power minimization for led-backlit tft-lcds
DESCRIPTION
Power Minimization for LED-backlit TFT-LCDs. Wei-Chung Cheng July 26, 2006. PODLAB – Perception Oriented Design Lab Department of Photonics and Display Institute National Chiao Tung University, Taiwan. (NY Times). Outline. Background Psychophysics Chromaticity scaling Conclusions. - PowerPoint PPT PresentationTRANSCRIPT
Power Minimization for LED-backlit TFT-LCDs
Power Minimization for LED-backlit TFT-LCDs
Wei-Chung ChengJuly 26, 2006
Wei-Chung ChengJuly 26, 2006
PODLAB – Perception Oriented Design LabDepartment of Photonics and Display Institute
National Chiao Tung University, Taiwan
(NY Times)
Outline
Background
Psychophysics
Chromaticity scaling
Conclusions
Brightness/lightness Demo
Luminance vs. Brightness
Luminance is a physical measure
Brightness and lightness are perceptual measures
Luminance can be measured by a light meter
How to measure brightness?Psychophysics
??
Reduce Backlight Power Consumption
100% x 70 = 7030W
Power Backlight x Transmittance = Luminance
LCD Panel
70% x 70 = 4925W 70% x 100 = 7025W
What is the optimal enhancement?
Previous Works
N. Chang, IEEE TCAD 2004Dynamic backlight luminance scaling
N. Chang, IEEE DTC 2004Battery-powered multimedia systems
W.-C. Cheng, DATE 2004Concurrent brightness and contrast scaling
N. Dutt, IEEE DTC 2004For video streaming
A. Iranli, DATE 2005Histogram equalization
A. Iranli, DAC 2005Dynamic tone mapping
L. Zhong, N. Jha, MobiSis 2005Minimum energy for displays
luminance scaling
Concurrent Brightness and Contrast Scaling (CBCS)
Cheng and Pedram, DATE 04
Scales brightness and contrast
Brightness and contrast are different qualities
Question unanswered:“Are brightness and contrast interchangeable?”
Hue Adjustment
Red Blue
Weak color memory
What’s the time?
Few people noticed the clock
The brightest object
The least important object
Psychophysical StudyPsychophysical Study
Brightness =? ContrastBrightness =? Contrast
Psychophysical Study
37 observers; 2 excluded after statistical analysis
The Method of Adjustment, a standard psychophysical methodby Gustav Fechner
Original100% backlightOriginal contrast
Contrast enhanced70% backlightAdjusted contrast
“ContrastL < ContrastR?”
“Yes”
Experimental Data
0
4
8
12
16
20
0.21 0.42 0.58 0.79 1.00 1.25 1.67 2.50 5.00
slope
co
un
t
Ascending
Descending
"Interaction between brightness and contrast of complex stimuli," Journal of Vision, 6(8), 2006.
Yes
Yes
No
No
1.5
1.3
0.9
0.7
Chromaticity ScalingChromaticity Scaling
Chromaticity Scaling
MIN{MAX(Luminance)}
MIN{MAX(Red)+MAX(Green)+MAX(Blue)}
0.00
10.00
20.00
30.00
40.00
50.00
0 50 100 150 200 250 300 350
Luminance (nit)
Pow
er (w
att)
R+G+B
Red
Blue
Green
Chromaticity Scaling
CIELAB Color Difference ∆E
Industry standard
RGGB LED backlights
Conclusions
Brightness and lightness are perceptual measures
Human vision can be negotiated to save power
Used psychophysical methods to guide low-power design
Scaling in the chromaticity (RGB) space
RGGB LED backlights; 30% to 75% power savings for USC-SIPI image database
Future directionsConsider viewing directionsHuman-display interaction
More details can be found in our related articlesIEEE J. Display Technology, 2006 (JDT)Color Imaging Conference, 2006 (CIC14)Society for Information Display, 2006 (SID06)
Thank YouThank You
Luminance Scaling
Transfer function f
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
0.2083 0.2917 0.4167 0.5 0.5833 0.7083 0.7917 0.9167 1 1.125 1.25 1.4167 1.6667 2 2.5 3.2917 5
Contrast fidelity f’
Histogram hX Image quality
Viewing Angle
Sample Pictures
RGB LED Backlighting
Superior to CCFLLarge gamut (high color saturation)Mercury-freeFast responseCompact sizeDC driving
ChallengesCostVariationHeat dissipation
Backlight Dimming vs. Image Enhancement
(a) Original image(b) Dim backlight to 50%
without compensation
(d) Optimal enhancement(c) Enhance contrast to recover brightness but pixels over-saturated
x
L(x)
x
L(x)
x
L(x)
x
L(x)
Identity transfer function
Light Efficiency of TFT-LCD
Transmittance
Front polarizer 90%
Color filter 30%
TFT array 80%
Liquid crystals 95%
Rear polarizer 50%
Total <5%
Apple iPod Video 60G
0.0
0.5
1.0
1.5
2.0
2.5
660 710 760 810 860 910 960 1010
Time (sec)
Pow
er (
W)
HD: 10%
BL: 49%
HD: 54%
BL: 16%
Power
µP: 14%
Energy