Activate the copy layer
Go to Filter > Stylise > Find Edges > OK
(Above:
'Find Edges)
Filter > Gaussian Blur > 1 to 2 pixels > OK
This small amount of Gaussian Blur is to remove tiny amounts of stray selection detail - see below.
Above: Section
of image showing original & blurred 'Find Edges' - Notice reduction
of detail in the blurred versionl