Is there any way to get the magnetic lasso tool to snap up to the edges of the canvas instead of wiggling its way along beside the edge? One would think that positioning the lasso pointer outside the edge would do it, but that leads to the following result:
The tool isn't perfect and will jump around if the edges have multiple colors. You can also quickly fix this with the Quick Selection Tool (W) and add those areas to the selection.– AndrewHDec 11, 2015 at 20:56
I've always hated the magnetic lasso, because it never behaves the way you want it to. It might take a little longer, to use the polygonal lasso tool, but it affords you WAY more control.– ManlyDec 11, 2015 at 22:59
If I wanted to get a really high quality cut out from that, I would probably use pen tool for the sharp edges ( pretty much anything that isn't hair ) and just kind of half ass the hair part (or even leave it out for now). Then continue working on the hair with like a Layer mask or Quick mask and soft round brush and perhaps Smudge tool (doable with a mouse but I'd use a drawing tablet).– JoonasDec 12, 2015 at 0:58
Prepared material for an answer based on what I wrote there, but I just couldn't really condense it enough. Some of these things are so difficult to explain with words. With the hope that this helps soneone... Here's a sped up video that kinda sort of shows the process. The picture I used in the video is perhaps a bit more extreme compared to your example image, but same process could be used.– JoonasDec 14, 2015 at 17:30
Clicking-and-holding during a magnetic lasso will cause the tool to "lose it's magic", and behave like the standard lasso tool, until you release the mouse button again.
So, when you're approaching the edge, click and hold, then move outside the edge of the doc, just as you tried. At the point you want to resume magnetic selection, let go of the button and continue tracing the edge.
While using the magnetic lasso tool, when you come near the edge hold the Alt key and click which will switch to straight line. Now move outside the edge, click, move to the other end, click. When you are ready to switch back to the magnetic lasso, Alt-Click on the next point. This will give you an on the fly switch lasso tools.
Of course, as suggested in the comments, using a quick selection tool is an option as well.