adobe Photoshop 6 Bibles phần 2 pot

70 Part I ✦ Welcome to Photoshop 6 Figure 3-2: Turn off the Resample Image check box to maintain a constant number of pixels in an image and to change only the printed resolution. To avoid confusion, most folks rely exclusively on the Resolution value and leave the Page Options dialog box Scale value set to 100 percent. The only exception is when printing tests and proofs. Because ink-jet and other consumer printers offer lower-resolution output than high-end commercial devices, you may find it helpful to proof images larger so you can see more pixels. Raising the Scale value lets you accomplish this without upsetting the Resolution value. Just be sure to restore the value to 100 percent after you make your test print. Changing the page-layout resolution The Scale value in the Print Options dialog box value has no effect on the size and resolution of an image imported into an object-oriented application, such as QuarkXPress or Illustrator. But these same applications do observe the Resolution setting from the Image Size dialog box. Specifying the resolution in Photoshop is a handy way to avoid resizing operations and printing complications in your page-layout program. For example, I preset the resolution of all the images in this book so the production team had only to import the images and print away. Tip Turn off 71 Chapter 3 ✦ Image Fundamentals Always remember: Photoshop is as good or better at adjusting pixels than any other program with which you work. So prepare an image as completely as possible in Photoshop before importing the image into another program. Ideally, you should never have to resize, rotate, or crop an image in any other program. That tip is so important I’m going to repeat it: Never resize, rotate, or crop an image in Illustrator, FreeHand, CorelDraw, PageMaker, InDesign, or QuarkXPress. Get your image fully ready to go in Photoshop and then place it in the drawing or page-layout program, position it on the page, and leave it alone. So what’s the perfect resolution? After all this explanation of pixels and resolution, you might be thinking, “Okay, this is all very interesting, but what’s my bottom line? What Resolution value should I use?” The answer is frustrating to some and freeing to others: Any darn resolution you like. It’s true — there is no right answer, there is no wrong answer. The images in this book vary from 100 ppi for screen shots to 300 ppi for color plates. I’ve seen low-resolution art that looks great and high-resolution art that looks horrible. As with all things, quality counts for more than quantity. You take the pixels you’re dealt and make the best of them. That said, I’ll share a few guidelines, but only if you promise to take them with a grain of salt: ✦ Most experts recommend that you set the Resolution value to somewhere between 150 percent and 200 percent of the screen frequency of the final output device. The screen frequency is the number of halftone dots per linear inch, measured in lpi (short for lines per inch). So ask your commercial printer what screen frequency he uses — generally 120 lpi to 150 lpi— and multiply that times 1.5 or 2. ✦ Want to be more specific? For high-end photographic print work, it’s hard to go wrong with a Resolution value of 267 ppi. That’s 200 percent of 133 lpi, arguably the most popular screen frequency. When in doubt, most profession- als aim for 267 ppi. ✦ If you’re printing on a home or small-office printer, the rules change slightly. Different manufacturers recommend different optimum resolutions for their various models, but the average is 250 to 300 ppi. Experiment to see how low you can go, though —sometimes you can get by with fewer pixels than the manufacturer suggests. And don’t forget that the quality of the paper you use may be more to blame than a lack of pixels for a lousy print. ✦ What if you don’t have enough pixels for 267 ppi? Say that you shoot a digital snapshot that measures 768× 1024 pixels and you want to print it at 6 × 8 inches. That works out to a relatively scant 128 ppi. Won’t that look grainy? Probably. Should you add pixels with Image Size or some other command? No, that typically won’t help. You have a finite number of pixels to work with, so you can print the image large and a little grainy, or sharp and small. The choice is yours. Tip 72 Part I ✦ Welcome to Photoshop 6 ✦ What if you have a photograph or slide and you can scan it at any resolution you want? Flat-bed scanners typically offer two maximum resolutions, a true optical maximum and an interpolated digital enhancement. The lower of the two values is invariably the true