One of the most common forms of image alteration involves the replacement of a poor quality background with a nice background. This might involve removing a distracting mass of branches and replacing it with a clean, blurred wash of color that makes the subject pop. It can also involve the removal of a dull, boring sky with a more dramatic sky. A common situation for many nature photographers occurs when the dynamic range of a scene is beyond the film's (or digital chip's) ability to record. With this in mind, let's look at the steps involved in removing a flat white sky from an image and replace it with a more dramatic sky.

To begin with, I open my original image and an image of the new sky that I want to add. Since learning this technique, I keep my eye out for dramatic skies that I can photograph for later use. In this case, I begin with a fall color shot I took in the mountains a short distance from my home. The fall colors are pleasing, but the sky is a washed out white that contributes nothing to the image. Looking at the image, I think how great it would be if there had been dramatic storm clouds in the distance. Fortunately, through the wonders of Photoshop, I can create just such a situation.

My second step is to select the new sky. From my collection, I like the dramatic impact of an approaching storm I captured in Botswana (moments before getting rained on). The storm clouds will add a feeling of drama to my fall color image, producing greater impact then the bland white sky that was present.

Now the combining process. I need to determine what the size of my original image is before I can match the new sky to fit within that image. This can be done at Image → Image Size. Once selected, a dialog box appears, showing the file's current size. I write down the pixel dimensions (located at the top of the dialog box) on a piece of paper and put it aside for later. I then click "cancel," which closes the dialog box without applying any changes to the image.

I now move to my new sky image. If there is a large portion of land in the image, as in my storm image image, I crop the image so that only sky remains. The last thing I want in my fall color image are the plains of Africa in the distance. Once the image is cropped, I open the image size dialog box (Image → Image Size). I uncheck the box entitled "Constrain Proportions" and then set the Pixel Dimensions to match those of the original image. By unchecking the Constrain Proportions box, I am telling Photoshop to stretch the image until it fits the desired dimensions. In most cases, this produces results that look warped and unreal. Fortunately, skies and clouds have abstract shapes and are unduly altered by stretching them.

With both image the same size, I can merge them together. I select the move tool, located at the top of the right hand column of the toolbar. I then click on my original image. Keeping the mouse button pressed, I drag my original image on top of my new sky image, at which point I release the button on my mouse. This creates a copy of my original image on a layer directly over the new sky image. If necessary, I can click and drag on this new layer until it is centered. At this point, I have two images stacked on top of each other, but only the top layer (my original fall image) is visible.

The next step involves selecting and removing the white sky. Photoshop comes with a variety of selection tools that can be used. In cases where the area to be selected is roughly uniform in color and tone, the magic wand (located on the tool bar directly below the move tool) is often the quickest and easiest selection tool to use.

The magic wand works by selecting pixels that are similar in color and tonality to the area clicked on. Once the magic wand is selected, there are several controls that work to make the selection process easier. The primary control is the tolerance setting. This acts as a volume control for the magic wand tool. A high setting will select a wider range of colors and tonality then a lower setting. A tolerance setting around 30 is usually a good place to start. If a single click selects too much, I lower the tolerance setting and start over. If the tolerance setting is too low, I have two choices. I can increase the tolerance setting and start over or I can hold down the shift key and apply the magic wand again. This will add to the current selection instead of replacing it. Similarly, holding down Alt while clicking will take away from the current selection. By making a quick rough selection, it is a fairly simple process to add and subtract until a quality selection is produced.

A key option available with the magic wand is the "Contiguous" option available on the option bar at the top of the screen. Checking contiguous instructs Photoshop to only select areas adjacent to the place that is actually clicked on. For example, if I am selecting an area of sky that is divided into two halves by a telephone wire, checking contiguous and clicking on the portion of the sky above the wire will result in only the top portion of sky being selected. The sky underneath the wire will not be selected. In contrast, unchecking contiguous will result in both parts of the sky being selected. The selection will, in effect, jump over the wire and continue to seek out areas that match the color and tonality of the selection point. Contiguous can be an excellent tool when working with the magic wand. In images where the area to be selected is unbroken, I check the contiguous option and start selecting. In cases where the area I want to select is broken into pieces (selecting the sky where patches of it can be seen between the leaves of a tree), I uncheck contiguous and then begin the selection process.

Returning to my image file, I have an unbroken piece of white sky that I want to select. Under these conditions, I check contiguous (the sky I want to select is unbroken), I set the tolerance to 30 (a good starting value that happens to work perfectly for this image), and I click in the center of the white sky. The result is a nice selection of the white sky.

For many, this would be the end of the selection process. To produce professional results, however, there are two more steps that need to be applied. Two problems exist with selections in Photoshop. First, selections frequently leave a fringe of color around the edge of the selection. In this case, we would end up with a small line of white around the edge of the fall colored mountains. Second, selections produce very hard edges that appear unrealistically sharp in the final image. These features are two of the telltale signs of digital composites. Removing them involves two easy steps. Once the basic selection has been made, expand the selection by 1-2 pixels (Select → Modify → Expand). This will enlarge the current selection slightly all the way around, thereby removing any color fringe. Next, apply feathering to the selection (Select → Feather). A value between 1 (for small images) and 2 pixels (for large images) works well. This helps to remove the hard edge from the selected area, blending it with the rest of the image. Once these steps are complete, the white sky is removed by pressing "delete." This removes the white sky from the original image and shows the new sky on the bottom layer.

As a final step, the new sky image can be moved up or down to create the best effect. Before it can be moved, however, the background layer must be unlocked. This can be done by going to the layer palette and renaming the background layer (double click on the word "Background" and enter a new name). Once the background is renamed, the move tool may be used to fine tune its placement within the final image.

For some nature photographers, the idea of altering the background in an image is a complete violation of their photographic ideals. For others, image alteration techniques open a world of creative options that enable them to create unique images that reflect their artistic vision. How digital composites and alterations fit within each photographer's approach to photography will vary from individual to individual. The use of digital compositing techniques is a personal decision. If they work for you, fantastic. If not, don't worry. Both traditional and digital photography offer enough challenges to keep you busy for years to come. Photographic expression is a creative path upon which we each walk. Determine your path and pursue it with passion.

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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