Photoshop Tools - The Spot Visualizer
Ridding the camera's sensor of dust spots is a 3-part approach:
Minimize (described at the end of this blog)
Locate (this blog’s content)
Remove (future blog)
Dust spots are a fact of life when it comes to DSLR cameras. Why is that? Anytime you remove the cover or the lens from the camera’s lens mount, the sensor is exposed to air. Even if you never remove the lens, dust gets inside the camera’s body. Dust does not damage the sensor, but it can appear in an image as dark spots that are unattractive and distracting. They simply do not belong in the image! At times a spot is barely noticeable and other times it sticks out like a sore thumb. Look at the image above where I identified several dust spots. Below is a zoomed in portion of that image so you can see the spots more easily. Wow, I really need to clean my camera’s sensor!
One thing I have learned the hard way is that I may not see a dust spot when I examine an image on the computer screen, but I may see it after editing or printing the image. At least while editing I can remove the spot, but after it’s printed it’s too late! To avoid that mistake again, I use a very effective technique to ensure I do not miss a dust spot. In fact, locating dust spots is the first step in my editing process. The second step is removing the spots (I’ll save for a future blog entry).
On an image, most dust spots are circular and look out of place. With practice, you can become good at identifying dust spots, even the obscure ones. Two things can make a dust spot appear noticeable. The first is the image itself (look again at the image above). If a dust spot is in a location that is bright (like the sky), it will be more obvious because of its shape and darker tone. If it lands somewhere in the image where it is quite busy or very dark, the spot will not be noticeable at all. In that image above, I am certain dust spots are on the silhouetted tree!
The second and most important thing that can affect a dust spot’s appearance is the aperture used to take the image. The smaller the aperture (like f16 to f22), the more noticeable will be the dust spots. They will appear darker and more defined, such as in the image above that was shot at f20. However, if you always shoot with a large aperture like f5.6, you may never notice the dust spots because they appear hazy and lighter. Look at the next three images to compare aperture settings. I used my neighbor’s white truck as the subject and zoomed in to fill the frame. Note the dust spots at an aperture of f22. Now compare that to f11 where the spots are less visible. And with a very wide aperture of f5.6, you can’t see them!
I guarantee if you zoom in and examine the f5.6 image carefully or print it, you will find dust spots. For that reason, I prefer to locate those elusive dust spots and remove them before I do anything else to that image. So how do I do that?
Camera Raw (Photoshop) or Lightroom has an important tool to help you locate dust spots – it’s called the visualize slide tool. Here’s how it works. After bringing the image into Camera Raw or Lightroom Develop, I open the spot removal tool as you see in the two images below.
Once the spot removal tool is open, the visualize slide tool will appear at the bottom of the screen. The magic begins when you click on that tool, as illustrated below. Note that in both examples, I set the slider about halfway to the right. The image looks like the night sky filled with stars. But those stars are actual dust spots! The visualizer also picks up on other aberrations (like dirt on the truck).
How well does the visualize tool work with the aperture f5.6 image? Remember, to the naked eye those spots are hardly visible, if at all. Now look at the visualize tool screen below. Dust spots galore!
Here’s an example where I used an aperture of f22.
Now look at the visualizer screen that helps you find those not-too-obvious spots.
The sensitivity of the visualize tool can be adjusted by moving the slider. Look at what happens when I take the visualizer tool and slide it farther to the right, illustrated in the image below. More spots appear! But it also starts to pick up a lot of other things that are not dust spots and things I do not want to remove.
Here’s one last example, an image shot at an aperture of f5.6. It’s a very bright image, so dust spots are invisible.
Now look what happens when I check the visualize tool. Notice that in order to see dust spots I had to move the slider all the way to the right to maximize sensitivity. Isn’t that amazing!
You may think it unnecessary to visualize and remove an “invisible” dust spot. But remember two things. First, invisible dust spot on a digital image may be visible in a printed image. Second, if you edit the image and make changes to the tones, invisible dust spots may become visible. For these reasons, my first step in editing is always to locate dust spots with the visualize slide tool. Then I remove them, including the invisible ones.
Removing dust spots is mostly a very simple process, but occasionally can be a little complicated. I’ll discuss this process in another blog. To wrap up, here are a few tips on how to minimize dust spot invasion to make your dust spot removal process much easier.
Occasionally run the camera’s sensor cleaning function. When you press the button, the camera will vibrate very quickly for about 1 second. This will shake off the dust from the sensor.
Take the cap off the lens mount and hold the camera facing downward. Take a rocket blower and gently blow air toward the sensor. Do not touch the sensor! If your camera has a mirror, you’ll have to flip that up first to expose the sensor.
You can examine the sensor and sometimes see specks of dust on it. If the above two steps do not remove the specks, you can use a special sensor cleaning brush to gently wipe the sensor. Be very careful with this!
Thanks for looking on and if you want to learn more about Photoshop editing techniques, need help with your editing workflow or simply want to get started in Photoshop, I offer Photoshop tutorials at $75/hour. Please check out my website and feel free to contact me at firstname.lastname@example.org.