“Retina” is Apple’s marketing name for a high resolution LCD display for smartphones (iPhone), tablets (iPad), media players (iPod Touch) and future products such as computer monitors and iMacs.
What does “Retina” mean?
The term Retina refers to the assumption that at a usable distance, the resolution of the display is as high or higher than the human eye’s ability to resolve detail. When a person cannot distinguish individual picture elements (pixels), a high-enough resolution image is touted as being ‘true to life’. According to Apple, a resolution above 300 pixels per inch is higher than human resolvability at a distance of 12 inches, this may be a bit optimistic as one display-industry figure gives a figure of 477 pixels per inch (54 micrometer pixels) at 12 inches for a person with perfect vision and 300 ppi would be high enough at 18 inches. Others disagree, and say that people with average vision would see a continuous image at 286 ppi (89 micrometer pixels) at 12 inches.
Products with Retina displays:
The first Apple Retina display product was the iPhone 4, with a 960×640 pixel Retina display, released June 2010
iPhone 4 and 4S Retina display: 960×640, 3.5″ (89 mm, diagonal) Pixels 78 micrometers wide, 326 pixels per inch contrast ratio of 800:1
iPod Touch Retina display: 960×640, 3.5″ (89 mm, diagonal) Pixels 78 micrometers wide, 326 pixels per inch, released September 2010
New iPad (third generation) Retina display: 2048 × 1536, 9.7″ (250 mm, diagonal) 264 pixels per inch, released March 2012. (The iPad is considered a Retina display despite its lower pixel per inch resolution, by virtue of the assumption that it will be used at a distance of 18″ – 24″ inches from the eyes, rather than the 12 inches of a smartphone.)
Anandtech has some good close up photographs which contrast the resolution of the New iPad Retina display against the earlier iPad 1 and 2 1024 x 768 resolution displays.
Where is the display technology going?
The obvious next step for Retina display technology is for use in computer monitors and MacBook Pro and iMac computers where the high resolution can make reading a computer screen as easy (finally!) as reading a printed page. Televisions could be next, however the fact that televisions are used at distances of feet rather than inches means that the resolution does not have to be as high. Some sites have speculated that Apple is getting ready for higher resolution displays in their computer line based on high resolution support in OSX 10.8.
Challenges:
A less obvious consideration is the cost and yield. Manufacturing LCD displays (and computer chips, which have some similarities in their manufacturing processes) depends on creating highly accurate grids of transistors and conductors on a solid substrate (glass for displays, silicon wafers for chips). The number of pixels, and therefore the associated transistors and connections, goes up as the square of the screen size – so a 9 inch screen has 4 times the number of components as a 3 inch screen. Then add the resolution – each doubling of resolution increases the number of components by four times. Display panel makers (and chip makers) are forced to destroy a relatively high percentage of flawed product, as there is no way to repair the circuitry deposited onto the substrate after the fact. With a smaller screen size, you can get a higher yield of saleable product.
What this means is that manufacturing a flawless 20 or 24 inch computer screen at Retina resolution is going to be much harder and more expensive than a 9.7 inch iPad screen. A 24 inch (diagonal) monitor at 200 pixels per inch will have a pixel count of 4000 x 2360, compared with today’s standard 1920 x 1080 – that’s 9.4 million pixels vs. 2.1 million.
A computer’s (or tablet’s, or television’s) video hardware will also have to have the processing power and memory to push out 8 times the number of pixels as it is called on to do today. This is one reason the new iPad uses the much more powerful A5 processor than the earlier version iPads, and we are never going to see Retina screen upgrades offered for earlier model tablets and smartphones.
Resolution is not the be-all and end-all of display quality. The realism of the display also hinges on colour accuracy, contrast ratio, black level and the speed of pixel response (for moving pictures). Once all of these are sorted out however, looking at a display could be like looking out a window.