The green channel was added to itself in multiply mode. This darkened the background. Then the blue channel was added to itself in screen mode, which lightened dandelion. The layers were then sharpened at maximum strength with a radius of 3. Edge was generated by stroking path with a brush on the layer mask, followed by smudging at a medium setting. If I was doing it over, I would have increased the canvas space at the bottom of the original, and then done the CS5 smart fill so that I could have had a little more room at the bottom after the feathered edge was generated.