Sometimes it might be of interest to extract the image data below a label for specific purposes (similar to export the image below an area list in TrakEM2). This can be done by attaching the Arithmetic tool to the image data (InputA) and the label field (InputB) and furthermore using the following expression:
(B==1)*A+(B!=1)*120
This extracts the grey values of InputA where InputB has a label value of 1 and sets the background grey value to 120.
Modification:
(B==1)*A+(B!=0)*120
Same as above, but everything outside of the label (=exterior) gets extracted.