无论出于何种原因，你偶然发现了这个页面，有一件事很清楚——你试图找出一些“简单”的东西，但它们就是没有意义的。关于这个主题的信息如此之多，分散在如此多的地方，以至于很难将所有内容组合在一起。不过不用担心，我们有解决方案。在本节中，您将找到大部分问题的答案。
考虑到定义可能因行业而异，并且某些术语一开始就非常主观。因此，如果您需要深入的信息，请将这些页面视为开胃菜，然后从那里开始。
让我们从头开始！
二进制计数系统是一种存储数据和处理信息的方式。系统的基数是 2。我们在现实世界中使用的十进制计数系统的基数是 10。从 0 到 9 有 10 个数字，我们可以计算多达 9 个对象（苹果、硬币、离假期还剩的天数等）和如果我们想计算更多，我们将在数字前面添加一个数字。例如，数字1 2告诉我们有1 *10+ 2 个我们已经计数的对象（其中 10 是系统的基础）。这同样适用于二进制计数系统。除了不是 10 个数字，只有 2 个。它是 0 和 1。
十进制的数字 1 也是二进制的 1。十进制的数字 2 是二进制的 10 (1*2+0)。十进制的数字 5 是二进制的1 0 1 ( 1 *2*2+ 0 *2+ 1 )。
| 十进制 | 二进制 |
|---|---|
| 0 | 0 |
| 1 | 1 |
| 2 | 10 |
| 3 | 11 |
| 4 | 100 |
| 5 | 101 |
| 6 | 110 |
| 7 | 111 |
| - | - |
| 254 | 11111110 |
| 255 | 11111111 |
请注意，二进制数据的 8 位（或 8 位）可以编码从 0 到 255 的十进制数。这 8 位通常组合在一个称为字节的逻辑块中。所以一个字节是八位。
字节是组合在一起的 8 位。字节可以从 0 到 255 计数。因此它总共可以编码 256 个数字。请注意，256 是 2^8（2 次方 8）。
Word（通常是 WORD）是组合在一起的两个字节。WORD 可以从 0 计数到 65535。WORD 可以编码 2^16 个数字。（不应与作为打字工具的 Microsoft Word® 混淆。）
双字（通常是 DWORD）是两个 WORD 组合在一起。DWORD 可以从 0 计数到 4,294,967,295。DWORD 可以编码 2^32 个数字。
根据行业的不同，术语“8 位设备”可以应用于：微控制器、开关、过滤器、计算机（早在一天前）等。但是在照片/视频行业，我们将术语 8 位设备应用于某些成像传感器、监视器、数字扫描仪和打印机。
电荷耦合器件 (CCD) 是一种用于捕获图像的光传感器。它包含许多排列成矩阵或线（线性 CCD）的单个单元（像素），可以感应光波（光子）。CCD 将光子转换为电子，然后对其进行计数。这些计数的电子形成我们可以从 CCD 读取的图像。现实有点复杂，但实际上与大多数应用程序无关。
互补金属氧化物半导体 (CMOS) 是一种用于捕获图像的光传感器。就像 CCD 一样，它将光子转换为电子并对其进行计数。尽管 CMOS 传感器的电子器件与 CCD 对应物非常不同。唯一实际的区别是可以从 CMOS 传感器获取部分图像，从而提高读取速度和帧速率。使用 CCD 只能获得整个图像。因此，CMOS 传感器在某些应用（如监视或对象跟踪）中具有优势。
像素是最小的感光或发光元件或数字图像的最小元件。CCD/CMOS 的单个单元可以称为像素。它也适用于将包含全彩色信息的最小元素称为像素的监视器。在数字成像中，像素是可能的最小点。
让我们看两个例子。首先让我们使用数码相机拍摄笔记本电脑屏幕并放大它。
DIY（自己动手）实验：如果你有镜头，你可以用自己的眼睛看到屏幕上的单个像素。只需将它放在显示器前面，就可以看到它美丽的像素。术语亚像素（或亚像素）既可以指机器视觉中的精度测量（如亚像素精度），也可以指显示器的每个像素（通常）由三个较小的元素组成，每个元素都包含颜色有关红色、绿色或蓝色通道的信息。
颜色通道（或颜色平面）是原始彩色图像的组成部分，它仅包含有关特定颜色的信息。让我们考虑一个标准的彩色图像。该图像的每个像素都包含有关红色、绿色和蓝色分量的信息。现在，如果我们将丢弃每个像素中的红色和绿色分量，我们将创建仅包含有关蓝色信息的新图像。这个新图像称为蓝色通道。它实际上是黑白（灰度），因为它只代表一种颜色。
这与通过蓝色玻璃（滤光片）查看彩色图像相同。图像的红色和绿色分量将被过滤掉，我们将只能看到图像中具有蓝色的部分。该图像的某些部分会更暗一些更亮。如果我们采用这些强度并丢弃蓝色，我们将得到一个灰度图像，它实际上是图像的蓝色通道。
通常红色、绿色和蓝色被称为原色（RGB 颜色模型）。所有其他颜色均来自这三种颜色的组合。RGB 颜色已被选为模拟人眼结构的主要颜色。它有锥细胞，其中一些只接受红光。其他套装仅接受蓝光和绿光。（人类也有杆状细胞，无论颜色如何，它们通常都能接受光，通常在晚上使用。）
尽管 RGB 是最常见的颜色编码格式，但也使用其他原色。例如，青色、黄色和品红色 (CYM) 在大多数打印机中用作原色。