optical resolution. Scan at this lower maxi- mum setting. Then use Image ➪ Image Size to resample the image down to the desired size and resolution, as explained in the “Resampling and Cropping” section near the end of this chapter. Orson Welles claimed that he relied on his inexperience when creating Citizen Kane. He didn’t know the rules of filmmaking, so they couldn’t hamper him. When his assistants and technicians told him, “You can’t do that,” he ignored them because he didn’t know any better. I feel the same about resolution. Take the pixels you have and try to make them look the best you can. Then print the image at the size you want it to appear. If you focus on the function of your image first and fret about resolution and other technical issues second, you’ll produce better art. The Resolution of Screen Images Regardless of the Resolution and Scale values, Photoshop displays each pixel on screen according to the zoom ratio (covered in Chapter 2). If the zoom ratio is 100 percent, for example, each image pixel takes up a single screen pixel. Zoom ratio and printer output are unrelated. This same rule applies outside Photoshop as well. Other programs that display screen images— including multimedia development applications, presentation programs, and Web browsers —default to showing one image pixel for every screen pixel. This means that when you’re creating an image for the screen, the Resolution value has no effect whatsoever. I’ve seen some very bright people recommend that screen images should be set to 72 ppi on the Mac or 96 ppi for Windows, and while there’s nothing wrong with doing this, there’s no benefit either. When publishing for the screen, the Resolution value is ignored. So all that counts is the 100-percent view. That means you want the image to fit inside the prospective monitor when you choose View ➪ Actual Pixels (Ctrl+Alt+zero) inside Photoshop. I say prospective monitor because although you may use a 17-inch moni- tor when you create the image, you most likely need the final image to fit on a 13-inch display. So even though your monitor probably displays as many as 1,024 × 768 pixels, most Web and screen artists prepare for the worst-case scenario, 640 × 480 pixels. This is the 13-inch VGA standard, shared by some of the first color Macs and PCs, most laptops, an endless array of defunct computers, and even televisions. 73 Chapter 3 ✦ Image Fundamentals Of course, a 640 × 480-pixel image would consume an entire 13-inch screen. If you want the image to share the page with text and other elements, the image needs to be smaller than that. A typical screen image varies from as small as 16 × 16 pixels for icons and buttons to 320 × 240 pixels for a stand-alone photograph. Naturally, these are merely guidelines. You can create images at any size you like. For more information on creating images specifically for the World Wide Web, read Chapter 19. How to Open, Duplicate, and Save Images Before you can work on an image in Photoshop— whether you’re creating a brand- new document or opening an image from disk— you must first load the image into an image window. Here are the four basic ways to create an image window: ✦ File ➪ New: Create a new window by choosing File ➪ New (Ctrl+N). After you fill out the desired size and resolution specifications in the New dialog box, Photoshop confronts you with a stark, white, empty canvas. You then face the ultimate test of your artistic abilities — painting from scratch. Feel free to go nuts and cut off your ear. ✦ File ➪ Open: Choose File ➪ Open (Ctrl+O) to open images scanned in other applications, images purchased from stock photo agencies, slides and trans- parencies digitized to a Kodak Photo CD, or an image you previously edited in Photoshop. A variation on the Open command, Open Recent, displays a list of the images that you recently opened. Click an image name to crack open the image file without taking that tedious trip to the Open dialog box. ✦ Edit ➪ Paste: Photoshop automatically adapts a new image window to the contents of the Clipboard (provided those contents are bitmapped). So if you copy an image inside a different application or in Photoshop and then choose File ➪ New, Photoshop enters the dimensions and resolution of the image into the New dialog box. You can just accept the settings and choose Edit ➪ Paste (Ctrl+V) to introduce the image into a new window. Photoshop pastes the Clipboard contents as a new layer. This technique is useful for editing screen shots captured to the Clipboard or for testing effects on a sample of an image without harming the original. ✦ File ➪ Import: If you own a scanner or a digital camera, it may include a plug-in module that lets you transfer an image directly into Photoshop. Just copy the module into Photoshop’s Plug-Ins folder and then run or relaunch the Photoshop application. To initiate a scan or to load an image into Photoshop, choose the plug-in module from the File➪ Import submenu. 