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Getting the Most of Your Web Images: Faking Depth of Field

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The photographic concept known as "depth of field" refers to the area of a photograph that is in focus. This can be a very shallow depth of field or a very deep one. Modifying the depth of field can help emphasize or de-emphasize certain portions of an image. Kyle Cassidy shows you how to use a graphics-manipulation program such as Photoshop or Paint Shop Pro to create depth of field effects.

In photography, the concept known as "depth of field" refers to the area of a photograph that is in focus. Depending on things such as the f-stop of the lens and its telephoto power, this can be very shallow (only a few inches) or very deep (with everything from the foreground to the background in sharp focus). At first, it may sound desirable to have a whole photograph in focus, but depth of field is a tool that photographers use to isolate certain portions of an image and de-emphasize others. The next time you're looking at a fashion magazine, check out the way photographers use a blurred background to focus your attention on a product or model.

One problem with consumer-model digital cameras is that they have very limited control over depth of field. Typically, the depth of field is very great, meaning that the foreground and background are both in focus. Such is the case in the image of the guitar player in Figure 1.

Figure 1 With a large depth of field, the image lacks a center of focus so there is nothing to draw your eye to it.

Apart from being decently lit, this image is wholly unremarkable and doesn't serve well as an advertising shot. The plant and the window in the background are distracting, as is the model himself. There's no visual draw to the image. Selectively adding some depth of field blur will bring the product to the forefront and render the background less distracting.

You can do this using the Blur feature of many image-manipulation programs, such as Photoshop or Paint Shop Pro. But first, a quick word about feathering.

What Is Feathering, and Why Should You Use It?

Feathering is an option on cutting tools (scissors, the magic wand, the box) that allows you to control the sharpness of the selection tool's edges. Feathering a cut causes it to fade away at the edges rather than appearing razor-sharp. Feathering can make a cut look softer and gentler. The higher the feathering value (in pixels) is, the softer the edges will be of the image part that you are selecting. The amount of feathering that you use will depend on the size of the image you're cutting from. To cut a soft-edged portion from a graphic 800 pixels square, feathering 12 or 18 pixels might be useful. For an image 300 pixels square, a value of 5 might be more appropriate.

For example, Figure 2 shows a freehand cut from the previous image with feathering set to 0.

Figure 2 No feathering will give you razor-sharp cuts, sometimes too sharp for what you want to do here.

Notice the sharp edges of the cut. Figure 3 shows the same thing, with feathering set to 12.

Figure 3 With feathering turned on, the cuts fade out.

The best way to become familiar with feathering is to practice cutting and pasting using it.

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