Two-phase SI (right column) generates residual lines (2ν) with a spatial frequency twice that of the ground-frequency. Thus, by increasing the ground-frequency, 1st, of the subimages (left column) the residuals become less apparent and eventually, they reside at border of the observable region were they are nearly indistinguishable.

FT = Fourier transform.

Example of a two-pulse (2P) SI image, in which the ground-frequency is ν = 0.50, thus generating residuals exactly at

resolution limit. These unwanted fringes are easily removed by means of a low-pass filter (LPF), which, because of the carefully chosen ground-frequency, hardly affects the image quality. fc = cut-off frequency.

- M. Storch, Y. Nath Mishra, M- Koegl, E. Kristensson, S. Will, L. Zigan and E. Berrocal, Two-phase SLIPI for instantaneous LIF and Mie imaging of transient fuel sprays, 41, 5422-5425, 2016.
- E. Kristensson, E. Berrocal and M. Aldén, Two-pulse structured illumination imaging, Opt. Letters, 9, 2014.