Tài liệu Photoshop cs5 by Dayley part 40

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Các công cụ Elliptical Marquee có thể được dùng để chọn tròn hoặc hình bầu dục các đối tượng trong hình ảnh của bạn, để sao chép các khu vực làm tròn của hình ảnh của bạn vào các tài liệu khác, hoặc tạo một hình nền. Tôi thường sử dụng nó khi điều chỉnh một trường hợp khó khăn của mắt đỏ.

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Nội dung Text: Tài liệu Photoshop cs5 by Dayley part 40

Part III: Selections, Layers, and Channels FIGURE 9.11 Using the Quick Mask makes it easy to see how feathering the edges of a selection softens it. The Elliptical Marquee tool The Elliptical Marquee tool can be used to select round or oval objects in your image, to copy rounded areas of your image into other documents, or to create a vignette. I often use it when cor- recting a tough case of red-eye. It’s a little trickier to use than the Rectangle Marquee tool, because you have to imagine a box around the oval you want to draw and start at the top corner of that box to get the selection placed just right. It’s mostly a matter of practice and trial and error. The good news is that if you get the right size, you can always pick the selection up and move it to the right position. Tip Holding down the Shift key while you use either the Rectangle or the Elliptical Marquee tool results in a per- fect square or a perfect circle, depending on the tool, of course. n Using the Lasso tools The Lasso Selection tools have been in Photoshop much longer than the Quick Selection tools and in many ways have been superseded by them. Before the Quick Selection tool, the Magnetic Lasso was the best tool in the arsenal for selecting irregular edges that blended into the background; now mine’s a bit dusty. The Lasso and the Polygonal Lasso tools can still be very useful, and I show you how to use them. Lasso tool options The options for the Lasso and the Polygonal Lasso tool are identical. They are also very similar to the options for the previous selection tools discussed in this chapter. The Magnetic Lasso tool has the most involved option menu of all the selections tools, so I cover the additional options in the Magnetic Lasso tool section. l Tool presets: You can save and retrieve your favorite tool settings using this drop-down list. Click the little black arrow to see a menu of available options. 272
Chapter 9: Creating Selections l New selection: When this option is highlighted, every time you use the Lasso tool, you create a new selection and the old selection disappears. l Add to selection: With this option highlighted, everything you select is added to the cur- rent selection. This makes it easy to do the detail work after the initial selection is made. l Subtract from selection: With this option highlighted, you can subtract areas from the current selection. l Intersect with selection: This option selects only those areas that were in the first selec- tion you made as well as the second, and deselects anything that was selected only once. l Feather: This makes the specified pixels on the edges of the selection gradually transpar- ent. This allows changes you make to the selection to blend with the surrounding areas, whether you apply an adjustment to the selection or create a mask with the selection. l Anti-Alias: This creates a smoother-edged selection. Lasso tool The Lasso tool is an easily understood selection tool. You use it to create a selection by drawing a free- hand border around the area you want to select, as shown in Figure 9.12. It can be useful for selecting areas that are easy to freehand or generalized areas for a start in using more specialized selection tech- niques, such as the Color Range dialog box. You also can use it to touch up other selections. FIGURE 9.12 The Lasso tool creates versatile selections by simply following wherever you draw. 273
Part III: Selections, Layers, and Channels Caution As you use the Lasso Selection tool, be sure to close your selection by finishing relatively close to where you started. Photoshop automatically draws a straight line between the beginning point and the end point, and if that line inter- sects other areas of the selection, you may end up with quite a different selection than you were envisioning. n The Polygonal Lasso tool The Polygonal Lasso tool is useful for selecting areas in your photo that are angular but not rectan- gular and hard to select with the Quick Selection tool because the colors and textures in the photo are very similar. Even rectangular objects usually are skewed in photographs, making the Polygonal Lasso tool a better choice than the Rectangle Marquee tool for selecting them. The photo in Figure 9.13 is a good example. The building pictured has several angles that are straightforward, but not easy to select with the Rectangle Marquee. The Quick Selection tool would be tricky to use because of the similarities in color and texture throughout the photo, so the Polygonal Lasso tool is the best choice. Use the Polygonal Lasso tool to make a selection by following these steps: 1. Choose the Polygonal Lasso tool by clicking and holding the triangle in the Lasso tool icon and selecting the Polygonal Lasso tool. The current Lasso tool can be accessed by typing L on your keyboard. 2. Click the corners of the object you want to select, and the Polygonal Lasso tool locks the selection to each corner you click and selects a straight line between each one, as shown in Figure 9.13. FIGURE 9.13 Click each corner of your selection to anchor the Polygonal Lasso tool. 274
