THE GIMP Bible PHẦN 2 ppt

Part I: Meet GIMP 3. With your mouse hovered over the action, press the shortcut you want to use. 4. Get out of the menu and enjoy the use of your new keyboard shortcut. Woohoo! Of course, that’s a kind of ‘‘quick ‘n’ dirty’’ way of assigning keyboard shortcuts. There is another way that has its own dialog. To access it, click Edit  Keyboard Shortcuts. When you do that, you’ll get a dialog like the one in Figure 1-25. FIGURE 1-25 The Configure Keyboard Shortcuts dialog Using this dialog is pretty simple. Just navigate through the available actions or use the search bar at the top to type in the name of a specific action you’re looking for. Then, when you find the action that you want, left-click it, and the item in the Shortcut column will say ‘‘New accel- erator ’’ When you see that, press the new keyboard shortcut that you want to use and it is instantly applied. One of the nice things about using this interface to configure your short- cuts rather than the dynamic keyboard shortcuts is that this dialog will notify you if the shortcut you’re trying to apply is already in use. Keeping you aware of conflicts helps ensure that you don’t accidentally supplant another shortcut that you use more often. 38 Chapter 1: What Is GIMP? Summary GIMP is heavy-hitting Free Software that, despite the assertions of some detractors, is a popular and effective tool for digital artists. This chapter’s purpose was to let you hit the ground running and not only get familiar with GIMP’s capabilities, but also start getting to know its interface. The goal here is to get you familiar with GIMP and to get GIMP familiar with you by way of customizing it to work with you rather than against you. Onward! 39 Thinking Digitally IN THIS CHAPTER Comparing digital images to traditional photographs Understanding the difference between types of digital images Working with the attributes of digital images B efore getting knee-deep in all of the detailed ins and outs of GIMP, it’s well worth your time to familiarize yourself with some of the details and terminology of digital media. If you’re a seasoned pro- fessional, much of this chapter might be a review for you. However, it never hurts to have a good reference that you can point to as a refresher or as a means of explaining things to someone else. As with any other creative medium, the more you know about how digi- tal imagery works, the more you can take advantage of its strengths and circumvent its deficiencies. You may even be able to find novel ways of using its perceived shortcomings to your advantage. Fortunately, there aren’t so many differences between digital work and traditional, meatspace (what some people refer to as ‘‘the real world’’) work. Digital graphics borrows a lot of terminology from the analog world and quite a few techniques have been ported to our digital realm. And these days it’s extremely common for artists to shift from analog to digital almost seamlessly, using the most effec- tive tools in each medium to create images that would be difficult to create in either one by itself. This is especially true in commercial photography and illustration where deadlines are tight and efficiency is paramount. By the time you finish this chapter, you should have a fairly complete under- standing of what goes into a digital image as well as the differences between different digital graphic types. Have at it! Digital Images vs. Traditional Photographs What’s the difference between a digital photograph and a traditional photograph that’s developed on film? Well, an obvious answer would be that 41 Part I: Meet GIMP you typically view the former on a screen and the latter on paper. However, it goes a lot further than that. From a purely visual standpoint, traditional photographs seem to have a lot more to offer than their digital counterparts. The reason for this has a lot to do with how the images are captured and stored. In film media, you’re literally capturing light and chemically recording it to acetate. An incredibly immense amount of light information is captured this way, including some things not immediately visible to the naked eye because of an overabundance or deficit of light. Once the film negative has been developed, you can use it (within reason) to reveal some of those difficult-to-see parts. Furthermore, because you’ve recorded the light, it’s pretty easy to enlarge an image to a size many times larger than the size of the negative without degrading the quality of that image. Digital photos are different. For one, the sensors on digital cameras generally capture a smaller range of light than film does, so it’s more difficult to reveal hidden detail in an image. Another difference is that digital images are, well, digitized. That is, where traditional film captures and records raw light information, digital cameras record samples of that light information. Two sorts of sampling take place. The first type deals with the area of the image itself. In digital images, the entire image area is divided into a grid. Each block in the grid is defined as a pixel, or ‘‘picture element.’’ That pixel stores only one thing: a single color. Then for each of these pixels, the color itself is a sample of possible colors within a finite range. This range of colors is referred to as the bit depth of the image and though the size and granularity of that range can be somewhat refined by increasing the bit depth, digital images are still limited to a much smaller range than traditional photographs. Figure 2-1 illustrates how a digital image is sampled into pixels of a finite number of colors. FIGURE 2-1 Digital images are sampled into a grid of pixels, each storing a single color defined by the image’s bit depth. (Photo credit: Chris Hoyer) 42 Chapter 2: Thinking Digitally All of this adds up to mean that it’s more difficult to drastically increase the size of an image, and it’s often impossible to pull a ‘‘hidden’’ image out of an over- or under-exposed portion of a photograph. If part of your image is white because it’s blown out, those white pixels are white pixels and there’s no way to pull more definition out of that. Now, digital cameras have improved and are continuing to improve to increase the size of the available image area. This is the megapixel rating that most cameras advertise. A megapixel is one million pixels, so a camera that can take an image that is 1280 x 1024 pixels in size is a 1.3 megapixel (1280 x 1024 = 1,310,720) camera. These days, most good-quality digital cam- eras can take in excess of 10-megapixel images and even cameras on mobile phones can take 3.2-megapixel images. To deal with the issue of limited bit depth in digital images, a relatively new technology called high dynamic range, or HDR, has grown in popularity. The technique starts by taking a series of photos where you bracket the exposures. That is, you take the photo at a base exposure that you consider to be normal, and then take one or more photos in both shorter and longer exposure times. Bracketing is actually a technique that traditional film photographers have used for years because film cameras don’t have an LCD screen to give you the instant feedback that digital cam- eras do. Photographers compensated by bracketing their shots around the exposure that they thought was correct. Digital photographers use this same technique, but instead of throwing out the extra exposures, they use the whole set of bracketed images. Using this range of images, you can capture a larger range of the available light than the camera’s sensor can take in a single shot. Incidentally, it’s also a higher range than what can be displayed on a typical computer monitor. With a bit of adjustment, though, you can use these images together in a process called tone mapping to create an image that shows better than visible detail. All of this editing and adjust- ment can be done in GIMP. However, it’s not uncommon for these images to be packed into a single HDR file format such as DPX or OpenEXR, and unfortunately at this time GIMP can- not read these files natively. Figure 2-2 compares a normal exposure photograph with one that’s been treated with HDR. I go more into using this bracketing technique in Chapter 9. FIGURE 2-2 On the left is an image taken with a single exposure and on the right is the same image tone mapped with bracketed exposures. (Photo credit: Chris Hoyer) 43 Part I: Meet GIMP Although digital images have these shortcomings, their digitized nature offers some advantages over traditional photographs. The most readily noticeable of them is the instant nature of digital photography. There’s no need to wait for the film to develop or to risk losing all of your images to mistakes in the darkroom. Additionally, digital images can be stored, copied, and archived multiple times on a variety of digital storage media such as hard drives, CD-ROMs, and USB thumbdrives without further degradation to image quality. This means that they can last much, much longer than film images, which are subject to the problems of aging. It also makes it a lot easier for you to share, modify, and reuse images for purposes ranging from simple scrapbooking to putting your friend’s face on video footage of a famous celebrity. Raster Graphics vs. Vector Graphics In the previous section, you started to learn about the differences between traditional pho- tographs and digital images. However, it doesn’t stop there. When it comes to digital images, there are actually two classifications: raster images and vector images. Both of these image types output in pixels to your computer monitor or to a printer, but that’s about the only similarity. Raster Images Raster images are what most people are familiar with. In their rawest form, they’re described as a bitmap; each pixel in the image has its own color and that color is mapped to a grid that forms the full size of the image. This is what’s described in Figure 2-1 and is the type of image that gets created by digital cameras. Raster images are at their best when you have high-detail images with large variations in color. For this reason, they’re particularly good when you need an image that looks natural or realistic. Because raster images can have a high level of variety, it feels very natural to draw and paint. You have paint strokes that can have nearly unlimited variety. At its core, GIMP is designed to edit raster images. The downside is that these images are difficult to increase in size or reuse output for media other than screen or print. Some resampling algorithms can help, but once you pass a certain thresh- old, the image becomes excessively blocky, or pixelated. This is because of the finite nature of pixels. The best you can do to upscale an image is increase the size of each pixel. Of course, you can compensate for this by starting with really large images (hence the reason why camera manu- facturers have been racing for higher and higher megapixel ratings), but the trade-off here is that these large images end up taking a large amount of hard drive space and become increasingly time-consuming for the computer to process. To this