{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2025,10,11]],"date-time":"2025-10-11T01:05:01Z","timestamp":1760144701778,"version":"build-2065373602"},"reference-count":24,"publisher":"MDPI AG","issue":"10","license":[{"start":{"date-parts":[[2024,5,12]],"date-time":"2024-05-12T00:00:00Z","timestamp":1715472000000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"funder":[{"name":"Deutsche Forschungsgemeinschaft (DFG)","award":["284158589"],"award-info":[{"award-number":["284158589"]}]}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["Sensors"],"abstract":"<jats:p>We have recently demonstrated that the 3D shape of micro-parts can be measured using LED illumination based on speckle contrast evaluation in the recently developed SPICE profilometry (shape measurements based on imaging with spatially partially coherent illumination). The main advantage of SPICE is its improved robustness and measurement speed compared to confocal or white light interferometry. The limited spatial coherence of the LED illumination is used for depth discrimination. An electrically tunable lens in a 4f-configuration is used for fast depth scanning without mechanically moving parts. The approach is efficient, takes less than a second to capture required images, is eye-safe and offers a depth of focus of a few millimeters. However, SPICE\u2019s main limitation is its assumption of a small illumination aperture. Such a small illumination aperture affects the axial scan resolution, which dominates the measurement uncertainty. In this paper, we propose a novel method to overcome the aperture angle limitation of SPICE by illuminating the object from different directions with several independent LED sources. This approach reduces the full width at half maximum of the contrast envelope to one-eighth, resulting in a twofold improvement in measurement accuracy. As a proof of concept, shape measurements of various metal objects are presented.<\/jats:p>","DOI":"10.3390\/s24103072","type":"journal-article","created":{"date-parts":[[2024,5,13]],"date-time":"2024-05-13T11:18:17Z","timestamp":1715599097000},"page":"3072","update-policy":"https:\/\/doi.org\/10.3390\/mdpi_crossmark_policy","source":"Crossref","is-referenced-by-count":0,"title":["Extended-Aperture Shape Measurements Using Spatially Partially Coherent Illumination (ExASPICE)"],"prefix":"10.3390","volume":"24","author":[{"ORCID":"https:\/\/orcid.org\/0000-0003-1618-824X","authenticated-orcid":false,"given":"Mostafa","family":"Agour","sequence":"first","affiliation":[{"name":"BIAS\u2014Bremer Institut f\u00fcr angewandte Strahltechnik, 28359 Bremen, Germany"},{"name":"Physics Department, Faculty of Science, Aswan University, Aswan 81528, Egypt"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"ORCID":"https:\/\/orcid.org\/0000-0001-6481-5709","authenticated-orcid":false,"given":"Claas","family":"Falldorf","sequence":"additional","affiliation":[{"name":"BIAS\u2014Bremer Institut f\u00fcr angewandte Strahltechnik, 28359 Bremen, Germany"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"ORCID":"https:\/\/orcid.org\/0000-0003-0214-2232","authenticated-orcid":false,"given":"Ralf B.","family":"Bergmann","sequence":"additional","affiliation":[{"name":"BIAS\u2014Bremer Institut f\u00fcr angewandte Strahltechnik, 28359 Bremen, Germany"},{"name":"MAPEX Center for Materials and Processes and Faculty of Physics and Electrical Engineering, University of Bremen, 28359 Bremen, Germany"}],"role":[{"role":"author","vocabulary":"crossref"}]}],"member":"1968","published-online":{"date-parts":[[2024,5,12]]},"reference":[{"key":"ref_1","unstructured":"Levi, P. (1983, January 5\u201316). Quality assurance and machine vision for inspection. Proceedings of the International Symposium on the Occasion of the 25th Anniversary of McGill University Centre for Intelligent Machines, Karlsruhe, Germany."},{"key":"ref_2","doi-asserted-by":"crossref","first-page":"611","DOI":"10.1007\/s00170-012-4352-4","article-title":"Progressive microforming process: Towards the mass production of micro-parts using sheet metal","volume":"66","author":"Ghassemali","year":"2013","journal-title":"Int. J. Adv. Manuf. Technol."},{"key":"ref_3","doi-asserted-by":"crossref","first-page":"531","DOI":"10.1016\/j.cirp.2012.03.131","article-title":"Automated surface inspection of cold-formed micro-parts","volume":"61","author":"Weimer","year":"2012","journal-title":"CIRP Ann."},{"key":"ref_4","doi-asserted-by":"crossref","first-page":"385","DOI":"10.1364\/OE.413182","article-title":"Fast 3D form measurement using a tunable lens profiler based on imaging with LED illumination","volume":"29","author":"Agour","year":"2021","journal-title":"Opt. Express"},{"key":"ref_5","unstructured":"Osten, W. (2013). Computational Optical Sensing and Imaging, Optica Publishing Group."},{"key":"ref_6","doi-asserted-by":"crossref","first-page":"28576","DOI":"10.1364\/OE.26.028576","article-title":"Spatial multiplexing and autofocus in holographic contouring for inspection of micro-parts","volume":"26","author":"Agour","year":"2018","journal-title":"Opt. Express"},{"key":"ref_7","doi-asserted-by":"crossref","unstructured":"Anand, V., Katkus, T., Linklater, D.P., Ivanova, E.P., and Juodkazis, S. (2020). Lensless three-dimensional quantitative phase imaging using phase retrieval algorithm. J. Imaging, 6.","DOI":"10.3390\/jimaging6090099"},{"key":"ref_8","doi-asserted-by":"crossref","first-page":"11332","DOI":"10.1364\/AO.410921","article-title":"Spatial axial shearing common-path interferometer for natural light","volume":"59","author":"Imbe","year":"2020","journal-title":"Appl. Opt."