Making masks

Yesterday I was asked how to mask a backstop region in DIALS processing, did not have a ready answer so (with the help of "dials.${program} -c -e2" and later pointers from colleagues) figured this out. For my own future reference here are my notes:

First load up the image, twiddle with the "brightness" and "color scheme" settings to allow you to easily see the region you want to mask:




Then press shift and left mouse button to draw out the region you want masking (only rectangles through this mechanism though the dials.generate_mask (command-line) tool can also handle circles. Should look like this:



Next select "save mask" which makes mask.pickle and exit. Reload the image viewer as before but this time also with mask=mask.pickle, select "show mask" and you should see something kin to:



Now, to use this start the usual dials.import with mask=mask.pickle added then everything else (find spots, index, refine, integrate etc.) as usual - when you look at the integration region you will see that there are no spots used on this area of the detector:



This is particularly useful when the rotation axis is not coincident with the backstop...