Abstract:

Objective Virtual fitting attracts much research attention for clothing digitalization. Existing studies regard the human body as rigid in body representation, adopt a one-way repulsion model in the contact mechanism, and implement a simple process of pushing the clothing away from the human body when dealing with contact. These studies focus on improving the visual effect of virtual fitting, while the clothing pressure simulation and pressure comfort evaluation are ignored. This study represents an annovation attempt to replace the existing one-way contact mechanism, and proposes a virtual skin model, which fully reflects the deformation of human skin and the mutual effect between clothing and the body, which is designed for perceiving the pressure transmitted from clothing to the body, thus providing a method for the prediction of pressure comfort in the scenario of virtual fitting.

Methods The skin with mechanical properties was constructed by volume constraint and shape constraint, and the variability of skin shape was controlled by the shape preserving factor, thus regulating the degree of skin firmness or relaxation. The particle spring system was used to construct the fabric model in order to facilitate skin contact and interaction, and the mapping between the spring coefficient and the real fabric mechanical properties was established. The contact behavior of particles was conducted by momentum reallocation, and the spatial displacement of particles was calculated by the integral of particle velocity on the time slices, so as to complete the contact deformation on both skin and clothing. By calculating the force of particles in the contact process, the real-time clothing pressure on human skin was obtained, and thus the clothing pressure in virtual space was simulated and evaluated.

Results The elastic coefficient of the fabric model was obtained from the tensile test of the real fabric, so that the mapping between the virtual fabric and the real fabric was established. The virtual fabric was tailored and sewn to produce virtual clothing. A live body model was scanned, and the skin was generated from the resulting body surface mesh. The virtual clothing was placed on the human body with the skin layer, and the interaction between skin and clothing was simulated with respect to the contact algorithm so as to calculate the clothing pressure. The pressure was mainly concentrated in the chest, shoulders, back and side waist, which is consistent with the intuitive experience. The pressure sensors were attached on the body skin, and the real pressure on the spots of the chest, shoulder, back and side waist was collected and compared with the simulated pressure. With the increased value of shape preserving factor α, the virtual pressure at each spot increased gradually, first approaching the real pressure value and then gradually deviating from it. The overall error of simulated pressure decreased first and then increased as the α value increased, and the shape preserving factor α=0.5 corresponding to the minimum error of 17.8% was regarded as the descriptive parameter for the personality of the subject's skin. The minimum errors of simulated pressure on the chest, shoulder, back and side waist points appeared at α=0.28, 0.81, 0.66 and 0.45 respectively, which was consistent with the fact that the skin flexibility of the chest is the largest, followed by the waist, the back and the shoulder successively. The skin was divided into four regions surrounding chest, shoulder, back and waist. The shape preserving factor in each region was set to the value corresponding to the minimum pressure error of the spot to form the so-called mixed shape preserving factors, and the virtual pressure was calculated and compared with the case in which the single preserving factor takes effect. The results show that the minimum error was 17.72% with single preserving factor and 8.92% when using mixed preserving factors. It is proved that using mixed preserving factors to describe body skin can effectively reduce the error and improve the precision of simulation by considering the difference of various parts of body skin.

Conclusion The skin model proposed in this study can simulate the contact and interaction between human body and clothing, and fetch the clothing pressure on the skin in real time, so as to provide theory and methods for high-level virtual fitting and comfort evaluation. The mechanical behavior of human skin is simulated by volume constraint and shape constraint, with the latter being manipulated by the shape preserving factors, and thus the expression of skin firmness or relaxation is achieved. In the particle space, the contact behavior of particles is conducted by the momentum reallocation rule, and the change of spatial position after contact is achieved by the integral of particle velocity, so as to introduce the contact deformation of skin and clothing. By calculating the force of clothing particles in the contact process, the clothing pressure on human body is obtained. In the verification experiment, the virtual skin is constructed from the real human body mesh, and the virtual fabric is built with the real fabric as the prototype. The measured real clothing pressure is compared with the simulated pressure, and the mixed shape preserving factor is employed to reflect the difference of the skin in different parts of human body, leading to a reduced error of 8.92%.

Key words: clothing engineering, virtual skin model, virtual clothing, clothing pressure, virtual fitting, skin flexibility