Structured Illumination (SI) - or patterned illumination - is the wide-field version of breaking the diffraction limit of light. SI relies on both specific microscopy
protocols and extensive software analysis post-exposure.
The main
concept of SI is to illuminate a sample with patterned light and
increase the resolution by measuring the fringes in the Moiré pattern
(from the interference of the illumination pattern and the sample).
"Otherwise-unobservable sample information can be deduced from the
fringes and computationally restored." (
Gustafsson MG,
PNAS 2005).
SI enhances spatial resolution by collecting information from frequency
space outside the observable region. This process is done in reciprocal
space (Frequency, or Fourier Space).