Bitmap Versus Vector Images Line art can be categorized as either a bitmap or vector image. A bitmap image (sometimes called a raster) is created from differently colored rows of pixels. Figures 6-6 and 6-7 provide an illustration of how a bitmap image works. The image that appears on your computer monitor is a bitmap. A vector image is constructed using complex mathematical formulas that describe shape, color, and placement. A vector image doesn’t consist of dots. It’s made of curves, lines, and other shapes, defined with mathematical precision. It’s the job of the graphic artist to combine the shapes to get the desired image. FIGURE 6-6 A bitmap image at the resolution it’s normally viewed at CHAPTER 6: Scanning Techniques for Different Types of Images 109 Please purchase PDF Split-Merge on www.verypdf.com to remove this watermark. FIGURE 6-7 An enlarged image showing the rows of pixels that make up the image You can convert a vector file into a bitmap file. Doing so will save some space, because vector files are generally much smaller than bitmap files. Vector files are often used for line art, but aren’t appropriate for reproducing complex images such as photos. On the other hand, it’s very difficult to convert a bitmap file to a vector file, but most likely you won’t want to. Vector files are often used for line art because they are easier to alter than bitmap files. Bitmap files can appear jagged if you enlarge them, or fuzzy if you shrink them, while vector files are easy to resize because the mathematical proportions that make up the various shapes are precisely changed. 110 How to Do Everything with Your Scanner Please purchase PDF Split-Merge on www.verypdf.com to remove this watermark. Produce High-Quality Grayscale Images A grayscale image is one that’s made of continuous shades of gray, ranging from pure black to pure white. The photos of Ansel Adams are good examples of grayscale. Adams was famous for his ability to capture subtle detail and shadows. This effect is achieved by reproducing hundreds of different shades of gray. The more shades of gray that can be produced, the more detailed a grayscale image. Figure 6-8 is an example of an image captured using a setting that reproduces 256 shades of gray. FIGURE 6-8 An image capturing 256 shades of gray CHAPTER 6: Scanning Techniques for Different Types of Images 111 Please purchase PDF Split-Merge on www.verypdf.com to remove this watermark. When scanning a grayscale image, use the grayscale setting on your scanner. If you’re planning on printing the image, scan at a resolution setting of 150 to 300 spi (or samples per inch). Opt for something at the higher end of that range if you’re planning on enlarging the photo. If you plan to view the image only on the Web, scan at a lower resolution of 72 to 75 spi, or 96 dpi. A higher resolution will increase file size considerably, without producing a noticeably better result on screen. Capture Vibrant Color Images Today’s scanners and printers allow you to create vivid color prints. To scan color images successfully, you need to pay attention to both the resolution and color-capture settings of your printer. Rules of thumb for color resolution are similar to those for grayscale. If you’re planning on printing a color photo, scan at a resolution setting of 150 to 300 spi. If you’re planning to enlarge the photo or reproduce it in a publication, don’t scan at a lower resolution than 300 spi. For Web images, scan at a resolution of 72 to 75 spi, or 96 dpi. A higher resolution will increase file size, without producing a better result on screen. Your scanner might offer several different capture settings for color photos, including true color, 256 color, and spot color. All these settings serve distinct color-capture functions. Maximize Quality with the True-Color Setting This setting is capable of producing 16,777,216 colors, referred to as 16.7 million colors. This is sometimes referred to as 24-bit color. Of course, the human eye cannot discern anywhere near 16 million colors, and this option might result in unnecessarily large files. Use this format only when you need to store as much image data as possible. Optimize Your 256-Color Images The 256-color setting, sometimes referred to as 8-bit color, allows you to capture up to 256 colors. Your scanner might have the following selections under this choice: Web Palette This setting uses a 216-color format that can be displayed by all Web browser software. Web browser software is the program on your computer that allows you to view images sent over the Internet. 112 How to Do Everything with Your Scanner Please purchase PDF Split-Merge on www.verypdf.com to remove this watermark. System Palette This option uses the 240 colors used by the Windows program. It’s meant for images that will be displayed using a Windows-based program. Optimized Palette This option creates a set of the best possible 256 colors to represent your image to its best advantage. It selects from the 16,777,216 true colors that are available. This option is often associated with GIF or other fixed- palette image formats restricted to 256 colors. By optimizing an image’s palette colors, only the minimum number of colors needed to reproduce the image are stored in the palette of the image file. For example, if only two are required, only two are stored. Save File Space with the Spot-Color Option The spot-color setting scans a limited range of colors. Solid colors are represented as single color data, rather than a gradation of hues. Spot color is great for scanning logos and graphics with limited color. Working with Half-Tone Images Laser printers and many commercial printing presses reproduce images such as grayscale and color photographs (sometimes called continuous-toned images) using a technique called half-toning. Why You Need to Know about Half-Toning Although half-toning can be done during the scanning process, it’s usually a function performed by your printer. Most color printers have sophisticated drivers that perform the process; however, you need to be aware that image data is reordered and discarded in the process of creating a half-tone (printable) image from a continuous-toned color photograph or grayscale piece. As image detail and complexity increases, there might be a trade off between the amount of color data that can be saved and the resolution of the photo. Images are divided into half-tone cells, each of which contains an appropriate number of color dots. The more dots than can be stored per cell, the more color combinations that can be produced. As you use printer dots to create color combinations, however, you decrease the amount of printer dots available to re-create other image detail. Thus, the increased color quality can decrease the overall resolution of the image, making it appear grainy. CHAPTER 6: Scanning Techniques for Different Types of Images 113 Please purchase PDF Split-Merge on www.verypdf.com to remove this watermark. . the program on your computer that allows you to view images sent over the Internet. 112 How to Do Everything with Your Scanner Please purchase PDF Split-Merge on www.verypdf.com to remove this. shrink them, while vector files are easy to resize because the mathematical proportions that make up the various shapes are precisely changed. 110 How to Do Everything with Your Scanner Please. you need to store as much image data as possible. Optimize Your 256-Color Images The 256-color setting, sometimes referred to as 8-bit color, allows you to capture up to 256 colors. Your scanner