Photoshop cs5 cho nhiếp ảnh gia part 28 doc

168 c h a p t e r 4: FOUNDATIONS ■ The third Lasso selection tool is the Polygonal Lasso tool. However, for nature photography this tool tends to be less useful than the tools described in this section because it is designed for creating selections comprised of straight lines. The Magic Wand When the Magic Wand tool creates a selection with a single click of the mouse, it seems truly magical. When too many clicks are required, it can be frustrating. The trick is knowing what type of image is best suited for this tool and how to configure the settings for the best result. The Magic Wand lives underneath the Quick Selection tool (covered in the next section). To access it, click the Quick Selection tool in the toolbar, and select the Magic Wand from the fly-out menu. (You can also press W and then Shift+W as needed to toggle between the Quick Select and Magic Wand tools.) The Magic Wand functions by sampling the pixel that you click and then comparing other pixels to see whether they are a close-enough match. If they are, they are included in the selection. Before setting the options for the Magic Wand tool, it’s important to check a setting on the Options bar for the Eyedropper tool . Although these tools don’t seem related, the Magic Wand tool uses the Sample Size setting from the Eyedropper tool to determine the actual value to use in evaluating pixels for inclusion in the selec- tion. Choose the Eyedropper tool from the Tools panel, and choose an option from the Sample Size drop-down menu on the Options bar, as shown in Figure 4.23. Figure 4.23 The rst step in using the Magic Wand tool is to set an appropriate option from the Sample Size drop-down menu on the Options bar for the Eyedropper tool. The most useful options available for your purposes when you select the Eye- dropper tool are 3 by 3 Average and 5 by 5 Average. As their names indicate, they sample a grid of pixels (a total of 9 or 25 pixels, respectively) surrounding the one you click and average their values. This average value is then used as the basis of the Magic Wand tool selection. Averaging helps to compensate for any local variation among pixels and is more reliable than sampling a single point. We recommend using the 3 by 3 Average setting, because it provides a good balance for most images. The 5 by 5 Average setting has a higher risk of averaging the pixel values to the point that the result isn’t as accurate based on the pixel area you clicked. Note: The Point Sample option causes the Magic Wand tool to use only a single pixel as the basis for pixel comparison. This can certainly increase precision, but it also introduces potential errors. For example, you could click a dust spot or a pixel with variation caused by grain or noise, and the resulting selection wouldn’t match what you were intending to create. For this reason, we don’t recommend using the Point Sample option. 607343c04.indd 168 4/11/10 11:04:26 PM 169 ■ SELECTION TOOLS After you’ve established an appropriate Sample Size setting on the Options bar for the Eyedropper tool, choose the Magic Wand tool so you can adjust the settings and create your selection. The key to using the Magic Wand tool effectively is the Tolerance setting on the Options bar (see Figure 4.24). This setting determines how different the pixel values can be and still be considered a match. With a low setting, pixels must be very similar to the value of the pixel you clicked to be included in the selection. With a high set- ting, even pixels with very different values can be included in the selection. The toler- ance ranges from 0, which would mean a pixel must be identical to the sampled pixel in order to be selected, to 255, which would result in the entire image being selected. Figure 4.24 The Tolerance setting on the Options bar for the Magic Wand tool is key to getting the best results. The Magic Wand tool is obviously best suited to images with broad areas of similar tone and color that you want to select. An example would be the out-of-focus green background in the image in Figure 4.25. Because the pixels already have similar values, a relatively low Tolerance setting should be appropriate. We often start with a value of 30 and work from there. Figure 4.25 The Magic Wand tool is best suited to images with broad areas of similar tone and color. Ph ot o by EllEn An on Click the area of the image you want to select, and adjust the Tolerance set- ting based on the result. If too many pixels from areas you don’t want to select are selected, the Tolerance is too high; cancel the selection (choose Select > Deselect from the menu) and reduce the Tolerance value. 