strokeWidth=1 on masks?

**Is your feature request related to a problem? Please describe.**
I'm trying to do pixel-level annotations. However, the smallest brush size seems to be too big. 

**Describe the solution you'd like**
Smallest brush size is pixel-level.

**Describe alternatives you've considered**
I've tried setting `strokeWidth=1` in the corresponding `Label` tag (shown above) but this doesn't seem to fix. It looks like the width is double the width of a pixel, but it's ambiguous because of the rounded corners. Would like to get more clarification on this.

Setting `strokeWidth=0.5` also doesn't seem to work (see image below). I had to click 4 times to get this result, which makes me think the brush width is half a pixel, but again, unsure because of the rounded corners.