Press Shift + Cmd/Ctrl + U to desaturate, generate a selection from your path by Cmd/Ctrl + clicking its thumbnail, then hit Shift + Cmd/Ctrl + I to invert the selection and fill with white. Now access the Levels (Cmd/Ctrl + L) and set the blackpoint to 71, the midpoint to 3.37 and the whitepoint to 187 to increase the contrast.
Intensify the contrast by selecting Image > Adjust > Posterize and entering a value of 3. We now need to simplify the level of detail to mimic the way a hand-cut stencil is produced. Paint within a selection from your path using a hard-edged brush on the black and white areas, then use the Eyedropper tool to sample the grey and paint on those areas. Now go Filter > Noise > Median and enter a radius of two pixels.
With the Magic Wand tool set to Contiguous and a tolerance of 2, select the black areas from the image. In the Channels palette, create a new channel. Now use the fly-out menu to access the Channel Options, and click the Selected Areas option. Changing the default channel settings will make the following steps clearer.