Backlight Compensation Using RetinexAlgorithm

Han-Sol Kang

ISL Lab Seminar

INDEX

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01 Retinex Theory

02 Retinex Algorithm

03 Experiment Results

04 Conclusion

2

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01 Retinex Theory

3

∑ What’s the Retinex Theory

* Land, Edwin H., and John McCann. "Lightness and retinex theory." JOSA 61.1 (1971): 1-11.

*

Retinex = Retina + Cortex

Both the eye and the brain are involved in the Image processing.

A B=

If we just use the eye,

A B≠

But actually we use both the eye and the brain

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02 Retinex Algorithm

4

∑ Retinex Algorithm

* Jobson, Daniel J., Zia-ur Rahman, and Glenn Woodell. "A multiscale retinex for bridging the gap between color images and the human observation of scenes." Image Processing, IEEE Transactions on 6.7 (1997): 965-976.

*

Weber-Fechner’s law Land의시각적모델

),(),(),( yxLyxRyxI iii +

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02 Retinex Algorithm

5

∑ Single-Scale Retinex (SSR)

Log

*),(F yx

),(I yxi

-

SSR∑

+

Log

)),(*),(log(),(logR yxIyxFyxI iii

* Jobson, Daniel J., Zia-ur Rahman, and Glenn Woodell. "A multiscale retinex for bridging the gap between color images and the human observation of scenes." Image Processing, IEEE Transactions on 6.7 (1997): 965-976.

outputRetinex:),(

functionSurround:),(

)3,2,1(colorth:),(

yxR

yxF

iiyxI

i

i

*

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02 Retinex Algorithm

6

∑ Surround Function

Log

*),(F yx

),(I yxi

-

SSR∑

+

Log

* Jobson, Daniel J., Zia-ur Rahman, and Glenn Woodell. "A multiscale retinex for bridging the gap between color images and the human observation of scenes." Image Processing, IEEE Transactions on 6.7 (1997): 965-976.

*

)(1

1),(

22 cryxF

2

2

),( c

r

eyxF

ConstantspaceSurround:

22

c

yxr

• Surround function by E.Land’86 (Inverse square spatial surround) • Surround function by Hurlbert’89(Gaussian)

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N

n

n

N

n

nnMSR WRWRii

11

1,

7

02 Retinex Algorithm

∑ Multi-Scale Retinex (MSR) & MSR with Color Restoration (MSRCR)

Log

*

*

*

X

X

X

∑ Log ∑

),(F1 yx

),(F2 yx

),(F3 yx

),(I yx

MSR

-++

+

+

W1

W2

W3

*

Log

),(F yx

),(I yx

Log

∑ SSR-

+

CR

X

X

Gain/

OffsetMSRCR

Log

α

MSR

CRF

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8

02 Retinex Algorithm

∑ Multi-Scale Retinex (MSR) & MSR with Color Restoration (MSRCR)

N

n

n

N

n

nnMSR WRWRii

11

1,

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9

02 Retinex Algorithm

∑ MSRCR

linearity-nonofstrengththeControls:

ConstantGain:

ueOffset valGain :b

ConstantGain:G

]),(*),([),( byxRyxCGyxRii MSRiMSRCR

S

i

iii yxIyxIyxC1

),(log)],(log[),(

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03 Experiment Results

∑ Backlight Compensation

Origin

MSR

SSR Gamma Correction

sigma = 250 Gamma = 2.2

MSRCR

sigma =15, 80, 250

G = 130, b = 1

sigma =15, 80, 250

MMSRCR

sigma =80, 250

G = 130, b = 1

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03 Experiment Results

∑ Backlight Compensation

Origin

MSR

SSR Gamma Correctionsigma = 250 Gamma = 2.2

sigma =15, 80, 250

G = 130, b = 1

sigma =15, 80, 250 sigma =80, 250

G = 130, b = 1

MSRCR MMSRCR

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03 Experiment Results

∑ Backlight Compensation

Origin MSRSSR Gamma Correction

sigma = 250Gamma = 2.2

MSRCRsigma =15, 80, 250

G = 200, b = -20, α=100, β=40

sigma =15, 80, 250

MMSRCRsigma =80, 250

G = 200, b = 30

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04 Conclusion

13

SSR 보다는 MSR, MSRCR의성능이더좋음을확인.

처리속도가훨씬오래걸림.

실시간적용은힘들것으로예상.

http://dragon.larc.nasa.gov/retinex/pao/news/

Q & A