Carefully choosing colors in OLED displays can prolong battery life
July 9, 2009
Researchers from the Simon Fraser University in Canada have developed two different color maps for organic LEDs that, thanks to an appropriate choice of colors and by exploiting characteristics of human perception, can consume up to 40 percent less power and could be used to increase battery life for a wide range of portable devices.
OLED as the next display technology
Organic Light Emitting Diode (OLED) is a general term describing a LED display using an organic film for its electroluminescent layer, which is deposited with a simple printing-like process. These systems are suitable to be used in TV sets and computer monitors as well as for illuminating large areas, and offer many advantages over standard LCD displays.
A first, important perk of OLED displays is their cost: since they can be printed using standard printing technology — even a common inkjet printer — so potentially their production costs can be considerably reduced.
More importantly, OLED displays are attractive because they don't require a backlight to function, which means that, among other things, they draw far less power than LCD displays while being much lighter, thinner, and with a wider viewing angle. Their power consumption is also dependent on the specific color being displayed: for instance, like with CRT, OLED monitors usually display black by turning off completely, which saves even more power.
These advantages can, for many applications, far outweigh the disadvantages of this technology, which are mainly the reduced lifetime of the devices caused by deterioration of the organic materials of the electroluminescent layer.
Using optimization algorithms to save on the energy bill
The team developed two separate algorithms with the aim to reduce OLED energy consumption as much as possible. Both methods are de facto optimization algorithms in that, given the original data, they search in the space of the "nearby" colors in a discrete palette to find the one with the best tradeoff between preserving the original color — using knowledge of how the human eye perceives them — and consuming less power.
"Color information arriving at the human eye is split into 3 channels: 1 achromatic and 2 chromatic. The achromatic channel carries luminance information and, amongst others, is responsible for motion detection and shape perception. In contrast, the chromatic channels carry color information useful for visual grouping and labeling. Since we focus on discrete color maps for labeling and grouping, we target colors that are constant in lightness and only vary in color," the paper published by the group explains.
In their first approach, the researchers simply gathered a large group of distinguishable colors characterized by the same lightness ("iso-lightness colors") and picked from it a subset chosen in such a way to minimize the sum of their associated energies.
The second method is slightly more complicated and entails finding the most energy-saving, iso-lightness color, also imposing a minimum "perceptual color distance" from the original input. This approach is particularly interesting because it will allow the end user to decide exactly how he or she will want to sacrifice the color resolution of the display to save more or less energy depending on the specific needs.
Paper: Energy Aware Colors Sets (Johnson Chuang, Daniel Weiskopf, Torsten Möller), Simon Fraser University.
Via OLED display.
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