Improved method for skin reflectance reconstruction from camera images

Abstract

A improved spectral reflectance reconstruction method is developed to transform camera RGB to spectral reflectance for skin images. Rather than using conventional direct or two-step processes, we transform camera RGB to skin reflectance directly using a principal component analysis (PCA) approach. The novelty in our direct method (RGB to spectra) is the use of a skin-specific colour characterisation chart with spectra closer to human skin spectra, and a new database of skin reflectances to derive the PCA bases. The experimental results using the facial images of 17 subjects demonstrate that our new direct method gives a significantly better performance than conventional, two-step methods and direct methods with traditional characterization charts. This new spectral reconstruction algorithm is sufficiently precise to reconstruct spectral properites relating to chromophores and its performance is within the acceptable range for maxillofacial soft tissue prostheses (error < 3 ΔE*_ab units).

Colour quality of facial prostheses in additive manufacturing

“…For the manufactured prostheses, 3D geometry and 2D colour information were acquired by dedicated digital imaging systems [10,42], namely, the 3dMD facial imaging system (3dMD, Atlanta, GA, USA) and Spectrum Z510 3D printer (Z Corp, Burlington, MA, USA).…”

“…3a, b. The difference between their spectra can be assessed with the RMSE and SSV [29,42], as defined in the following sections.…”

“…The evaluation of the spectral differences between two spectra, the original and test spectra, can be performed with the RMSE and SSV [29,42]. The definitions are given below.…”

“…The RMSE and SSV between the printed faces and ground truth for the three individual subjects are summarised in SSV levels were achieved when compared to the study investigating spectral reconstruction of human skin from RGB digital values [42].…”

An investigation into the variability of skin colour measurements

“…The colour of skin is probably one of the colours that we see most in our daily lives, and it plays an important role in many multidisciplinary applications. Apart from the reproduction of skin colour in general amateur and professional photography, cinematography and printing, these include the photography of skin for medical recording and diagnosis and the potential manufacture of prosthetics, skin colour based faced detection for computer vision applications, the identification of the skin colour preference for applications in, for example, the cosmetics industries and, more recently, skin colour reproduction in 3D printing . For all these applications, a reliable technique to quantify the colour of skin objectively, in all its many variations, is of vital importance.…”