Tài liệu Photoshop cs5 by Dayley part 63 ppsx

437 CHAPTER Sharpness, Blur, and Noise Adjustments IN THIS CHAPTER Using sharpening filters to sharpen images Applying an unsharp mask to sharpen images Using blurring filters to soften the background in an image Simulating a lens blurring effect in a photo Reducing noise in images Removing dust and scratches from images A common problem to overcome when working with photos is correct- ing blurriness and noise. Photoshop provides three classes of filters to overcome these problems: the sharpen, blur, and noise filters. It is important to remember that when you apply filters to an image, you are altering the pixels based on computer algorithms and not optical data. Therefore, the adjustments that Photoshop can make are limited in their effectiveness. This chapter discusses using the sharpening filters to enhance blurry images and make edges stand out, using blur filters to apply softening effects to images, and using noise reduction filters to remove noise and unwanted arti- facts from images. Cross-Ref Sharpening, blurring, and noise reduction are done through the use of filters. Filters are discussed in much greater detail in Chapter 20. Because the use of filters is a fairly destructive adjustment, you should at least review the section in Chapter 20 that discusses creating and using non-destructive Smart Filters before getting too far in this chapter. n Cross-Ref When you apply the sharpening, blurring, and noise reduction filters in this chapter as Smart Filters, you can use Blend modes to really change how the fil- ters are applied. Chapter 10 discusses Blend modes in much better detail. You should look at that section before reading this chapter so you will understand some of the additional options available by blending the filters rather than just applying them normally. n 21_584743-ch14.indd 43721_584743-ch14.indd 437 5/3/10 10:35 AM5/3/10 10:35 AM Part IV: Enhancing, Correcting, and Retouching 438 Using Sharpen Filters to Sharpen Images The best way to get a sharp photo is to shoot a sharp photo in the first place. Nothing can take the place of an optically sharp image. Unfortunately, shooting perfectly sharp photos doesn’t always happen. And even if you do, you may lose some sharpness when making adjustments to the photo in Photoshop. For these reasons, Photoshop includes some powerful sharpening filters that make your images look better. To sharpen the photo, Photoshop uses some algorithms that analyze the image and find edges of objects and then adjusts the pixels in the image to maximize the contrast between the edges with minimal impact on the overall appearance of the photo. Tip The best way to apply sharpening filters is to create a duplicate layer of the background and then turn that layer into a Smart Object. Then apply the filter to the Smart Object so you can add several filters, turn them on and off, and try different settings. n Keep in mind that the more sharpening you do, the more anomalies you introduce, such as false edges and ringing artifacts in your images. The amount of sharpening you can do is limited by the amount of detail in your image as well as the size of the image; when it comes to sharpening, big- ger is better. Note Ringing artifacts can appear in images when you sharpen areas with abrupt transitions. They show up as “echos” radiating away from the transition, almost like ripples in a pond. n This section discusses using the basic sharpening tools in Photoshop as well as some of the more advanced ones. Note The sharpening filters alter the pixels in the image quite a bit. You should always apply the sharpening filters after you have made all other adjustments to avoid spreading some of the anomalies caused by sharpening the image through the other adjustments. n Applying basic sharpening filters The simplest way to sharpen images is to use one of the three basic filters supplied by Photoshop. These filters apply slightly different techniques to sharpen images. The basic sharpening filters per- form a predefined amount of sharpening to the image and do not provide an interface to customize the amount of sharpening that takes place. The following list describes the basic sharpening filters available by selecting Filter ➪ Sharpen from the main menu in Photoshop: 21_584743-ch14.indd 43821_584743-ch14.indd 438 5/3/10 10:35 AM5/3/10 10:35 AM Chapter 14: Sharpness, Blur, and Noise Adjustments 439 l Sharpen: Performs a simple sharpening on an image. The filter scans the pixels in the image looking