6 Photoshop 6 Caution 74 Part I ✦ Welcome to Photoshop 6 After you choose the command, Photoshop launches the device’s download software. If you’re scanning, select the scanner settings and initiate the scan as usual; the scanned picture appears in a new image window inside Photoshop. If you’re transferring images from a digital camera, the camera software typically creates thumbnail previews of images in the camera’s memory so that you can select the ones you want to transfer to Photoshop, as I’m doing in Figure 3-3. Figure 3-3: Most digital cameras ship with TWAIN plug-ins that enable you to view images stored in the camera’s memory and open them up directly inside Photoshop. Save your images to disk immediately after you scan or download them; unlike some other programs, Photoshop doesn’t automatically take this step for you. Also, if your digital camera stores images on removable memory cards (Compact Flash, SmartMedia, Memory Stick, and the like), do yourself a favor and invest in a card reader or adapter that enables your computer to see the memory card as just another hard drive. Then you can just drag and drop images from the memory card to your computer’s hard drive —a much faster and more convenient option than transferring images via a cable connection. You’ll spend between $10 and $75, depending on what type of reader or adapter you buy, but trust me, even if you wind up at the high end of that price range, you’ll never regret the purchase. Creating a new image Whether you’re creating an image from scratch or transferring the contents of the Clipboard to a new image window, choose File ➪ New or press Ctrl+N to bring up the New dialog box shown in Figure 3-4. If the Clipboard contains an image, the Tip 75 Chapter 3 ✦ Image Fundamentals Width, Height, and Resolution option boxes show the size and resolution of this image. Otherwise, you can enter your own values in one of five units of measure- ment: pixels, inches, centimeters, picas, or points. If you’re uncertain exactly what size image you want to create, enter a rough approximation. You can always change your settings later. Figure 3-4: Use the New dialog box to specify the size, resolution, and color mode of your new image. Although Photoshop matches the contents of the Clipboard by default, you can also match the size and resolution of other images: ✦ Press Alt when choosing File➪ New, or press Ctrl+Alt+N to override the contents of the Clipboard. Photoshop displays the size and resolution of the last image you created, whether or not it came from the Clipboard. Use this technique when creating many same-sized images in a row. ✦ You can also match the size and resolution of the new image to any other open image. While the New dialog box is open, choose the name of the image you want to match from the Window menu. It’s that simple. Units of measure The Width and Height pop-up menus contain the five common units of measure mentioned earlier: pixels, inches, centimeters, points, and picas. But the Width pop-up menu offers one more, called Columns. If you want to create an image that fits exactly within a certain number of columns when it’s imported into a desktop publishing program, select this option. You can specify the width of a column and the gutter between columns by pressing Ctrl+K and Ctrl+5 to display the Units & Rulers preferences. Then enter values into the Column Size option boxes. Tip 76 Part I ✦ Welcome to Photoshop 6 The Gutter value affects multiple-column images. Suppose you accept the default setting of a 15-pica column width and a 1-pica gutter. If you specify a one-column image in the New dialog box, Photoshop makes it 15 picas wide. If you ask for a two-column image, Photoshop adds the width of the gutter to the width of the two columns and creates an image 31 picas wide. The Height pop-up menu in the New dialog box lacks a Column option because vertical columns have nothing to do with an image’s height. You can set the default unit of measurement for the Width and Height pop-up menus in the Units & Rulers panel of the Preferences dialog box. (Select the value from the Rulers pop-up menu; the Type menu sets the measurement unit for text-related controls.) But if the dialog box isn’t already open, here are two quicker options: ✦ Press Ctrl+R to display the rulers and then right-click