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.
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."
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).