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From the author of Using the Magic Brush to Mask Pixels

Using the Magic Brush to Mask Pixels

Once you’ve identified the colors you want to work with, the Magic Brush can then use those colors to intelligently remove (or “spare”) the pixels underneath as you brush across the canvas. When you select the Magic Brush tool, the Inspector will display several important settings (Figure 9):

Figure 9 Magic Brush settings in the Inspector.

  • Brush Size and Brush Feather: These two settings work exactly as you would expect. The former defines to diameter of the brush, and the latter defines a region around the brush to create a “transition zone” between the pixels that are masked and those that remain untouched.
  • Transition: This setting defines how hard the cut-off is between Keep and Drop colors. A low value creates a harder edge between the Keep and Drop colors. A higher setting will create a softer transition. The Transition value must always be higher than the Threshold value.
  • Threshold: The threshold setting determines the tolerance level used when the Magic Brush is defining whether a color is a “keeper” or a “drop.” A low value will keep only the exact colors in the keep pane, while a higher one ensures more colors that lie close to the “keepers” on the color spectrum will be protected.

To start the workflow, place the brush cursor over your image, and size it down so that it can fit between the narrowest regions that you have to navigate. I find a Feather value between 10 and 20 pixels usually works well. Next, decrease the default Transition setting to 20-30 points, and then increase the Threshold value slightly. This ensures any colors that are very close to your “Keeps” and “Drops” will not be ignored. The settings I used for this image were shown in Figure 9.

Next zoom back out far enough so that you can see the entire area you wish to mask, and then begin to “paint out” the pixels you wish to remove. As you do so, the “drop pixels” will be masked and the background image’s pixels will show through, as seen in Figure 10. Don’t worry at first if you remove small bits of your subject; we will correct that soon enough.

Figure 10 The Magic Brush is a great way to remove entire sections of an image with just a few brush strokes.

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