{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2025,10,11]],"date-time":"2025-10-11T01:49:53Z","timestamp":1760147393403,"version":"build-2065373602"},"reference-count":30,"publisher":"MDPI AG","issue":"3","license":[{"start":{"date-parts":[[2023,2,1]],"date-time":"2023-02-01T00:00:00Z","timestamp":1675209600000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"funder":[{"DOI":"10.13039\/501100012166","name":"National Key Research and Development Program of China","doi-asserted-by":"publisher","award":["2019YFB1803700","20YFZCGX00440","2021SYS-04"],"award-info":[{"award-number":["2019YFB1803700","20YFZCGX00440","2021SYS-04"]}],"id":[{"id":"10.13039\/501100012166","id-type":"DOI","asserted-by":"publisher"}]},{"name":"Key Technologies R&amp;D Program of Tianjin","award":["2019YFB1803700","20YFZCGX00440","2021SYS-04"],"award-info":[{"award-number":["2019YFB1803700","20YFZCGX00440","2021SYS-04"]}]},{"name":"Shaanxi Key Laboratory of Deep Space Exploration Intelligent Information Technology","award":["2019YFB1803700","20YFZCGX00440","2021SYS-04"],"award-info":[{"award-number":["2019YFB1803700","20YFZCGX00440","2021SYS-04"]}]}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["Sensors"],"abstract":"<jats:p>Face masks can effectively prevent the spread of viruses. It is necessary to determine the wearing condition of masks in various locations, such as traffic stations, hospitals, and other places with a risk of infection. Therefore, achieving fast and accurate identification in different application scenarios is an urgent problem to be solved. Contactless mask recognition can avoid the waste of human resources and the risk of exposure. We propose a novel method for face mask recognition, which is demonstrated using the spatial and frequency features from the 3D information. A ToF camera with a simple system and robust data are used to capture the depth images. The facial contour of the depth image is extracted accurately by the designed method, which can reduce the dimension of the depth data to improve the recognition speed. Additionally, the classification process is further divided into two parts. The wearing condition of the mask is first identified by features extracted from the facial contour. The types of masks are then classified by new features extracted from the spatial and frequency curves. With appropriate thresholds and a voting method, the total recall accuracy of the proposed algorithm can achieve 96.21%. Especially, the recall accuracy for images without mask can reach 99.21%.<\/jats:p>","DOI":"10.3390\/s23031596","type":"journal-article","created":{"date-parts":[[2023,2,1]],"date-time":"2023-02-01T06:49:36Z","timestamp":1675234176000},"page":"1596","update-policy":"https:\/\/doi.org\/10.3390\/mdpi_crossmark_policy","source":"Crossref","is-referenced-by-count":2,"title":["Face Mask Identification Using Spatial and Frequency Features in Depth Image from Time-of-Flight Camera"],"prefix":"10.3390","volume":"23","author":[{"given":"Xiaoyan","family":"Wang","sequence":"first","affiliation":[{"name":"Institute of Modern Optics, Nankai University, Tianjin 300350, China"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Tianxu","family":"Xu","sequence":"additional","affiliation":[{"name":"National Center for International Joint Research of Electronic Materials and Systems, School of Electrical and Information Engineering, Zhengzhou University, Zhengzhou 450001, China"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Dong","family":"An","sequence":"additional","affiliation":[{"name":"Institute of Modern Optics, Nankai University, Tianjin 300350, China"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Lei","family":"Sun","sequence":"additional","affiliation":[{"name":"Shphotonics, LLC, Tianjin 300450, China"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Qiang","family":"Wang","sequence":"additional","affiliation":[{"name":"Angle AI (Tianjin) Technology Co., Ltd., Tianjin 300450, China"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"ORCID":"https:\/\/orcid.org\/0000-0003-2325-2254","authenticated-orcid":false,"given":"Zhongqi","family":"Pan","sequence":"additional","affiliation":[{"name":"Department of Electrical & Computer Engineering, University of Louisiana at Lafayette, Lafayette, LA 70504, USA"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Yang","family":"Yue","sequence":"additional","affiliation":[{"name":"School of Information and Communications Engineering, Xi\u2019an Jiaotong University, Xi\u2019an 710049, China"}],"role":[{"role":"author","vocabulary":"crossref"}]}],"member":"1968","published-online":{"date-parts":[[2023,2,1]]},"reference":[{"key":"ref_1","doi-asserted-by":"crossref","first-page":"1439","DOI":"10.1126\/science.abg6296","article-title":"Face Masks Effectively Limit the Probability of SARS-CoV-2 Transmission","volume":"372","author":"Cheng","year":"2021","journal-title":"Science"},{"key":"ref_2","doi-asserted-by":"crossref","first-page":"205","DOI":"10.1016\/j.cogr.2021.11.001","article-title":"Unbundling the Significance of Cognitive Robots and Drones Deployed to Tackle COVID-19 Pandemic: A Rapid Review to Unpack Emerging Opportunities to Improve Healthcare in Sub-Saharan Africa","volume":"1","author":"Mbunge","year":"2021","journal-title":"Cogn. 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