Displays are one of the major system energy consumers in smartphones. Power consumption of Organic Light-Emitting Diode (OLED) displays have direct relationship with the colour and intensity of the contents being displayed. Games are one of the most popular smartphone applications that consume relatively more resources and power. In this paper, we present Human Visual System (HVS) aware algorithms and techniques to reduce OLED display power consumption up to 45% while retaining the perceived quality of game content. We have implemented and evaluated our solution in the game Quake III and its Android port Kwaak3.

1. +
PARVAI - HVS Aware Adaptive Display Power
Management for Mobile Games
Bhojan Anand, Li Kecen, Akkihebbal L. Ananda

2. +
Limitations of Mobile Computing
Weight Size
Performance Energy

3. +
Well Known Problem
Demand and Supply

4. +
Where does the energy go?
HOW DID WE MEASURE?
Bhojan Anand et al., ‘Adaptive Display Power Management for Mobile Games’, Mobisys
2011

5. +
Why Organic LED (OLED)?
 Alternate display technology to LCD. (Growing faster!)
Samsung Panasonic Motorola Nokia HTC LG
> 20 models 102p RAZR i Lumia820 One-S
Optimus
5.5” note II
Larger
Screens
7.7” Galaxy Tab
Much wider use – TVs,
Cameras, etc
55” OLED TV

6. +
Why bother?
* Sources: Engadget & LG Display

7. +
Why Games?
Candy Crush Brings
In An Estimated
$633,000 A Day
© Alex Cocotas,
provided by
BUSINESS INSIDER

8. +
Why Games?
Demand and Supply
HTC
8h 10
Desire
min,
HD
420h
5h 20
min, 490h
1h 50 min

9. +
Power Consumption of Organic LED
(OLED)
Factor 1: Brightness / Luminance
Brighter contents
consumes more power
Each pixel is individually
illuminated in OLEDs
700 mW
255 mW

10. +
Power Consumption of Organic LED
(OLED)
Factor 2: Color / Hue
Disparity in OLED sub-pixel power
consumption
two sub-pixels per pixel
RGBG - Pentile
Eg. Blue OLED material
 Lowest luminance efficiency
(lu/Watt)
 Higher current is used to
match luminance with Green
 Results in Lower Lifetime
 Solution: Larger Blue Sub-pixel.
(Variation in Size & Current for
each sub-pixel)

11. +
Power Consumption of Organic LED
(OLED)
Factor 2: Color / Hue (Google Nexus One )
For any given color, we can generate power
efficient color with same brightness level

12. +
Power Consumption of Organic LED
(OLED)
a) Nexus S
b) Galaxy S2
c) Galaxy Nexus
d) Galaxy S3
Dashed lines ->
normalized to 4
inch2 display.

13. +
Basic Power Saving Approaches
Darken the contents
Make everything Green or Red

14. +
HVS
Unequal sensitivity to different colours
• The blue cones detect only colour due to low relative sensitivity.
• Light from the blue subpixels does little to help the eye resolve
images, most of it goes to waste.

15. +
HVS
Sensitive to local contrast

16. +
HVS
Area of Interest

17. +
PARVAI System
We leverage on HVS characteristics to
manipulate the contents with minimum visual
distortion

18. +
Power Efficient Colour Mapping
(Optimization problem)
Input: bLUT - (Look Up Table ordered by Blue) – All Colors (C)- 32bits
Output: bLUT with power efficient color C’
For each color C = {r, g, b},
Map to a new color C’= {r’,g’,b’} with
- Minimum power consumption
- Minimum b’
With constraints:
- Hue change
- Saturation change
- Constant brightness/luminance
- b’ should be less than b
- Only Top half is searched

19. +
Grid Based Transformations
HVS Sensitive to local contrast
Local colors and intensities are important
Pixel-by-pixel transformation is computation
intensive
Use Grid Based Transformations with opengl
Blend Function to Blend the colors to get the
target color

20. +
Power Efficient Colour Mapping
Original
63 mW
Colour Mapped
55 mW
13% Power Saving

21. +
Saliency Based Darkening
Saliency Based Darkening
Center Part is more important then regions
Greater pressure when the sight angle is moving
vertically
 For 640x480 screen, 480/640 = 0.75
For each gird cell X,Y:-
Distance = abs(X+0.5-Xcenter) * 0.75 + abs(Y+0.5-Ycenter)

22. +
Saliency Based Darkening
(187 mW) (151 mW)
20% power saving

23. +
Saliency Based Darkening

24. +
Two Modes
Conservative:-
 Quality Comparable to Original
Applies only Power Efficient Color Mapping
Aggressive
 Applies Power Efficient Color Mapping
 Darker content outside the Area of Interest
Power Efficient Color
Mapping
Saliency Based
Darkening
+

25. + Final Run-Time Algorithm
Input: Frame, Mode (aggressive or conservative)
Output: Power efficient Frame
Segment Frame to Virtual Grids
For Each Grid
Compute RAVE, GAVE, BAVE
Blue
Dominant?
Color Map using bLUT
Aggressive
mode?
Calculate Distance and
Apply Darkening

26. + Evaluation
Original Conservative (Best Quality)
GCL: 0; MSSIM: 1 GCL: 0.75; MSSIM: 0.82 (6%)
Aggressive Simple Linear Darkening
GCL: 3.713; MSSIM: 0.85 (27%) GCL: 4.488; MSSIM: 0.70 (27%)

27. + Evaluation
Original Conservative (Best Quality)
GCL: 1.411; MSSIM: 0.81 (13%)
Aggressive Simple Linear Darkening
GCL: 10.466; MSSIM: 0.78 (47%)
GCL: 9.283; MSSIM: 0.80 (47%)

28. +
Evaluation - User Study
Images and Game Play Video
Randomly selected images from a pool of
Images.
Randomly Selected Version: Original,
Simple Darkening, Conservative and
Aggressive
Select the Best - Colour, Brightness, Clarity

29. +
Evaluation - Demography

30. +
Evaluation – User Study (Image)

31. +
Evaluation – User Study (Video)

32. +
Contribution
Our approach
Color Mapping Algorithm for Energy Efficiency
leveraging on the Non-linear response of HVS
System
 Saliency based gradual darkening – uses non-linear
pressure in change of sight angle
Can save about 10% energy without any loss in
Visual quality - Conservative
Can save upto 45% energy with some losses in
Visual quality - Aggressive

33. +
Limitations & Future Work
User study with Game play
Evaluation with more quality metrics
 Eg. Video Quality Evaluation Metrics
Generalisation to multiple devices
Application on Videos
Pre-computation
 Applying on the Static Textures files

34. +
Limitations & Future Work
 If the color fidelity is not very Important, then Power
Efficient Color mapping constraints can be relaxed
further
 Demo Videos:
 https://www.dropbox.com/sh/ez6huzfvks75h68/-XDbINocUt

35. +
Thank you!