Nondestructive determination of fiber orientation distribution of paper surface by image analysis

SUMMARY Fiber orientation is a criterion used to ascertain the manufacturing district and manufacturing technique of ancient paper as a material of cultural properties. Image analysis using fast Fourier transform with suitable modifications was demonstrated to be an applicable and nondestructive method to determine the orientation angle and anisotropy. In order to improve its accuracy, two new procedures—the binarization process of the microscopic images of the paper surface and precise calculations of the average Fourier coefficients as an angular distribution by linear interpolation—have been introduced to the existing procedures. This analytical method was applied to digital optical micrographs of paper surfaces. As predicted, the method was able to distinguish among laboratory handsheet, copier paper, Japanese paper, and wood-containing paper in terms of the papermaking processes. Traditionally manufactured Korean and Japanese papers showed their own characteristic orientation behavior in accordance with the motion of the bamboo wire in papermaking.