QE of 50%, only half of the photons will be converted to electrons and information will be lost. 这种转换的速率称为量子效率 （QE）。在50%的QE下，只有一半的光子会转化为电子，信息会丢失。
2. The generated electrons are stored in a well in each pixel, giving a quantitative count of electrons per pixel 生成的电子存储在每个像素的孔well中，从而给出每个像素的电子定量计数
   • The maximum number of electrons that can be stored in the well is known as the full well capacity, which determines the dynamic range of the sensor. 阱中可以存储的最大电子数称为全阱容量，它决定了传感器的动态范围。
3. The electron charge in each pixel’s well is amplified into a readable voltage, this is the analogue signal. 每个像素阱中的电子电荷被放大成可读的电压，这就是模拟信号。
4. The analogue signal is converted from a voltage into a digital signal with an analogue to digital converter (ADC). This arbitrary digital signal is known as a grey level, as most scientific cameras are monochrome. 模拟信号通过模数转换器（ADC）从电压转换为数字信号。这种任意数字信号被称为灰度电平，因为大多数科学相机都是单色的。
   • The rate of this conversion is known as gain. With a gain of 1.5, 100 electrons are converted to 150 grey levels. 这种转换的速率称为增益gain。增益为 1.5 时，100 个电子被转换为 150 个灰度级别。[gain解释不够]
5. The bit-depth of the camera determines how many grey levels are available for the signal to be converted into, a 12-bit camera has 4096(2^12) available grey levels, a 16-bit camera has (2^16). 相机的位深度决定了有多少灰度级别可用于转换信号，12位相机有4096(2^{12)个可用灰度级别，16位相机有65,536(2}16)。
   • The bit depth also determines the full well capacity and therefore the dynamic range. 位深度还决定了整井容量，从而决定了动态范围。
6. The map of grey levels is displayed on the computer monitor in the imaging software as an image. 灰度图以图像形式显示在成像软件的计算机显示器上。
   • The generated image depends on the software settings, such as brightness, contrast, etc. 生成的图像取决于软件设置，例如亮度、对比度等。

These steps are visualized in Figure 4.

Generating-an-image.png

Figure 4: The process of taking an image with a scientific camera. Photons impact the sensor, which produces photoelectrons, the rate of production is known as quantum efficiency. These electrons go into the well of each pixel and are counted, amplifed and converted into grey levels by an analogue to digital converter (ADC). These grey levels are then displayed on a computer monitor, with the image appearance controlled by display settings in the software (contrast, brightness, etc).

图4：使用科学相机拍摄图像的过程。光子撞击传感器，产生光电子，产生速率称为量子效率。这些电子进入每个像素的阱，并由模数转换器(ADC)进行计数、放大并转换为灰度电平。然后，这些灰度级别显示在计算机显示器上，图像外观由软件中的显示设置(对比度、亮度等)控制。

In this manner, photons are converted to electrons, which are converted into a digital signal and displayed as an image. These main stages of imaging with a scientific camera are consistent across all modern camera technologies, but there are several different types of sensor architecture and design. 以这种方式，光子被转换为电子，电子被转换为数字信号并显示为图像。科学相机成像的这些主要阶段在所有现代相机技术中都是一致的，但有几种不同类型的传感器架构和设计。

Types Of Camera Sensor

Camera sensors are at the heart of the camera and have been subject to numerous different iterations over the years. Researchers are constantly on the lookout for better sensors which can improve their images, bringing better resolution, sensitivity, field of view, and speed. The three main camera sensor technologies are:

相机传感器是相机的核心，多年来经历了许多不同的迭代。研究人员一直在寻找更好的传感器，以改善他们的图像，带来更好的分辨率、灵敏度、视野和速度。三种主要的相机传感器技术是：

• Charge-coupled device (CCD)电荷耦合器件 （CCD）
• Electron-multiplied charge-coupled device (EMCCD)电子倍增电荷耦合器件 （EMCCD）
• Complementary metal-oxide-semiconductor (CMOS)互补金属氧化物半导体 （CMOS）

Each of these sensors is discussed in detail in our next article, Camera Sensor Types