There are many ways to control density or selectively lighten shadows or darken highlights in
order to bring out detail in that part of the tonal range. One of
our favorite methods is to use the Screen and Multiply layer modes
- we find that in many cases this creates a better balance of exposing
detail and changing density in a realistic way than some of the
other techniques such as dodging and burning or simply using a curve
to lighten or darken an area.
To control overall exposure, open a Curves Adjustment Layer and immediately close it without making any changes. Change the Mode of the layer in the layer palette to Screen (if you want to lighten the area) or Multiply (if you want to darken the area).
You will notice that the resulting change, while in the right direction,
is much too extreme. Now reduce the degree of the change by lowering
the opacity of the layer - you can find the layer opactiy slider
near the top of the layer palette. An opacity of 40% is approximately 1 f-stop of exposure adjustment. You will often need to lower
the opacity quite a bit, perhaps to even less than 10%, to fine-tune your image.
If you want to apply this technique to only a portion of your image, such as a shadow or highlight area, a selection should first be made that isolates the targeted area.
If you want to make even more selective corrections at this point,
you can reopen the curve by double clicking on the layer icon. You
can make normal curve corrections to change density or contrast
- remember, however, that if you have lowered the opacity of the
layer significantly, you may need to make larger than normal changes
to the curve before the desired effect is seen.