你有没有想过什么是PPI？也许您听说过公司谈论高DPI屏幕并想知道那是什么？为什么有些厂商吹嘘他们的高端设备拥有巨大的像素密度(pixel density)屏幕？为什么PPI(PPI matter)如此重要，尤其是在提到智能手机时？阅读本文，您将了解它的含义，PPI 和 DPI(PPI and DPI)是否相同，以及在谈论各种尺寸的屏幕时，这种测量是否重要：
什么是 PPI？
PPI 是Pixels Per Inch的首字母缩写。它是一种度量单位，用于量化在平方英寸表面上发现的像素数。为了清楚地理解它的含义，想象一个平方英寸被划分和组织在一个单元格的网格中。该网格中的每个单元格内部都有一个像素。网格内的单元数（也称为像素）告诉您PPI。
通常，每英寸像素(Pixels Per Inch)值用于测量显示器的像素密度(pixel density)，例如计算机或笔记本电脑(computer or laptop)上的显示器、电视屏幕(TV screen)和智能手机上的显示器。
但是，PPI是一个术语，也广泛用于描述扫描仪、相机屏幕或以数字方式存储的图像的像素密度。有些人甚至使用PPI来告诉您打印机在纸上打印的分辨率。
PPI和DPI是一样的吗？
PPI 是Pixels Per Inch的缩写版本，DPI是Dots Per Inch的缩写版本。常识(Common sense)可能会让你相信它们是不一样的。你是对的！尽管这两个术语都指的是密度，并且您很容易将像素与点混淆（可能是因为它们太小了），但PPI 和 DPI(PPI and DPI)是不同的东西。虽然PPI主要指的是屏幕和数字元素，但DPI是一个在您指代印刷纸之类的东西时正确使用的术语。
印刷纸的分辨率和质量可以通过任何给定字符或图形(character or drawing)中的墨点数量来正确衡量。DPI 和 PPI(DPI and PPI measure)都测量类似的东西，但点不是像素，像素也不是点，所以DPI和(DPI)PPI不一样。
但是，PPI 和 DPI(PPI and DPI)通常用于描述同一事物。这是不正确的，但是像谷歌和微软(Google and Microsoft)这样的大公司和许多硬件制造商经常互换使用这些术语，因此人们也开始松散地使用它们。
(Does PPI matter)在选择电视、电脑显示器或智能手机时， (computer display or smartphone)PPI 重要吗？
是的，确实如此，而且非常重要。当您购买新的智能手机、电脑显示器(computer monitor)、电视或任何其他类型的具有显示屏的设备时，您可能会倾向于选择对角线尺寸最大的设备。当你可以的时候，做大是很自然的，对吧？但这并不总是正确的选择，这里有一个例子：
假设您想购买一部新智能手机，并且希望它有一个大屏幕。介于 5.5" 和 6" 之间。浏览互联网后，您决定喜欢三星 Galaxy S8(Samsung Galaxy S8)和索尼 Xperia XA1 Ultra(Sony Xperia XA1 Ultra)。钱对你来说并不重要——重要的是你下一部智能手机的屏幕。三星Galaxy S8(Samsung Galaxy S8)拥有 5.8 英寸显示屏，分辨率为 1440 x 2960像素，像素密度为 570 PPI。索尼 Xperia XA1 Ultra(Sony Xperia XA1 Ultra)拥有 6.0 英寸的屏幕，分辨率为 1080 x 1920(x 1920)像素，像素密度为 367 PPI。尽管它们的屏幕尺寸相似(screen size)，三星 Galaxy S8(Samsung Galaxy S8)的分辨率和PPI 像素(PPI pixel)密度远高于索尼 Xperia XA1 Ultra(Sony Xperia XA1 Ultra)所提供的。这意味着有更多的像素分布在类似的物理表面——屏幕上。我们不能在一英寸大小的图像中绘制 570 像素，甚至 367 像素，因为您看不到它们。但这里是不同PPI 像素(PPI pixel)密度的图示：
那么你不会选择PPI更高的智能手机三星Galaxy S8(Samsung Galaxy S8)吗？
更高的PPI或像素密度意味着您可以获得屏幕上显示的任何内容的更多细节。这(Which)意味着更好的图像、更好的字体、更流畅的线条，或者换句话说，更高的质量。每个人都想要那个，对吧？
PPI什么时候变得如此之高以至于变得毫无意义？
尽管理论上较高的PPI总是更好，但在进行任何购买之前，您还应该知道大多数人的眼睛可能无法感知高于某个限制的PPI的任何差异。(PPI)
但是，当人眼不再能够在屏幕上看到更多细节并且像素密度(pixel density)不再重要时，这个限制是一个有争议的问题。目前，无论是研究人员还是普通人都无法直接回答你说“像素密度在 570 (pixel density)PPI之后变得毫无意义”。