Chapter 9: Creating Selections 3. Close the selection by clicking the corner where you started or by double-clicking to release the Polygonal Lasso Tool. Your selection is created as seen in Figure 9.14. FIGURE 9.14 The Polygonal Lasso tool helps you make angular selections. The Magnetic Lasso tool The Magnetic Lasso tool is a precursor to the Quick Selection tool, and it works very similarly by looking for edges close to the area where you are dragging and sticking to them. This makes your selection more precise than a freehand selection, but using the Magnetic Lasso is not usually as fast as using the Quick Selection tool. The Magnetic Lasso tool options In addition to the Lasso tool option listed above, the Magnetic Lasso tool has several additional options, as shown in Figure 9.15: FIGURE 9.15 The Magnetic Lasso tool has several additional options that allow you to customize it for the best selection. 275
Part III: Selections, Layers, and Channels l Width: This determines how many pixels from the pointer the Magnetic Lasso tool searches for edges. This can be a benefit over the Quick Selection tool because the Quick Selection tool samples the entire document looking for similarities in what you are select- ing and can sometimes select more than you were anticipating. l Contrast: This allows you to adjust the level of contrast needed for the Magnetic Lasso tool to determine an edge. If the area you are selecting blends into the background, you want to set your contrast low. l Frequency: This sets the frequency of the anchor points that are used. l Use tablet pressure to change pen width: Use this option with a stylus tablet. With this option selected, you can increase the width of your pen by increasing the pressure on your tablet. Using the Magnetic Lasso tool Use the Magnetic Lasso tool by clicking once on your beginning point and dragging as close the border of the area you want to select as possible. The Magnetic Lasso looks within a certain radius (set by the Width option) for areas that contrast enough to be considered edges and places anchor points along your selection. As you drag, anchor points are set down to show where the edges of your selection are going to be, as shown in Figure 9.16. As long as you are making your selection, these anchor points can be changed in one of two ways. If an anchor point isn’t set automatically in a place where you need one, click once and an anchor point is added. If anchor points are set in areas where you don’t want them, you can use the Delete key to back up your anchor line one point at a time. FIGURE 9.16 You see a line of anchors following your selection with the Magnetic Lasso tool. 276
Chapter 9: Creating Selections On the Web Site You can try your hand at creating this selection by downloading Figure 9-16 from the Web site. n Caution As you work with the anchors in the Magnetic Lasso tool, remember that the tool itself is still carrying a selec- tion line that leaves a wake of anchors no matter where you take it. If you are not careful, you’ll create a selec- tion mess reminiscent of trying to work with hot glue. n Your selection is open and changeable until you close it by either returning to the beginning and clicking the first anchor point or double-clicking to release the selection. After you’ve done that, the anchor points disappear and your selection is created. Refining Your Selection Every once in a while, you have one of those lottery-winning, green-light hitting, pick-the-fastest- checkout-line kind of days. The rest of the time, you have to make adjustments to your selection after the first try. The first step is to actually add and subtract areas to and from your selection that weren’t right the first time, and you can do this in lots of different ways. After your selection bor- der is right where you want it, the next step is to refine the edges of your selection so that whatever it is you want to do with that selected area, the changes blend right in. Adjusting a selection After you’ve made your initial selection, chances are good that you need to add areas into the selec- tion or subtract areas from the selection. You can do this in several ways. First, you can use the selection tools. Second, you can transform your selection. Third, you can create and adjust a path. And last, and probably the most precise way, is to use the Quick Mask mode and paint areas in or out of your selection. Using the selection tools As I’ve already shown you, all the selection tools have the option to either add to or subtract from the selection. It doesn’t matter what tool you used to create the original selection, you can use any other selection tool to add to or subtract from that selection. This makes using the selection tools a very versatile process. For instance, in Figure 9.17, the Magic Wand did a great job of selecting an almost perfect outline of the snapdragon. Of course, a few spots here and there need to be added to or subtracted from this selection. Adjusting the tolerance levels or trying to add or subtract using the Magic Wand tool is an effort in frustration. Remember that the Magic Wand tool samples colors every time you use it. You could click to add or subtract areas you don’t want and end up with even more areas that are wrong. 277