Techniques For Removing Dust And Other Marks From Images In Photoshop

30th July 2018 Image Editing


Introduction

No matter how well you store your originals, or how well you clean your materials prior to scanning, there will always be dust visible in high resolution scans of both film and print. Some film scanners -- Nikons, and Epson's V600V800, and V850, for example -- utilise an infra-red technology called Digital ICE to reduce this problem, but such an automated solution is not offered by all film scanners, including premium film scanners such as our Flextight 949. However, given that the Flextight can provide a huge advantage in terms of image quality over home film scanners, and automated solutions for removing dust are often far from perfect, learning to effectively and quickly remove dust from scans is an essential part of your image editing workflow.

Here follows an illustrated introduction to five techniques that one might use to remove dust (and other marks) in Photoshop: the Spot Healing Brush tool, the Healing Brush tool, Content-Aware Fill, the Patch tool, and the Dust & Scratches filter.

Check Your Work!

One thing to remember about any of the methods mentioned below (and the many others that exist and are not mentioned!) - is that it is a good idea to first duplicate the layer you're working on (e.g. duplicate the background layer) - and then work on this duplicate. 

Especially when retouching larger areas of an image, you can then swap back and forth between the corrected and uncorrected layers, viewing the area at various magnifications, to check that the repair work is in visual sympathy with the rest of the image.   Sometimes corrections can look ok at one zoom level, but become more obvious at another.  So check carefully as you work for best results!

1. Spot Healing Brush tool

The Spot Healing Brush tool is quick and effective, especially for discrete marks on a simple or uniform background, so it's a very useful tool for removing dust. It's easy to use, too: with the tool selected, one needs only to adjust the brush size and softness and then paint over what should be concealed. Photoshop will automatically analyse and replace the selected area with interpolated data that is visually matched.

If there are only a small number of discrete spots to be removed, this may be the only technique that you'll need. But if it fails to produce a sound result (as it often does if your spot is near a high contrast edge) - or there are many spots (or larger spots) to be removed, you might consider another approach.

→ Keyboard shortcut: J

2. Healing Brush tool

Use of the Healing Brush tool involves copying data from a source that is selected manually, unlike the Spot Healing Brush whose data is inferred from the image automatically.

However, the data is not just copied but also made to look seamless at the destination by Photoshop's excellent Content-Aware algorithm. Most sources of a similar tone or similar texture will be usable, and stipulating the source can help with the problem of a tricky spot that the fully automatic Spot Healing Brush will not effectively heal.

Firstly hold Alt and use the cursor to select a source, then apply the source to the destination with the tool's brush.

→ Keyboard shortcut: J

3. Lasso selection and Content-Aware Fill

It's quicker and easier to make broad or complex selections with the Lasso tool rather than a brush, and Content-Aware can be applied from the Fill dialog too. Incidentally, it's possible to select multiple, discrete parts of an image with the Lasso, which can be processed simultaneously. Content-Aware Fill may not be dissimilar in result from the Spot Healing Brush, but this technique may be preferable given the efficiency and control of the selector.

→ Keyboard shortcut: L for the Lasso tool, and Shift+F5 for the Fill dialog, or Delete subsequent to making a selection.

3A. Selection detail

It is worthwhile to compare a broad-brush selection and a fine selection with respect to the spot removal. Generally it's true to say that the smallest possible selection will yield the most naturalistic result from Photoshop.

3A-1: A broad-brush selection
3A-1: A broad-brush selection

In 3A-1, the Lasso tool selects two pieces of dust within a circle for Content-Aware Fill. Although the result is serviceable, it doesn't closely resemble the original image.

3A-2: A finer selection
3A-2: A finer selection

In 3A-2, a finer selection is made with an appropriately small, soft brush, which produces a considerably better result.

→ Keyboard shortcut: [ and ] to change the brush size.  Shift [ and Shift ] change the hardness of the brush edge.

4. Content-Aware Patch tool

Like the Healing Brush, the Patch tool involves manually specifying the source of the data that the Content-Aware algorithm will use for filling, which may be preferable if the fully automatic Content-Aware Fill fails to produce a naturalistic effect. A comparison of results is shown below: 4-1 features the Patch tool, and 4-2 features an application of the fully automatic Content-Aware Fill to a selection.

4-1: The Patch tool
4-1: The Patch tool
4-2: Content-Aware Fill
4-2: Content-Aware Fill

→ Keyboard shortcut: J

5. Dust & Scratches filter

Dust & Scratches, located in Filters within the Noise category, can make quick work of removing dust. It works especially well for selections that don't contain a lot of detail - a plain background, say, or clear sky - whose colour admits of some contrast with any dust that might be sitting upon it.

It can be used in the following way, beginning by making an appropriate selection:

1. Magnify the image to its full size, showing the selected area;
2. Open Dust & Scratches, and set the radius and threshold to values of 10-20 and 50+ respectively;
3. Decrease the threshold value until the image's inherent texture (film grain, noise, etc.) is on the cusp of being affected;
4. Zoom-Out in order to see the full selection and ensure that no desired details will be affected by the process;
5. Apply the filter.

5-1: The Dust & Scratches filter can make quick work of hiding small spots of dust.
5-1: The Dust & Scratches filter can make quick work of hiding small spots of dust.
5-2: The filter is best applied to small selections that don't illustrate complex details or specular highlights.
5-2: The filter is best applied to small selections that don't illustrate complex details or specular highlights.

Incidentally, once the filter has been used, it can be applied with the same values to subsequent selections quickly using the keyboard shortcut of Ctrl + Alt + F (Windows), or Cmd + Shift + F (macOS). For instance, with the Lasso tool selected, one can make a small selection, then apply the filter using that keyboard shortcut, then immediately make another selection and apply the process there, and so on. Otherwise, while holding Shift on either Windows or macOS, the Lasso tool can select multiple discrete areas of the image at once for processing.

→ Keyboard shortcuts: L for the Lasso selection tool, and ;Ctrl + Alt + F or Cmd + Shift + F to repeat the most recently used Filter.

Happy cleaning!

Of course there are yet more techniques, but by and large they are variations on these themes.  Don't forget you can always duplicate your image to another layer, clean that new layer, and use that for checking - and/or then use a layer mask to just allow through the corrected areas back to the original image).

Using these techniques, one can easily remove virtually any spot or mark from a scan. It should be noted that fully cleaning a scan of a dirty image can still take some time, but some familiarity with Adobe's excellent Content-Aware tools will generally make it a simple task.

If the prospect of cleaning your film seems too tricky or too time-consuming, then our practiced team can perform this work for you as as part of our retouching service.