Perhaps the most common problem with digital photography is the accumulation of dust spots on the digital sensor. However, not all dust spots are created equally. Some spots are less obvious than others and can be difficult to detect. Here’s an easy way to find the elusive spots.
1) After opening your file, create a new blank layer (Layer>New>Layer…, Click OK). This will create a checkerboard-looking layer.
2) Select the clone tool. I love using keystrokes, so select it by pressing ‘S’. This will open a Clone Stamp menu just below the Photoshop menu. Make sure the Sample menu is set to “Current & Below”.
3) Click on the blank layer and begin normally cloning by sampling an adjacent space near the spot and cloning over the spot. You’ll be painting on the blank layer, but that’s OK since it’s sampling the pixels of the layer(s) below the blank one.
4) Here’s where we go after the subtle spots. Above the “blank” layer (it’s not blank anymore since it contains data from the sampled layers below), create a curves adjustment layer (Layer>New Adjustment Layer>Curves…>. This will create a new layer ABOVE all the other layers. Grab the diagonal line and drag it down. Your image will look horrible, but that’s OK. Continue adjusting the curved line until you see other spots. You can also put another point on the curve and move that around to bring out spot details in the sky; creating an S shaped curve can be quite helpful. Your picture will probably look really horrible by now, but that’s OK.
5) Once you can see the dust spots, click back on the “blank” clone layer. Again, and this is very important, make sure the “Current & Below” sample menu is selected. Begin cloning the other spots. Once done, simply delete the above curves layer. Your picture will return to normal and the elusive pesky spots will be gone.