Magic Prints: Image-Changing Prints Observed under Visible and 365 nm UV Light

In this paper we propose a novel layered-printing method consisting of superposed visible cmy and invisible fluorescent ultraviolet (UV) rgb inks. Our approach can be used to generate a variety of visual color-alteration effects such as revealing two completely distinct images when the print is illuminated with either standard visible or 365 nm ultraviolet (UV) light (Figure 1). This is achieved by computing the maximum achievable color gamuts for both illumination conditions, generating accurate estimates, and applying a spatial-varying gamut mapping to minimize potential ghosting artifacts and calculate the optimal ink surface coverages that, when printed, generate the desired image-alteration effect. Our method uses invisible UV-rgb fluorescent inks which are printed onto a transparent film. It is placed on top of a visible print consisting of standard cmy inks. By separating the UV and the visible inks using the transparent film, physical mixing of the two different ink types is avoided. This significantly increases the intensity of the fluorescent emission resulting in stronger and more vivid color-alteration effects. Besides the revealing of two different images, the same method can be applied for other use cases as well, such as enhancing or adding specific parts to an image under one illumination condition, generating personalized document security features, or aiding color-blind people in color distinction. (C) 2019 Society for Imaging Science and Technology.