Tips for effective dust spotting…
No matter how careful you are with changing lenses on your DSLR or changing over the digital back, it’s a fact of life that you are going to eventually get dust (sometimes it’s oil) spots on your sensor.
It’s one of the areas that would cause an image to fail a stock agency’s quality-control checks, so they have to be removed. And removing dust one image at a time is one real pain in the aperture…
To see the dust spots (unless it’s a huge piece that’s on the rear lens element or sensor) you need to be zoomed right into the image at 100% view. 1:1 ratio. Actual pixel level. This is the level of magnification at which your images will be scrutinised for cleanliness and quality by a stock library. You will need to be able to scrutinise every piece of the image and do it at 100% view. Obviously, even at 100% magnification you’d be hard pressed to see faint dust spots against a busy image element with multiple textures (such as a wall or rocks etc) so your main areas of interest will be large areas of flat tone (like skies).
Lets use a typical image where seeing dust is difficult. It’s there though and if you get inspected on an image like this it will show up (that’s known as Sod’s law!) so you must remove all of the dust spots before submission.
Here’s how I dust spot skies and other large areas of flat tone (where the dust will be visible) quickly and efficiently (i.e. not missing any!).
First we need to make the dust easier to see. Add a new curves layer in Photoshop and drag down a point roughly in the middle (see screenshot below). This will darken the image to aid visibility of the spots. It’s easy to miss the faint ones in an image like this.
This darkens the image nicely.
Now we can see the dust spots far easier let’s start spotting them in a methodical fashion so we don’t miss any. Zoom in to 100% view. Make sure the Navigator pane is visible. Move the red square to the top left hand corner of your image.
Select your weapon of choice. I prefer the Healing Brush Tool (diameter 50px, hardness 20px) but some use the Spot Healing Brush Tool. There’s no right or wrong way.
Useful Tip: Dust spots can be far easier to spot if the image is moving rather than your eyes scanning the image.
With your healing tool selected depress and hold down the space bar. This will turn the tool into the ‘Hand Tool’ and allow you to click in the image (with mouse or graphics tablet pen) and literally push/scroll the image left or right up or down across it’s width and height in a fluid movement.
Start scrolling right. While the image is moving along you *must* keep concentration on the same area of the screen. The idea is for the image to pass your eyes, not for your eyes to scan the image. Your eyes will detect the spots as they pass. When one shows up, stop the scrolling, release the Space Bar and spot the dust away. Repeat until you get to the right hand side of the image. Then, scroll down about ¾ of the height of your red box (so there’s some overlap – use the navigator to guide you) and start scrolling the image left.
Repeat this until you’ve scrolled along, down (remember to overlap a bit) , along, down etc. right to the bottom of the problem areas (in this case I’d look at the whole image as dust spots would show in the flatter areas of the sea too).
Once finished, delete your curves layer and you’ll have a dust free image to take to the next stage of your processing.
I use Photoshop as much as I use Lightroom. I have dust spotted in Lightroom too but personally find it easier and faster doing it this way on every image in Photoshop. The dust map feature in Lightroom is great but not for batch processing unless the image is one of a number of very similarly composed images. An automated heal/clone that crosses into an area of the image that is not on a flat tone can leave a very bad retouching mark that would quickly fail a quality control inspection.
If you do prefer to work on dust spots in Lightroom alone here’s a good way of finding the dust that’s hiding:
Feel free to add any additional tips in the comments below.