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Cloning Around


How often have you had a "perfect" shot marred by something as simple as a telephone pole in the middle of the frame, or a distracting object in the background? With the "cloning" tools available in many image manipulation programs, you can escape the limits of mundane reality! By copying other parts of the picture digitally, you can wipe out the offending subject matter in a matter of minutes. (Well, maybe a lot of minutes...)

Look out Below!
Frequently, an otherwise good picture is spoiled by a single distracting element. Using "cloning," you can copy other parts of the image over the offending object. Here, the bather in the background detracts from the main subject, "Cannonball Chris."

"Cloning" in digital imaging refers to digitally copying parts of images from one area to another; in some cases, even between different pictures entirely. To use a cloning tool, you select a sample point on the image, where you want to begin copying from, and then move the cursor to the location you want to copy to. When you click the mouse button, the cursor begins painting with the part of the image under the sample point. As you move the mouse, the brush and sample-point cursors track each other in lockstep, copying as much of the image as you choose.
Cloning is easy and fun to do, but some skill and a good bit of patience is required to achieve truly "invisible" results. In this article, I'll share a few simple tips with you to help improve your cloning technique.
Patience Furthers!
Patience is a worthy virtue for any endeavor, but is particularly important to achieving good results in digital retouching. Be willing and prepared to go back and start over on a part of the picture, if your first attempt doesn't please you. If your program doesn't support multiple levels of "undo" (few do), saving multiple copies of your working file at various stages of retouching will make it much easier to go back and redo something you don't like.
Watch Gradients & Colors!
The most common "rookie error" in cloning is to ignore tonal or color gradients in the image. The key is to adjust the direction of your cloning to follow the tonal contours of the subject. If you have a light-to-dark gradient slicing across your subject, set your sample-point and initial painting location to align across the gradient, rather than along it. Most beginners simply align their sample-point and painting cursors horizontally or vertically, which leads to tone or color breaks when cloning across shadows or other gradients in the image.

A Plethora of Problems
This picture (where we began cloning-out the light pole) illustrates several common problems encountered by beginning "cloners:" At top, the pavement was cloned without regard to the orientation of the shadows. The result is misplaced tone breaks. (Also, a hard-edged brush was used, generally a bad idea for smooth surfaces.)

In the middle, a low-opacity brush made it hard to eliminate all signs of the pole, leaving a shadow under the rear window.

The bottom dart points out what happens when you use a brush diameter too large for the detail you're duplicating: Notice how the front wheel of the second car began to be repeated above the roof of the front one. (Image cropped from Kai's Power Photos, volume 3, by MetaCreations.)

Match Your Brush to the Subject
Most painting programs give you a range of brush sizes to choose from when painting, and these are usually available for use in cloning as well. Large brush sizes let you copy large areas quickly, but give poor control over details. For best efficiency, use a smaller brush to copy the boundaries of an object, and a larger one to fill in the interior. This may seem like a trivial recommendation, but probably the biggest single giveaway in poor cloning is unintentionally included pieces of a copied object's background.
Another important brush attribute is opacity: Most programs allow you to specify whether you want the cloned image to completely replace the underlying picture (100% opaque), or to be partially transparent. Transparent brushes can be especially useful for blending objects into low-contrast backgrounds, or for coping with gradients in sky colors when you don't have enough "raw material" to work with. Transparent brushes can wreak havoc with high-contrast textures though, when the copied image blends with the underlying one, resulting in an obvious "flattening" of the contrast in a local area. Likewise, high-contrast edges in copied objects need to be maintained, calling for a more opaque brush. A little experimentation with opacity will do a lot to help your retouching technique.
Pay Attention to Textures
Another common giveaway in cloned images is mismatched textures. This can easily happen if you clone material from the background (finer texture) to the foreground (coarser texture) or vice versa. Texture differences can also result from differences in lighting angle, or simply differences in the subject itself. Our eyes are very sensitive to texture in an image, so you should be too, when cloning.
The previous notes about gradients also apply to textured surfaces as well: If there's a strong orientation to a textured surface (for instance, wood grain), you'll do well to align your sample-point and brush cursors with the main direction of the texture. This will help avoid disturbing the texture as you copy it.
Short Strokes in Tight Quarters
Often, you'll find yourself with only a limited amount of image that needs to be stretched across a large area. This situation calls for particular caution, to avoid an effect I call "puffing." (I've also heard it called an "echo," or simply "repeat.") If your sample-point and painting cursors are set close to each other, and you paint along the line defined by the two cursors, the sample-point will soon run over an area already copied once by the brush. When this happens, the same area will be repeated again at the current location of the brush. If you continue, you'll end up with a series of "puffs" of image, repeated with the spacing between your sample and brush cursors.

 Watch out for "Puffing!"

If you set your sample point too close to your clone brush, and blithely paint a large area, you'll end up repeating details over and over again. I call this "puffing," because it reminds me of a poorly adjusted airbrush. In this enlargement, you can see the artificial-looking, repeated detail in the water that was cloned-in to cover the standing figure (whose disembodied head still remains).

The key to avoiding this problem is to take short enough strokes to avoid running the sample-point cursor over the top of an area that's already been cloned in the same stroke. Instead, take multiple, short strokes, resetting the sample-point frequently in between.
Know When to Change Techniques
Perhaps most important to good retouching is knowing when to call it quits with one approach and try another. While cloning can be used to move or copy objects in a picture, you'll usually find it most valuable for removing or covering up distracting elements. If you have to move an object with fairly well-defined edges, you may find it more effective to silhouette the object with a selection tools, and then use a simple copy/paste operation to move it.
Finis
Cloning can be an exceptionally powerful tool for fixing problem compositions, and is a lot of fun just to play with, besides. What's more, simple patience and attention to detail can produce excellent results, a real boon to those who are artistically challenged (like the author)!

Use multiple, short strokes for complex textures.
Here's the successfully-cloned image. By using multiple, short strokes, and frequently resetting the sample point, I avoided repeating obvious features. Rocks which were "behind" the figure are built from pieces of other rocks in the image, and one was copied in its entirety. Can you tell which?

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