然而，根据Roger Bourne的《医学数字成像基础》，(Fundamentals of Digital Imaging in Medicine)如果您查看距离眼睛大约 16 英寸或 40 厘米的图像，那么神奇的数字似乎是 400 PPI 。这是因为人眼每毫米视网膜表面有 400 个传感器细胞。然而，夏普(Sharp)的人认为人眼能够看到高达 1000 PPI(the human eye is capable of seeing up to 1000 PPI)，这比现在电子产品提供的要高得多。
Eizo还有一篇很棒的文章，叫做Confused about HiDPI and Retina display? ― 了解 4K 时代的像素密度(Confused about HiDPI and Retina display? ― Understanding pixel density in the age of 4K)，您可以在其中找到一些表格，其中包含显示当今使用的屏幕分辨率和像素密度的数据。您将在现代显示器上看到的大多数像素密度值，无论是智能手机显示器、平板电脑显示器还是计算机显示器，都是由制造公司根据用户查看这些屏幕的常见距离计算得出的。例如，屏幕尺寸为 5.6 英寸的智能手机应具有至少 2560 x 1440 像素的分辨率和大约 525 PPI的像素密度。像素密度(Pixel density)很重要，但无论哪些公司推销他们的产品，在您看到下一个设备的屏幕外观之前不要开始花钱。
你会寻找最高的 PPI 吗？
我们很好奇：既然您知道像素密度越高越好，那么您下次购买(pixel density)电视屏幕(TV screen)、电脑显示器(computer monitor)或新智能手机时会考虑到这一点吗？或者，无论每英寸像素(Pixels Per Inch)数如何，您都会选择最高尺寸吗？
Simple questions: What is PPI and does it matter?
Have you ever wondered what PPI is? Mауbe you've heard companies talking aboυt high DPI screens and wanted to know what that is? Why are some manufaсturers bragging about theіr high-end devices with huge pixеl density ѕcreens? Why dоes PPI matter so much, especially when referring to smartphones? Reаd this article, and you'll find out what it means, whether PPI and DPI arе the ѕame and whether this measurement mattеrs when talking aboυt screens оf all sizes:
What is PPI?
PPI is the acronym from Pixels Per Inch. It is a unit of measure used to quantify the number of pixels found on a square inch surface. To get a clear idea of what it means, imagine a square inch that's divided and organized in a grid of cells. Each and every cell in that grid has a pixel inside. The number of cells inside the grid, also known as pixels, tells you the PPI.
Usually, the Pixels Per Inch value is used to measure the pixel density of displays, such as the monitor you have on your computer or laptop, on your TV screen, and on your smartphone.
However, PPI is a term that's also loosely used for describing the pixel density of scanners, camera screens, or images that are stored digitally. Some people use PPI even for telling you the resolution at which printers print on paper.
Are PPI and DPI the same?
