Tài liệu Photoshop cs5 by Dayley part 65 doc

Part IV: Enhancing, Correcting, and Retouching 454 l Quality: Allows you to specify either Draft, Good, or Best. The better the quality, the bet- ter the results look; however, the Radial Blur filter takes lots of processing power, so you should try it out in Draft mode first and then increase the quality after you get the desired results. l Blur Center: Allows you to drag the center of the blur to any location in the image. The lines show the amount of blurring that will take place. FIGURE 14.17 The Radial Blur has several possibilities with the Spin and Zoom options available. On the Web Site The project file used to create the image shown in Figure 14.17 can be found on this book’s Web site as Figure 14-17.psd. You can open it in Photoshop to see the effects of the Radial Blur filter and play around with the direction and amount of the blur. n Surface Blur The Surface Blur filter is the opposite of the Blur and Blur More filters. Rather than softening the edges, the Surface Blur works by softening the midtones, leaving the edges sharp and crisp. This is perfect for smoothing out slight imperfections or noise in an image without losing the crispness of the file. Smart Blur The Smart Blur allows you to blur with more precision using radius and threshold settings that allow you to specify the number of pixels involved and what the difference in the pixels should be before the filter is applied to them. To apply a Smart Blur, select Filter ➪ Blur ➪ Smart Blur from the main menu and set the following options, as shown in Figure 14.18: l Radius: Specifies the area of pixels searched to determine whether a pixel is dissimilar to its neighbors and should be blurred. l Threshold: Specifies the amount of dissimilarity a pixel must have with its neighbors before it is considered dissimilar. 21_584743-ch14.indd 45421_584743-ch14.indd 454 5/3/10 10:35 AM5/3/10 10:35 AM Chapter 14: Sharpness, Blur, and Noise Adjustments 455 l Quality: Allows you to specify either a Low, Medium, or High quality. The better the quality, the better the results look; however, the Smart Blur filter takes lots of processing power, so you should try it out in Low mode first and then increase the quality after you get the desired results. l Mode: Allows you to specify a Normal, Edge Only, or Overlay Edge blur. The Normal set- ting gives you basic blurring results. The Edge Only setting turns the image entirely black and creates white edges. The Overlay Edge overlays the edges in the image with white. FIGURE 14.18 The Smart Blur allows you to specify the area of pixels and threshold to use when blurring the image. Lens Blur The Lens Blur is by far the most advanced Blur filter available. It includes a very involved dialog box that allows you to change the field of depth to the specular highlights of your image. The whole point of the Lens Blur is to allow you to blur parts of your image while leaving other areas in sharp focus. The Lens Blur dialog box shows a full preview of your image by default. Because the changes you make probably affect different areas of your image differently, you can see the effects your changes have on your full image. Because the precise changes made by the Lens Blur can take time, you have the option of choosing between a faster or more accurate preview. The following sections dis- cuss the adjustments that can be made in the Lens Blur dialog box shown in Figure 14.19. 21_584743-ch14.indd 45521_584743-ch14.indd 455 5/3/10 10:35 AM5/3/10 10:35 AM Part IV: Enhancing, Correcting, and Retouching 456 FIGURE 14.19 The Lens Blur dialog box is loaded with options for creating a custom blur. Preview The preview for the lens blur is very big and can be slow when rendering large images. To help out, Photoshop provides the Faster and More Accurate options. The faster preview renders more quickly but is less like the actual filter than the more accurate setting. Which option you use is entirely dependent on whether you have time to wait or not. Depth Map An image or video file in Photoshop is just a pixel map. Photoshop can’t determine which areas of an image should be in focus and which shouldn’t be, unless you show it. Setting the Depth Map tells Photoshop which pixels to keep sharp and which ones to blur. You can create a Depth Map in several ways. Selecting None from the Source drop-down blurs the pixels in your image indiscrimi- nately. Choosing Transparency blurs the pixels based on their Transparency values. If you select Layer Mask, the blurring is