Sample pixels from more than just the active layer (Photoshop CS2/CS3/CS4/CS5)

You can sample pixels from layers other than the active one. To do so, select one of the tools that requires Photoshop to sample pixels, such as the Clone Stamp, Healing Brush, Smudge, Blur or Sharpen tool from the Tools panel. Then, select the Use All Layers or Sample All Layers option on the tool Options bar. The tool you chose samples pixels from all visible layers, not just the active layer.