Lilong Shi and Brian Funt School of Computing Science, Simon Fraser University, Canada

Normalize skin tones of human faces Eliminate the effects of illumination Preserve skin colour Allow variations of melanin concentration Normalize skin tones of human faces Eliminate the effects of illumination Preserve skin colour Allow variations of melanin concentration

Two-layered Skin Model [1] Epidermis Layer: Melanin Absorbance Dermis Layer: Hemoglobin Absorbance A layer has properties of an optical filter Two-layered Skin Model [1] Epidermis Layer: Melanin Absorbance Dermis Layer: Hemoglobin Absorbance A layer has properties of an optical filter

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. 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. 4

Wien’s blackbody radiation models where, I is power of radiation, c 1 and c 2 are constants, T is blackbody temperature, Wien’s blackbody radiation models where, I is power of radiation, c 1 and c 2 are constants, T is blackbody temperature, 5

Proposed to combine Skin & Illum. Models Assume narrowband sensors used: In log space: Then, let Π represent camera RGB: Proposed to combine Skin & Illum. Models Assume narrowband sensors used: In log space: Then, let Π represent camera RGB: 6

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 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 7 σmσm 1 ω c log G log B log R σhσh

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 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. 8

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. 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. 9

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. 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. 10

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 Melanin and blood concentration in a human skin model studied by multiple regression analysis: assessment by Monte Carlo simulation. Phys. Med. Biol. 46(9): [2] Marszalec, E., B. Martinkauppi, M. Soriano, M. Pietikäinen A physics-based face database for color research. Journal of Electronic Imaging 9(1): 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 Melanin and blood concentration in a human skin model studied by multiple regression analysis: assessment by Monte Carlo simulation. Phys. Med. Biol. 46(9): [2] Marszalec, E., B. Martinkauppi, M. Soriano, M. Pietikäinen A physics-based face database for color research. Journal of Electronic Imaging 9(1):