Phase Retrieval is the process of extracting the phase shift, induced by the sample on the beam, acquired on the detector. This phase shift is then used to reconstruct a map of the (deviation from unity of the real part of) refractive index through tomographic reconstruction.
Nabu implements the following non-iterative phase retrieval methods.
## Paganin phase retrieval
This phase retrieval method was first described in [[1]](#references).
The implementation [PaganinPhaseRetrieval](apidoc/nabu.preproc.html#nabu.preproc.phase.PaganinPhaseRetrieval) follows the normalization of [[2]](#references) and is compatible with the implementation of [tomopy](https://github.com/tomopy/tomopy).
## Single-Distance CTF phase retrieval
This method, although based on Contrast Transfer Function (CTF) rather than Transport of Intensity (TIE), can also be expressed as a single step "filtering" processing. See for example [[2]](#references).
## References
[1] D. Paganin Et Al, "Simultaneous phase and amplitude extraction from a single defocused image of a homogeneous object", Journal of Microscopy, Vol 206, Part 1, 2002
[2] Boliang Yu Et Al, "Evaluation of phase retrieval approaches in magnified X-ray phase nano computerized tomography applied to bone tissue," Opt. Express 26, 11110-11124 (2018)