Retina Display is a brand name used by Apple for liquid crystal displays which they claim have a high enough pixel density that the human eye is unable to notice pixelation at a typical viewing distance. The term is used for several Apple products, including the iPhone, iPod Touch, iPad, and MacBook Pro. As the typical viewing distance would be different depending on each device's usage, the pixels per inch claimed to be of retina quality can be different for the smallest devices (326, iPhone and iPod Touch), greater than the mid-sized devices (264, iPad) and greater than the larger devices (220, MacBook Pro). When an Apple product has retina display, each user interface widget is doubled in width and height to compensate for the smaller pixels. This mode is referred to as HiDPI mode by Apple. 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.
Retina Display models 
The displays are manufactured by different suppliers. Currently, the iPad's display comes from Samsung while the Macbook Pro displays are made by LG and Samsung, along with the iPhone and iPod Touch displays.
Apple markets the following devices as having Retina Displays.
|Model||PPI (pixels per inch)||ppcm (pixels per cm)||Resolution||Typical Viewing Distance (in/cm)||Pixels per Degree (PPD)|
|iPhone 4/4S and iPod Touch (4th generation)||326||128||960×640||10 inches (25 cm)||57|
|iPhone 5 and iPod Touch (5th generation)||1136×640|
|iPad (3rd)/4th generation)||264||105||2048×1536||15 inches (38 cm)||69|
|MacBook Pro with Retina Display 15"||220||87||2880×1800||20 inches (51 cm)||77|
|MacBook Pro with Retina Display 13"||227||89||2560×1600||20 inches (51 cm)||79|
- For comparisons, see also: List of displays by pixel density
Technical definition 
When introducing the iPhone 4, Steve Jobs said the magic number 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' magic number of 300, the threshold for a Retina Display starts at a PPD value of 53. 53 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 53 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. 1024 x 800 pixels) or relative pixel density (e.g. 72 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 multiplying the distance to the screen times the resolution of the screen in pixels per unit length times twice the Tan of π divided by 360 (equal to half a degree in radians). Remember to use units, whether imperial or metric, consistently in applying this formula. If the distance to the screen is measured in inches, then the resolution of the screen must be in PPI. If the distance to the screen is measured in centimetres, the resolution of the screen must be in PPC. Two times the Tan of π divided by 360 can also be approximated with π divided by 180 (= 0.01745).
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 resolve (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' pixels are resolved. The picture will look pixellated. 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 due to the fact that Soneira misinterpreted the manner by which the acuity of the human eye can be tested. The retinal neuroscientist Bryan Jones offers a more detailed but similar analysis and comes to a similar conclusion: "...I'd find Apple’s claims stand up to what the human eye can perceive."
See also 
- "Apple - Learn about the Retina Display". Retrieved 2010-06-21.
- United States Patent and Trademark Office. "Latest Status Info - Serial Number 85056807". Trademark Applications and Registrations Retrieval. Retrieved 2012-06-19. Claims priority filing date with respect to prior application in Jamaica.
- Canadian Intellectual Property Office. "Canadian Trade-Mark Data - Application Number 1483982". Canadian Trade-marks Database. Retrieved 2012-06-19. Also cites prior application in Jamaica.
- "Why Samsung makes Retina displays -- but not for its own tablets". Wired. "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."
- "iFixit Teardown". Retrieved 2012-07-09.
- "Apple - iPod Touch - Technical Specifications".
- "Apple - iPhone - Technical Specifications".
- "Apple - iPad - Technical Specifications".
- "Apple - MacBook Pro - Technical Specifications".
- NPR Live Blog of iPhone 4 Introduction
- "Analyst Challenges Apple's iPhone 4S 'Retina Display' Claims". Retrieved 2010-06-10.
- "Resolving the iPhone resolution". Retrieved 2010-06-21.
- "iPhone 4 Retina Display vs the human eye". Retrieved 2013-04-30.
- "Apple Retina Display". Retrieved 2012-07-25.