Invert mask behavior

As we have a “subtract masked” approach (instead of “keep masked”) for particle subtraction, it’s convenient to turn local refinement masks into subtraction masks by inverting them. Currently, a threshold must be given in order for Volume Tools / Invert Mask to run, then a new soft edge can be added. This means that a threshold of 1.0 will lead to a much smaller region of interest than in the input mask. A work around is to use a very small threshold like 1e-7, but this is somewhat counter intuitive and can require some trial and error to match the soft edge width.

What if the default behavior for Invert Mask, with no threshold, was changed to simply return 1 minus the input mask (clipping values to 0 and 1 where necessary)?