[Preview of the GPA user interface showing the measurement of elastic strains from a high-resolution micrograph.]
The GPA software is developed as a plugin to the commercial software DigitalMicrograph from Gatan Inc for lattice-distortion measurements from high-resolution transmission electron microscopy (HRTEM) images. In the use of GPA, two strong yet noncollinear reflections in the Fourier transform of an HRTEM image are masked with small apertures. Thereafter, displacement fields are obtained from the phases of the inverse Fourier transforms of the selected reflections. Finally, stain fields are computed from the displacement fields. The GPA software is written in pure DigitalMicrograph script language, and in principle should run well independent on the DigitalMicrograph version used.
Users of the GPA plugin are kindly asked to refer to its use by referring to: Du, H. (2018) GPA – geometrical phase analysis software
Author: Hongchu Du
 M. Takeda and J. Suzuki, Crystallographic heterodyne phase detection for highly sensitive lattice-distortion measurements, J. Opt. Soc. Am. A. 13 (1996) 1495–1500. doi:10.1364/JOSAA.13.001495.
 M.J. Hÿtch, E. Snoeck and R. Kilaas, Quantitative measurement of displacement and strain fields from HREM micrographs, Ultramicroscopy 74 (1998) 131–146. doi:10.1016/S0304-3991(98)00035-7.