參考鏈接：https://99designs.com/blog/tips/ppi-vs-dpi-whats-the-difference/
PPI describes the number of square pixels that show up in an inch of digital screen (usually between 67-300). DPI, on the other hand, is a printing term referring to the number of physical dots of ink in a printed document.
PPI表示每英寸上像素的個(gè)數(shù)。DPI是關(guān)于打印的術(shù)語(yǔ)，表示印刷中打印文件的物理油墨的點(diǎn)數(shù)。
在弄懂上面兩者的區(qū)別是，我們需要搞清楚什么是像素？
Pixel stands for “picture element”. It’s the smallest physical element of a digital display device that the eye can discern.
像素代表的是圖像的元素，是人眼能看到的電子顯示屏上最小的物理單元。
In fact, pixels are actually made up of “sub-pixels” — red, green and blue light elements that the human eye cannot see because additive color processing blends them into a single hue which appears on the pixel level. But this fact is not directly relevant to designers.
實(shí)際上，還有比像素更小的元素存在，像素是由這些sub-pixels組成，這些是人眼看不到的。加色處理將這些顏色混合成一種單一的色調(diào)。
像素是物理單位且是固定的大小。
Printers do not reproduce an image by tiling pixel squares directly on top of one another. Rather, they reproduce an image by spitting out tiny dots consisting of a mix of four colors, Cyan, Magenta, Yellow and Key (black), which combine to create a range of hues by the subtractive color model.
打印機(jī)不會(huì)通過(guò)平鋪像素單元的方式來(lái)重現(xiàn)圖像。相反，它們通過(guò)由四種顏色混合的小點(diǎn)來(lái)再現(xiàn)圖像。
例如，一個(gè)150ppi的圖片在600dpi的設(shè)備上顯示，每個(gè)pixel有16個(gè)dot (600dots/150pixels)
