why not use layers and skip duplicate picture process...
1) open image.
2) duplicate background layer.
3) "image" > "apply image"...select blending: "screen"
4) apply the blur.
5) on the Layers panel, change Blending Mode from "Normal" to "Multiply"
this will produce exactly the same results as gilbz way and you get to see the effects right away and you can undo or adjust back and fourth.
procedure 3 to 5 can be mixed up to produce slightly different output

example, if you try doing procedure 3 to 5 in reverse,(1,2,5,4,then 3) midtones will be a little darker.
note: apply image affect the layer only...not everything...