based on the grayscale values in the layer mask. If you create a gradient layer mask, for example, the lighter areas of the gradient are less blurry than the darker areas. The best way to create a Depth Map is to create and load an alpha channel. (See Chapter 11 for more information on creating an alpha channel.) The dark areas of the alpha channel are treated as the foreground of the image, and the light areas are treated as the background. Figure 14.20 shows 21_584743-ch14.indd 45621_584743-ch14.indd 456 5/3/10 10:35 AM5/3/10 10:35 AM Chapter 14: Sharpness, Blur, and Noise Adjustments 457 an alpha channel that matches the shape of the bison in the Lens Blur dialog box (refer to Figure 14.19). When you’ve created an alpha channel, it appears in the Source drop-down menu, and you can use it to determine which pixels are blurred. Click anywhere on your image to choose the pixel brightness that determines which areas of your picture stay in focus. FIGURE 14.20 The Channels palette contains an alpha channel created with a selection. If you select a source other than None, you can choose the focal distance of the blur by adjusting the slider. As the focal distance changes, the area inside of the alpha channel becomes sharper and the area outside the alpha channel becomes more blurred. You also can invert the effects on the respective parts of the alpha channel by selecting the Invert option. Iris The Iris determines the size and shape of the aperture of a camera. The Iris settings in this dialog box allow you to simulate the different types of irises found in different cameras. The Iris setting allows you to change the following options: l Shape: Allows you to specify the shape of the iris in terms of number of blades from 3 to 8. l Radius: Determines the number of pixels sampled to create the blur effect. l Blade Curvature: Specifies the curvature of the blade in a range between 0 and 100. The curvature of the blade affects the amount of blurring around the edges in the image. l Rotation: Specifies the rotation of the Iris in degrees. This allows you to apply the filter at different rotations that affect the results of the blur. Specular Highlights When you blur a photograph using a mathematical formula, your whitest whites tend to dissipate and get replaced with duller tones. This would never happen in a real photo, no matter how blurry it became. You can readjust the whites in your image by using the following settings to add Specular Highlights: 21_584743-ch14.indd 45721_584743-ch14.indd 457 5/3/10 10:35 AM5/3/10 10:35 AM Part IV: Enhancing, Correcting, and Retouching 458 l Brightness: Specifies the value to increase the whites by to bring back the brilliance. l Threshold: Specifies the levels affected by the Brightness setting. The default is 255, meaning only pure white. As you adjust the slider down, less bright pixels are included. Noise Noise is found in a true photograph, even a blurry one. To create a more realistic blur, you can add noise to your image using the following settings: l Amount: Specifies the amount of noise to add when blurring. l Uniform: Adds noise uniformly to the image in a linear fashion, so the effect is consistent. l Gaussian: Adds noise based on the amount of sharpening or blurring occurring in the pixels. The Gaussian effect appears more natural but does occasionally create some arti- facts in the image. l Monochromatic: Adds noise as gray instead of based on the color of the surrounding pix- els. This can appear more natural, but the overall effect is typically better by not selecting this option. Reducing Noise in an Image Noise results from any pixels in the image that don’t belong. Types of noise include things such as excessive grain, pixelization, and half-toning. Excessive grain can be caused by low lighting, high ISO settings, and even by some adjustments in Photoshop. Pixelization is artifacts left over when an image is resampled to a higher resolution, rotated, or transformed in other ways. Half-toning is an artifact most commonly generated when a scan is made of a printed image. The two basic types of noise are color (chroma) noise and luminance noise. Color noise manifests itself as colored artifacts that don’t match the image and become more apparent the farther you zoom in on the image. Typically, color noise is more visible in one color channel than the others. Luminance noise manifests itself as bright gray pixels, such as grainy images or halos. Reducing noise and removing dust and scratches can improve the look of images. This section