Troy Ferrell
Liancheng Shen
ECE 256 – 2/26/2012
What’s the Problem?
What’s the Problem?
 OLED displays consume dramatically different power for
showing different colors than LCD displays
 WHY?
 OLED displays do not require a backlight as LCD displays do
because OLED pixels, themselves, are emissive
 The color of an OLED pixel directly impacts it’s power
 Displaying dark colors such as black require little if no power on
OLED displays yet bright colors such as white actually consume
more power on OLED displays than LCD
Solutions/Related Work?
 Web content providers solve problem by
providing web pages in energy-efficient color
 Problem solved by configuring web browsers
with most energy-efficient color scheme?
 Implement color transformation at mobile
Solutions/Related Work?
 HP Labs
 Darkening display regions outside of focal area
 IBM Linux Watch
 Only studied GUI with two colors
 Studies for energy-aware color
transformation for LCD targeted for data
visualization applications
• A color adaptive web browser that
renders web pages with power optimized
color schemes under user-supplied
Important Considerations
 OLED Display Power
 OLED display power model is a linear function of
linear RGB intensity levels.
 Different displays have different power
 Chromaticity makes a big difference even when the
lightness is identical
Important Considerations
 Web Usage
 Mobile users still visit web pages that are not
optimized for mobile devices.
 ~50% of web pages visited by mobile users are not optimized
for mobile devices at all
 A small number of websites account for most web
 65% of pixels in web pages visited by 25 users over
3 months are white
Important Considerations
 Modern web page contains visual objects of different
fidelity requirements
 Divide element of web page into GUI objects & images
 The Clash of the Images
Important Considerations
User Preferences for Color Transformations
 Different users prefer different transformations for a
web site
 Even same user may favor different color
transformations for different web sites
How does it work?
Key design decisions
 Treat GUI Objects and Images Differently
 Keep Color Consistency per Web site
 Generate Device Specific OLED Power Model
 Calculate Color Maps Offline
 Give User Options
How does it work?
 Utilize Color Transformations!
 Objective of a color transformation is to find a color
map, or N transformed colors to substitute the
original N colors on a page so that:
 the display power consumption is minimized
 perception constraints such as fidelity and usability are met
 Color-dependent energy consumption
E  M X D
 M is the OLED power model;
 X’ is a matrix called the color map
 D is the color contribution vector for the web site
Event-driven Time
Pixel Counting
Pixel Counting
Key Evaluations
 How long do user need to train chameleon
 Two weeks for training
 How well does the past predict the future?
 Past predicts future well
 Overhead issues & time Delay?
 Minimal – on order of 10’s of milliseconds
Our Thoughts
Our Thoughts
 Devise “OLED-Friendly” user setting for
mobile devices at the OS level to save
battery life
Our Thoughts
 Off-line mode means history not present
 Static page
 Reducing brightness of the foreground and change the
color of background may result in low contrast.
 Questions?
 Qualms?
 Ideas?
 Considerations?
 Issues?
 Concerns?
 Inquiries?
 Proposals?
 Problems?