Sharpening and Removing Color Noise

You will now learn techniques to both sharpen and blur images to enhance edges and remove unwanted color noise.

Open the file Basilique St Nazaire de Carcassonne.jpg from the CD. A version of this image is included in the color section.

Choose Filter > Sharpen > Unsharp Mask to open the Unsharp Mask dialog box, as shown in Figure 3.22.

Change Amount to 100%, Radius to 2.0 pixels, and Threshold to 3 levels, and click OK.

NOTE For best results when using Unsharp Mask, the Amount slider should range only from 50% to 100%, Radius between 1 and 3 pixels, and Threshold between 3 and 10 levels. Although greater amount and radius values result in increased sharpening, threshold is counterintuitive with greater sharpening occurring with fewer levels.

4. Immediately choose Edit > Fade Unsharp Mask, or press Shift+Ctrl+F to open the Fade dialog box (see Figure 3.23). Fade only works immediately after you perform an action. If you select another tool, Fade will not work.

Figure 3.22

The Unsharp Mask dialog box

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Figure 3.23

Fading the last command

5. Click the Mode pop-up and select Luminosity. Leave the Opacity slider at 100% and click OK. By fading all but this blending mode, you are effectively sharpening only the luminosity, where the detail in the image resides.

TIP For close-up images of people, try sharpening only the Red channel in RGB color mode. This will produce the least amount of edge detail and helps keep skin smooth.

6. Even though you only sharpened the luminosity, some color halos in the stained glass have resulted from the increase in contrast. You can remove this color noise by using blur. Choose Filter > Blur > Gaussian Blur to open the Gaussian Blur dialog box.

TIP Professionals always use Unsharp Mask and Gaussian Blur because they offer the most options of the available tools in Photoshop.

7. Set the Radius to 2 pixels and click OK. You want a heavy blur to obscure any color noise brought out by sharpening.

8. Press Shift+Ctrl+F to open the Fade dialog box. Choose Color from the Mode pop-up and click OK.

By fading all but this blending mode, you are effectively blurring only the color, where halos and noise reside. Figure 3.24 shows a grayscale version of this image. A version of this image is also included in the color section for a "before and after" comparison.

A technique many professional photographers use starts by converting an RGB image to Lab color mode. They sharpen the Lightness channel, which carries the luminosity detail, and blur the two color channels (a and b) before converting back to RGB. This has an effect almost identical to the technique just presented.

On the other hand, you can use a layer-based technique for more flexibility. Start by duplicating your background layer, sharpen the new layer, and convert its blending mode to luminosity. Duplicate another layer, blur it, and convert its blending mode to color. You can then adjust the amount of sharpening and blurring by adjusting the opacity of the corresponding layers.

Whichever technique you choose, it helps to record the steps you take as an action to save time. You can then apply the action with one click to sharpen your image and remove the noise all at once. Let's make an action for the first technique presented in this section.

1. Click the Actions palette to select it. Click the Create New Action button along the lower edge of the palette to open the New Action dialog box.

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2. Type Sharpen and Blur for the name of your new action, and click Record.

3. Repeat steps 1 through 8 in the previous exercise to sharpen the luminosity and blur the color in the stained glass image.

4. Click the Stop Playing/Recording button on the lower edge of the Actions palette. That's it— your action is ready for use on other images.

5. If you want the option to set parameters in the Unsharp Mask and Gaussian Blur dialog boxes when you apply the action, toggle on the dialog box icons as shown in Figure 3.25.

Figure 3.25

Click the icons next to Unsharp Mask and Gaussian Blur to toggle the dialog boxes "on."

6. Choose File > Revert to test your recorded action in this image.

7. Click Sharpen And Blur in the Actions palette. Click the Play Selection button along the lower edge of the Actions palette.

8. You will see both the Unsharp Mask and Gaussian Blur dialog boxes appear, giving you a chance to alter the parameters to suit whichever image you are working on. Click OK to close each dialog box. Your action successfully automated this process and reduced the number of steps you have to perform.

9. Close the file without saving when you're finished.

TIP Any time you find a series of steps tedious, record an action and reduce a lengthy series of steps to a few. You'll save tons of time in the long run.

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