tailieunhanh - How to Do Everything With Your Scanner- P11

How to Do Everything With Your Scanner- P11: My thanks to the terrifically creative and knowledgeable staff at Osborne, particularly acquisitions editor Megg Bonar and acquisitions coordinator Alissa Larson for their responsiveness and flexibility. Special thanks to technical editor Steve Bain, not only for his insight and attentiveness to accuracy, but also for actively coming up with many ideas for content. | 34 How to Do Everything with Your Scanner 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. TIP 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 .