Retina display

This article is about the HD screens of Apple products. Not to be confused with Virtual retinal display.

Part of a Retina Display on an iPhone 4. The pixels are not visible at viewing distance, creating an impression of sharp print-like text.

Part of a non-Retina Display on an iPhone 3GS. The pixels are visible at viewing distance.

Retina Display (marketed by Apple with a lowercase 'D' as Retina display) is a brand name used by Apple for screens that have a higher pixel density than their previous models.

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 users view the screen at a closer distance to their eyes, as on smaller devices with smaller displays, the displays have more PPI (Pixels Per Inch), whilst larger devices with larger displays where the user views the screen further away use fewer 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.

Models

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	Marketing name	Screen size	Resolution	Pixel density		Pixel size (mm)	Angular pixel density (px/°; at typ. distance)	Typical viewing distance	Total pixels
				(ppi)	(px/cm)
Apple Watch 38mm	Retina Display	33.5 mm (1.32 in)	272×340	330	114	0.087	57.6	10 in (25 cm)	92,480
Apple Watch 42mm		39 mm (1.5 in)	312×390	333	119	0.083	58.2		121,680
iPhone 4, and 4S and iPod Touch (4th generation)		3.5-inch	960×640	326	128	0.078	57.9		614,400
iPhone 5, 5C, and 5S and iPod Touch (5th generation, 6th generation)		4-inch	1136×640				57.5		727,040
iPhone 6 and iPhone 6S	Retina HD Display	4.7-inch	1334×750				57.6		1,000,500
iPhone 6 Plus and iPhone 6S Plus		5.5-inch	1920×1080	401	157	0.063	71.2		2,073,600
iPad Mini 2, 3, and 4	Retina Display	7.9-inch	2048×1536	326	128	0.078	86.1	15 in (38 cm)	3,145,728
iPad (3rd, 4th generation, Air, and Air 2)		9.7-inch		264	105	0.096	70.6
iPad Pro		12.9-inch	2732×2048				71.9		5,595,136
MacBook (2015) 12"		12-inch	2304×1440	226	89	0.11	80.7	20 in (51 cm)	3,317,760
MacBook Pro (3rd generation) 13"		13.3-inch	2560×1600	227			81.3		4,096,000
MacBook Pro (3rd generation) 15"		15.4-inch	2880×1800	220	87	0.12	79.6		5,184,000
iMac with Retina 4K Display 21.5"	Retina 4K Display	21.5-inch	4096×2304	219	86		81.6		9,437,184
iMac with Retina 5K Display 27"	Retina 5K Display	27-inch	5120×2880	218			84		14,745,600

Technical definition

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

$2dr\tan(0.5^{\circ })$

where $d$ is the distance to the screen and $r$ 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.

Reception

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.

As is common with Apple, there was also criticism of Apple's higher prices and profit margins. Reviewing the iPhone 4 in 2010, writer Joshua Topolsky commented:

"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 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.

Criticism

See also: Angular size of foveal cones in the fovea centralis article.

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.

See also

• Pixel density
• Resolution independence