Here, we will use the dust speck from our example in Retouching and Repairing Images that we retouched directly on the background layer. Using this direct method means we have to start the entire correction process again (or reload the RAW original) if we are not happy with the results.
We prefer to make a copy of the background layer to work on by dragging it to the 
button at the bottom of the panel (or by using 
).
Remember to give your layer copy a descriptive name (here “Remove dust”). You can now remove the speck using the Clone Stamp tool (
Saving and Loading Selections). If you hide your new layer by clicking the 
icon, you can see that the speck is still part of the original background layer.
Instead of using a copy of the background, you can also retouch using the Clone Stamp on a new, empty layer (created by clicking 
). Make sure that you select the Current & Below option in the tool’s Sample menu, otherwise you will not be able to apply the selected pixels to your background layer. This is a straightforward way to perform selective corrections.
Our new Remove dust layer (Figure 7-5) will only contain the retouched pixels (i.e., fewer pixels than a retouched copy of the background layer). Using a new, empty layer to perform image retouching makes it easier to see what is going on and also saves disk space.
New layers have a default opacity setting of 100% (i.e., lower layers are completely invisible). This setting can be changed to make a layer partially transparent or completely transparent (at the 0% end of the scale).
We change opacity values often during the workflow. This setting allows us to start out applying high strength effects and then fine-tune them by reducing opacity.
Figure 7-6. Clicking the arrow in the upper-right of the Opacity value pops up a slider that you can use to change the value.
Test the effect for yourself by changing the opacity value for our dust speck example. You will see how the speck appears more pronounced with decreasing opacity. We generally reduce opacity on adjustment layers to help us fine-tune the effects of other corrections, such as increased color saturation.
Blending modes determine how the pixels and other adjustments on the active layer are sampled and merged into lower layers, and how the effect appears in the final image. The following are the most important modes for use in the photo workflow:
Normal selects only the pixels in the active layer and applies the current opacity value.
Darken, Multiply work in a similar way to the Burn tool. White areas on the top layer have a neutral effect, darker areas show moderate effects, and black applies the maximum effect.
Lighten, Negative Multiply are the opposites of the effects described above (equivalent to the Dodge tool). Black areas on the top layer have a neutral effect, brighter areas show moderate effects, and white applies the maximum effect.
Overlay selectively brightens or darkens specific image areas. A 50% gray value has no effect. Values below 50% gray brighten the relevant areas in lower layers, while higher values darken lower layers. There is an Overlay example in Dodge and Burn Using Layers. This is one of our favorite modes.
Soft Light/Hard Light allows you to increase color saturation. The effects of white/black/gray values in the top layer are similar to those produced by Overlay mode.
Luminosity is important for reducing unwanted color shifts. (See Auto Color Correction for Better Contrast and Some Tricks for Improving Saturation and Contrast.) Only luminosity (brightness) is affected.
Color effects only color (not luminosity) for most details.
Saturation changes color saturation but not luminosity or hue.
Hue affects hue without affecting luminosity or color saturation.