end, when working in GIMP it’s in your best interest to consider the final output medium of your image ahead of time. It’s very frustrating to spend hours modifying an image with a size that’s best suited for a postcard only to find out that it’s supposed to go on a billboard. Vector Images In contrast to rasters, vector images are described and stored more procedurally as a sum of mathematical functions. When you want to see what the image is, the computer translates those 44 Chapter 2: Thinking Digitally functions to fit whatever pixel size you stipulate. And because you’re just storing the mathemati- cal functions, the amount of disk space that a vector image takes up can be incredibly small. The reasons previously discussed make vector images an excellent choice when you have an image that has to look good regardless of size or output. Vectors can easily be scaled to any size with no noticeable degradation of quality. You can use the same vector image on letterheads, bill- boards, or even embroidered on a shirt. It’s for this very reason that the majority of company logos and illustrations are created with vector drawing tools. Figure 2-3 compares what happens when you scale up a raster image versus when you scale up a vector image. FIGURE 2-3 Scaling a raster image (left) produces pixelated results, whereas scaling a vector image (right) keeps edges and colors crisp and clean. (Photo credit: Melody Smith; Image credit: gopher on openclipart.org) The unfortunate thing about vector graphics is that they don’t have nearly the same capacity as raster images to store images with a lot of color variation. The more variation that you add to an image, the less efficient a vector image becomes and you start running into a point of dimin- ishing returns on the advantages that vectors give you. If you were to attempt to get the same color variation of a raster image in a vector format, you would quickly notice that the file size becomes unmanageably large and your computer takes excessive amounts of time to process the image. This is because the math becomes a lot more complex with that much variation and the computer still has to translate all of those functions on the fly. What often happens is that the high-variation image looks banded or posterized when you try to use a vector format. Figure 2-4 shows what a vector image looks like when you try to include a lot of color variation. In a nutshell, the best times to use raster tools are for images with high color variety like pho- tographs and high-color paintings. Vector tools are best suited for images with a limited number 45 Part I: Meet GIMP of defined colors and a need to scale to any size, such as logos. Although GIMP is primarily a raster graphics application, it can import vector images and convert them into raster images for further refinement. Additionally, GIMP’s paths and its text tool are actually vector-based. This makes it incredibly easy to edit and reuse these elements without drastically increasing file size. Chapters 5 and 10, respectively, cover these tools in greater detail. FIGURE 2-4 A raster image converted to vector. Notice how the colors get flattened out and simplified. (Photo credit: Melody Smith) Resolution and Image Size One of the things that even some seasoned artists get mixed up is the difference between image size and image resolution. To put it simply, a digital image’s size refers to its exact dimensions in real-world units, whereas the resolution attempts to relate those real-world units to the pixel size of that image. Real-world units include standard measurements like inches and millimeters, but they also include typographical units like points and picas. They can actually even include pixels if your final output is destined for a web site or computer monitor. Resolution is typically defined by a pixels per inch, or ppi, value. Modern computer monitors tend to have a standard ppi that they display best. Usually that range is between 72 and 100ppi and the monitor’s drivers report that resolution to your computer’s operating system. For older monitors that don’t do this or for standard-definition television, the convention is to use 72ppi. For print, the conventions are a bit more varied. High-quality printing, like what is used for magazine covers and photographs, is typically done at 300ppi or higher. The typical low 46 Chapter 2: Thinking Digitally bar for professional printing is at about 150ppi, but this is used only if you know that the print quality of the final output can’t exceed a certain level, such as with newspaper printers. What this all boils down to is that if you want to have a high-quality print of your digital image at 9 x 12 inches, the image size should be no less than 2700 x 3600 pixels (9’’ x 300ppi = 2700px; 12’’ x 300ppi = 3600px). By default, GIMP includes the image size in pixels in the title bar of the image window. As explained in Chapter 1, you can customize this as well as the status bar of the image window by going to the Title & Status section of the Preferences dialog (Edit  Preferences  Image Windows  Title & Status). For a more complete view of the size and resolution of any given image in GIMP, use the Image Properties dialog, as shown in Figure 2-5, by clicking Image  Image Properties in the menu or pressing Alt+Enter. FIGURE 2-5 The Image Properties dialog. The image’s size and resolution are shown in the first three values listed. Tip In GIMP, if you need to use non-pixel units like inches, millimeters, or picas, it’s recommended that you disable Dot for Dot from the View menu (View  Dot for Dot). The Dot for Dot feature makes a pixel in your image the same size as a pixel on your monitor. When you’re just working in pixels, this is great. However, assume you’re working on a print image with a resolution of 300ppi. This resolution is higher than your monitor natively displays, so if you have Dot for Dot enabled, the image at 100% will appear larger than its actual print size. If you disable Dot for Dot, then GIMP adjusts the image’s display resolution so what appears on-screen matches the size of what gets printed.  