Have you ever seen traditional scrapbook collages? Images are cut out and pasted together to form a unifying theme. While the results can be unique, even stunning, no one looks at a collage and confuses it with a traditional photograph. No matter how much effort is put into it, the individual elements do not blend together. The same is true with digital composites created in Photoshop. Fortunately, the digital artist can overcome the problems and seamlessly blend one image into another. The key is feathering.

Cutting out pieces of a digital image produces abrupt transitions. Like using scissors on a printed photograph, Photoshop selections create an unrealistic edge around the selected area. In the space of a single pixel, the image goes from complete to non-existent. No matter how sharp an image is, real transitions occur over two to three pixels, not one. To test this, open any digital image on the computer. Zoom to a display size of 100% and look at the edges within the image. The sharp edge of a rock does not just stop; rather it fades over a two pixel space. Softer edges, like a lion's fur, might take three or even four pixels before disappearing completely. No matter how careful the selection is, an abrupt edge transition does not appear real in a digital composite.

To overcome the problem of abrupt transitions, Photoshop introduced the concept of feathering. By default, selections have no feathering when they are created. This means that when an area is selected, all pixels inside of the selection are included while all areas outside the selection are excluded. The cutoff between inclusion and exclusion occurs in the range of a single pixel, creating an abrupt transition. To alter a selection's transition into something more gradual, I apply feathering to the selection. Feathering is the range over which a transition occurs. For example, once a selection is made, applying a three pixel feather means that the difference between what is included and what is not included is spread over a three pixel area. All pixels 1.5 pixels distance inside of the selected area will be included in the selection. All pixels 1.5 pixels distance outside of the selected area will be excluded from the selection. Those pixels within the three pixel range will gradually fade out, with some being included while others are excluded. The more feathering applied, the more gradual the transition from image to edge. Of course, this brings up the question of how much feathering should be applied when compositing images? As a general guideline, low resolution images only need a single pixel feather to look realistic. Larger images might need a two or three pixel feather, but much beyond that creates a fuzzy edge that looks fake. Remember, the goal with feathering is to blend various image pieces together so that they realistically merge into a single image.

Now that the importance of feathering is clear, how is it applied? Photoshop provides two different ways to apply feathering to a selection. The first, and most common, is in the option bar of the selection tools. When the lasso tool is used, for example, the option box (located above the image) includes "feather." To apply feathering, insert the number of pixels the feather should cover and start the selection. The feather will be applied automatically. Now, having said that, let me make a very important point: NEVER USE THIS METHOD OF FEATHERING!

What!?! Using the option box to apply feathering is a very bad idea for two reasons. First, there is a very good chance that I will forget to reset the feathering amount to zero once I am finished. That means the next time I use the lasso tool, my previous feather will be applied, whether I wanted it or not. Second, feathering can't be undone if it is applied during the selection process. I can't reduce the feathering to a lower value. Additional feathering can be applied, but excess feathering can't be removed. Imagine the frustration that would occur after spending the time to create a complex selection, only to discover that a five pixel feather has been applied when only a two pixel feather was desired. Without being able to undo the excess feathering, the only option would be to discard the selection and start over.

A far better method is to apply feathering after the selection has been completed. To do this, I create a selection using whatever method I prefer. Once the selection is created, I go to Select ' Feather. When the dialog box opens, I enter the size of the feather and click OK. The feathering is then applied to the selection. The feathering can then be removed (Edit ' Undo) or increased (Select ' Feather again; another application of feathering will be in addition to what has already been applied) as needed. This method is superior to the first because I will never be forced to redo a selection because of excessive feathering. It also makes it possible to save a basic selection and apply the appropriate amount of feathering for different uses.

Chris Gamel has been an active wildlife photographer for the past 14 years. The combination of his biological research and photographic interests has taken him around the world. In 2001, Chris discovered the joys of digital photography and he hasn't looked back. Chris lives with his wife and daughter in Salt Lake City where he teaches courses at Weber State University and Salt Lake Community College. To see more of Chris's photography, visit his web site at www.Animal-Antics.net.

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