607343c04.indd 169 4/11/10 11:04:26 PM 170 c h a p t e r 4: FOUNDATIONS ■ Of course, you could spend a lot of time chasing the right Tolerance value. We recommend taking a tempered approach, trying to find a good value without spending too much time finding the perfect value. Opt for a Tolerance setting that is a bit lower than needed. Then use the Add to Selection option and the Refine Edge feature (which we’ll describe later in this chapter) to build up the final selection. Note: It’s usually preferable to start with a Tolerance value for the Magic Wand that results in a selection that encompasses less than the area you are trying to select, and then build up the selection with the Add to Selection option. It’s important to keep in mind that when you add pixels to or subtract pixels from a selection by using the appropriate options with the Magic Wand tool, the selec- tion is modified based on the pixel you click after making your initial selection. Also, keep in mind that you can adjust the Tolerance setting between mouse clicks when using the Add and Subtract options, giving you even greater control. Each time you click with the Magic Wand tool, pixels throughout the image are evaluated based on the Tolerance setting, regardless of whether the pixels are already selected. Although the Tolerance setting is the pivotal setting for the Magic Wand tool, the Contiguous option is also important. The Contiguous option affects which pix- els are evaluated. When you click a pixel with the Magic Wand, Photoshop looks outward from that pixel to find matching pixels. If it encounters a pixel that doesn’t match closely enough based on the Tolerance setting, that pixel creates a border so that pixels outside the areas defined by that border aren’t considered. In other words, all pixels in the final selection are contiguous, or touching each other. Using the Contiguous option is helpful when a tonality appears not only in the area you want to select, but also in areas you don’t want to select. By clicking Con- tiguous, the Magic Wand will not include pixels that are in other areas of the image. For example, if you wanted to select the two swans shown in Figure 4.26, by select- ing Contiguous you help the Magic Wand limit the selection to the swans rather than including the snow in the mountains. Figure 4.26 Using the Contiguous option enables you to select a subject when similar tones are present elsewhere in the image. Ph ot o by EllEn An on 607343c04.indd 170 4/11/10 11:04:27 PM 171 ■ SELECTION TOOLS At other times, you need to select similar areas that are noncontiguous. For example, you may need to select a sky in an image where the sky shows between the leaves and branches of a tree. Turning off the Contiguous option causes Photoshop to evaluate every pixel based on the pixel you click with the Magic Wand tool, as shown in Figure 4.27. Figure 4.27 Turning o the Contiguous option for the Magic Wand tool allows you to select multiple noncontiguous areas in a single step. Ph ot o by EllEn An on The Sample All Layers check box allows you to determine whether Photoshop evaluates pixel values based on all layers in the image or on only the currently active layer. Because you’re viewing the image based on all visible layers, it usually makes sense to keep this option turned on. In fact, you can use this setting to make the Magic Wand tool more effective by creating a temporary adjustment layer that accentuates the differ- ence between areas you do want to select and those you don’t. The Anti-Aliased check box serves the same purpose as it does with the other selection tools discussed earlier in this chapter, and we recommend leaving it selected. The Magic Wand tool is best for selecting areas of an image that have similar tone and color. If the area you’re trying to select contains too much variation, evaluate the image to see whether you can easily select the opposite of what you really want. For example, if you want to select everything in an image except the sky, it might be easier to select the sky and then invert the selection (Select > Inverse). When using the Magic Wand tool, it’s important to check your selection at 100% magnification. At other magnifications there may be small “blinkies” that you can’t see. These “blinkies” are actually pixels that may be erroneously selected or not selected. Rather than have to click over and over with the Magic Wand and use Add to Selection/Subtract from Selection, it’s often much easier to refine the selection with the Freehand Lasso set to Add to Selection/Subtract from Selection. We’ll talk more about this in the next section of this chapter. 