Fig. 6: Detection of CSRs and removal of background using retroreflection. | Light: Science & Applications

Fig. 6: Detection of CSRs and removal of background using retroreflection.

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

Fig. 6

Two fiducial markers made using CSRs with green and violet retroreflection, respectively, photographed with a regular smart phone (iPhone X) at about 45° angle with respect to the surface normal, using diffuse office ceiling lamp as sole illumination (a) and with the torch of the phone activated as well (b). In (c), the photo in (a) has been subtracted from that in (b). This is then separated into blue, green and red channels, after which the green channel is subtracted from the blue, following by a switch to monochrome mode with a threshold value of 15% to obtain (d). The image manipulations for obtaining (c) and (d) were done using Graphic Converter 9 (Lemkesoft)

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