Daugman, John; Downing, Cathryn: 'Iris image quality metrics with veto power and nonlinear importance tailoring' (Security, 2017), 'Iris and Periocular Biometric Recognition', Chap. 4, pp. 83-100, DOI: 10.1049/PBSE005E_ch4
IET Digital Library, https://digital-library.theiet.org/;jsessionid=183zjpy56woi3.x-iet-live-01content/books/10.1049/pbse005e_ch4