dis- cusses some of the methods of reducing noise in images using the noise filters found in the Filter ➪ Noise menu. Despeckle The Despeckle filter is much like the Surface Blur. It detects the edges in your image by finding high contrast areas and blurs the areas in between the edges, reducing the overall noise in the image. The Despeckle filter is applied to the image or layer by selecting Filter ➪ Noise ➪ Despeckle from the main menu. The Despeckle filter has no dialog box to control the amount of blurring that takes place, so it is fairly limited in what it can do. However, you can apply the Despeckle filter as many times as you want to the image. Each time you apply the Despeckle filter, more smoothing occurs. 21_584743-ch14.indd 45821_584743-ch14.indd 458 5/3/10 10:35 AM5/3/10 10:35 AM Chapter 14: Sharpness, Blur, and Noise Adjustments 459 Median The Median filter removes noise from the images by searching the radius of each pixel to find pix- els that are a similar brightness. If it finds pixels that are different from their surrounding pixels, it replaces them with a pixel value that is determined by the median brightness value of the pixels around it. Pixels that vary too much from the rest of the neighboring pixels are ignored when cal- culating the median, so they don’t skew the median value. The Median filter allows you to specify the radius of the area to use when calculating the median. The best value of the radius varies depending on the variance of pixels in the image. You can use a higher radius value for images that contain little variance. To add a Median filter to an image, select Filter ➪ Noise ➪ Median from the main menu. Figure 14.21 shows an example of using the median filter on an image. Notice that when we zoom in on the hawk’s tail, the sky and even the feathers show some noise. When we use a median filter with a radius of 2, the noise is cleaned up. Some detail is lost due to blurring, but it is still acceptable. However, when we use a median filter with a radius of 5, we lose a great deal of detail. You need to play around with the filter to figure out the best radius value to remove the noise while minimizing detail loss. FIGURE 14.21 The Median filter will allow you to configure a radius setting that controls the area affected by the filter. Too little of a radius will not clean up the noise, but too large of a radius will remove too much detail. 21_584743-ch14.indd 45921_584743-ch14.indd 459 5/3/10 10:35 AM5/3/10 10:35 AM Part IV: Enhancing, Correcting, and Retouching 460 Dust & Scratches You can reduce the imperfections in your video file by choosing Filter ➪ Noise ➪ Dust and Scratches. The key to success with this filter is to find a good balance between the Radius and Threshold settings. Turning up the Radius while leaving the Threshold at 0 quickly reduces the dust in your image but just as quickly adds blur to it. By increasing the Threshold, you can keep most of the sharpness in the image and still reduce the imperfections, as shown in Figure 14.22. FIGURE 14.22 Getting a good result from the Dust & Scratches Filter is a balancing act between the Radius and Threshold settings. Cross-Ref Using the Clone and Heal tools is usually a much better method of removing dust and scratches from images. We discuss the Clone and Heal tools in much more detail in Chapter 15. n Reducing noise The Reduce Noise filter provides the most flexibility of all the Noise filters. The different settings in the Reduce Noise dialog box help you customize the Reduce Noise filter to best match the needs of each specific image. To use the Reduce Noise filter, choose Filter ➪ Noise ➪ Reduce Noise to open the Reduce Noise dialog box shown in Figure 14.23. From this dialog box, you can adjust the following settings: l Basic/Advanced: Toggles between Basic and Advanced modes. In Basic mode, you change the settings for all channels at once. In Advanced mode, you adjust settings to reduce noise in each channel individually. l Presets: The drop-down menu allows you to select the default option or one of the previ- ously saved presets. Presets can be saved by clicking the Save button and deleted by click- ing the Trashcan button. l Strength: Specifies the amount to reduce the luminance noise in the image when the filter is applied by increasing or decreasing the intensity of the overall noise reduction. 