Schlieren masks: square root monomials, sigmoidal functions, and off-axis Gaussians

By using an effective transfer function, one can describe conveniently the nonlinear mapping between an input thin transparent structure and its image irradiance distribution. This effective transfer function is useful for making sound comparisons between several spatial filters employed for phase rendering. Here, we unveil three nonconventional Schlieren techniques, which employ absorption masks whose amplitude distributions are described by square root monomials, by sigmoidal functions, or by off-axis Gaussian functions. We apply the effective transfer function for analyzing the similarities between the proposed masks and other Schlieren techniques.