More salient border of the minimap

[mzur]

@ghattab mentioned that the boundary between the minimap and the actual image is very hard to see for his greyscale images:

The minimap border is grey as well and only 1px thick. Maybe use two different colors (like the viewport rectangle in the minimap) or a subtle light shadow?

[ghattab]

Thanks for the mention, indeed or give the possibility to switch from a black to a white frame.

[ghattab]

Here is my current solution (for publication purposes), that is making the frame thicker.

[mzur]

This is the new version:

(dark image)

(lighter image)