Sensor spots are one of my biggest photographic pet peeves. All over the web, I see so many (otherwise) beautifully captured and edited photos that have annoying little specks in the background. Here’s our quick and easy method for finding and removing these pesky image invaders…
WHAT ARE SENSOR SPOTS?
Sensor spots are dust and debris that get inside a camera and stick to the surface of the image sensor. They can usually be noticed as fuzzy dots in areas of images that have low detail, like open skies in landscapes, or gray backdrops in studio images. Despite new camera technologies that claim to repel dust, sensor spots still accumulate over time and need to be dealt with by cleaning the sensor, or removing them in post production.
Your aperture settings affect how visible the sensor spots will appear, as can be seen in the 2 images below. The top image was shot at f/2.8 and with a shallow depth of field, the background appears nice and clean. But at f/22, the depth of field is so great that everything is in focus… even the dust on the image sensor.
FINDING THEM IS 1/2 THE BATTLE
To check how dirty your image sensor is, first make sure to clean the front and back surfaces of your lens. Then set your aperture to the largest f/stop available (usually around f/16 or f/22) and take a photo of a clear blue sky, or a neutral surface like a plain wall. You’ll probably need to turn off auto-focus for this.
Large sensor spots can be seen just by reviewing the image right on the camera display. But it’s better to review the image on a larger monitor, to get the full story. Using Photoshop and contrast enhancements can really bring out sensor spots that aren’t noticeable to the naked eye.
The blue sky images below are the same photo (click for larger versions). On the left is the unedited raw shot, and about 10 sensor spots are visible. On the right, I used Photoshop and Image > Adjustments > Curves, then clicked the Auto button to enhance the image. Now there’s over 30 visible sensor spots, in addition to the three large circles to the lower left which are actually dust on the lens. Big difference, right?
REMOVING SENSOR SPOTS
I always recommend investing the extra effort to remove more than just the sensor spots that can be easily seen in your images. Why? Because you never really know what your viewers are seeing. You may be editing on a perfectly calibrated monitor, not seeing spots that are obvious to viewers using a display or device with the brightness or contrast maxed out. The same can be said of making prints. The best method I have found so far goes like this, and only takes an extra minute or two:
1. Use the Magic Wand tool to separate the background. You can use a high Tolerance setting and work a little sloppy, since perfection isn’t necessary. I set my wand to 30% tolerance and shift-clicked around the backdrop area a few times to select most of the gray.
2. With the gray backdrop areas still selected, create a new Curves adjustment layer using Layer > New Adjustment Layer > Curves and then click the Auto button. This will leave the main subject un-altered, but apply quite a bit of contrast and levels adjustment to the backdrop, making it easier to find all the sensor spots.
3. Click back on the original image layer below (make sure you’re not on the Adjustment layer) and begin to remove the sensor spots. The old Photoshop standard tools still work best: Healing Brush and Clone Stamp. I prefer the Healing Brush most of the time, but clone stamp is handy when working close to areas with lots of detail. You’ll want to set the size of your brush only slightly larger than the size of the spot you are removing.
4. After all the spots have been removed, delete the Curves adjustment layer and you’re done.