Three important performance parameters that need to be borne in mind are the signal-to-noise ratio (SNR), resolution and modular transfer function (MTF) and lifetime of an II. SNR is the measure of the light signal reaching the eye divided by the perceived noise as seen by the eye. Higher the SNR, better the ability to resolve image details under low light conditions. MTF is the maximum line density on a target that can be resolved by human eye. High MTF values at low spatial frequencies provide sharp images with a good contrast. Lifetime of an II is extremely important for night vision applications.