21_584743-ch14.indd 46021_584743-ch14.indd 460 5/3/10 10:35 AM5/3/10 10:35 AM Chapter 14: Sharpness, Blur, and Noise Adjustments 461 l Preserve Details: Specifies the percentage of detail that must be preserved. To reduce noise, you must sacrifice some detail lost. Use this setting to make certain you maintain at least the minimum amount of detail in the image. Typically, you should set this option at least 60% or higher. l Reduce Color Noise: Specifies the percentage of color noise to remove from the image. If this value is set too high, Photoshop has a hard time distinguishing between color noise artifacts and simple variations in the image. This option is necessary only if color noise exists in the image. l Sharpen Details: Specifies the percentage of detail to try to gain back during the filter process. This is a great feature in the Reduce Noise tool. Noise reduction is done by blur- ring and results in lost detail. This option specifies the amount of sharpening to take place after the blurring to get back some of that lost detail. Be careful not to set this value too high or you introduce new noise into the image. l Remove JPEG Artifact: Causes the Reduce Noise filter to reduce the blocky image arti- facts and halos that can be created when a JPEG file is resampled and then saved again. l Per Channel: Allows you to select specific color channels so you can individually custom- ize the Strength and Preserve Details options differently for each color channel. FIGURE 14.23 The Reduce Noise dialog box allows you to balance the strength of the noise reduction with preserving detail. You also can fine-tune the noise reduction based on color channel. Tip Removing the noise blurs your picture. Photoshop built the Sharpen Details setting into this feature to counter- act that. You can use this setting or use a more powerful sharpening filter after you have reduced the noise. n 21_584743-ch14.indd 46121_584743-ch14.indd 461 5/3/10 10:35 AM5/3/10 10:35 AM Part IV: Enhancing, Correcting, and Retouching 462 Add noise In addition to removing noise, Photoshop also allows you to introduce noise into the image. Adding noise to an image adds graininess to it that can simulate film grain, add a texture effect, or camouflage areas that have been corrected. To add noise to an image, select Filter ➪ Noise ➪ Add Noise to open the Add Noise dialog box seen Figure 14.24. You can add noise using the Uniform setting that randomizes the values used to cre- ate the noise pattern or using a Gaussian that utilizes the bell curve to create the values. When you add noise to an image, it can appear in varied colors, which can change the color integrity of your file. Choose the monochromatic option to create noise as shades of gray. FIGURE 14.24 The Add Noise dialog box allows you to introduce noise into the image to simulate film grain, add a tex- ture effect, or camouflage areas that have been corrected. Summary Using the Photoshop filters allows you to correct problems with blurriness or noise in images and make adjustments to soften harsh areas of a photo. This chapter discussed using the sharpening fil- ters to fix blurry images and enhance edges, blurring filters to apply softening effects, and noise reduction filters to remove noise and unwanted artifacts from images. 21_584743-ch14.indd 46221_584743-ch14.indd 462 5/3/10 10:35 AM5/3/10 10:35 AM Chapter 14: Sharpness, Blur, and Noise Adjustments 463 In this chapter, you learned about these things: l The Smart Sharpen filter allows you to fine-tune the sharpening effect to match the type of blurring problems in the photo. l Using an Unsharp Mask filter can add missing detail in an image. l Applying a blurring filter to the background of a photo softens the overall appearance of the image. l Using Motion Blur can make an object in a photo appear in motion. l Applying a noise reduction filter removes unwanted noise from images. l How to remove dust and scratches from damaged images. l How to remove the JPEG artifacts caused by the compression algorithm used when saving JPEG images multiple times. 21_584743-ch14.indd 46321_584743-ch14.indd 463 5/3/10 10:35 AM5/3/10 10:35 AM . file in Photoshop is just a pixel map. Photoshop can’t determine which areas of an image should be in focus and which shouldn’t be, unless you show it. Setting the Depth Map tells Photoshop. pixelization, and half-toning. Excessive grain can be caused by low lighting, high ISO settings, and even by some adjustments in Photoshop. Pixelization is artifacts left over when an image. saved by clicking the Save button and deleted by click- ing the Trashcan button. l Strength: Specifies the amount to reduce the luminance noise in the image when the filter is applied by increasing