},{"key":"ref_9","doi-asserted-by":"crossref","first-page":"056101","DOI":"10.1088\/1361-6633\/ab092d","article-title":"A review of selected topics in interferometric optical metrology","volume":"82","year":"2019","journal-title":"Rep. Prog. Phys."},{"key":"ref_10","doi-asserted-by":"crossref","first-page":"98","DOI":"10.1117\/12.474947","article-title":"White light interferometry. Holography: A tribute to Yuri Denisyuk and Emmett Leith","volume":"4737","author":"Wyant","year":"2002","journal-title":"Proc. SPIE"},{"key":"ref_11","doi-asserted-by":"crossref","first-page":"106407","DOI":"10.1016\/j.optlaseng.2020.106407","article-title":"Lens-based phase retrieval under spatially partially coherent illumination-part II: Shape measurements","volume":"139","author":"Agour","year":"2021","journal-title":"Opt. Lasers Eng."},{"key":"ref_12","doi-asserted-by":"crossref","first-page":"4003","DOI":"10.1364\/AO.48.004003","article-title":"Characterization of a spatial light modulator and its application in phase retrieval","volume":"48","author":"Kohler","year":"2009","journal-title":"Appl. Opt."},{"key":"ref_13","doi-asserted-by":"crossref","first-page":"2161","DOI":"10.1364\/OL.41.002161","article-title":"Enhanced intensity variation for multiple-plane phase retrieval using a spatial light modulator as a convenient tunable diffuser","volume":"41","author":"Almoro","year":"2016","journal-title":"Opt. Lett."},{"key":"ref_14","doi-asserted-by":"crossref","first-page":"024004","DOI":"10.1088\/2515-7647\/abe3da","article-title":"The instrument transfer function for optical measurements of surface topography","volume":"3","year":"2021","journal-title":"J. Phys. Photonics"},{"key":"ref_15","doi-asserted-by":"crossref","first-page":"106507","DOI":"10.1016\/j.optlaseng.2020.106507","article-title":"Lens-based phase retrieval under spatially partially coherent illumination\u2014Part I: Theory","volume":"139","author":"Falldorf","year":"2021","journal-title":"Opt. Lasers Eng."},{"key":"ref_16","unstructured":"Danzl, R., Helmli, F., and Scherer, S. (2009, January 1\u20133). Focus variation\u2014A new technology for high resolution optical 3D surface metrology. Proceedings of the 10th International Conference of the Slovenian Society for Non-Destructive Testing, Ljubljana, Slovenia."},{"key":"ref_17","unstructured":"Danzl, R., and Helmli, F. (2007, January 20\u201324). Form measurement of engineering parts using an optical measurement system based on focus variation. Proceedings of the 7th European Society for Precision Engineering and Nanotechnology International Conference, Bremen, Germany."},{"key":"ref_18","doi-asserted-by":"crossref","first-page":"10453","DOI":"10.1364\/OE.23.010453","article-title":"Coherence modulation by deterministic rotating diffusers","volume":"23","author":"Lehtolahti","year":"2015","journal-title":"Opt. Express"},{"key":"ref_19","doi-asserted-by":"crossref","first-page":"4530","DOI":"10.1364\/OE.412047","article-title":"Scatter-plate microscopy with spatially coherent illumination and temporal scatter modulation","volume":"29","author":"Ludwig","year":"2021","journal-title":"Opt. Express"},{"key":"ref_20","doi-asserted-by":"crossref","unstructured":"Agour, M., Falldorf, C., and Bergmann, R. (2023, January 15). Improved 3D form profiler based on extending illumination aperture. Proceedings of the Optical Measurement Systems for Industrial Inspection XIII, Munich, Germany.","DOI":"10.1117\/12.2673783"},{"key":"ref_21","unstructured":"(2024, May 06). Standard Ring Lights: LDR2 Series. Available online: https:\/\/www.ccs-grp.com\/products\/series\/1."},{"key":"ref_22","doi-asserted-by":"crossref","unstructured":"Dainty, J.C. (1975). Laser Speckle and Related Phenomena, Springer.","DOI":"10.1007\/978-3-662-43205-1"},{"key":"ref_23","doi-asserted-by":"crossref","unstructured":"Leach, R. (2011). Optical Measurement of Surface Topography, Springer.","DOI":"10.1007\/978-3-642-12012-1"},{"key":"ref_24","first-page":"1","article-title":"Robust autofocusing in microscopy","volume":"39","author":"Geusebroek","year":"2000","journal-title":"Cytom. J. Int. Soc. Anal. Cytol."}],"container-title":["Sensors"],"original-title":[],"language":"en","link":[{"URL":"https:\/\/www.mdpi.com\/1424-8220\/24\/10\/3072\/pdf","content-type":"unspecified","content-version":"vor","intended-application":"similarity-checking"}],"deposited":{"date-parts":[[2025,10,10]],"date-time":"2025-10-10T14:41:02Z","timestamp":1760107262000},"score":1,"resource":{"primary":{"URL":"https:\/\/www.mdpi.com\/1424-8220\/24\/10\/3072"}},"subtitle":[],"short-title":[],"issued":{"date-parts":[[2024,5,12]]},"references-count":24,"journal-issue":{"issue":"10","published-online":{"date-parts":[[2024,5]]}},"alternative-id":["s24103072"],"URL":"https:\/\/doi.org\/10.3390\/s24103072","relation":{},"ISSN":["1424-8220"],"issn-type":[{"type":"electronic","value":"1424-8220"}],"subject":[],"published":{"date-parts":[[2024,5,12]]}}}