How-To



Tuesday, August 4, 2009

Defringing


How to defeat edge artifacts in composited landscape images

Labels: How-To

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Burn Tool
Using the Burn tool from the Tool palette is another option for dealing with edge fringing. Although this method can be used to remove fringing from all selection edges, it’s best for dealing with smaller highly detailed areas. To illustrate this example, I’m using an interesting early-morning shot of Glacier National Park’s famous red buses.

The exposure difference between the foreground and sky was such as to render the sky totally blown out (Figure 3a). In order to incorporate a more pleasing sky, I used the Expand Selection method as a first step, as in the previous example. However, in this instance, I used the Lasso tool from the Tools palette to remove part of the selection around the tree on the right (Figure 3b). Then I proceeded to remove the halo along the mountain ridge by expanding the selection—in this case, 2 pixels.

The Burn tool now is used to eliminate the halo effect from the tree leaves and the small portion of remaining mountain ridge adjacent to them. Select the Burn tool from the Tools palette, and set the range for Highlights.

Move the cursor over the area you want to darken and left-click your mouse. Repeat this process as necessary—the trick is not to paint a continuous stroke, but to move the cursor around and left-click one or more times over each area where fringing occurs until it disappears.

One good thing about the Burn tool is that the effects are cumulative with each mouse click even when set at 100% opacity. Keep in mind, the Burn tool basically is used to darken areas, so you may want to turn down the opacity, at least initially, until you have a feel for how dark the area under the brush becomes; otherwise, too much darkening may result. Working with a small brush size and low opacity (around 25%) will allow you to gradually dial in the desired result. Each image is different and will require some experimentation to find out what works best.

Figure 3c shows a close-up before-and-after comparison of the effect using the Burn tool. Figure 3d is the final image after removal of edge fringing.

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