Fig. 7: Near-IR and near-UV-reflecting fiducial markers in indoor environment. | Light: Science & Applications

Fig. 7: Near-IR and near-UV-reflecting fiducial markers in indoor environment.

From: Unclonable human-invisible machine vision markers leveraging the omnidirectional chiral Bragg diffraction of cholesteric spherical reflectors

Fig. 7

Macroscopic views of fiducial markers made of CSRs with near-IR (columns 1–2) and near-UV (columns 3–4) retroreflection, respectively, in NOA160, as seen by a modified DSLR camera without UV/IR blocking filter (top row) and by a regular mobile phone camera (bottom row). The markers are illuminated by the regular white ceiling light in (a/e) and (c/g), additionally by a 940 nm night vision LED in (b/f) and by a black light lamp in (d/h). While the pattern of each marker is difficult to see under ordinary light illumination only, it becomes very clear with the IR/UV-imaging camera when the corresponding near-IR/UV light is turned on. Note that no polarization filters are used, hence the background is not subtracted. The near-UV marker placed on a printed magazine page is photographed using a regular mobile phone camera in (i), showing that it is nearly fully transparent and difficult to notice by the naked eye (as a guide to the eye, a white frame highlights its location). The few scattering dots are CSR beads rather than shells. The outer side length of each marker is 5 cm

Back to article page