anywhere in the rulers to display a pop-up menu of units. Click the unit you want to use. ✦ Display the same pop-up menu by pressing F8 to display the Info palette and then clicking or dragging on the cross icon (next to the X and Y coordinate values) in the palette’s lower-left corner. Again, just click the unit you prefer. New image size In most cases, the on-screen dimensions of an image depend on your entries in the Width, Height, and Resolution option boxes. If you set both the Width and Height values to 10 inches and the Resolution to 72 ppi, the new image will measure 720× 720 pixels. The exception occurs if you choose pixels as your unit of measurement. In this case, the on-screen dimensions depend solely on the Width and Height options, and the Resolution value determines the size at which the image prints. Color mode Use the Mode pop-up menu to specify the number of colors that can appear in your image. Choose Bitmap to create a black-and-white image and choose Grayscale to access only gray values. RGB Color, CMYK Color, and Lab Color all provide access to the full range of 16 million colors, although their methods of doing so differ. RGB stands for red-green-blue, CMYK for cyan-magenta-yellow-black, and Lab for luminosity and two abstract color variables: a and b. To learn how each of these color modes works, read the “Working in Different Color Modes” section of Chapter 4. Background color The New dialog box also provides three Contents radio buttons that enable you to change the color of the background for the new image. You can fill the new image with white, with the current background color (assuming, of course, that the back- ground color is something other than white), or with no color at all. This last setting, Transparent, results in a floating layer with no background image whatsoever, which can be useful when editing one layer independently of the rest of an image or when preparing a layer to be composited with an image. (For an in-depth examination of the more nitty-gritty aspects of layering, see Chapter 12.) Cross- Reference 6 Photoshop 6 Tip 77 Chapter 3 ✦ Image Fundamentals If you do select a transparent background, you must later flatten the layer by choosing Layer ➪ Flatten Image if you want to save the image to a format that doesn’t support layers (see the upcoming discussion “Saving an image to disk” for information about new options for retaining layers when saving). The advantage of the Transparent setting, however, is that Photoshop doesn’t create a new layer when you press Ctrl+V to paste the contents of the Clipboard. In the long run, you don’t gain much —you still must flatten the image before you save it to some formats —but at least you needn’t fuss with two layers, one of which is completely empty. Incidentally, just because you create an image with a transparent background doesn’t mean that you can automatically import a free-form image with transparency intact into an object-oriented program such as Illustrator or QuarkXPress. To carve a trans- parent area out of the naturally rectangular boundaries of an image, you have to use the pen tool to create a clipping path. I explain how in the “Retaining transparent areas in an image” section of Chapter 8. Naming the new image The New dialog box provides a Name option. If you know what you want to call your new image, enter the name now. Or don’t. It doesn’t matter. Either way, when you choose File ➪ Save, Photoshop asks you to specify the location of the file and confirm the file’s name. So don’t feel compelled to name your image anything. The only reason for this option is to help you keep your images organized on screen. Lots of folks create temporary images they never save; Photoshop offers a way to assign temporary images more meaningful names than Untitled-4, Untitled-5, Untitled-6, and so on. Unlike some traditionalists, I whole-heartedly endorse using long files names under Windows 95, NT 4, and later. But naturally you should be aware of the implications. If you send a file to someone using Windows 3.1, DOS, or some other ancient operating system, the long file name gets truncated to eight characters with a tilde symbol (~) and number. (You can view the truncated DOS-style name at the desktop by right-clicking on the file and choosing Properties.) This can also happen when exchanging files with Macintosh users, depending on how you do it. If you give a Mac artist a PC-formatted floppy disk, Zip disk, or the like, the file names get the ax when the disk is popped into the Mac. But if you network your PC to a Mac using Miramar Systems’ (www.miramarsys.com) PC MACLAN or the like, the long file names come through swimmingly. In fact, this is precisely how I exchange files over my own cross-platform Ethernet LAN. Opening an existing image Photoshop 6 provides a new File menu command, Open Recent, which displays a list of the images you worked on in recent Photoshop sessions. Click the name of the image you want to open. You set the number of files that appear on the list by entering a value in the Recent File List Contains option box, found on the Saving Files panel of the Preferences dialog box (Ctrl+K and then Ctrl+2). The maximum value is 30. 