This is a projections-based rings artefacts removal.
This is a projections-based rings artefacts removal.
Some defects might remain in the projections even after flat-fielding. These defects are visible as structured noise in the projections or sinograms.
Some defects might remain in the projections even after flat-fielding. These defects are visible as structured noise in the projections or sinograms.
By doing the average of all projections, the genuine features are canceled out and only the defects remain. This "average image" is used to remove the defects from the radios. Schematically, this method does `radio = radio / mean(radios)` (or other operations if the logarithm of radios was already taken).
Be aware that by doing so, you might lose the quantitativeness of the reconstructed data.
This method assumes that when averaging all the radios, the genuine feature will cancel and only spurious artefacts will remain. This assumption can fail if genuine features are (more or less) independent from the projection angle, ex. ring-shaped.
This method assumes that when averaging all the radios, the genuine feature will cancel and only spurious artefacts will remain. This assumption can fail if genuine features are (more or less) independent from the projection angle, ex. ring-shaped.
API: [DoubleFlatField](apidoc/nabu.preproc.double_flatfield.rst#nabu.preproc.double_flatfield.DoubleFlatField) and [CudaDoubleFlatField](apidoc/nabu.preproc.double_flatfield_cuda.rst#nabu.preproc.double_flatfield_cuda.CudaDoubleFlatField)
### Logarithm
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@@ -67,7 +67,7 @@ See also: [Phase retrieval](phase.md)
### Paganin phase retrieval
The Paganin method consists in applying a band-pass filter on the radios.
The Paganin method consists in applying a band-pass filter on the radios.
It depends on the δ/β ratio (assumed to be constant in all the image) and the incoming beam energy.