Optimizing hybrid images for an easy screening of the visual acuity

The development of a hybrid image (HI) is a method to create a single illusive picture, merging two images with different content in terms of spatial frequencies. Recently such a kind of optical illusion has also been used in the research area of optometry and psychology. Our study is based on the most famous HI, “Einstein-Marilyn face”, created in 2007 for the “New Scientist” magazine. This study aims to observe the role of the spatial frequencies in the interpretation of a HI in function of the visual acuity. The results show that a correct selection of the cut-off frequencies is fundamental to generating an optimal HI, i.e., with an optical illusion characterized by a non-ambiguous and stable interpretation. The design of working HIs can open the way for new kinds of tests in the field of optometry, in particular for the screening of myopia.