607343c04.indd 171 4/11/10 11:04:27 PM 172 c h ap ter 4: FO U NDAT IONS ■ The Magic Wand is a favorite selection tool for many nature photographers, and it’s one that we used frequently in earlier versions of Photoshop. However, we find that now we turn more often to the Quick Selection and Color Range Select tools. Try It! Open the image MagicWand on this book’s companion website, www.sybex.com /go/photoshopnature , and practice by creating a selection of the sky that doesn’t encroach on the clouds. For Photoshop Elements Users: The Magic Wand and Quick Selection Tools These two tools are available in Elements and work similarly to their Photoshop counterparts, but are separate on the toolbar. Elements provides an additional selection tool to help you refine selections, called the Selection Brush. With this brush, you begin with another tool to create the initial, rough selection and then use the Selection Brush to refine the selection. You use it to paint on areas that you want to add or remove from the selection. To access the Selection Brush, click and hold the Quick Selection icon until a drop-down menu appears; then choose Selection Brush. The menu shown here will appear at the top of the screen. The Selection Brush is set to initially Add to Selection . Click the Subtract from Selection button to remove pixels from the selection. Tip: When using the Selection Brush, especially while removing from a selection, setting Mode to Mask makes it easier to see the selected area and to see what effect a softer or harder brush has. Mask mode places a transparent red overlay (customize the color by clicking on the color well and picking a new color) over every part of the image that’s not selected. The Quick Selection Tool The Quick Selection tool is one of our favorite selection tools. It’s easy to use, and it actually gets “smarter” as you work with the Add to Selection and Subtract from Selection options. Rather than having to trace along the edges to make a selection, you click and drag the cursor over the areas you want to select. The selection grows as you drag the cursor. The Quick Selection tool is actually a brush tool. To determine the size of the tool, set the brush size in the Options bar, or use the bracket keys to increase and decrease the size. We find that using a fairly small brush gives the best results; the larger the brush, the less precise the area that is selected. By using a small brush in 607343c04.indd 172 4/11/10 11:04:28 PM 173 ■ SELECTION TOOLS detailed areas, we can make reasonably accurate selections in many cases, as shown in Figure 4.28. Figure 4.28 It was easy to make a reasonably good selection of the penguin by using the Quick Selection tool. We’ll need to use Rene Edge (covered in the next section) to perfect the selection of the tail. Ph ot o by EllEn An on If the selection is not updating fast enough, you may need to drag a little more slowly and continue to hold down the mouse. If you stop dragging and then click elsewhere, the tool will automatically change to Add to Selection. The selection will grow to incorporate the new area but not neces- sarily areas in between the original selection and the new area. To remove an area from the selection, choose the Subtract from Selection option in the Options bar and then drag over the area to be removed. You may need to reduce the size of the tool. In areas of lower contrast, you may need to alternate between adding to and subtracting from the selection. Holding down the Alt/Option key will enable you to rapidly toggle between the two modes. As you do so, Photoshop is actually refining the algorithm to make the selection more accurately and quickly. To further adjust the edges of the selection, click the Refine Edges button, dis- cussed in the next section. Using the Rene Edge Controls The Refine Edge tool (Figure 4.29) has been completely overhauled in CS5 to make it even more powerful and easier to use. Its purpose is to enable you to modify the edges of a selection so that it blends with or separates from the background as needed. When using the selection tools, a Refine Edge button appears on the tool Options bar . It’s also available from within the Masks panel from the Mask Edge button. It is our method of choice for controlling the appearance of the edges of a selection no matter how we made the initial selection. It’s taken the place of the simple Feather command in our workflow and it eliminates the need for the elaborate procedure we used to use, in which we created a layer mask for a selection and blurred the edges of the layer mask. The Refine Edge interface is divided into several sections. View Mode contains options for viewing the selection. By default it places your selection against a white background, but it is sticky and will open with the view you used last. Click the View 607343c04.indd 173 4/11/10 11:04:28 PM . 607343c04.indd 172 4/11/10 11:04 :28 PM 173 ■ SELECTION TOOLS detailed areas, we can make reasonably accurate selections in many cases, as shown in Figure 4 .28. Figure 4 .28 It was easy to make a reasonably. book’s companion website, www.sybex.com /go/photoshopnature , and practice by creating a selection of the sky that doesn’t encroach on the clouds. For Photoshop Elements Users: The Magic Wand and. Selection Tools These two tools are available in Elements and work similarly to their Photoshop counterparts, but are separate on the toolbar. Elements provides an additional selection tool