What do you know about Retina Display?

We may firstly heard about the Retina Display at 2010 when Apple released the iPhone 4. With a pretty high pixel density, the Retina Display amazed many people at that time. Nowadays many electronic equipments has adopted the Retina Display, especially notebook and cellphone. You may get curious about it, so this article will just reveal the mysteries of Retina Display. 

What is Retina Display?
The concept of Retina Display was first put forward by Apple. Generally speaking , A Retina Display is a kind of LCD with high enough pixel density that the human eye is unable to notice pixelation at a typical viewing distance. The iPhone 4 is the first equipment adopted Retina Display.

What is the standard of Retina Display?
As mentioned above, Retina Display is a display with high pixel density. So what’s the standard? With what pixel density a LCD can be called Retina Display? Apple set a formula:

So what does this stange formula mean?
a stands for angle of view, h stands for pixel pitch, d stands for viewing distance.
We can see that the standard may differ in different devices. For a device held 10 to 12 inches from our eye, 300 PPI(pixel per inch, a way of expressing pixel density) can be enough so that you can not notice pixelation.
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).

What is real  Retina Display?
Actually Retina Display is not a new invention, not even a new technology.It means a high-quality display effect.High pixel density is just a basic element.
A real Retina Display include two aspects:hardware and software
Hardware technology
1.High pixel density
This is the basic and most important feature of Retina Display.
2.High-quality panel
A Retina Display usually adopted LPS(In-Plane Switching technology) panel which provides wide field, little light leak, wide colour gamut, good colour rendition.
3.High-capacity battery
High pixel density means much more battery consumption.
Software technology
A real Retina Display needs the support of both operating system and applications to display text and image perfectly, without any distortion. For Apple, they adopt a technologh called HiDPI mode. With the support of HiDPI mode, each user interface widget is doubled in width and height to compensate for the smaller pixels. This technology is also promoted to application developers. In this way all apps of iOS could be developed or modified to adapt the high density display mode.

Products with Retina Display
                Model                          PPI (pixels per inch)    Resolution    Typical Viewing Distance
iPhone 4/4S and iPod Touch 4                  326                  960*640        10 inches (25 cm)
iPhone 5 and iPod Touch 5                       26                   1136*640        10 inches (25 cm)
iPad (3rd)/4th generation)                         260                2048*1536      15 inches (38 cm)
MacBook Pro with Retina Display 15"        220                2880*1800      20 inches (51 cm)
MacBook Pro with Retina Display 13"        227                2560*1600      20 inches (51 cm)