for boundaries denoted by a pixel not matching adjacent pixels in one direction or another. The filter then changes the value around the boundaries to increase the contrast and make the edge more definable. l Sharpen Edges: Works similarly to the Sharpen and Sharpen More filters except that the Sharpen Edges filter is even more aggressive when it finds areas of higher contrast. It sharp- ens those areas even more than the Sharpen More filter. This filter is great if you have items in the image that have edges that contrast highly against the surrounding background. l Sharpen More: Works the same way as the Sharpen filter except that the Sharpen More filter is much more aggressive about finding edges and how much to increase the contrast. This has the effect of increasing the sharpness around the edges, but it can introduce a considerable amount noise in images. l Smart Sharpen: Gives you more control over the sharpening effect by allowing you to set the sharpening amount, method, radius, and angle. l Unsharp Mask: Uses a different method of sharpening by finding pixels that are different from the surrounding pixels and then increasing the contrast in the surrounding pixels. Unsharp masks will be discussed in the next section. The following example takes you through the process of using the basic sharpening filters to sharpen an image: 1. Open the image in Photoshop as shown in Figure 14.1. Notice that the image is fairly blurry. FIGURE 14.1 A very blurry image opened in Photoshop 21_584743-ch14.indd 43921_584743-ch14.indd 439 5/3/10 10:35 AM5/3/10 10:35 AM Part IV: Enhancing, Correcting, and Retouching 440 2. Right-click the background layer, and select Duplicate Layer from the pop-up menu, as shown in Figure 14.2. This displays the Duplicate Layer dialog box. 3. Name the duplicate layer in the Duplicate Layer dialog box, shown in Figure 14.2, and click OK to create the layer. The new layer is added to the Layers panel. FIGURE 14.2 Duplicating the background allows us to create a copy of the image to work with with- out damaging the original pixels. 4. Right-click the new layer, and select Convert to Smart Object from the pop-up menu, as shown in Figure 14.3. 5. Select Filter ➪ Sharpen ➪ Sharpen from the main menu to apply the Sharpen filter to the Smart Object. 6. Select Filter ➪ Sharpen ➪ Sharpen More from the main menu to apply the Sharpen More filter to the Smart Object. 7. Select Filter ➪ Sharpen ➪ Sharpen Edges from the main menu to apply the Sharpen Edges filter to the Smart Object. 21_584743-ch14.indd 44021_584743-ch14.indd 440 5/3/10 10:35 AM5/3/10 10:35 AM Chapter 14: Sharpness, Blur, and Noise Adjustments 441 FIGURE 14.3 Making the duplicate layer a Smart Object allows us to apply the filters as Smart Filters. The Sharpen, Sharpen More, and Sharpen Edges filters are applied as Smart Filters to the Smart Object, as shown in Figure 14.4. The results of applying the Sharpen, Sharpen More, and Sharpen Edges filters are shown in Figure 14.5. Notice that the Sharpen filter does not make nearly as drastic of an effect on the image as the Sharpen More filter and that the Sharpen Edges filter applied even more sharpness to the image. 21_584743-ch14.indd 44121_584743-ch14.indd 441 5/3/10 10:35 AM5/3/10 10:35 AM Part IV: Enhancing, Correcting, and Retouching 442 FIGURE 14.4 Applying the Sharpen, Sharpen More, and Sharpen Edges filters as Smart Filters to the blurry image FIGURE 14.5 Notice the results of the Sharpen, Sharpen More, and Sharpen Edges filters on the image. Sharpen More makes a much bigger difference than Sharpen, and the Sharpen Edges changes mostly around the edges of the wing and body. Original Sharpen filter Sharpen More filter Sharpen Edges filter 21_584743-ch14.indd 44221_584743-ch14.indd 442 5/3/10 10:35 AM5/3/10 10:35 AM Chapter 14: Sharpness, Blur, and Noise Adjustments 443 On the Web Site The project file used to create the image shown in Figure 14.5 can be found on this book’s Web site as Figure 14-5.psd. You can open it in Photoshop and see the effects of the Sharpen, Sharpen More, and Sharpen Edges filters. The sharpen filters are applied as a separate layer, so you can delete that layer or hide it and try to make your own adjustments as you follow along with the exercises. n Unsharp Mask The Unsharp Mask filter is a bit more advanced method of sharpening images. Unsharp masking is different than the basic sharpening methods. Instead of detecting the edges in the image, the Unsharp Mask filter finds pixels that are different from the surrounding