Creating masks from copied layers
Open web\samples\jpgs\_HOF4431.jpg
Use Layer->Duplicate Layer to make a copy of the layer which will become a mask. The best masks are made from layers which have some contrast.
Move the duplicated layer to the top of the layer stack, if necessary, using Cntl->Shift->] (right bracket).
Use Layer->New Adjustment Layer->Hue/Saturation to desaturate the new layer to black & white.
Select the Hue/Saturation adjustment Layer and click Layer->Merge Down to merge the two layers.
Create a levels adjustment layer and make the entire image brighter in order to lighten the shadows.
Increase the contrast of the mask layer at least 100%. Note that we don't use a layer here because everything must be contained in this layer.
Use Cntl-I to invert the image tones. We do this because we want to mask the light areas to avoid making them lighter.
Use Select->All (Cntl-A) to select the entire mask layer, making sure that the mask layer is selected in the Layers Palette.
Use Edit->Copy (Cntl-C) to copy the mask layer to the clipboard.
Use Alt-Left click to select the mask of the adjustment layer to which this new mask will be applied. You should see a white mask.
Use Edit->Paste (Cntl-V) to to replace the old mask with the new one.
Make the mask layer invisible.
Click Alt-left click on the mask to view the effect on the image.
Click the eye icon to make the adjustment layer invisible and visible examining lighter areas carefully to see if they have been affected.
Modify the mask as required by adding contrast or painting.
