Using Levels and Curves With Color Ranges

Both the Levels and Curves dialog boxes make it easy to edit by color channel.  But is it possible to use Levels and Curves to edit by color ranges?  Yes, but not directly.  Basically, we create a selection of one or more color ranges and then use this selection in a Levels or Curves adjustment layer mask.

An example is shown in Figure 1.  Figure 1A is our image.  By clicking Select > Color Range, we get the Color Range dialog box as seen in Figure 1B.  By using the left most eyedropper and clicking the blue sky, the Color Range dialog box created a selection for us.  The Color Range dialog box shows us the selection as a mask.  White areas are selected and black areas are not selected.  We can use the Fuzziness slider to increase or decrease the selected color range.  After making the selection, click OK and the classic marching ants will appear on the image.  We now have a selection.  Next, click Layer > New Adjustment Layer > Levels, a Levels adjustment layer is created for us.  This can be seen in Figure 2.  Looking closely at Figure 2A, we can see that the Levels adjustment layer mask is filled.  Figure 2B shows the contents of the layer mask.  It is identical to the mask created by the Color Range command.  Because a selection was active when the Levels adjustment layer was created, Photoshop automatically filled in the layer mask based on the selection.  The end result is whatever adjustment we make with the Levels command, only the area of the image containing the selected color range will be affected.