Sử dụng photoshop cs5 part 23 doc

ptg SELECTIONS & MASKS IN THIS CHAPTER Creating layer-based selections. . . . .147 Using the Rectangular and Elliptical Marquee tools . . . . . . . . . . . . . .148 Using two of the lasso tools . . . . . . .149 Deselecting and reselecting selections . . . . . . . . . . . . . . . . .150 Deleting selected pixels . . . . . . . . .150 Moving a selection marquee . . . . . . .151 Moving selection contents . . . . . . . .151 Using the Quick Selection tool . . . . .152 Using the Magic Wand tool . . . . . . . .154 Using the Color Range command . . . .156 Hiding and showing selection edges .158 Swapping the selected and unselected areas . . . . . . . . . . . . .158 Creating a frame-shaped selection . . .159 Saving and loading selections . . . . .160 Refi ning selection edges . . . . . . . . .161 Using Quick Masks . . . . . . . . . . . . .166 Creating layer masks . . . . . . . . . . . .168 Editing layer masks . . . . . . . . . . . .169 Working with layer masks. . . . . . . . .172 Comparing the selection methods . . .174 9 When you select part of a layer, only that area can be edited, and the rest of the layer is protected. If you were to apply a lter, for example, only pixels within the selection area on the currently selected layer would be aected. In this chapter, you’ll learn how to create and modify selections using a wide assortment of methods, rene their edges, and store them for future use. You will also learn how to use layer masks to hide layer pixels from view — an essential Photoshop skill that you will practice again in other chapters. Each of the mechanisms discussed in this chapter represents the isolation of image areas in a unique way. A selection is displayed as a marquee of “march- ing ants,” a channel or mask is displayed as black and white areas, and a Quick Mask is displayed as red and clear areas. (For a comparison of the selection methods in Photoshop, see page 174.) Creating layer-based selections To select pixels on a layer: On the Layers panel, do either of the following: Click a layer or the Background, then choose Select> All or press Ctrl-A/Cmd-A. A marquee of “marching ants” will surround the entire layer. To select only the nontransparent areas on a layer, Ctrl-click/Cmd-click the layer thumbnail, A–B or right-click the layer thumbnail and choose Select Pixels. A Ctrl-click/Cmd-click a layer thumbnail… B …to select only nontransparent pixels on that layer. ptg 148 Chapter 9 Using the Rectangular and Elliptical Marquee tools To create a rectangular or elliptical selection: 1. Click a layer. 2. Choose the Rectangular Marquee or Elliptical Marquee tool (M or Shift-M). 3. Optional: For a smoother edge on an elliptical selection, check Anti-alias on the Options bar (see the sidebar on page 155), and keep the Feather value at 0 px. 4. Drag diagonally, A or Shift-drag to create a perfect square or circle. A marquee appears. 5. Optional: To add to the selection, Shift-drag again; to subtract from it, Alt-drag/Option-drag. ➤ To move the marquee while drawing it, keep the mouse button down, then hold down the Spacebar and continue to drag. To move the marquee after releasing the mouse, drag inside it with any selection tool. ➤ As you draw a marquee, its dimensions are listed in the W and H areas on the Info panel. ➤ To draw a marquee from the center, hold down Alt/Option while dragging. ➤ To create the thinnest possible selection, choose the Single Row Marquee or Single Column Marquee tool, then click in the image. To create a selection with a fixed ratio or specific dimensions: 1. Click a layer. 2. Choose the Rectangular Marquee or Elliptical Marquee tool (M or Shift-M). 3. On the Options bar, set the Feather value to 0, then do either of the following: From the Style menu, choose Fixed Ratio, enter Width and Height values to be used as the ratio of the selection (e.g., 5 to 7), B then drag in the image diagonally to make a marquee appear. C From the Style menu, choose Fixed Size, enter exact Width and Height values, then click in the image. D ➤ Click the Swap Height and Width button on the Options bar to swap the current values. A Drag diagonally with the Rectangular Marquee tool. D Choose Fixed Size, enter values, then click in the image: e marquee appears. You can drag the marquee to reposition it, as we are doing here. C With the Fixed Ratio option chosen, any size selection marquee you draw will have that ratio. B We chose Fixed Ratio for the Rectangular Marquee tool and entered a Width to Height ratio of 5 to 7. ptg Selections & Masks 149 Using two of the lasso tools We like to use the Lasso tool to select an area loosely, say, to limit subtle color adjustments to a general area. We also use this tool to clean up selections we have made with other tools, such as the Magic Wand or Quick Selection tool. To create a free-form selection: 1. Click a layer. 2. Choose the Lasso tool (L or Shift-L). 3. Optional: For a smoother edge on an elliptical selection, check Anti-alias on the Options bar. (Keep the Feather value at 0 px.) 4. Drag around an area on the layer. A  i s i n i t i a l selection doesn’t have to be precise, as you will be able to rene it easily in the next step. When you release the mouse, the open ends of the selection will be joined automatically. 