  The history of computing started with analog computers consisting of physical
devices performing specialized functions such as predicting the trajectory of
cannon balls. In modern times, this idea has been extended, for example, to
ultrafast nonlinear optics serving as a surrogate analog computer to probe the
behavior of complex phenomena such as rogue waves. Here we discuss a new
paradigm where physical phenomena coded as an algorithm perform computational
imaging tasks. Specifically, diffraction followed by coherent detection, not in
its analog realization but when coded as an algorithm, becomes an image
enhancement tool. Vision Enhancement via Virtual diffraction and coherent
Detection (VEViD) introduced here reimagines a digital image as a spatially
varying metaphoric light field and then subjects the field to the physical
processes akin to diffraction and coherent detection. The term "Virtual"
captures the deviation from the physical world. The light field is pixelated
and the propagation imparts a phase with an arbitrary dependence on frequency
which can be different from the quadratic behavior of physical diffraction.
Temporal frequencies exist in three bands corresponding to the RGB color
channels of a digital image. The phase of the output, not the intensity,
represents the output image. VEViD is a high-performance low-light-level and
color enhancement tool that emerges from this paradigm. The algorithm is
interpretable and computationally efficient. We demonstrate image enhancement
of 4k video at 200frames per second and show the utility of this physical
algorithm in improving the accuracy of object detection by neural networks
without having to retrain model for low-light conditions. The application of
VEViD to color enhancement is also demonstrated.
