The goal of Retina Displays is to make the display of text and images extremely crisp, so pixels are not visible to the naked eye. This allows displays to rival the smooth curves and sharpness of printed text and immediacy of photographic prints.
These better quality 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 Pro, and iMac. Apple uses slightly different versions of the term for these models, including Retina HD Display (iPhone 6 models), and Retina 5K Display, Retina HD Display or Retina 4K/5K Display (iMac).
Apple's Retina Displays are not an absolute standard but vary depending on the size of the display on the device, and how close the user would typically be viewing the screen. Where the user views the screen closer to them, as on smaller devices with smaller displays, they have higher PPI, while on larger devices with larger displays where the user views the screen further away, have a lower PPI. Later device versions have had additional improvement, either counted by an increase in the screen size (the iPhone 6 Plus) and/or by PPI (the iPhone 6 and 6 Plus, and iMac with Retina 4K/5K Display), thus Apple using the name "Retina HD Display" or "Retina 4K/5K Display".
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. Apple has applied to register the term "Retina" as a trademark in regard to computers and mobile devices with the United States Patent and Trademark Office, Canadian Intellectual Property Office, and in Jamaica. On November 27, 2012 the US Patent and Trademark office approved Apple's application and "Retina" is now a registered trademark for computer equipment.
The displays are manufactured worldwide by different suppliers. Currently, the iPad's display comes from Samsung, while the MacBook Pro, iPhone, and iPod Touch displays are made by LG and Japan Display Inc. There was a shift of display technology from twisted nematic (TN) liquid-crystal displays (LCDs) to in-plane switching (IPS) LCDs starting with the iPhone 4 models.
Apple markets the following devices as having a Retina Display, Retina HD Display, or Retina 4K/5K Display:
|Model||Screen size||Marketing name||PPI (pixels per inch)||PPCM (pixels per cm)||PPD (pixels per degree)||Resolution||Number of pixels||Typical viewing distance (in/cm)|
|Apple Watch 38mm||33.5 millimetres (1.32 in)||Retina Display||290||114||57.6||272×340||92,480||10 inches (25 cm)|
|Apple Watch 42mm||39 millimetres (1.5 in)||303||119||58.2||312×390||121,680|
|iPhone 4/4S and iPod Touch (4th generation)||3.5-inch||326||128||57.9||960×640||614,400|
|iPhone 5/5C/5S and iPod Touch (5th generation, 6th generation)||4-inch||57.5||1136×640||727,040|
|iPhone 6 and iPhone 6S||4.7-inch||Retina HD Display||57.6||1334×750||1,000,500|
|iPhone 6 Plus and iPhone 6S Plus||5.5-inch||401||157||71.2||1920×1080||2,073,600|
|iPad Mini 2/3/4||7.9-inch||Retina Display||326||128||86.1||2048×1536||3,145,728||15 inches (38 cm)|
|iPad (3rd/4th generation/Air/Air 2)||9.7-inch||264||105||70.6|
|MacBook (2015) 12"||12-inch||226||89||80.7||2304×1440||3,317,760||20 inches (51 cm)|
|MacBook Pro (3rd generation) 13"||13.3-inch||227||81.3||2560×1600||4,096,000|
|MacBook Pro (3rd generation) 15"||15.4-inch||220||87||79.6||2880×1800||5,184,000|
|iMac with Retina 4K Display 21.5"||21.5-inch||Retina 4K Display||219||86||81.6||4096×2304||9,437,184|
|iMac with Retina 5K Display 27"||27-inch||Retina 5K Display||218||84||5120×2880||14,745,600|
When introducing the iPhone 4, Steve Jobs said the number of pixels needed for a Retina Display is about 300 PPI for a device held 10 to 12 inches from the eye. One way of expressing this as a unit is pixels-per-degree (PPD) which takes into account both the screen resolution and the distance from which the device is viewed. Based on Jobs' predicted number of 300, the threshold for a Retina Display starts at the PPD value of 57 PPD. 57 PPD means that a tall skinny triangle with a height equal to the viewing distance and a top angle of one degree will have a base on the device's screen that covers 57 pixels. Any display's viewing quality (from phone displays to huge projectors) can be described with this size-independent universal parameter. Note that the PPD parameter is not an intrinsic parameter of the display itself, unlike absolute pixel resolution (e.g. 1920×1080 pixels) or relative pixel density (e.g. 401 PPI), but is dependent on the distance between the display and the eye of the person (or lens of the device) viewing the display; moving the eye closer to the display reduces the PPD, and moving away from it increases the PPD in proportion to the distance. It can be calculated by the formula
where is the distance to the screen and is the resolution of the screen in pixels per unit length.
In practice, thus far Apple has converted a device's display to Retina by doubling the number of pixels in each direction, quadrupling the total resolution. This increase creates a sharper interface at the same physical dimensions. The sole exception to this has been the iPhone 6 Plus, which renders its display at triple the number of pixels in each direction, before down-sampling to a 1080p resolution.
