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Motivated by the traditional iris-localization algorithm and the robustness of the YOLO model, we propose a novel iris-localization algorithm. First, we design a novel iris detector with a modified you only look once v4 (YOLO v4) model. We can approximate the position of the pupil center. Then, we use a modified integro-differential operator to precisely locate the iris inner and outer boundaries. Experiment results show that iris-detection accuracy can reach 99.83% with this modified YOLO v4 model, which is higher than that of a traditional YOLO v4 model. The accuracy in locating the inner and outer boundary of the iris without glasses can reach 97.72% at a short distance and 98.32% at a long distance. The locating accuracy with glasses can obtained at 93.91% and 84%, respectively. It is much higher than the traditional Daugman\u2019s algorithm. Extensive experiments conducted on multiple datasets demonstrate the effectiveness and robustness of our method for iris localization in non-cooperative environments.<\/jats:p>","DOI":"10.3390\/s22249913","type":"journal-article","created":{"date-parts":[[2022,12,16]],"date-time":"2022-12-16T04:30:00Z","timestamp":1671165000000},"page":"9913","update-policy":"https:\/\/doi.org\/10.3390\/mdpi_crossmark_policy","source":"Crossref","is-referenced-by-count":9,"title":["Robust Iris-Localization Algorithm in Non-Cooperative Environments Based on the Improved YOLO v4 Model"],"prefix":"10.3390","volume":"22","author":[{"ORCID":"https:\/\/orcid.org\/0000-0003-0396-4836","authenticated-orcid":false,"given":"Qi","family":"Xiong","sequence":"first","affiliation":[{"name":"MOE Key Lab for Intelligent Networks and Network Security, School of Automation Science and Engineering, Faculty of Electronic and Information Engineering, Xi\u2019an Jiaotong University, Xi\u2019an 710049, China"},{"name":"International Collage, Hunan University of Arts and Sciences, Changde 415000, China"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Xinman","family":"Zhang","sequence":"additional","affiliation":[{"name":"MOE Key Lab for Intelligent Networks and Network Security, School of Automation Science and Engineering, Faculty of Electronic and Information Engineering, Xi\u2019an Jiaotong University, Xi\u2019an 710049, China"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Xingzhu","family":"Wang","sequence":"additional","affiliation":[{"name":"International Collage, Hunan University of Arts and Sciences, Changde 415000, China"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Naosheng","family":"Qiao","sequence":"additional","affiliation":[{"name":"International Collage, Hunan University of Arts and Sciences, Changde 415000, China"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-9403-7140","authenticated-orcid":false,"given":"Jun","family":"Shen","sequence":"additional","affiliation":[{"name":"School of Computing and Information Technology, University of Wollongong, Wollongong, NSW 2522, Australia"}],"role":[{"role":"author","vocabulary":"crossref"}]}],"member":"1968","published-online":{"date-parts":[[2022,12,16]]},"reference":[{"key":"ref_1","doi-asserted-by":"crossref","first-page":"125","DOI":"10.1109\/TIFS.2006.873653","article-title":"Biometrics: A tool for information security","volume":"1","author":"Jain","year":"2006","journal-title":"IEEE Trans. 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