Light and Water Drops

Water drops are present throughout our daily lives. Microscopic droplets create fog and mist, and large drops fall as rain. Because of their shape and refractive properties, water drops exhibit a wide variety of visual effects. If not directly illuminated by a light source, they are difficult to see. But if they are directly illuminated, they can become the brightest objects in the environment. This thesis has two main components. First, we will show how to create two- and three-dimensional displays using water drops and a projector. Water drops act as tiny spherical lenses, refracting light into a wide angle. To a person viewing an illuminated drop, it will appear that the drop is the same color as the incident light ray. Using a valve assembly, we will fill a volume with non-occluding water drops. At any instant in time, no ray from the projector will intersect with two drops. Using a camera, we will detect the drops locations, then illuminate them with the projector. The final result is a programmable, dynamic, and three-dimensional display. Second, we will show how to reduce the effect of water drops in videos via spatio-temporal frequency analysis, and in real life, by using a projector to illuminate everything except the drops. To remove rain (and snow) from videos, we will use a streak model in frequency space to find the frequencies corresponding to rain and snow in the video. These frequencies can then be suppressed to reduce the effect of rain and snow. We will also suppress the visual effect of water drops by selectively "missing" them by not illuminating them with a projector. In light rain, this can be performed by tracking individual drops. This kind of drop-avoiding light source could be used for many nighttime applications, such as car headlights.