pixels by a specified threshold. Then it increases the contrast in the surrounding pixels in a specified neighborhood. In other words, if a pixel is darker than the surrounding neighborhood, then the neighborhood is lightened even more. Figure 14.6 shows the Unsharp Mask filter dialog box that is displayed when you select Filter ➪ Sharpen ➪ Unsharp Mask from the main menu. Using the Unsharp Mask dialog box, you can set the following values to use when sharpening an image: l Preview Size: The minus and plus buttons adjust the size of the image in the preview window of the Unsharp Mask dialog box. You can drag on the image inside the preview window to adjust the position of the preview or simply click the preview image itself. l Amount: This specifies the amount used to increase the contrast of the pixels in the neighborhood when sharpening. A greater value here creates a more dramatic sharpening effect in the image. l Radius: This specifies the size of the neighborhood to use when calculating whether a pixel doesn’t match the surrounding pixels. A greater radius means that a larger area of the image is affected by the sharpening, so the edge transitions are more gradual. A smaller radius means that a smaller number of pixels is affected, so the edge transitions are more abrupt. l Threshold: This specifies the threshold used to calculate whether a pixel matches the surrounding neighborhood. A larger value here means that only significant differences between a pixel and its neighbors are sharpened. Typically, you want to use a threshold value between 4 and 20 pixels. Use the following steps to apply an Unsharp Mask filter to an image in Photoshop: 1. Open the image in Photoshop. 2. Right-click the background layer and select Duplicate Layer from the pop-up menu to display the Duplicate Layer dialog box. 3. Name the duplicate layer in the Duplicate Layer dialog box, and click OK to create the layer. The new layer is added to the Layers panel. 21_584743-ch14.indd 44321_584743-ch14.indd 443 5/3/10 10:35 AM5/3/10 10:35 AM Part IV: Enhancing, Correcting, and Retouching 444 4. Right-click the new layer, and select Convert to Smart Object from the pop-up menu, as shown in Figure 14.3. 5. Select Filter ➪ Sharpen ➪ Unsharp Mask from the main menu to apply the Unsharp Mask filter to the Smart Object. The Unsharp Mask dialog box is displayed, as shown in Figure 14.6. FIGURE 14.6 The Unsharp Mask filter allows you to set the amount of sharpening, the radius of the neigh- borhood to sharpen, and the threshold to use to determine pixels that need sharpening. 6. Adjust the size of the preview using the plus and minus buttons and drag the image until you have a preview area that includes the part of the image you are most inter- ested in sharpening. In Figure 14.6, we adjusted the size and dragged the image so that the tiger’s face is visi- ble in the preview area. 7. Adjust the Amount value to set the amount of sharpening to take place. In the example, we set the value to 100% to make a large change. 8. Adjust the Radius to include enough of the surrounding pixels to detect the change and provide a smooth transition along edges. In the example, we set the radius to 9 pixels so we can get enough of the surrounding pixels. 21_584743-ch14.indd 44421_584743-ch14.indd 444 5/3/10 10:35 AM5/3/10 10:35 AM Chapter 14: Sharpness, Blur, and Noise Adjustments 445 9. Adjust the Threshold value until only the areas you want sharpened are being sharpened by the filter. You may need to go back and adjust the Amount and Radius values if you don’t get a threshold setting that you like. 10. Click OK to apply the Unsharp Mask filter as a Smart Filter to the layer. The results of applying the Unsharp Mask filter are shown in Figure 14.7. FIGURE 14.7 Notice the results of the Unsharp Mask filters on the image. The grass and stripes on the tiger have been sharpened by the filter. Original Unsharp Mask filter On the Web Site The project file used to create the image shown in Figure 14.7 can be found on this book‘s Web site as Figure 14-7.psd. You can open it in Photoshop to see the effects of the Unsharp Mask filter and try making your own adjustments. n Smart Sharpen The most powerful tool that Photoshop has to sharpen images is the Smart Sharpen filter. The Smart Sharpen filter uses the same algorithm as the Unsharp Mask filter. However, the Smart Sharpen filter also includes the ability to fine-tune the amount of sharpening that takes place in the highlights and shadow areas of the image. The Smart Sharpen filter also allows you to specify the type of blurring to sharpen in the image. Figure 14.8 shows the Smart Sharpen filter dialog box that is displayed when you select Filter ➪ Sharpen ➪ Smart Sharpen from the main menu. Using the Smart Sharpen dialog box, you can set the following values to use when sharpening the image: l Preview Size: The minus and plus buttons adjust the size of the image in the preview window of the Smart Sharpen dialog box. You can drag on the image inside the preview window to adjust the position of the preview or simply click the preview image itself. 