一百万像素是一百万像素。所以 10 兆像素的相机包含一千万像素或一千万个可以记录光的单个单元。实际上，数字与确切的 10,000,000 略有不同，但这并不重要。
与流行的看法相反，没有彩色光传感器之类的东西。CCD 和 CMOS 都只能将光线“看到”为灰色阴影。他们无法区分颜色。因此，使用这些传感器获得的所有图像实际上都是黑白的（灰度）。那么颜色是如何获得的呢？其实很简单。CCD 或 CMOS 的每个单独单元都覆盖有红色、绿色或蓝色滤光片。这意味着每个细胞只能看到落在它上面的部分光（光谱的一部分）。为了获得颜色信息，我们从相邻像素中插入原色。这样每个像素都具有所有三种颜色值。与流行的看法相反，没有彩色光传感器之类的东西。CCD 和 CMOS 都只能将光线“看到”为灰色阴影。他们无法区分颜色。因此，使用这些传感器获得的所有图像实际上都是黑白的（灰度）。那么颜色是如何获得的呢？其实很简单。CCD 或 CMOS 的每个单独单元都覆盖有红色、绿色或蓝色滤光片。这意味着每个细胞只能看到落在它上面的部分光（光谱的一部分）。为了获得颜色信息，我们从相邻像素中插入原色。这样每个像素都具有所有三个颜色值。
（注意！Foveon X3 ® 与现在的颜色传感器非常接近，但它是一种非常特殊的情况，我们不会在这里介绍）。
拜耳彩色滤光片是在光传感器表面上进行一定排列的彩色滤光片。原始滤镜的基本尺寸为 2x2，包含两个绿色、一个红色和一个蓝色滤镜。它在传感器的整个表面上重复。如今，这些过滤器种类繁多，具有不同的基本尺寸、位置和红色、绿色和蓝色元素的百分比。
动态范围是设备可以可靠地捕获或再现的最亮与最暗强度的比率。
让我们以标准电脑液晶显示器为例。我们看到的每个像素实际上由三个子像素组成，每个子像素都覆盖着彩色滤光片——红色、绿色和蓝色。每个子像素后面都有一个液晶，所有这些后面都有一个光源。光源的强度是恒定的，因此每个子像素的感知“强度”受其背后液晶的透明度控制。所有标准显示器都是 8 位设备。这意味着每个液晶的透明度可以设置256种不同的方式（控制它的电子设备可以施加2^8=256种不同的电压来调整它的透明度）。换句话说，我们可以显示 256 种不同的强度或 256 种灰度。我们最暗的强度（液晶是 100% 不透明）将被称为黑色，我们最亮的强度（液晶是 100% 透明）称为白色。因此，每个像素可以有 256*256*256 (16.7M) 的颜色变化。然而，这种监视器的动态范围只有 8（位），因为它只能再现 256 (2^8) 种灰度。
显示器可以可靠再现的最亮强度和最暗强度之间的比率称为对比度或简称对比度（在显示器相关行业中）。
让我们考虑两个不同的显示器。它们具有相同的电子设备、相同的背光源，并且都是 8 位设备。它们在一件事上有所不同 - 漏光（或基础光）。碰巧的是，即使液晶是 100% 不透明的，仍然有一定量的光到达观察者。所以显示器永远不会变黑——我们总是看到一些光，这些光来自显示器本身（与显示器反射或散射的光相反）。假设第一台显示器的基光是第二台显示器的一半，对比度为 1000:1。这意味着可以显示的最亮强度是最暗强度的 1000 倍。第二台显示器的对比度为 500:1。严格来讲，这些值（或这些值的对数）应称为动态范围（无需详细介绍最新液晶显示器的动态对比度）。然而，历史上发生过它们被称为对比度或简称为对比度。
We must note that pixels' intensities of both monitors can still be adjusted in 256 different ways only for standard non HDR monitors. So their "dynamic range" is 8 (bit).
High Dynamic Range photography (or video) is a technique which allows the combination of images with different exposures to produce one output image showing the entire dynamic range of the scene. This allows the viewer to see both very bright and very dark regions of the scene. HDR images can hold up to 65,535 shades of gray.
Wide Dynamic Range (WDR) is the term mostly used in surveillance video industry. The meaning of WDR is pretty much the same as HDR. WDR cameras allow to capture images which contain very dark and very bright regions. WDR images are often combined from two images only - one dark and one bright.
