MEASURING AND REPRODUCING THE 3D APPEARANCE OF HUMAN FACIAL SKIN UNDER VARYING ILLUMINATION CONDITIONS: A 3D IMAGING SYSTEM FOR HUMAN FACIAL SKIN

了解人类皮肤外观是科学、医学和技术领域非常感兴趣的课题。在医学上，皮肤外观是手术/假体重建、医疗化妆/纹身和疾病诊断的重要因素。生产面部假体以替换缺失的面部结构需要训练有素的再造学家的技能，以使假体的形状和颜色与宿主皮肤的形状和颜色正确匹配。随着人类皮肤的3D打印技术的发展，匹配天然和人造皮肤样本的过程变得至关重要;需要一个强大、准确和高效的成像系统来获取相关的皮肤信息，预测良好的匹配，并通过这种新的创新制造过程来翻译这些信息。人造皮肤的主要问题是，与个体的天然皮肤的匹配不仅必须在特定的环境照明下保持准确，而且当个体在不同环境之间移动时，例如当个体从办公室或LED照明移动到日光时，需要保持匹配。为了实现这种照明不变性，需要考虑皮肤的物理特性。成功的皮肤复制的另一个要求是外观模型的开发。这些可以被认为是每种皮肤类型的个人“食谱”或“蓝图”，这些不仅代表了个人间的差异-不同的种族群体和年龄范围，而且还代表了个人内部的差异-对于每个人来说。人类皮肤的特征（皱纹、毛孔、雀斑、斑点等）使人类皮肤像指纹一样个体化，因此，对于面部修复应用，皮肤外观模型也需要针对每个个体区域进行微调。这项工作的目的是开发一个完整的基于光谱的3D成像系统，这将使我们能够增材制造软组织假体或提供可预测的纹身技术，这将完全匹配特定个体的肤色。（应用1）或具有以高准确度快速制造/3D打印代表特定种族/年龄/性别组的软组织替代物的能力（应用2）。在应用1中，对该3D成像系统的输入将包括利用3D相机结合其他特定皮肤特征获得的（特定个体的）3D彩色皮肤图像。然后，将使用打印机配置文件打印皮肤样本，该打印机配置文件在不同的环境照明下最大限度地提高自然皮肤和打印皮肤之间的匹配。在应用2中，皮肤制造过程不会针对特定个体进行微调，但3D成像系统的输入将包括有关年龄、性别和种族的基本信息。然后将从预先计算的库中加载该组的代表性皮肤样本（颜色;纹理;透明度;几何形状），而不是使用来自个体的测量值。

Understanding human skin appearance is a subject of great interest in science, medicine and technology. In medicine, skin appearance is a vital factor in surgical/prosthetic reconstruction, medical make-up/tattooing and disease diagnosis. The production of facial prostheses to replace missing facial structures requires the skills of highly trained anaplastologists to correctly match the shape and colour of the prosthesis to that of the host skin. With the 3D printing of human skin now available the process involved in matching natural and manufactured skin samples has become essential; a robust, accurate and efficient imaging system is required that acquires the relevant skin information and predicts a good match and translates this information through this new and innovative manufacturing process. A major problem with manufactured skin is that the match to the individual's natural skin must hold not only be accurate under a particular ambient illumination but the match needs to be preserved when the individual is moving between different environments, e.g. when the individual moves from office or LED lighting into daylight. To achieve this illumination invariance, the physical properties of the skin need to be taken into account. A further requirement for successful skin reproduction is the development of appearance models. These can be considered as individual "recipes' or 'blueprints" for each skin type and these not only represent inter-personal differences - different ethnic groups and age ranges, but also intra-personal differences - for each individual. Features of the human skin (wrinkles, pores, freckles, spots etc) make human skin as individual as a finger prints and thus, for facial prosthetics applications, skin appearance models also need to be fine-tuned for each individual area. The purpose of this work is to develop a complete spectral-based 3D imaging system which will allow us to additively manufacture soft tissue prosthetics or deliver predictable tattooing techniques that will exactly match the skin colour of a particular individual (Application 1) or have the capability to rapidly manufacture/3D print soft tissue replacements representative of a particular ethnic/age/gender group with a high degree of accuracy (Application 2). In application 1, the input to this 3D imaging system will consist of a 3D colour skin image (of a particular individual) obtained with a 3D camera in conjunction other specific skin characteristics. The skin sample will then be printed using a printer profile that maximises the match between the natural and printed skin across different ambient illuminations. In application 2, the skin manufacturing process will not be fine-tuned for a particular individual, but input to the 3D imaging system will consist of basic information about the age, gender and ethnicity. Representative skin samples (colour; texture; translucency; geometry) for this group will then be loaded from a pre-computed library instead of using the measurements from an individual.