6 Photoshop 6 Caution Cross- Reference 78 Part I ✦ Welcome to Photoshop 6 Of course, you can always open images the old-fashioned way, by choosing File ➪ Open or pressing its keyboard shortcut, Ctrl+O, to display the Open dialog box. You also can double-click an empty spot in the Photoshop program window to open the dialog box. The Open dialog box behaves just like the ones in other Windows applications, with a folder bar at top, a scrolling list of files, and the usual file management and navigation options. You can also open multiple files at one time. To select a range of files, click the first file name and Shift-click the last file in the range. Ctrl-click to add a single file to the group you want to open. Ctrl-click again to deselect a file from the group. The Photoshop Open dialog box also includes a few controls that most other programs lack. You can read about these options in the next sections. But first, two other brief notes about opening files in Version 6: ✦ When you choose File ➪ Open, Photoshop displays the folder that contained the last file you opened. Similarly, when you save a file, the folder to which you saved last is selected automatically. ✦ When you open an image, Photoshop may display a dialog box telling you that the color profile of the image doesn’t match the default color profile you’ve established. You have the option of converting the image to the default profile or leaving well enough alone. See Chapter 16 for help with this issue. Viewing the thumbnail To help you assess an image before you open it, Photoshop displays a thumbnail preview of the selected file at the bottom of the Open dialog box, as shown in Figure 3-5. In Version 6, Photoshop displays thumbnails for any files saved in the native format (PSD). If you’re running Windows 98 or Windows 2000, the operating system may generate thumbnails for files saved in other formats. To generate thumbnails when saving images in Photoshop, press Ctrl+K, Ctrl+2 to display the Saving Files panel of the Preferences dialog box. Then set the Image Previews pop-up menu to Always Save or Ask When Saving, as discussed in Chapter 2. If you select Ask When Saving, Photoshop gives you the option of adding a thumbnail to the image inside the Save dialog box. If you’ve received images from Macintosh users in the past, you’ve probably wondered why the heck they saved their files without previews. The truth is, they couldn’t. See, Photoshop for the Mac saves thumbnails in the so-called resource fork of the file, but Windows programs can’t even see the resource fork, much less translate it. Fortunately for all, both versions of Photoshop can save Windows thumbnails. On the Mac, the Saving Files panel of the Preferences dialog box contains a check box called Windows Thumbnail. When turned on, a thumbnail is added to the data fork of the file, which translates to Windows fully intact. Note 6 Photoshop 6 6 Photoshop 6 79 Chapter 3 ✦ Image Fundamentals Figure 3-5: You can see a preview of an image if you previously saved it in Photoshop with the thumbnails option enabled. Sadly, thumbnails don’t work in the other direction. Because Windows doesn’t recognize the resource fork, Photoshop for Windows can’t save a Macintosh-style thumbnail. And because Photoshop on the Mac relies on Apple’s QuickTime to interpret thumbnails, it can’t see data-fork thumbnails. Dang. Previewing outside Photoshop Under Windows 95 and later, the Open dialog box isn’t the only place you can preview an image before you open it. In fact, provided you save the image in the native Photoshop (.psd) format, you can peek at an image without even opening the program. Right-click a file with a .psd extension —either at the desktop, in a folder window, or in Windows Explorer — and choose Properties from the pop-up menu. When the Properties dialog box opens, click the Photoshop Image tab to look at your image, as shown in Figure 3-6. Again, you must have saved a thumbnail preview along with the image for this feature to work. Tip [...]... Resource, TIFF, and DCS 2. 