5. To add to the selection, position the pointer inside it, then Shift-drag around the area to be added. B To subtract from the selection, position the pointer outside it, then Alt-drag/Option-drag around the area to be removed. C–D ➤ To feather an existing selection, see pages 161 and 237. ➤ To create a straight side with the Lasso tool, with the mouse button still down, hold down Alt/ Option and click to create corners. To resume creating free-form edges, press the mouse button, release Alt/Option, then continue to drag. To create a straight-edged selection: 1. Click a layer. 2. Choose the Polygonal Lasso tool (L or Shift-L). 3. Click to create points. E To create a selection edge at a multiple of 45°, hold down Shift while clicking. 4. To join the open ends of the selection, do either of the following: Click the starting point (make sure you see a small circle next to the pointer). Ctrl-click/Cmd-click or double-click anywhere in the document. ➤ To create a free-form segment while creating a polygonal selection, Alt-drag/Option-drag. Release Alt/Option and click to resume creating straight sides. ➤ To erase the last corner while using the Polygonal Lasso tool, press Backspace/Delete. E We created this straight-edged selection with the Polygonal Lasso tool. A With the Lasso tool, we are selecting the left part of the ice cream. B Using Shift, we are adding to the selection, to complete the shape. C We want to remove the pistachio nut from the selection. D We Alt-drag/Option-drag with the Lasso tool to remove the nut. ptg 150 Chapter 9 Deselecting and reselecting selections If you don’t like having to retrace your steps (we sure don’t), deselect your selections only when you’re sure you’re nished using them. Selections register as states on the History panel, but histories are short-lived. To preserve a selection for future access and use, save it in an alpha channel (see page 160) or convert it to a layer mask (see page 168). To deselect a selection: Do one of the following: Choose the Lasso, Rectangular Marquee, or Elliptical Marquee tool, then click inside or outside the selection. A Press Ctrl-D/Cmd-D. Right-click anywhere in the document and choose Deselect. To reselect the last selection: Do one of the following: Press Ctrl-Shift-D/Cmd-Shift-D. With any selection tool except the Magic Wand chosen, right-click in the document and choose Reselect. On the History panel, click the state that bears the name of the tool or command that was used to create the selection. Deleting selected pixels When you delete a selection of pixels from a layer, B that area is lled automatically with transparent pixels. C When you delete a selection of pixels from the Background, that area is lled with the current Background color. D To delete selected pixels: 1. On the Layers panel, click a layer or the Background. If you click the Background, also choose a Background color (see Chapter 11). 2. Do one of the following: If a layer is active, press Backspace/Delete; if the Background is active, press Ctrl-Backspace/ Cmd-Delete. ★ Choose Edit > Cut (Ctrl-X/Cmd-X) to put the selection on the Clipboard. (To learn about the Clipboard, see pages 233–236.) Choose Edit > Clear. D Here, we deleted pixels from the Background instead of from a layer, so they were replaced with the current Background color (which in this case is red). C Because the pixels we deleted were on a selected layer, they were replaced by transparent pixels. B We selected the blue sky, then pressed Backspace/Delete. A Click inside a selection to deselect it. ptg Selections & Masks 151 Moving a selection marquee You can move a selection marquee to a dierent area of the image without moving its contents. To move a selection marquee: 1. Choose any selection tool except the Quick Selection tool, and make sure the New Selection button is activated on the Options bar (you can also hold down M, L, or W to spring-load a selection tool). 2. Do either of the following: Drag inside an existing selection. A To constrain the movement to a multiple of 45°, start drag- ging, then hold down Shift and continue to drag. Press any arrow key to nudge the marquee by one pixel at a time, or press Shift-arrow to nudge the marquee by 10 pixels at a time. ➤ With a selection tool, you can drag a selection marquee from one image window into another. ➤ To transform a selection marquee (but not its contents), choose any selection tool except the Magic Wand. Right-click the image and choose Transform Selection. Drag a handle on the trans- form box to scale, rotate, skew, or distort the selection (see pages 312–313). A A selection mar- quee is moved with a selection tool. B Selection con- tents are moved on a layer with the Move tool. Moving selection contents In these steps, you will move a selection and its contents on a layer. To move the contents of a selection: 1. Create a selection. 2. Optional: To help you position the selection precisely at a specic location in the document, display the rulers (Ctrl-R/Cmd-R), drag a guide from the horizontal or vertical ruler, and turn on View > Snap To > Guides. 