Using Selections and Filters

If you look carefully, you will notice that we forgot to dust before scanning in this image. In the dark background near the upper left corner of the image there are little specks that look like dust (if they aren't clear, zoom in on that portion of the picture a bit and then return to the 1:1 ratio). We will now process the image to reduce these flaws and learn how to use Photoshop's tools for selection in the process.

Photoshop includes a "filter" designed to deal with imperfections like the dust in our picture. It is called "Dust & Scratches". To see how it works:

• Depress the mouse on the "Filter" menu.

• Slide down to the "Noise" item in the menu that appeared when you first depressed the mouse and an additional sub-menu should appear.

• Move the mouse into the sub-menu to highlight the "Dust & Scratches" item in the sub-menu and then release the mouse button.

• Use the title bar of the dialog box that appears to drag it to the lower right so that you can see as much of the image as possible while still seeing the entire dialog box.

• Within the dialog box there is a check-box labeled "Preview". This controls whether Photoshop show a preview of the effect of the filter in the actual image window. Use the mouse to click that box on and off a few times while keeping your eyes on the specks of dust in the upper left corner of the full image.

• You should notice that the specks disappear when a preview is being shown. If not, adjust the "Radius" and "Threshold" sliders up a bit until they do.

• Now, continue turning the preview on and off but keep your eye on the butterfly in the center of the image. Notice what happens to the details of the butterfly when the dust disappears elsewhere.
• Click "CANCEL" to dismiss the dialog box.

The "Dust & Speckles filter works by blurring adjacent pixels together. This is great for removing dust, but as you should have noticed it also makes the details in the image look blurry. Accordingly, to apply it effectively it must be applied to carefully selected subregions of the image rather than the entire image.

We will show how to do this using several of Photoshop's selection tools.