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Retina Display LG (marketed by Apple with a stylized lowercase 'D' as Retina display) is a brand name used by Apple for screens that have a pixel density of around 300 PPI. The term is used for several Apple products, including the iPhone, iPod Touch, iPad, MacBook Pro, iPad Mini, and iPad Air. Because the typical viewing distance is different, depending on each device's use, the pixels per inch claimed to be of Retina quality can differ, depending on the size of the display, with higher PPI for smaller displays and lower PPI for larger displays: 326 PPI for the smallest devices (iPhone, iPod Touch, and iPad Mini (2nd generation)), 264 PPI for mid-sized devices (iPad (3rd & 4th generations), iPad Air), and 220 PPI for larger devices (MacBook Pro). Many other manufacturers' displays have similar or higher pixel density. 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 LG Display, 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 Retina Displays:
|Model||PPI (pixels per inch)||PPCM (pixels per cm)||PPD (pixels per degree)||Resolution||Total Pixels||Typical viewing distance (in/cm)|
|iPhone 4/4S and iPod Touch (4th generation)||326||128||57||960×640||614,400||10 inches (25 cm)|
|iPhone 5/5C/5S and iPod Touch (5th generation)||1136×640||727,040|
|iPad (3rd/4th generation/iPad Air)||264||105||69||2048×1536||3,145,728||15 inches (38 cm)|
|iPad Mini (2nd generation)||326||128||85||2048×1536||3,145,728||15 inches (38 cm)|
|MacBook Pro (3rd generation) 15"||220||87||77||2880×1800||5,184,000||20 inches (51 cm)|
|MacBook Pro (3rd generation) 13"||227||89||79||2560×1600||4,096,000||20 inches (51 cm)|
When introducing the iPhone 4, Steve Jobs said the amount 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' magic number of 300, the threshold for a Retina Display starts at a the PPD value of 53 PPD. 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 53.53 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. 1024×800 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 the formula
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.
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."
On the topic of 20/20 vision, Apple fan website CultOfMac 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.