Tutorial: Dust and Scratch Removal With Photoshop

Dust and Scratches

No matter how hard you work to keep your slides, negatives and prints clean and protected from damage it seems that some minor dirt and damage can't be avoided. When you scan your slides, negatives and prints, these minor (or major!) imperfections can become very apparent. ICE and other techniques can minimize the effect of minor damage, but sometimes can't eliminate it entirely. Even digital cameras can suffer from dust which becomes lodged on the camera sensor and shows up (in the same spot) on every image.

Removing Dust and Scratches

Once your images are in digital form, there are a number of techniques to reduce the effect of dust and scratches in the images. Dust and scratch repair is a tedious yet important process, in particular if you intend to deal with old photographs or scanned black and white films (where ICE is not effective). Photoshop and other photo editors provide a fairly reliable, simple fix to repair old photos that are damaged. You can use the "Healing Brush" in Photoshop to remove scratches, dust, marks from fungus, or even other imperfections like bruises or blemishes on a person, or gashes on a tree.

First, in order to use the healing brush, you need to know where it's located. If you look on the tool bar, the healing brush is beneath under the crop tool. Be careful though, there are several tools in that menu, make sure you have "Healing Brush" selected, or you may have very unexpected results. The image below shows the Photoshop tool bar with the fly out for the healing brush shown (right click on the tool to see this). Select the healing brush tool.

The healing brush works like other brushes — you have a tool with a certain size and the tool affects only the area it touches. The difference between the healing brush and a paint brush, however, is that the healing brush paints using material from another part of the same picture. This means I can copy one part of my picture onto another part. We will use this to copy "good" material over a scratch or imperfection.

The healing brush has several options. The first (like other brushes) is brush size. This chooses the area that you will affect with your brush. For repairing thin scratches, use a small brush size, because you will want to minimize the effect on parts of your image that is not scratched. In the example below, a brush of size 5 was used. The next option is the "Mode" option. By default it is "Normal", which means Photoshop will try to correct the lighting and shadows to more accurately match surroundings. This actually is quite reliable and improves the quality of the fix quite a bit. Other options are to "replace", which doesn't blend the edges of the cloned area and the original together. The rest are more complicated to explain and use -- "lighten" lightens the copied area, "darken" darkens it, "screen" filters the copied area, and "multiply" amplifies it. (These different modes - "lighten", "darken", "screen", and "multiply" - correspond to different layering modes in Photoshop. We will discuss this more extensively in another tutorial.) You can play with these settings to produce interesting effects, but for removing scratches, "Normal" is usually the best choice. The next setting is the "source". You can either have the tool replace certain areas with the sample from the image or you can have it use a predefined pattern which you can select from the "Pattern" menu. For scratch repair, you should use the "Sample" option.

The Healing Brush Tool	Healing Brush Options

After you have set all the options, you can start editing the image. First, you alt (Windows) or option (Mac) click the area you want to sample. This will tell the computer that you want to start sampling at the point you clicked. The sampled point will move with your cursor as you replace the damaged section of your photograph. You should note the direction of the scratch. If you have a scratch running top to bottom, you should sample beside the scratch on either the left or right. Try to sample as close as you can to the scratch without being so close that you will actually run into it. One thing that works well is to sample on one side of the scratch, and then start replacing on the other side of the scratch so that the tool does not end up copying the scratch itself. You should resample often so the computer gets all the shading correct and so that the repair looks natural.

That's it! You should be able to repair a scratch now. The sample image below shows one use of this powerful tool. The original image has a major scratch (created manually for this example). The scratch has been repaired. Even with a full-sized image, it is difficult to detect the repair unless you know where the original was scratched.

Original blemished image	Image Repaired Using Healing Brush

Remember that the healing brush can never add information. If important parts of your image are scratched, you won't be able to get back the detail you began with, so don't use this tool too lavishly or you may end up losing parts of the image you wanted. Also remember to use as small a brush as possible while still replacing enough of the scratch in order to avoid losing detail in your picture. And, as always, save a backup of the original picture in case something goes awry, so you won't have lost a good photograph.