Retina Display Retina Display is a brand name used by Apple
for liquid crystal displays 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 , and 220 PPI for larger
devices . While not currently common, many other manufacturers' displays have similar
PPI 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 by different suppliers in the world. 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 (TN) LCDs to In-plane switching (IPS) 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 (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.
1024×800 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). 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, combined with the size-doubling of the user interface,
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 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 eyesight,
then at one foot away the iPhone 4S's pixels are resolved. The picture will look pixelated.
If you have average eyesight, 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.