energy-proportional image sensing for
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ENERGY-PROPORTIONAL IMAGE SENSING
FOR
Robert LiKamWa
Bodhi PriyanthaMatthai
PhiliposeVictor BahlLin Zhong
CONTINUOUS MOBILE VISION
http://roblkw.comhttp://research.microsoft.com
The Devil Wears Prada
CONTINUOUS MOBILE VISION
CONTINUOUS
MOBILE
VISION
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CONTINUOUS MOBILE VISION
CONTINUOUS
MOBILE
VISION
Gestures
Object Memory
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Face RecognitionVictor
Fine-grained Localization
BATTERY LIFEBATTERY DEATH
Google Glass2-3 hours
LooxCie2-3 hours
GoPro Hero2-3 hours
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2000 mWh10 h200 mW
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Image SensorGoal < 25 mW
Sensors~ 5 mW
Processor
~150 mW
Network Stack~20 mW
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Image SensorGoal < 25 mW
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Image SensorReality > 250
mW
KEY IDEA: ENERGY α QUALITYPo
wer
Frame rate
Powe
r
Resolution
ENERGY PROFILE OF AN IMAGE SENSOR
1 MP, 5 fps250 mW
0.3 MP, 15 fps245 mW
1 MP, 15 fps295 mW
< 25 mWGoal:
Reality: > 230 mW
0.3 MP, 5 fps232 mW
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ENERGY-EFFICIENTIMAGE SENSING
Image Sensor Characterization
Energy Reduction Techniques
Energy vs. Vision Performance
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IMAGE SENSOR MEASUREMENT
Camera Module
Programmable Clock (I2C)
NI DAQ Device
Power RailResistors
PowerVDD CLK
* Profiled 5 state-of-the-artimage sensors from 2 manufacturers
*
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Camera Module
Programmable Clock (I2C)
NI DAQ Device
Power RailResistors
IMAGE SENSOR MEASUREMENT
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IMAGE SENSOR WAVEFORMSActive Period
Idle Period
Analog
DigitalPLL
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IMAGE SENSOR WAVEFORMSActive Period
Idle Period
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IMAGE SENSOR WAVEFORMSActive Period
Idle Period
Pixel Count divided by
Clock Frequency
Frame Timeminus
Active Time
IMAGE SENSOR PIXEL COUNT (N)
Region-of-Interest(Windowing)
Active Active
Powe
r
TimePo
wer
Time 16 of 38
Scaled Resolution(Pixel Skipping)
IMAGE SENSOR PIXEL COUNT (N)
Active Active
Powe
r
TimePo
wer
Time
Video (30 FPS) Power vs. Resolution
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ActiveFrame
Readout
ActivePo
wer
Time
Active
IMAGE SENSOR FRAME RATE (R)
Video (0.1 MP) Power vs. FPS
ActiveFrame
ReadoutActive
Powe
r
Time
Active ActiveActive Active
1.0s
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CHARACTERIZATION CONCLUSION:NO ENERGY PROPORTIONALITY
Video (0.1 MP) Power vs. FPS
Video (30 FPS) Power vs. Resolution
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ENERGY-EFFICIENTIMAGE SENSING
Image Sensor Characterization
Energy Reduction Techniques
Energy vs. Vision Performance
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TECHNIQUE #1: AGGRESSIVE STANDBY
Active Active
Active Active
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Active Active
Active Active
CAVEAT TO AGGRESSIVE STANDBY
Active Active
Not enough exposure time
This won’t work for long active periods,i.e., high resolution, high frame rate.
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TECHNIQUE #2: CLOCK SCALING (f)
One pixel per clock period
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TECHNIQUE #2: CLOCK SCALING (f)
Faster clockLower Active TimeHigher Active PowerHigher Idle Power
Slower clock
Higher Active TimeLower Active PowerLower Idle Power
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TECHNIQUE #2: CLOCK SCALING (f)
Active
Active
Low Pixel CountLow Frame Rate
Slowed Clock
Optimal clock frequency depends onPixel Count & Frame Rate
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AGGRESSIVE STANDBY + CLOCK OPTIMIZATION
Sped-upClock
Aggressive Standby
ActiveReadout
Active
Readout
Optimal clock frequency depends onPixel Count & Frame Rate
Exposure Time26 of 38
ENERGY α QUALITYFr
ame
rate
(FPS
)
Resolution (MP)
30
25
20
15
10
5
021 3 4 5
Fram
e ra
te (
FPS)
Resolution (MP)
30
25
20
15
10
5
021 3 4 5
Pow
er (
mW
)
350
300
250
200
150
100
500
Aggressive Standby &Clock OptimizationUnoptimized
Pow
er (
mW
)
350
300
250
200
150
100
500
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CPU
Driv
er
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CURRENT IMAGE SENSOR DESIGN
Image Processor
Pixel ArrayColumn Output Gain, ADC
Analog Signal Chain70-85% Power Consumption
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Image Processor
Pixel ArrayColumn Output
High-Speed ADC
Mid-Speed ADC
Low-Speed ADC
Gain
HETEROGENEOUS SENSOR DESIGN
Analog Signal ChainHeterogeneous
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ENERGY α QUALITY
Default
Clock select
Standby
HW Fix
Power vs. Framerate (at 0.1 MP)
Power vs. Resolution(at 5 FPS)
DefaultClock select
StandbyHW Fix
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ENERGY-EFFICIENTIMAGE SENSING
Image Sensor Characterization
Energy Reduction Techniques
Energy vs. Vision Performance
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ENERGY vs. VISION: VISION TASKIMAGE REGISTRATION
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ENERGY vs. VISION: PERFORMANCE Image
Registration Success
Power Reduction with software
assist
Estimated Power Reduction with hardware assist
Full VGA Resolution0.1 MP, 30 FPS 99.9% 51% 84%Frame Rate Reduction0.1 MP, 3 FPS 95.7% 95% 98%30% Window0.06 MP, 30 FPS 96.5% 63% 91%Subsampled by 20.3 MP, 30 FPS 91.8% 71% 94%
185 mW
TypicalAverage Power
10 mW
With aggr. standby& optimal clock
3 mW
With heterogeneousanalog signal chain
Scalable
Computer Vision
Algorithms
IntegratedSystems Design
DeveloperSupport
EnergyProportional
Image Sensing
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Continuous Mobile Vision
ENERGY-PROPORTIONAL IMAGE SENSINGFOR
CONTINUOUS MOBILE VISION
http://roblkw.comhttp://research.microsoft.com
Image sensors are not energy-proportional…
Fram
e ra
te (
FPS)
Resolution (MP)
30
20
10
01 3 5
…but we can make them energy-proportional…
Aggressive Standby
Clock Optimization
Sensor Modifications
… and this is just the beginning.
CMV
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