Adjusting a Single Layer
You can limit an Adjustment Layer to affecting a single layer by creating a Clipping Mask. Create a new Adjustment Layer and hold the Option key (Mac) or Alt key (Windows) when choosing an adjustment from the Adjustment Layer pop-up menu at the bottom of the Layers palette. Then, when the New Layer dialog box appears, turn on the Use Previous Layer to Create Clipping Mask checkbox, which will cause a small down-pointing arrow to appear next to the Adjustment Layer, which indicates that it is only applying to the underlying layer (Figures 11.57 and 11.58). If the Adjustment Layer is pre-existing, position it directly above the layer you'd like to affect and with the Adjustment Layer active, choose Layer > Create Clipping Mask.
Figure 11.57. The New Layer dialog box.
Figure 11.58. The down-pointing arrow indicates the adjustment will only affect the underlying image.
You can clip more than one Adjustment Layer to a single layer by holding the Option key (Mac) or Alt key (Windows) and clicking on the horizontal line that separates the Adjustment Layers from the layer you'd like to adjust (Figure 1.59). When using this technique, start from the bottom-most Adjustment Layer and work your way to the top Adjustment Layer that you want to apply to the image.
Figure 11.59. Option-clicking between two layers will also create a Clipping Mask.