None. It is the same thing. Names differ between industries. HDR is mostly used in photography. WDR in video surveillance industry.
Low dynamic range (LDR) refers to standard 8bit monitors or image formats. It only makes sense to use term LDR when talking about HDR imaging since all standard cameras, monitors, projectors and jpeg images all use same 8bit format hence none of them is HDR or LDR.
Contrast is a measure which allows to define how well object or part of the image stands out from its surroundings. It is highly subjective and depends on many factors including the individual observer.
Local contrast is pretty much the same as contrast in terms of what it defines. It is the same measure of how well object or part of the image stands out of its background. However it is used to highlight the fact that we are talking about contrast in a part of the image or the scene as opposed to the contrast of the entire image or the scene, which in this case is called global contrast.
Local contrast enhancement is a technique of increasing contrast of certain part of the image without affecting the rest of the image. It is very important step of tone mapping process. Without local contrast enhancement, HDR images will have very low contrast or "foggy" look once compressed to fit standard monitor.
Tone mapping is a process of reducing dynamic range of the HDR image while trying to retain local contrast of the parts of the image. Monitors can reproduce only 256 shades of gray where is HDR image can contain up to 65,000+ shades of gray. Dynamic range of HDR image must be reduced because it is impossible to show it straight away on the standard monitor.
WDR camera can combine underexposed and overexposed images inside itself and provide combined image as its output. Camera achieves it but making a quick succession of (usually) two shots. First one is underexposed (dark) and captures details in the bright regions of the scene. Second shot is normal (or overexposed, depending on settings) and captures mid and dark regions of the scene.
Recent years have seen the slow rise of Wide Dynamic Range (WDR) cameras especially in the surveillance industry.
Let's consider one pixel of the camera which is looking at the something. It sees one photon (we wish we had a camera which sees individual photons, but let's just imaging that we do) and give us one count back. If it sees two photons it gives us two counts back. If it sees 1000 photons it gives as 1000 counts. In general its output (O) is linearly proportional to its input (I) with some coefficient (a), which in our example is equal to 1. So in general O=a*I. If [a=1/100], then the camera will give us 1 count per 100 photons it observes. Actually O=a*I+b, where b is dark current (or dark noise of the camera).
Just like with linear response let's consider one pixel of the camera which is looking at the something. It sees one photon and gives us one count back. Now if it sees 10 photons it gives us 2 counts back. If it sees 1000 photons it gives us 4 counts back. So the more photons it sees the less it reacts to it. Output of the camera will be O=a*log(I)+b (where b is dark noise). (Base of the logarithm can be 10 or 2 or 2.71828 or anything else.)
If we cover camera with something so that no light reaches the sensor we still can see something at the image we get from it. What we see is actually noise or dark noise. Intensity of dark noise varies from camera to camera. One can never get rid of it, only to minimize it. Having camera with better electronics helps so does cooling the camera to absolute zero (We mean Kelvin scale.)
Camera noise consists of dark noise + amplifier noise + readout noise (for CCD cameras).
CCD stands for Charged-Coupled Device. In reality it is a piece of silicon which can convert light (photons) to electrical current (electrons). If we add a little bit of electronics it can become a camera. One very important thing to know about CCD camera is that it is only possible to read the entire image from it. It is impossible to get a portion of the image. Another important thing to know is that it has only one (usually) amplifier which is good because it means that manufacturers can use good low-noise amplifiers.
CMOS stands for Complementary Metal-Oxide Semiconductor. CMOS sensor is also a piece of silicon which can convert light to electrical current. It works a little bit different from CCD. Important things for us are: 1) it is possible to read any portion of the image without the need to read the entire image, and 2) each pixel has its own amplifier - which means (in general) CMOS cameras are a bit more noisy than CCD (in the same price range).
Just by looking at the camera it is impossible to tell if CCD or CMOS version is better. It is preferable to use a datasheet for comparison. As a matter of fact, the question of "better" is very complex. Before purchasing a camera you should ask yourself what it is you NEED. Is it low noise? High frame rate? A lot of megapixels? or you need it to be inexpensive? Remember that you cannot have all of the above. As for CCD vs CMOS both technologies are very well developed nowadays. Compare datasheets and make a choice based on your need. Don't waste money on the features you are not going to use.
Let's consider grayscale cameras. (RGB will act the same in terms of dynamic range. Color information takes more bits to transfer from the camera but doesn't provide any significantly different information on dynamic range of the scene.)
Regular grayscale cameras provide the output image in 8 bit format. So each image can consist of 256 (2 power 8) shades of gray. Some cameras provide 10 or even 12 bits of information.
The regular camera response curve is linear. It means that camera output is directly proportional to the light. Drawback of these cameras is that they usually have low details in the low light regions of the image.
WDR 相机的响应曲线是对数的。这意味着它们对弱光更敏感。这些相机的缺点是它们在图像的明亮区域的对比度相对较低。
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