This short presentation wants to clarify the notion of optical density (OD) and put it into context with signal to noise ratio (SNR).
In our daily work as filter manufacturer we often talk to customers with an electrical engineering or imaging background. In these and other fields SNR is an important quantity to describe system or detector performance.
Filters on the other hand are described by transmission and rejection performance. The former often on a scale from 0 to 1 (preferably) or on a %-scale. The latter is often described as optical density.