Retina Display is a brand name used by Apple for screens that have a pixel density high
enough that the human eye is unable to discern individual pixels at a typical viewing distance.
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), 264 PPI for mid-sized devices,
iPad Air), and 220 PPI for larger devices. 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.
Retina Display 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, Samsung and Japan Display Inc. There
was a shift of display technology from Twisted nematic Liquid-crystal displays to In-plane
switching LCDs starting with the iPhone 4 models.
Apple markets the following devices as having Retina Displays:
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 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 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 or relative pixel density,
but is dependent on the distance between the display and the eye of the person 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. 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. 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.
Criticism 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. 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". 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
References