Sometimes you may come across a situation where the background is a simple shade of color. However, the color may be a similar tone as the object you are cutting out, so blend modes won't work. Also, the object being cut is so complicated, that manually selecting isn't an option. Then using "Color range" to select the background my be a viable option.
1. In this example, I want to remove the background of the tree. First, unlock the layer from the background. Next, go to "Select>Color Range". A dialogue box will appear.
2. Sample a color in the background with the eyedropper, in this case, the black background. Next, adjust the Fuzziness by moving the slider which fine tunes the selection.
3. Click OK and the background will now be selected. From there, you can either delete the selection, or turn the selection in a mask allowing it to be edited later.