Be Sure to Look at the Optical Resolution of a Scanner Optical resolution is the most commonly used specification to compare the capabilities of different scanners. It refers to how many pixels, dots, or samples per inch the scanner’s sensors can detect. Generally, the higher the resolution, the better the quality of the scanned image. Low-end scanners have a resolution of 300 ppi, while high-end scanners can detect as many as 4,000 ppi. The 300-ppi variety will provide adequate resolution for computer-screen images, since most computer graphics cards can’t handle much more detail than this. (You can learn more about how a graphics card functions in Chapter 4.) On the other hand, if your objective is a nice copy from a laser or color printer, the results from a scanner with a 300-ppi optical resolution are likely to disappoint you. A 400 to 600 resolution will probably give you the quality you’re looking for in a printed copy. Optical resolution is most important when you need to print good-quality photos to include in publications such as books, magazines, newsletters, or scrapbooks. If you need good-quality printed photos, choose as high a resolution as you can afford. Economize with a lower optical resolution if you’re producing images to be viewed on a computer monitor or in PowerPoint presentations. Avoid Comparisons of Interpolated Resolution Suppose you have a choice of two scanners in your price range, one advertising a resolution of 300 dpi (or spi or ppi) and another boasting a 600-ppi resolution. The 600-ppi resolution is a better deal, right? Not necessarily. A recent trend has been for manufacturers to market their scanners based on interpolated, or software-enhanced, resolution. Based on some technical guesswork, interpolation uses a mathematical algorithm to add more pixels to the ones the scanner has sampled with its sensors. The result is an image with more pixels or dots per inch, but not necessarily more accuracy as to detail. Interpolated resolution produces good results for images on the Web, but is less satisfactory for scanning photographs for archiving or publication. Generally, it is not a good option if you need to scan negatives, since negatives require a resolution capability of at least 1,200 ppi. 34 How to Do Everything with Your Scanner Please purchase PDF Split-Merge on www.verypdf.com to remove this watermark. When comparing the resolution of various scanners in your price range, make sure you’re comparing apples to apples. Do not compare the optical resolution of one model to the interpolated resolution specifications of another. Testing the Tonal Sensitivity Not all 30-bit scanners are created equal. A scanner might be able to detect a large number of colors, but over a relatively narrow range. Also, bit depth doesn’t tell you how well scanners distinguish among similar shades. This is called tonal sensitivity, and is not disclosed by manufacturers. Generally, high-end, more expensive scanners exhibit greater tonal sensitivity. You can evaluate the tonal sensitivity of different scanners by comparing the scanning results using the same original. Skin tones are particularly useful for comparing tonal sensitivity between scanner models. Certain models of scanners often cast a slight greenish tinge to skin tones, which can significantly alter the appearance of your subject. Read the Manufacturer’s Resolution Rating When you check the optical resolution of a particular scanner, you find it expressed in two numbers. For example, a scanner might have a 300×600 ppi resolution, or a 400×800 ppi capability. The first number refers to the number of pixels that can be sampled horizontally, and the second number specifies the vertical sampling. The number of samples for the vertical sampling is greater, but because of the blurring effect that occurs as the scanner moves vertically from line to line, not all of the sampled data is useful for reconstructing the image. For this reason, when you are shopping for a scanner, it is most useful to compare scanners based on the their horizontal resolution, or the lower of the two numbers. CHAPTER 2: How Scanning Technology Works 35 2 Please purchase PDF Split-Merge on www.verypdf.com to remove this watermark. Coordinating Your Scanner with Your Printer and Monitor An issue that causes constant confusion is that of coordinating the capabilities of your scanner with those of your printer and monitor to get the best final image. Although your scanner might have the capability to detect large amounts of color data, your printer might not have the capability to print it, and your monitor likely cannot display all of it. Measuring the Monitor’s Resolution Computer monitors have resolution specifications all their own, usually provided to you by the manufacturer in horizontal and vertical pixels. A common monitor resolution is 800×600 pixels, or 800 pixels horizontally and 600 pixels vertically. Another common monitor resolution is 1024×768. The higher the resolution setting on your computer, the more detail you can display from a scanned image on your computer screen. In contrast, lower resolutions do not make full use of all the image data your scanner might have captured. The Effect of Changing the Monitor and Scanner Resolution Settings Increasing the resolution setting on your monitor makes images, such as the icons on your screen, appear smaller because the pixels display closer together. The overall image at a higher resolution level is more detailed, and appears seamless. Figures 2-6 and 2-7 show images displayed at monitor resolution settings of 1024×768 and 640×480, respectively. Higher resolutions—1024×768 or greater—usually work better on a larger monitor. If you currently have a 17-inch monitor, you might want to invest in a 19- or 21-inch one if you plan on doing a lot of graphics work. The effect of increasing or decreasing the resolution settings on your scanner also has a marked effect on what you see on your screen. For example, suppose you create two different scans of the same original image. You scanned the first using a resolution of 600 ppi, and the second using 100 ppi, as shown in Figures 2-8 and 2-9. When viewed, the 600-ppi scanned image appears physically larger than its 100-ppi counterpart. This is due to the fact that while the original image was the same, the amount of pixel information scanned and displayed has increased. So, your monitor simply has more pixels to display. 36 How to Do Everything with Your Scanner Please purchase PDF Split-Merge on www.verypdf.com to remove this watermark. FIGURE 2-6 An image displayed on a monitor set at a resolution of 1024×768 appears smaller. FIGURE 2-7 An image displayed on a monitor set at a resolution of 640×480 appears larger. CHAPTER 2: How Scanning Technology Works 37 2 Please purchase PDF Split-Merge on www.verypdf.com to remove this watermark. FIGURE 2-8 An image scanned at 100 ppi FIGURE 2-9 An image scanned at 600 ppi 38 How to Do Everything with Your Scanner Please purchase PDF Split-Merge on www.verypdf.com to remove this watermark. . 1,200 ppi. 34 How to Do Everything with Your Scanner Please purchase PDF Split-Merge on www.verypdf.com to remove this watermark. When comparing the resolution of various scanners in your price. 100 ppi FIGURE 2-9 An image scanned at 600 ppi 38 How to Do Everything with Your Scanner Please purchase PDF Split-Merge on www.verypdf.com to remove this watermark. . capabilities of your scanner with those of your printer and monitor to get the best final image. Although your scanner might have the capability to detect large amounts of color data, your printer