Evaluating distribution and variation of strains near eyes in blinking using digital image correlation

Background Strain is occurred due to deformation such as the change of facial expression and is expected as a new evaluation approach to know the condition of skins applied to cosmetics. In this study, a noncontact in‐site method by using digital image correlation for measuring the strain on the skin surface near the eyes where deformation always occurs by blinking is proposed. In this method, skin microrelief and irregularities are utilized for the measurement. Materials and Methods Images on the skin surface below the eyes of the four female subjects are pictured during a blink using high‐speed cameras. The principal strains as well as the principal directions are obtained using digital image correlation. The reference updating algorism is used when the movement of the skin surface due to blink is large, and the eyelashes elimination algorism is used when the long eyelashes hide their skin surface in an image. The strain distributions in the local area below the right eye and the time histories of the strain near the eye under several skin conditions are evaluated for each subject. Results The strain can be obtained for each subject under each condition and the different strain distributions and time histories under different condition are visualized. Conclusion The individual behavior of the subject and the different condition of the skin can be captured by the proposed method.