3. Do either of the following: On the Layers panel, click the Back ground, then choose a Back ground color (see Chapter 11). e area that becomes exposed when you move the selection will ll with this color. Click a layer. e area you expose when you move the selection will ll with transparent pixels. 4. Choose the Move tool (or hold down V to spring-load the Move tool). 5. Position the pointer over the selection, then drag. B Let the edge of the selection snap to a ruler guide, if you created one. 6. Deselect (Ctrl-D/Cmd-D). ➤ In Chapter 14, Combining Images, you will learn how to copy the contents of a selection within the same le and between les, and to use align- ment aids, such as ruler guides and Smart Guides. ➤ With the Move tool chosen, you can press an arrow key to nudge a selection and its contents by one pixel at a time, or press Shift-arrow to nudge the marquee by 10 pixels at a time. REMEMBER TO USE THE LAYERS PANEL! Before editing the pixels within a selection area, always remember to let Photoshop know which part of your document you want to edit by clicking a layer or the Background. ptg 152 Chapter 9 Using the Quick Selection tool e Photoshop features we’re going to discuss next — the Quick Selection tool, Magic Wand tool, and Color Range command — create selections in a more automatic way than the marquee and lasso tools. With these tools, the work of detecting the color boundaries is done for you, and the resulting selections tend to be very precise. If the area you want to select has well-dened bor- ders, instead of using a lasso tool, try using the Quick Selection tool. Rather than tediously tracing a precise contour, with this tool, you merely drag across a shape and stand by as it detects and selects the shape’s color boundary. You can push the result- ing selection outward to include an adjacent color boundary or inward to make it smaller. To use the Quick Selection tool: 1. Click a layer. 2. Choose the Quick Selection tool (W or Shift-W). 3. On the Options bar: Click the New Selection button to replace any existing selections with the one you’re about to create (or press Ctrl-D/Cmd-D to deselect). Use the Sample All Layers check box to control whether you want the tool to detect color bound- aries on just the current layer or on all layers. Check Auto-Enhance for a smoother, more rened selection edge. 4. To choose a brush diameter, Alt-right-click-drag/ Control-Option-drag to the left or right or press ] or [ , then drag within the area to be selected. A e selection will expand to the rst signicant color or shade boundary that the tool detects. e selection will preview as you drag, and will become more precise when you release the mouse. 5. Do any of the following optional steps: To enlarge the selection, click or drag in an adjoining area; the selection will expand to include it. B–C To shrink the selection, Alt-drag/Option-drag along the edge of the area to be subtracted (this is a temporary Subtract From button) ( A–B , next page). Note: To block an adjacent area from becom- ing selected by the Quick Selection tool as you A We selected the kumquat in the center of this image by dragging the Quick Selection tool across it. C Next, we dragged across the green leaf above the kumquats. e selection spread beyond the edge of the leaf to include some of the background area, which wasn’t our intention. B After enlarging the brush diameter, we clicked the kumquat on the right to add it to the selection. ptg Selections & Masks 153 enlarge an existing selection, Alt-click/Option- click or drag in that area, release Alt/Option, then drag to enlarge the selection area. e block will remain in eect until you click the blocked area again with the Quick Selection tool. C–E ➤ To undo the last click or drag of the Quick Selection tool, press Ctrl-Z/Cmd-Z. ➤ To save any kind of selection to an alpha channel, see page 160. ➤ To clean up a Quick Selection, you can use another selection tool, such as the Lasso. To rene the selection, see page 161. D We dragged along the stems to select them, then Alt- clicked/Option-clicked the background areas between the stems to remove them from the selection. B …and did the same thing to subtract the area below the kumquats. E To nalize our selection, we cleaned up the selection of the stems. A We Alt-dragged/Option-dragged below the leaf to subtract the background area from the selection… C We zoomed in, reduced the brush diameter, then Alt-clicked/Option-clicked areas around the stems to prevent them from becoming selected. . remember to let Photoshop know which part of your document you want to edit by clicking a layer or the Background. ptg 152 Chapter 9 Using the Quick Selection tool e Photoshop features. (Ctrl-X/Cmd-X) to put the selection on the Clipboard. (To learn about the Clipboard, see pages 233 236 .) Choose Edit > Clear. D Here, we deleted pixels from the Background instead of from. Quick Mask is displayed as red and clear areas. (For a comparison of the selection methods in Photoshop, see page 174.) Creating layer-based selections To select pixels on a layer: On the Layers