PPI is the short version from Pixels Per Inch, and DPI is the abbreviated version of Dots Per Inch. Common sense will probably lead you to believe that they're not the same. And you'd be right! Although both terms refer to density, and you could easily confuse pixels with dots (probably because they're so tiny), PPI and DPI are different things. While PPI refers mostly to screens and digital elements, DPI is a term that's used correctly when you refer to things like printed paper.
The resolution and the quality of a printed paper are rightly measured by the number of ink dots in any given character or drawing. Both DPI and PPI measure similar things, but dots are not pixels, and pixels are not dots, so DPI is not the same as PPI.
However, PPI and DPI are often used to describe the same thing. It's not correct, but big companies like Google and Microsoft and many hardware manufacturers often use these terms interchangeably, and thus people started to use them loosely too.
Does PPI matter when choosing your TV, computer display or smartphone?
Yes, it does, and it matters quite a lot. When you go buy a new smartphone, or computer monitor, or TV, or any other type of device that has a display, you might be tempted to choose the one that has the largest diagonal size. It's only natural to go big when you can, right? But that's not always the right choice and here's an example why:
Let's say that you want to get a new smartphone, and you want it to have a large screen. Something between 5.5" and 6". After looking around the internet, you decide that you like Samsung Galaxy S8 and Sony Xperia XA1 Ultra. Money doesn't matter to you - what does matter however is the screen of your next smartphone. The Samsung Galaxy S8 has a 5.8-inch display, a resolution of 1440 x 2960 pixels and a pixel density of 570 PPI. The Sony Xperia XA1 Ultra has a 6.0-inch screen, a resolution of 1080 x 1920 pixels and a pixel density of 367 PPI. Although they both have a similar screen size, the resolution and the PPI pixel density of the Samsung Galaxy S8 are much higher than what the Sony Xperia XA1 Ultra has to offer. That means that there are a lot more pixels spread across a similar physical surface, the screen. We can't draw 570 pixels, or even 367, in an image the size of an inch, because you wouldn't see them. But here's an illustration of what different PPI pixel densities look like:
So wouldn't you choose the smartphone with the higher PPI, the Samsung Galaxy S8?
A higher PPI, or pixel density, means that you get a whole lot more detail for anything that's displayed on your screen. Which means better images, better fonts, smoother lines, or in other words, higher quality. Everybody wants that, right?
When does the PPI become so high that it becomes meaningless?
Although higher PPI is always theoretically better, before making any purchase, you should also know that the eyes of most humans are probably not able to perceive any differences in a PPI that's higher than a certain limit.
But what that limit is when the human eye stops being able to see more details on a screen and the pixel density stops being important, is a matter of debate. For now, neither researchers nor ordinary people can give you a straight answer and say that "pixel density becomes meaningless after, say, a value of 570 PPI."
However, according to the Fundamentals of Digital Imaging in Medicine by Roger Bourne, it seems that the magic number would be 400 PPI if you look at an image found at roughly 16 inches or 40 cm distance from your eyes. That's because the human eye has 400 sensor cells per millimeter of retina surface. However, people at Sharp think that the human eye is capable of seeing up to 1000 PPI, which is considerably higher than what electronics offer these days.
Eizo also has an excellent article, called Confused about HiDPI and Retina display? ― Understanding pixel density in the age of 4K, in which you can find a few tables with data that show what are the screen resolutions and pixel densities used today. Most of the pixel density values you'll see used on modern displays, be they smartphone displays, tablet displays or computer monitors, are calculated by the manufacturing companies depending on the common distances users look at those screens. For instance, a smartphone with a screen size of 5.6 inches should have a resolution of at least 2560 x 1440 pixels and a pixel density of about 525 PPI. Pixel density matters, but regardless of what companies market their products, don't start spending money until you see what the screen of your next device looks.
Will you look for the highest PPI?
We're curious: now that you know that a higher pixel density is better than a lower one, will you take it into consideration the next time you buy a TV screen, a computer monitor or a new smartphone? Or will you go for the highest size no matter its Pixels Per Inch?
