Retinal display screen is also called retina screen. Retina is actually the name of a display technology. This technology compresses more pixels into one screen, thus achieving an exquisite screen with amazing resolution. In fact, the word Retnia is closer to a marketing term than a technical ranking. Because in a sense, this is a term created by Apple to promote its products. Apple did apply for a patent for this term.
Although the resolution of the screen usually appears in the format of "number of pixels x number of pixels", it is the number of pixels per inch, that is ppi, that really determines the clarity of the screen, not the number of pixels. In addition to ppi, the distance between eyes and screen also determines whether a screen is clear enough to be called "retina". For smart phones, the ppi of 326 can be called retina display, for tablet computers, it is 264 ppi, and for notebook computers, 220 ppi is enough.
What is Retina HD display?
At present, only iPhone6/6 Plus and iPhone6s/6s Plus are equipped with Retina HD display. In fact, the definition of retina high-definition display screen is more vague than retina display screen.
So what are the advantages of Retina HD over Retina display? From Apple's explanation of this term, we can probably think that Retina HD displays have higher contrast, higher bicolor pixels and better polarizers.
Higher contrast: better reading and browsing experience, darker and sharper text.
Bicolor domain pixels: wider viewing angle
Better polarizer: Even if you wear sunglasses, the retina high-definition display can let you see the content on the screen better.