Digital image processing and illumination techniques for yarn characterization

Abstract

This paper describes various illumination and image processing techniques for yarn characterization. Darkfield and back-lit illuminations are compared in terms of depth of field tolerance and image quality. Experiments show that back-lit illumination is superior in terms of depth of field tolerance and contrast. Three different back-lit illumination configurations are studied: one simply employing a light source placed behind the yarn, the other incorporating a field lens to increase the light intensity passing through the aperture, and the third using a mirror placed at 45° to the optical axis to enable imaging of two orthogonal views of the yarn core. Problems in defining the hair–core boundaries in high resolution yarn pictures are addressed and a filtering process is introduced for back-lit images. A comparison of the diameter and diameter coefficient of variation percentage measurements for different illumination and image processing techniques is given for several yarn samples. The data are also correlated with Premier 7000 diametric irregularity tester and Uster Tester 3 irregularity measurements.