Changing Image Size and Resolution When you create a new image in GIMP (File  New or Ctrl+N), you have to set the size and resolution of your image before you actually get started on your work. While you’re working, it’s not uncommon for specifications to change, so you may need to change your image’s size 47 [...]... attempt to force that to be the file’s type This is a pretty useful function However, more often than not, if GIMP can’t read the image file, it’s either in a format GIMP doesn’t understand or the file itself is corrupted FIGURE 3-4 The Select File Type panel at the bottom of the Open File dialog, expanded Other Ways to Open an Image Besides using the File Open function, GIMP has a few other pretty slick ways... off of the menu, so there’s no way you could bring up the menu and then go into GIMP and try to take an immediate screenshot To do that, you need to use the Delay feature of the Screenshot tool Simply increase the number in the Delay field to the number of seconds you would like GIMP to wait before taking the screenshot Normally, 5 seconds is more than enough time Then when you click the Snap button, you’ll... notice that, other than the folder icon, GIMP shows either an icon that looks like a sheet of paper or a thumbnail of the image Initially, GIMP may not show a thumbnail for any of the images in a given folder However, if you click an image file, GIMP generates a preview of the image and displays it in the Preview panel to the right, along with some statistical information, such as its file size, the image’s... each holding either a one or zero GIMP uses a combination of 8 of these bits to define a channel This means that there are 28 , or 25 6, different combinations per channel Or stated in another way, there are 25 6 levels of intensity for each of the red, green, and blue channels This may not seem like a very large number, but consider the fact that your colors are based on a combination of these three channels... want to set the resolution to something higher, like 300ppi Resolution is not one of the options available to you in the basic New Image dialog To control that and other options, you need to expand the Advanced Options at the bottom of the dialog by clicking its arrow Figure 3-8 shows the New Image dialog with the Advanced Options visible The first thing you can control with these options is the image’s... color depth 1.3-megapixel images have 1,310, 720 pixels ( 128 0 x 1 024 = 1,310, 720 ) Each pixel has a color that’s stored by 24 bits (8 bits x 3 color channels = 24 ) This means that to store that image in a simple bitmap form takes about 3.75 megabytes (24 bits x 1,310, 720 pixels = 31,457 ,28 0 bits and 31,457 ,28 0 bits / 8 bits per byte / 1 024 bytes per kilobyte / 1 024 kilobytes per megabyte = 3.75 MB) That... breadcrumb to your path at the top of the dialog To add a bookmark in the Places panel, simply left-click the folder you want to add the Current Folder panel and click the Add button beneath the Places panel Alternatively, you can right-click that folder and choose Add to Bookmarks from the context menu that pops up Once you have the bookmark added to the Places panel, you have the ability to give it a... simply use it The only colors available to you are the ones that are defined by that color mode When you take an RGB image and change its color mode to Grayscale or Indexed, GIMP will do a conversion to that new mode In the case of Grayscale, it happens automatically For the Indexed color mode, however, GIMP pops up the dialog shown in Figure 2- 9 to facilitate the conversion FIGURE 2- 9 The Convert Image... from the Current Folder panel, simply double-click it or click the Open button in the bottom-right corner of the dialog You can also select more than one file in the Current Folder dialog by holding Ctrl and clicking the files you want to select GIMP also allows you to select a series of images by clicking the first image in the series and then holding Shift 64 Chapter 3: Working with Files and clicking the. .. how the Current Folder panel sorts its listing By default, it’s sorted in ascending alphabetical order (0, 1, 2 A, B, C ) and you can tell this from the downward-pointing triangle next to Name at the top of the panel If you click Name, the arrow reverses direction and the files are sorted in reverse alphabetical order You can also click the Modified button to sort the files by the date that they . x 12 inches, the image size should be no less than 27 00 x 3600 pixels (9’’ x 300ppi = 27 00px; 12 ’ x 300ppi = 3600px). By default, GIMP includes the image size in pixels in the title bar of the. or zero. GIMP uses a com- bination of 8 of these bits to define a channel. This means that there are 2 8 , or 25 6, different combinations per channel. Or stated in another way, there are 25 6 levels. new mode. In the case of Grayscale, it happens automatically. For the Indexed color mode, however, GIMP pops up the dialog shown in Figure 2- 9 to facilitate the conversion. FIGURE 2- 9 The Convert