Spring 2015 Science Seminars

A Pot of Gold: Rainbows as a Calibration Cue

Abstract:   Rainbows are ephemeral, optical and meteorological phenomena caused by reflection, refraction and dispersion of light in water droplets in the air, most often after a storm. In this talk, I will present our work on how rainbows captured on photographs provide unique camera calibration cues. Rainbows are centered exactly opposite the sun and have an outer radius of 42 degrees. I will formally define the geometry and describe minimal sets of constraints that are sufficient for estimating camera calibration. I will present both semi-automatic and fully automatic methods to calibrate a camera using an image of a rainbow.  To demonstrate our methods, we collected a large database  of rainbow images and use these to evaluate the calibration accuracy and created an empirical model of rainbow appearance.  I will show how this model can be used to edit rainbow appearance in natural images and how rainbow appearance together with a horizon line estimate and capture time, provide an estimate of camera location on Earth.