Scale‐robust fibre orientation analysis of hair using two‐dimensional Fourier transform

Objective To address the current lack of standardized tools for evaluating hair appearance in the beauty industry, this study presents a robust and accessible method for objectively quantifying hair fibre orientation using two‐dimensional discrete Fourier transform (2D‐DFT). Methods We analysed hair images of 120 Japanese women using 2D‐DFT and extracted the principal orientation angle and anisotropy index by fitting an ellipse to the directional Fourier spectrum. The robustness of the method at the image scale was tested by evaluating its performance across various image resolutions. Results The proposed method accurately quantified hair orientation and showed consistent performance across differing image scales provided that individual hair fibres were visually distinguishable. As the method requires only standard digital images and basic computational processing, it is well suited for practical applications. Conclusion Our 2D‐DFT‐based approach offers a simple yet robust framework for analysing overall hair orientation. Although further validation is required for different hair types and local orientation analyses, this method provides a foundation for objective evaluation of hair appearance in cosmetic diagnostics and hair science research.