21_584743-ch14.indd 44521_584743-ch14.indd 445 5/3/10 10:35 AM5/3/10 10:35 AM Part IV: Enhancing, Correcting, and Retouching 446 l Settings: This allows you to save the current settings as a preset filter and select it later. This allows you to perform the same filter on several images to correct similar blurring caused by lens or camera issues. You also can delete a preset filter by clicking the trash can. l Amount: This specifies the amount used to increase the contrast of the pixels in the neighborhood when sharpening. A greater value here creates a more dramatic sharpening effect in the image. l Radius: This specifies the size of the neighborhood to use when calculating whether a pixel matches the surrounding pixels. This value also is used to determine the size of the area affected by the Smart Sharpen filter. A greater radius means that a larger area of the image is affected by the sharpening, so the edge transitions are more gradual. A smaller radius means that fewer pixels are affected, so the edge transitions are more abrupt. l Remove: This specifies the type of blur you are trying to remove from the image. You can specify Gaussian, Lens, or Motion. Gaussian Blurs are introduced into images when you make image adjustments such as noise reduction or image resizing. Lens Blurs are intro- duced in the image due to focus problems. Motion problems are introduced into images by either camera or subject motion. l Angle: This allows you to select the angle of motion when you select the Motion option in the Remove setting. This gives Photoshop an idea of the motion of the target in the image and allows the algorithms to be much more aggressive in fixing motion blur. l More Accurate: When you select the More Accurate option, Photoshop takes much more time processing the Smart Sharpen filter, but it gives you a much better sharpening effect. FIGURE 14.8 The Smart Sharpen filter allows you to set the amount of sharpening, the radius of the neighborhood to sharpen, and the type of blur to be corrected by the sharpening filter. 21_584743-ch14.indd 44621_584743-ch14.indd 446 5/3/10 10:35 AM5/3/10 10:35 AM [...]... AM Part IV: Enhancing, Correcting, and Retouching FIGURE 14.10 The Smart Sharpen filter allows you to fine-tune the filter to set the amount of sharpening that takes place in the highlights range Using Blur Filters to Soften Images Blurring applies the opposite effect to images that Sharpening does Instead of finding edges and adding contrast, blurring reduces the contrast, making edges softer Photoshop. .. opposite effect to images that Sharpening does Instead of finding edges and adding contrast, blurring reduces the contrast, making edges softer Photoshop has 11 Blur filters Caution Blurring images is done by smoothing out some of the details The detail is permanently lost You likely want to apply the blurring filters on a separate duplicate layer to avoid data loss problems n Each Blur filter reduces the... each pixel is compared to pixels around it in an even radius, and pixels that are closer receive higher weight than pixels that are farther away Choosing the Blur filter softens the edges in your image by blurring only those pixels that are in high contrast areas If you choose a Box Blur, each pixel is compared to pixels around it in a box shape, giving the end result an edgier appearance If you really . adjustments to the photo in Photoshop. For these reasons, Photoshop includes some powerful sharpening filters that make your images look better. To sharpen the photo, Photoshop uses some algorithms. caused by sharpening the image through the other adjustments. n Applying basic sharpening filters The simplest way to sharpen images is to use one of the three basic filters supplied by Photoshop. . additional options available by blending the filters rather than just applying them normally. n 21_584743-ch14.indd 43721_584743-ch14.indd 437 5/3/10 10:35 AM5/3/10 10:35 AM Part IV: Enhancing, Correcting,