Retina display is a term coined by Apple Inc. to describe display device specification having a pixel density such that the human eye fails to distinguish between two adjacent pixels in a pixelated image.
Every image that we see on a modern display device is pixelated. Pixels can be thought of as fine dots which when collected together make the image complete. For example, when we draw a line, thousands of pixels follow each other in a straight pattern to make up the line. The pixel density, the size, the intensity of display all depend upon the architecture of the underlying hardware of the device. To display a pixel, the parameters of a pixel like the colour, the intensity are varied according to different algorithms like Bresenham’s line drawing algorithm, DDA algorithm, Xiaolin Wu’s line algorithm and many more advanced algorithms. To display the colour, different colour models like the RGB, CMYK are used.
Apple uses this term to describe most of their devices such as the iPad, the iPod Touch(the tablet), the iPod and MacBook Pro. This term refers to the the pixel density of 326 pixels per inch that it uses in its devices. It boasts of having an image quality that the human eye cannot detect the use of pixels to describe the image. It says that 300 pixels per inch is the limit of the human eye to understand the use of pixels.
Some of the display devices released by Apple have the following pixel ratings:
| Device | Pixel rating (ppi)* |
|---|---|
| iPad(1st and 2nd generation) | 132 |
| iPad(3rd generation) | 264 |
| iPhone 3G, iPhone 3GS | 163 |
| iPhone 4, iPhone 4S, iPhone 5 and iPod Touch (4th & 5th generation) | 326(the acclaimed Retina Display) |
*The pixel density is calculated as follows:
Use Pythagoras’ theorem to calculate the diagonalwise pixels of the display as follows:
1) Multiply the lengthwise pixels with itself
2) Multiply the breadthwise pixels with itself
3) Add step (1) and step (2)
4) Take the square root(√) of step (3)
5) Divide step (4) by the diagonalwise size of the display. The number you get is its pixel density.
This however, has been said to be an advertisement stunt by Apple to enhance sales, as research from various corners suggests that the human limit is actually 447 pixels per inch. However, this limit is for a perfect human vision which very few people possess and, therefore, is safely applicable to the general audience.
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