Abstract
The current underwater image formation model descends from atmospheric dehazing equations where attenuation is a weak function of wavelength. We recently showed
that this model introduces significant errors and dependencies in the estimation of the direct transmission signal because underwater, light attenuates in a wavelengthdependent manner. Here, we show that the backscattered
signal derived from the current model also suffers from dependencies that were previously unaccounted for. In doing
so, we use oceanographic measurements to derive the physically valid space of backscatter, and further show that the
wideband coefficients that govern backscatter are different
than those that govern direct transmission, even though the
current model treats them to be the same. We propose a revised equation for underwater image formation that takes
these differences into account, and validate it through in
situ experiments underwater. This revised model might explain frequent instabilities of current underwater color reconstruction models, and calls for the development of new
methods.