Lilong Shi and Brian Funt
School of Computing Science, Simon Fraser University, Canada
Skin Colour Imaging That Is Insensitive to Lighting
Conditions
Normalize skin tones of human faces
Eliminate the effects of illumination
Preserve skin colour
Allow variations of melanin concentration
Goal
Paper 102, slide [1/11] Paper 102 [Shi&Funt] ~2/11~
Two-layered Skin Model [1] Epidermis Layer: Melanin Absorbance Dermis Layer: Hemoglobin Absorbance
A layer has properties of an optical filter
Skin Appearance
Paper 102 [Shi&Funt] ~3/11~
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Reflection spectrum of skin [1]:
where, ’s are pigment densities of melanin & hemoglobin ’s are absorbance of melanin and hemoglobin, l’s are mean path lengths of photons, is other scattering loss and absorbance.
Skin Model
)]()()()()(exp[)( hhhmmm llS
Paper 102, slide [3/11] Paper 102 [Shi&Funt] ~4/11~
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Wien’s blackbody radiation models
where, I is power of radiation, c1 and c2 are constants, T is blackbody temperature,
Illumination Model
Paper 102, slide [4/11]
Tc
eIcTE2
51),(
Paper 102 [Shi&Funt] ~5/11~
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Proposed to combine Skin & Illum. Models Assume narrowband sensors used:
In log space:
Then, let Π represent camera RGB:
Skin-Illum Model
Paper 102 [Shi&Funt] ~6/11~
},,{),,()( BGRiTESP iii
)]log(5)[log()log()(
)()()()()()log(
112
ii
iihihhimimmi
cITcllP
c1ωσσΠ bτb hhmmhm ),,,(
7
where, m & h are melanin & hemoglobin bases, is a blackbody radiator basis, b = log(I), = 1/T, c is a constant vector.
m & h span all possible skin colours
Skin-Illum Model
Paper 102 [Shi&Funt] ~7/11~
c1ωσσΠ bτb hhmmhm ),,,(
σm
1
ωc
log G
log B
log R
σh
8
Our simplified Skin-Illumination Model
For varying illumination colour temperature; For varying skin melanin concentration; m and span the chromaticity space of arbitrary skin under different illuminations.
Given a skin pixel, melanin concentration can be recovered, so is true skin colour.
Our Skin Model
Paper 102, slide [1/10]
ωσΠ τmmm ),(
Paper 102 [Shi&Funt] ~8/11~
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Results based on UOPB[2] database (#94)
(a) a series of 16 face images under different camera calibration and illumination conditions. (faces segmented from the background) (b) the same images with corrected
skin tones based on our model.
Experiments
Paper 102 [Shi&Funt] ~9/11~
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Results based on UOPB[2] database (#111)
(a) a series of 16 face images under different camera calibration and illumination conditions. (faces segmented from the background) (b) the same images with corrected
skin tones based on our model.
Experiments
Paper 102 [Shi&Funt] ~10/11~
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Based on physical models Estimate skin melanin concentration Skin colour varies along melanin axis Shift colour along illum. axis Simple and computationally inexpensive
References: [1] Shimada, M., Y. Yamada, M. Itoh and T. Yatagai. 2001. Melanin and blood concentration in a human skin model studied by multiple regression analysis: assessment by Monte Carlo simulation. Phys. Med. Biol. 46(9):2397-2406.
[2] Marszalec, E., B. Martinkauppi, M. Soriano, M. Pietikäinen. 2000. A physics-based face database for color research. Journal of Electronic Imaging 9(1):32-38.
Conclusion
Paper 102, slide [5/11] Paper 102 [Shi&Funt] ~11/11~
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