In this article, we explore how the eye perceives colour and how colour is produced on mobile phone displays. We’ll then go on to compare and contrast how different phones create colour and look at how the design of our eyes informs the design of mobile phone displays. In particular, we’ll look at the PenTile display on the Samsung Galaxy S III, explore why it’s taken such a beating in the tech press and ask whether it's deserved.
Rods and Cones
Using a combination of rods and cones, our eyes are able to give us great vision regardless of the time of day and the light level. During the day, cones and rods work together: rods provide basic vision whilst cones allow us to distinguish between different colours. At night, when is it much darker, we retain the ability to see using rods, albeit without the cone-provided ability to distinguish between different colours.
Forming Colour: Red, Green and Blue
All of the colours that we perceive on a daily basis can be broken down into different proportions of red, green and blue. Combining these three colours in certain ways can create any other colour: for example the combination of blue and green makes cyan, the combination of red and green makes yellow and the combination of blue and red makes magenta. Combining red, green and blue together at the same time in equal proportions creates white light.
Creating Colour: RGB Colour Displays
The first mobile phone with a colour display was the Sony Ericsson T68i. Released in 2001, the T68i featured a 101x80 resolution screen with the ability to show 256 different colours. More than 10 years on, almost every single mobile phone in the world now features a colour display with many smartphones now having high-resolution displays that can rival those found even on televisions.
High-end handsets such as the HTC One X now pack more than 2.7 million sub-pixels into a pocket-sized 4.7-inch display: this is how they can create their super-sharp and realistic colour images. That’s a ton of sub-pixels, each updating themselves dozens of times every second simply to bring you a rich multimedia experience on your smartphone. Amazing stuff.
PenTile Displays & Galaxy S III: Another Way to Create Colour
Proponents of PenTile point out that the cones in our eyes are more sensitive to green than they are to either red or blue. Indeed, with many things in nature such as grass, plants and trees being green, our eyes have evolved over time to become more sensitive to green light. This comparative sensitivity of the human eye to green light suggests that by focussing on providing a larger number of green sub-pixels than those of other colours, the perceived quality of a picture can be improved. This is the approach that Samsung have followed with the use of PenTile technology on the Galaxy S III.
The sensitivity of the human eye to different colours (Wikipedia). The human eye’s vision system is more sensitive to green light than red light or blue light. The standard formula for brightness/luminosity is Luminosity = 0.3 R + 0.59 G + 0.11 B where R, G, B are the red, green and blue components.
Many smartphones with organic LED displays make use of the PenTile RGBG sub-pixel matrix rather than a full RGB sub-pixel matrix. This is because blue organic LEDs have comparatively shorter lifetimes than red and green organic LEDs. Reducing the number of blue organic LEDs can make displays easier to manufacture and can also increase their lifetimes. Criticisms of PenTile include jagged edges on some straight lines – particularly on low resolution screens. For the most part, this is incredibly difficult to notice on a high-resolution 720p display so the downsides of PenTile could be limited in the most recent handsets.
|
Phone |
Resolution |
Sub-Pixel Matrix |
|
320x480 |
RGB |
|
|
640x960 |
RGB |
|
|
640x960 |
RGB |
|
|
640x480 |
RGB |
|
|
1280x720 |
RGB |
|
|
800x480 |
PenTile RGBG |
|
|
800x480 |
RGB |
|
|
1280x720 |
PenTile RGBG |
|
|
1280x800 |
PenTile RGBG |
|
|
800x480 |
PenTile RGBG |
|
|
800x480 |
RGB |
|
|
1280x720 |
PenTile RGBG |
Other variants of PenTile technology include the RGBW PenTile matrix. Designed for use with LCD displays, RGBW PenTile features an additional white sub-pixel to increase the brightness of the display and to improve outdoor visibility.
Your Thoughts…
In this article, we looked at how the rods and cones in your eye work together to allow you to perceive the wonders of the world. We discussed the role of cones in helping you to perceive colour and looked at how mobile phone displays make use of this fact to present vibrant and realistic images in the palm of your hand. Finally, we looked at how the Samsung Galaxy S III caused controversy with its use of a PenTile matrix and looked at what that really means for you as the consumer.
What are your thoughts on the Galaxy S III’s display? Do you prefer an RGB display (such as the one found on the HTC One X) or a PenTile display (such as the one found on the Galaxy S III)? If you could build your own perfect smartphone, would you use PenTile technology? We’d love to hear your thoughts and views – please do drop us a comment below!
Ken Lo writes about mobile technology and the mobile industry at Ken's Tech Tips.