Full-Field Displacement Measurement Technique by Using Repeated Patterns and JPEG Compressed Images

Abstract

This paper presents an experimental technique for measuring displacement distribution from an image of repeated patterns and JPEG compressed images. The measurement accuracy of the developed method is insusceptible to the degree of JPEG compression because only lower spatial frequency components of the repeated pattern are used to calculate the displacement distribution, and high spatial frequency components have high priority to cut-off according to the JPEG compression algorithm. The insensitivity to the JPEG compression was confirmed by a displacement measurement using JPEG images of various compression ratios or image qualities. We found that by using the highest quality JPEG image, the accuracy of displacement measurement could research 1/1000 of the repeated pattern pitch, as same the uncompressed BMP images. In addition, displacement with accuracy of 1/500 pitch could be measured from a compressed JPEG image of which the file size was 1/50 of that of the BMP image. This technique is useful for measurement using a high-speed camera with high-resolution digital images for a long-term or wireless image transfer.