The `if linewidth <= 1` was necessary because the coordinate systems
(pixel/point) were all muddled up. Now that it has been clarified,
`linewidth=1` works transparently!
It's important to distinguish between pixels and points. A square set
of points belongs to one pixel. When users type `linewidth=3`, they
usually mean a line 3 pixels wide. The distance between the pixel
center points, then, is 2.
The profile_line function is currently part of the skimage LineProfile
plugin. However, it's useful in non-interactive contexts, and importing
it from the viewer is awkward, mostly hidden, and depends on PyQt for
no good reason. By moving the function to `skimage.measure`, it is
usable in many more contexts.
blink1073