Reviews of Apple devices with retina displays have generally been positive on technical grounds, with comments describing it as a considerable improvement on earlier screens and praising Apple for driving third-party application support for high-resolution displays more effectively than on Windows. While high-dpi displays such as IBM's T220 and T221 had been sold in the past, they had seen little takeup due to their cost of around $8400.
"to our eyes, there has never been a more detailed, clear, or viewable screen on any mobile device. Not only are the colors and blacks deep and rich, but you simply cannot see pixels on the screen. Okay, if you take some macro camera shots or get right up in there you can make them out [but] webpages that would be line after line of pixelated content when zoomed out on a 3GS are completely readable on the iPhone 4, though the text is beyond microscopic."
Former Microsoft employee Bill Hill, an expert on font rendering, offered similar comments:
That much resolution is stunning. To see it on a mainstream device like the iPad - rather than a $13,000 exotic monitor - is truly amazing, and something I've been waiting more than a decade to see. It will set a bar for future resolution that every other manufacturer of devices and PCs will have to jump.
Writer and programmer John Gruber suggested that the arrival of retina displays on computers would trigger a need to redesign interfaces and designs for the new displays:
The sort of rich, data-dense information design espoused by Edward Tufte can now not only be made on the computer screen but also enjoyed on one. Regarding font choices, you not only need not choose a font optimized for rendering on screen, but should not. Fonts optimized for screen rendering look cheap on the retina MacBook Pro — sometimes downright cheesy — in the same way they do when printed in a glossy magazine.
Raymond Soneira, president of DisplayMate Technologies, has challenged Apple's claim. He says that the physiology of the human retina is such that there must be at least 477 pixels per inch in a pixelated display for the pixels to become imperceptible to the human eye at a distance of 12 inches (305 mm). The astronomer and science blogger Phil Plait notes, however, that, "if you have [better than 20/20] eyesight, then at one foot away the iPhone 4S's pixels are resolved. The picture will look pixelated. If you have average eyesight [20/20 vision], the picture will look just fine... So in my opinion, what Jobs said was fine. Soneira, while technically correct, was being picky." Shortly after Soneira's challenge, the Boys of Tech podcast published their own analysis and concluded that Soneira's claim was invalid and that Jobs' claim was correct. This was primarily because Soneira misinterpreted the manner in which the acuity of the human eye can be tested. The retinal neuroscientist Bryan Jones offers a similar analysis of more detail and comes to a similar conclusion: "I'd find Apple’s claims stand up to what the human eye can perceive."
Apple fan website CultOfMac stated that the resolution the human eye can discern at 12 inches is 900 PPI, concluding "Apple’s Retina Displays are only about 33% of the way there." On the topic of 20/20 vision, they said "most research suggests that normal vision is actually much better than 20/20. In fact, people with normal vision usually won't see their eyesight degrade to 20/20 until they are 60 or 70 years of age" (confirmed by vision testing experts Precision Vision). CultOfMac also noted that people do not always view displays at a constant distance, and will sometimes move closer, at which point the display could no longer be classed as Retina.
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If you haven't yet laid eyes on the new iPad's screen, you must. "Sharp" doesn't begin to describe Apple's upgrade in display quality. But here's the kicker: Samsung, a company firmly aligned with Android and one of Apple's largest competitors in the mobile space, is manufacturing the new iPad's flagship feature.
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There’s only one problem: Steve Jobs said that the human eye, viewing a display from 12 inches away, can’t discern individual pixels if the density is over 300 pixels per inch. Except that this “magic” number is wrong. The real number is closer to 900 pixels per inch. Apple’s Retina Displays are only about 33% of the way there... But while 20/20 vision might traditionally refer to “standard vision”, most research suggests that normal vision is actually much better than 20/20. In fact, people with normal vision usually won’t see their eyesight degrade to 20/20 until they are 60 or 70 years of age!... J. Blackwell of the Optical Society of America determined back in 1946 that the resolution of the human eye was actually closer to 0.35 arc minutes. Again, this means that for an iPhone 4S to have a true Retina Display, it would need pixels that were 65% smaller than it currently has... Such an argument is faulty. For one thing, no one sits a uniform average distance away from their devices. When you text on your iPhone, you might hold it at 12 inches, but if you’re squinting at it in the middle of the night to answer a phone call, you might hold it 6 inches away. And while you might write an email on your MacBook Pro at 24 inches, you might lean in on the edge of your seat during an exciting movie or game to closer to 18.
- "Visual Acuity". Precision Vision.
“Normal” visual acuity for healthy eyes is one or two lines better than 20/20. In population samples the average acuity does not drop to the 20/20 level until age 60 or 70. Always remember that the 20/20 reference standard does not refer to the average acuity of American eyes, just as the US standard foot is defined independently of the “normal” length of American feet.