The origin refinement part of CIP relies on the definition of the plane symmetry group types as provided by the International Tables of Crystallography, where all symmetry equivalent positions in the unit cell and their respective site symmetries are listed along with systematic absences in reciprocal space. Besides plane symmetry groups p1, p3, p3m1 and p31m, all other plane group symmetries are centrosymmetric so that the origin refinement simplifies to the determination of the correct signs of the amplitudes of the Fourier coefficients. When crystallographic image processing is utilized in scanning probe microscopy, the symmetry groups to be considered are just the 17 plane space group types in their possible 21 settings. Crystallographic processing of images that were recorded from 2D periodic arrays with other types of microscopes Because digitized 2D periodic images are in the information theoretical approach just data organized in 2D arrays of pixels, core features of Crystallographic Image Processing can be utilized independent of the type of microscope with which the images/data were recorded. The CIP technique has, accordingly been applied (on the basis of the 2dx program) to atomic resolution Z-contrast images of Si-clathrates, as recorded in an aberration-corrected scanning transmission electron microscope. Images of 2D periodic arrays of flat lying molecules on a substrate as recorded with scanning tunneling microscopes were also crystallographic processed utilizing the program CRISP. References External links MRC Image Processing programs, the classical standard for structural biology, free for academic usages (Fortran source code) CRISP commercial, but superior for inorganic electron crystallography (for Windows PCs) VEC free for academic usages, particularly useful for the analysis of incommensurately modulated structures (for Windows PCs) IPLT open source, structural biology (for Mac PCs, Linux, and a Windows PC demo version) EMAN Vers. 2, open source, structural biology including single particle reconstruction (Linux) 2dx open source, mainly for structural biology (for Mac PCs, Linux) EDM open source, free for non-commercial purposes - a ready to go version of EDM is implemented on the elmiX Linux live CD Further reading see also the Wiki on Electron Crystallography Crystallography