The selected frame is subtracted from the chosen display frame (or all frames if a cine mode is in use) before display, if no other method of subtraction is specified.
Normally, in DICOM subtraction is specified via the subtraction sequence (00028,6100) either within the image itself or it’s associated Presentation State.  This method allows such features as frame averaging.  If however, subtraction is activated using the Mask property, and no such sequence is present, then this property is used to specify a simple single-frame mask, which is subtracted from the chosen display frame (or all frames if a cine mode is in use) before display.

If 0, and the other methods are not used, then no subtraction occurs, irrespective of the Mask property.
The default value is 0.

Note  This method of specifying the subtraction frame was previously, incorrectly, documented as the function of the Mask property, which is now used solely as a switch.

DicomImage Object  | DicomImage Members