REMOVING DUST AND SCRATCHES USING PHOTOSHOP

Sunday, November 20, 2005

It would have happened to most dSLR owners. You come home after a shooting session, happy about getting some good images from your outing, but you see annoying dust marks on the image. It may be quite a job to go back and do a retake of all the images, especially so if you were coming back from a long trip. Photoshop offers many options for removing dust and scratches from your image. While some dust marks can be fixed in a moment, some may take a good lot of time depending on the complexity of the image. I have listed here some ways in which you can remove the dust. Choose the appropriate method based on the image and the dust in each case.

1. USING THE DUST AND SCRATCHES FILTER

This is a very primitive means of removing dust and can be useful only if the area surrounding the dust does not have much details(for example - cloudless sky, background of an image such as a wall, or see the example below). Perform the following steps:

1. Select the area having dust. This is important. If you apply the filter on the entire image, you will end up with a very degraded image. Make a close selection.



2. Open dust and scratch filter from the Menu Filter >> Noise >> Dust & Scratches.



3. Keep the threshold to zero and drag the radius slowly until the noise disappears and merges smoothly with the background. It is that simple, and the job is done!

The threshold value indicates how much variation should the pixels have with neighboring pixels to be considered as dust. A smaller threshold value means small variations would be considered as dust, and higher threshold means small variations are not assumed to be dust and will not be corrected. The value of radius indicates how much fixing must be applied. To understand more about how the threshold and radius values are used, see my article on sharpening images using photoshop.

For the image in example, since the variation between dust and the background is very distinct, smallest threshold is ideal and hence set to zero. With a given value of threshold, move the radius to find an ideal value where the dust disappears.

The Dust and Scratch filter can be used only with simple images like the example. This is not recommended for more complex images.


2. USING THE HEALING BRUSH

The healing brush gives some more control over removing dust. The idea here is to choose an area very similar to how the area with dust should have looked like, then sample it using the healing brush, and paint with the brush on the area with dust. Photoshop will turn the painted area into a region similar to sampled area. You get more control here than the Dust & Scratches filter because you fix only the area that you are painting and not a selection, and you can get fine results by controlling the size of the healing brush.

1. Select the healing brush too from Tools palette.



2. From the toolbar that appears on the top, set the appropriate brush size depending on the size of the dust. Set mode to normal and opacity to 100%. Change the opacity if that could be useful.



3. First sample an area. This is the area which is similar to how the dusty area should have actually appeared. To make a sample, point to that area, hold "Alt" key and click. The areas is now sampled. When you paint with the brush on the area with dust, Photoshop changes it to appear similar to sampled area.

4. Use the brush carefully on the area with dust to remove it.

The healing brush is suitable for use in areas which are more complex than the first example, but it is still not suitable in areas where there is lot of color and tone variations.

3. USING THE PACTH TOOL

Use this for dust in areas with lot of color and tonal variations. It may not replace the dust exactly as it should, but does an excellent job in hiding it.



1. Select the Patch Tool from the tool palette.



2. Select destination in the tool bar on the top. Drag the mouse pointer around an area similar to the area with dust. Make sure the selected area has almost the same size as the area with dust. This area will be used for patching the dust.



3. After selection, simply drag the selected area over the dust. Photoshop will mask the area with dust to look like the sampled area as seen below.




These are the easiest ways for removing the dust. For more complex specks of dust, working more carefully with smaller healing brush or using the patch tool with small selections many times over may help. But that requires some time, effort and patience.