Differences

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--- processing:backgroundgeneral [2019/09/04 18:57] – smerkel
+++ processing:backgroundgeneral [2019/09/05 14:55] (current) – smerkel
@@ Line 23: / Line 23: @@
 The diffraction from the //sample grains//, that give rise to well-defined diffraction spots are removed and **//do not contribute//** to the median image!
-Creating an average image can be done with [[xray_data:averagemanyedf|timelessMeanFileSeries]] which is part of the [[software:timelesstools|TIMEleSS tools]]. Creating the median can be done with ''median.py'' which comes with [[software:fabian|Fabian]].
+Creating an average image can be done with [[xray_data:averagemanyedf|timelessMeanFileSeries]] which is part of the [[software:timelesstools|TIMEleSS tools]]. Creating the median can be done with ''median.py'' which comes with [[software:fabian|Fabian]]. You can also calculate median and average images with [[software:imagemath|ImageMath]] but we have not used it in a while. There is an issue with file formats.
 The median image is less affected by outliers than the average and is probably a better representation of your background. For some purposes you might still need to use the average image.
+===== Testing and subtracting the background =====
+The most efficient way is to test your background with [[software:fabian|Fabian]]. You can
+  * load an example diffraction image,
+  * select ''Image'' > ''Correction'' > ''Background image''
+  * select ''Image'' > ''Correction'' > ''Subtract background''
+You will be able to visualize the effect you the background subtraction and whether your evaluation is satisfactory.
+Typically, subtracting the ω-median from a single ω-step diffraction image will be efficient at removing
+  * noise, from the detector, the source, etc
+  * diffraction from anything within the path of the x-ray beam, which is not your sample, as long as it is in the form of a powder,
+  * diffraction from the smaller sample grains (i.e. a fine matrix), that does not show up as well-defined diffraction spots but rather continuous diffraction rings.
+It will not work, however, for complex environments such as diamond anvil cells for which the diamond anvils give rise to strong and well defined diamond diffraction spots.
 ===== When to subtract the background? =====