Experienced imaging specialists usually use up to three types of sharpening on their images:

You can also increase local contrast to perform a kind of color sharpening, which accentuates. The color differences between neighboring pixels of different colors. If you want to apply this type of sharpening to your images, we advise you to do so before step 2 above (once most other corrections have taken place). Generally, creative sharpening should be applied less if it is performed after increasing local contrast. We will discuss how to increase local contrast in detail in Enhancing Local Contrast.

Once you understand the basic principles of sharpening, you can take a look at some of the specialized sharpening tools and plug-ins available for use with Photoshop. You can find some recommendations for sharpening tools that we use as part of our workflow at our Digital Outback Photo website (www.outbackphoto.com). Advanced Sharpening Using Photoshop Layers looks at some of these tools and describes sharpening techniques in detail.

Unsharp Mask (USM) is the classic Photoshop sharpening tool. Remember that it is not always easy to judge the effects of sharpening accurately on a monitor. An image that appears hopelessly oversharpened on a monitor can look ideal when printed on an inkjet printer.

The main types of artifacts caused by sharpening should be kept to a minimum:

There are a great number of sharpening tools available, and it is up to you to decide which is the best for you with regard to functionality and your wallet.^[66]

Of all the options Photoshop offers for sharpening digital images, Unsharp Mask (USM) is probably the most widely used. Most other sharpening tools are variations on the same theme. In order to sharpen your images effectively you need to understand the unsharp mask technique and its limitations. The filter can be found under Filter ▸ Sharpen ▸ Unsharp Mask, and the dialog (Figure 4-32) has three controls: Amount, Radius, and Threshold, which function as follows.

Amount •. This value determines how strongly edge contrast is increased. Start by trying values between 90 and 120 percent. Usable values can reach as much as 150 to 250 percent.

Figure 4-31. Image before sharpening

You can see the effects different values have in the image preview. The greater your image resolution, the higher the value you can effectively use.

Radius •. This value determines the number of neighboring pixels that are affected by the sharpening process. Values of 0.5 to 1.0 are often sufficient to achieve effective results; too, the higher your image resolution, the larger the radius value you can effectively use. Too large a radius value can lead to hard-looking contrast effects and to the formation of image artifacts.

Figure 4-32. Unsharp Mask filter dialog.

Figure 4-33. Image after sharpening using “Unsharp Mask”

Threshold •. This value defines how many pixels to consider as an “edge”. Start at 0 and work up; larger values produce effective edge sharpening without accentuating image imperfections too much. For images with smooth gradients (e.g., skies), we usually use a value of 5–10.

Unfortunately, it is easy to sharpen too little or too much. Too much sharpening can cause significant image quality loss, especially in the form of black or white halo effects. We recommend that you start small and sharpen only a little until you get a feel for how sharpening affects your images.

The effects of sharpening depend on how an image is to be used (e.g., print or Web,), and it can take some time and a lot of experimenting to find the right settings. This is where the main limitation of the USM process comes in to play: all USM corrections affect the entire image. It is often desirable to sharpen different parts of an image to different degrees (e.g., the face and the hair in a portrait). It is difficult to avoid amplifying minor noise effects when using USM.

This is why there are a large number of specialized sharpening programs and plug-ins available for making sharpening easier and more effective. Most of these tools are based on edge masking techniques.

There is no single, universal solution to the problem of sharpening, so you will have to experiment to find out the best techniques and tools to use in each individual situation.

Figure 4-34. This image has been over-sharpened and displays obvious sharpening artifacts.

The CS2 version of Photoshop introduced an enhanced sharpening process called Smart Sharpen. This process uses Amount and Radius values like USM and includes an additional Remove control (Figure 4-35). We nearly always select Gaussian Blur. You can also compensate for slight camera shake using the Motion Blur option; here, you need to experiment to find the appropriate Angle setting for the supposed angle of movement of the camera relative to the subject.

If you activate the Advanced option (A), you can sharpen shadows and highlights separately. The settings you make on the Sharpen tab then apply to the midtones.

Figure 4-35. The Smart Sharpen filter, available since Photoshop CS2

Generally, you shouldn’t sharpen as much in the shadows as in the highlights in order to avoid strengthening any noise artifacts that may already be present. If you are working on a bright sky with mainly soft edges, you should sharpen less there and concentrate on the midtones. We always check the More Accurate option, even if it costs us some computing power.

If you want to sharpen selectively, you first have to select your image area using one of the Photoshop selection tools with a soft edge setting. (The Photoshop selection tools are explained in Selection Tools.) You can then open the sharpening filter, which will then only affect the selected area. The best option is to sharpen on a separate layer using layer masks (as described in Making Selective Adjustments Using Layer Masks).

Where Photoshop tools aren’t sufficient for our everyday needs, we use additional plug-ins selected from the ever-increasing range available on today’s market. These range from our own cheap and simple EasyS Plus to powerful and expensive options like FocalBlade. The following are the sharpening tools we like best:

Sharpening plug-ins are constantly being developed, and it is worth keeping an eye out for new tools and newer versions of older tools. The authors of this book host a web page on the subject of Photoshop filters, where you can get test reports and update information (www.outbackphoto.com/workshop/photoshop_corner/filters.html). We will discuss more sharpening techniques in Advanced Sharpening Using Photoshop Layers and Third-Party Sharpening Tools.