Retina display is a brand name used by Apple for its series of IPS LCD and OLED displays that have a higher pixel density than traditional Apple displays. Apple applied to register the term “Retina” as a trademark with regards to computers and mobile devices with the United States Patent and Trademark Office, Canadian Intellectual Property Office. The applications were approved in 2012 and 2014 respectively. The Canadian application cited a 2010 application in Jamaica.
When an Apple product has a Retina display, each user interface widget is doubled in width and height to compensate for the smaller pixels. Apple calls this mode HiDPI mode. In simpler words, it is one logical pixel = four physical pixels at the very beginning. The advantage of this equation is that the CPU “sees” a small portion of the data and calculates the relative positions of each element, and the GPU renders these elements with high quality assets to make the output much sharper and clearer. The goal of Retina displays is to make the text and images being displayed extremely crisp, so that pixels are not visible to the naked eye or at viewing distance. This allows displays to rival the smooth curves and sharpness of printed text and immediacy of photographic prints.
Retina displays have been gradually released over a number of years, and the term is now used for nearly all of Apple products containing a screen, including the Apple Watch, iPhone, iPod Touch, iPad, MacBook, MacBook Air, MacBook Pro, and iMac. Apple uses slightly different versions of the term for these models, including Retina HD display for the iPhone 6 and later versions, and Retina 4K/5K display for the iMac.
Apple’s Retina displays are not an absolute standard for display sharpness, but vary depending on the size of the display on the device, and at what distance the user would typically be viewing the screen. Where on smaller devices with smaller displays users would view the screen at a closer distance to their eyes, the displays have more PPI (Pixels Per Inch), while on larger devices with larger displays where the user views the screen further away, the screen uses a lower PPI value. Later device versions have had additional improvements, whether an increase in the screen size (the iPhone 6 Plus), contrast ratio (the iPhone 6 Plus, and iMac with Retina 4K/5K display), and/or, more recently, PPI count (iPhone X, XS, XS Max, 11 Pro, and 11 Pro Max); as a result, Apple uses the names “Retina HD display”, “Retina 4K/5K display”, “Super Retina HD display”, “Super Retina XDR display”, and “Liquid Retina display” for each successive version.