0 — support extra channels ✦ Spot Colors: Did you create an image that incorporates spot colors? If so, select this option to retain the spot color channels in the saved image file You must save the file in the native Photoshop, PDF, TIFF, or DCS 2. 0 format to use this option ✦ Layers: In Version 6, TIFF and PDF can retain independent image layers, as can the native Photoshop format... Filter ➪ Distort ➪ Displace, you have to create a Photoshop 2. 0–compatible file The best bet is to save the image in the Photoshop 2. 0 format Otherwise the Displace filter won’t see the grayscale image I tell you more about this filter in Chapter A on the CD-ROM that accompanies this book 85 86 Part I ✦ Welcome to Photoshop 6 Special-purpose formats With 20 file formats to choose from, you can imagine... technique enables you to spot defects that may not be noticeable in draft proofs that you output on a low-res printer 89 90 Photoshop Part I ✦ Welcome to Photoshop 6 6 ✦ You need a convenient way to distribute images for approval or input You can save an image as a PDF file and send it to clients and colleagues, who can view the image in Acrobat if they don’t have Photoshop In Photoshop 6, you can even add... Image ➪ Mode ➪ CMYK Color (DCS 2. 0 also supports grayscale images with spot-color channels.) Then bring up the Save dialog box and select Photoshop DCS 1.0 or 2. 0 from the Format pop-up menu Photoshop 5 introduced support for DCS 2. 0 to accommodate images that contain extra spot-color channels, as explained in Chapter 18 If you add a Pantone channel to an image, DCS 2. 0 is the only PostScript format... black-and-white printer, select the 72 pixel/inch grayscale option; if you’re using a color printer, select the final option Be forewarned, however, that the composite image significantly increases the size of the master document on disk 97 98 Part I ✦ Welcome to Photoshop 6 Photoshop Figure 3- 12: The extra options for the DCS 1.0 format (top) and those for the DCS 2. 0 format (bottom) 6 Notice the two new options... does the least damage 101 1 02 Part I ✦ Welcome to Photoshop 6 Figure 3-14: The JPEG Options dialog box provides a total of 12 compression settings, ranging from 0 (heaviest compression) to 12 (best quality) Note JPEG evaluates an image in 8 × 8-pixel blocks, using a technique called Adaptive Discrete Cosine Transform (or ADCT, as in “Yes, I’m an acronym ADCT”) It averages the 24 -bit value of every pixel... compression, you can spot other people’s overly compressed JPEG images a mile away This isn’t something you want to exaggerate in your images Maximum 66 K High 50K Medium 33K Low 28 K Figure 3-15: Four JPEG settings applied to a single image, with the highest image quality setting illustrated at the upper left and the lowest at the bottom right 103 104 Part I ✦ Welcome to Photoshop 6 CrossReference Caution... special In Photoshop, the TIFF format supports up to 24 channels, the maximum number permitted in any image In fact, TIFF is the only format other than DCS 2. 0, “raw,” and the native Photoshop format that can save more than four channels To save a TIFF file without extra mask channels, deselect the Alpha check box in the Save dialog box (For an introduction to channels, read Chapter 16. ) Photoshop Chapter... file In addition to annotations, Photoshop PDF supports layers, transparency, embedded color profiles, spot colors, duotones, and more This enables you to route an image for approval without having to flatten the image or otherwise strip it of its Photoshop 6 features Of course, features not supported by Acrobat aren’t accessible to the viewer When you save to PDF in Photoshop, you have a choice of... details Photoshop ✦ PostScript Color Management: Like JPEG compression, this check box is compatible with Level 2 and 3 printers only It embeds a color profile, which helps the printer to massage the image during the printing cycle to generate more accurate colors Unless you plan on printing to a Level 2 or later device, leave the option off (For more information about color profiles, read Chapter 16. ) 6 . to be as streamlined as possible, and that means shaving away the preview. 6 Photoshop 6 6 Photoshop 6 Tip 6 Photoshop 6 83 Chapter 3 ✦ Image Fundamentals Choosing other save options Certain save. Windows fully intact. Note 6 Photoshop 6 6 Photoshop 6 79 Chapter 3 ✦ Image Fundamentals Figure 3-5: You can see a preview of an image if you previously saved it in Photoshop with the thumbnails. Preferences dialog box (Ctrl+K and then Ctrl +2) . The maximum value is 30. 6 Photoshop 6 Caution Cross- Reference 78 Part I ✦ Welcome to Photoshop 6 Of course, you can always open images the old-fashioned