Adobe 23101335 User Guide - Page 104

94 CHAPTER 2 Getting Images into Photoshop and ImageReady For example, when you display a 1-by-1 inch, 144-ppi image on a 72-dpi monitor, it appears in a 2-by-2 inch area on-screen. Because the monitor can display only 72 pixels per inch, it needs 2 inches to display the 144 pixels that make up one edge of the image. Printer resolution The number of ink dots per inch (dpi) produced by all laser printers, including imagesetters. Most desktop laser printers have a resolution of 600 dpi and imagesetters have a resolution of 1200 dpi or higher. To determine the appropriate resolution for your image when printing to any laser printer, but especially to imagesetters, see "screen frequency." Ink jet printers produce a spray of ink, not actual dots; however, most ink jet printers have an approximate resolution of 300 to 600 dpi and produce good results when printing images up to 150 ppi. Screen frequency The number of printer dots or halftone cells per inch used to print grayscale images or color separations. Also known as screen ruling or line screen, screen frequency is measured in lines per inch (lpi)-or lines of cells per inch in a halftone screen. The relationship between image resolution and screen frequency determines the quality of detail in the printed image. To produce a halftone image of the highest quality, you generally use an image resolution that is from 1.5 to at most 2 times the screen frequency. But with some images and output devices, a lower resolution can produce good results. To determine your printer's screen frequency, check your printer documentation or consult your service provider. Note: Some imagesetters and 600-dpi laser printers use screening technologies other than halftoning. If you are printing an image on a nonhalftone printer, consult your service provider or your printer documentation for the recommended image resolutions. A B C D A. 65 lpi: Coarse screen typically used to print newsletters and grocery coupons. B. 85 lpi: Average screen typically used to print newspapers. C. 133 lpi: High-quality screen typically used to print four-color magazines. D. 177 lpi: Very fine screen typically used for annual reports and images in art books. File size The digital size of an image, measured in kilobytes (K), megabytes (MB), or gigabytes (GB). File size is proportional to the pixel dimensions of the image. Images with more pixels may produce more detail at a given printed size, but they require more disk space to store and may be slower to edit and print. For instance, a 1-by-1-inch, 200-ppi image contains four times as many pixels as a