Assessment of Autofocus Techniques for Isolated Cellulose Microfiber 3D Imaging by Digital Holography

Studying the three-dimensional structure of paper fibrous networks is an important step towards understanding the relationship between manufacturing conditions and the resulting microstructural and mechanical properties. Digital holography is a promising three-dimensional imaging technique enabling quantitative phase evaluation of micro and nano-fibres. One of the advantages of this high-resolution method is the ability to perform numerical refocusing at several depths from a single shot acquisition. In this work, the suitability of 22 focusing functions to accurately identify the positions of cellulose microfibers, using digital holography, was inspected. The best performing metrics were identified and the trade-off between metric accuracy and robustness to variable conditions and their computational complexity were discussed. Keywords: digital holography, autofocus, cellulose microfibre, morphology, tomography