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processing:backgroundgeneral
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processing:backgroundgeneral [2019/09/04 16:57] smerkel |
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| The diffraction from the //sample grains//, that give rise to well-defined diffraction spots are removed and **//do not contribute//** to the median image! | 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. | 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. | ||
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| + | ===== 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? ===== | ===== When to subtract the background? ===== | ||
processing/backgroundgeneral.1567616225.txt.gz · Last modified: 2019/09/04 16:57 by smerkel
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